CN109179781B - Device and method for treating desulfurization wastewater based on active ferrite microcrystal - Google Patents

Abstract

The invention discloses a device and a method for treating desulfurization wastewater based on active ferrite microcrystals, wherein the method comprises the following steps: step 1, preprocessing desulfurization wastewater to remove suspended solids contained in the desulfurization wastewater; step 2, adding medicament materials into the fluidized bed reactor to obtain ferrite microcrystals or directly adding ferrite microcrystals with a certain concentration, and removing dissolved heavy metals in the desulfurization wastewater through the ferrite microcrystals; step 3, carrying out subsequent treatment on the desulfurization wastewater to remove dissolved iron, ferrite microcrystals and other suspended particles carried in the desulfurization wastewater; and 4, discharging the desulfurization wastewater treated in the step 3. The device comprises: the input end of the pretreatment sedimentation tank is connected with the pretreatment reaction tank, and the output end of the pretreatment sedimentation tank is connected with the input end of the fluidized bed reactor; the input end of the post-treatment reaction barrel is connected with the output end of the fluidized bed reactor, and the output end of the post-treatment reaction barrel is connected with the input end of the post-treatment sedimentation tank; the input end of the rapid sand filter tank is connected with the output end of the treatment sedimentation tank, and the output end is connected with the water outlet pipe.

Description

Device and method for treating desulfurization wastewater based on active ferrite microcrystal

Technical Field

The invention relates to the technical field of desulfurization wastewater treatment, in particular to a device and a method for treating desulfurization wastewater based on active ferrite microcrystals.

Background

Heavy metal contaminated wastewater from flue gas desulfurization

The widespread and persistent nature of heavy metal pollution on human health and environmental safety hazards is increasingly attracting great attention to governments and the masses. Various industrial production activities, including energy exploitation, power generation, metallurgy, electroplating, mining and the like, involve the processing and use of a large amount of heavy metal-containing minerals and raw materials, thereby generating a large amount of heavy metal-polluted wastewater, waste gas and waste residue. If not treated effectively, the surface water, groundwater and soil in the relevant area are inevitably subjected to serious threat of heavy metal pollution. With the development of Chinese economy entering a new stage, the sustainable development of social economy by protecting the health of people and realizing the sustainable development of social economy through strict environmental protection standards and measures has become a social consensus. In recent years, government environmental protection departments set heavy metal emission standards of various industrial waste water more and more strictly, and treatment and monitoring are gradually in place. The complexity of heavy metal polluted wastewater treatment increasingly challenges the existing conventional technology treatment capacity, and particularly the standard treatment of certain difficult industrial wastewater.

First, the world of the power industry in China continues to grow in the foreseeable future. Although the new energy duty ratio has been greatly increased in recent years in the newly increased power generation capacity, the conventional coal-fired power plant still provides more than 60% of electric power. At present, a wet flue gas desulfurization system is commonly installed in coal-fired power plants in China, and the pollution of the coal-fired flue gas is greatly reduced by leaching the flue gas by alkaline lime slurry, so that the environmental benefit is remarkable. Raw coal contains various impurities and pollutants, mercury, selenium, arsenic and other volatile toxic and harmful elements are released in the high-temperature combustion process, and are eluted in a desulfurizing tower and enriched in a liquid phase. Therefore, the flue gas desulfurization wastewater of the coal-fired power plant often contains various heavy metal pollutants, and the common pollutants comprise mercury, selenium, arsenic, lead and the like. The quality of desulfurization wastewater of each power plant tends to be greatly different, and main influencing factors include (1) the coal quality of raw coal, such as chlorine content, sulfur content, heavy metal content such as mercury, arsenic, selenium and the like, (2) the quality of lime raw materials used by a desulfurization tower; (3) supplementing the quality of water to the desulfurizing tower; and (4) the process and the running operation of the desulfurizing tower. In general, desulfurization wastewater contains higher Total Dissolved Solids (TDS), and the main components comprise high-concentration chloride ions (5000-20000 mg/L), sulfate radicals (500-5000 mg/L), and cations are mainly sodium, calcium and magnesium. In addition, desulfurization wastewater generally contains borate, silicate, nitrate and the like in a considerable concentration, and contains manganese in a dissolved state in a concentration of up to hundreds of milligrams per liter. In addition, certain strong oxides such as bromates, iodates, persulfates, etc. may also be generated in desulfurization towers operating in a strong oxidizing environment. The desulfurization waste water may contain heavy metal (including metalloid) pollutants in various types and forms. For the coal-fired power industry, the main monitoring target heavy metals in the U.S. environmental protection department include arsenic, mercury and selenium. The monitoring and controlling of desulfurization wastewater in China should also comprise arsenic, selenium and mercury. Selenium in desulfurization wastewater usually exists in the form of selenate or selenite, and the concentration is generally in the order of mg/L. Arsenic and mercury concentrations are generally lower than selenium and sometimes can be as high as the order of mg/L. In addition, the desulfurization waste water needs to be detected and also comprises nickel, zinc, copper, lead, cadmium and the like in a cationic form, and molybdate, chromate, vanadate and the like in an anionic form.

