A method for treating waste acid in a process for preparing a saturated zinc sulfate solution

Abstract

The application discloses a kind of polluted acid treatment methods in the preparation process of zinc sulfate saturated solution, including pretreatment, leaching process, iron arsenic lead removal process, fluorine removal process, secondary purification, chlorine removal process, evaporation concentration, obtain zinc sulfate saturated solution.A kind of polluted acid treatment methods in the preparation process of zinc sulfate saturated solution of the application, can significantly remove heavy metals, fluorine, chlorine, arsenic and other elements in polluted acid stock solution, reduce the impurity content of zinc sulfate saturated solution of external sale product, meet customer demand, greatly reduce water, electricity, steam and reagent use, greatly reduce operating cost;Processing facilities size or scale is smaller, also indirectly reduces the construction cost of polluted acid treatment system.The application discloses a kind of polluted acid treatment methods in the preparation process of zinc sulfate saturated solution, which converts polluted acid into zinc sulfate saturated solution product, realizes the recycling of polluted acid, reduces secondary discharge and environmental pollution.

Description

Technical Field

[0001] This invention relates to the field of waste acid wastewater recovery technology, and to a method for treating waste acid during the preparation of zinc sulfate saturated solution, specifically a method for simultaneously treating waste acid generated by enterprises during the preparation of zinc sulfate saturated solution. Background Technology

[0002] The wastewater produced during the preparation of saturated zinc sulfate solution contains high concentrations of elements such as arsenic, fluorine, and chlorine, with zinc as the main component. These elements are introduced from nickel smelting flue gas. During the purification and washing process, after the gas phase enters the liquid phase, arsenic, fluorine, and chlorine exist in a free state in the wastewater. This wastewater is extremely corrosive and causes significant damage to soil, equipment, and converter catalysts.

[0003] Currently, common methods for treating acidic wastewater in China mainly include: pretreatment + three-stage neutralization, lime-iron salt method, sulfide neutralization method, and high-efficiency gas-liquid enhanced sulfide technology. Traditional acidic wastewater treatment methods typically generate large amounts of neutralization sludge, for which there is currently no effective treatment method. Treatment is difficult and costly. Furthermore, traditional methods involve adding large amounts of chemicals during the process, resulting in higher salt content in the wastewater than before treatment, making the wastewater difficult to reuse. Annual operating costs can account for 30% or even higher of the system investment cost.

[0004] To reduce the high arsenic content in raw acid wastewater, conventional processes often employ highly efficient gas-liquid enhanced sulfidation methods. This method involves the initial preparation of hydrogen sulfide gas, with varying processes. One method uses hydrogen from methanol cracking to synthesize hydrogen sulfide gas with sulfur in a synthesis tower; this method has extremely low safety and stringent requirements for equipment materials. Another method uses sodium sulfide or sodium hydrosulfide to react with dilute sulfuric acid to produce hydrogen sulfide gas; this method uses large quantities of reagents and is expensive. Furthermore, the removal of chloride and fluoride ions requires triple-effect evaporation, resulting in high steam consumption and easy scaling in the evaporator. Although this method can improve the purification effect of heavy metal arsenic, the large amount of slag and the difficulty in controlling arsenic pollution remain significant challenges. Summary of the Invention

[0005] In order to solve the problems in the background art, the purpose of this invention is to provide a method for treating waste acid in the process of preparing zinc sulfate saturated solution.

[0006] This invention discloses a method for treating waste acid during the preparation of a saturated zinc sulfate solution, comprising the following steps:

[0007] (1) Pretreatment: The waste acid is pretreated to obtain pretreated waste acid;

[0008] (2) Intermediate leaching process: Add zinc dust to the pretreated waste acid obtained in step (1), leach and then filter press to obtain the filter liquid and leaching residue;

[0009] (3) Iron, arsenic and lead removal process: Zinc slag is added to the filtrate obtained in step (2) to carry out a displacement reaction, producing acid salt precipitates of elements such as iron, arsenic and lead. Then hydrogen peroxide is added to change the valence state of iron and arsenic. After solid-liquid separation, iron, arsenic and lead slag and waste acid are obtained.

