Process for the preparation of arsenic trioxide from arsenic sulfide residues

Abstract

The application belongs to the field of chemical production, and particularly designs a method for preparing arsenic trioxide from arsenic sulfide residue, comprising the following steps: step SA1: mixing and slurrying arsenic sulfide residue with a first residue leaching solution, passing in oxygen, and catalytically oxidizing leaching to obtain first leaching residue and first leaching solution; the first residue leaching solution is a solution comprising sulfuric acid, an iron salt, and nitrate and / or nitrite; step SA2: cooling and crystallizing the first leaching solution to obtain arsenic trioxide product and first arsenic precipitation solution. Compared with the prior art, the scheme of the application can prepare the target product using environmentally friendly oxygen, and since the catalytic components in the first residue leaching solution are consumed as catalysts, the first arsenic precipitation solution can be continuously recycled without a special regeneration step, which is more green, cost-saving, and efficient.

Description

Technical Field

[0001] This invention relates to the field of chemical production, and in particular to a method for the wet preparation of arsenic trioxide from arsenic sulfide slag. Background Technology

[0002] Arsenic trioxide is an industrial raw material with significant applications in chemical engineering and materials science. Currently, the preparation of arsenic trioxide often uses arsenic sulfide slag, a byproduct of wastewater treatment in the metallurgical industry, as a raw material. The main component of this waste slag is arsenic trisulfide. Using arsenic sulfide slag to prepare arsenic trioxide not only yields the target product but also enables the resource-based and harmless disposal of arsenic sulfide slag, a byproduct of metallurgical wastewater treatment. This effectively reduces the environmental pollution risks caused by the direct discharge of such hazardous waste, aligning with the current development needs for industrial solid waste reduction and resource utilization.

[0003] In existing technologies, arsenic trioxide is often prepared from arsenic sulfide slag via a wet process using ferric sulfate—utilizing Fe 3+ The oxidizing property of arsenic sulfide is used to oxidize arsenic acid to soluble arsenic acid, which is then reduced to arsenous acid by sulfur dioxide. Taking advantage of the fact that the solubility of arsenous acid decreases with decreasing temperature, crude arsenic trioxide is obtained by cooling and crystallization. The crystallized liquid is then oxidized with sodium chlorate to obtain Fe. 2+ This method aims to recycle iron ions. However, the process is complex, and the large-scale use of sulfur dioxide and sodium hypochlorite poses a risk of toxic gas emissions, which is environmentally unfriendly. Furthermore, the cost of using sodium hypochlorite for iron regeneration is high. Summary of the Invention

[0004] Based on this, the purpose of this invention is to overcome the defects or shortcomings of the prior art, such as being environmentally unfriendly and costly, and to provide a method for preparing arsenic trioxide from arsenic sulfide slag, comprising the following steps:

[0005] Step SA1: Mix the first leaching residue with the arsenic sulfide residue and slurry, then introduce oxygen and catalytically oxidize and leach to obtain the first leaching residue and the first leaching solution; the first leaching residue is a solution containing sulfuric acid, iron salts, and nitrate and / or nitrite. Step SA2: Cool the first leachate to crystallize and obtain arsenic trioxide product and first arsenic precipitation solution; Compared to existing technologies, the present invention can produce the target product using environmentally friendly oxygen. Furthermore, since the catalytic components in the first leaching solution are consumed at minimal rate as catalysts, the first arsenic precipitation solution can be continuously recycled without special regeneration steps, making it more environmentally friendly, cost-effective, and efficient.

[0006] In one embodiment, in the first leaching solution, the nitrate is provided by nitric acid and / or nitrate; the nitrite is provided by nitrite and / or nitrite; the concentration of the sulfuric acid is 0.2~2 mol / L; the overall concentration of the nitrate and / or nitrite is 0.02~0.5 mol / L; and the overall concentration of the iron salt is 0.1~0.5 mol / L.

[0007] In one embodiment, the method further includes step SA3: using the first arsenic precipitation solution to perform secondary catalytic oxidation on the first leaching residue to obtain a second leaching residue and a second leachate; the second leachate is returned to step SA1 as a supplement to the first leaching residue solution to participate in the catalytic oxidation of the arsenic sulfide residue. This secondary catalytic oxidation further improves the conversion rate of arsenic sulfide.

