Method for recovering selenium and mercury from lead filter cake

Abstract

The invention belongs to the field of metallurgy, and particularly relates to a method for recovering selenium and mercury from a lead filter cake, which comprises the following steps: (1) leaching; (2) selenium reduction; (3) neutralizing; and (4) mercury precipitation. Hg in the lead filter cake is mainly Hg (metallic mercury), HgS (cinnabar), HgSe (mercury selenide) and HgCl (mercuric chloride), and Se is mainly Se (elemental selenium), SeO (selenium dioxide), PbSe (lead selenide) and CuSe (copper selenide), the scheme comprises the following steps: extracting selenium and mercury in the lead filter cake by adopting a leaching system consisting of hydrochloric acid and hydrogen peroxide, oxidizing and dissolving out selenium and mercury in the lead filter cake by utilizing the strong oxidizing property of Cl2 generated by hydrogen peroxide and HCl, and separating the selenium and mercury from the lead filter cake. And the leaching rates of selenium and mercury are greatly improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metallurgy, and particularly relates to a method for recovering selenium and mercury from lead filter cake. BACKGROUND

[0002] In the process of copper smelting, a by-product, lead filter cake, containing copper, selenium, lead and trace amounts of precious metals such as gold and silver, is produced. This filter cake is formed in the process of washing copper smelting flue gas and is composed of solid particles that are insoluble in dilute acid. The lead filter cake mainly contains lead, bismuth, copper, selenium, mercury, arsenic and other elements, and also contains a small amount of gold and silver. Specifically, the composition of the lead filter cake containing mercury is approximately: copper 1-3%, selenium 10-30%, lead 30-40%, mercury 5-20%, gold 1-5 g / t, and silver 50-200 g / t.

[0003] Currently, there are two main process methods for treating materials such as mercury and selenium: fire method and wet method. The fire method usually involves mixing lime with lead filter cake and then roasting. In this process, mercury is volatilized into flue gas, while selenium is solidified in the slag by lime, thereby achieving the separation and recovery of mercury and selenium. However, the fire method has many shortcomings, such as high investment cost, complex process, generation of large amounts of waste slag, difficulty in flue gas treatment, and the secondary slag being classified as hazardous waste, so it is gradually being phased out.

[0004] The wet treatment process includes various methods, such as: using high-pressure acid leaching (sulfuric acid + sodium chloride, hydrochloric acid + sodium chloride) to leach and separate mercury and selenium from lead filter cake; using sodium sulfite to precipitate selenium, followed by reduction with hydrazine hydrate or precipitation with sodium sulfide; or performing acid leaching after oxygen pressure alkaline leaching to separate selenium and mercury. However, the existing methods for treating lead filter cake by wet method generally have the disadvantages of large amount of leaching acid and base, low leaching rate, and increased amount of secondary slag.

[0005] Due to the complexity of the composition of lead filter cake, especially the potential harm of mercury and selenium to the environment and human health, it is urgent to develop a safe and environmentally friendly process method to treat these substances and effectively recover the precious metals therein. The current technology has the problems of low recovery rate, complex operation process and high cost in the treatment of lead filter cake, which need to be solved. SUMMARY

[0006] The purpose of the present application is to provide a method for recovering selenium and mercury from lead filter cake, which can efficiently recover selenium and mercury from lead filter cake, has a simple process, and uses a small amount of easily obtained auxiliary reagents.

[0007] To achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows: a method for recovering selenium and mercury from lead filter cake, comprising the following steps:

[0008] (1) Leaching: add hydrochloric acid solution and hydrogen peroxide to the lead filter cake, stir evenly and react at 60-80℃ for 4-8h, and then solid-liquid separation to obtain filter residue a and leaching solution;

[0009] (2) Selenium reduction: add a reducing agent to the leaching solution and reduce at 60-80℃, and then solid-liquid separation to obtain filter residue b and reduction liquid; the reducing agent is sulfur dioxide and / or sodium sulfite;

[0010] (3) Neutralization: add an alkaline reagent to the reduction liquid until neutral, and then solid-liquid separation to obtain filter residue c and neutralization liquid;

[0011] (4) Mercury precipitation: add sodium sulfide to the neutralization liquid, and then use sampling to detect the mercury content after reaction; when the mercury content reaches the discharge standard, the filter residue obtained after solid-liquid separation is the mercury sulfide product, and the filtrate is sent to a wastewater treatment system for treatment.

