CN114671421B - Method and system for preparing ferric phosphate by utilizing ferric acid pickling waste liquid resource - Google Patents

Abstract

The invention relates to a method and system for preparing iron phosphate by utilizing iron-containing hydrochloric acid pickling waste liquid as a resource. The method sequentially oxidizes, reacts with phosphoric acid, homogenizes and ages the iron-containing hydrochloric acid pickling waste liquid, and slurries and washes it. and drying and discharging to obtain iron phosphate. The hydrogen chloride generated during the synthesis reaction at 130-200°C can be recovered to obtain regenerated hydrochloric acid with a concentration of 18-21wt% suitable for cold rolling pickling; the aging mother liquor and washing water formed during the process can also be obtained Can be recycled again; the invention also provides a system for implementing the method, which system includes an oxidation unit, a synthesis unit, a hydrochloric acid recovery unit, an aging separation unit, a slurry washing unit and a drying and discharging unit; applying the invention It can not only realize the resource utilization of hydrochloric acid waste liquid, prepare new energy material iron phosphate, and significantly increase the value and quality, but also realize the regeneration cycle of hydrochloric acid without the discharge of three wastes and no environmental pollution.

Description

A method and system for preparing iron phosphate by utilizing iron-containing hydrochloric acid pickling waste liquid as a resource

Technical field

The invention belongs to the field of resource utilization of waste liquid and preparation of new energy materials, and relates to a method and system for preparing iron phosphate by utilizing iron-containing hydrochloric acid pickling waste liquid as a resource.

Background technique

Our country has a large number of cold-rolled strip steel, pickled strip steel, steel pipe and steel wire production lines. During the deep processing of these products, their surfaces need to be pickled to remove the iron oxide scale on the surface. Among them, the most commonly used pickling liquid is It is hydrochloric acid, so a large amount of hydrochloric acid pickling waste liquid will be produced. Hydrochloric acid pickling waste liquid contains a small amount of free acid, ferric iron and a large amount of divalent iron. Due to its serious corrosiveness, it has been included in the "National Hazardous Waste List". At present, the methods for treating steel pickling waste liquid at home and abroad mainly include direct roasting method, evaporation concentration crystallization method and membrane method. Among them, direct roasting method is undoubtedly the most thorough method to solve the problem of waste acid, which can achieve the maximum reuse of hydrochloric acid. However, the direct roasting method has a higher threshold and a large investment in equipment, which is generally unaffordable for small enterprises, which will limit the development of enterprises in this area; the product market capacity of the evaporation concentration and crystallization method is small, and product quality is difficult to guarantee; and the membrane method It can only process relatively dilute waste liquid, but cannot handle high concentrations. Moreover, this method only produces a volume reduction effect and cannot completely solve the problem of large-scale effective utilization of hydrochloric acid pickling waste liquid.

Iron phosphate has been widely used in agriculture, ceramic glass, steel and surface passivation. Because of its unique catalytic properties, ion exchange capabilities and electrochemical properties, it has attracted widespread attention in recent years, resulting in its increasingly important applications in the fields of catalysis and lithium battery electrode materials. For example, lithium iron phosphate is an important The cathode material of lithium-ion power batteries is widely used in new energy vehicles. Iron phosphate is an important precursor for the synthesis of lithium iron phosphate. The current preparation method of iron phosphate is mainly precipitation method, including ferrous sulfate as the iron source and phosphoric acid. Ammonium dihydrogen is used as the phosphorus source for reaction or ferric chloride is used as the iron source and phosphoric acid is used as the phosphorus source for synthesis. The former will produce a large amount of iron-containing ammonium sulfate by-products, while the latter requires a larger phosphorus-to-iron ratio.

CN112661129A discloses a method for preparing ferric phosphate. Ferrous sulfate solution is used as raw material, and ferrous phosphate is first generated with phosphorus, and then complexed and oxidized to obtain dihydrated ferric phosphate, and finally calcined at high temperature to obtain anhydrous ferric phosphate; this method requires more The phosphorus source is added at the first time, and the process flow is longer.

CN112479174A discloses a method for synthesizing iron phosphate by utilizing titanium dioxide by-product ferrous sulfate as raw material to prepare iron phosphate finished product. This method uses inorganic acids such as sulfuric acid or hydrogen chloride to partially replace phosphoric acid as the acidifying agent. The liquid method can effectively reduce the content of impurities Mn, Mg and S. However, due to the introduction of strong acid, it has strict requirements on the equipment and can easily cause pollution.

CN113955732A discloses a method for preparing iron phosphate using ferric chloride as a catalyst. This method prepares iron phosphate by circulating ferric chloride to dissolve an iron source and react with phosphoric acid. It requires nitric acid as a catalyst, has high equipment requirements, and is easy to produce. Nitrogenous wastewater.

It can be seen from the above that it is necessary to develop a new technology method that can not only utilize hydrochloric acid pickling waste liquid on a large scale to solve its resource problem, but also realize the preparation of iron phosphate in a low-cost and short-process manner, and the medium can be recycled It is very necessary.

Contents of the invention

In view of the problems existing in the prior art, the object of the present invention is to provide a method and system for preparing iron phosphate by utilizing iron-containing hydrochloric acid pickling waste liquid as a resource. The method uses iron-containing hydrochloric acid pickling waste liquid as raw material, and sequentially Carry out oxidation, reaction with phosphoric acid at 130-200°C, homogeneous aging, slurry washing and drying and discharging processes to obtain iron phosphate. The hydrogen chloride generated by the synthesis reaction carried out at high temperature can be recovered to obtain regenerated hydrochloric acid suitable for cold rolling pickling; the aging mother liquor and washing water formed during the process can also be recycled again; applying the method of the present invention and The system can make the recovery rate of hydrochloric acid in the iron-containing hydrochloric acid pickling waste liquid reach more than 95%, the recovery rate of iron element can reach more than 95%, and can obtain iron phosphate with a purity of 99.5% to 99.9%; therefore, the present invention can not only achieve The hydrochloric acid pickling waste liquid is utilized to produce new energy material iron phosphate, which significantly increases the value and quality. It can also realize the regeneration cycle of hydrochloric acid without the discharge of three wastes and no environmental pollution.

To achieve this goal, the present invention adopts the following technical solutions:

In a first aspect, the present invention provides a method for preparing iron phosphate by utilizing iron-containing hydrochloric acid pickling waste liquid as a resource. The method includes the following steps:

(1) Add the oxidant to the iron-containing hydrochloric acid pickling waste liquid for oxidation treatment to obtain ferric acid liquid;

(2) Add phosphoric acid to the ferric acid solution described in step (1), and perform a synthesis reaction at 130 to 200°C to obtain crude ferric phosphate slurry and gaseous hydrogen chloride;

(3) Use an absorbent to absorb the gaseous hydrogen chloride described in step (2) and purify the tail gas to obtain regenerated hydrochloric acid;

(4) Add water to the crude ferric phosphate slurry described in step (2) for homogeneous aging, and then perform solid-liquid separation to obtain the first filter cake and aging mother liquor; wherein the aging mother liquor is returned to Step (2) and add to the ferric acid solution;

(5) Use water to slurry, wash and filter the first filter cake described in step (4) to obtain a second filter cake and washing water; wherein the washing water is returned to step (4) and added to the crude In ferric phosphate slurry;

(6) Drying and dehydrating the second filter cake described in step (5) to obtain iron phosphate;

Wherein, step (3) is performed simultaneously during steps (4)-(6).

The iron-containing hydrochloric acid pickling waste liquid of the present invention originates from the waste liquid of cold rolling pickling in the steel industry. The method of the present invention can be used to prepare a new energy material iron phosphate from the waste liquid, and can recover hydrogen chloride to generate regeneration. Hydrochloric acid can be reused in the cold-rolling pickling process, and the pickling waste liquid formed can be re-entered into the present invention for recycling; in the process of recovering hydrochloric acid, the remaining tail gas is purified and discharged up to standard. There is no emission of three wastes in the whole process, and the resource utilization rate is high , the added value of the product is greatly increased, and it can realize the organic coupling of the two fields of waste liquid recycling and new energy material preparation.

