CN114671421B

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

Info

Publication number: CN114671421B
Application number: CN202210472453.9A
Authority: CN
Inventors: 安学斌; 杨刚; 王云山
Original assignee: Institute of Process Engineering of CAS
Current assignee: Institute of Process Engineering of CAS
Priority date: 2022-04-29
Filing date: 2022-04-29
Publication date: 2023-10-10
Anticipated expiration: 2042-04-29
Also published as: CN114671421A

Abstract

The invention relates to a method and a system for preparing ferric phosphate by utilizing ferric acid pickling waste liquid as a resource. The hydrogen chloride generated in the synthesis reaction process carried out at 130-200 ℃ can be recovered to obtain the regenerated hydrochloric acid with the concentration of 18-21 wt% which is suitable for cold rolling pickling; the ageing mother liquor and the washing water formed in the process can be recycled; the invention also provides a system for realizing the method, which comprises an oxidation unit, a synthesis unit, a hydrochloric acid recovery unit, an aging separation unit, a chemical pulp washing unit and a drying discharging unit; the invention can realize the resource utilization of the hydrochloric acid waste liquid, prepare the new energy material ferric phosphate, obviously improve the value and quality, realize the regeneration cycle of hydrochloric acid, and have no three wastes discharge and no environmental pollution.

Description

Method and system for preparing ferric phosphate by utilizing ferric acid pickling waste liquid resource

Technical Field

The invention belongs to the fields of waste liquid recycling and new energy material preparation, and relates to a method and a system for preparing ferric phosphate by utilizing ferric acid pickling waste liquid recycling.

Background

In China, a plurality of production lines such as cold-rolled steel strip, acid-washed steel strip, steel pipe and steel wire are provided, and the surfaces of the products are required to be acid-washed in the deep processing process to remove oxidized iron scales on the surfaces, wherein the most commonly used acid washing liquid is hydrochloric acid, so that a large amount of hydrochloric acid pickling waste liquid is generated. The hydrochloric acid pickling waste liquid contains a small amount of free acid, ferric iron and a large amount of ferrous iron, and is listed in the national hazardous waste directory due to the serious corrosiveness. The current method for treating the steel pickling waste liquid at home and abroad mainly comprises a direct roasting method, an evaporation concentration crystallization method, a membrane method and the like, wherein the direct roasting method is certainly the most thorough method for solving the problem of waste acid, and can realize the maximum recycling of hydrochloric acid, but the direct roasting method has higher threshold, large device investment and difficult bearing of common small enterprises, so that the development of the enterprises in this aspect is limited; the product market capacity of the evaporation concentration crystallization method is small, and the product quality is difficult to ensure; the membrane method can only treat relatively dilute waste liquid, and cannot treat high concentration, and the method also only has the effect of reducing the amount, so that the problem of large-scale effective utilization of the hydrochloric acid pickling waste liquid cannot be thoroughly solved.

Iron phosphate has been well applied in the fields of agriculture, ceramic glass, steel, surface passivation and the like. Because of the unique catalytic properties, ion exchange capacity and electrochemical performance, the lithium iron phosphate has attracted attention in recent years, and has been used in the fields of catalysis, lithium battery electrode materials and the like, for example, lithium iron phosphate is an important lithium ion power battery anode material, and is widely applied to new energy automobiles, and iron phosphate is an important precursor for synthesizing lithium iron phosphate; the current preparation method of ferric phosphate mainly comprises a precipitation method, which comprises the steps of reacting ferrous sulfate as an iron source with ammonium dihydrogen phosphate as a phosphorus source or synthesizing ferric chloride as an iron source with phosphoric acid as a phosphorus source, wherein the former method generates a large amount of ferric ammonium sulfate byproducts, and the latter method requires a large phosphorus-iron ratio.

CN112661129a discloses a preparation method of ferric phosphate, wherein ferrous sulfate solution is used as raw material, ferrous phosphate is generated by ferrous sulfate solution and phosphorus, then impurity removal, complexation and oxidation are carried out to obtain ferric phosphate dihydrate, and finally, anhydrous ferric phosphate is obtained by high-temperature calcination; the method needs to add the phosphorus source for multiple times, and has longer process flow.

CN112479174a discloses a method for synthesizing ferric phosphate by using ferrous sulfate as a titanium white byproduct, and the ferrous sulfate as a raw material is used for preparing a finished product of ferric phosphate.

CN113955732a discloses a method for preparing ferric phosphate by using ferric trichloride as a catalyst, the method prepares ferric phosphate by reacting a ferric trichloride circularly dissolved iron source with phosphoric acid, nitric acid is required as the catalyst, the requirement on equipment is high, and nitrogenous wastewater is easy to produce.

From the above, it is necessary to develop a new technical method that not only can the hydrochloric acid pickling waste liquid be utilized on a large scale to solve the recycling problem, but also the preparation of ferric phosphate can be realized in a low-cost short-flow manner, and the medium can be recycled.

