Method for preparing high-purity gypsum and recycling zinc and copper by utilizing gradient acid characteristics

Abstract

The invention provides a method for preparing high-purity gypsum and recycling zinc and copper by using gradient acid characteristics. The method comprises the following steps: mixing high-concentration sulfuric acid and neutralization slag to dissolve calcium sulfate to obtain a mixed solution; adding low-concentration sulfuric acid wastewater into the mixed solution to crystallize calcium sulfate, and filtering to obtain high-purity gypsum and first filtrate; adding a neutralizer into the first filtrate for pre-neutralization, and filtering to obtain a first precipitate and a second filtrate; uniformly mixing the first precipitate with a neutralizer, and aging to obtain a mixed slag material; adding sodium sulfide into the second filtrate, mixing and reacting, and filtering to obtain high-purity zinc-copper concentrate and third filtrate; adding a neutralizer into the third filtrate for neutralization, and filtering to obtain a second precipitate and a fourth filtrate; and returning the second precipitate to the next batch of high-concentration sulfuric acid for recycling. According to the method provided by the invention, the utilization rate of the carbide slag and the dehydration performance of the neutralization slag can be improved in the sulfuric acid wastewater treatment process, and resources such as sulfur, calcium, zinc and copper in the sulfuric acid wastewater treatment process can be effectively recycled.

Description

Technical Field

[0001] The present invention relates to the technical field of sulfuric acid wastewater treatment, and particularly relates to a method for preparing high-purity gypsum by utilizing the characteristics of gradient acid and realizing the resource utilization of zinc and copper. Background Art

[0002] During the gold smelting process of gold smelting enterprises, a large amount of sulfuric acid wastewater with different sulfuric acid concentrations will be generated. The main characteristics of high-concentration sulfuric acid are that the sulfuric acid concentration is 10wt% - 30wt%, preferably waste acid wastewater. The main characteristics of low-concentration sulfuric acid wastewater are that the pH is less than 1, and each ton of acidic wastewater contains about 1.2wt% - 1.5wt% H2SO4, 0.2wt% - 2.17wt% FeSO4, 0.2wt% - 2.3wt% ZnSO4, 0.09wt% - 0.71wt% CuSO4. It is a mixed solution of one or several of titanium white acidic wastewater, copper raffinate, mine acidic wastewater, and coal mine acidic wastewater, preferably copper raffinate acidic wastewater. If these wastewaters are directly discharged, they will cause environmental pollution, with characteristics such as a wide pollution area, a long pollution duration, and a large degree of harm. For the convenience of treatment, enterprises generally mix and treat them uniformly.

[0003] The general treatment method for acidic wastewater is the neutralization precipitation method. The process is to put carbide slag slurry into the acidic wastewater, neutralize it to strong alkalinity and then press-filter it to obtain wastewater meeting the discharge standard and neutralization slag. This treatment method has low utilization rate of carbide slag, poor dehydration performance of neutralization slag, and a large amount of sulfur, calcium, zinc, and copper resources are not recovered, resulting in resource waste.

[0004] There is also a method of treating acidic wastewater by two-stage neutralization. The method is to use the neutralization slag generated by the neutralization reaction of acidic wastewater and carbide slag as a neutralizing agent to be recycled for the treatment of the next batch of acidic wastewater according to the principle of crystal seed circulation, and so on in a cycle. This method can effectively reduce the dosage of calcium oxide and reduce the water content of the neutralization slag. However, the calcium, sulfur, zinc, and copper resources in it still cannot be recovered, still causing resource waste and relatively low economic benefits.

[0005] Therefore, there is an urgent need for a method that can resourcefully treat the acidic wastewater generated during the gold smelting process, so as to improve the utilization rate of carbide slag and the dehydration performance of neutralization slag during the acidic wastewater treatment process, and can effectively recover resources such as sulfur, calcium, zinc, and copper during the acidic wastewater treatment process. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing high-purity gypsum by utilizing the characteristics of gradient acid and realizing the resource utilization of zinc and copper, so as to improve the utilization rate of carbide slag and the dehydration performance of neutralization slag during the sulfuric acid wastewater treatment process, and can effectively recover resources such as sulfur, calcium, zinc, and copper during the sulfuric acid wastewater treatment process.

[0007] To solve the above technical problems, the present invention provides a method for preparing high-purity gypsum by utilizing the gradient acid characteristic and realizing the resource utilization of zinc and copper, comprising the following steps:

[0008] Mix high-concentration sulfuric acid with the neutralization residue to dissolve calcium sulfate in the neutralization residue to obtain a mixed solution;

[0009] Add low-concentration sulfuric acid wastewater to the mixed solution to crystallize calcium sulfate, and then filter to obtain high-purity gypsum and a first filtrate;

[0010] Add a neutralizing agent to the first filtrate for pre-neutralization, adjust the end point pH value to 2.5-3.0, and then filter to obtain a first precipitate and a second filtrate;

[0011] Mix the first precipitate with the neutralizing agent and age to obtain a mixed slag material;

[0012] Add sodium sulfide to the second filtrate and mix, adjust the solution pH value to 3.0, and then filter to obtain high-purity zinc and copper concentrate and a third filtrate;

[0013] Add a neutralizing agent to the third filtrate for neutralization, adjust the end point pH value to 10.0-10.5, and then filter to obtain a second precipitate and a fourth filtrate;

[0014] The second precipitate is returned to the next batch of high-concentration sulfuric acid for recycling use, and the fourth filtrate is discharged up to standard.

[0015] Further, the high-concentration sulfuric acid is the waste acid wastewater with a concentration of 10wt%-30wt% generated during the gold concentrate smelting process; the neutralization residue is the neutralization residue obtained by neutralizing the acidic wastewater generated during the gold concentrate smelting process with carbide slag to strong alkalinity and then pressure filtering.