[0010] (4) Defluorination process: The waste acid obtained in step (3) is defluorinated by resin to obtain defluorinated waste acid;

[0011] (5) Secondary purification: Add zinc slag to the defluorinated waste acid obtained in step (4), and pass steam to carry out secondary purification to remove elements such as copper and cadmium, and obtain waste acid after copper and cadmium removal.

[0012] (6) Dechlorination process: The waste acid obtained in step (5) after copper and cadmium removal is subjected to a dechlorination reaction to obtain dechlorinated waste acid;

[0013] (7) Evaporation and concentration: The dechlorinated waste acid obtained in step (6) is evaporated and concentrated to obtain a saturated zinc sulfate solution.

[0014] In a preferred embodiment, during the treatment of the waste acid, a saturated zinc sulfate solution is prepared, thereby enabling the waste acid to be utilized as a resource and reducing the operating cost of the waste acid treatment process.

[0015] In the preferred embodiment, in step (1), the waste acid is pretreated by using an inclined plate settler to remove suspended solids and heavy metals from the waste acid in advance.

[0016] In a more preferred embodiment, step (1) specifically involves the preprocessing as follows:

[0017] After the waste acid is pumped to the waste acid storage tank, it undergoes three-stage sedimentation through an inclined plate settling device to achieve a turbidity of ≤5 and remove most of the sludge.

[0018] The waste acid separated from the upper part of the inclined plate settling device flows into the intermediate soaking tank by gravity.

[0019] The sludge separated at the bottom of the inclined plate settler is periodically discharged into the sludge thickening tank.

[0020] Adding flocculant to the final stage sedimentation tank achieves graded purification and sedimentation of the waste acid, making the sedimentation more thorough and the supernatant of the waste acid clearer.

[0021] In a further preferred embodiment, the acidic sludge in the sludge thickening tank is pumped into a sludge centrifuge via a lift pump. The sludge separated after dewatering is then sent to a raw material plant for batching processing.

[0022] In a preferred embodiment, in step (2), the zinc fume contains 54-59 wt% Zn, 1.0-2.4 wt% Pb, 0.1-1.2 wt% Cu, 6-10 wt% Fe, 0-0.1 wt% As, and 0.05-0.3 wt% Cd.

[0023] In the preferred embodiment, in step (2), the pretreated waste acid enters the intermediate leaching process, and zinc dust is added to the waste acid to adjust the pH value and concentration of the zinc sulfate solution.

[0024] In a more preferred embodiment, in step (2), the supernatant overflowing from the inclined plate settling tank is added to the intermediate immersion tank using a pump, and the concentration of the prepared zinc fume is controlled at 1–1.05 kg / m³. 3 The zinc sulfate immersion reaction time was controlled to be 0.5–5 h, and the final pH value of the zinc sulfate solution was 4.5, to obtain a zinc sulfate solution of the predetermined concentration.

[0025] During the intermediate soaking, the reaction time of the dirty acid is controlled at 2.5 hours, and the pH value reaches 4.5 at the final stage. By adding an excessive amount of zinc dust, some of the copper, lead, and cadmium sulfates are replaced in the early stage.

[0026] In a more preferred embodiment, in step (2), the leaching residue after pressure filtration is dried by microwave and then used as a slag-forming solvent for nickel side blowing, which greatly reduces the amount of silica used.

[0027] In a preferred embodiment, in step (3), the zinc slag contains 68-72 wt% Zn, 0.01-0.1 wt% F, 0.1-1.0 wt% Cl, 0.05-0.3 wt% Fe, 0.01-0.1 wt% Sb, 0.1-2.0 wt% Pb, and 0.01-0.6 wt% SiO2.

[0028] In the preferred embodiment, in step (3), the filtered liquid enters the solution tank for removing metal ions such as iron, arsenic, and lead through the overflow pipe. Zinc slag is added to the solution tank, and the reaction time is controlled at 2 to 12 hours. Most of the iron, arsenic, and lead in the solution are replaced. At the same time, the pH value of the reaction is controlled at 5 to 5.5. During the reaction, hydrogen peroxide with a concentration of 15 to 35 wt% is added, and an appropriate amount of iron salt is added. After the bottom liquid is released, it is filtered by a filter press. The iron, arsenic, and lead slag produced is treated as hazardous waste.