Disclosure of Invention

In view of the problems existing in the prior art, the invention aims to provide a method and a system for preparing ferric phosphate by utilizing ferric acid pickling waste liquid as resources. 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 and pickling; the ageing mother liquor and the washing water formed in the process can be recycled; by using the method and the system, the recovery rate of hydrochloric acid in the waste pickle containing ferric salt acid can reach more than 95%, the recovery rate of iron element can reach more than 95%, and the ferric phosphate with the purity of 99.5-99.9% can be obtained; therefore, the invention not only can realize the resource utilization of the hydrochloric acid pickling waste liquid to prepare the new energy material ferric phosphate, but also can obviously improve the value and quality, and can realize the regeneration cycle of hydrochloric acid, and has no three-waste discharge and no environmental pollution.

To achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the invention provides a method for preparing ferric phosphate by recycling ferric acid pickling waste liquid, which comprises 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 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, and then carrying out 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).

The iron-containing acid pickling waste liquid is derived from cold rolling pickling waste liquid in the iron and steel industry, new energy material ferric phosphate can be prepared from the waste liquid by using the method, hydrogen chloride can be recovered to generate regenerated hydrochloric acid, the regenerated hydrochloric acid can be reused in the cold rolling pickling process, and the formed pickling waste liquid can enter the method for recycling; the residual tail gas in the process of recycling the hydrochloric acid is purified and then discharged up to the standard, the whole process has no three-waste discharge, the resource utilization rate is high, the added value of the product is greatly improved, and the organic coupling in the two fields of waste liquid recycling and new energy material preparation can be realized.

The synthesis reaction in the step (2) of the method means that ferric chloride reacts with phosphoric acid to generate ferric phosphate and gaseous hydrogen chloride, the synthesis reaction is carried out at a high temperature of 130-200 ℃, so that the volatilization of the hydrogen chloride from a solution can be promoted, the hydrogen chloride is brought into an absorbent through evaporated water vapor to be recycled, a large amount of hydrogen chloride is taken away, the reverse reaction of the synthesis of the ferric phosphate can be weakened, the precipitation rate of the ferric phosphate is improved, and the obtained product is slurry with crude ferric phosphate and high viscosity due to evaporation of a large amount of water; therefore, the invention needs to carry out the subsequent water adding and aging process, so that the ferric phosphate crystal is homogenized and aged again in the liquid phase with larger mass transfer coefficient, the granularity and the morphology of the ferric phosphate crystal are controlled and optimized, the adsorption of impurities is reduced to a certain extent, and the ferric phosphate dihydrate product is prepared; and removing excessive impurities through dissolving and washing, improving the purity of the product, and drying to remove free water from the ferric phosphate crystals to obtain the ferric phosphate product.

The synthesis reaction at 130 to 200℃in the step (1) of the method of the present invention is, for example, 130℃135℃140℃145℃150℃155℃160℃165℃170℃175℃180℃185℃190℃195℃200℃or the like, but is not limited to the values listed, and other values not listed in the above-mentioned ranges are equally applicable.

The following technical scheme is a preferred technical scheme of the invention, but is not a limitation of the technical scheme provided by the invention, and the technical purpose and beneficial effect of the invention can be better achieved and realized through the following technical scheme.

As a preferred embodiment 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, for example, 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, the molar amount of the divalent iron ions in the iron-containing acid pickling waste liquid, but the oxidizing agent is not limited to the recited values, and other non-recited values within the above-recited ranges are equally applicable.

The ferric acid pickling waste liquid contains a large amount of iron elements, but most of the ferric acid pickling waste liquid exists in a solution in the form of ferrous ions, the amount of the oxidant in the invention can be calculated according to the molar amount of the ferrous ions in the solution, and the amount of the oxidant ensures that all the ferrous ions are oxidized into ferric ions.

Preferably, the oxidation treatment of step (1) is performed with stirring.

In a preferred embodiment of the present invention, the phosphoric acid in step (2) is used in an amount of 1 to 1.2 times, for example, 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, 1.2 times, etc., the molar amount of the iron element in the ferric acid solution, but the phosphoric acid is not limited to the above-mentioned values, and other values not mentioned in the above-mentioned ranges are equally applicable.

Preferably, the synthesis reaction of step (2) is carried out with stirring.

Preferably, the time of the synthesis reaction in step (2) is 3 to 7 hours, for example, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours or 7 hours, etc., but not limited to the recited values, and other non-recited values within the above-mentioned range are equally applicable.

The temperature of the synthesis reaction in the step (2) is related to the time, when the temperature of the synthesis reaction used in the range is higher, the reaction time can be properly reduced in the range, but the reaction time cannot be too short, otherwise, the volatilization amount of hydrogen chloride can be influenced, the excessive evaporation of water can be caused by the excessive reaction time, and the obtained crude ferric phosphate slurry is too dry, has poor fluidity and is unfavorable for the subsequent technological process.

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

Preferably, the absorbent of step (3) comprises water.

Preferably, the internal recycle of the tail gas clean-up produces hydrochloric acid with a concentration of less than 5wt% and is refluxed directly to the absorption as an absorbent, for example, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt% or 4.9wt%, etc., but is not limited to the recited values, and other non-recited values within the above-recited range are equally applicable.

Preferably, the internal recycle of the absorption produces the regenerated hydrochloric acid at a concentration of 18 to 21wt%, for example 18wt%, 18.5wt%, 19wt%, 19.5wt%, 20wt%, 20.5wt% or 21wt%, etc., but is not limited to the recited values, and other non-recited values within the above range are equally applicable.

