Heavy metal polluted underground water remediation method

Abstract

The invention discloses a heavy metal polluted underground water remediation method which comprises the following steps: S1, mixing a sodium sulfide solution with an ammonium ferrous sulfate solution, continuously adding zero-valent iron powder in a stirring process to prepare a solution containing particulate matters, and separating to obtain the particulate matters in the solution, the particles are zero-valent iron particles coated with ferrous sulfide on the surfaces; adjusting the pH value of the heavy metal polluted underground water to be less than 7; and S2, filling the particulate matters prepared in the step S1 into a first flow column, and treating the heavy metal polluted underground water adjusted in the step S1 through the first flow column to remove heavy metals in the heavy metal polluted underground water. The heavy metal polluted underground water remediation method solves the technical problem of low removal efficiency of heavy metal ions in sewage in the prior art.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental pollution remediation, and specifically relates to a method for remediating groundwater contaminated by heavy metals. Background Art

[0002] At present, the main method for treating contaminated groundwater in the factory area is to capture and collect the groundwater in the factory area through water collection tanks, water collection wells, extraction wells and capture wells, and then treat it in the sewage treatment plant. The hexavalent chromium in the sewage is highly toxic. Considering the treatment effect and cost issues, the heavy metals in the sewage are mainly treated with active reaction media.

[0003] At present, active reaction media mainly include five categories: adsorption media, precipitation media, reduction media, degradation and combination media. For example, China's invention patent authorization announcement number CN106277274A discloses a method for treating wastewater containing heavy metal ions by mixing pyrite and zero-valent iron, which includes the following steps: (1) crushing zero-valent iron into iron powder, and washing and acid washing to leak out the fresh surface of zero-valent iron for standby use; (2) crushing natural pyrite by ball mill, and washing or acid washing to leak out the fresh surface of pyrite for standby use; (3) adjusting the pH of heavy metal ion wastewater to 2-10; (4) mixing the treated zero-valent iron, pyrite and heavy metal ion-containing wastewater in the same oscillator, and the mass concentration of zero-valent iron and pyrite after mixing is not less than 2g / L. This invention can significantly improve the reduction activity and stability of zero-valent iron, thereby enhancing the reduction removal efficiency of heavy metal ions in wastewater, and is a simple, effective and low-cost method for treating wastewater containing heavy metal ions. Although pyrite is relatively cheap and easy to obtain, its reaction is unstable and sensitive to changes in the external environment. Therefore, in practical applications, more optimization and control are needed to ensure its stability and removal efficiency. When pyrite and zero-valent iron work together to remove heavy metal ions, the sulfide in pyrite has a weak surface activation effect on zero-valent iron, and iron oxides will be generated on the surface of zero-valent iron over time, thus affecting the removal efficiency of heavy metal ions. Summary of the invention

[0004] In view of the current technical problems, the present invention aims to provide a method for remediating heavy metal-contaminated groundwater, which can solve the technical problem of low removal efficiency of heavy metal ions in sewage in the prior art.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for remediating groundwater contaminated by heavy metals comprises the following steps:

[0007] S1. Mixing a sodium sulfide solution and an ammonium ferrous sulfate solution, and continuously adding zero-valent iron powder during stirring to prepare a solution containing particles, and separating the particles therein, wherein the particles are zero-valent iron particles with ferrous sulfide coated on the surface; adjusting the pH of the heavy metal contaminated groundwater to less than 7;

[0008] S2. Filling the particles obtained in step S1 into the first flow column, and removing the heavy metals from the heavy metal-contaminated groundwater adjusted in step S1 through the first flow column.

[0009] When sodium sulfide solution is mixed with ammonium ferrous sulfate solution, a chemical reaction occurs to form ferrous sulfide (FeS) precipitation. Ferrous sulfide continuously coats zero-valent iron (ZVI) during precipitation, thereby forming a composite system of ferrous sulfide-coated zero-valent iron (Fe@FeS) particles. In this composite system, the surface of ZVI is tightly covered with FeS to form highly active Fe@FeS particles. Fe@FeS is more hydrophobic than the iron oxide layer on the surface of ZVI, and it will enrich more pollutants on the solid surface to accept electrons. At the same time, the Fe adsorbed on its surface 2+ and S 2- It can also contribute to the reduction and removal of heavy metals in pollutants. In addition, the electronegativity of FeS is higher than that of ZVI. This large potential difference allows FeS and ZVI to form a galvanic couple, in which FeS is the cathode and ZVI is the anode. This accelerates the spontaneous transfer of ZVI electrons to FeS, and the electron transfer process promotes the breakdown of ZVI's own passivation layer. Furthermore, FeS has good electronic conductivity, which can promote the transfer of electrons to pollutants adsorbed on the surface and promote the removal of heavy metals in pollutants.