[0029] When removing iron, arsenic, and lead, adding hydrogen peroxide changes the oxidation state of the elements from divalent to trivalent, which facilitates the precipitation of arsenates. Later, some iron salts can be added to meet the iron requirement for precipitation.

[0030] In the preferred embodiment, in step (4), after the resin adsorbs fluorine to a saturated state, sodium hydroxide solution is used for analysis. After the analysis solution reacts with calcium hydroxide, calcium fluoride precipitate is generated. After solid-liquid separation, sodium hydroxide is reused in the analysis system, and calcium fluoride is recovered separately.

[0031] In a more preferred embodiment, in step (4), the resin is of type CH-32.

[0032] In the preferred embodiment, in step (5), the defluorinated waste acid and zinc slag are added into the reaction tank, steam at 75°C is introduced, the reaction temperature is controlled at 50-60°C, and secondary purification is carried out. The copper and cadmium bottom flow is released, and the residue is filtered by a filter press and then used for ore bin batching.

[0033] During the secondary purification process, zinc slag is added again. Zinc ions displace inert metal ions from the zinc sulfate solution without introducing new metal elements, thus promoting the formation of zinc sulfate. Simultaneously, external steam is supplied to ensure the reaction temperature remains between 50 and 60°C, further removing elements such as copper, cadmium, and lead.

[0034] In the preferred embodiment, in step (5), a neutralization reaction is carried out by introducing steam to maintain a set temperature, thereby removing most of the sulfuric acid. The pH after the reaction is adjusted to 2, and the temperature is controlled at 50-60°C to meet the conditions for the dechlorination process.

[0035] In the preferred embodiment, in step (6), cuprous oxide is added to carry out a dechlorination reaction for 0.5 to 4 hours to generate cuprous chloride precipitate, and the chloride ion concentration is controlled to be below 200 mg / L.

[0036] In the preferred embodiment, in step (7), the dechlorinated waste acid, namely zinc sulfate solution, is concentrated and crystallized through an evaporation system. The resulting ZnSO4 saturated solution is sold externally. The sulfuric acid resources in the waste acid are recovered in the form of zinc sulfate products. The condensate generated during the evaporation process is collected and can be used for the fluidized bed flue gas scrubbing power wave replenishment.

[0037] In the preferred embodiment, in step (3), a small amount of arsine gas overflowing from the top of the solution tank for removing iron, arsenic, and lead is drawn by a fan to the lower part of the removal tower recovery tower, rises to the packing section and combines with the alkaline solution sprayed down from the upper part of the tower to form a sodium sulfate solution. The solution falls to the bottom of the tower and is pumped back to the gas-liquid separator.

[0038] In the preferred configuration, when the entire system is operating normally, the residual hydrogen sulfide is drawn into the exhaust gas treatment system for absorption using the principle of negative pressure, and then discharged after treatment to meet the standards.

[0039] This invention employs a new resource-optimized waste acid treatment technology that can directly treat heavy metal ions, fluorine, chlorine, copper, cadmium, and other elements in waste acid. While avoiding the consumption of large amounts of reagents, it utilizes zinc dust and zinc slag, byproducts of the enterprise's own production, to remove medium and heavy metal elements from the waste acid. After evaporation and concentration, no waste acid post-treatment liquid is produced, and the resulting saturated zinc sulfate solution is sold externally, thus achieving resource utilization of waste acid treatment.

[0040] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0041] 1) This invention provides a method for treating waste acid during the preparation of zinc sulfate saturated solution, which can significantly remove heavy metals, fluorine, chlorine, arsenic and other elements from the waste acid raw solution, reduce the impurity content of the zinc sulfate saturated solution sold externally, meet customer needs, greatly reduce the use of water, electricity, steam and reagents, and greatly reduce operating costs; the size or scale of the treatment facility is reduced, which also indirectly reduces the construction cost of the waste acid treatment system.

[0042] 2) This invention provides a method for treating waste acid during the preparation of zinc sulfate saturated solution, which converts waste acid into zinc sulfate saturated solution product, realizes waste acid recycling, and reduces secondary emissions and environmental pollution.