[0016] Further, the temperature during the mixing of the high-concentration sulfuric acid and the neutralization residue is controlled at 70°C-90°C, and 100-300 g of the neutralization residue is added to each liter of the high-concentration sulfuric acid.

[0017] Further, the low-concentration sulfuric acid wastewater is the sulfuric acid wastewater with a pH less than 1 and a sulfuric acid content of 1.2wt%-3wt% generated during the gold concentrate smelting process.

[0018] Further, the low-concentration sulfuric acid wastewater is one or more of titanium white acidic wastewater, copper raffinate, mine acidic wastewater, coal mine acidic wastewater, and waste acid wastewater.

[0019] Further, the volume ratio of the low-concentration sulfuric acid wastewater to the mixed solution is controlled at 8:1-12:1, the end point pH value after mixing the low-concentration sulfuric acid wastewater and the mixed solution is controlled at 1.0-2.0, and the purity of calcium sulfate dihydrate of the obtained high-purity gypsum is above 99%.

[0020] Further, the mass ratio of the first precipitate to the neutralizing agent is 15:1 to 20:1, and the aging time is 24 to 36 h.

[0021] Further, the neutralizing agent is one or more of calcium carbonate, calcium oxide, calcium hydroxide, and carbide slag.

[0022] Further, the main component of the carbide slag is calcium hydroxide, and it contains a small amount of calcium carbonate and silicon dioxide.

[0023] Further, the high-purity zinc-copper concentrate includes zinc sulfide, copper sulfide, and iron sulfide. The grade of copper in the high-purity zinc-copper concentrate is above 12%, and the grade of zinc is above 52%.

[0024] A method for preparing high-purity gypsum by utilizing the gradient acid characteristic and realizing the resource utilization of zinc and copper provided by the present invention combines three methods: crystal seed recycling, calcium sulfate dissolution-recrystallization, and sulfide precipitation. High-concentration sulfuric acid is used to dissolve calcium sulfate in the neutralization residue, and then the solution is diluted with low-concentration sulfuric acid wastewater to reach a supersaturated state, and calcium sulfate crystallizes out under strong acidic conditions, and then high-purity gypsum is obtained by filtration. Then, through pre-neutralization and adjusting the pH of the solution to 2.5 - 3.0 and filtering, since there is still a small amount of dissolved calcium sulfate in the solution, it can exist as crystal seeds, enabling the growth of new crystals along its surface, thereby reducing the moisture content of the filter residue. Then, an appropriate amount of sodium sulfide is added to the filtrate to precipitate zinc and copper ions in the solution in the form of zinc sulfide and copper sulfide to obtain high-purity zinc-copper concentrate. Finally, a neutralizing agent containing carbide slag is added to the filtrate to adjust the pH of the solution to strong alkalinity so that the tail liquid can meet the standards and be discharged. The filter residue is continuously returned to the next batch of high-concentration sulfuric acid to enable the unreacted carbide slag in the filter residue to continue to react to improve the utilization rate of the carbide slag, and this cycle is repeated. Thus, while improving the utilization rate of the carbide slag and reducing the moisture content of the neutralization residue, the recovery and utilization of resources such as calcium, sulfur, zinc, and copper in the slag can be realized. Description of the Drawings

[0025] Figure 1 It is a process flow diagram of the method for preparing high-purity gypsum by utilizing the gradient acid characteristic and realizing the resource utilization of zinc and copper provided by the embodiment of the present invention. Detailed Embodiments

[0026] See Figure 1 , a method for preparing high-purity gypsum by utilizing the gradient acid characteristic and realizing the resource utilization of zinc and copper provided by the embodiment of the present invention includes the following steps:

[0027] Step 1) Mix high-concentration sulfuric acid with the neutralization residue to dissolve calcium sulfate in the neutralization residue to obtain a mixed solution.

[0028] Among them, the highly concentrated sulfuric acid is the waste acid wastewater with a concentration of 10 wt% to 30 wt% generated by gold smelting enterprises during the gold concentrate smelting process described in the background technology of the present invention. The neutralization residue is the neutralization residue obtained by filtering under pressure after neutralizing the acidic wastewater generated by gold smelting enterprises during the gold concentrate smelting process with carbide slag to a strong alkaline level.

[0029] Among them, the main component of carbide slag is calcium hydroxide, and it contains a small amount of calcium carbonate and silicon dioxide. The main component of the neutralization residue obtained by filtering under pressure after neutralizing the acidic wastewater generated by gold smelting enterprises during the gold concentrate smelting process with carbide slag to a strong alkaline level is calcium sulfate dihydrate.

[0030] The reason why the present invention uses highly concentrated sulfuric acid to dissolve calcium sulfate in the neutralization residue is that the solubility of calcium sulfate in highly concentrated sulfuric acid is related to its chemical properties. Calcium sulfate reacts with highly concentrated sulfuric acid to form calcium bisulfate, and its chemical equation is:

[0031] CaSO4 + H2SO4 (concentrated) = Ca(HSO4);

[0032] 2CaSO4 + H2SO4 (concentrated) = Ca(HSO4)2.

[0033] The reaction increases the solubility of calcium sulfate in concentrated sulfuric acid. In addition, the physical properties of calcium sulfate also affect its solubility in concentrated sulfuric acid. Calcium sulfate is a white crystalline powder, slightly soluble in water, but its solubility is significantly increased in concentrated sulfuric acid due to its high ionic strength and low solvation effect.