The desulfurization wastewater of the power plant has complex water quality and large fluctuation, and particularly the treatment difficulty is greatly increased due to the characteristic of the high-salt background. In addition, various industrial wastewater of the power plant, such as boiler acid washing wastewater, is often discharged into a desulfurization wastewater system to be mixed with the wastewater, and the uncertainty of the quality of the desulfurization wastewater and the treatment difficulty are increased. The traditional chemical neutralization flocculation precipitation method is difficult to achieve very high removal rate, and the treated effluent cannot meet increasingly strict discharge standards. The new technology represented by membrane treatment is used for treating heavy metal polluted wastewater, which faces the problem of high cost, and the membrane separation process only concentrates heavy metals in the abandoned liquid, so that how to treat the abandoned liquid is a big problem. The method can effectively treat the difficult industrial wastewater, meets the increasingly strict heavy metal wastewater discharge standard, and needs to develop a novel efficient and economically feasible novel technical support.

Technology for treating waste water polluted by heavy metal in flue gas desulfurization

The traditional neutralization flocculation precipitation method is realized by adding Ca (OH) ₂ The traditional water treatment chemical agents such as aluminum salt, ferric salt and organic sulfur can remove a plurality of heavy metals, however, the chemical mechanism involved in the treatment process is single, mainly uses adsorption precipitation as a main mechanism, has quite limitations, and particularly for some heavy metals, the minimum concentration which can be achieved by the treated water is often more than 1 mg/L, and cannot meet some new emission standards. Conventional flocculant adsorbents are substantially ineffective for removal of dissolved selenium in selenate form. In addition, organosulfur is also very expensive.

Electrochemical methods, such as electrodialysis (electroflocculation) and electroflocculation (electroflocculation), can also be used to treat heavy metal wastewater. However, despite some unique advantages, electrochemical processes still face economic and technical barriers, the control of which is complex, and in particular the problem that the treated effluent often fails to meet the latest strict emission standards.

Zero-valent iron can also be used for treating heavy metal wastewater, and is mainly used for reducing some heavy metals existing in an oxidation state form, such as chromate, selenate and the like, and converting the heavy metals into a low-valence state form which is easy to remove based on the chemical reducibility of iron powder. After the zero-valent iron is used as reaction medium and contacted with waste water, the surface of the zero-valent iron is quickly rusted to form stable rust coating, and the zero-valent iron is quickly passivated and deactivated, so that a great amount of iron powder is consumed and wasted. In addition, chemical reduction processes are generally slower and often require longer reaction times than processes such as neutralization adsorption precipitation. These greatly reduce the economic and technical feasibility of the traditional zero-valent iron technology for treating heavy metal wastewater.

Iron oxides (such as magnetite) have been used for the removal of various heavy metals (such as arsenic) from wastewater and have been widely studied in the literature. However, the practical use in industry is limited, especially in the treatment of various problematic waste waters, where simple iron oxide surface adsorption is not particularly effective for many heavy metal ions.

In summary, the traditional chemical flocculation precipitation method, including newer zero-valent iron technology, and various electrochemical methods for treating heavy metal polluted industrial wastewater, generally cannot meet the increasingly strict environmental emission standard of various relevant countries and places. The industry has an urgent need for a wastewater treatment technology which is simple to operate, reasonable in cost, and capable of efficiently removing heavy metal pollutants to achieve the stabilization and reduction of the pollutants.