[0043] 3) This invention discloses a method for treating waste acid during the preparation of a zinc sulfate saturated solution. The design for removing arsenic and iron allows for both series and parallel operation, adapting to different operating conditions and increasing operational flexibility. It can operate in series when the waste acid volume is normal and the incoming water quality is poor; it can operate in parallel when the waste acid volume is large and the water quality is normal; and it can operate as a single tower when the waste acid volume is small.

[0044] 4) This invention provides a method for treating waste acid during the preparation of zinc sulfate saturated solution. It utilizes the reaction mechanism of zinc slag replacing copper and cadmium, avoiding the introduction of other elements by adding reagents. This helps to ensure the purity of the zinc sulfate solution and alleviates the problem of quality standards for the product after the zinc sulfate solution is concentrated and crystallized.

[0045] 5) This invention provides a method for treating waste acid during the preparation of a zinc sulfate saturated solution, which avoids the generation of waste acid post-treatment liquid and eliminates the chemical water treatment process. Only the condensate generated during the evaporation and concentration process is reused for acid production and purification. Attached Figure Description

[0046] Figure 1 This is a process flow diagram in Embodiment 1 of the present invention. Detailed Implementation

[0047] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0048] This invention discloses a method for treating waste acid during the preparation of a saturated zinc sulfate solution, comprising the following steps:

[0049] (1) Pretreatment: The waste acid is pretreated to obtain pretreated waste acid;

[0050] (2) Intermediate leaching process: Add zinc dust to the pretreated waste acid obtained in step (1), leach and then filter press to obtain the filter liquid and leaching residue;

[0051] (3) Iron, arsenic and lead removal process: Zinc slag is added to the filtrate obtained in step (2) to carry out a displacement reaction, producing acid salt precipitates of elements such as iron, arsenic and lead. Then hydrogen peroxide is added to change the valence state of iron and arsenic. After solid-liquid separation, iron, arsenic and lead slag and waste acid are obtained.

[0052] (4) Defluorination process: The waste acid obtained in step (3) is defluorinated by resin to obtain defluorinated waste acid;

[0053] (5) Secondary purification: Add zinc slag to the defluorinated waste acid obtained in step (4), pass steam through, and carry out secondary purification to remove copper and cadmium elements, and obtain copper and cadmium-free waste acid.

[0054] (6) Dechlorination process: The waste acid obtained in step (5) after copper and cadmium removal is subjected to a dechlorination reaction to obtain dechlorinated waste acid;

[0055] (7) Evaporation and concentration: The dechlorinated waste acid obtained in step (6) is evaporated and concentrated to obtain a saturated zinc sulfate solution.

[0056] In the production of zinc sulfate, this invention utilizes a hydrogen peroxide method to remove large amounts of iron and arsenic ions. This method fully leverages the strong oxidizing properties of hydrogen peroxide to remove Fe... 2+ Oxidized to Fe 3+ As 3+ Oxidized to As 5+ This process facilitates the precipitation and exudation of arsenic and iron ions in their trivalent state, forming arsenates. It exhibits high efficiency in removing iron and arsenic, with stable operation. No external reagents are required to enhance the efficiency of iron and arsenic removal.

[0057] During the defluorination process, after the selective adsorption material reaches saturation, it is eluented with sodium hydroxide solution. The eluent reacts with calcium hydroxide to form calcium fluoride precipitate. After solid-liquid separation, the sodium hydroxide is reused in the eluent system, while the calcium fluoride is recovered separately.

[0058] The dechlorination process is placed after the secondary purification to remove a large amount of sulfate ions and control the pH value at 2. The dechlorination is carried out by copper and copper oxide slag. The dechlorination is carried out by the disproportionation reaction of copper. Copper and copper ions interact with chloride ions in the solution to form insoluble cuprous chloride precipitate, which removes chloride ions from the solution. The cuprous chloride precipitate can be regenerated with sodium hydroxide to generate cuprous oxide for reuse in the front-end dechlorination.

[0059] This solution boasts numerous advantages, including stable operation, low investment cost, minimal waste, few hazardous sources, and low risk. Furthermore, it does not generate new wastewater during the preparation of saturated zinc sulfate solution, and the evaporation condensate after evaporation and concentration is reused in the acid purification process. This method is a significantly more suitable new process than treating waste acid alone, achieving resource utilization of waste acid treatment.