At the beginning of the absorption and tail gas purification, the invention preferably adds pure water as an absorbent, uses the pure water to absorb the hydrogen chloride gas first, and then uses the pure water to further absorb the residual gas so as 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 the concentration of less than 5wt%, the hydrochloric acid is directly refluxed to the absorption as an absorbent, and after the internal circulation of absorption, the regenerated hydrochloric acid with the concentration of 18-21 wt% can be finally obtained, and the regenerated hydrochloric acid can be directly used for cold rolling; it is emphasized that the invention needs to recycle the low-concentration hydrochloric acid generated by tail gas purification to the absorption process, and the concentration of the obtained regenerated hydrochloric acid can reach the requirement through the internal circulation of the absorption, so that the high recovery rate of hydrogen chloride is ensured, and the internal circulation of the tail gas purification is also beneficial to realizing the standard emission of the tail gas, if only the absorption is arranged without the purification process, the recovery rate of the hydrogen chloride is low, and the tail gas is difficult to reach the standard.

As a preferred embodiment of the present invention, the amount of the water used in the step (4) is 3 to 5 times, for example, 1 time, 1.5 times, 2 times, 2.5 times, 3 times, 3.5 times, 4 times, 4.5 times, or 5 times, the mass of the iron phosphate in the crude iron phosphate slurry, but is not limited to the recited values, and other non-recited values within the above-mentioned range are equally applicable; and the mass of the ferric phosphate in the crude ferric phosphate slurry is the theoretical yield of the ferric phosphate, and the theoretical yield of the ferric phosphate is calculated according to the molar quantity of the iron element in the trivalent ferric acid liquid obtained in the step (3) and calculated according to the conversion yield of 100 percent.

Preferably, the homogeneous ageing of step (4) is carried out with stirring.

Preferably, the time of the homogeneous aging in the step (4) is 2 to 6 hours, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours or 6 hours, etc., but not limited to the recited values, and other non-recited values within the above-mentioned range are equally applicable.

The aging time of the invention is related to the synthesis reaction performed in step (2), and when the synthesis reaction is performed at a higher temperature, the aging time required should be properly prolonged within a range so that the iron phosphate crystals are sufficiently aged.

In a preferred embodiment of the present invention, the amount of water used in the step (5) is 3 to 5 times, for example, 1 time, 1.5 times, 2 times, 2.5 times, 3 times, 3.5 times, 4 times, 4.5 times, or 5 times the mass of the first cake, but the present invention is not limited to the above-mentioned values, and other values not mentioned in the above-mentioned range are applicable.

Preferably, the slurrying washing of step (5) is performed under agitation.

Preferably, the temperature of the drying and dehydrating in the step (6) is 80 to 90 ℃, for example 80 ℃, 81 ℃, 82 ℃, 83 ℃, 84 ℃, 85 ℃, 86 ℃, 87 ℃, 88 ℃, 89 ℃, or 90 ℃, etc., but the present invention is not limited to the above-mentioned values, and other values not mentioned in the above-mentioned value range are equally applicable.

Preferably, the drying and dehydrating time in the step (6) is 1 to 3 hours, for example, 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours or 3 hours, etc., but not limited to the recited values, and other non-recited values within the above-mentioned range are equally applicable.

In order to obtain the ferric phosphate dihydrate product, the drying and dehydrating time is set to be 1-3 hours, and the longer drying time or the addition of the subsequent heat treatment process can lead to the reduction of the crystal water in the ferric phosphate, but the selection and adjustment can be carried out according to actual needs by a person skilled in the art.

As a preferred technical scheme of the invention, the method comprises the following steps:

(1) Hydrogen peroxide and/or oxygen is/are added into the ferric acid pickling waste liquid as an oxidant, 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 the ferric acid liquid is obtained through oxidation treatment under stirring;

(2) Adding phosphoric acid into the ferric acid liquid in the step (1), and carrying out synthesis reaction for 3-7 h 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 an internal circulation in the absorption and the tail gas purification 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; 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 carrying out 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 h to obtain ferric phosphate;

In a second aspect, the invention provides a system for preparing ferric phosphate by recycling ferric acid pickling waste liquid, which comprises 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 comprises 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.

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

Preferably, 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.

Preferably, 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.

Preferably, a synthetic kettle discharge pump is arranged between the synthetic 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 device is connected with the inlet of the aging separation unit.

Preferably, the aging separation unit comprises a homogenizing aging tank and an aging filter press which are connected in sequence; wherein 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.

Preferably, an ageing tank discharging pump is arranged between the homogenizing ageing tank and the ageing 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.

Preferably, 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.

Preferably, the slurry dissolving and washing unit comprises a slurry dissolving tank and a washing filter press which are 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.

Preferably, a slurry dissolving tank discharging pump is arranged between the slurry dissolving tank and the washing filter press; 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.

Preferably, a belt conveyor is arranged between the pulp dissolving and washing unit and the drying and discharging 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.

Preferably, the drying discharging unit comprises a dryer.

Preferably, the oxidation tank, the synthesis kettle, the homogenizing aging tank and the slurry dissolving tank are all acid-resistant and oxidation-resistant equipment with stirring modules.