Disclosure of Invention

In order to solve the problems, the invention aims to provide a device and a method for treating desulfurization wastewater based on active ferrite microcrystals, which are simple to operate, reasonable in cost and capable of efficiently removing heavy metal pollutants.

The invention provides a method for treating desulfurization wastewater based on active ferrite microcrystals, which comprises the following steps:

step 1, preprocessing desulfurization wastewater to remove suspended solids contained in the desulfurization wastewater;

step 2, adding medicament materials into the fluidized bed reactor to obtain ferrite microcrystals or directly adding ferrite microcrystals with a certain concentration, and removing dissolved heavy metals in the desulfurization wastewater through the ferrite microcrystals;

step 3, carrying out subsequent treatment on the desulfurization wastewater treated in the step 2, and removing dissolved iron, ferrite microcrystals and other suspended particles carried in the desulfurization wastewater;

and 4, discharging the desulfurization wastewater treated in the step 3.

As a further improvement of the present invention, the pharmaceutical material in the step 2 includes: metal iron powder, ferrous salts, ferric salts, alkali, sodium nitrate and air.

As a further improvement of the invention, the concentration of ferrite micro-crystals in the step 2 is controlled to be in the range of 50-200 g/L.

As a further improvement of the present invention, the ferrite microcrystals in the step 2 are a heterogeneous mixture of iron compounds, the active ingredients of which include: non-standard iron oxide of ferroferric oxide-like configuration, chloridecontaining green rust and sulfate-containing green rust.

As a further improvement of the present invention, the subsequent processing in the step 3 includes: adding alkali, aerating, flocculating and precipitating.

The invention also provides a device for treating desulfurization wastewater based on the active ferrite microcrystal, which comprises:

the input end of the pretreatment sedimentation tank is connected with the pretreatment reaction tank, and the output end of the pretreatment sedimentation tank is connected with the input end of the fluidized bed reactor;

the input end of the post-treatment reaction barrel is connected with the output end of the fluidized bed reactor, and the output end of the post-treatment reaction barrel is connected with the input end of the post-treatment sedimentation tank;

the input end of the rapid sand filter tank is connected with the output end of the treatment sedimentation tank, and the output end of the rapid sand filter tank is connected with the water outlet pipe.

As a further improvement of the invention, the fluidized bed reactor is provided with a reaction zone and a sedimentation zone, wherein the sedimentation zone is arranged outside the reaction zone and along the circumferential direction, and an opening is arranged at the bottom of the sedimentation zone and is communicated with the reaction zone.

As a further improvement of the invention, the bottom of the sedimentation zone is of an inclined design and the inclination angle is not less than 45 degrees, and a depletion medium discharge pipe is arranged at the inclined position of the sedimentation zone.

As a further improvement of the invention, the pretreatment reaction tank, the reaction zone and the post-treatment reaction barrel are all provided with stirring devices, and a plurality of stirring devices are arranged in the reaction zone.

As a further improvement of the invention, an aeration device is arranged in the post-treatment reaction barrel.

The beneficial effects of the invention are as follows: the main pollutants in the desulfurization wastewater such as selenium, mercury, arsenic and the like can be treated with high efficiency, and the removal efficiency is far higher than that of the prior conventional physicochemical method; the process flow is relatively simple, the medicament consumption is less, the yield of solid waste residues is obviously reduced compared with the existing main flow process, and the operation cost is lower; the operation is simple and convenient, the control is flexible, the operation parameters of the device can be optimized according to the characteristics of the wastewater and the treatment targets, and the device is suitable for the treatment of water quality with different characteristics.

Drawings

FIG. 1 is a flow chart of a method for treating desulfurization wastewater based on active ferrite micro-crystals according to an embodiment of the invention;

fig. 2 is a schematic structural diagram of an apparatus for treating desulfurization wastewater based on active ferrite microcrystals according to an embodiment of the present invention.

In the drawing the view of the figure,

1. a pretreatment reactor; 2. a stirring device; 3. pretreating a sedimentation tank; 4. a first sludge discharge pipe; 5. a fluidized bed reactor; 51. a reaction zone; 52. a precipitation zone; 6. post-treatment reaction barrels; 7. an aeration device; 8. a post-treatment sedimentation tank; 9. a second sludge discharge pipe; 10. a rapid sand filtration tank.

