Bismuth salt dechlorination method for acidic wastewater

Abstract

The invention provides a bismuth salt dechlorination method for waste acid wastewater, which comprises the following steps: adding hydrogen sulfide into the waste acid wastewater to react with heavy metals, filtering to obtain sulfurized slag and high fluorine-chlorine filtrate, returning the sulfurized slag to zinc concentrate, and feeding into a fluidized bed furnace for reutilization; performing electrodialysis on the high-fluorine-chlorine filtrate to obtain dialysis fresh water and dialysis residual liquid, returning the dialysis fresh water to a zinc wet-process smelting system for replenishing water: evaporating and stripping the dialysis residual liquid to obtain high-fluorine-chlorine distillate and a sulfuric acid solution, and preparing 98% concentrated sulfuric acid by using the sulfuric acid solution; adding lime into the high-fluorine-chlorine distillate for defluorination, and filtering after reaction to obtain fluorite and a defluorination liquid with the fluorine content reaching the standard; adding bismuth salt into the defluorination liquid for dechlorination, and filtering after reaction to obtain dechlorinated residues and dechlorinated water with the fluorine and chlorine content reaching the standard; and regenerating the dechlorinated residues to obtain bismuth hydroxide, and converting the bismuth hydroxide into bismuth salt for dechlorination. According to the bismuth salt dechlorination method for the waste acid wastewater, the fluorine and chlorine content in the waste acid wastewater can reach the requirement standard of zinc hydrometallurgy on secondary return water, and the method is green, environmentally friendly, economical and efficient.

Description

Technical Field

[0001] The invention relates to the technical field of zinc hydrometallurgy, and in particular to a bismuth salt dechlorination method for dirty acid wastewater. Background Art

[0002] Zinc is a commonly used metal. China's production capacity exceeds 6.5 million tons, and 85% of the smelting processes use hydrometallurgy. At present, the water resource consumption of hydrometallurgy is more than 9 tons of water / ton of zinc, and the amount of wastewater discharged that meets the standard is 10 tons of water / ton of zinc. Although the discharged wastewater meets the industry standard, it still contains trace amounts of heavy metals, which will not only cause certain harm to the environment, but also cause waste of resources. Therefore, the zero-discharge technology and application research of hydrometallurgy industrial wastewater is of great significance.

[0003] In the process of zinc hydrometallurgy, the flue gas produced by the roasting of zinc concentrate in a fluidized bed furnace can be treated by the acid-making process to obtain 98% concentrated sulfuric acid products and dirty acid wastewater. The dirty acid wastewater is prepared by lead and arsenic impurity removal, electrodialysis and evaporation stripping to obtain sulfuric acid with a concentration greater than 68%, distillate and fresh water, wherein the content of F and Cl in fresh water is less than 100 mg / L, pH=2-4, pH=0.5-4 in distillate, and the content of F and Cl reaches 600 mg / L and 900 mg / L respectively. Cl is toxic and is a harmful element in the hydrometallurgical zinc smelting process. When the chloride ion concentration in the zinc sulfate electrolyte reaches 300 mg / 1, the qualified rate of cathode zinc will be affected to a certain extent. When the chloride ion concentration reaches 500 mg / I, it will accelerate the corrosion rate of the anode lead plate and the lead content in the cathode zinc will exceed the standard. When the chloride ion concentration exceeds 800 mg / 1, chlorine gas will be precipitated on the anode, which will lead to serious problems such as deterioration of the working environment, aggravation of equipment corrosion and a sharp increase in power consumption per ton of zinc. Therefore, it is necessary to strictly implement zero discharge of wastewater. After the acid wastewater is treated, the valuable heavy metals are returned to the zinc concentrate and recovered by roasting in a boiling furnace. 68% sulfuric acid is used as an absorbent to produce 98% concentrated sulfuric acid. The fresh water is returned to the zinc hydrometallurgical system for recovery. However, the distillate cannot be directly returned to the zinc hydrometallurgical system due to its high F and Cl content. It needs to be removed from F and Cl to meet the standards before it can be returned to the zinc hydrometallurgical system for recovery.

[0004] The commonly used dechlorination methods for domestic zinc hydrometallurgical enterprises include copper slag method, ion exchange method and bismuth salt method. - It reacts with chloride ions to generate Cu2Cl2 precipitation and dechlorinate. The copper slag method is commonly used in industry, but the copper slag method has strict requirements on the copper content of copper slag, and the low copper content has poor dechlorination effect. The ion exchange method uses the exchangeable anions of ion exchange resin to react with the chloride ions in the new solution, so that the chlorine in the solution is adsorbed on the resin, and the corresponding exchangeable anions on the resin enter the solution. The dechlorination efficiency of this method is as low as 50%, and the water consumption of the resin regeneration is large, and the regeneration cost is as high as 200 yuan / ton of zinc.