[0012] The Hg in the lead filter cake mainly includes (mercury), HgS (cinnabar), HgSe (mercury selenide), and HgCl2 (mercury chloride), and the Se mainly includes (elemental selenium), SeO2 (selenium dioxide), PbSe (lead selenide), and Cu2Se (copper selenide). In the above scheme, the leaching system composed of hydrochloric acid and hydrogen peroxide is used to extract selenium and mercury from the lead filter cake, the strong oxidizing property of Cl2 generated by hydrogen peroxide and HCl is used to dissolve selenium and mercury in the lead filter cake, and the leaching rate of selenium and mercury is greatly improved. BRIEF DESCRIPTION OF DRAWINGS

[0013] The accompanying drawings illustrate the technical scheme of the present application. Figure 1 The accompanying drawings illustrate the technical scheme of the present application.

[0014] In the drawings, the red arrow represents the main process line; the blue arrow represents the reagent added to the reaction or the treatment performed in the process; and the green arrow represents resource recycling. DETAILED DESCRIPTION

[0015] The technical scheme of the present application is described in detail as follows.

[0016] A method for recovering selenium and mercury from a lead filter cake, comprising the following steps:

[0017] 1. Slurry and leaching: place the lead filter cake in a slurry tank with a stirring device, add hydrochloric acid solution and hot water to stir into a uniform slurry, and then add a hydrogen peroxide solution with a mass concentration of 30% and react at 80℃ for 6h; the amount of hydrogen peroxide is calculated according to the content of selenium and mercury in the lead filter cake, and the amount added is 1.2 times the theoretical calculation value; the concentration of hydrochloric acid is 200g / L, and the liquid-solid ratio of the slurry is 5:1; pump the slurry after reaction into a filter press for pressure filtration to obtain filter residue a and leaching solution; the filter residue a is treated by circulating leaching in the slurry tank.

[0018] The slurry process can significantly increase the surface area of the material particles, which is essential for improving the leaching efficiency of selenium and mercury. By increasing the contact area of solid particles with the leaching solution, more selenium and mercury can be transferred from the solid material to the solution, significantly improving the leaching rate of selenium and mercury. Slowly adding 30% hydrogen peroxide ensures more uniform distribution in the slurry, effectively avoiding the local high concentration of chlorine gas that may cause chlorine gas overflow and loss due to rapid addition.

[0019] The reaction equation is as follows:

[0020] H2O2 + 2HCl = Cl2 + 2H2O

[0021] HgSe + 3H2O + 3Cl2 = H2SeO3 + HgCl2 + 4HCl

[0022] Se + 2H2O2 = H2SeO3 + 2H2O

[0023] HgS + Cl2 + H2O → HgCl2 + H2SO4

[0024] HgSe + 3H2O + 3Cl2 = H2SeO3 + HgCl2 + 4HCl

[0025] PbSe + Cl2 + H2O → PbCl2 + H2SeO3

[0026] Cu2Se + Cl2 + H2O → CuCl2 + H2SeO3

[0027] Here, the concentration of hydrochloric acid should not be too high, because high concentration of chloride ions has strong complexing ability, which can generate more stable tetrachloro lead acid ion when in contact with lead sulfate, thereby enhancing the solubility of lead sulfate. The reaction equation is:

[0028] PbSO4 + 4HCl = H2PbCl4 + H2SO4

[0029] During the leaching process, according to the concentration of selenium and mercury in the leaching solution, the leaching is repeated 2-3 times, and the concentration of selenium + mercury is ≥100g / L. The leaching filtrate is used for slurry leaching again to increase the concentration of selenium and mercury and reduce the consumption of hydrochloric acid and wastewater.

[0030] 2, "Chase chlorine" and selenium reduction: pass the smelting flue gas containing sulfur dioxide into the leaching solution, react at 70℃ for 6h, then slowly add sodium sulfite solution with mass concentration of 20%, take sample and detect with thiourea solution, if no red precipitate is produced, it is the reaction endpoint, filter the reaction liquid to get filter residue b (i.e. crude selenium) and reduction liquid.

[0031] The smelting flue gas containing sulfur dioxide is introduced into the leaching solution, which effectively removes the residual chlorine in the leaching solution (i.e., "chlorine removal"), avoiding the adverse effects of chlorine on the subsequent reduction reaction; on the other hand, the sulfur dioxide in the flue gas can be used to reduce about 90% of selenium, significantly reducing the dependence on and the amount of sodium sulfite used, thereby reducing the overall reduction cost.