[0034] Among them, in order to enable the calcium sulfate in the neutralization residue to dissolve rapidly when the highly concentrated sulfuric acid is mixed with the neutralization residue to improve the process efficiency, the temperature during the mixing of the highly concentrated sulfuric acid and the neutralization residue is controlled at 70 °C to 90 °C. And, in order to enable the calcium sulfate dihydrate in the neutralization residue to dissolve fully, 100 - 300 g of the neutralization residue is added to each liter of highly concentrated sulfuric acid.

[0035] After the process method provided by the present invention can be carried out cyclically, the neutralization slag added to the next batch of highly concentrated sulfuric acid is the second precipitate obtained in step 6). The second precipitate generated in step 6) is similar in physical and chemical properties to the neutralization slag added for the first time before the start of the cycle of the process method of the present invention, and its main component is calcium sulfate dihydrate. Moreover, there are still unreacted calcium hydroxide, iron hydroxide, zinc hydroxide and other impurities in the second precipitate generated in step 6). Therefore, in the cycle of the process method of the present invention, the second precipitate obtained in step 6) is put into highly concentrated sulfuric acid. By using the strong acidity of the highly concentrated sulfuric acid, not only can most of the calcium sulfate in the second precipitate obtained in step 6) be dissolved, and the small part of undissolved calcium sulfate is left as crystal nuclei to improve the utilization rate of carbide slag, but also the impurities such as copper and zinc in the second precipitate obtained in step 6) can be further dissolved, so that the resources such as calcium, sulfur, zinc and copper in the slag can be fully recovered and utilized.

[0036] The specific reaction equations that occur when the neutralization slag added to the highly concentrated sulfuric acid for the first time before the start of the cycle of the present invention and the second precipitate obtained in step 6) during the cycle are added to the highly concentrated sulfuric acid are as follows:

[0037] CaSO4·2H2O(s)=Ca 2+ (aq)+SO4 2- (aq)+2H2O

[0038] Fe(OH)3(s)=Fe 3+ (aq)+3OH - (aq)

[0039] Zn(OH)2(s)=Zn 2+ (aq)+2OH - (aq), and so on.

[0040] In step 2), low-concentration sulfuric acid wastewater is added to the mixed solution to crystallize calcium sulfate, and then high-purity gypsum and the first filtrate are obtained by filtration.

[0041] Among them, the low-concentration sulfuric acid wastewater is also the sulfuric acid wastewater with a pH less than 1 and a sulfuric acid content of 1.2 wt% to 3 wt% generated by gold smelting enterprises during the gold concentrate smelting process as described in the background art of the present invention.

[0042] Among them, the low-concentration sulfuric acid wastewater is one or several of titanium white acidic wastewater, copper raffinate, mine acidic wastewater, coal mine acidic wastewater and waste acid wastewater.

[0043] These low-concentration sulfuric acid wastewaters not only contain about 1.2 wt% - 1.5 wt% H2SO4, but also contain 0.2 wt% - 2.17 wt% of FeSO4, 0.2 wt% - 2.3 wt% of ZnSO4, and 0.09 wt% - 0.71 wt% of CuSO4. Therefore, the method for preparing high-purity gypsum by utilizing the gradient acid characteristics and realizing the resource utilization of zinc and copper provided by the present invention not only needs to obtain high-purity gypsum, but also needs to recover valuable resources such as copper and zinc from the acidic waste liquid generated during the gold concentrate smelting process by gold smelting enterprises.

[0044] Among them, the volume ratio of the low-concentration sulfuric acid wastewater to the mixed liquid is controlled at 8:1 - 12:1, and the final pH value after mixing the low-concentration sulfuric acid wastewater and the mixed liquid is controlled at 1.0 - 2.0.

[0045] According to the solubility product law,

[0046] A m B n (s) === mA n+ (aq) + nB m- (aq)

[0047] Ionic product Q c = c[A n+ m ·c[B m- n

[0048] When Q c = c[A n+ m ·c[B m- n > K sp That is, when Q c = c[Ca 2+ ·c[SO4 2- > K sp The precipitation begins to separate out. Since there are a large number of dissolved Ca 2+ in the solution before dilution, adding low-concentration sulfuric acid wastewater to it at this time will increase c[SO4 2- , promoting the re-precipitation of calcium sulfate along the crystal nucleus longitudinally.

[0049] ​​​​A method for preparing high-purity gypsum by utilizing the gradient acid property and realizing the resource utilization of zinc and copper. First, the strong acidity of high-concentration sulfuric acid is used to dissolve calcium sulfate and impurity ions, and the undissolved calcium sulfate in the solution exists as crystal nuclei. Then, by adding low-concentration sulfuric acid wastewater, the calcium sulfate in the solution precipitates supersaturated. At this time, the newly precipitated calcium sulfate crystals grow by dislocation extension along the surface of the crystal nuclei, and ion transfer and superposition on the crystal surface occur, so as to obtain high-purity gypsum with uniform particle size, high whiteness, high purity and good crystallization performance. The purity of calcium sulfate dihydrate in the obtained high-purity gypsum is above 99%.

[0050] Step 3): Add a neutralizing agent to the first filtrate for pre-neutralization, adjust the end-point pH value to 2.5 - 3.0, and filter to obtain the first precipitate and the second filtrate.

[0051] Due to the accumulation in the first two steps, the first filtrate contains relatively high concentrations of impurity ions such as Fe 3+ , Zn 2+ , Cu 2+ , etc. Since the solubility products of ZnS and Fe2S3 are similar. To ensure the purity of the subsequent zinc and copper concentrates, it is necessary to pre-neutralize the Fe 3+ in the solution. According to the Fe 3+ concentration, it can be known that it will start to hydrolyze when the pH value reaches 2.0. And according to the experimental results, the purity of zinc sulfide is the highest at pH = 3.0. Therefore, when adding a neutralizing agent to the first filtrate for pre-neutralization, the end-point pH value of the solution is adjusted to 2.5 - 3.0 through pre-neutralization, and then the next operation is carried out.