[0005] The bismuth salt method is to react bismuth oxide with bismuth salt under acidic conditions. 3+ The bismuth chloride is generated by reacting with chloride ions, and then hydrolyzed to generate insoluble bismuth oxychloride precipitation, which is then washed with alkali to regenerate bismuth oxide under high temperature conditions, and can be reused to reduce production costs. As disclosed in Chinese patent application CN113930806A, a wet electro-zinc dechlorination and chlorine recovery process is firstly acidified to obtain bismuth ions, and bismuth ions react with chloride ions and hydrolyze to generate bismuth oxychloride precipitation. Although more than 80% of the chlorine in the high-chloride zinc sulfate solution can be removed in the dechlorination process of this method, the regeneration process adopts sulfuric acid roasting, which has large environmental pollution, and the volatilized HCl has serious corrosion on the equipment, which has high requirements on the equipment, and the equipment investment is large and the maintenance cost is high.

[0006] Moreover, in the conventional method of dechlorinating the acid wastewater in zinc hydrometallurgy with bismuth salt, zinc will be carried into the dechlorination slag, resulting in a loss of 0.5-1% of zinc. Most of the zinc enters the regeneration liquid of the dechlorination slag, which will reduce the quality of the product sodium chloride, thereby increasing production costs and having poor economic benefits.

[0007] Therefore, there is an urgent need for a new method for dechlorinating polluted acid wastewater with bismuth salt, which can not only effectively recover valuable heavy metals such as lead and zinc, sulfuric acid, water and other resources in the polluted acid wastewater, and realize efficient utilization of all components of the polluted acid wastewater, but also reduce the fluorine and chlorine elements in the polluted acid wastewater to the required standard for the fluorine and chlorine content of secondary return water in zinc hydrometallurgy, so that the polluted acid wastewater can be returned to the zinc hydrometallurgy system for reuse after treatment, thereby realizing zero wastewater discharge from zinc hydrometallurgy. Summary of the invention

[0008] The technical problem to be solved by the present invention is to provide a bismuth salt dechlorination method for contaminated acid wastewater, which can make the fluorine and chlorine content in the contaminated acid wastewater meet the requirements of zinc hydrometallurgy for secondary return water and is green, environmentally friendly, economical and efficient.

[0009] In order to solve the above technical problems, the present invention provides a bismuth salt dechlorination method for acid wastewater, comprising the following steps:

[0010] Add hydrogen sulfide to the acid wastewater to react with heavy metals and then filter to obtain sulfide slag and high-fluorine and chlorine filtrate. The sulfide slag returns to the zinc concentrate and is reused in the boiling furnace.

[0011] The high-fluorine and chlorine filtrate is electrodialyzed to obtain dialysis fresh water and dialysis residual liquid. The dialysis fresh water is returned to the zinc hydrometallurgical system as water replenishment:

[0012] The dialysis residue is evaporated and stripped to obtain a high-fluorine and chlorine distillate and a sulfuric acid solution, which is used to prepare 98% concentrated sulfuric acid;

[0013] Add lime to the high-fluorine and chlorine distillate to defluorinate, and filter after the reaction to obtain the defluorinated liquid with fluorite and fluorine content meeting the standards;

[0014] Add bismuth salt to the defluorination liquid for dechlorination, and filter after the reaction to obtain dechlorination residue and dechlorinated water with fluorine and chlorine content meeting the standard;

[0015] The dechlorination slag is regenerated to obtain bismuth hydroxide, which is then converted into bismuth salt and then dechlorinated.

[0016] Furthermore, the temperature for the reaction of hydrogen sulfide with heavy metals in the polluted acid wastewater is 45-60° C., and the reaction time is 120-180 min.

[0017] Furthermore, the amount of hydrogen sulfide added is 1.5-3 times the theoretical molar amount of hydrogen sulfide required to convert all heavy metals in the acid wastewater into sulfide precipitation.

[0018] Furthermore, the temperature of the reaction of the lime and the high-fluorine-chlorine distillate is 50-75° C., the reaction time is 90-150 min, and the pH at the end point of the reaction is controlled at 8-9.