[0032] After completing the selenium reduction step, air is introduced into the reaction solution to effectively resolve the dissolved sulfur dioxide in the solution, avoiding the generation of byproduct sulfur when sodium sulfide is added in the subsequent mercury precipitation process. In this way, not only is the amount of sodium sulfide significantly reduced, thereby reducing the consumption of chemical reagents and related costs, but also the purity and quality of the mercury sulfide product are effectively improved.

[0033] The reaction equation for reduction with sulfur dioxide is:

[0034] H2SeO3 + 2SO2 + H2O = Se ↓+ 2H2SO4

[0035] Reduction with sodium sulfite:

[0036] Na2SO3 + 2HCl = 2NaCl + SO2 + H2O

[0037] H2SeO3 + 2SO2 + H2O = Se ↓+ 2H2SO4

[0038] Reduction with sodium sulfite can reduce the amount of neutralizing alkali. To ensure complete reduction of H2SeO3, the actual amount of Na2SO3 added is about 10% higher than the theoretical calculation, and the excess SO2 gas overflows the liquid surface and enters the alkali absorption tower along with the acid mist for treatment.

[0039] 3. Neutralization and impurity removal: The reduced liquid is concentrated by low-temperature evaporation at 55°C. The volume of the reduced liquid is concentrated to 30%, and the evaporated HCl is condensed and collected, and returned to the leaching step for recycling. Then, 30% sodium hydroxide solution is added to the concentrated reduced liquid, the pH is adjusted to 7-8, and the reaction is carried out for 2h (at room temperature). Solid-liquid separation is performed to obtain filter residue c and neutralization liquid.

[0040] Due to the high content of hydrochloric acid in the reduced liquid, it will cause a large consumption of sodium hydroxide and produce a large amount of salt byproduct. In order to solve this problem, the process introduces low-temperature heat pump evaporation and condensation technology, which can effectively evaporate 90% of the hydrochloric acid in the solution and recover it through the condensation process for recycling in the leaching reactor, while reducing a large amount of wastewater.

[0041] Maintaining the pH of the solution to 7-8 during the neutralization step is crucial for improving the quality of mercuric sulfide products. Adjusting the pH to neutral effectively promotes the hydrolysis of dissolved metal ions such as iron, lead, bismuth, and zinc in the solution, forming water-insoluble metal hydroxides and sulfate precipitates. This process significantly reduces the content of these metal impurities in the final product, thereby significantly improving the purity and quality of mercuric sulfide.

[0042] The reducing solution is neutralized with NaOH to adjust the pH to 7-8, in preparation for mercury precipitation. The chemical reaction equation is:

[0043] 2NaOH + H₂SO₄ = Na₂SO₄ + 2H₂O

[0044] NaOH + HCl = NaCl + H₂O

[0045] During the neutralization process, bismuth, lead, copper, and zinc undergo hydrolysis:

[0046] CuCl₂ + 2NaOH = Cu(OH)₂↓ + 2NaCl

[0047] ZnCl₂ + NaOH = Zn(OH)↓ + 2NaCl

[0048] 2BiCl3+6NaOH=Bi2O3↓+6NaCl+3H2O

[0049] H2PbCl4+6NaOH+H2SO4=PbSO4↓+6NaCl+4H2O

[0050] 4. Mercury precipitation: Add a 10% sodium sulfide solution to the neutralization solution and react for 2 hours (at room temperature). Take a sample and use a mercury detector to determine the mercury content. The reaction ends when the mercury content meets the emission standards. After filtration in a filter press, the filter residue is the mercury sulfide product. The filtrate is sent to the wastewater treatment system for treatment.

[0051] Mercuric chloride reacts with sodium sulfide to form a black precipitate of mercuric sulfide. The reaction equation is as follows:

[0052] HgCl2 + Na2S = HgS↓ + 2NaCl

[0053] The above-mentioned method for processing lead filter cake achieves a comprehensive selenium recovery rate of 98.0% and a mercury recovery rate of 98.0%. Not only is the process simple, but it also achieves high comprehensive selenium and mercury recovery rates, reduces raw material consumption, and, in particular, produces crude selenium and relatively pure mercury sulfide products.