Because the reaction process is in a strong acid environment, an oxidation tank, a synthesis kettle, a homogenizing ageing tank, a slurry melting tank and the like are required to be acid-resistant and oxidation-resistant equipment, for example, the oxidation tank and the slurry melting tank are both made of steel-lined tetrafluoro, and the inner lining of the synthesis kettle is made of graphite; it should be noted that the heating mode of the synthesis kettle in the present invention is indirect heating, for example, the synthesis kettle is provided with a jacket, and low-pressure hot vapor is introduced into the jacket as a heating source, but the heating mode is not limited to this, and other indirect heating modes are also suitable for the present invention, and those skilled in the art can select according to practical situations.

As a preferable technical scheme of the invention, a bottom liquid outlet of the hydrochloric acid absorption tower is respectively connected with an inlet of the regenerated hydrochloric acid storage device and a top liquid inlet of the hydrochloric acid absorption tower; 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.

According to the invention, the liquid inlet at the top of the tail gas purifying tower is connected with a water inlet pipe, and water is added into a hydrochloric acid recovery unit through the water inlet pipe to serve as an absorbent; at first, before the hydrogen chloride gas enters the hydrochloric acid recovery unit, pure water is added through a water inlet pipe, so that the hydrochloric acid absorption tower and the tail gas purification tower reach a working state capable of carrying out absorption treatment, and then the hydrogen chloride gas enters the hydrochloric acid recovery unit for absorption.

After hydrogen chloride gas enters the hydrochloric acid absorption tower, pure water in the tower absorbs the gas, and then the gas is output through the tower bottom liquid outlet in two paths, and one path of the gas enters the hydrochloric acid absorption tower from the tower top liquid inlet of the hydrochloric acid absorption tower again for absorption so as to increase the concentration of regenerated hydrochloric acid; the other way outputs the regenerated hydrochloric acid product with the concentration reaching the requirement or stores the regenerated hydrochloric acid product; after the unabsorbed gas in the hydrochloric acid absorption tower enters the tail gas purification tower, purifying and absorbing the gas by pure water in the tower, discharging the residual tail gas up to the standard through a tail gas outlet at the tower top, outputting the obtained low-concentration regenerated hydrochloric acid through a tower bottom liquid outlet in two ways, and recycling the low-concentration regenerated hydrochloric acid through a tower top liquid inlet of the tail gas purification tower into the tail gas purification tower for recycling, wherein the low-concentration regenerated hydrochloric acid is continuously used for purifying the gas, and hydrochloric acid with the concentration of less than 5wt% can be obtained through the recycling; the other way is to input the hydrochloric acid with the concentration of less than 5 weight percent into the hydrochloric acid absorption tower through a tower top liquid inlet of the hydrochloric acid absorption tower to be used as an absorbent; it should be noted that, for the flow ratio relationship between the branches, those skilled in the art may adjust the flow ratio relationship according to actual situations.

The invention realizes the step absorption of the hydrogen chloride through the process, namely, pure water is added into a tail gas purifying tower and the concentration is increased after repeated circulation in the tower to obtain low-concentration hydrochloric acid (the concentration of the hydrogen chloride is less than 5 percent), then the low-concentration regenerated hydrochloric acid is used as an absorbent to be conveyed into a hydrochloric acid absorbing tower and repeated circulation is carried out, and finally high-concentration regenerated hydrochloric acid (the concentration of the hydrogen chloride is 18-21 wt%) is obtained, thereby realizing the regeneration and the cyclic utilization of the hydrochloric acid; after the hydrochloric acid absorption tower outputs a part of regenerated hydrochloric acid product reaching the requirement, the tail gas purification tower should timely convey low-concentration hydrochloric acid to the hydrochloric acid absorption tower as an absorbent to be supplemented, and then pure water should be supplemented into the tail gas purification tower through a water inlet pipe, so that the dynamic balance is maintained in the whole process; it should be noted that, in the present invention, pure water is preferably added as an absorbent in the initial stage, if hydrochloric acid with a concentration of less than 5wt% is selected to be directly added from the water inlet pipe as an absorbent, a basic tail gas treatment device is further added after the tail gas purifying tower in order to solve the problem of tail gas in the initial stage.

Preferably, an acid-resistant tail gas fan is arranged 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.

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

Preferably, the bottom liquid outlet of the tail gas purifying tower is connected with a purifying tower circulating pump, the outlet of the purifying tower circulating pump is divided into two paths, the first branch is connected with the top liquid inlet of the hydrochloric acid absorbing tower, and the second branch is connected with the top liquid inlet of the tail gas purifying tower.

Compared with the prior art, the invention has at least the following beneficial effects:

(1) The invention takes the iron-containing acid pickling waste liquid of the steel cold rolling as an iron source, realizes the separation and recovery of iron and chlorine, changes the iron into ferric phosphate, changes the chlorine into hydrochloric acid and can be recycled, and realizes the recycling of the iron-containing acid pickling waste liquid;

(2) According to the invention, the new energy material ferric phosphate is prepared from the low-cost ferric acid pickling waste liquid, so that the value and quality of the product are improved, and the waste liquid recycling and the new energy material preparation are organically coupled;

(3) The process of the invention adopts the step absorption to recycle the hydrochloric acid, has no three-waste discharge and no environmental hidden trouble.