[0052] Among them, the neutralizing agent is one or more of calcium carbonate, calcium oxide, calcium hydroxide and carbide slag. Among them, the main component of carbide slag is calcium hydroxide, and it contains a small amount of calcium carbonate and silicon dioxide.

[0053] The specific reaction equations in this pre-neutralization process are as follows:

[0054] Ca 2+ +SO4 2- +2H2O == CaSO4·2H2O↓

[0055] Fe 3+ +3OH - == Fe(OH)3↓

[0056] In this way, the components of the first precipitate obtained by filtration are mainly CaSO4·2H2O and the hydrolysis product Fe(OH)3 of Fe 3+ . And by controlling the end-point pH value of the solution at 2.5 - 3.0, the water content of the first precipitate obtained by filtration under strong acidic conditions can still be controlled below 40%, reducing the amount of wet slag, and effectively ensuring the stability of the quality of downstream products.

[0057] Step 4) Mix the first precipitate with a neutralizing agent and age to obtain a mixed residue.

[0058] Among them, the mass ratio of the first precipitate to the neutralizing agent is 15:1 to 20:1, and the aging time is 24 to 36 h.

[0059] Among them, the neutralizing agent is one or more of calcium carbonate, calcium oxide, calcium hydroxide, and carbide slag. The main component of the carbide slag is calcium hydroxide, and it contains a small amount of calcium carbonate and silicon dioxide.

[0060] The sediment produced by the traditional neutralization precipitation method has a high moisture content, and subsequent recycling will directly cause a decline in the relevant properties of the product. However, for a method for preparing high-purity gypsum and realizing the resource utilization of zinc and copper by utilizing the gradient acid characteristics provided by the present invention, the moisture content of the first precipitate obtained in step 3) has been effectively reduced to less than 40%. Then, it is mixed and aged with a neutralizing agent (such as calcium hydroxide, carbide slag, etc.). Since the first precipitate still contains some free acids and soluble salts, during the process of uniformly mixing and aging the first precipitate with the neutralizing agent, it can be converted into a mixed residue composed of insoluble salts such as CaF2, CaHPO4, CaSO4, etc., which can be recycled as cement auxiliary materials, building materials, etc. In this way, the first precipitate is made into cement products and building materials with good performance at low cost, which can not only reduce the impact of by-product gypsum storage on the environment, but also generate certain economic benefits.

[0061] Step 5) Add sodium sulfide to the second filtrate and mix. Adjust the pH value of the solution to 3.0 and then filter to obtain high-purity zinc-copper concentrate and a third filtrate.

[0062] Among them, for the second filtrate obtained in step 3), its pH value is about 3.0, and this filtrate contains a large amount of Zn 2+ and Cu 2+ , a small amount of Fe that has not been completely removed 3+ and sulfate ions. At this time, adding Na2S·9H2O to this filtrate can produce and recover high-purity zinc-copper concentrate. The specific reaction equations are as follows:

[0063] ZnSO4 + Na2S·9H2O == Na2SO4 + ZnS

[0064] CuSO4 + Na2S·9H2O == Na2SO4 + CuS.

[0065] Therefore, the high-purity zinc-copper concentrate includes components such as zinc sulfide, copper sulfide, and iron sulfide. The copper grade in the high-purity zinc-copper concentrate is above 12%, and the zinc grade is above 52%.

[0066] Step 6) Add a neutralizing agent to the third filtrate for neutralization. Adjust the end-point pH value to 10.0 - 10.5 and filter to obtain a second precipitate and a fourth filtrate. The fourth filtrate meets the standards and is discharged.

[0067] Among them, the neutralizing agent is one or more of calcium carbonate, calcium oxide, calcium hydroxide and carbide slag. The main component of the carbide slag is calcium hydroxide, and it contains a small amount of calcium carbonate and silicon dioxide.

[0068] Among them, for the third filtrate obtained in step 5), its pH value remains at about 3.0, but most of the zinc and copper ions in the solution have reacted with sodium sulfide and precipitated out in step 5). At this time, only a small amount of un-precipitated completely Fe 3+ and sulfate ions exist in this filtrate. During the process of adding a neutralizing agent to neutralize the third filtrate, the specific reaction equations are as follows:

[0069] Ca 2+ +SO4 2- +2H2O == CaSO4·2H2O↓

[0070] Fe 3+ +3OH - == Fe(OH)3↓

[0071] The second precipitate in step 7) is returned to the next batch of highly concentrated sulfuric acid for recycling. Due to the excessive addition of the neutralizing agent, the second precipitate can still be used as an alkaline neutralizing agent and recycled to step 1) in the form of crystal seeds, thus realizing process recycling.

[0072] Traditional neutralization precipitation method has problems such as low utilization rate of the neutralizing agent, high water content of by-product gypsum in the neutralization process, poor dehydration performance, many impurities and poor purity, etc. This is because during the neutralization process, iron ions will form colloids and coat the surface of the neutralizing agent to form a film, resulting in a decrease in the utilization rate of the neutralizing agent. Moreover, the existence of colloids will also cause the crystallization performance of calcium sulfate to deteriorate, the particles to be fine, resulting in a high water content of by-product gypsum. At the same time, the existence of impurities will also directly affect the purity and whiteness.