[0054] Example

[0055] The lead filter cake was processed using the method described above:

[0056] Lead filter cake composition:

[0057]

[0058] 1. Slurry, leaching: take 1000g of lead filter cake, leach twice:

[0059] First 500g + hydrochloric acid 1170ml, water 567ml, 30% hydrogen peroxide 80ml, leach at 70℃ for 6 hours;

[0060] Second filtrate + 30% hydrogen peroxide 80ml, leach at 70℃ for 6 hours

[0061] Leaching rate: Cu 99.7%, Hg 98.7%, Se 98.2%, Bi 99.2%.

[0062] 2. Selenium reduction:

[0063] Sulfur dioxide content in flue gas 12%, dosage 2.981 Nm 3 / h;

[0064] Anhydrous sodium sulfite dosage 43.66g;

[0065] Output crude selenium product 91g, selenium content 75%.

[0066] 3. Neutralization:

[0067] Evaporate and condense to recover 17.4% hydrochloric acid 2.038L;

[0068] Consumption of 30% sodium hydroxide 188g;

[0069] Get neutralized slag 113g.

[0070] 4. Sulfidation:

[0071] Add 10% sodium sulfide 302g;

[0072] Get 89.8% sulfidized mercury 87g.

[0073] As can be seen from the above examples, by adopting the scheme of the present application to recover selenium and mercury in lead filter cake, not only the economic benefit is improved, but also the environmental burden is significantly reduced. This efficient resource recovery and recycling strategy reduces wastewater discharge and neutralized slag, which means the demand for water treatment facilities is reduced, thereby reducing the overall operating cost and environmental impact.

Claims

1. A method for recovering selenium and mercury from lead filter cake, comprising the following steps: (1) leaching: adding hydrochloric acid solution and hydrogen peroxide to the lead filter cake, stirring and reacting at 60-80℃ for 4-8h, and then solid-liquid separation to obtain filter residue a and leaching solution; (2) selenium reduction: adding a reducing agent to the leaching solution and reducing at 60-80℃, and then solid-liquid separation to obtain filter residue b and reduction solution; the reducing agent is sulfur dioxide and / or sodium sulfite; (3) neutralization: adding an alkaline reagent to the reduction solution until the pH is 7-8, and then solid-liquid separation to obtain filter residue c and neutralization solution; (4) mercury precipitation: adding sodium sulfide to the neutralization solution, detecting the mercury content after reaction, and then solid-liquid separation to obtain mercury sulfide product, and the filtrate is sent to a wastewater treatment system for treatment.

2. The process for recovering selenium and mercury from lead filter cake according to claim 1, characterized in that: In the step (1), hot water and hydrochloric acid solution are first added to the lead filter cake, stirred, and then 30% hydrogen peroxide solution is added.

3. The method of recovering selenium and mercury from a lead filter cake of claim 1, wherein: In the step (1), the amount of hydrogen peroxide is 1.2 times the theoretical calculation value, the concentration of hydrochloric acid is 200g / L, and the liquid-solid ratio is 5:

1.

4. The method of recovering selenium and mercury from a lead filter cake of claim 1, wherein: In the step (1), the lead filter cake leaching step is repeated for 2-3 times until the sum of the concentrations of selenium and mercury is ≥100g / L.

5. The method of recovering selenium and mercury from a lead filter cake of claim 1, wherein: In the step (2), sulfur dioxide is first introduced into the leaching solution before adding sodium sulfite, and the reaction is carried out for 1-2h.

6. The method of recovering selenium and mercury from lead filter cake according to claim 1 or 5, characterized in that: The sulfur dioxide is smelting flue gas containing sulfur dioxide.

7. The method of recovering selenium and mercury from lead filter cake of claim 1, wherein: In the step (2), sodium sulfite solution is gradually added to the leaching solution until no red precipitate is produced when the sample is detected with thiourea solution, and then the addition of sodium sulfite solution is stopped.

8. The method of recovering selenium and mercury from a lead filter cake of claim 1, wherein: In the step (2), air is introduced into the reaction solution after the reduction of selenium.

9. The method of recovering selenium and mercury from a lead filter cake of claim 1, wherein: In the step (3), the reduction solution is first evaporated at 50-60℃, and the volume of the reduction solution is concentrated to 30%, and the hydrochloric acid is recovered by condensation and returned to step (1) for reuse.

10. The method of recovering selenium and mercury from a lead filter cake of claim 1, wherein: In the step (3), 30% sodium hydroxide solution is added to the reduction solution until the pH is 7-8.

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