[0060] Waste acid design: Waste acid water quality and conditions:

[0061] The waste acids processed in the examples are waste acids generated from the zinc-nickel smelting acid production system and waste acids generated during the tail gas desulfurization process.

[0062] Waste acid emissions after merger:

[0063] Table 1.1 Characteristics of Mixed Waste Acid Water (g / L)

[0064] dilute acid discharge (m3 / h) sulfuric acid in dilute acid As Zn Fe F Cl Hg 16 30～60 1.25 0.25 0.035 0.12 0.59 0.004

[0065] Note: 1) Waste acid temperature: 0℃±10℃; solid content of waste acid ≤0.1g / l.

[0066] 2) The amount of sulfuric acid in the waste acid fluctuates greatly. It is assumed that the waste acid after merging contains 60g / l of sulfuric acid.

[0067] Table 1.2 Chemical Composition of Zinc Flue Dust (%)

[0068]

[0069] Table 1.3 Chemical composition of zinc slag (%)

[0070]

[0071] Unless otherwise specified, all reagents used in this embodiment are commercially available products or prepared by conventional means, and all equipment used is conventional equipment in the art. The following are some examples from the inventors' experiments:

[0072] The following detailed description, along with specific embodiments and accompanying drawings, further illustrates the following:

[0073] Example 1

[0074] This invention discloses a method for treating waste acid during the preparation of a saturated zinc sulfate solution, comprising the following steps:

[0075] (1) Pretreatment: First, the waste acid is pretreated by three-stage inclined plate sedimentation. The supernatant flows into the intermediate leaching tank and reacts with zinc roasting flue dust sand.

[0076] (2) Intermediate Leaching Process: During the intermediate leaching process, zinc dust is added to adjust the pH of the solution. The reaction conditions are controlled to an endpoint of 4.5. The original waste acid concentration is 60 g / L, and the zinc sulfate solution concentration reaches 126 g / L. The leaching residue generated during the intermediate leaching process is filtered by a filter press and then used as feedstock. The reaction time is controlled to be approximately 1.5 hours. Zinc oxide dust is used to neutralize the waste acid and adjust the pH. Zinc oxide and waste acid are used to generate relatively stable zinc sulfate compounds. The sulfate ions brought in by the waste acid raw solution react with metal ions such as Fe, Pb, and Cd in the added zinc oxide dust. At the same time, a portion of the leaching residue is generated, which is filtered and dried before being used as a slag-forming solvent feedstock. The chemical formulas involved are:

[0077] Zn₀ + H₂SO₄ = ZnSO₄ + H₂O

[0078] Cd + H₂SO₄ = CdSO₄ + H₂

[0079] Pb + H₂SO₄ = PbSO₄ + H₂

[0080] Fe + H₂SO₄ = FeSO₄ + H₂

[0081] (3) Iron, arsenic and lead removal process: The zinc sulfate solution after intermediate leaching enters the solution tank for removing arsenic, iron and other metal ions through the overflow pipe. Utilizing the principle of zinc slag replacing ferrous sulfate and lead sulfate in zinc sulfate, the zinc slag is made into a solution and pumped into the reaction tank. Most of the lead, arsenic and iron are replaced. At the same time, the reaction pH is controlled at 5-5.5. During the reaction, more than 70% oxygen-enriched air is introduced and an appropriate amount of iron salt is added. The arsenic, lead and iron slag produced is filtered and then treated as hazardous waste.

[0082] The process utilizes zinc scum to neutralize acidic wastewater and adjust its pH. Arsenic is removed by taking advantage of the property that arsenic reacts with iron to form a relatively stable ferric arsenate compound, which co-precipitates with ferric hydroxide. Iron hydroxides possess strong adsorption and flocculation capabilities, effectively removing harmful heavy metals such as arsenic and cadmium from the acidic wastewater. Increasing the pH further removes heavy metal ions from the acidic wastewater as hydroxides.

[0083] Fe3+ +AsO3 3- =FeAsO3↓

[0084] Fe 3+ +AsO4 3- =FeAsO4↓

[0085] Besides forming ferric arsenate, iron ions react with arsenic, and ferric hydroxide can act as a carrier to co-precipitate with arsenate ions and ferric arsenate.