[0019] Furthermore, the amount of lime added is 1.01-1.05 times the theoretical molar amount of lime required to convert all fluorine in the high-fluorine chlorine distillate into fluorite.

[0020] Furthermore, the reaction temperature of the bismuth salt and the defluorination liquid is 45-50° C., and the reaction time is 35-45 min.

[0021] Furthermore, the amount of the bismuth salt added is 1.03-1.10 times the theoretical molar amount of the bismuth salt required to convert all the chlorine in the defluorination liquid into bismuth oxychloride.

[0022] Furthermore, the bismuth salt is bismuth sulfate or bismuth sulfate obtained by activating bismuth oxide and / or bismuth hydroxide with a sulfuric acid solution.

[0023] Furthermore, when the bismuth oxide and / or bismuth hydroxide are activated to obtain bismuth sulfate, the liquid-solid weight ratio of the sulfuric acid solution to the bismuth salt is 5:1-8:1, the concentration of the sulfuric acid solution for activation is 120 g / L-180 g / L, the activation temperature is 75-85° C., and the activation time is 90-120 min.

[0024] Furthermore, the regeneration temperature of the dechlorinated slag is 55-68°C, the regeneration time is 130-180 min, the regeneration agent is a NaOH alkaline solution with activator soda ash added, the liquid-solid weight ratio of the regeneration agent to the dechlorinated slag is 5:1-8:1, the NaOH content is 70-85 g / L, and the amount of soda ash added is 5-10 g / L.

[0025] The present invention provides a bismuth salt dechlorination method for polluted acid wastewater. By introducing a certain amount of hydrogen sulfide into the polluted acid wastewater, valuable heavy metals such as zinc, lead, copper, and cadmium in the polluted acid wastewater can be separated and enriched into zinc-containing sulfide slag, the grade of which meets the requirements of zinc hydrometallurgy for zinc ore, and the zinc concentrate is returned to the boiling furnace for reuse, so that the recovery rate of valuable heavy metals such as zinc, lead, copper, and cadmium exceeds 99%. At the same time, the sulfur in the hydrogen sulfide enters the zinc hydrometallurgy as sulfide slag, and can eventually be converted into sulfuric acid products, thereby realizing the recycling of valuable materials.

[0026] Moreover, the bismuth salt dechlorination method of the polluted acid wastewater provided by the present invention can effectively reduce the fluorine in the polluted acid wastewater to the use requirement standard of the second return water of zinc hydrometallurgy by adding low-priced and easily available lime to the polluted acid wastewater from which heavy metals are removed, and also convert the fluorine in the polluted acid wastewater into fluorite with high economic value. Moreover, the present invention returns the dialysis fresh water obtained by electrodialysis in the process to the zinc hydrometallurgy system for reuse, and uses the sulfuric acid solution obtained by evaporation-stripping to prepare 98% concentrated sulfuric acid. At the same time, the dechlorination slag produced by the dechlorination of bismuth salt can be regenerated and continuously used for the dechlorination of bismuth salt for recycling, so that the products in the process are basically recycled and reused, which not only realizes the comprehensive and efficient utilization of various resources, but also can greatly reduce the production cost, improve the economic benefits, and greatly improve the industry competitiveness of zinc hydrometallurgy enterprises.

[0027] At the same time, the bismuth salt dechlorination method of the polluted acid wastewater provided by the present invention can reduce the fluorine and chlorine in the polluted acid wastewater with fluorine and chlorine contents of 5 g / L and 8 g / L or more to less than 50 mg / L respectively through lime defluorination and bismuth salt dechlorination, so that the polluted acid wastewater treated by the process of the present invention meets the use standard requirements of the recycled secondary water of the zinc hydrometallurgical system, the treated polluted acid wastewater can be recycled, and the internal production costs of the enterprise such as defluorination and chlorination in the subsequent zinc hydrometallurgical process can be reduced, the economic benefits are good, industrialization is easy to realize, and the application prospects are relatively broad. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A step diagram of a bismuth salt dechlorination method for acid wastewater provided in an embodiment of the present invention;

[0029] Figure 2 A structural flow chart of a bismuth salt dechlorination method for acid wastewater provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] See also Figure 1 The present invention provides a method for dechlorinating acid wastewater with bismuth salt, comprising the following steps:

[0031] Step 1) adding hydrogen sulfide to the polluted acid wastewater to react with heavy metals and filtering to obtain sulfide slag and high-fluorine and chlorine filtrate; the sulfide slag is returned to the zinc concentrate and put into the boiling furnace for reuse.