The synthesis reaction in step (2) of the method of the present invention refers to the reaction between ferric chloride and phosphoric acid to generate ferric phosphate and gaseous hydrogen chloride. In the present invention, the synthesis reaction is set at a high temperature of 130 to 200°C, which can promote the volatilization of hydrogen chloride from the solution. out and brought into the absorbent for hydrochloric acid recovery through evaporated water vapor. After a large amount of hydrogen chloride is taken away, it can weaken the reverse reaction of iron phosphate synthesis and increase the precipitation rate of iron phosphate. Due to the evaporation of a large amount of water, the final result The product is a slurry containing crude iron phosphate and having a relatively high viscosity; therefore, the present invention requires a subsequent water-adding aging process so that the iron phosphate crystals can be homogeneously aged again in a liquid phase with a large mass transfer coefficient. Control and optimize the particle size and morphology of iron phosphate crystals, and reduce the adsorption of impurities to a certain extent, to prepare iron phosphate dihydrate products; then remove excess impurities through slurry washing, improve product purity, and dry the iron phosphate Free water is removed from the crystal to obtain iron phosphate product.

It should be noted that in step (1) of the method of the present invention, the synthesis reaction is carried out at 130-200°C, such as 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C , 170°C, 175°C, 180°C, 185°C, 190°C, 195°C or 200°C, etc., but are not limited to the listed values, and other unlisted values within the above numerical range are also applicable.

The following are preferred technical solutions of the present invention, but are not limited to the technical solutions provided by the present invention. Through the following technical solutions, the technical purposes and beneficial effects of the present invention can be better achieved and realized.

As a preferred technical solution of the present invention, the oxidizing agent in step (1) includes hydrogen peroxide and/or oxygen.

Preferably, the amount of the oxidizing agent is 1.02 to 1.1 times the molar amount of divalent iron ions in the iron-containing hydrochloric acid pickling waste liquid, such as 1.02 times, 1.03 times, 1.04 times, 1.05 times, 1.06 times, 1.07 times, 1.08 times, 1.09 times or 1.1 times, etc., but are not limited to the listed values. Other unlisted values within the above numerical range are also applicable.

The iron-containing hydrochloric acid pickling waste liquid of the present invention contains a large amount of iron elements, but most of them exist in the form of ferrous iron ions in the solution. The amount of oxidant used in the present invention can be calculated according to the molar amount of ferrous iron ions in the solution. , and the amount of oxidant should be used to ensure that all ferrous iron ions are oxidized into ferric iron ions.

Preferably, the oxidation treatment in step (1) is performed under stirring.

As a preferred technical solution of the present invention, the amount of phosphoric acid used in step (2) is 1 to 1.2 times the molar amount of iron element in the ferric acid solution, such as 1 time, 1.02 times, 1.04 times, 1.06 times, 1.08 times , 1.1 times, 1.12 times, 1.14 times, 1.16 times, 1.18 times or 1.2 times, etc., but are not limited to the listed values. Other unlisted values within the above numerical range are also applicable.

Preferably, the synthesis reaction in step (2) is performed under stirring.

Preferably, the synthesis reaction time in step (2) is 3 to 7 h, such as 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h or 7h, etc., but is not limited to the listed values. , other unlisted values within the above range are also applicable.

The temperature of the synthesis reaction in step (2) of the present invention is related to the time. When the temperature of the synthesis reaction used is higher within the range, the reaction time can be appropriately reduced within the range, but the reaction time cannot be too short, otherwise it will affect The volatilization amount of hydrogen chloride, and too long reaction time will cause excessive evaporation of water, and the resulting crude iron phosphate slurry will be too dry and have poor fluidity, which is not conducive to the subsequent process.

As a preferred technical solution of the present invention, the absorbent forms an internal circulation in the absorption and exhaust gas purification respectively.

Preferably, the absorbent in step (3) includes water.

Preferably, the internal circulation of the exhaust gas purification produces hydrochloric acid with a concentration of less than 5wt%, and directly flows back to the absorption as an absorbent, such as 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt% , 3.5wt%, 4wt%, 4.5wt% or 4.9wt%, etc., but are not limited to the listed values, other unlisted values within the above numerical range are also applicable.

Preferably, the internal circulation of the absorption produces the regenerated hydrochloric acid with a concentration of 18 to 21wt%, such as 18wt%, 18.5wt%, 19wt%, 19.5wt%, 20wt%, 20.5wt% or 21wt%, etc., but not Not limited to the listed values, other unlisted values within the above range of values are also applicable.

At the beginning of the absorption and tail gas purification of the present invention, the present invention preferably adds pure water as an absorbent, uses pure water to absorb the hydrogen chloride gas first, and then uses pure water to further absorb the remaining gas to realize the purification of the tail gas. ; After the internal circulation of tail gas purification, pure water absorbs hydrogen chloride to generate hydrochloric acid with a concentration of less than 5wt%. This hydrochloric acid is directly returned to the absorption as an absorbent. After the internal circulation of absorption, a final concentration of 18 to 18% can be obtained. 21wt% regenerated hydrochloric acid, this regenerated hydrochloric acid can be directly used for cold rolling; it should be emphasized that the present invention requires the low-concentration hydrochloric acid produced by tail gas purification to be reused in the absorption process, and the resulting regeneration can be achieved through the internal circulation of the absorption The concentration of hydrochloric acid meets the requirements to ensure a high recovery rate of hydrogen chloride, and the internal cycle of tail gas purification is also conducive to achieving the standard emission of tail gas. If only absorption is set up without a purification process, not only the recovery rate of hydrogen chloride is low, but also the tail gas is also Difficult to meet standards.

As a preferred technical solution of the present invention, the amount of water used in step (4) is 3 to 5 times the mass of iron phosphate in the crude iron phosphate slurry, such as 1 time, 1.5 times, 2 times, 2.5 times, 3 times, 3.5 times, 4 times, 4.5 times or 5 times, etc., but are not limited to the listed values. Other unlisted values within the above range are also applicable; and it should be noted that in crude iron phosphate slurry The mass of iron phosphate is the theoretical yield of iron phosphate, which is calculated based on the molar amount of iron element in the ferric acid solution obtained in step (3) and the conversion yield rate of 100%.

Preferably, the homogeneous aging described in step (4) is performed under stirring.

Preferably, the homogeneous aging time in step (4) is 2 to 6h, such as 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h or 6h, etc., but is not limited to those listed values, other unlisted values within the above range are also applicable.

The aging time of the present invention is related to the synthesis reaction carried out in step (2). When the synthesis reaction is carried out at a higher temperature, the required aging time should be appropriately extended within the range so that the iron phosphate crystals are fully The aging effect.

As a preferred technical solution of the present invention, the amount of water used in step (5) is 3 to 5 times the mass of the first filter cake, such as 1 time, 1.5 times, 2 times, 2.5 times, 3 times, 3.5 times , 4 times, 4.5 times or 5 times, etc., but are not limited to the listed values, and other unlisted values within the above numerical range are also applicable.

Preferably, the slurry washing in step (5) is performed under stirring.

Preferably, the drying and dehydration temperature in step (6) is 80-90°C, such as 80°C, 81°C, 82°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C, 89°C or 90°C, etc., but are not limited to the listed values, and other unlisted values within the above numerical range are also applicable.

Preferably, the drying and dehydration time in step (6) is 1 to 3h, such as 1h, 1.2h, 1.4h, 1.6h, 1.8h, 2h, 2.2h, 2.4h, 2.6h, 2.8h or 3h, etc., However, it is not limited to the listed values, and other unlisted values within the above range of values are also applicable.

In order to obtain ferric phosphate dihydrate product, the present invention sets the drying and dehydration time to 1 to 3 hours. Longer drying time or increasing the subsequent heat treatment process will cause the crystallization water in the ferric phosphate to decrease, but those skilled in the art can Actual selection and adjustment is required.

As a preferred technical solution of the present invention, the method includes the following steps:

(1) Add hydrogen peroxide and/or oxygen as an oxidant to the iron-containing hydrochloric acid pickling waste liquid, and the usage amount of the oxidant is 1.02 to 1.02 to the molar amount of divalent iron ions in the iron-containing hydrochloric acid pickling waste liquid. 1.1 times, and then perform oxidation treatment under stirring to obtain ferric acid solution;

(2) Add phosphoric acid to the ferric acid solution described in step (1), and perform a synthesis reaction at 130 to 200°C for 3 to 7 hours under stirring. The amount of phosphoric acid used is the iron element in the ferric acid solution. 1 to 1.2 times the molar amount to obtain crude ferric phosphate slurry and gaseous hydrogen chloride;

(3) Use water as an absorbent to absorb the gaseous hydrogen chloride in step (2) and purify the tail gas; the absorbent forms an internal cycle in the absorption and the tail gas purification respectively; the internal cycle of the tail gas purification Hydrochloric acid with a concentration of less than 5wt% is produced, and is directly returned to the absorption as an absorbent; the internal circulation of the absorption produces regenerated hydrochloric acid with a concentration of 18 to 21wt%;

(4) Add water to the crude ferric phosphate slurry described in step (2), and perform homogeneous aging under stirring for 2 to 6 hours. The amount of water used is the iron phosphate in the crude ferric phosphate slurry. 3 to 5 times the mass, and then perform solid-liquid separation to obtain the first filter cake and aging mother liquor; wherein the aging mother liquor is returned to step (2) and added to the ferric acid solution;

(5) Under stirring, use water to slurry, wash and filter the first filter cake described in step (4). The amount of water used is 3 to 5 times the mass of the first filter cake to obtain the second filter cake. Filter cake and washing water; wherein, the washing water is returned to step (4) and added to the crude ferric phosphate slurry;

(6) Dry and dehydrate the second filter cake described in step (5) at 80-90°C for 1-3 hours to obtain iron phosphate;

Wherein, step (3) is performed simultaneously during steps (4)-(6).