[0086] FeAsO4 is relatively stable, but a re-dissolution reaction will occur when pH > 10, so the pH value is generally best controlled between 5 and 6. The re-dissolution reaction formula is as follows:

[0087] FeAsO4+3OH - →Fe(OH)3+AsO4 3-

[0088] After adjusting the pH of the system with zinc scum, hydrogen peroxide is added. The strong oxidizing properties of hydrogen peroxide are used to oxidize Fe. 2+ Oxidized to Fe 3 + As 3+ Oxidized to As 5+ This is conducive to the precipitation and exudation of arsenic and iron ions.

[0089] Table 1.4 Effluent Quality and Quantity from Arsenic and Iron Removal Process Sections

[0090]

[0091] (4) Defluorination process: After removing arsenic, iron, lead, and other metal ions from the zinc sulfate solution, the pH value of the solution is controlled to be less than 2. A fluorine-specific adsorbent material is used to specifically adsorb and remove fluorine from the high-acid, high-salt system of the zinc-nickel smelting system. Due to the high selectivity of the resin, the fluorine removal rate can reach over 90%, without introducing other impurities into the original solution. The fluorine loaded on the adsorbent material can be desorbed using sodium hydroxide solution. After the desorbent reacts with calcium hydroxide, calcium fluoride precipitate is generated and recovered. The sodium hydroxide can be reused for further desorption. The entire process achieves efficient fluorine removal while enabling the reuse of the regenerated solution, thus reducing the cost of fluorine treatment.

[0092] Table 1.5 Effluent quality and quantity from the defluorination process section

[0093]

[0094] (5) Secondary purification: Add zinc slag to the defluorinated waste acid obtained in step (4), pass steam through, and carry out secondary purification to remove copper and cadmium elements, and obtain copper and cadmium-free waste acid.

[0095] During the purification process, steam at 50-60℃ is introduced into the top of the primary purification tank, which is conducive to the precipitation of copper sulfate and cadmium sulfate. At the same time, zinc slag is made into a solution and pumped into the reaction tank. The sulfate precipitates of copper, cadmium, lead and iron are released through the bottom flow. After being filtered by a filter press, the residue is used for batching in the ore bin.

[0096] In the secondary purification process, the temperature of the zinc sulfate solution is maintained at 50-60℃, and zinc slag solution is continuously introduced to react and remove the remaining unreacted copper, cadmium, and lead ions. The copper and cadmium precipitates are released through the bottom flow, and the slag is filtered by a filter press and then used for batching in the ore bin.

[0097] Table 1.6 Effluent Quality and Quantity from the Purification Process Section

[0098]

[0099] (6) Dechlorination process: The waste acid obtained in step (5) after copper and cadmium removal is subjected to a dechlorination reaction to obtain dechlorinated waste acid;

[0100] The copper slag dechlorination technology utilizes the cadmium leaching residue from the copper-cadmium slag produced during the wet zinc smelting purification process, employing a copper disproportionation reaction for dechlorination. It leverages the interaction between copper and copper ions with chloride ions in the solution to form a sparingly soluble cuprous chloride precipitate, thus removing chloride ions from the solution. Because of the presence of Cl in the solution... - The presence of [a substance] can form a sparingly soluble CuCl precipitate, and the overall reaction is: 2Cl [acid] ... - +Cu+Cu 2+ =2CuCl↓.

[0101] Studies have shown that the Cu-Cl-H₂O potential-pH diagram indicates that the formation of CuCl precipitate is related to temperature, pressure, solution potential, pH, and ion concentration. Under alkaline conditions, cuprous chloride cannot form a precipitate. The stability region of CuCl(s) is related to E, pH, [Cu]T, and [Cl]T. - This is related to factors such as […]. Under otherwise constant conditions, the dechlorination efficiency increases with increasing total copper ion concentration.

[0102] If the cuprous chloride slag obtained after dechlorination is subjected to further dechlorination treatment, the chlorine in the solid cuprous chloride will be leached into the solution. This reaction process is the reverse of the precipitation method for dechlorination.