[0073] Therefore, a method for preparing high-purity gypsum by utilizing the gradient acid property and realizing the resource utilization of zinc and copper provided by the present invention is as follows: (1) Firstly, the by-product gypsum is put into the acidic wastewater as an alkaline neutralizing agent. This step has two purposes: Firstly, the calcium sulfate in the by-product gypsum is used as a seed crystal so as to form high-purity gypsum subsequently; the unreacted neutralizing agent is completely reacted, thereby improving the utilization rate of the neutralizing agent. Secondly, the strong acidity of the high-concentration sulfuric acid wastewater is used to dissolve the impurity ions and most of the calcium sulfate ions. (2) The low-concentration sulfuric acid wastewater is put into it for dilution. That is, through the dilution of the low-concentration sulfuric acid wastewater, calcium ions and sulfate ions in the solution are precipitated and crystallized again to form high-purity gypsum with high purity and good whiteness, realizing the reuse of the by-product gypsum. (3) In order to improve the grades of subsequent zinc and copper concentrates, pre-neutralization is carried out in the filtrate to remove impurity ions. In addition, since there are still calcium ions in the solution, they can exist as invisible seed crystals, realizing the reduction of the water content of the by-product gypsum, that is, the reduction. This part of the filter residue with low water content can be recycled by mixing and aging with the neutralizing agent to make cement. (4) Sodium sulfide is added to the filtrate, and by controlling the pH value of the solution, high-purity zinc and copper concentrates are obtained. (5) The filtrate is neutralized to strong alkalinity, and the impurity ions in the solution are completely removed to obtain up-to-standard external drainage. The obtained filter residue enters the next batch of high-concentration sulfuric acid wastewater to realize the process cycle.

[0074] The present invention realizes the combined use of seed crystal recycling, calcium sulfate dissolution-recrystallization, and sulfide precipitation. According to the characteristics of the concentration difference between high and low sulfuric acid wastewaters, by controlling the pH value, five technological purposes are simultaneously achieved, namely the purification and recovery of calcium sulfate in the by-product gypsum, the recovery of zinc and copper in the wastewater, the reduction and recycling of the by-product gypsum, the treatment of industrial wastewater, and the improvement of the utilization rate of the neutralizing agent, realizing the comprehensive resource recovery in the efficient utilization of the neutralizing agent and the treatment of industrial acidic wastewater.

[0075] The following specifically describes a method for preparing high-purity gypsum by utilizing the gradient acid property and realizing the resource utilization of zinc and copper provided by the present invention through examples.

[0076] Example 1

[0077] S1: Take 40 mL of high-concentration sulfuric acid with a sulfuric acid concentration of 23.5 wt%, heat it to 70 °C, and add 55.56 g of precipitate ② to the reaction vessel under the condition of a stirring intensity of 600 r / min, and stir for 1 h.

[0078] S2: Add 400 mL of sulfuric acid wastewater to the above mixture for dilution, stir for 1 h under the condition of a stirring intensity of 600 r / min, adjust the pH to 1.2, and then filter.

[0079] S3: Next, add 12 g of calcium carbide slag slurry with a concentration of 30 wt% to the obtained filtrate. Under the condition of a stirring intensity of 600 r / min, adjust the pH to 2.7 and then filter.

[0080] S4: Continue to add 1.53 g of sodium sulfide nonahydrate to the obtained filtrate. Under the condition of a stirring intensity of 600 r / min, add a small amount of sulfuric acid to slightly adjust the pH value of the solution to about 3.0, stir for 30 min and then filter.

[0081] S5: Continue to add 28 g of calcium carbide slag slurry with a concentration of 30 wt% to the obtained filtrate. Under the condition of a stirring intensity of 600 r / min, adjust the pH to 10.1 and then filter. Take the precipitate ② and add it to the next batch of high-concentration sulfuric acid for reuse.

[0082] S6: Stir the precipitate obtained in S3 and the neutralizing agent evenly at a mass ratio of 20:1 and age for 24 h.

[0083] Under the above conditions, the calcium content in the high-purity gypsum obtained in S2 is 29.83%, the zinc content is 0.58%, and the total iron content is 5.75%; the moisture content of the precipitate ① obtained in S3 is 32.1%, which is 29.4% lower than that of the traditional neutralization precipitation method. The stability of the mixed ore is good after the precipitate ① is treated by S6; the zinc content in the zinc concentrate obtained in S4 is 53%, and the copper content is 12.5%; the filtrate obtained in S5 can meet the standard for external discharge; for every 400 mL of acidic wastewater treated, the consumption of calcium carbide slag is reduced by about 6.4 g.

[0084] Example 2

[0085] S1: Take 40 mL of high-concentration sulfuric acid with a sulfuric acid concentration of 23.5 wt%, heat it to 80 °C, and add 59.67 g of precipitate ② to the reaction vessel under the condition of a stirring intensity of 600 r / min. The stirring time is 1 h.

[0086] S2: Add 400 mL of sulfuric acid wastewater to the above mixture for dilution. Under the condition of a stirring intensity of 600 r / min, the stirring time is 1 h. Adjust the pH to 1.5 and then filter.

[0087] S3: Next, add 12 g of calcium carbide slag slurry with a concentration of 30 wt% to the obtained filtrate. Under the condition of a stirring intensity of 600 r / min, adjust the pH to 2.7 and then filter.

[0088] S4: Continue to add 1.53 g of sodium sulfide nonahydrate to the obtained filtrate. Under the condition of a stirring intensity of 600 r / min, add a small amount of sulfuric acid to slightly adjust the pH value of the solution to about 3.0, stir for 30 min and then filter.

[0089] S5: Continuously add 28 g of carbide slag slurry with a concentration of 30 wt% to the obtained filtrate. Under the condition of a stirring intensity of 600 r / min, adjust the pH to 10.1 and then filter. Take the precipitate ② and add it to the next batch of high-concentration sulfuric acid for reuse.

[0090] S6: Stir the precipitate obtained in S3 and the neutralizing agent evenly at a mass ratio of 20:1 and age for 24 h.