Detailed Description

Example 1

As shown in fig. 1, embodiment 1 of the present invention is a method for treating desulfurization wastewater based on active ferrite microcrystals, the method comprising:

step 1, preprocessing desulfurization wastewater to remove suspended solids contained in the desulfurization wastewater.

The slurry discharged from the desulfurizing tower contains a large amount of gypsum powder, and the waste liquid generated in the solid-liquid separation and dehydration processes such as cyclone, centrifugal dehydration, plate-frame filter pressing or belt filter pressing is discharged to become desulfurization waste water. Often, the desulfurization wastewater still contains a large amount of suspended solids, and the desulfurization wastewater is suitable for being treated in an iron oxide microcrystal reactor after the suspended solids are removed. The pH value of the desulfurization wastewater is generally close to neutral, usually between pH 6 and pH 8, and no adjustment is needed. However, the pH of the wastewater may also fluctuate greatly, and pH 3-4 is also possible. In particular, power plants are not always fed with other waste water into desulfurization waste water systems, such as boiler acid wash waste water into desulfurization waste water systems, resulting in waste water being acidic and containing significant amounts of complexing agents to aid in digestion of rust and scale. The wastewater containing a large amount of acid and complexing agent directly enters the ferrite microcrystal treatment unit and can interfere the normal operation of the active iron process. Therefore, the desulfurization wastewater is pretreated, interference factors in the wastewater are removed in advance through necessary medicament treatment, the fluctuation of wastewater quality is reduced, and the stable operation and standard discharge of the system are facilitated.

And 2, adding a medicament material into the fluidized bed reactor to obtain ferrite microcrystals or directly adding ferrite microcrystals with a certain concentration, and removing dissolved heavy metals in the desulfurization wastewater through the ferrite microcrystals.

The step is a core process in the method, and almost all heavy metals in the desulfurization wastewater can be removed. The ferrite microcrystal treatment is completed in a specially made fluidized bed reactor. Adding a certain amount of medicament material for generating ferrite microcrystals into a fluidized bed reactor or directly adding a certain amount of ferrite microcrystals, and fully fluidizing the ferrite microcrystals through mechanical stirring or aeration auxiliary stirring, wherein the high-efficiency contact reaction of the wastewater and the ferrite microcrystals is promoted, the capture of the medium to heavy metals in the wastewater is promoted, and the reaction contact time is preferably 2-4 hours. Meanwhile, the fluidized bed reactor can generate more active ferrite microcrystals during wastewater treatment by adding proper medicament materials. Thus, the fluidized bed reactor may also be an active ferrite microcrystal generator.

And step 3, carrying out subsequent treatment on the desulfurization wastewater treated in the step 2, and removing dissolved iron, ferrite microcrystals and other suspended particles carried in the desulfurization wastewater.

The subsequent treatment is to remove dissolved iron that may be carried in the fluidized bed reactor effluent and to remove small amounts of reaction medium or other suspended particulate matter carried in the effluent.

And 4, discharging the desulfurization wastewater treated in the step 3.

The principle of the method is based on iron powder and mixed ferrous and ferric salts, and a proper oxidant is selected, and the multifunctional active ferrite microcrystal medium is synthesized in a specially designed reactor through specific formula and reaction condition control. Unlike common iron oxide minerals produced in nature, the synthesized active iron oxide microcrystal mainly comprises an unstable iron oxide mixture which is easy to convert, and the main active components are similar to certain rust structures and non-standard iron oxides, have no fixed components and structural compositions and have high chemical activity. The active ferrite microcrystal has high capacity of anion exchange capacity and cation lattice substitution capacity, certain chemical reduction capacity and inherent surface affinity adsorption capacity of ferric oxide. The active ferrite microcrystal can be used for converting and removing heavy metal pollutants in various forms in wastewater through the complex actions and synergistic mechanisms of surface adsorption, ion exchange, lattice substitution, chemical reduction and the like, and is absorbed and fixed in a ferrite microcrystal structure so as to achieve the treatment aims of stabilization, reduction and harmlessness.