In a second aspect, the present invention provides a system for preparing iron phosphate by recycling iron-containing hydrochloric acid pickling waste liquid. The system includes an oxidation unit, a synthesis unit, an aging separation unit, a chemical unit and a chemical unit connected in sequence along the direction of material flow. The slurry washing unit and the drying and discharging unit also include a hydrochloric acid recovery unit connected to the gas outlet of the synthesis unit; wherein the liquid outlet of the aging separation unit is connected to the inlet of the synthesis unit; the slurry washing unit The liquid outlet is connected to the inlet of the aging separation unit; the hydrochloric acid recovery unit includes a hydrochloric acid absorption tower and a tail gas purification tower connected in sequence along the gas flow direction.

As a preferred technical solution of the present invention, the oxidation unit includes an oxidation tank.

Preferably, an oxidation tank discharge pump is provided between the oxidation unit and the synthesis unit; the inlet of the oxidation tank discharge pump is connected to the outlet of the oxidation unit, and the outlet of the oxidation tank discharge pump is connected to the The entrance to the synthesis unit.

Preferably, the synthesis unit includes a synthesis kettle; the synthesis kettle is provided with a material outlet and a gas outlet, and the gas outlet serves as the gas outlet of the synthesis unit.

Preferably, a synthesis kettle discharge pump is provided between the synthesis unit and the aging separation unit; the inlet of the synthesis kettle discharge pump is connected to the material outlet of the synthesis unit, and the synthesis kettle discharge device The outlet is connected to the inlet of the aging separation unit.

Preferably, the aging separation unit includes a homogeneous aging tank and an aging filter press connected in sequence; wherein the aging filter press is provided with a material outlet and a liquid outlet, and the liquid outlet serves as the aging filter press. Liquid outlet of the separation unit.

Preferably, an aging tank discharge pump is provided between the homogeneous aging tank and the aging filter press; the inlet of the aging tank discharge pump is connected to the outlet of the homogeneous aging tank, The outlet of the aging tank discharge pump is connected to the inlet of the aging filter press.

Preferably, a screw conveyor is provided between the aging separation unit and the pulping washing unit; the inlet of the screw conveyor is connected to the material outlet of the aging separation unit, and the outlet of the screw conveyor is connected to the Entrance to the slurry washing unit.

Preferably, the slurry washing unit includes a slurry tank and a washing filter press connected in sequence; wherein the washing filter press is provided with a material outlet and a liquid outlet, and the liquid outlet serves as the outlet of the slurry washing unit. Liquid outlet.

Preferably, a slurry tank discharge pump is provided between the slurry tank and the washing filter press; the inlet of the slurry tank discharge pump is connected to the outlet of the slurry tank, and the slurry tank is The outlet of the discharging pump is connected with the inlet of the drying discharging unit.

Preferably, a belt conveyor is provided between the slurrying washing unit and the drying and discharging unit; the inlet of the belt conveyor is connected to the material outlet of the slurrying washing unit, and the outlet of the belt conveyor is connected to the The entrance of the dry discharging unit.

Preferably, the drying and discharging unit includes a dryer.

Preferably, the oxidation tank, synthesis kettle, homogeneous aging tank and slurry tank are all acid-resistant and oxidation-resistant equipment equipped with a stirring module.

Since the reaction process of the present invention is in a strongly acidic environment, the oxidation tank, synthesis kettle, homogeneous aging tank, and slurry tank need to be acid-resistant and oxidation-resistant equipment. For example, the materials of the oxidation tank and slurry tank are steel-lined PTFE. The lining material of the synthesis kettle is graphite; it should also be noted that the heating method of the synthesis kettle of the present invention is indirect heating. For example, the synthesis kettle is equipped with a jacket, and low-pressure hot steam is introduced into the jacket as Heating source, but not limited to this heating method, other indirect heating methods are also suitable for the present invention, and those skilled in the art can choose according to actual conditions.

As a preferred technical solution of the present invention, the bottom liquid outlet of the hydrochloric acid absorption tower is respectively connected to the inlet of the regenerated hydrochloric acid storage device and the top liquid inlet of the hydrochloric acid absorption tower; the bottom liquid outlet of the tail gas purification tower is respectively connected to The top liquid inlet of the hydrochloric acid absorption tower and the top liquid inlet of the tail gas purification tower; the top liquid inlet of the tail gas purification tower is connected with a water inlet pipe; the top of the tail gas purification tower is provided with a tail gas outlet.

The liquid inlet at the top of the tail gas purification tower of the present invention is connected to a water inlet pipe. In the present invention, water is added into the hydrochloric acid recovery unit through the water inlet pipe as an absorbent; initially, before hydrogen chloride gas enters the hydrochloric acid recovery unit, it first needs to pass through the inlet pipe. Pure water is added to the water pipe to make the hydrochloric acid absorption tower and tail gas purification tower reach a working state capable of absorption treatment, and then the hydrogen chloride gas enters the hydrochloric acid recovery unit for absorption.

When the hydrogen chloride gas enters the hydrochloric acid absorption tower, the pure water in the tower absorbs the gas, and then is divided into two channels for output through the liquid outlet at the bottom of the tower. One channel is re-entered into the hydrochloric acid absorption tower through the top liquid inlet of the hydrochloric acid absorption tower for absorption. To increase the concentration of regenerated hydrochloric acid; the other channel outputs regenerated hydrochloric acid products whose concentration reaches the required level or for storage; after the unabsorbed gas in the hydrochloric acid absorption tower enters the tail gas purification tower, the gas is purified and absorbed by the pure water in the tower, and the remaining tail gas The tail gas outlet at the top of the tower is discharged according to the standard. The obtained low-concentration regenerated hydrochloric acid is output from the liquid outlet at the bottom of the tower in two ways. One line is re-entered into the tail gas purification tower through the top liquid inlet of the tail gas purification tower for circulation, and continues to be used to purify gas. , this internal cycle can obtain hydrochloric acid with a concentration less than 5wt%; the other way is to input these hydrochloric acids with a concentration less than 5wt% into the hydrochloric acid absorption tower through the top liquid inlet of the hydrochloric acid absorption tower as an absorbent; it should be noted that for the above The flow proportional relationship between branches can be adjusted by those skilled in the art according to the actual situation.

The present invention realizes the cascade absorption of hydrogen chloride through the above process, that is, adding pure water to the tail gas purification tower and increasing the concentration after multiple cycles in the tower to obtain low-concentration hydrochloric acid (hydrogen chloride concentration <5%), and then the low-concentration Regenerated hydrochloric acid is transported into the hydrochloric acid absorption tower as an absorbent and undergoes multiple cycles to finally obtain high-concentration regenerated hydrochloric acid (hydrogen chloride concentration 18-21wt%), realizing the regeneration and recycling of hydrochloric acid; it should be noted that when the hydrochloric acid absorption tower outputs After a part of the regenerated hydrochloric acid product meets the requirements, the tail gas purification tower should promptly transport low-concentration hydrochloric acid to the hydrochloric acid absorption tower as an absorbent to supplement, and then pure water should be replenished into the tail gas purification tower through the water inlet pipe, and the entire process should maintain a dynamic balance. ; It should also be noted that at the beginning of the present invention, it is preferred to add pure water as the absorbent. If you choose to add hydrochloric acid with a concentration of less than 5wt% directly from the water inlet pipe as the absorbent, you also need to add the exhaust gas purification tower after the present invention. An alkaline exhaust gas treatment device was further added to solve the initial exhaust gas problem.

Preferably, an acid-resistant tail gas fan is provided between the hydrochloric acid absorption tower and the tail gas purification tower; the inlet of the acid-resistant tail gas fan is connected to the gas outlet of the hydrochloric acid absorption tower, and the outlet of the acid-resistant tail gas fan is connected to the tail gas Gas inlet of the purification tower.