[0032] Among them, the polluted acid wastewater is the polluted acid wastewater produced during the zinc hydrometallurgy process, with fluorine and chlorine contents reaching 5g / L and 8g / L respectively.

[0033] After hydrogen sulfide is introduced into the polluted acid wastewater, the hydrogen sulfide reacts with valuable heavy metals such as lead, zinc, copper, and cadmium in the polluted acid wastewater to generate corresponding sulfide precipitates to obtain insoluble zinc-containing sulfide slag, thereby separating the valuable heavy metals in the polluted acid wastewater.

[0034] Among them, the chemical reaction between hydrogen sulfide and valuable heavy metals such as lead, zinc, copper, and cadmium in polluted acid wastewater is as follows.

[0035] ZnSO4+H2S=ZnS↓+H2SO4;

[0036] CuSO4+H2S=CuS↓+H2SO4;

[0037] PbSO4+H2S=PbS↓+H2SO4.

[0038] In order to make the reaction fully and thoroughly, the reaction temperature of hydrogen sulfide and valuable heavy metals such as lead, zinc, copper, and cadmium is controlled at 45-60°C, and the reaction time is controlled at 120-180 minutes.

[0039] Among them, the zinc-containing sulfide slag obtained by filtration is returned to the zinc concentrate and enters the boiling furnace for reuse, thus realizing the recycling of resources and achieving the purpose of saving resources.

[0040] Furthermore, in order to completely react valuable heavy metals such as lead, zinc, copper, and cadmium in the acid wastewater, the amount of hydrogen sulfide added is 1.5-3 times the theoretical molar amount of hydrogen sulfide required to convert all valuable heavy metals in the acid wastewater into sulfide precipitation.

[0041] Wherein, hydrogen sulfide is hydrogen sulfide gas or hydrogen sulfide solution. Of course, in order to reduce the waste of water resources, as a best embodiment of the present invention, hydrogen sulfide is selected from hydrogen sulfide gas.

[0042] By reacting hydrogen sulfide gas with valuable heavy metals such as lead, zinc, copper, cadmium, etc. in the polluted acid wastewater, the valuable heavy metals such as lead, zinc, copper, cadmium, etc. are basically all retained in the sulfide slag, and the sulfide slag is returned to the zinc concentrate and enters the boiling furnace for re-circulation, so that the recovery rate of valuable heavy metals such as lead, zinc, copper, cadmium, etc. can exceed 99%. The filtrate obtained by filtration does not basically contain valuable heavy metals such as lead, zinc, copper, cadmium, etc., and the filtrate is a high-fluorine and chlorine filtrate mainly containing fluorine, chlorine and sulfuric acid.

[0043] Step 2) The high-fluorine and chlorine filtrate is electrodialyzed to obtain dialysis fresh water and dialysis residual liquid, and the dialysis fresh water is returned to the zinc hydrometallurgical system as water replenishment.

[0044] The water in the high-fluorine and chlorine filtrate can be initially separated from the fluorine, chlorine and sulfuric acid by electrodialysis to obtain fresh water. The fluorine and chlorine content of the fresh water is very low, which meets the use standard requirements of the zinc hydrometallurgical system for secondary return water. Therefore, the obtained fresh water can be directly returned to the zinc hydrometallurgical system as secondary return water for replenishment, which can not only further enrich the acid in the dialysis residual liquid and reduce the production cost of the next step of separation and purification, but also improve the utilization rate of water in the process and improve economic benefits.

[0045] Step 3) The dialysis residue is evaporated and stripped to obtain a high-fluorine-chlorine distillate and a sulfuric acid solution, and the sulfuric acid solution is used to prepare 98% concentrated sulfuric acid.

[0046] Among them, the dialysis residue obtained by electrodialysis of high-fluorine-chlorine filtrate is rich in fluorine, chlorine and sulfuric acid. In order to further separate them, the dialysis residue is evaporated and stripped. The volatile fluorine and chloric acid in the dialysis residue can be volatilized and separated from sulfuric acid by evaporation and stripping, thereby obtaining a high-fluorine-chlorine distillate rich in fluorine and chlorine and the remaining sulfuric acid solution. The remaining sulfuric acid solution is further evaporated to obtain dilute sulfuric acid with a concentration of 68%, and the sulfuric acid solution is used to prepare concentrated sulfuric acid with a concentration of 98%. Comprehensive and efficient utilization of sulfuric acid resources is achieved, which greatly reduces production costs and improves economic benefits.