[0008] In one embodiment, in step SA1, the first leaching residue solution and arsenic sulfide slag are mixed and slurried at a liquid-to-solid volume ratio of 3 to 10:1, then oxygen is introduced and the oxygen pressure is maintained at 0.1 to 0.5 MPa. The temperature is raised to 70 to 95 °C, and the mixture is stirred to carry out a catalytic oxidation reaction for 1 to 3 hours. After the reaction is completed, the mixture is filtered to obtain the first leaching solution and the first leaching residue.

[0009] In one embodiment, in step SA3, the first arsenic precipitation solution from step SA2 and the first leaching residue from step SA1 are mixed and slurried at a liquid-to-solid volume ratio of 10-20:1. The slurry is then added to a sealed reactor, oxygen is introduced, the oxygen pressure inside the reactor is maintained at 0.1-0.5 MPa, the temperature is raised to 60-100 °C, and the reaction is stirred for 3-5 h. After the reaction is completed, the mixture is filtered to obtain the second leaching solution and the second leaching residue.

[0010] Based on the same concept, the present invention also provides another method for preparing arsenic trioxide from arsenic sulfide slag, comprising the following steps: Step SB1: Mix the first leaching residue with the arsenic sulfide residue and slurry, then introduce oxygen and catalytically oxidize and leach to obtain the first leaching residue and the first leaching solution; the first leaching residue is a solution containing sulfuric acid, iron salts, and nitrate and / or nitrite. Step SB2: Use the second leaching solution to mix and leach the first leaching residue to obtain the third leaching solution and the third leaching residue; Step SB3: Cool the second leachate to crystallize and obtain arsenic trioxide product and second arsenic precipitation solution; The second leaching solution includes water and / or the second arsenic precipitation solution.

[0011] In one embodiment, in the first leaching solution, the nitrate is provided by nitric acid and / or nitrate; the nitrite is provided by nitrite and / or nitrite; the concentration of the sulfuric acid is 0.2~2 mol / L; the overall concentration of the nitrate and / or nitrite is 0.02~0.5 mol / L; and the overall concentration of the iron salt is 0.1~0.5 mol / L.

[0012] In one embodiment, in step SB1, the first leaching residue solution and arsenic sulfide slag are mixed and slurried at a liquid-to-solid volume ratio of 3 to 10:1, then oxygen is introduced and the oxygen pressure is maintained at 0.1 to 0.5 MPa. The temperature is raised to 70 to 95 °C, and the mixture is stirred to carry out a catalytic oxidation reaction for 1 to 3 hours. The mixture is then filtered to obtain the first leaching solution and the first leaching residue.

[0013] In one embodiment, in step SB2, the second leaching residue solution and the first leaching residue are mixed and slurried at a liquid-to-solid volume ratio of 5 to 20:1, then heated to 60 to 100°C, stirred and reacted for 0.5 to 3 hours, and filtered to obtain a third leaching solution and a third leaching residue.

[0014] In one embodiment, in step SB3, the third leachate is cooled to 0~30°C for crystallization, and the filter residue after filtration is arsenic trioxide product, and the filtrate is the second arsenic precipitation solution.

[0015] To better understand and implement this method, a detailed explanation is provided below. Detailed Implementation

[0016] To address the environmental unfriendliness and high preparation costs of existing technologies, this invention first considers the need for more environmentally friendly treatment reagents. Secondly, if the reagents used to treat arsenic sulfide slag do not require special reduction and recovery treatment, costs can be further reduced. Finally, through analysis and experimentation, this invention provides a leaching solution for catalytic oxidation of arsenic sulfide slag using an auxiliary oxidant, comprising nitrate and / or nitrite, as well as sulfuric acid and iron salts.

[0017] Wherein, the nitrate is provided by nitric acid and / or nitrate, wherein the nitrate is one or more of sodium nitrate, potassium nitrate, magnesium nitrate, and ammonium nitrate; the nitrite is provided by nitrite and / or nitrite, wherein the nitrite is one or more of sodium nitrite, potassium nitrite, magnesium nitrite, and ammonium nitrite; and the iron salt is one or two of ferrous sulfate and ferric sulfate.

