Method for recovering arsenic trioxide by leaching arsenic sulfide slag from ferrihydrite

Abstract

The invention belongs to the technical field of dangerous solid waste resource recovery in the nonferrous smelting industry, and discloses a method for recovering arsenic trioxide by leaching arsenic sulfide slag from ferrihydrite. The arsenic sulfide slag is leached by ferrihydrite in an acid solution under the normal pressure condition, so that the leaching rate of arsenic in the arsenic sulfide slag is increased; and sulfur dioxide gas is introduced into the leachate to reduce arsenic in the solution, finally arsenic trioxide is obtained through evaporation concentration and cooling crystallization, meanwhile, oxygen is introduced into the crystallized liquid to oxidize and recycle iron, and cyclic utilization of resources is achieved. The method has the characteristics of simplicity and convenience in operation, low cost, safety, reliability and the like, the arsenic sulfide slag can be effectively recycled to prepare the arsenic trioxide product, and the purpose of treating waste with waste is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of hazardous solid waste resource recovery in nonferrous smelting industry, and more particularly to a method for recovering arsenic trioxide by leaching arsenic sulfide slag from ferrihydrite. Background Art

[0002] In the production process of metallurgy, chemistry and other industries, sulfide precipitation method is often used to treat arsenic-containing wastewater, thus producing a large amount of arsenic sulfide slag. As a hazardous waste, arsenic in arsenic sulfide slag will cause serious harm to the environment and human health if it is not properly handled. However, arsenic is also an important industrial raw material with a high recovery value. With the increasing depletion of arsenic mineral resources, recovering arsenic from arsenic sulfide slag has become an effective way to solve the problems of resource shortage and environmental pollution. Therefore, it is very important to develop an efficient, environmentally friendly and easy-to-operate arsenic resource recovery technology from arsenic sulfide slag. It can not only solve the environmental risks brought by arsenic sulfide slag, but also realize the effective recycling of resources to meet the needs of sustainable development.

[0003] In the prior art, CN 201611246172.2 discloses a method for directly producing metallic arsenic by reducing and fixing sulfur in roasting of arsenic sulfide slag, in which the arsenic sulfide slag is subjected to low-temperature reduction and fixing sulfur roasting, and the roasting product is subjected to vacuum separation in a reducing atmosphere by utilizing the volatility of arsenic to obtain crude metallic arsenic. This method is highly efficient in removing arsenic, but the process is relatively complicated, involving multiple steps and precise control of reaction conditions. In actual large-scale production applications, the operation is difficult, and the recovery efficiency is easily unstable due to improper operation.

[0004] Therefore, developing a method for preparing arsenic trioxide by leaching arsenic sulfide slag from ferrihydrite in an acidic solution under normal pressure is an urgent problem to be solved by those skilled in the art. Summary of the invention

[0005] In view of this, the present invention provides a method for preparing arsenic trioxide by leaching arsenic sulfide slag from ferrihydrite in an acidic solution under normal pressure, wherein the method utilizes trivalent iron in ferrihydrite to oxidize trivalent arsenic in the arsenic sulfide slag, and the equation involved is shown in formula (1). The method has the characteristics of simple operation, low cost, safety and reliability, and can effectively recycle the arsenic sulfide slag to prepare arsenic trioxide products, thereby achieving the purpose of "treating waste with waste".

[0006] As2S3+2Fe5HO8+10H2SO4=2H3AsO4+10FeSO4+8H2O+3S↓ (1)

[0007] To achieve the above object, the present invention provides a method for recovering arsenic trioxide by leaching arsenic sulfide slag with ferrihydrite. Under normal pressure, the arsenic sulfide slag is leached with ferrihydrite in an acidic solution, which improves the leaching rate of arsenic in the arsenic sulfide slag. Sulfur dioxide gas is introduced into the leaching solution to reduce arsenic in the solution, and finally arsenic trioxide is obtained by evaporation and concentration, followed by cooling crystallization. At the same time, the post-crystallization solution is introduced with oxygen to oxidize iron and recycle it, realizing the recycling of resources.