[0047] Step 4) adding lime to the high-fluorine and chlorine distillate to defluorinate, filtering after the reaction to obtain fluorite and defluorinated liquid with fluorine content meeting the standard.

[0048] Since the fluorine and chlorine in the high-fluorine and chlorine distillate are basically in the form of hydrochloric acid and hydrofluoric acid, in order to make the distillate meet the use standard requirements of the zinc hydrometallurgical system for secondary return water, quicklime is first added to the high-fluorine and chlorine distillate for dechlorination.

[0049] The reactions that occur during the dechlorination of high-fluorine and chlorine distillate by quicklime are as follows:

[0050] CaO+H2O=Ca(OH)2;

[0051] Ca(OH)2+2HF=CaF2+2H2O.

[0052] By dechlorinating the high-fluorine-chlorine distillate with quicklime, the fluorine content in the high-fluorine-chlorine distillate can be reduced to below 50 mg / L. Not only can the fluorine content in the defluorinated liquid meet the standard requirements for the fluorine content in the secondary return water of the zinc hydrometallurgical system, but the process also produces fluorite calcium fluoride with high economic value, which has good economic benefits and can greatly improve the industry competitiveness of zinc hydrometallurgical enterprises.

[0053] In order to make the lime and the high-fluorine-chlorine distillate fully react, the reaction temperature of the lime and the high-fluorine-chlorine distillate is controlled at 50-75°C, and the reaction time is controlled at 90-150 minutes.

[0054] Furthermore, in order to make the lime react completely with the high-fluorine chlorine distillate and completely remove the fluorine, the amount of lime added is controlled to be 1.01-1.05 times the theoretical molar amount of lime required to convert all the fluorine in the high-fluorine chlorine distillate into fluorite.

[0055] At the same time, after the pH value at the reaction end point is controlled at 8-9, the post-reaction solution is filtered to obtain a defluoridation liquid whose fluorine content can meet the standard requirements for the fluorine content of secondary return water in the zinc hydrometallurgical system and fluorite calcium fluoride with high economic value.

[0056] Step 5) adding bismuth salt to the defluorination liquid for dechlorination, filtering after the reaction to obtain dechlorination residue and dechlorinated water with fluorine and chlorine content meeting the standards.

[0057] Although the fluorine content in the defluorination liquid meets the use standard of secondary return water in the zinc hydrometallurgical system, the chlorine content in the defluorination liquid does not meet the standard, so bismuth salt is needed to dechlorinate the defluorination liquid.

[0058] The bismuth salt is bismuth sulfate or bismuth sulfate obtained by activating bismuth oxide and / or bismuth hydroxide with a sulfuric acid solution.

[0059] When bismuth oxide and / or bismuth hydroxide are activated to obtain bismuth sulfate, the liquid-solid weight ratio of the sulfuric acid solution to the bismuth salt is 5:1-8:1, the concentration of the sulfuric acid solution for activation is 120g / L-180g / L, the activation temperature is 75-85°C, and the activation time is 90-120min.

[0060] Among them, bismuth oxide and bismuth hydroxide are activated to obtain bismuth sulfate, which undergoes the following reaction:

[0061] Bi2O3+3H2SO4=Bi2(SO4)3+3H2O;

[0062] 2Bi(OH)3+3H2SO4=Bi 2( SO4)3+6H2O.

[0063] In order to fully dechlorinate the defluorination liquid to meet the use standard of secondary return water in the zinc hydrometallurgical system, the amount of bismuth salt added is 1.03-1.10 times the theoretical molar amount of bismuth salt required to convert all the chlorine in the defluorination liquid into bismuth oxychloride.

[0064] Furthermore, in order to fully and completely dechlorinate the defluorination liquid, the reaction temperature of the bismuth salt and the defluorination liquid is controlled at 45-50° C., and the reaction time is controlled at 35-45 minutes.

[0065] The following reaction occurs when bismuth salt is added to the defluorination liquid:

[0066] Bi2(SO4)3+HCl=BiOCl↓+H2SO4;

[0067] H2SO4+2OH - =SO4 2- +2H2O.

[0068] By dechlorinating the defluorination liquid with bismuth salt, the chlorine content in the defluorination liquid can be reduced to below 50 mg / L, so that the obtained dechlorinated water meets the use standard requirements of the zinc hydrometallurgical system for recycled and reused secondary return water, and the final treated dirty acid wastewater can be recycled and reused.

[0069] It can also reduce the internal production costs of enterprises such as defluorination and chlorination in the subsequent zinc hydrometallurgical process, has good economic benefits, is easy to realize industrialization, and has a broad application prospect.