The chemical mechanisms mainly involved in the heavy metal removal process include:

anion exchange for removal of heavy metal oxyanions, e.g. selenate (SeO) ₄ ^2- ) Vanadate (VO) ₄ ^3- ) Chromic acid radical (CrO) ₄ ^2- ) Etc.;

removal of heavy metal ions in oxidation state by chemical reduction, e.g. copper ions (Cu ²⁺ ) Silver ion (Ag) ⁺ ) Etc.;

direct adsorption of heavy metal ions on the surface of iron oxides, e.g. arsenic (AsO) ₄ ^3- ) Etc.;

lattice substitution methods incorporate heavy metal ions into lattice structures, such as manganese (Mn ²⁺ ) Nickel (Ni) ²⁺ ) Zinc (Zn) ²⁺ ) Etc.

Further, the medicament material in step 2 includes: metal iron powder, ferrous salts, ferric salts, alkali, sodium nitrate and air.

Wherein the metal iron powder is zero-valent iron, the ferrous salt can be ferrous chloride or ferrous sulfate, the ferric ferrous salt can be ferric trichloride or ferric sulfate, the alkali is sodium hydroxide, and the air can be replaced by oxygen.

Further, the concentration of ferrite microcrystals in the step 2 is controlled to be in the range of 50-200 g/L.

The concentration of ferrite micro-crystals is generally controlled in the range of 50-200 g/L. At the beginning of the treatment of the desulfurization wastewater, the desulfurization wastewater is loaded to a target concentration, such as 100g/L, at a time. The lifetime of ferrite microcrystals in a fluidized bed reactor depends on the quality of the treated water and is also related to the running operating conditions of the fluidized bed reactor. If the reactant concentration in the wastewater is low, the average lifetime of ferrite crystallites may exceed one year. Conversely, if the wastewater contains a significant amount of strong oxides, such as a significant amount of persulfate, ferrite microcrystals may consume significantly more, such as over a period of weeks. The consumed ferrite micro-crystals must be replenished, and a stepwise replenishment, such as adding 10% of new ferrite micro-crystals in total once a week, may be considered.

Further, the ferrite microcrystals in the step 2 are heterogeneous iron compound mixtures, and the active ingredients of the ferrite microcrystals comprise: non-standard iron oxide of ferroferric oxide-like configuration, chloridecontaining green rust and sulfate-containing green rust.

The ferrite microcrystal is apparent as black solid particles, has stronger magnetism and large density (true density>5.0-5.5g/cm ³ ) The X-ray diffraction crystal has obvious characteristics, single crystals are mostly smaller than 50nm, but are suspended in liquid phase to be polymerized into crystal clusters naturally, and the crystal clusters have larger specific surface area (10 m ² /g)。

In the ferrite microcrystal active component, ferroferric oxide (Fe ₃ O ₄ I.e., magnetite) structure, but at the same time comprises other secondary crystalline structures, as well as amorphous structures (amorphorus). After the active ferrite microcrystal is used for wastewater treatment, the green rust component is consumed, and is converted into stable ferric oxide or ferroferric oxide crystal through ion exchange, chemical oxidation and structural transformation.

The iron of the active ferrite microcrystal is in a mixed valence state, namely ferrous iron and ferric iron, wherein the proportion of the ferrous iron is larger and is far higher than that of the conventional Fe ₃ O ₄ Fe in crystal ^(II) /Fe ^(III) Valence ratio=1/2. At the same time, the composition also comprises a microcrystalline structure containing exchangeable anions such as Cl ^- And SO ₄ ^2- Etc., in the presence of amorphous structural components resembling green rust. The ferrite microcrystal rich in ferrous iron with strong reducing capability has unstable chemical structure, and when the ferrous iron contacts with oxidizing reactant in water or atmosphere, the ferrous iron is partially or completely oxidized and gradually converted into more stable conventional Fe ₃ O ₄ Or Fe (Fe) ₂ O ₃ . The structural anions in the water can be replaced by free anions in the water. For example, ferrous iron in ferroferrite crystallites may be gradually oxidized by dissolved oxygen in water to be converted to Fe ₂ O ₃ . As another example, the structural anions therein Cl ^- Or SO ₄ ^2- Can be SeO ₄ ^2- And (5) replacing. The non-standard structure and components give the ferroferric oxide microcrystal the flexibility of internal structural variation, and the ferroferric oxide microcrystal is highly reactive, and structurally allows various heterogeneous components to be absorbed. For example, many metallic elements can flexibly enter into the ferrite micro-crystal structure, occupy lattice positions of iron atoms, and become a part of the ferrite micro-crystal structure.