[0103] 2CuCl + 2OH - = 2CuOH + 2Cl -The solubility of cuprous hydroxide is nearly ten orders of magnitude less than that of cuprous chloride. Therefore, the aforementioned alkaline regeneration reaction will proceed quantitatively, completely converting cuprous chloride to cuprous oxide, thus ensuring the recycling of the copper salt required for dechlorination. The main reaction formula is 2CuOH = Cu₂O + H₂O. In acidic solution, cuprous oxide reacts with chloride ions to regenerate cuprous chloride precipitate, with the reaction: Cu₂O + 2H⁺ + 2Cl⁻. - = 2CuCl(s) + H₂O. To convert the chlorine in the dechlorinated copper slag into the solution, according to the Cu-Cl-H₂O potential-pH diagram, the OH⁻ concentration needs to be increased. - concentration.

[0104] First, zinc oxide is added to the neutralization reaction tank, and a certain temperature is maintained by steam to carry out the neutralization reaction and remove most of the sulfuric acid. After the reaction, the pH is adjusted to about 2, and the temperature is controlled at 50-60℃ to meet the conditions for dechlorination. The overflow of the neutralization reaction tank enters the dechlorination reaction tank through a chute, and a certain amount of cuprous oxide is added to carry out the dechlorination reaction. After about 2 hours of reaction, cuprous chloride precipitate is generated. The chloride ion concentration is controlled to be below 200mg / L. After flocculation and sedimentation in the flocculation tank, it enters the thickening tank. The supernatant in the thickening tank enters the defluorination system. The bottom flow of the thickening tank is filtered by a filter press. The filtrate enters the subsequent system, while the cuprous chloride slag enters the regeneration system. It is regenerated by reacting with sodium hydroxide in the regeneration reaction tank. The filter residue obtained by the regeneration reaction is washed with water to remove the alkaline solution on the surface and returned to the dechlorination reaction tank for recycling to remove chloride ions from the waste acid. The filtrate and a small amount of wash water are discharged into the water treatment system for treatment.

[0105] Table 1.7 Effluent Quality and Quantity of Dechlorination Process Section (Unit: g / L)

[0106]

[0107] (7) Evaporation and concentration: After the zinc sulfate solution is soaked, arsenic, iron and lead are removed, and copper and cadmium are removed in three stages of purification, the metal ions brought in by the dirty acid and zinc dust are removed to ensure that the zinc sulfate solution meets the quality requirements proposed by the manufacturer. Finally, ENFI's proprietary low temperature evaporation and concentration equipment is used to produce saturated zinc sulfate solution products to meet the requirements for external sales.

[0108] Evaporation crystallization technology involves preheating brine before it enters an evaporator for partial evaporation. The resulting secondary steam is compressed by a compressor and introduced to the heating side of the evaporator. The condensed steam is then drawn off as product water, thus achieving the recycling of thermal energy. The circulation of the solution within the equipment relies primarily on forced flow generated by an external power source (forced circulation pump). The feed liquid is pumped in from bottom to top by the circulation pump, flowing upwards along the heating chamber. As the circulating liquid flows through the heat exchanger, it is heated, and then partially evaporates as the pressure decreases in the separator. The steam and feed liquid components separate in the evaporation chamber; the steam exits from the top, while the feed liquid falls and is drawn back into the heating chamber by the circulation pump through the conical bottom, continuing the circulation.

[0109] Table 1.8 Water Quality of Saturated Zinc Sulfate Solution in Evaporation and Concentration Process Section

[0110] Serial Number Metal elements content Remark 1 <![CDATA[ZnSO4 content]]> 22％～24％ 2 Turbidity ≤3 3 5.6～6.2 4 Cl 3mg / L~4mg / L The allowable range can be appropriately relaxed based on the amount of Cl in the mother liquor. 5 Cd ≤1.5ppm 6 Ni ≤1.5ppm 7 Mn ≤1.5ppm 8 Fe ≤1.8ppm 9 Cu ≤1.5ppm 10 Pb ≤2.5ppm

[0111] As shown in Table 2, compared with the prior art, the new technology of the present invention has the following advantages:

[0112] Table 2 Comparative Analysis of Waste Acid Treatment Technologies

[0113]