[0091] Under the above conditions, the calcium content in the high-purity gypsum obtained in S2 is 31.21%, the zinc content is 0.71%, and the total iron content is 0.82%; the water content of the precipitate ① obtained in S3 is 32.5%, which is 29% lower than that of the traditional neutralization precipitation method. The stability of the mixed ore is good after the precipitate ① is treated by S6; the zinc content in the zinc concentrate obtained in S4 is 52.6% and the copper content is 12.7%; the filtrate obtained in S5 can meet the discharge standard; for every 400 mL of acidic wastewater treated, the dosage of carbide slag is reduced by about 6.4 g.

[0092] Example 3

[0093] S1: Take 40 mL of high-concentration sulfuric acid with a sulfuric acid concentration of 23.5 wt%, heat it to 90 °C, and add 64.39 g of precipitate ② to the reaction vessel under the condition of a stirring intensity of 600 r / min. Stir for 1 h.

[0094] S2: Add 400 mL of sulfuric acid wastewater to the above mixture for dilution. Under the condition of a stirring intensity of 600 r / min, stir for 1 h, adjust the pH to 1.9 and then filter.

[0095] S3: Then add 12 g of carbide slag slurry with a concentration of 30 wt% to the obtained filtrate. Under the condition of a stirring intensity of 600 r / min, adjust the pH to 2.7 and then filter.

[0096] S4: Continuously add 1.53 g of sodium sulfide nonahydrate to the obtained filtrate. Under the condition of a stirring intensity of 600 r / min, slightly adjust the pH value of the solution to about 3.0 with a small amount of sulfuric acid, stir for 30 min and then filter.

[0097] S5: Continuously add 28 g of carbide slag slurry with a concentration of 30 wt% to the obtained filtrate. Under the condition of a stirring intensity of 600 r / min, adjust the pH to 10.1 and then filter. Take the precipitate ② and add it to the next batch of high-concentration sulfuric acid for reuse.

[0098] S6: Stir the precipitate obtained in S3 and the neutralizing agent evenly at a mass ratio of 20:1 and age for 24 h.

[0099] Under the above conditions, the calcium content in the high-purity gypsum obtained in S2 is 27.17%, the zinc content is 0.65%, and the total iron content is 13.17%; the water content of the precipitate ① obtained in S3 is 31.7%, which is 29.8% lower than that of the traditional neutralization precipitation method. After the precipitate ① is treated by S6, the stability of the mixed ore is good; the zinc content in the zinc concentrate obtained in S4 is 53.1%, and the copper content is 12.4%; the filtrate obtained in S5 can meet the discharge standards; for every 400 mL of acidic wastewater treated, the dosage of carbide slag is reduced by about 6.4 g.

[0100] Example 4

[0101] S1: Take 40 mL of high-concentration sulfuric acid with a sulfuric acid concentration of 23.5 wt%, heat it to 70 °C, and add 69.88 g of precipitate ② to the reaction vessel under the condition of a stirring intensity of 600 r / min, and the stirring time is 1 h.

[0102] S2: Add 400 mL of sulfuric acid wastewater to the above mixed solution for dilution, stir for 1 h under the condition of a stirring intensity of 600 r / min, adjust the pH to 2.1 and then filter.

[0103] S3: Then add 12 g of carbide slag slurry with a concentration of 30 wt% to the obtained filtrate, adjust the pH to 2.7 under the condition of a stirring intensity of 600 r / min, and then filter.

[0104] S4: Continue to add 1.53 g of sodium sulfide nonahydrate to the obtained filtrate, under the condition of a stirring intensity of 600 r / min, add a small amount of sulfuric acid to slightly adjust the pH value of the solution to about 3.0, stir for 30 min and then filter.

[0105] S5: Continue to add 28 g of carbide slag slurry with a concentration of 30 wt% to the obtained filtrate, adjust the pH to 10.1 under the condition of a stirring intensity of 600 r / min, and then filter. Take the precipitate ② and add it to the next batch of high-concentration sulfuric acid for reuse.

[0106] S6: Stir the precipitate obtained in S3 and the neutralizing agent evenly according to a mass ratio of 20:1 and age for 24 h.

[0107] Under the above conditions, the calcium content in the high-purity gypsum obtained in S2 is 26.65%, the zinc content is 0.78%, and the total iron content is 49.91%; the water content of the precipitate ① obtained in S3 is 32.3%, which is 29.2% lower than that of the traditional neutralization precipitation method. After the precipitate ① is treated by S6, the stability of the mixed ore is good; the zinc content in the zinc concentrate obtained in S4 is 52.7%, and the copper content is 12.8%; the filtrate obtained in S5 can meet the discharge standards; for every 400 mL of acidic wastewater treated, the dosage of carbide slag is reduced by about 6.4 g.

[0108] Example 5

[0109] S1: Take 40 mL of highly concentrated sulfuric acid with a sulfuric acid concentration of 23.5 wt%, heat it to 90 °C, and add 59.67 g of precipitate ② to the reaction vessel under the condition of a stirring intensity of 600 r / min, with a stirring time of 1 h.

[0110] S2: Add 400 mL of sulfuric acid wastewater to the above-mentioned mixture for dilution, stir for 1 h under the condition of a stirring intensity of 600 r / min, adjust the pH to 1.5 and then filter.

[0111] S3: Then add 12 g of calcium carbide slag slurry with a concentration of 30 wt% to the obtained filtrate, adjust the pH to 2.7 under the condition of a stirring intensity of 600 r / min and then filter.

[0112] S4: Continue to add 1.53 g of sodium sulfide nonahydrate to the obtained filtrate, add a small amount of sulfuric acid to slightly adjust the pH value of the solution to about 1.0 under the condition of a stirring intensity of 600 r / min, stir for 30 min and then filter.