Drawings

FIG. 1 is a schematic flow chart of a method for preparing ferric phosphate by recycling ferric acid pickling waste liquid;

FIG. 2 is a schematic diagram of a system for preparing iron phosphate by recycling waste pickle liquor containing ferric acid, which is used in the embodiment of the invention;

in the figure: 1-oxidation tank, 2-oxidation tank discharge pump, 3-synthetic kettle, 4-hydrochloric acid absorption tower, 5-absorption tower circulating pump, 6-acid-proof tail gas fan, 7-tail gas purifying tower, 8-purifying tower circulating pump, 9-synthetic kettle discharge pump, 10-homogenizing ageing tank, 11-ageing tank discharge pump, 12-ageing filter press, 13-screw conveyor, 14-pulping tank, 15-pulping tank discharge pump, 16-washing filter press, 17-belt conveyor and 18-dryer.

Detailed Description

The technical scheme of the invention is further described by the following specific embodiments. It will be apparent to those skilled in the art that the examples are merely to aid in understanding the invention and are not to be construed as a specific limitation thereof.

The flow chart of the method for preparing ferric phosphate by utilizing the recycling of the waste hydrochloric acid liquid containing iron is shown in fig. 1, and the method can be seen from the chart, and comprises the following steps:

The schematic diagrams of the system for preparing ferric phosphate by utilizing the ferrous hydrochloric acid waste liquid resource adopted in the embodiment and the comparative example are shown in fig. 2, and as can be seen from fig. 2, the system comprises an oxidation tank 1 and an oxidation tank discharging pump 2; a synthesis kettle 3; a hydrochloric acid absorption tower 4, an absorption tower circulating pump 5, an acid-resistant tail gas fan 6, a tail gas purifying tower 7 and a purifying tower circulating pump 8; a discharge pump 9 of the synthesis kettle; a homogenizing ageing tank 10, an ageing tank discharge pump 11, an ageing filter press 12 and a screw conveyor 13; a slurry melting tank 14, a slurry melting tank discharge pump 15, a washing filter press 16, a belt conveyor 17 and a dryer 18; wherein, the outlet of the oxidation tank 1 is connected with the inlet of the oxidation tank discharging pump 2, and the outlet of the oxidation tank discharging pump 2 is connected with the inlet of the synthesis kettle 3; the gas outlet of the synthesis kettle 3 is connected with the gas inlet of the hydrochloric acid absorption tower 4, the gas outlet of the hydrochloric acid absorption tower 4 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; a water inlet pipe is arranged at the tower top liquid inlet of the tail gas purifying tower, and a tail gas outlet is arranged at the tower top of the tail gas purifying tower; the bottom liquid outlet of the hydrochloric acid absorption tower 4 is connected with the inlet of the absorption tower circulating pump 5, and the outlet of the absorption tower circulating pump 5 is respectively connected with the top liquid inlet of the hydrochloric acid absorption tower 4 and the regenerated hydrochloric acid storage device or directly uses the regenerated hydrochloric acid for cold rolling and pickling; the bottom liquid outlet of the tail gas purifying tower 7 is connected with the inlet of the purifying tower circulating pump 8, and the outlet of the purifying tower circulating pump 8 is respectively connected with the top liquid inlet of the tail gas purifying tower 7 and the top liquid inlet of the hydrochloric acid absorbing tower 4; the material outlet of the synthesis kettle 3 is connected with the inlet of a synthesis kettle discharge pump 9, and the outlet of the synthesis kettle discharge pump 9 is connected with the inlet of a homogenizing ageing tank 10; the outlet of the homogenizing ageing tank 10 is connected with the inlet of an ageing tank discharge pump 11, and the outlet of the ageing tank discharge pump 11 is connected with the inlet of an ageing 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 with the inlet of the screw conveyor 13, and the outlet of the screw conveyor 13 is connected with the inlet of the slurry melting tank 14; the outlet of the slurry melting tank 14 is connected with the inlet of a slurry melting tank discharge pump 15, and the outlet of the slurry melting tank discharge pump 15 is connected with the inlet of a washing filter press 16; the liquid outlet of the washing filter press 16 is connected with the inlet of the homogenizing ageing tank 10, the material outlet of the washing filter press 16 is connected with the inlet of the belt conveyor 17, and the outlet of the belt conveyor 17 is connected with the inlet of the dryer 18.

The ferric salt acid pickling waste liquid adopted in the embodiment and the comparative example is from a cold rolling pickling workshop of a certain domestic iron and steel enterprise, and the main component content of the waste liquid is shown in table 1.

TABLE 1

Example 1

The embodiment provides a method for preparing ferric phosphate by recycling ferric hydrochloric acid waste liquid, which comprises the following steps:

(1) Adding ferric acid pickling waste liquid into an oxidation tank, adding hydrogen peroxide serving as an oxidant, wherein the usage amount of the oxidant is 1.05 times of the molar amount of ferrous ions in the ferric acid pickling waste liquid, and then performing oxidation treatment under stirring to obtain ferric acid liquid;

(2) The ferric acid liquid flows into a synthesis kettle through an oxidation tank discharge pump, phosphoric acid is added into the synthesis kettle, synthesis reaction is carried out for 7 hours at 130 ℃ under stirring, the consumption of the phosphoric acid is 1.1 times of the molar quantity of iron element in the ferric acid solution, and crude ferric phosphate slurry and gaseous hydrogen chloride are generated;