[0008] Further, the specific steps are as follows:

[0009] S1. Under normal pressure, arsenic sulfide and ferrihydrite are added to a sulfuric acid solution. After the reaction is completed, the solution is filtered and the filtrate is collected.

[0010] S2. Sulfur dioxide gas is introduced into the filtrate for a reduction reaction, and then filtered to obtain a filtrate containing trivalent arsenic.

[0011] S3. The filtrate containing trivalent arsenic is evaporated and concentrated, followed by cooling crystallization. The precipitated crystals are filtered, and the post-crystallization solution is collected for standby use. The crystals are washed to obtain arsenic trioxide.

[0012] S4. Oxygen is introduced into the post-crystallization solution for pressure oxidation, and at the same time, the pH value of the solution is adjusted. After the reaction is completed, the solution is filtered and the filtrate is collected.

[0013] Preferably, in step S1, the molar ratio of arsenic sulfide to ferrihydrite is 1:2, the pH value of the sulfuric acid solution is 0.5 - 1, and the solid-liquid ratio of arsenic sulfide and ferrihydrite to the sulfuric acid solution is 1:2.

[0014] The beneficial effects of adopting the above technical solution are as follows: There are different differences in arsenic in the arsenic sulfide slag. By reasonably controlling the ratio, to a certain extent, it can ensure that the arsenic sulfide slag is fully leached, and at the same time, it can also avoid the generation of iron vanadium insoluble in acid due to excessive trivalent iron in the solution. The pH of the solution not only affects the leaching of arsenic, but also affects other substances in the arsenic sulfide slag entering the solution. If the pH is too low, bismuth in the arsenic sulfide slag will form BiOSO, and this product is easily decomposed. Therefore, it is necessary to strictly control the pH of the solution to avoid substances other than arsenic in the leaching solution.

[0015] Preferably, in step S1, the reaction temperature is 80 - 90 °C and the time is 1 - 2 h.

[0016] The beneficial effects of adopting the above technical solution are as follows: Temperature is the decisive factor determining the reaction rate. Too low or too high temperature will affect the leaching of arsenic sulfide. Controlling within the reaction temperature range can fully leach the arsenic sulfide slag.

[0017] Preferably, in step S2, the flow rate of the sulfur dioxide gas is 10 - 15 L / h.

[0018] Preferably, in step S2, the temperature of the reduction reaction is 20-30 °C and the time is 1-2 h.

[0019] Preferably, in step S3, the temperature of the evaporation and concentration is 120-150 °C and the time is 0.5-1 h; the temperature of the cooling crystallization is 1-10 °C and the time is 1-2 h.

[0020] More preferably, the volume ratio of the filtrate before and after evaporation and concentration is 2:1-3:1.

[0021] Preferably, in step S4, the flow rate of oxygen is 1-5 L / h and the pH value is 3-4.

[0022] Preferably, in step S4, the pressure of the reaction is 0.5-1 MPa, the temperature is 60-70 °C, and the time is 1-2 h.

[0023] Furthermore, the method of the present invention further includes returning the solution after oxidation in S4 to the arsenic sulfide residue leaching step for reuse.

[0024] Furthermore, in the above step S1, the specific preparation method of the ferrihydrite is as follows:

[0025] a. Dissolve ferric chloride hexahydrate in deionized water, and the solid-liquid ratio is 1:10-1:13;

[0026] b. Prepare a solution of one of potassium hydroxide and sodium hydroxide with a concentration of 0.1-1 mol / L;

[0027] c. Adjust the pH of the solution in step a to 7-8 with the solution in step b;

[0028] d. Stir at 60-70 °C for 1-2 h, and the stirring speed is 300-600 rpm;

[0029] e. After stirring, centrifuge 3-4 times at 4000-6000 r / min, and after centrifugation, place it in a drying oven at 50-80 °C for drying for 15-24 h to finally obtain ferrihydrite.