[0010] Preferably, in step S1, the amount of sodium sulfide substance in the sodium sulfide solution is equal to the amount of ammonium ferrous sulfate substance in the ammonium ferrous sulfate solution.

[0011] Preferably, in step S1, the concentration of the sodium sulfide solution is 0.5-0.8 mol / L, and the concentration of the ammonium ferrous sulfate solution is 0.5-0.8 mol / L.

[0012] Preferably, in step S1, the amount of the added zero-valent iron powder is not greater than 75% of the amount of sodium sulfide or ammonium ferrous sulfate; preferably, the particle size of the zero-valent iron powder is not greater than 0.075 mm.

[0013] Preferably, in step S1, the solution containing the particulate matter is separated by a centrifuge to obtain the particulate matter therein, and the particulate matter is dried in a vacuum environment at 50 to 60° C.; preferably, the drying time is 24 to 48 hours.

[0014] Preferably, in step S2, the flow rate of the heavy metal contaminated groundwater in the first flow column is 10 -2 ~10 -4cm / s.

[0015] Preferably, in step S2, the heavy metal contaminated groundwater in step S1 is treated by the second flow column and then by the first flow column; the medium filled in the second flow column is a mixture of pyrite and zero-valent iron, and the mass ratio of pyrite to zero-valent iron is 1-2:0.5-1. ZVI has great advantages in repairing Cr(VI) contaminated groundwater, but there are problems such as reduced permeability, easy oxidation and inactivation, and co-precipitated substances (pH increase) are easy to adhere to its surface to reduce its reactivity, which hinder the application of ZVI. The reason for selecting natural pyrite as the medium material is that sulfidation can greatly inhibit the corrosion rate of iron-based materials, can achieve depassivation, enhance catalytic activity and conductivity, reduce the blockage of medium materials, and maintain high selectivity for target pollutants. In addition, pyrite can reduce the pH of the reaction medium when reacting with pollutants. Therefore, when an appropriate amount of pyrite is mixed with zero-valent iron, it can effectively buffer the pH change of the reaction system, alleviate the passivation phenomenon of the ZVI surface, and improve the ability to remove pollutants. When the ratio of pyrite to zero-valent iron (ZVI) is 1.5:1, the removal effect of Cr(VI) is ideal. 2+ By setting two flow columns, heavy metal pollutants in heavy metal-contaminated groundwater are removed through two flow columns, further improving the heavy metal removal efficiency.

[0016] Preferably, the particle sizes of pyrite and zero-valent iron filled in the second flow column are both no greater than 0.075 mm.

[0017] Preferably, the pH of the heavy metal contaminated groundwater is adjusted to 3-4 before entering the second flow column. The lower the pH value in the medium system, the more obvious the synergistic effect of the ZVI / FeS2 system is. The reason is that the lower the pH value, the more FeS2 generated by the reaction of ZVI and Cr(VI) in the system will be. 3+ The higher the concentration, the more normal the reaction can be when the pH value is between 2 and 7, and the best effect is when the pH value is between 3 and 4.