(3) Pure water is added into a water inlet pipe connected to a liquid inlet at the top of the tail gas purifying tower to serve as an absorbent, so that the hydrochloric acid purifying tower and the tail gas purifying tower reach an absorption treatment state, gaseous hydrogen chloride is introduced into the hydrochloric acid absorbing tower and is absorbed by the absorbent in the absorbing tower to form primary regenerated hydrochloric acid, unabsorbed hydrogen chloride gas enters the tail gas purifying tower through an acid-resistant tail gas fan to be purified and absorbed, secondary regenerated hydrochloric acid is obtained, and purified residual tail gas is discharged through a tail gas outlet of the tail gas purifying tower; at the moment, one part of the secondary regenerated hydrochloric acid is circulated in the tail gas purification tower through a purification tower circulating pump, and the other part of the secondary regenerated hydrochloric acid is conveyed into a hydrochloric acid absorption tower through the purification tower circulating pump to serve as an absorbent for further absorption; at the moment, one part of primary regenerated hydrochloric acid obtained in the hydrochloric acid absorption tower circulates in the hydrochloric acid absorption tower through an absorption tower circulating pump, the other part of primary regenerated hydrochloric acid outputs a regenerated hydrochloric acid product through an outlet of the absorption tower circulating pump and is directly used for cold rolling and pickling, and the formed ferric salt acid pickling waste liquid is reused in the invention;

(4) The crude ferric phosphate slurry is conveyed to a homogenizing ageing tank through a discharge pump of a synthesis kettle, water is added to the homogenizing ageing tank and is subjected to homogenizing ageing for 2 hours under stirring, the water consumption is 3 times of the mass of ferric phosphate in the crude ferric phosphate slurry, and then the obtained system is conveyed to an ageing filter press through a discharge pump of the ageing tank for solid-liquid separation, so that a first filter cake and an ageing mother liquor are obtained; wherein, the aging mother liquor returns to the synthesis kettle in the step (2) and is added into the ferric acid liquid;

(5) Step (4), the first filter cake enters a slurry melting tank through a screw conveyor, water is added to perform slurry melting washing on the first filter cake in a stirring state, and the water consumption is 3 times of the mass of the first filter cake; pumping the obtained system into a washing filter press through a slurry melting tank discharge pump, and filtering to obtain a second filter cake and washing water; wherein the wash water is returned to the homogeneous aging tank of step (4) and added to the crude ferric phosphate slurry;

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

Example 2

(1) Adding ferric acid pickling waste liquid into an oxidation tank, and then introducing oxygen serving as an oxidant, wherein the usage amount of the oxidant is 1.04 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) The ferric acid liquid flows into a synthesis kettle through an oxidation tank discharge pump, phosphoric acid is added into the synthesis kettle, synthesis reaction is carried out for 6 hours at 150 ℃ under stirring, the consumption of the phosphoric acid is 1 time of the molar quantity of iron element in the ferric acid solution, and crude ferric phosphate slurry and gaseous hydrogen chloride are generated;

(4) The crude ferric phosphate slurry is conveyed to a homogenizing ageing tank through a discharge pump of a synthesis kettle, water is added to the homogenizing ageing tank and is subjected to homogenizing ageing for 3 hours under stirring, the water consumption is 4 times of the mass of ferric phosphate in the crude ferric phosphate slurry, and then the obtained system is conveyed to an ageing filter press through a discharge pump of the ageing tank for solid-liquid separation, so that a first filter cake and an ageing mother liquor are obtained; wherein, the aging mother liquor returns to the synthesis kettle in the step (2) and is added into the ferric acid liquid;

(5) Step (4), the first filter cake enters a slurry melting tank through a screw conveyor, water is added to perform slurry melting washing on the first filter cake in a stirring state, and the water consumption is 4 times of the mass of the first filter cake; pumping the obtained system into a washing filter press through a slurry melting tank discharge pump, and filtering to obtain a second filter cake and washing water; wherein the wash water is returned to the homogeneous aging tank of step (4) and added to the crude ferric phosphate slurry;

(6) The second filter cake in the step (5) enters a dryer through a belt conveyor, and is dried and dehydrated for 2 hours at the temperature of 85 ℃ to obtain ferric phosphate;

Example 3

(1) Adding ferric acid pickling waste liquid into an oxidation tank, adding oxygen serving as an oxidant, wherein the usage amount of the oxidant is 1.02 times of the molar amount of ferrous ions in the ferric acid pickling waste liquid, and then performing oxidation treatment under stirring to obtain ferric acid liquid;

(2) The ferric acid liquid flows into a synthesis kettle through an oxidation tank discharge pump, phosphoric acid is added into the synthesis kettle, synthesis reaction is carried out for 4 hours at 170 ℃ under stirring, the consumption of the phosphoric acid is 1.2 times of the molar quantity of iron element in the ferric acid solution, and crude ferric phosphate slurry and gaseous hydrogen chloride are generated;

(4) The crude ferric phosphate slurry is conveyed to a homogenizing ageing tank through a discharge pump of a synthesis kettle, water is added to the homogenizing ageing tank and is subjected to homogenizing ageing for 4 hours under stirring, the water consumption is 5 times of the ferric phosphate mass in the crude ferric phosphate slurry, and then the obtained system is conveyed to an ageing filter press through a discharge pump of the ageing tank for solid-liquid separation, so that a first filter cake and an ageing mother liquor are obtained; wherein, the aging mother liquor returns to the synthesis kettle in the step (2) and is added into the ferric acid liquid;