[0030] From the above technical solutions, it can be seen that compared with the prior art, the beneficial effects obtained by the present invention are:

[0031] (1) The present invention provides a method for leaching arsenic sulfide residue with ferrihydrite in an acidic solution under normal pressure to prepare arsenic trioxide. Under acidic conditions, ferrihydrite dissolves to form ferric ions to oxidize arsenic, and at the same time, the generated pentavalent arsenic can cooperate with ferrihydrite to continue to oxidize trivalent arsenic, so that arsenic can be fully leached, and the safety problem of leaching arsenic sulfide residue under high pressure can also be avoided. The leaching rate of arsenic can reach more than 90%.

[0032] (2) The method of obtaining arsenic trioxide by evaporation and crystallization in the method of the present invention is simple to operate, and the purity of the obtained arsenic trioxide can reach more than 99%.

[0033] (3) The leaching solution used in the method of the present invention can be circulated in the system, which can save production costs, and can quickly achieve efficient leaching and recycling of arsenic, and the operation process is simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0035] Figure 1 The process flow chart of the method for recovering arsenic trioxide by leaching arsenic sulfide slag from ferrihydrite in an example of the present invention.

[0036] In the figure: 1. Feeding tank; 2. Reaction tank; 3. Filter; 4. Reduction tank; 5. Evaporation concentration tank; 6. Cooling tower; 7. Pressurized oxidation tank; 8. Sulfur storage tank; 9. Filtrate tank; 10. Arsenic trioxide storage tank; A. Arsenic sulfide slag; B. Filtrate; C. Sulfur dioxide reduction liquid; D. Coolant; E. Trivalent iron regeneration liquid. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] The ferrihydrite preparation method used in the following examples is as follows:

[0039] a. Dissolve 40 g of ferric chloride hexahydrate in 500 mL of deionized water and stir until the ferric chloride hexahydrate is completely dissolved and the solution turns dark yellow.

[0040] b. Prepare 330mL of 1mol / L sodium hydroxide solution;

[0041] c. Add the solution in step b to the solution in step a, and finally add 20 mL dropwise to adjust the pH to 7.5;

[0042] d. Stir at 65°C for 1.5 h at a stirring speed of 600 rpm;

[0043] e. After the stirring is completed, centrifuge 4 times at 6000 r / min, and the single centrifugation time is 10 min. After centrifugation, place it in a drying oven and dry at 60 °C for 24 h to finally obtain ferrihydrite.

[0044] Example 1

[0045] (1) Mix 10 g of arsenic sulfide residue with 33.25 g of ferrihydrite, add 86.5 mL of sulfuric acid solution with a pH of 0.5, and leach at 80 °C for 1 h using a water bath. After the leaching is completed, filter to obtain the filter residue and filtrate. The arsenic content in the obtained filter residue is <3%, and the sulfur content is >95%. The leaching rate of arsenic in the obtained filtrate is 91%.

[0046] (2) Pass sulfur dioxide gas into the filtrate obtained in step (1) and carry out reduction at 20 °C (the feeding rate of sulfur dioxide is 15 L / h), reduce for 1 h, and the content of trivalent arsenic in the obtained solution accounts for 91% of the total arsenic after the reduction is completed.

[0047] (3) Evaporate and concentrate the solution obtained in step (2) at 130 °C for 1 h until the solution volume is 30 mL. Cool and crystallize the concentrated solution at 1 °C for 1 h. After the solution precipitates crystals, filter to obtain crystals and filtrate. The obtained crystals are washed and dried to obtain arsenic trioxide with a purity of 99%.

[0048] (4) Adjust the pH of the filtrate obtained in step (3) to 3, pass oxygen into the solution with the adjusted pH (the feeding rate of oxygen is 1 L / h), oxidize the divalent iron in the solution at a pressure of 0.5 Mpa, react at 60 °C using a water bath for 1 h, and after the reaction is completed, filter to obtain the filter residue and filtrate. The filter residue is dissolved with sulfuric acid and returned to leaching.

[0049] Comparative Example 1

[0050] (1) Mix 10 g of arsenic sulfide residue with 33.25 g of ferrihydrite, add it to 86.5 mL of sulfuric acid solution with a pH of 1.5, and leach at 80 °C for 1 h using a water bath. After the leaching is completed, filter to obtain the filter residue and filtrate. The arsenic content in the obtained filter residue is >48%, and the sulfur content is <30%.