[0018] Preferably, in step S2, the pyrite added to the second flow column is modified, the pyrite is added to the NH4H2PO4 solution, stirred in a water bath at 55-75°C for 3-5h, then filtered and dried, the filter residue is heated to 550-600°C in a tube furnace, cooled to room temperature and then taken out to obtain phosphorus-modified pyrite, and the phosphorus-modified pyrite is mixed with zero-valent iron as a filling medium in the second flow column; preferably, when the pyrite added to the second flow column is modified, the ratio of the mass of pyrite to the sum of the mass of NH4H2PO4 and the mass of pyrite in the NH4H2PO4 solution is 35-55wt%. Ammonium dihydrogen phosphate is selected to modify the pyrite, thereby enhancing the diversity of functional groups on the surface of the pyrite. NH4H2PO4 modification of pyrite can enrich its polar groups and mineral components and improve its ion exchange capacity. The content of acidic functional groups on the surface of phosphorus-modified pyrite increases, which can not only adjust the medium environment to acidic conditions, but also the oxygen-containing functional groups on it can form complexes with metals such as lead. After pyrite modification, the ability to adjust the pH value of water bodies is further enhanced. Due to the introduction of groups such as phosphoric acid, the complexing effect of modified pyrite on heavy metals such as lead is enhanced. The filter residue is heated to 550-600°C in a tubular furnace, which can burn off organic impurities in pyrite, remove moisture and volatile components, and thus improve the purity and quality of the material. Materials calcined at high temperatures can form a more stable crystal structure, enhance the mechanical properties, thermal stability or chemical reactivity of the material. In addition, calcination helps to form active sites and enhance the reactivity of the material.

[0019] The principle of removing hexavalent chromium from heavy metal-contaminated groundwater of the present invention is as follows:

[0020] The synergistic effect between ferrous sulfide and zero-valent iron helps to increase the Cr 6+ Removal rate, Cr(VI) is usually 0 and Fe 0 Fe 2+ Reduction to Cr(III) is the main process of ZVI removing Cr(VI). The related equations of the reaction between sodium sulfide and ammonium ferrous sulfate to generate ferrous sulfide and the reduction reaction between ZVI and Cr(VI) are as follows:

[0021] (NH4)2Fe(SO4)2 + Na2S → FeS↓ + Na2SO4 + (NH4)2SO4 (1)

[0022] 2HCrO4 - + 3Fe 0 + 14H + → 3Fe 2+ +2Cr 3+ + 8H2O (2)

[0023] 2CrO42- + 3Fe 0 + 16H + → 3Fe 2+ +2Cr 3+ + 8H2O (3)

[0024] Cr2O7 2- +3Fe 0 + 14H + → 3Fe 2+ +2Cr 3+ +7H2O (4)

[0025] HCrO4 - + 3Fe 2+ + 7H + → 3Fe 3+ + Cr 3+ + 4H2O (5)

[0026] CrO4 2- + 3Fe 2+ + 8H + → 3Fe 3+ + Cr 3+ + 4H2O (6)

[0027] Cr2O7 2- + 6Fe 2+ + 14H + → 6Fe 3+ +2Cr 3+ + 7H2O (7)

[0028] When pyrite reacts with pollutants, it can reduce the pH of the reaction medium, as shown in chemical reaction formula (8). Therefore, when an appropriate amount of pyrite is mixed with zero-valent iron, it can effectively buffer the pH change of the reaction system, alleviate the passivation phenomenon of the ZVI surface, and improve the ability to remove pollutants.

[0029] 2FeS2 +7O2(aq) +2H2O → 2Fe 2+ + 4H + +4SO4 2- (8)

[0030] The lower the pH value in the medium system, the more obvious the synergistic effect of the ZVI / FeS2 system is. The reason is that the lower the pH value, the more FeS2 generated by the reaction of ZVI and Cr(VI) in the system 3+ The higher the concentration, the more normal the reaction can be when the pH value is between 2 and 7, and the best effect is achieved when the pH value is between 3 and 4. Moreover, FeS2 can more effectively convert the Fe generated by ZVI and FeS2 into 3+Converted back into reduced Fe 2+ , thereby improving the removal rate of Cr(VI), and the synergistic effect is more obvious. The reaction equation is as follows:

[0031] 4Fe 2+ + 1 / 4O2+H + →4 Fe 3+ + 1 / 2H2O (9)

[0032] FeS2+14Fe 3+ +8H2O→15Fe 2+ +16H + +2SO4 2- (10)

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. The heavy metal contaminated groundwater remediation method of the present invention compounds zero-valent iron and ferrous sulfide to prepare Fe@FeS granular material, which not only enhances the heavy metal removal ability of zero-valent iron, but also enhances the surface activation of zero-valent iron, does not passivate the surface of zero-valent iron, and still maintains a high surface activity.