(5) Step (4), the first filter cake enters a slurry melting tank through a screw conveyor, water is added to perform slurry melting washing on the first filter cake in a stirring state, and the water consumption is 5 times of the mass of the first filter cake; pumping the obtained system into a washing filter press through a slurry melting tank discharge pump, and filtering to obtain a second filter cake and washing water; wherein the wash water is returned to the homogeneous aging tank of step (4) and added to the crude ferric phosphate slurry;

(6) The second filter cake in the step (5) enters a dryer through a belt conveyor, and is dried and de-watered for 1h at 90 ℃ to obtain ferric phosphate;

Example 4

(1) Adding ferric acid pickling waste liquid into an oxidation tank, adding hydrogen peroxide serving as an oxidant, wherein the usage amount of the oxidant is 1.08 times of the molar amount of ferrous ions in the ferric acid pickling waste liquid, and then performing oxidation treatment under stirring to obtain ferric acid liquid;

(2) The ferric acid liquid flows into a synthesis kettle through an oxidation tank discharge pump, phosphoric acid is added into the synthesis kettle, and the synthesis reaction is carried out for 3 hours at 190 ℃ under stirring, wherein the dosage of the phosphoric acid is 1.1 times of the molar quantity of iron element in the ferric acid solution, and crude ferric phosphate slurry and gaseous hydrogen chloride are generated;

(4) The crude ferric phosphate slurry is conveyed to a homogenizing ageing tank through a discharge pump of a synthesis kettle, water is added to the homogenizing ageing tank and is subjected to homogenizing ageing for 5 hours under stirring, the water consumption is 5 times of the mass of ferric phosphate in the crude ferric phosphate slurry, and then the obtained system is conveyed to an ageing filter press through a discharge pump of the ageing tank for solid-liquid separation, so that a first filter cake and an ageing mother liquor are obtained; wherein, the aging mother liquor returns to the synthesis kettle in the step (2) and is added into the ferric acid liquid;

Example 5

(1) Adding ferric acid pickling waste liquid into an oxidation tank, adding hydrogen peroxide serving as an oxidant, wherein the usage amount of the oxidant is 1.1 times of the molar amount of ferrous ions in the ferric acid pickling waste liquid, and then performing oxidation treatment under stirring to obtain ferric acid liquid;

(2) The ferric acid liquid flows into a synthesis kettle through an oxidation tank discharge pump, phosphoric acid is added into the synthesis kettle, synthesis reaction is carried out for 3 hours at 200 ℃ under stirring, the consumption of the phosphoric acid is 1.1 times of the molar quantity of iron element in the ferric acid solution, and crude ferric phosphate slurry and gaseous hydrogen chloride are generated;

(4) The crude ferric phosphate slurry is conveyed to a homogenizing ageing tank through a discharge pump of a synthesis kettle, water is added to the homogenizing ageing tank and is subjected to homogenizing ageing for 6 hours under stirring, the water consumption is 4 times of the mass of ferric phosphate in the crude ferric phosphate slurry, and then the obtained system is conveyed to an ageing filter press through a discharge pump of the ageing tank for solid-liquid separation, so that a first filter cake and an ageing mother liquor are obtained; wherein, the aging mother liquor returns to the synthesis kettle in the step (2) and is added into the ferric acid liquid;

Example 6

This example provides a method for preparing iron phosphate by recycling waste hydrochloric acid solution containing iron, which is identical to example 5 except that the synthesis reaction time is adjusted from 3 hours to 1 hour in step (2).

Example 7

This example provides a method for preparing iron phosphate by recycling waste hydrochloric acid solution containing iron, which is identical to example 1 except that the synthesis reaction time is adjusted from 7 hours to 9 hours in step (2).

Example 8

This example provides a method for preparing iron phosphate by recycling waste hydrochloric acid solution containing iron, which is identical to example 1 except that the time for homogenizing and aging is adjusted from 2 hours to 1 hour in step (4).

Example 9

This example provides a method for preparing iron phosphate by recycling waste hydrochloric acid solution containing iron, which is identical to example 5 except that the time for homogenizing and aging is adjusted from 6 hours to 7 hours in step (4).

Comparative example 1

The comparative example provides a method for preparing ferric phosphate by utilizing ferric hydrochloric acid waste liquid resource, wherein the method is not subjected to homogenizing aging, namely, the step (4) of the method is as follows: conveying the crude ferric phosphate slurry obtained in the step (2) to a homogenizing ageing tank through a discharge pump of a synthesis kettle, and conveying the crude ferric phosphate slurry to an ageing filter press through a discharge pump of the ageing tank for solid-liquid separation to obtain a first filter cake and an ageing mother liquor; wherein, the aging mother liquor returns to the synthesis kettle in the step (2) and is added into the ferric acid liquid; except for this step, the other conditions were exactly the same as in example 5.

Comparative example 2

This comparative example provides a method for preparing iron phosphate by recycling waste hydrochloric acid solution containing iron, which is exactly the same as example 1 except that the temperature of the synthesis reaction is adjusted from 130 ℃ to 100 ℃ in step (2).