[0051] Conclusion: If the pH value of the sulfuric acid solution is adjusted to 1.5, the leaching rate of arsenic is only 32.4%.

[0052] Example 2

[0053] (1) Mix 20 g of arsenic sulfide residue with 66.5 g of ferrihydrite, add 173 mL of sulfuric acid solution with a pH of 0.8, and leach at 90 °C for 2 h using a water bath. After the leaching is completed, filter to obtain the filter residue and filtrate. The arsenic content in the obtained filter residue is <2.2%, and the sulfur content is >98%. The leaching rate of arsenic in the obtained filtrate is 92.3%.

[0054] (2) Sulfur dioxide gas is introduced into the filtrate obtained in step (1) for reduction at 30 °C (the introduction rate of sulfur dioxide is 10 L / h), and the reduction is carried out for 2 h. The content of trivalent arsenic in the solution obtained after reduction accounts for 92% of the total arsenic.

[0055] (3) The solution obtained in step (2) is evaporated and concentrated at 150 °C for 0.5 h until the solution volume is 80 mL. The concentrated solution is cooled and crystallized at 3 °C for 2 h. After the solution precipitates crystals, it is filtered to obtain crystals and a filtrate. The obtained crystals are washed and dried to obtain arsenic trioxide with a purity of 99.4%.

[0056] (4) The pH of the filtrate obtained in step (3) is adjusted to 4. Oxygen is introduced into the solution with the adjusted pH (the oxygen introduction rate is 5 L / h) to oxidize divalent iron in the solution under a pressure of 1 Mpa. The reaction is carried out in a water bath at 70 °C for 2 h. After the reaction is completed, it is filtered to obtain a filter residue and a filtrate. The filter residue is dissolved with sulfuric acid and returned to leaching.

[0057] Comparative Example 2

[0058] (1) 20 g of arsenic sulfide slag is mixed with 66.5 g of goethite, and 173 mL of sulfuric acid solution with a pH of 1 is added. The mixture is leached in a water bath at 90 °C for 2 h. After the leaching is completed, it is filtered to obtain a filter residue and a filtrate. The obtained filter residue contains more than 38% arsenic and less than 40% sulfur.

[0059] Conclusion: If the pH value of the sulfuric acid solution is adjusted to 1.5, the arsenic leaching rate is only 40.4%.

[0060] Example 3

[0061] (1) 10 g of arsenic sulfide slag is mixed with 33.25 g of goethite, and 86.5 mL of sulfuric acid solution with a pH of 0.6 is added. The mixture is leached in a water bath at 90 °C for 1 h. After the leaching is completed, it is filtered to obtain a filter residue and a filtrate. The obtained filter residue contains less than 2.6% arsenic and more than 98% sulfur. The arsenic leaching rate in the obtained filtrate is 91.8%.

[0062] (2) Sulfur dioxide gas is introduced into the filtrate obtained in step (1) for reduction at 25 °C (the introduction rate of sulfur dioxide is 10 L / h), and the reduction is carried out for 2 h. The content of trivalent arsenic in the solution obtained after reduction accounts for 91.4% of the total arsenic.

[0063] (3) The solution obtained in step (2) is evaporated and concentrated at 130 °C for 1 h until the solution volume is 30 mL. The concentrated solution is cooled and crystallized at 5 °C for 2 h. After the solution precipitates crystals, it is filtered to obtain crystals and a filtrate. The obtained crystals are washed and dried to obtain arsenic trioxide with a purity of 99.2%.

[0064] (4) Adjust the pH of the filtrate obtained in step (3) to 4. Pass oxygen into the solution with the adjusted pH (the oxygen passing rate is 5 L / h). Oxidize the divalent iron in the solution under a pressure of 1 Mpa. React for 2 h in a water bath at 70 °C. After the reaction is completed, filter to obtain a filter residue and a filtrate. Dissolve the filter residue with sulfuric acid and return it to leaching.