[0035] 2. The heavy metal contaminated groundwater remediation method of the present invention enhances the heavy metal removal capability of the filling medium by phosphorus modification of pyrite. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a scanning electron microscope image of zero-valent iron in the heavy metal contaminated groundwater remediation method of the present invention;

[0037] Figure 2 This is a scanning electron microscope image of Fe@FeS particles in the heavy metal contaminated groundwater remediation method of the present invention;

[0038] Figure 3 is a graph showing the change of total chromium concentration of groundwater inlet and outlet water over time in Example 1 of the present invention;

[0039] Figure 4 is a graph showing the change of hexavalent chromium concentration of groundwater inlet and outlet water over time in Example 1 of the present invention;

[0040] Figure 5 It is a curve chart showing the change of total chromium concentration in effluent over time in Example 2, Comparative Example 1 and Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0041] The present invention will be described in detail below in conjunction with the embodiments. It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present invention can be combined with each other. Unless otherwise specified, the following percentages are all weight percentages.

[0042] Example 1

[0043] The preparation of phosphorus-modified pyrite in a heavy metal contaminated groundwater remediation method of this embodiment mainly includes the following steps:

[0044] 1) The pyrite raw stone is crushed and ground, and passed through a 200-mesh sieve to obtain pyrite powder, and the pyrite particle size is less than or equal to 0.075 mm;

[0045] 2) NH4H2PO4 solid is mixed with water to prepare NH4H2PO4 solution, the mass ratio of NH4H2PO4 solid to liquid water is 1:20, and the concentration of the prepared NH4H2PO4 solution is 50g / L; 45wt% of pyrite powder is added to the NH4H2PO4 solution, and the ratio of the mass of pyrite powder to the sum of the mass of NH4H2PO4 solid and pyrite powder is 45%; after stirring in a water bath at 60°C for 4h, the mixture is filtered and dried, and the mixture is heated to 600°C in a tubular furnace, and the mixture is taken out after naturally cooling to room temperature to obtain phosphorus-modified pyrite.

[0046] A heavy metal contaminated groundwater remediation method of this embodiment includes the following steps:

[0047] S1. Fe@FeS particles were prepared by liquid-liquid precipitation method: 1L 0.8mol / L (NH4)2Fe(SO4)2 solution was mixed with 1L 0.8mol / L Na2S solution and stirred continuously. During the stirring process, zero-valent iron powder was continuously added. The amount of zero-valent iron powder added was 33.5g, so that the zero-valent iron was continuously coated during the precipitation of FeS. The solution was centrifuged to obtain Fe@FeS particles, and the particles were dried in a vacuum oven for 1 day for use. If the FeS coating effect was not good, the zero-valent iron and FeS mixture was further ball-milled by a ball mill. Figure 1 As shown, the surface of zero-valent iron is smooth and free of attachments. Figure 2 As shown, when the zero-valent iron surface is coated with FeS, the zero-valent iron surface is no longer smooth;

[0048] S2. Adjust the pH of heavy metal contaminated groundwater to less than 7. Heavy metal contaminated groundwater is generally acidic and does not require additional acid addition;

[0049] S3. Fill the second flow column with phosphorus-modified pyrite and zero-valent iron in a mass ratio of 1.5:1. The heavy metal-contaminated groundwater in step S2 is treated in the second flow column and then enters the first flow column for treatment. The first flow column is filled with Fe@FeS particles.