[0070] Step 6) regenerating the dechlorinated slag to obtain bismuth hydroxide, which is converted into bismuth salt and then dechlorinated.

[0071] Dechlorination slag contains rich bismuth elements. In order to save resources, avoid unnecessary waste, and prevent the discharge of dechlorination slag from burdening the environment, the dechlorination slag is recycled.

[0072] The regeneration of the dechlorination slag is to add a regeneration agent to the dechlorination slag to convert the bismuth in the dechlorination slag into bismuth hydroxide, and the bismuth hydroxide is then acidified with a sulfuric acid solution with a concentration of 120g / L-180g / L to obtain a bismuth salt that can be used for dechlorination of the defluorination liquid.

[0073] As a specific embodiment of the present invention, the regeneration agent is a NaOH alkaline solution added with an activator soda ash.

[0074] The liquid-solid weight ratio of the regeneration agent to the dechlorination slag is 5:1-8:1, the NaOH content is 70-85 g / L, the amount of soda added is 5-10 g / L, the temperature of the regeneration reaction of the regeneration agent to the dechlorination slag is 55-68°C, and the regeneration time is 130-180 min.

[0075] By regenerating the dechlorination slag produced by bismuth salt dechlorination and continuously using it for bismuth salt dechlorination and recycling it, the products in the process can be basically recovered and reused, which not only realizes the comprehensive and efficient utilization of various resources, but also can greatly reduce production costs, improve economic benefits, and greatly enhance the industry competitiveness of zinc hydrometallurgical enterprises.

[0076] The following is a specific description of the bismuth salt dechlorination method for acid wastewater provided by the present invention through examples.

[0077] Example 1

[0078] For a kind of acid wastewater with fluorine, chlorine and sulfuric acid mass concentrations of 273mg / L, 915mg / L and 35.06g / L respectively, and containing heavy metals such as Zn, Cd, Pb, Cu, As, etc., according to Figure 2 The process comprises the following steps:

[0079] The first step of pretreatment is to introduce 1.5 times of hydrogen sulfide gas into the acid wastewater, with a reaction time of 180 minutes and a reaction temperature of 45°C. The obtained high-fluorine and chlorine-containing clean water with valuable metals and heavy metals removed is subjected to electrodialysis. The high-fluorine and chlorine-containing dilute acid after electrodialysis is evaporated and stripped to separate sulfuric acid from the fluorine-containing and chlorine-containing distillate.

[0080] Step 2: Preparation of fluorite: slowly add 1.05 times the theoretical amount of lime required to the 50°C distillate, react for 90 minutes, control the end point pH to 9, filter, and obtain defluorinated liquid and fluorite.

[0081] The third step is bismuth salt dechlorination: 1.03 times bismuth sulfate is activated in 180g / L sulfuric acid solution at a liquid-solid ratio of 5:1, the activation time is 90min, the activation temperature is 85°C, the activated bismuth sulfate is added to the defluorination liquid, dechlorinated at T=45°C, t=45min, and the dechlorinated slag and qualified low-fluorine and low-chlorine dechlorinated water for the zinc hydrometallurgical system are obtained by filtration.

[0082] The fourth step is the regeneration of dechlorination slag: the dechlorination slag is added into a NaOH alkaline solution with a liquid-to-solid ratio of 5:1, the addition amount of the activating agent soda ash is 5g / L, the content of the regeneration agent NaOH is 85g / L, the regeneration temperature is 55°C, the regeneration time is 180min, and the regenerated dechlorination slag is returned to the bismuth salt dechlorination cycle for reuse.

[0083] The water from the polluted acid wastewater is returned to the zinc smelting wet process system in the form of secondary return water and is recovered as water resources. The output sulfuric acid solution with a mass percentage concentration of 75.84% is used to prepare 98% concentrated sulfuric acid, and the resource utilization rate of sulfuric acid is 98.54%. The heavy metal valuable metals zinc, lead, and cadmium are recovered in the form of sulfides as zinc concentrate returned to the boiling furnace, with a recovery rate of 99.18%. The F and Cl contents in the secondary return water returned to the system as water resources are 18 mg / L and 32.81 mg / L, respectively, and the removal rates of fluorine and chlorine are 93.41% and 96.41%, respectively.