[0114] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for treating waste acid in a process for producing a saturated zinc sulfate solution, characterized by, The method comprises the following steps: (1) Pretreatment: pretreating the waste acid to obtain pretreated waste acid; (2) Middle leaching process: adding zinc dust into the pretreated waste acid obtained in step (1), the pH value of the middle leaching reaction is 4.5, and after leaching, pressure filtration is performed to obtain pressure filtered liquid and leaching residue; (3) Iron, arsenic and lead removal process: adding zinc dross into the pressure filtered liquid obtained in step (2) to perform displacement reaction, the pH value of the displacement reaction is controlled to be 5-5.5, most of the iron ions, arsenic ions and lead ions in the solution are displaced, then hydrogen peroxide is added to change the valence of iron and arsenic, and a precipitate is generated, after solid-liquid separation, iron, arsenic and lead residue and waste acid are obtained; (4) Fluorine removal process: removing fluorine from the waste acid obtained in step (3) by using a resin to obtain fluorine-removed waste acid; (5) Secondary purification: adding zinc dross into the fluorine-removed waste acid obtained in step (4), and introducing steam to perform secondary purification to remove copper and cadmium elements, and obtain copper and cadmium-removed waste acid; (6) Chlorine removal process: performing chlorine removal reaction on the copper and cadmium-removed waste acid obtained in step (5) to obtain chlorine-removed waste acid; (7) Evaporation and concentration: performing evaporation and concentration on the chlorine-removed waste acid obtained in step (6) to obtain a saturated zinc sulfate solution. The zinc dust contains Zn 54-59wt%, Pb 1.0-2.4wt%, Cu 0.1-1.2wt%, Fe 6-10wt%, As 0-0.1wt% and Cd 0.05-0.3wt%; The zinc dross contains Zn 68-72wt%, F 0.01-0.1wt%, Cl 0.1-1.0wt%, Fe 0.05-0.3wt%, Sb 0.01-0.1wt%, Pb 0.1-2.0wt% and SiO2 0.01-0.6wt%.

2. The method of claim 1, wherein the spent acid is treated by adding a neutralizing agent to the spent acid. In step (1), the pretreatment is specifically as follows: After the waste acid is pumped into a waste acid storage tank by a waste acid pump, three-stage sedimentation is performed on the waste acid through an inclined plate settler, so that the turbidity of the waste acid is ≤5, and most of the sludge is removed; The waste acid separated from the upper part of the inclined plate settler flows into a middle leaching tank; The sludge separated from the bottom of the inclined plate settler is periodically discharged into a sludge concentration tank; A flocculating agent is added in the last stage of the settler, so that the precipitation is more complete, and the supernatant of the waste acid is clearer.

3. The method according to claim 2, wherein the spent acid is treated by adding a neutralizing agent to the spent acid. In step (2), the supernatant overflowed from the inclined plate settler enters the tank, and the prepared zinc fume slurry is added by a pump, with the density controlled at 1-1.05 kg / m 3 The control of the leaching reaction time is 0.5-5 h, and a zinc sulfate solution with a predetermined concentration is obtained.

4. The method for treating waste acid in the process of preparing saturated zinc sulfate solution according to claim 1, characterized in that, In step (3), the pressure filtered liquid enters a solution tank through an overflow pipe, the zinc dross is put into the solution tank, the reaction time is controlled to be 2-12h, most of the iron ions, arsenic ions and lead ions in the solution are displaced, then hydrogen peroxide with a concentration of 15-35wt% is added, an appropriate amount of iron salt is added, the underflow liquid is discharged, and pressure filtration is performed on the underflow liquid by a pressure filter, and the generated iron, arsenic and lead residue is treated as hazardous waste.

5. The method for treating waste acid in the process of preparing saturated zinc sulfate solution according to claim 1, characterized in that, In step (5), the fluorine-removed waste acid and the zinc dross are added into a reaction tank, steam at 75℃ is introduced, the reaction temperature is controlled to be 50-60℃, secondary purification is performed, the copper and cadmium underflow is discharged, and the residue after pressure filtration by a pressure filter is used for ore bin batching.

6. The method for treating waste acid in the process of preparing saturated zinc sulfate solution according to claim 1, characterized in that, In step (6), cuprous oxide is added to perform chlorine removal reaction, the reaction is performed for 0.5-4h, cuprous chloride precipitate is generated, and the chlorine ion content in the chlorine-removed waste acid is controlled to be lower than 200mg / L.

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