[0050] The heavy metal-contaminated groundwater was treated by the second flow column and the first flow column for ten consecutive days, and 300 mL of the inlet and outlet water were sampled at 10 am every day. Each sample was divided into two portions, each 150 mL, and the total chromium and hexavalent chromium concentrations of the water samples were measured respectively. After the total chromium sample (150 mL / portion) was collected, nitric acid was added to the pH ≤ 2 to prevent the hydrolysis of metal ions. After the hexavalent chromium sample (150 mL / portion) was collected, it was filtered with a 0.45um filter membrane, and 1.5 mL of nitric acid was added to the filtrate. The total chromium water sample was first subjected to microwave digestion (refer to HJ678), and the total chromium concentration was determined by "flame atomic absorption spectrophotometry" with a measurement wavelength of 357.9 nm, a passband width of 0.2 nm, and an air-acetylene flame. Hexavalent chromium was determined by ultraviolet spectrophotometry (reference: Water Quality, Determination of Hexavalent Chromium Diphenylcarbazide Spectrophotometry GB7467-87), with a wavelength of 540 nm. Figure 3 As shown in the figure, the total chromium concentration in the inlet and outlet water was measured. The total chromium concentration in the inlet water was between 0.14 and 0.16 mg / L, while the effluent concentration was between 0.4 and 0.6 mg / L. The total chromium concentration dropped significantly, indicating that the second flow column and the first flow column adsorbed a part of the chromium ions, which does not prove that the filling medium reduced the hexavalent chromium therein. Therefore, the concentration of hexavalent chromium was also measured. Figure 4 As shown in the data, the influent concentration of hexavalent chromium was between 0.12 and 0.16 mg / L, and the effluent concentration was between 0.01 and 0.03, and only reached 0.012 mg / L on the first day. Comparing the influent concentrations of total chromium and hexavalent chromium, it was found that the concentrations were almost the same, which shows that the chromium in the water body mainly exists in the hexavalent form. And from the 2nd to the 10th day, the hexavalent chromium concentration in the water body met the standard of Class III water in the "Surface Water Environmental Quality Standard" (GB3838-2002), which was lower than 0.05 mg / L.

[0051] In order to further prove the reducing effect of the filling medium in this embodiment on hexavalent chromium, the concentration difference of total chromium and hexavalent chromium in the effluent was compared, as shown in Table 1-1. The effluent concentrations of total chromium and hexavalent chromium are not the same, and the concentration of hexavalent chromium is significantly lower than that of total chromium, indicating that part of the hexavalent chromium is reduced to trivalent chromium, and the difference in the table is the concentration of trivalent chromium. This result shows that the filling medium in this embodiment has a significant reducing and purifying effect on chromium pollution in heavy metal-contaminated groundwater.

[0052] Table 1-1. Difference in the concentration of total chromium and hexavalent chromium in effluent Unit: mg / L

[0053]

[0054] Example 2

[0055] A heavy metal contaminated groundwater remediation method of this embodiment uses only Fe@FeS particles as the filling medium of the first flow column to treat groundwater. In order to verify the treatment effect of the filling medium on heavy metals, the effect test of Fe@FeS material is carried out. The heavy metal contaminated groundwater remediation method of this embodiment includes the following steps:

[0056] S1. Preparation steps of Fe@FeS: Mix 1L 0.8mol / L (NH4)2Fe(SO4)2 solution with 1L 0.8mol / L Na2S solution, stir the obtained solution continuously, add 33.5g of zero-valent iron powder during the stirring process, centrifuge the solution to obtain zero-valent iron particles (Fe@FeS) coated with ferrous sulfide on the surface; dry the Fe@FeS particles in a vacuum oven at 60°C for 1 day, and pass through a 200-mesh sieve;

[0057] S2. Use K2Cr2O7 to prepare a 0.15 mg / L standard chromium solution as the test water, and adjust the pH to 5;

[0058] S3. The Fe@FeS particles in step S1 are filled into the 1# flow column. The test water in step S2 is treated by the 1# flow column to remove the heavy metals therein. The water flow rate is 10 -4 cm / s, and water was continuously introduced for 10 days. Water samples were taken out to test the total chromium concentration.

[0059] Comparative Example 1

[0060] The heavy metal contaminated groundwater remediation method of this comparative example only uses common pyrite and zero-valent iron as the filling medium of the 2# flow column, wherein the mass ratio of common pyrite to zero-valent iron is 1.5:1. The test water inlet is consistent with that in Example 2, and the water inlet flow rate is 10 -4 cm / s, and water was continuously introduced for 10 days. Water samples were taken out to test the total chromium concentration.

[0061] Comparative Example 2

[0062] The heavy metal contaminated groundwater remediation method of this comparative example only uses single zero-valent iron as the filling medium of the 3# flow column. The test water inlet is consistent with that in Example 2, and the water inlet flow rate is 10 -4 cm / s, and water was continuously introduced for 10 days. Water samples were taken out to test the total chromium concentration.