[0084] Example 2

[0085] For a kind of acid wastewater with fluorine, chlorine and sulfuric acid mass concentrations of 318.05mg / L, 1014.63mg / L and 38.15g / L respectively, and containing heavy metals such as Zn, Cd, Pb, Cu, As, etc., according to Figure 2 The process comprises the following steps:

[0086] The first step of pretreatment is to introduce 3 times of hydrogen sulfide gas into the acid wastewater, with a reaction time of 120 minutes and a reaction temperature of 60°C. The obtained high-fluorine and chlorine-containing clean water with valuable metals and heavy metals removed is subjected to electrodialysis. The high-fluorine and chlorine-containing dilute acid after electrodialysis is evaporated and stripped to separate sulfuric acid from the fluorine-containing and chlorine-containing distillate.

[0087] Step 2: Preparation of fluorite: slowly add 1.01 times the theoretical amount of lime required to the 75°C distillate, react for 150 minutes, control the end point pH to 8, filter, and obtain defluorinated liquid and fluorite.

[0088] The third step is bismuth salt dechlorination: 1.10 times bismuth oxide is activated in 120g / L sulfuric acid solution at a liquid-solid ratio of 8:1, the activation time is 120min, the activation temperature is 75°C, the activated bismuth oxide is added to the defluorination liquid, dechlorinated at T=50°C, t=35min, and the dechlorinated slag and qualified low-fluorine and low-chlorine dechlorinated water for the zinc hydrometallurgical system are obtained by filtration.

[0089] The fourth step is the regeneration of dechlorination slag: the dechlorination slag is added into a NaOH alkaline solution with a liquid-to-solid ratio of 8:1, the addition amount of the activating agent soda ash is 10g / L, the content of the regeneration agent NaOH is 70g / L, the regeneration temperature is 68°C, the regeneration time is 130min, and the regenerated dechlorination slag is returned to the bismuth salt dechlorination cycle for reuse.

[0090] The water from the polluted acid wastewater is returned to the zinc smelting wet process system in the form of secondary return water and is recovered as water resources. The produced sulfuric acid solution with a mass percentage concentration of 73.19% is used to prepare 98% concentrated sulfuric acid, and the resource utilization rate of sulfuric acid is 99.03%. The heavy metal valuable metals zinc, lead, and cadmium are recovered in the form of sulfides as zinc concentrate returned to the boiling furnace, with a recovery rate of 99.37%. The F and Cl contents in the secondary return water returned to the system as water resources are 16.31 mg / L and 34.15 mg / L, respectively, and the removal rates of fluorine and chlorine are 94.87% and 96.63%, respectively.

[0091] Example 3

[0092] For a kind of acid wastewater with fluorine, chlorine and sulfuric acid mass concentrations of 362.81mg / L, 1305.23mg / L and 39.55g / L respectively, and containing heavy metals such as Zn, Cd, Pb, Cu, As, etc., according to Figure 2 The process comprises the following steps:

[0093] The first step of pretreatment is to introduce 2.4 times of hydrogen sulfide gas into the dirty acid wastewater, with a reaction time of 150 minutes and a reaction temperature of 55°C. The obtained high-fluorine and chlorine-containing clean water with valuable metals and heavy metals removed is subjected to electrodialysis. The high-fluorine and chlorine-containing dilute acid after electrodialysis is evaporated and stripped to separate sulfuric acid from the fluorine-containing and chlorine-containing distillate.

[0094] Step 2: Preparation of fluorite: slowly add 1.03 times the theoretical amount of lime required to the 60°C distillate, react for 120 minutes, control the end point pH to 8.5, filter, and obtain defluorinated liquid and fluorite.

[0095] The third step is bismuth salt dechlorination: 1.07 times bismuth hydroxide is activated in 150g / L sulfuric acid solution at a liquid-solid ratio of 6.5:1, the activation time is 105min, the activation temperature is 80°C, the activated bismuth hydroxide is added to the defluorination liquid, dechlorinated at T=48°C, t=40min, and the dechlorinated slag and qualified low-fluorine and low-chlorine dechlorinated water for the zinc hydrometallurgical system are obtained by filtration.

[0096] The fourth step is the regeneration of dechlorination slag: the dechlorination slag is added into a NaOH alkaline solution with a liquid-to-solid ratio of 6.5:1, the addition amount of the activating agent soda ash is 7.5g / L, the content of the regeneration agent NaOH is 80g / L, the regeneration temperature is 62°C, the regeneration time is 150min, and the regenerated dechlorination slag is returned to the bismuth salt dechlorination cycle for reuse.