[0113] S5: Continue to add 28 g of calcium carbide slag slurry with a concentration of 30 wt% to the obtained filtrate, adjust the pH to 10.1 under the condition of a stirring intensity of 600 r / min and then filter, take precipitate ② and add it to the next batch of high-concentration sulfuric acid for reuse.

[0114] S6: Stir the precipitate obtained in S3 and the neutralizing agent evenly according to a mass ratio of 20:1 and age for 24 h.

[0115] Under the above conditions, the calcium content in the high-purity gypsum obtained in S2 is 31.03%, the zinc content is 0.7%, and the total iron content is 0.85%; the moisture content of precipitate ① obtained in S3 is 31.5%, which is 30% lower than that of the traditional neutralization precipitation method, and the stability of the mixed ore is good after precipitate ① is treated by S6; the zinc content in the zinc concentrate obtained in S4 is 35.77%, and the copper content is 10.9%; the filtrate obtained in S5 can meet the standard for external discharge; for every 400 mL of acidic wastewater treated, the consumption of calcium carbide slag is reduced by about 6.4 g.

[0116] Example 6

[0117] S1: Take 40 mL of highly concentrated sulfuric acid with a sulfuric acid concentration of 23.5 wt%, heat it to 70 °C, and add 59.67 g of precipitate ② to the reaction vessel under the condition of a stirring intensity of 600 r / min, with a stirring time of 1 h.

[0118] S2: Add 400 mL of sulfuric acid wastewater to the above-mentioned mixture for dilution, stir for 1 h under the condition of a stirring intensity of 600 r / min, adjust the pH to 1.5 and then filter.

[0119] S3: Then, add 12 g of carbide slag slurry with a concentration of 30 wt% to the obtained filtrate. Under the condition of a stirring intensity of 600 r / min, adjust the pH to 2.7 and then filter.

[0120] S4: Continue to add 1.53 g of sodium sulfide nonahydrate to the obtained filtrate. Under the condition of a stirring intensity of 600 r / min, add a small amount of sulfuric acid to slightly adjust the pH value of the solution to about 2.0, stir for 30 min and then filter.

[0121] S5: Continue to add 28 g of carbide slag slurry with a concentration of 30 wt% to the obtained filtrate. Under the condition of a stirring intensity of 600 r / min, adjust the pH to 10.1 and then filter. Take the precipitate ② and add it to the next batch of high-concentration sulfuric acid for reuse.

[0122] S6: Stir the precipitate obtained in S3 and the neutralizing agent evenly according to a mass ratio of 20:1 and age for 24 h.

[0123] Under the above conditions, the calcium content in the high-purity gypsum obtained in S2 is 31.15%, the zinc content is 0.79%, and the total iron content is 0.9%; the moisture content of the precipitate ① obtained in S3 is 32.5%, which is 29% lower than that of the traditional neutralization precipitation method. The stability of the mixed ore is good after the precipitate ① is treated by S6; the zinc content in the zinc concentrate obtained in S4 is 47.65%, and the copper content is 11.3%; the filtrate obtained in S5 can meet the standard for external discharge; for every 400 mL of acidic wastewater treated, the dosage of carbide slag is reduced by about 6.4 g.

[0124] Example 7

[0125] S1: Take 40 mL of high-concentration sulfuric acid with a sulfuric acid concentration of 23.5 wt%, heat it to 80 °C, and add 59.67 g of precipitate ② to the reaction vessel under the condition of a stirring intensity of 600 r / min. The stirring time is 1 h.

[0126] S2: Add 400 mL of sulfuric acid wastewater to the above mixture for dilution. Under the condition of a stirring intensity of 600 r / min, the stirring time is 1 h. Adjust the pH to 1.5 and then filter.

[0127] S3: Then, add 12 g of carbide slag slurry with a concentration of 30 wt% to the obtained filtrate. Under the condition of a stirring intensity of 600 r / min, adjust the pH to 2.7 and then filter.

[0128] S4: Continue to add 1.53 g of sodium sulfide nonahydrate to the obtained filtrate. Under the condition of a stirring intensity of 600 r / min, add a small amount of sulfuric acid to slightly adjust the pH value of the solution to about 3.0, stir for 30 min and then filter.

[0129] S5: Continuously add 28 g of carbide slag slurry with a concentration of 30 wt% to the obtained filtrate. Under the condition of a stirring intensity of 600 r / min, adjust the pH to 10.1 and then filter. Take the precipitate ② and add it to the next batch of high-concentration sulfuric acid for reuse.

[0130] S6: Stir the precipitate obtained in S3 and the neutralizing agent evenly at a mass ratio of 20:1 and age for 24 h.

[0131] Under the above conditions, the calcium content in the high-purity gypsum obtained in S2 is 31.25%, the zinc content is 0.75%, and the total iron content is 0.88%; the water content of the precipitate ① obtained in S3 is 32.13%, which is 29.37% lower than that of the traditional neutralization precipitation method. The stability of the mixed ore is good after the precipitate ① is treated by S6; the zinc content in the zinc concentrate obtained in S4 is 53.3%, and the copper content is 12.4%; the filtrate obtained in S5 can meet the discharge standard; for every 400 mL of acidic wastewater treated, the dosage of carbide slag is reduced by about 6.4 g.

[0132] Example 8

[0133] S1: Take 40 mL of high-concentration sulfuric acid with a sulfuric acid concentration of 23.5 wt%, heat it to 70 °C, and add 59.67 g of precipitate ② to the reaction vessel under the condition of a stirring intensity of 600 r / min. Stir for 1 h.

[0134] S2: Add 400 mL of sulfuric acid wastewater to the above mixture for dilution. Under the condition of a stirring intensity of 600 r / min, stir for 1 h, adjust the pH to 1.5 and then filter.

[0135] S3: Then add 12 g of carbide slag slurry with a concentration of 30 wt% to the obtained filtrate. Under the condition of a stirring intensity of 600 r / min, adjust the pH to 2.7 and then filter.