Preferably, the bottom liquid outlet of the hydrochloric acid absorption tower is connected to an absorption tower circulation pump. The outlet of the absorption tower circulation pump is divided into two branches, and the first branch is connected to the inlet of the regenerated hydrochloric acid storage device. The second branch is connected to the top liquid inlet of the hydrochloric acid absorption tower.

Preferably, the bottom liquid outlet of the tail gas purification tower is connected to a purification tower circulation pump. The outlet of the purification tower circulation pump is divided into two paths, and the first branch is connected to the top liquid of the hydrochloric acid absorption tower. Inlet, the second branch is connected to the top liquid inlet of the tail gas purification tower.

Compared with existing technical solutions, the present invention at least has the following beneficial effects:

(1) The present invention uses the iron-containing hydrochloric acid pickling waste liquid from cold rolling of steel as the iron source to realize the separation and recovery of iron and chlorine. The iron becomes iron phosphate and the chlorine becomes hydrochloric acid and can be recycled, realizing the Resource utilization of iron hydrochloric acid pickling waste liquid;

(2) The present invention uses cheap iron-containing hydrochloric acid pickling waste liquid to prepare new energy material iron phosphate, which realizes the value increase and quality improvement of the product and organically couples the waste liquid resource utilization with the preparation of new energy materials;

(3) The process of the present invention adopts cascade absorption and recovery of hydrochloric acid, without the discharge of three wastes and no environmental hazards.

Description of the drawings

Figure 1 is a schematic flow chart of the method for preparing iron phosphate by recycling iron-containing hydrochloric acid pickling waste liquid according to the present invention;

Figure 2 is a schematic diagram of a system for preparing iron phosphate by recycling iron-containing hydrochloric acid pickling waste liquid used in the embodiment of the present invention;

In the picture: 1-oxidation tank, 2-oxidation tank discharge pump, 3-synthetic kettle, 4-hydrochloric acid absorption tower, 5-absorption tower circulation pump, 6-acid-resistant tail gas fan, 7-tail gas purification tower, 8-purification tower Circulation pump, 9-synthetic kettle discharge pump, 10-homogeneous aging tank, 11-aging tank discharge pump, 12-aging filter press, 13-screw conveyor, 14-slurry tank, 15- Slurry tank discharge pump, 16-washing filter press, 17-belt conveyor, 18-dryer.

Detailed ways

The technical solution of the present invention will be further described below through specific implementations. Those skilled in the art should understand that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

The schematic flow chart of the method for preparing iron phosphate by recycling iron-containing hydrochloric acid waste liquid according to the present invention is shown in Figure 1. As can be seen from the figure, the method includes the following steps:

(1) Add hydrogen peroxide and/or oxygen as an oxidant to the iron-containing hydrochloric acid pickling waste liquid, and the usage amount of the oxidant is 1.02 to 1.02 to the molar amount of divalent iron ions in the iron-containing hydrochloric acid pickling waste liquid. 1.1 times, then perform oxidation treatment under stirring, and obtain ferric acid solution;

(2) Add phosphoric acid to the ferric acid solution described in step (1), and perform a synthesis reaction at 130 to 200°C for 3 to 7 hours under stirring. The amount of phosphoric acid used is the iron element in the ferric acid solution. 1 to 1.2 times the molar amount to obtain crude ferric phosphate slurry and gaseous hydrogen chloride;

(3) Use water as an absorbent to absorb the gaseous hydrogen chloride in step (2) and purify the tail gas; the absorbent forms an internal cycle in the absorption and the tail gas purification respectively; the internal cycle of the tail gas purification Hydrochloric acid with a concentration of less than 5wt% is produced, and is directly returned to the absorption as an absorbent; the internal circulation of the absorption produces regenerated hydrochloric acid with a concentration of 18 to 21wt%;

(4) Add water to the crude ferric phosphate slurry described in step (2), and perform homogeneous aging under stirring for 2 to 6 hours. The amount of water used is the iron phosphate in the crude ferric phosphate slurry. 3 to 5 times the mass, and then perform solid-liquid separation to obtain the first filter cake and aging mother liquor; wherein the aging mother liquor is returned to step (2) and added to the ferric acid solution;

(5) Under stirring, use water to slurry, wash and filter the first filter cake described in step (4). The amount of water used is 3 to 5 times the mass of the first filter cake to obtain the second filter cake. Filter cake and washing water; wherein, the washing water is returned to step (4) and added to the crude ferric phosphate slurry;

(6) Dry and dehydrate the second filter cake described in step (5) at 80-90°C for 1-3 hours to obtain iron phosphate;

Wherein, step (3) is performed simultaneously during steps (4)-(6).

A schematic diagram of a system for preparing iron phosphate by recycling iron-containing hydrochloric acid waste liquid used in the embodiments and comparative examples of the present invention is shown in Figure 2. It can be seen from Figure 2 that the system includes an oxidation tank 1, an oxidation tank discharge Pump 2; synthesis kettle 3; hydrochloric acid absorption tower 4, absorption tower circulation pump 5, acid-resistant tail gas fan 6, tail gas purification tower 7, purification tower circulation pump 8; synthesis kettle discharge pump 9; homogeneous aging tank 10, aging Tank discharge pump 11, aging filter press 12, screw conveyor 13; slurry tank 14, slurry tank discharge pump 15, washing filter press 16, belt conveyor 17 and dryer 18; among them, the oxidation tank The outlet of 1 is connected to the inlet of the oxidation tank discharge pump 2, and the outlet of the oxidation tank discharge pump 2 is connected to the inlet of the synthesis kettle 3; the gas outlet of the synthesis kettle 3 is connected to the gas inlet of the hydrochloric acid absorption tower 4, and the hydrochloric acid absorption tower 4 The gas outlet is connected with the inlet of the acid-resistant tail gas fan 6, and the outlet of the hydrochloric acid tail gas fan 6 is connected with the gas inlet of the tail gas purification tower 7; the top liquid inlet of the tail gas purification tower is provided with a water inlet pipe, and the top of the tail gas purification tower is provided with tail gas Discharge port; the bottom liquid outlet of the hydrochloric acid absorption tower 4 is connected to the inlet of the absorption tower circulation pump 5, and the outlet of the absorption tower circulation pump 5 is respectively connected to the top liquid inlet of the hydrochloric acid absorption tower 4 and the regenerated hydrochloric acid storage device or the regenerated hydrochloric acid. Directly used for cold rolling pickling; the bottom liquid outlet of the tail gas purification tower 7 is connected to the inlet of the purification tower circulation pump 8, and the outlet of the purification tower circulation pump 8 is respectively connected to the top liquid inlet of the tail gas purification tower 7 and the hydrochloric acid absorption tower 4 The top liquid inlet of the tower is connected; the material outlet of the synthesis kettle 3 is connected with the inlet of the synthesis kettle discharge pump 9, and the outlet of the synthesis kettle discharge pump 9 is connected with the inlet of the homogeneous aging tank 10; the homogeneous aging tank 10 The outlet is connected with the inlet of the aging tank discharge pump 11, and the outlet of the aging tank discharge pump 11 is connected with the inlet of the aging filter press 12; the liquid outlet of the aging filter press 12 is connected with the inlet of the synthesis kettle 3, The material outlet of the aging filter press 12 is connected to the inlet of the screw conveyor 13, the outlet of the screw conveyor 13 is connected to the inlet of the slurry tank 14; the outlet of the slurry tank 14 is connected to the inlet of the slurry tank discharge pump 15 , the outlet of the slurry tank discharge pump 15 is connected to the inlet of the washing filter press 16; the liquid outlet of the washing filter press 16 is connected to the inlet of the homogenizing aging tank 10, and the material outlet of the washing filter press 16 is connected to the belt conveyor The inlet of the machine 17 is connected, and the outlet of the belt conveyor 17 is connected with the inlet of the dryer 18.

The iron-containing hydrochloric acid pickling waste liquid used in the Examples and Comparative Examples of the present invention comes from the cold rolling pickling workshop of a domestic steel enterprise. The contents of the main components in the waste liquid are as shown in Table 1.