The chemical formula of the green rust component in the active ferrite microcrystal can be simplified as follows: fe (Fe) ^(II) _x Fe ^(III) _y ·[A ^-1 _m ·A ^-2 _n ]·O _z Structurally, it is a layered double hydroxide (layered double hydroxide), wherein [ A ] ^-1 _m ·A ^-2 _n ]As exchangeable structure interlayer anions, analysis shows that the mole ratio of the composition can reach more than 10 percent of the mole number of iron in the composition, and the composition can be used for preparing oxygen anion type pollutants in water such as selenate (SeO) ₄ ^2- ) Or arsenate (AsO) ₄ ^3- ) And the like. Fe (II) in the green rust has stronger chemical reduction capability, selenate entering the green rust structure has oxidation-reduction reaction with Fe (II), se ^(VI) Is reduced to Se ⁽⁰⁾ And Se (Se) ^(-II) ,Fe ^(II) Oxidized to Fe ^(III) Gradual conversion of green rust to Fe ₃ O ₄ Wherein part O ^-2 Lattice sites are surrounded by Se ^(-II) Substituted.

Further, the subsequent processing in step 3 includes: adding alkali, aerating, flocculating and precipitating. In general, the required treatment comprises alkali addition, aeration, flocculation and sedimentation, and an integrated dosing sedimentation tank can be considered, and the additional filtration treatment can be considered when the discharge requirement is high or the effluent recycling is considered. The subsequent processing may be omitted entirely in some cases.

Small experiments were performed in the laboratory as follows:

testing of wastewater sources

Actual desulfurization wastewater: the power plant enterprise provides actual desulfurization wastewater raw water

Artificial synthetic simulated wastewater: preparing synthetic simulated wastewater by adding soluble heavy metal salt and auxiliary agent into deionized water

Active ferrite microcrystal

Synthetic ferrite microcrystal (20-90% of mass fraction) and iron powder (10-80% of mass fraction) are mixed and processed into active ferrite microcrystal slurry containing 20% of dry medium. The ratio (mass fraction) of ferrite micro-crystals to iron powder in the slurry is determined according to the specific test and use conditions in the test and actual application.

Water quality detection method

Heavy metal detection, which is used for detecting quantitative analysis of various metal elements such as total Cu, ni, zn, pb, cd, se, as, cr, sb, fe, mn, K, na, ca, mg in water: the total weight metal or dissolved heavy metal in the water sample is detected by an inductively coupled plasma mass spectrometer (ICP-MS, instrument model is Agilent 7700+), and the lower detection limit of the instrument on each relevant heavy metal is lower than 1ug/L

Detection of anionic heavy metals, for quantitative analysis of selenate, molybdate, chromate, vanadate, arsenate: ion chromatography (IC, apparatus model Dionex DX 500) was used with a suitable separation column (IonPac AS22, AS18, or AS 16) at a detection limit of 0.1 mg/L.

Ammonia nitrogen and nitric acid nitrogen: the detection was carried out by ion chromatography (IC, instrument model Dionex DX 500) with a lower limit of 0.1 mg/l, all results being measured in nitrogen.

Conventional anion detection for Cl ^- ,SO ₄ ^2- ,PO ₄ ^3- ,NO ^3- ,Br ^- ,F ^- : ion chromatography detection (IC, instrument model Dionex DX 500) was used with a lower detection limit of 0.1 mg/l.

Dissolved Fe ²⁺ Total Fe is tested by a phenanthroline colorimetric method, fe ³⁺ Total Fe-Fe2 ⁺

Phosphorus: spectrophotometry of ammonium molybdate

COD potassium dichromate process

The reactor comprises: the effective reaction volume, i.e. the fluidized reaction zone volume, was 4 liters and the settling zone volume was 1 liter. The reactor is loaded with a pre-processed active ferrite micro-crystal slurry with the concentration of about 50g/L, the mass ratio of ferrite micro-crystals in the slurry is 80 percent, and the iron powder is 20 percent.