[0097] The water from the polluted acid wastewater is returned to the zinc smelting wet process system in the form of secondary return water and is recovered as water resources. The output sulfuric acid solution with a mass percentage concentration of 77.13% is used to prepare 98% concentrated sulfuric acid, and the resource utilization rate of sulfuric acid is 98.16%. The heavy metal valuable metals zinc, lead, and cadmium are recovered in the form of sulfides as zinc concentrate returned to the boiling furnace, with a recovery rate of 99.35%. The F and Cl contents in the secondary return water returned to the system as water resources are 16.83 mg / L and 31.06 mg / L, respectively, and the removal rates of fluorine and chlorine are 95.36% and 97.62%, respectively.

[0098] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for dechlorinating acid wastewater with bismuth salt, characterized in that: The steps include: Add hydrogen sulfide to the acid wastewater to react with heavy metals and then filter to obtain sulfide slag and high-fluorine and chlorine filtrate, and return the sulfide slag to the zinc concentrate and put it into the boiling furnace for reuse; The high-fluorine and chlorine filtrate is electrodialyzed to obtain dialysis fresh water and dialysis residual liquid. The dialysis fresh water is returned to the zinc hydrometallurgical system as water replenishment: The dialysis residue is evaporated and stripped to obtain a high-fluorine and chlorine distillate and a sulfuric acid solution, which is used to prepare 98% concentrated sulfuric acid; Add lime to the high-fluorine and chlorine distillate to defluorinate, and filter after the reaction to obtain the defluorinated liquid with fluorite and fluorine content meeting the standards; Add bismuth salt to the defluorination liquid for dechlorination, and filter after the reaction to obtain dechlorination residue and dechlorinated water with fluorine and chlorine content meeting the standard; The dechlorination slag is regenerated to obtain bismuth hydroxide, which is converted into bismuth salt and then dechlorinated.

2. The method for dechlorinating dirty acid wastewater with bismuth salt according to claim 1, characterized in that: The temperature for the reaction of hydrogen sulfide with heavy metals in the acid wastewater is 45-60° C., and the reaction time is 120-180 min.

3. The bismuth salt dechlorination method for dirty acid wastewater according to claim 2, characterized in that: The amount of hydrogen sulfide added is 1.5-3 times the theoretical molar amount of hydrogen sulfide required to convert all heavy metals in the acid wastewater into sulfide precipitation.

4. The method for dechlorinating dirty acid wastewater with bismuth salt according to claim 1, characterized in that: The temperature for the reaction of the lime and the high-fluorine-chlorine distillate is 50-75° C., the reaction time is 90-150 min, and the pH at the end point of the reaction is controlled at 8-9.

5. The method for dechlorinating dirty acid wastewater with bismuth salt according to claim 4, characterized in that: The amount of lime added is 1.01-1.05 times the theoretical molar amount of lime required to convert all the fluorine in the high-fluorine chlorine distillate into fluorite.

6. The method for dechlorinating dirty acid wastewater with bismuth salt according to claim 1, characterized in that: The reaction temperature of the bismuth salt and the defluorination liquid is 45-50° C., and the reaction time is 35-45 minutes.

7. The method for dechlorinating the dirty acid wastewater with bismuth salt according to claim 6, characterized in that: The amount of bismuth salt added is 1.03-1.10 times the theoretical molar amount of bismuth salt required to convert all the chlorine in the defluorination liquid into bismuth oxychloride.

8. The method for dechlorinating the dirty acid wastewater with bismuth salt according to claim 7, characterized in that: The bismuth salt is bismuth sulfate or bismuth sulfate obtained by activating bismuth oxide and / or bismuth hydroxide with a sulfuric acid solution.

9. The method for dechlorinating dirty acid wastewater with bismuth salt according to claim 8, characterized in that: When the bismuth oxide and / or bismuth hydroxide are activated to obtain bismuth sulfate, the liquid-solid weight ratio of the sulfuric acid solution to the bismuth salt is 5:1-8:1, the concentration of the sulfuric acid solution for activation is 120g / L-180g / L, the activation temperature is 75-85°C, and the activation time is 90-120min.

10. The method for dechlorinating dirty acid wastewater with bismuth salt according to claim 1, characterized in that: The regeneration temperature of the dechlorinated slag is 55-68°C, the regeneration time is 130-180 min, the regeneration agent is a NaOH alkaline solution with activator soda ash added, the liquid-solid weight ratio of the regeneration agent to the dechlorinated slag is 5:1-8:1, the NaOH content is 70-85 g / L, and the amount of soda ash added is 5-10 g / L.

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