Table 1

Example 1

This embodiment provides a method for preparing iron phosphate by utilizing iron-containing hydrochloric acid waste liquid as a resource. The method includes the following steps:

(1) Add the iron-containing hydrochloric acid pickling waste liquid into the oxidation tank, and then add hydrogen peroxide as an oxidant. The usage amount of the oxidant is the molar amount of divalent iron ions in the iron-containing hydrochloric acid pickling waste liquid. 1.05 times, and then perform oxidation treatment under stirring to obtain ferric acid solution;

(2) The ferric acid solution flows into the synthesis kettle through the oxidation tank discharge pump, and then phosphoric acid is added thereto, and the synthesis reaction is carried out at 130°C for 7 hours under stirring. The amount of phosphoric acid used is the iron element in the ferric iron solution. 1.1 times the molar amount to generate crude ferric phosphate slurry and gaseous hydrogen chloride;

(3) Add pure water as an absorbent through the water inlet pipe connected to the liquid inlet at the top of the tail gas purification tower, so that the hydrochloric acid purification tower and the tail gas purification tower reach the absorption treatment state, and pass the gaseous hydrogen chloride into the hydrochloric acid absorption tower. is absorbed by the absorbent to form first-level regenerated hydrochloric acid. The unabsorbed hydrogen chloride gas enters the tail gas purification tower through the acid-resistant tail gas fan, and is purified and absorbed to obtain the second-level regenerated hydrochloric acid. The remaining tail gas after purification passes through the tail gas outlet of the tail gas purification tower. Discharge; at this time, a part of the secondary regenerated hydrochloric acid is circulated in the tail gas purification tower through the purification tower circulation pump, and the other part is transported to the hydrochloric acid absorption tower as an absorbent for further absorption through the purification tower circulation pump; at this time, the hydrochloric acid Part of the primary regenerated hydrochloric acid obtained in the absorption tower circulates in the hydrochloric acid absorption tower through the absorption tower circulation pump, and the other part outputs the regenerated hydrochloric acid product through the outlet of the absorption tower circulation pump, which is directly used for cold rolling pickling to form iron-containing hydrochloric acid. The pickling waste liquid is reused in the present invention;

(4) The crude ferric phosphate slurry described in step (2) is transported to the homogeneous aging tank through the discharging pump of the synthesis kettle, water is added to the homogeneous aging tank and homogenized aging is carried out for 2 hours under stirring. The amount of water used is 3 times the mass of iron phosphate in the crude iron phosphate slurry, and then the obtained system is transported to the aging filter press through the aging tank discharge pump for solid-liquid separation to obtain the first Filter cake and aging mother liquor; wherein, the aging mother liquor is returned to the synthesis kettle of step (2) and added to the ferric acid solution;

(5) The first filter cake in step (4) enters the slurrying tank through the screw conveyor. Under stirring, water is added to slurry and wash the first filter cake. The amount of water used is the amount of the first filter cake. 3 times the mass of the cake; then the resulting system is sent to the washing filter press through the slurry tank discharge pump for filtration to obtain the second filter cake and washing water; wherein the washing water is returned to the homogenizer of step (4) Aging tank and added to the crude ferric phosphate slurry;

(6) The second filter cake described in step (5) enters the dryer through a belt conveyor, and is dried and dehydrated at 80°C for 3 hours to obtain iron phosphate;

Wherein, step (3) is performed simultaneously during steps (4)-(6).

Example 2

This embodiment provides a method for preparing iron phosphate by utilizing iron-containing hydrochloric acid waste liquid as a resource. The method includes the following steps:

(1) Add the iron-containing hydrochloric acid pickling waste liquid into the oxidation tank, and then introduce oxygen as the oxidant. The usage amount of the oxidant is 1.04 of the molar amount of divalent iron ions in the iron-containing hydrochloric acid pickling waste liquid. times, and then perform oxidation treatment under stirring to obtain ferric acid solution;

(2) The ferric acid solution flows into the synthesis kettle through the oxidation tank discharge pump, and then phosphoric acid is added thereto, and the synthesis reaction is carried out at 150°C for 6 hours under stirring. The amount of phosphoric acid used is the iron element in the ferric iron solution. 1 times the molar amount to generate crude ferric phosphate slurry and gaseous hydrogen chloride;

(3) Add pure water as an absorbent through the water inlet pipe connected to the liquid inlet at the top of the tail gas purification tower, so that the hydrochloric acid purification tower and the tail gas purification tower reach the absorption treatment state, and pass the gaseous hydrogen chloride into the hydrochloric acid absorption tower. is absorbed by the absorbent to form first-level regenerated hydrochloric acid. The unabsorbed hydrogen chloride gas enters the tail gas purification tower through the acid-resistant tail gas fan, and is purified and absorbed to obtain the second-level regenerated hydrochloric acid. The remaining tail gas after purification passes through the tail gas outlet of the tail gas purification tower. Discharge; at this time, a part of the secondary regenerated hydrochloric acid is circulated in the tail gas purification tower through the purification tower circulation pump, and the other part is transported to the hydrochloric acid absorption tower as an absorbent for further absorption through the purification tower circulation pump; at this time, the hydrochloric acid Part of the primary regenerated hydrochloric acid obtained in the absorption tower circulates in the hydrochloric acid absorption tower through the absorption tower circulation pump, and the other part outputs the regenerated hydrochloric acid product through the outlet of the absorption tower circulation pump, which is directly used for cold rolling pickling to form iron-containing hydrochloric acid. The pickling waste liquid is reused in the present invention;

(4) The crude ferric phosphate slurry described in step (2) is transported to the homogeneous aging tank through the discharge pump of the synthesis kettle, water is added to the homogeneous aging tank and homogenized aging is carried out for 3 hours under stirring. The amount of water used is 4 times the mass of iron phosphate in the crude iron phosphate slurry, and then the obtained system is transported to the aging filter press through the aging tank discharge pump for solid-liquid separation to obtain the first Filter cake and aging mother liquor; wherein, the aging mother liquor is returned to the synthesis kettle of step (2) and added to the ferric acid solution;

(5) The first filter cake in step (4) enters the slurrying tank through the screw conveyor. Under stirring, water is added to slurry and wash the first filter cake. The amount of water used is the amount of the first filter cake. 4 times the mass of the cake; then the resulting system is sent to the washing filter press through the slurry tank discharge pump for filtration to obtain the second filter cake and washing water; wherein the washing water is returned to the homogenizer of step (4) Aging tank and added to the crude ferric phosphate slurry;

(6) The second filter cake described in step (5) enters the dryer through a belt conveyor, and is dried and dehydrated at 85°C for 2 hours to obtain iron phosphate;

Wherein, step (3) is performed simultaneously during steps (4)-(6).

Example 3

This embodiment provides a method for preparing iron phosphate by utilizing iron-containing hydrochloric acid waste liquid as a resource. The method includes the following steps:

(1) Add the iron-containing hydrochloric acid pickling waste liquid into the oxidation tank, and then add oxygen as the oxidant. The usage amount of the oxidant is 1.02 times the molar amount of divalent iron ions in the iron-containing hydrochloric acid pickling waste liquid. , and then perform oxidation treatment under stirring to obtain ferric acid solution;

(2) The ferric acid solution flows into the synthesis kettle through the oxidation tank discharge pump, and then phosphoric acid is added thereto, and the synthesis reaction is carried out at 170°C for 4 hours under stirring. The amount of phosphoric acid used is the iron element in the ferric iron solution. 1.2 times the molar amount to generate crude ferric phosphate slurry and gaseous hydrogen chloride;

(3) Add pure water as an absorbent through the water inlet pipe connected to the liquid inlet at the top of the tail gas purification tower, so that the hydrochloric acid purification tower and the tail gas purification tower reach the absorption treatment state, and pass the gaseous hydrogen chloride into the hydrochloric acid absorption tower. is absorbed by the absorbent to form first-level regenerated hydrochloric acid. The unabsorbed hydrogen chloride gas enters the tail gas purification tower through the acid-resistant tail gas fan, and is purified and absorbed to obtain the second-level regenerated hydrochloric acid. The remaining tail gas after purification passes through the tail gas outlet of the tail gas purification tower. Discharge; at this time, a part of the secondary regenerated hydrochloric acid is circulated in the tail gas purification tower through the purification tower circulation pump, and the other part is transported to the hydrochloric acid absorption tower as an absorbent for further absorption through the purification tower circulation pump; at this time, the hydrochloric acid Part of the primary regenerated hydrochloric acid obtained in the absorption tower circulates in the hydrochloric acid absorption tower through the absorption tower circulation pump, and the other part outputs the regenerated hydrochloric acid product through the outlet of the absorption tower circulation pump, which is directly used for cold rolling pickling to form iron-containing hydrochloric acid. The pickling waste liquid is reused in the present invention;

(4) The crude ferric phosphate slurry described in step (2) is transported to the homogeneous aging tank through the discharging pump of the synthesis kettle, water is added to the homogeneous aging tank and homogenized aging is carried out for 4 hours under stirring. The amount of water used is 5 times the mass of iron phosphate in the crude iron phosphate slurry, and then the obtained system is transported to the aging filter press through the aging tank discharge pump for solid-liquid separation to obtain the first Filter cake and aging mother liquor; wherein, the aging mother liquor is returned to the synthesis kettle of step (2) and added to the ferric acid solution;

(5) The first filter cake in step (4) enters the slurrying tank through the screw conveyor. Under stirring, water is added to slurry and wash the first filter cake. The amount of water used is the amount of the first filter cake. 5 times the mass of the cake; then the resulting system is sent to the washing filter press through the slurry tank discharge pump for filtration to obtain the second filter cake and washing water; wherein the washing water is returned to the homogenizer of step (4) Aging tank and added to the crude ferric phosphate slurry;

(6) The second filter cake described in step (5) enters the dryer through a belt conveyor, and is dried and removed at 90°C for 1 hour to obtain iron phosphate;

Wherein, step (3) is performed simultaneously during steps (4)-(6).