Waste water: artificially synthesizing wastewater by deionized water, adding a certain amount of sodium selenate and sodium arsenate, and concentrating to obtain selenate (SeO) ₄ ^2- ) 5mg/L (calculated as Se), arsenate (AsO) ₄ ^3- ) 3mg/L (As). Adding acid and alkali to adjust the pH value to be neutral 7.0.

Pilot plant operating conditions: the inflow of wastewater is 2 liters/hour, and the corresponding reaction time is 2 hours. The water outlet of the reactor is sampled and analyzed, water samples are taken every 24 hours, and the water samples are filtered (0.45 um) and then analyzed. The test run time was 5 days.

Test results:

target pollutants	SeO 4 2- --Se(mg/L)	AsO 4 3- --As(mg/L)
			Raw water	5.0	3.0
Treated effluent (Day 1)	0.003	＜0.001
			Treated effluent (Day 2)	0.002	＜0.001
Treated effluent (Day 3)	0.003	＜0.001
			Treated effluent (Day 4)	0.004	＜0.001
Treated effluent (Day 5)	0.002	＜0.001
			Treating the water output average value	0.003	＜0.001

The test structure shows that for simple synthetic wastewater, the active ferrite microcrystal has excellent effect of removing selenate and arsenate, the selenium in treated water is stably reduced to below 5 mug/L (ppb), the arsenic is below 1 mug/L (ppb), and the removal rate can be more than 99.99 percent by simple single-stage treatment. Effluent detectionIt was found that there was a certain increase in chloride ion concentration in the effluent, approximately 8 mg/l. This is consistent with our understanding of the mechanism that the active ferrite microcrystals possess anion exchange capacity, seO ₄ ^2- With AsO ₄ ^3- By reaction with Cl in the structure ^- The ion equivalent replacement enters the active ferrite microcrystal, so that the active ferrite microcrystal can be removed efficiently. We determined, through a series of shake flask samples, that the selectivity of reactive iron oxide crystallites for various anions is prioritized by SeO ₄ ^2- >SO ₄ ^2- >>NO ^3- >Cl ^- . Selenate entering the active ferrite microcrystal structure is gradually reduced, and by X-ray photoelectron spectroscopy (XPS), we confirm that Se (VI) is rapidly reduced to zero-valent Se. SeO (SeO) ₄ ^2- Once reduced and converted, the selenium is stably fixed in the ferrite microcrystal structure and can not be exchanged and replaced. Similarly, we have observed the reduction of As (V) to As (III) by the active ferrite crystallites. The process of ion exchange of ferrite crystallites and also anions is rapid and is typically completed within 10 minutes. In the test process, the concentration of dissolved iron in the effluent is very low,<0.3 mg/l, so that a subsequent iron removal treatment is not required.

Example 2

As shown in fig. 2, embodiment 2 of the present invention is an apparatus for treating desulfurization wastewater based on active ferrite microcrystals, comprising:

the input end of the pretreatment sedimentation tank 3 is connected with the pretreatment reaction tank 1, and the output end of the pretreatment sedimentation tank 3 is connected with the input end of the fluidized bed reactor 5;

the input end of the post-treatment reaction barrel 6 is connected with the output end of the fluidized bed reactor 5, and the output end of the post-treatment reaction barrel 6 is connected with the input end of the post-treatment sedimentation tank 8;

the input end of the rapid sand filter tank 10 is connected with the output end of the treatment sedimentation tank 8, and the output end of the rapid sand filter tank 10 is connected with a water outlet pipe.

The desulfurization wastewater is conveyed to a pretreatment reaction tank 1, neutralization reaction is carried out on the desulfurization wastewater and an alkaline agent in the pretreatment reaction tank 1, the pH value of the desulfurization wastewater is approximately neutral between 6 and 8, and then the neutralized desulfurization wastewater is conveyed to a pretreatment sedimentation tank 3 to remove suspended solids in the desulfurization wastewater. And then the desulfurization wastewater is conveyed to a fluidized bed reactor 5, and various dissolved heavy metals in the wastewater are removed through treatment of ferrite microcrystals. The desulfurization waste water after treatment of ferrite microcrystal may carry dissolved iron and a small amount of reaction medium or other suspended particles, so that a post-treatment reaction barrel 6 and a post-treatment sedimentation tank 8 are required to be arranged, neutralization reaction is carried out between the desulfurization waste water and alkali liquor in the post-treatment reaction barrel 6, sediment in the desulfurization waste water is discharged through the post-treatment sedimentation tank 8, and finally the treated waste water is discharged through a rapid sand filtration tank 10.