[0065] Comparative Example 3

[0066] Adopt the biological oxidation and regeneration of ferric iron leaching arsenic sulfide residue process disclosed in Chinese Patent CN103031436A. The specific steps are as follows:

[0067] Grind 10 g of the residue to -100 μm and add it to the ferric sulfate solution for leaching. The concentration of Fe 3+ is 5 g / L, and the pulp concentration is 200 g / L. Adjust the pH value of the system to 0.6 and the temperature to 90 °C. After reacting for 3 hours, perform liquid-solid separation. The arsenic leaching rate is 87%;

[0068] Compare the arsenic leaching rates in Example 3 and Comparative Example 3. The arsenic leaching rate in the present invention is higher than that in Comparative Example 3, and the leaching time is shorter than that in Comparative Example 3.

[0069] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for recovering arsenic trioxide from ferrihydrite leaching of arsenic sulfide residue, characterized in that, Under atmospheric pressure, arsenopyrite slag is leached in an acidic solution using ferrihydrite. Sulfur dioxide gas is introduced into the leaching solution to reduce arsenic in the solution. Finally, arsenic trioxide is obtained by evaporation, concentration, cooling and crystallization. At the same time, the solution after crystallization is introduced with oxygen to oxidize iron and recycle it, realizing the recycling of resources.

2. A method for recovering arsenic trioxide from arsenopyrite slag by leaching with ferrihydrite according to claim 1, characterized in that, It includes the following steps: S1. Under atmospheric pressure, arsenopyrite and ferrihydrite are added into sulfuric acid solution. After the reaction is completed, the filtrate is filtered and collected. S2. Sulfur dioxide gas is introduced into the filtrate for reduction reaction, and then filtered to obtain a filtrate containing trivalent arsenic. S3. The filtrate containing trivalent arsenic is evaporated and concentrated, cooled and crystallized, filtered, and the solution after crystallization is collected for standby. The crystals are washed to obtain arsenic trioxide. S4. Oxygen is introduced into the solution after crystallization for pressure oxidation, and at the same time, the pH value of the solution is adjusted. After the reaction is completed, the filtrate is filtered and collected.

3. A method for recovering arsenic trioxide from arsenic sulfide residue by leaching with ferrihydrite according to claim 2, characterized in that, In step S1, the molar ratio of arsenopyrite to ferrihydrite is 1:2, the pH value of the sulfuric acid solution is 0.5 - 1, and the solid-liquid ratio of arsenopyrite and ferrihydrite to the sulfuric acid solution is 1:

2.

4. A method for recovering arsenic trioxide from arsenopyrite slag by leaching with ferrihydrite according to claim 2, characterized in that, In step S1, the reaction temperature is 80 - 90 °C and the time is 1 - 2 h.

5. A method for recovering arsenic trioxide from arsenic sulfide slag by leaching with ferrihydrite according to claim 2, characterized in that, In step S2, the flow rate of the sulfur dioxide gas is 10 - 15 L / h.

6. A method for recovering arsenic trioxide from arsenic sulfide slag by leaching with ferrihydrite according to claim 2, characterized in that, In step S2, the reduction reaction temperature is 20 - 30 °C and the time is 1 - 2 h.

7. A method for recovering arsenic trioxide from arsenic sulfide slag by leaching with ferrihydrite according to claim 2, characterized in that, In step S3, the evaporation and concentration temperature is 120 - 150 °C and the time is 0.5 - 1 h; the cooling and crystallization temperature is 1 - 10 °C and the time is 1 - 2 h.

8. A method for recovering arsenic trioxide from arsenopyrite slag by leaching with ferrihydrite according to claim 2, characterized in that, In step S4, the flow rate of oxygen is 1 - 5 L / h and the pH value is 3 - 4.

9. A method for recovering arsenic trioxide from sulfide arsenic slag by leaching with ferrihydrite according to claim 2, characterized in that, In step S4, the reaction pressure is 0.5 - 1 MPa, the temperature is 60 - 70 °C, and the time is 1 - 2 h.

10. A method for recovering arsenic trioxide from arsenopyrite slag by leaching with ferrihydrite according to claim 2, characterized in that, It also includes returning the filtrate in S4 to step S1 for reuse.

Images