Example 4

This embodiment provides a method for preparing iron phosphate by utilizing iron-containing hydrochloric acid waste liquid as a resource. The method includes the following steps:

(1) Add the iron-containing hydrochloric acid pickling waste liquid into the oxidation tank, and then add hydrogen peroxide as an oxidant. The usage amount of the oxidant is the molar amount of divalent iron ions in the iron-containing hydrochloric acid pickling waste liquid. 1.08 times, and then perform oxidation treatment under stirring to obtain ferric acid solution;

(2) The ferric acid solution flows into the synthesis kettle through the oxidation tank discharge pump, and then phosphoric acid is added thereto, and the synthesis reaction is carried out at 190°C for 3 hours under stirring. The amount of phosphoric acid used is the iron element in the ferric iron solution. 1.1 times the molar amount to generate crude ferric phosphate slurry and gaseous hydrogen chloride;

(3) Add pure water as an absorbent through the water inlet pipe connected to the liquid inlet at the top of the tail gas purification tower, so that the hydrochloric acid purification tower and the tail gas purification tower reach the absorption treatment state, and pass the gaseous hydrogen chloride into the hydrochloric acid absorption tower. is absorbed by the absorbent to form first-level regenerated hydrochloric acid. The unabsorbed hydrogen chloride gas enters the tail gas purification tower through the acid-resistant tail gas fan, and is purified and absorbed to obtain the second-level regenerated hydrochloric acid. The remaining tail gas after purification passes through the tail gas outlet of the tail gas purification tower. Discharge; at this time, a part of the secondary regenerated hydrochloric acid is circulated in the tail gas purification tower through the purification tower circulation pump, and the other part is transported to the hydrochloric acid absorption tower as an absorbent for further absorption through the purification tower circulation pump; at this time, the hydrochloric acid Part of the primary regenerated hydrochloric acid obtained in the absorption tower circulates in the hydrochloric acid absorption tower through the absorption tower circulation pump, and the other part outputs the regenerated hydrochloric acid product through the outlet of the absorption tower circulation pump, which is directly used for cold rolling pickling to form iron-containing hydrochloric acid. The pickling waste liquid is reused in the present invention;

(4) The crude ferric phosphate slurry described in step (2) is transported to the homogeneous aging tank through the discharging pump of the synthesis kettle, water is added to the homogeneous aging tank and homogenized aging is carried out for 5 hours under stirring. The amount of water used is 5 times the mass of iron phosphate in the crude iron phosphate slurry, and then the obtained system is transported to the aging filter press through the aging tank discharge pump for solid-liquid separation to obtain the first Filter cake and aging mother liquor; wherein, the aging mother liquor is returned to the synthesis kettle of step (2) and added to the ferric acid solution;

(5) The first filter cake in step (4) enters the slurrying tank through the screw conveyor. Under stirring, water is added to slurry and wash the first filter cake. The amount of water used is the amount of the first filter cake. 5 times the mass of the cake; then the resulting system is sent to the washing filter press through the slurry tank discharge pump for filtration to obtain the second filter cake and washing water; wherein the washing water is returned to the homogenizer of step (4) Aging tank and added to the crude ferric phosphate slurry;

(6) The second filter cake described in step (5) enters the dryer through a belt conveyor, and is dried and dehydrated at 80°C for 3 hours to obtain iron phosphate;

Wherein, step (3) is performed simultaneously during steps (4)-(6).

Example 5

This embodiment provides a method for preparing iron phosphate by utilizing iron-containing hydrochloric acid waste liquid as a resource. The method includes the following steps:

(1) Add the iron-containing hydrochloric acid pickling waste liquid into the oxidation tank, and then add hydrogen peroxide as an oxidant. The usage amount of the oxidant is the molar amount of divalent iron ions in the iron-containing hydrochloric acid pickling waste liquid. 1.1 times, and then perform oxidation treatment under stirring to obtain ferric acid solution;

(2) The ferric acid solution flows into the synthesis kettle through the oxidation tank discharge pump, and then phosphoric acid is added thereto, and the synthesis reaction is carried out at 200°C for 3 hours under stirring. The amount of phosphoric acid used is the iron element in the ferric iron solution. 1.1 times the molar amount to generate crude ferric phosphate slurry and gaseous hydrogen chloride;

(3) Add pure water as an absorbent through the water inlet pipe connected to the liquid inlet at the top of the tail gas purification tower, so that the hydrochloric acid purification tower and the tail gas purification tower reach the absorption treatment state, and pass the gaseous hydrogen chloride into the hydrochloric acid absorption tower. is absorbed by the absorbent to form first-level regenerated hydrochloric acid. The unabsorbed hydrogen chloride gas enters the tail gas purification tower through the acid-resistant tail gas fan, and is purified and absorbed to obtain the second-level regenerated hydrochloric acid. The remaining tail gas after purification passes through the tail gas outlet of the tail gas purification tower. Discharge; at this time, a part of the secondary regenerated hydrochloric acid is circulated in the tail gas purification tower through the purification tower circulation pump, and the other part is transported to the hydrochloric acid absorption tower as an absorbent for further absorption through the purification tower circulation pump; at this time, the hydrochloric acid Part of the primary regenerated hydrochloric acid obtained in the absorption tower circulates in the hydrochloric acid absorption tower through the absorption tower circulation pump, and the other part outputs the regenerated hydrochloric acid product through the outlet of the absorption tower circulation pump, which is directly used for cold rolling pickling to form iron-containing hydrochloric acid. The pickling waste liquid is reused in the present invention;

(4) The crude ferric phosphate slurry described in step (2) is transported to the homogeneous aging tank through the discharging pump of the synthesis kettle, water is added to the homogeneous aging tank and homogeneously aged for 6 hours under stirring, The amount of water used is 4 times the mass of iron phosphate in the crude iron phosphate slurry, and then the obtained system is transported to the aging filter press through the aging tank discharge pump for solid-liquid separation to obtain the first Filter cake and aging mother liquor; wherein, the aging mother liquor is returned to the synthesis kettle of step (2) and added to the ferric acid solution;

(5) The first filter cake in step (4) enters the slurrying tank through the screw conveyor. Under stirring, water is added to slurry and wash the first filter cake. The amount of water used is the amount of the first filter cake. 4 times the mass of the cake; then the resulting system is sent to the washing filter press through the slurry tank discharge pump for filtration to obtain the second filter cake and washing water; wherein the washing water is returned to the homogenizer of step (4) Aging tank and added to the crude ferric phosphate slurry;

(6) The second filter cake described in step (5) enters the dryer through a belt conveyor, and is dried and dehydrated at 85°C for 2 hours to obtain iron phosphate;

Wherein, step (3) is performed simultaneously during steps (4)-(6).

Example 6

This embodiment provides a method for preparing iron phosphate by recycling iron-containing hydrochloric acid waste liquid. Except for adjusting the synthesis reaction time from 3h to 1h in step (2), the other conditions of the method are completely the same as those in Example 5. same.

Example 7

This embodiment provides a method for preparing iron phosphate by recycling iron-containing hydrochloric acid waste liquid. Except for adjusting the synthesis reaction time from 7h to 9h in step (2), the other conditions of the method are completely the same as those in Example 1. same.

Example 8

This embodiment provides a method for preparing iron phosphate by utilizing iron-containing hydrochloric acid waste liquid as a resource. In addition to adjusting the homogeneous aging time in step (4) from 2h to 1h, other conditions of the method are the same as those in the embodiment. 1 is exactly the same.

Example 9

This embodiment provides a method for preparing iron phosphate by utilizing iron-containing hydrochloric acid waste liquid resources. In addition to adjusting the homogeneous aging time in step (4) from 6h to 7h, other conditions of the method are the same as those in the embodiment. 5 are exactly the same.