Further, the fluidized bed reactor 5 is provided with a reaction zone 51 and a sedimentation zone 52, the sedimentation zone 52 is arranged outside the reaction zone 51 along the circumferential direction, and an opening is arranged at the bottom of the sedimentation zone 52 and is communicated with the reaction zone 51.

The reaction zone 51 and the sedimentation zone 52 are designed integrally, active ferrite microcrystals are synthesized in the reaction zone 51, and can be used for converting and removing various forms of heavy metal pollutants in wastewater through surface adsorption, ion exchange, lattice substitution, chemical reduction and other composite action mechanisms, and are absorbed and fixed in an ferrite microcrystal structure, sediment generated in the sedimentation zone 52 is separated from liquid, and finally the sediment containing heavy metal is discharged. The sedimentation zone 52 provides a stable static environment, the iron oxide microcrystal particles with large specific gravity are separated from the slowly-flowing water body to separate and sediment, a concentrated slurry layer is formed at the bottom of the sedimentation zone 52, the treated water flows upwards through pores among media, the iron oxide microcrystal particles are trapped at the bottom, the slurry concentration and density are increased, and the slurry is exchanged with the slurry in the reaction zone 51 in a turbulent flow interaction way at a communication opening, and the slurry returns to the reaction zone 51.

Further, the bottom of the sedimentation zone 52 is inclined at an angle of not less than 45 °, and a depletion medium drain is provided at the inclination of the sedimentation zone 52.

The tilt angle should be considered 57 degrees (corresponding to a slope of 1.5) when conditions allow. Too small inclination angle, poor slurry backflow and easiness in depositing the bottom of the pool, and influences the operation efficiency of the system. The deactivated and depleted ferrite crystallites must be discharged to avoid continuous accumulation of inert medium, too high a slurry concentration, e.g., >300g/L, exceeding the load carrying capacity of the reactor stirring system, resulting in insufficient fluidization of the slurry, accumulation of material at the bottom of the reactor pool, etc. The spent media may be discharged in a concentrated manner at regular intervals, such as 10% of the old slurry being discharged once a week. Continuous sludge discharge, such as a spent media discharge pipe disposed from the mid-height of the inner settling zone, may also be considered, with a constant flow.

Further, the pretreatment reaction tank 1, the reaction zone 51 and the post-treatment reaction barrel 6 are provided with stirring devices 2, and the stirring devices 2 in the reaction zone 51 are provided with a plurality of stirring devices.

Further, an aeration device 7 is arranged in the post-treatment reaction barrel 6.

The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (2)

1. A method for treating desulfurization wastewater based on active ferrite microcrystals, which is characterized by comprising the following steps:

step 1, preprocessing desulfurization wastewater to remove suspended solids contained in the desulfurization wastewater;

step 2, adding medicament materials into the fluidized bed reactor to obtain ferrite microcrystals, removing dissolved heavy metals in the desulfurization wastewater through the ferrite microcrystals,

the medicament material comprises: metal iron powder, ferrous salt, ferric salt, alkali, sodium nitrate and air, wherein the ferrite microcrystal is a heterogeneous iron compound mixture, and the effective components comprise: iron oxides of non-standard ferroferric oxide-like configuration, chloridecontaining green rust and sulfate-containing green rust;

the concentration of the ferrite microcrystal is controlled within the range of 50-200 g/L;

step 3, carrying out subsequent treatment on the desulfurization wastewater treated in the step 2, and removing dissolved iron, ferrite microcrystals and other suspended particles carried in the desulfurization wastewater;

and 4, discharging the desulfurization wastewater treated in the step 3.

2. The method according to claim 1, wherein the subsequent processing in step 3 comprises: adding alkali, aerating, flocculating and precipitating.