[0063] like Figure 5As shown in the graph of the change of the total chromium concentration of the effluent in Example 2, Comparative Example 1 and Comparative Example 2 over time, after 10 days of flow column treatment, the total chromium concentration of the water treated with Fe@FeS material is 0.072-0.079 mg / L (total chromium removal rate is 45.4%-52%), the total chromium concentration of the water treated with ordinary pyrite + ZVI material is 0.083-0.093 mg / L (total chromium removal rate is 38.2%-44.7%), and the highest concentration of the water treated with ZVI is 0.111-0.124 mg / L (total chromium removal rate is 17.3%-26%). It shows that the heavy metal treatment capacity of each medium material is: Fe@FeS material>ordinary pyrite+ZVI>single ZVI.

[0064] The contents explained in the above embodiments should be understood as these embodiments are only used to more clearly illustrate the present invention, and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

Claims

1. A method for remediating groundwater contaminated by heavy metals, characterized in that: The following steps are involved: S1. Mixing a sodium sulfide solution and an ammonium ferrous sulfate solution, and continuously adding zero-valent iron powder during stirring to prepare a solution containing particles, and separating the particles therein, wherein the particles are zero-valent iron particles with ferrous sulfide coated on the surface; adjusting the pH of the heavy metal contaminated groundwater to less than 7; S2. Filling the particles obtained in step S1 into the first flow column, and removing the heavy metals from the heavy metal-contaminated groundwater adjusted in step S1 through the first flow column.

2. The method for remediating heavy metal contaminated groundwater according to claim 1, characterized in that: In step S1, the amount of sodium sulfide substance in the sodium sulfide solution is equal to the amount of ammonium ferrous sulfate substance in the ammonium ferrous sulfate solution.

3. The method for remediating heavy metal contaminated groundwater according to claim 2, characterized in that: In step S1, the concentration of the sodium sulfide solution is 0.5-0.8 mol / L, and the concentration of the ammonium ferrous sulfate solution is 0.5-0.8 mol / L.

4. The method for remediating heavy metal contaminated groundwater according to claim 1, characterized in that: In step S1, the amount of the added zero-valent iron powder is no more than 75% of the amount of the sodium sulfide or ammonium ferrous sulfate; preferably, the particle size of the zero-valent iron powder is no more than 0.075 mm.

5. The method for remediating heavy metal contaminated groundwater according to claim 1, characterized in that: In step S1, the solution containing the particles is separated by a centrifuge to obtain the particles therein, and the particles are dried in a vacuum environment at 50 to 60° C.; preferably, the drying time is 24 to 48 hours.

6. The method for remediating heavy metal contaminated groundwater according to claim 1, characterized in that: In step S2, the flow rate of heavy metal contaminated groundwater in the first flow column is 10 -2 ~10 -4 cm / s.

7. The method for remediating heavy metal contaminated groundwater according to claim 1, characterized in that: In step S2, the heavy metal contaminated groundwater in step S1 is treated by the second flow column and then by the first flow column; the medium filled in the second flow column is a mixture of pyrite and zero-valent iron, and the mass ratio of pyrite to zero-valent iron is 1-2:0.5-1.

8. The method for remediating heavy metal contaminated groundwater according to claim 6, characterized in that: The particle sizes of the pyrite and zero-valent iron filled in the second flow column are both no greater than 0.075 mm.

9. The method for remediating heavy metal contaminated groundwater according to claim 6, characterized in that: Before the heavy metal contaminated groundwater enters the second flow column, the pH of the heavy metal contaminated groundwater is adjusted to 3-4.

10. The method for remediating heavy metal contaminated groundwater according to claim 6, characterized in that: In step S2, the pyrite added to the second flow column is modified by adding the pyrite to an NH4H2PO4 solution, stirring in a water bath at 55-75°C for 3-5 hours, then filtering and drying, heating the filter residue to 550-600°C in a tubular furnace, cooling to room temperature and then taking out to obtain phosphorus-modified pyrite, which is mixed with zero-valent iron as a filling medium in the second flow column; preferably, when the pyrite added to the second flow column is modified, the ratio of the mass of pyrite to the sum of the mass of NH4H2PO4 and the mass of pyrite in the NH4H2PO4 solution is 35-55wt%.

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