Comparative example 3

This comparative example provides a method for preparing iron phosphate by recycling waste hydrochloric acid solution containing iron, which is exactly the same as example 5 except that the temperature of the synthesis reaction in step (2) is adjusted from 200 to 220 ℃.

The concentrations of the regenerated hydrochloric acid obtained in the examples and the comparative examples were tested according to the analytical method of GB/T622-2006 chemical hydrochloric acid, the recovery rates of Cl and Fe elements in the iron-containing acid pickling waste liquid were respectively tested by using the general method mercury content method for chloride content determination in GB/T3051-2000 inorganic chemical products and inductively coupled plasma-atomic emission spectrometry (ICP-AES), and the purity of the obtained iron phosphate product was also tested by using the iron phosphate for HG/T4701-2014 batteries, and the above obtained results are shown in Table 2.

TABLE 2

Project	Concentration of regenerated hydrochloric acid	Recovery rate of Cl in waste liquid	Recovery rate of Fe in waste liquid	Purity of iron phosphate
					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％

As can be seen from table 2:

(1) In comparison with example 1, in example 7, step (2), the time of the synthesis reaction was adjusted from 7h to 9h, which is 3 to 7h higher than the preferable range; in comparison with example 5, the time of the synthesis reaction in step (2) of example 6 was adjusted from 3 hours to 1 hour, which is lower than the preferred range of 3 to 7 hours; the synthesis reaction time is related to the reaction temperature, the reaction temperature is high, the needed synthesis time is short, and the other is long; the longer the synthesis time is, the yield of Cl and Fe is not deteriorated, but the production efficiency is reduced, and the energy consumption is increased; when the synthesis time is too short, hydrogen chloride gas is easy to cause that the hydrogen chloride gas cannot completely escape and volatilize from the slurry, so that the yields of Cl and Fe are relatively low;

(2) In comparison with example 1, example 8 adjusts the time of the homogeneous aging in step (4) from 2 hours to 1 hour, which is lower than the preferable range of 2 to 6 hours; in comparison with example 5, example 9 adjusts the time of the homogeneous aging in step (4) from 6 hours to 7 hours, more than the preferred range of 2 to 6 hours; the aging reaction is a key step for preparing the yield and crystal form size of the ferric phosphate, and the longer the aging reaction time is, the promotion effect is provided for the yield of phosphorus and iron, and the yield of the ferric phosphate can be improved, but the agglomeration of ferric phosphate crystal grains can be caused, so that the grain size of the ferric phosphate is enlarged, the purity is influenced to a certain extent, the impurity removal is not facilitated, and the product performance is further influenced; too short an aging reaction time may result in iron phosphate grains being transported to the next stage without being formed or being formed smaller, and thus the yield of the product may be affected; in comparison with the Fe yield (99.2 wt%) obtained in example 5, comparative example 1 was not aged, so that the Fe yield was severely reduced, only 76wt%, and thus, it was necessary to set a homogeneous aging for improving the yield of phosphoric acid product;

(3) In comparison with example 1, comparative example 2 the temperature of the synthesis reaction in step (2) was adjusted from 130 ℃ to 100 ℃ below the preferred range of 120 to 200 ℃; in comparison with example 5, comparative example 3 adjusts the temperature of the synthesis reaction in step (2) from 200 ℃ to 220 ℃ higher than the preferred range of 120 to 200 ℃; too low a synthesis reaction temperature can cause that the slurry in the synthesis system cannot reach the boiling point of boiling, so that the volatilization rate of hydrogen chloride gas is seriously influenced, even the hydrogen chloride gas cannot escape from the slurry and volatilize, the reaction cannot be carried out, ferric phosphate cannot be prepared, and high-concentration regenerated hydrochloric acid cannot be recovered; however, the use of excessively high synthesis reaction temperature may cause side reactions in the synthesis reaction to produce ferric pyrophosphate, ferric hydroxychloride, etc., and reduce the purity of the iron phosphate product, such as the purity of the iron phosphate obtained in comparative example 3, which is only 97.91wt%, and in addition, the volatilization of hydrogen chloride gas may carry phosphoric acid, thereby reducing the product yield.

(4) According to the analysis comparison, the method for preparing the ferric phosphate by utilizing the ferric salt acid pickling waste liquid resource can realize the preparation of the ferric phosphate and the remanufacturing and recycling of the hydrochloric acid by separating the iron and the chlorine in the hydrochloric acid pickling waste liquid, and the method utilizes a low-cost iron source to prepare the high-valued ferric phosphate, so that the value and the quality are improved, and the waste liquid resource utilization is organically coupled with the preparation of new energy materials, the three wastes are not discharged in the whole process, and no environmental hazard is caused.

The detailed structural features of the present invention are described in 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 be implemented depending on the above detailed structural features. It should be apparent to those skilled in the art that any modifications of the present invention, equivalent substitutions of selected components of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope of the present invention and the scope of the disclosure.

The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the specific details of the above embodiments, and various simple modifications can be made to the technical solution of the present invention within the scope of the technical concept of the present invention, and all the simple modifications belong to the protection scope of the present invention.

In addition, the specific features described in the above embodiments may be combined in any suitable manner, and in order to avoid unnecessary repetition, various possible combinations are not described further.

Moreover, any combination of the various embodiments of the invention can be made without departing from the spirit of the invention, which should also be considered as disclosed herein.

Claims

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

(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;

(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;

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;

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

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.