Comparative example 1

This comparative example provides a method for preparing iron phosphate by utilizing iron-containing hydrochloric acid waste liquid as a resource. The method does not perform homogeneous aging, that is, step (4) of the method is: the step (2) is The crude ferric phosphate slurry is transported to the homogeneous aging tank through the discharge pump of the synthesis kettle, and then transported to the aging filter press through the discharge pump of the aging tank for solid-liquid separation to obtain the first filter cake and aging Mother liquor; wherein, the aged mother liquor is returned to the synthesis kettle of step (2) and added to the ferric acid solution; except for this step, other conditions are exactly the same as in Example 5.

Comparative example 2

This comparative example provides a method for preparing iron phosphate by recycling iron-containing hydrochloric acid waste liquid. In addition to adjusting the temperature of the synthesis reaction from 130°C to 100°C in step (2), the method has other conditions and examples. 1 is exactly the same.

Comparative example 3

This comparative example provides a method for preparing iron phosphate by recycling iron-containing hydrochloric acid waste liquid. In addition to adjusting the temperature of the synthesis reaction from 200°C to 220°C in step (2), the method has other conditions and examples. 5 are exactly the same.

According to the analysis method of "GB/T 622-2006 Chemical Reagent Hydrochloric Acid", the concentration of the regenerated hydrochloric acid obtained in the Examples and Comparative Examples was tested, and "GB/T 3051-2000 General Method for Determination of Chloride Content in Inorganic Chemical Products Mercury Measurement Method 》 and Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) were used to test the recovery rates of Cl and Fe elements in the iron-containing hydrochloric acid pickling waste liquid. At the same time, HG/T4701-2014 Phosphoric Acid for Batteries was also used. Iron》The purity of the obtained iron phosphate product was tested, and the above results are listed in Table 2.

Table 2

project Regeneration hydrochloric acid concentration Cl recovery rate in waste liquid Fe recovery rate in waste liquid Iron phosphate purity Example 1 18wt% 96.6wt% 98.9wt% 99.77wt% Example 2 19wt% 95.5wt% 98.3wt% 99.76wt% Example 3 20wt% 98.3wt% 99.7wt% 99.84wt% Example 4 21wt% 98.1wt% 99.3wt% 99.85wt% Example 5 21wt% 98.0wt% 99.2wt% 99.83wt% Example 6 19wt% 95.7wt% 97.9wt% 99.81wt% Example 7 18wt% 97.2wt% 99.1wt% 99.46wt% Example 8 18wt% 96.6wt% 97.1wt% 99.45wt% Example 9 21wt% 98.1wt% 99.3wt% 99.85wt% Comparative example 1 21wt% 98.1wt% 76wt% 99.88wt% Comparative example 2 3wt% 10wt% 0wt% / Comparative example 3 21wt% 98.5wt% 96.6wt% 97.91wt%

It can be seen from Table 2:

(1) Compared with Example 1, the synthesis reaction time in step (2) of Example 7 was adjusted from 7h to 9h, which is higher than the preferred range of 3 to 7h; compared with Example 5, step (2) of Example 6 ), the synthesis reaction time is adjusted from 3h to 1h, which is lower than the preferred range of 3 to 7h; the length of the synthesis reaction is related to the reaction temperature. The higher the reaction temperature, the shorter the synthesis time required, and vice versa; and the longer the synthesis time, the shorter the synthesis time. If the synthesis time is too long, the yields of Cl and Fe will not become worse, but the production efficiency will decrease and the energy consumption will increase. When the synthesis time is too short, it is easy to cause the hydrogen chloride gas to not completely escape and volatilize from the slurry, resulting in Cl and Fe The yield is relatively low;

(2) Compared with Example 1, Example 8 adjusts the homogeneous aging time in step (4) from 2h to 1h, which is lower than the preferred range of 2 to 6h; compared with Example 5, Example 9 adjusts the homogeneous aging time in step (4) from 2h to 1h. The homogeneous aging time in step (4) is adjusted from 6h to 7h, which is higher than the preferred range of 2 to 6h; the aging reaction is a key step in preparing iron phosphate yield and crystal size. The longer the aging reaction time, the better the phosphorus content. , has a promoting effect on the yield of iron and can increase the yield of iron phosphate, but it will also cause the iron phosphate crystal grains to agglomerate, making the crystal particle size larger, and has a certain impact on the purity, which is not conducive to impurity removal, thereby affecting the product performance; and too short an aging reaction time will cause the iron phosphate grains to be formed before being formed or to be smaller before being transported to the next stage, so the yield of the product will be affected; the Fe yield obtained in Example 5 (99.2wt%), Comparative Example 1 did not undergo aging, so the yield of Fe was seriously reduced, only 76wt%. Therefore, to increase the yield of phosphoric acid products, it is very necessary to set up homogeneous aging;

(3) Compared with Example 1, Comparative Example 2 adjusted the temperature of the synthesis reaction in step (2) from 130°C to 100°C, which is lower than the preferred range of 120-200°C; compared with Example 5, Comparative Example 3 Adjust the synthesis reaction temperature in step (2) from 200°C to 220°C, which is higher than the preferred range of 120-200°C; too low a synthesis reaction temperature will cause the slurry in the synthesis system to fail to reach the boiling point, so the hydrogen chloride gas The volatilization rate is seriously affected, and it will not even evaporate from the slurry. The reaction cannot proceed, iron phosphate cannot be produced, and high-concentration regenerated hydrochloric acid cannot be recovered; and using too high a synthesis reaction temperature will cause the synthesis reaction to occur. Side reactions produce ferric pyrophosphate and ferric hydroxychloride, which reduces the purity of the ferric phosphate product. For example, the purity of the ferric phosphate obtained in Comparative Example 3 is only 97.91wt%. In addition, the volatilization of hydrogen chloride gas may carry phosphoric acid, thus reducing the product quality. Yield.

(4) It can be seen from the above analysis and comparison that the method of using iron-containing hydrochloric acid pickling waste liquid to prepare iron phosphate as a resource according to the present invention can realize the production of iron phosphate by separating iron and chlorine in the hydrochloric acid pickling waste liquid. Preparation, regeneration and recycling of hydrochloric acid, the present invention uses low-cost iron sources to prepare high-value iron phosphate, which not only achieves value improvement and quality improvement, but also organically couples the resource utilization of waste liquid with the preparation of new energy materials, and fully There is no emission of three wastes in the process and no environmental hazards.

The present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent replacements of the selected components of the present invention, addition of auxiliary components, selection of specific modes, etc., all fall within the protection scope and disclosure scope of the present invention.

The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, a variety of simple modifications can be made to the technical solutions of the present invention. These simple modifications All belong to the protection scope of the present invention.

In addition, it should be noted that each of the specific technical features described in the above-mentioned specific embodiments can be combined in any suitable manner without conflict. In order to avoid unnecessary repetition, the present invention combines various possible combinations. The combination method will not be further explained.

In addition, any combination of various embodiments of the present invention can also be carried out. As long as they do not violate the idea of the present invention, they should also be regarded as the disclosed content of the present invention.

Claims (37)

1. A method for preparing ferric phosphate by utilizing ferric acid pickling waste liquid resource is characterized by comprising the following steps:

(1) Adding an oxidant into the ferric acid pickling waste liquid to perform oxidation treatment to obtain ferric acid liquid;

(2) Adding phosphoric acid into the ferric acid liquid in the step (1), and carrying out synthesis reaction for 3-7 hours at 130-200 ℃ to obtain crude ferric phosphate slurry and gaseous hydrogen chloride;

(3) Absorbing the gaseous hydrogen chloride in the step (2) by using an absorbent and purifying tail gas to obtain regenerated hydrochloric acid;

(4) Adding water into the crude ferric phosphate slurry obtained in the step (2) for homogenizing and aging for 2-6 hours, and then performing solid-liquid separation to obtain a first filter cake and an aging mother solution; wherein the aging mother liquor returns to the step (2) and is added into the ferric acid liquor;

(5) Performing slurry-dissolving washing and filtering on the first filter cake obtained in the step (4) by using water to obtain a second filter cake and washing water; wherein the wash water is returned to step (4) and added to the crude ferric phosphate slurry;

(6) Drying and dehydrating the second filter cake in the step (5) to obtain ferric phosphate;

wherein step (3) is performed simultaneously during the process of steps (4) - (6).

2. The method of claim 1, wherein the oxidizing agent of step (1) comprises hydrogen peroxide and/or oxygen.

3. The method of claim 1, wherein the amount of the oxidizing agent is 1.02 to 1.1 times the molar amount of ferrous ions in the iron-containing acid pickling waste liquid.

4. The method of claim 1, wherein the oxidizing treatment of step (1) is performed with stirring.

5. The method of claim 1, wherein the phosphoric acid in step (2) is used in an amount 1 to 1.2 times the molar amount of iron in the ferric acid solution.