[0136] S4: Continuously add 1.53 g of sodium sulfide nonahydrate to the obtained filtrate. Under the condition of a stirring intensity of 600 r / min, add a small amount of sulfuric acid to slightly adjust the pH value of the solution to about 4.0, stir for 30 min and then filter.

[0137] S5: Continuously add 28 g of carbide slag slurry with a concentration of 30 wt% to the obtained filtrate. Under the condition of a stirring intensity of 600 r / min, adjust the pH to 10.1 and then filter. Take the precipitate ② and add it to the next batch of high-concentration sulfuric acid for reuse.

[0138] S6: Stir the precipitate obtained in S3 and the neutralizing agent evenly at a mass ratio of 20:1 and age for 24 h.

[0139] Under the above conditions, the calcium content in the high-purity gypsum obtained in S2 is 31.14%, the zinc content is 0.74%, and the total iron content is 0.86%; the moisture content of the precipitate ① obtained in S3 is 32.17%, which is 29.33% lower than that of the traditional neutralization precipitation method. After being treated by S6, the stability of the mixed ore of the precipitate ① is good; the zinc content in the zinc concentrate obtained in S4 is 49.64%, and the copper content is 11.8%; the filtrate obtained in S5 can meet the standard for external discharge; for every 400 mL of acidic wastewater treated, the dosage of carbide slag is reduced by about 6.4 g.

[0140] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the examples, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing high-purity gypsum and realizing zinc and copper resource utilization by utilizing gradient acid characteristics, characterized in that: The steps include: Mixing highly concentrated sulfuric acid with the neutralized slag to dissolve calcium sulfate in the neutralized slag to obtain a mixed solution; Adding low-concentration sulfuric acid wastewater to the mixed solution to crystallize calcium sulfate, and then filtering to obtain high-purity gypsum and the first filtrate; Add a neutralizing agent to the first filtrate for pre-neutralization, adjust the endpoint pH value to 2.5-3.0, and filter to obtain a first precipitate and a second filtrate; The first precipitate is mixed with a neutralizer and then aged to obtain a mixed slag material; Sodium sulfide is added to the second filtrate and mixed, and the pH value of the solution is adjusted to 3.0 and then filtered to obtain a high-purity zinc-copper concentrate and a third filtrate; Add a neutralizing agent to the third filtrate for neutralization, adjust the endpoint pH value to 10.0-10.5, and filter to obtain a second precipitate and a fourth filtrate; The second precipitate is returned to the next batch of highly concentrated sulfuric acid for recycling, and the fourth filtrate is discharged after meeting the standards.

2. The method for preparing high-purity gypsum and realizing zinc and copper resource utilization by utilizing gradient acid characteristics according to claim 1, characterized in that: The highly concentrated sulfuric acid is the acid wastewater with a concentration of 10wt% to 30wt% produced in the process of gold concentrate smelting; the neutralized slag is the neutralized slag obtained by filtering after the acid wastewater produced in the process of gold concentrate smelting is neutralized with carbide slag to strong alkalinity.

3. The method for preparing high-purity gypsum and realizing zinc and copper resource utilization by utilizing gradient acid characteristics according to claim 1, characterized in that: The temperature of the highly concentrated sulfuric acid and the neutralization slag when mixed is controlled at 70° C. to 90° C., and 100 to 300 g of the neutralization slag is added to each high concentration of sulfuric acid.

4. The method for preparing high-purity gypsum and realizing zinc and copper resource utilization by utilizing gradient acid characteristics according to claim 1, characterized in that: The low-concentration sulfuric acid wastewater is sulfuric acid wastewater with a pH value less than 1 and a sulfuric acid content of 1.2 wt% to 3 wt% generated during the gold concentrate smelting process.

5. The method for preparing high-purity gypsum and realizing zinc and copper resource utilization by utilizing gradient acid characteristics according to claim 4, characterized in that: The low-concentration sulfuric acid wastewater is one or more of titanium dioxide acid wastewater, copper raffinate, mine acid wastewater, coal mine acid wastewater and dirty acid wastewater.

6. The method for preparing high-purity gypsum and realizing zinc and copper resource utilization by utilizing gradient acid characteristics according to claim 5, characterized in that: The volume ratio of the low-concentration sulfuric acid wastewater to the mixed solution is controlled at 8:1-12:1, the endpoint pH value after the low-concentration sulfuric acid wastewater and the mixed solution are mixed is controlled at 1.0-2.0, and the purity of calcium sulfate dihydrate of the obtained high-purity gypsum is above 99%.

7. The method for preparing high-purity gypsum and realizing zinc and copper resource utilization by utilizing gradient acid characteristics according to claim 2, characterized in that: The mass ratio of the first precipitate to the neutralizer is 15:1 to 20:1, and the aging time is 24 to 36 hours.

8. The method for preparing high-purity gypsum and realizing zinc and copper resource utilization by utilizing gradient acid characteristics according to claim 7, characterized in that: The neutralizing agent is one or more of calcium carbonate, calcium oxide, calcium hydroxide and carbide slag.

9. The method for preparing high-purity gypsum and realizing zinc and copper resource utilization by utilizing gradient acid characteristics according to claim 8, characterized in that: The carbide slag is mainly composed of calcium hydroxide and contains a small amount of calcium carbonate and silicon dioxide.

10. The method for preparing high-purity gypsum and realizing zinc and copper resource utilization by utilizing gradient acid characteristics according to claim 1, characterized in that: The high-purity zinc-copper concentrate comprises zinc sulfide, copper sulfide and iron sulfide. The copper grade in the high-purity zinc-copper concentrate is above 12%, and the zinc grade is above 52%.

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