6. The process of claim 1, wherein the synthesis reaction of step (2) is carried out with stirring.

7. The method according to claim 1, wherein the absorbent in step (3) forms an internal circulation during the absorption and the exhaust gas purification, respectively.

8. The method of claim 1, wherein the absorbent of step (3) comprises water.

9. The method according to claim 1, wherein the internal recycle of tail gas cleanup produces hydrochloric acid with a concentration of less than 5wt% and is refluxed directly to the step of absorption as an absorbent.

10. The method of claim 1, wherein the internal recycle of the absorption produces the regenerated hydrochloric acid at a concentration of 18-21 wt%.

11. The method of claim 1, wherein the amount of water used in step (4) is 3 to 5 times the mass of iron phosphate in the crude iron phosphate slurry.

12. The method of claim 1, wherein the homogenizing aging of step (4) is performed with agitation.

13. The method of claim 1, wherein the amount of water used in step (5) is 3-5 times the mass of the first filter cake.

14. The method of claim 1, wherein the slurrying washing of step (5) is performed with agitation.

15. The method of claim 1, wherein the temperature of the drying and dewatering in step (6) is 80-90 ℃.

16. The method of claim 1, wherein the drying and dehydrating time in the step (6) is 1-3 hours.

17. The method according to claim 1, characterized in that it comprises the steps of:

(1) Adding hydrogen peroxide and/or oxygen as an oxidant into the ferric acid pickling waste liquid, wherein the usage amount of the oxidant is 1.02-1.1 times of the molar amount of ferrous ions in the ferric acid pickling waste liquid, and then carrying out oxidation treatment under stirring to obtain ferric acid liquid;

(2) Adding phosphoric acid into the ferric acid liquid in the step (1), and carrying out synthesis reaction for 3-7 hours at 130-200 ℃ under stirring, wherein the dosage of the phosphoric acid is 1-1.2 times of the molar quantity of iron element in the ferric acid liquid, so as to obtain crude ferric phosphate slurry and gaseous hydrogen chloride;

(3) Using water as an absorbent to absorb the gaseous hydrogen chloride in the step (2) and purifying tail gas; the absorbent forms internal circulation in the absorption process and the tail gas purification process respectively; the internal circulation of the tail gas purification generates hydrochloric acid with the concentration of less than 5 weight percent and is used as an absorbent to directly reflux to the absorption step; the absorbed internal circulation generates regenerated hydrochloric acid with the concentration of 18-21 wt%;

(4) Adding water into the crude ferric phosphate slurry obtained in the step (2), homogenizing and aging for 2-6 hours under stirring, wherein the water consumption is 3-5 times of the mass of ferric phosphate in the crude ferric phosphate slurry, and then performing solid-liquid separation to obtain a first filter cake and an aging mother solution; wherein the aging mother liquor returns to the step (2) and is added into the ferric acid liquor;

(5) In the stirring state, performing slurry dissolving washing on the first filter cake in the step (4) by using water, and filtering, wherein the water consumption is 3-5 times of the mass of the first filter cake, so as to obtain a second filter cake and washing water; wherein the wash water is returned to step (4) and added to the crude ferric phosphate slurry;

(6) Drying and dehydrating the second filter cake in the step (5) at 80-90 ℃ for 1-3 hours to obtain ferric phosphate;

wherein step (3) is performed simultaneously during the process of steps (4) - (6).

18. The device system for preparing the ferric phosphate by utilizing the ferric acid pickling waste liquid is characterized by comprising an oxidation unit, a synthesis unit, an aging separation unit, a slurry washing unit and a drying discharging unit which are sequentially connected along the material flow direction, and further comprising a hydrochloric acid recovery unit connected with a gas outlet of the synthesis unit; wherein the liquid outlet of the aging separation unit is connected with the inlet of the synthesis unit; the liquid outlet of the slurry melting washing unit is connected with the inlet of the aging separation unit; the hydrochloric acid recovery unit comprises a hydrochloric acid absorption tower and a tail gas purification tower which are sequentially connected along the gas flow direction.

19. The plant system of claim 18, wherein the oxidation unit comprises an oxidation tank.

20. The plant system according to claim 18, characterized in that an oxidation tank discharge pump is arranged between the oxidation unit and the synthesis unit; the inlet of the oxidation tank discharging pump is connected with the outlet of the oxidation unit, and the outlet of the oxidation tank discharging pump is connected with the inlet of the synthesis unit.

21. The plant system of claim 18, wherein the synthesis unit comprises a synthesis tank; the synthesis kettle is provided with a material outlet and a gas outlet, and the gas outlet is used as a gas outlet of the synthesis unit.

22. The plant system according to claim 18, characterized in that a synthesis tank discharge pump is arranged between the synthesis unit and the aging separation unit; the inlet of the synthesis kettle discharging pump is connected with the material outlet of the synthesis unit, and the outlet of the synthesis kettle discharging pump is connected with the inlet of the aging separation unit.

23. The plant system according to claim 18, wherein the aging separation unit comprises a homogeneous aging tank and an aging filter press connected in sequence; the aging filter press is provided with a material outlet and a liquid outlet, and the liquid outlet is used as a liquid outlet of the aging separation unit.

24. The plant system according to claim 23, characterized in that an aging tank discharge pump is arranged between the homogenizing aging tank and the aging filter press; the inlet of the ageing tank discharging pump is connected with the outlet of the homogenizing ageing tank, and the outlet of the ageing tank discharging pump is connected with the inlet of the ageing filter press.

25. The plant system according to claim 18, characterized in that a screw conveyor is arranged between the aging separation unit and the slurry washing unit; the inlet of the screw conveyor is connected with the material outlet of the aging separation unit, and the outlet of the screw conveyor is connected with the inlet of the slurry melting washing unit.

26. The plant system according to claim 18, wherein the slurry wash unit comprises a slurry tank and a wash filter press connected in sequence; the washing filter press is provided with a material outlet and a liquid outlet, and the liquid outlet is used as a liquid outlet of the slurry-melting washing unit.

27. The plant system according to claim 26, characterized in that between the headbox and the wash filter press a headbox discharge pump is arranged; the inlet of the slurry melting tank discharging pump is connected with the outlet of the slurry melting tank, and the outlet of the slurry melting tank discharging pump is connected with the inlet of the drying discharging unit.

28. The system of claim 18, wherein a belt conveyor is disposed between the slurry wash unit and the dry discharge unit; the inlet of the belt conveyor is connected with the material outlet of the slurry melting and washing unit, and the outlet of the belt conveyor is connected with the inlet of the drying discharging unit.

29. The apparatus system of claim 18, wherein the dry discharge unit comprises a dryer.

30. The plant system of claim 19, wherein the oxidation tank is an acid-resistant oxidation-resistant apparatus with a stirring module.

31. The plant system of claim 21, wherein the synthesis tank is an acid-resistant oxidation-resistant apparatus with a stirring module.

32. The plant system of claim 23, wherein the homogeneous aging tank is an acid and oxidation resistant apparatus with a stirring module.

33. The plant system of claim 26, wherein the slurry tank is an acid and oxidation resistant apparatus with a stirring module.

34. The plant system according to claim 18, wherein the bottom liquid outlet of the hydrochloric acid absorption tower is connected to the inlet of the regenerated hydrochloric acid storage device and the top liquid inlet of the hydrochloric acid absorption tower, respectively; the bottom liquid outlet of the tail gas purifying tower is respectively connected with the top liquid inlet of the hydrochloric acid absorbing tower and the top liquid inlet of the tail gas purifying tower; the tower top liquid inlet of the tail gas purifying tower is connected with a water inlet pipe; the top of the tail gas purifying tower is provided with a tail gas outlet.

35. The plant system according to claim 18, wherein an acid-resistant tail gas blower is provided between the hydrochloric acid absorption tower and the tail gas purification tower; the inlet of the acid-resistant tail gas fan is connected with the gas outlet of the hydrochloric acid absorption tower, and the outlet of the acid-resistant tail gas fan is connected with the gas inlet of the tail gas purification tower.

36. The system of claim 34, wherein the bottom liquid outlet of the hydrochloric acid absorber is connected to an absorber circulating pump, the absorber circulating pump outlet being divided into two branches, a first branch being connected to the inlet of the regenerated hydrochloric acid storage device and a second branch being connected to the top liquid inlet of the hydrochloric acid absorber.

37. The plant system according to claim 18, wherein the bottom liquid outlet of the tail gas purification tower is connected to a purification tower circulation pump, the outlet of the purification tower circulation pump being divided into two branches, a first branch being connected to the top liquid inlet of the hydrochloric acid absorption tower and a second branch being connected to the top liquid inlet of the tail gas purification tower.