[0018] In the leaching solution, the concentration of sulfuric acid is 0.2~2 mol / L; the overall concentration of nitrate and / or nitrite is 0.02~0.5 mol / L; and the overall concentration of iron salt is 0.1~0.5 mol / L. The leaching solution is used to slurry and mix the raw arsenic sulfide slag, and then oxygen is introduced to catalytically oxidize the arsenic sulfide slag, first forming arsenic acid and elemental sulfur.

[0019] The principle of the catalytic oxidation reaction is as follows.

[0020] In the leaching solution, sulfuric acid provides an acidic environment, nitrate and / or nitrite ions act as catalysts, and iron salts act as electron transport substances. Oxygen is introduced into the sealed reactor as an oxidant. The leaching solution provided by this invention can significantly increase the rate of arsenic sulfide oxidation to arsenous acid and elemental sulfur, while lowering the temperature required for arsenic sulfide oxidation, allowing the reaction to proceed below 100°C. This eliminates the need for expensive pressurized reaction equipment in production, greatly reducing production costs. The catalytic oxidation reaction equation is as follows.

[0021] Under acidic conditions, nitrate or nitrite ions oxidize arsenic sulfide to produce arsenic acid, elemental sulfur, nitrogen dioxide, or nitric oxide. As2S3+6NO3 - = 2AsO3 3- +6NO2+3S(1); As2S3+2NO3 - +2H₂O = 2AsO₃ 3- +2NO+3S(2); As2S3+6NO2 - = 2AsO3 3- +6NO+3S(3).

[0022] Under acidic conditions, nitrate ions oxidize arsenic sulfide to produce arsenic acid, elemental sulfur, and nitrogen dioxide. As2S3+10HNO3= 2H3AsO4+10NO2+3S+2H2O(4).

[0023] Under acidic conditions, arsenic acid reacts with arsenic sulfide through oxidation-reduction to produce arsenous acid and elemental sulfur. 3H3AsO4+As2S3+3H2O = 5H3AsO3+3S(5).

[0024] Nitrogen dioxide undergoes a disproportionation reaction with water to produce nitric acid and nitrite. Simultaneously, nitric oxide and nitrogen dioxide can be oxidized by oxygen to reform nitric acid. Thus, nitrate and nitrite ions are regenerated after being oxidized with the assistance of arsenic sulfide, repeatedly playing a role in this process. 3NO2 + 2H2O = 2HNO3 + 2HNO2 (6); 3O2 + 4NO + 2H2O = 4HNO3 (7); O2 + 4NO2 + 2H2O = 4HNO3 (8).

[0025] Iron salts, acting as electron transport substances, undergo the following reactions: As2S3+ 6Fe 3+ +6H₂O = 6Fe 2+ + 2AsO3 3- +3S+12H + (9); 2NO3 - +2Fe 2+ +4H + = 2Fe 3+ +2NO2+2H2O(10); 2NO3 - +6Fe 2+ +8H + =6Fe 3+ +2NO+4H2O(11).

[0026] In this way, the leaching solution as a whole can act as a catalyst, assisting oxygen in converting arsenic sulfide in the arsenic sulfide slag into sulfur and arsenic trioxide. Arsenic acid dissolves in the liquid, and elemental sulfur forms a precipitate; arsenic and sulfur can be separated through solid-liquid separation. Then, taking advantage of the property that the solubility of arsenic acid decreases with lower temperatures, the solution is cooled to saturate the arsenic acid, causing it to precipitate as arsenic trioxide crystals, thus obtaining the arsenic trioxide product. The reaction equation for the precipitation of arsenic trioxide precipitate by saturation of arsenic acid is as follows: 2H3AsO3 = As2O3 + 3H2O (12).

[0027] Based on the above concept, the present invention provides two specific methods for preparing arsenic trioxide from arsenic sulfide slag.

[0028] The following is an overview of one of the methods.

[0029] Step SA1: Use the first leaching solution to catalytically oxidize and leach the arsenic sulfide slag to obtain the first leaching residue and the first leaching solution.

[0030] The first leaching solution is the leaching solution described above used to assist the catalytic oxidation of arsenic sulfide slag with an oxidant—it is a solution comprising sulfuric acid, iron salts, and nitrate and / or nitrite. In the first leaching solution, the nitrate is provided by nitric acid and / or nitrates, wherein the nitrates are one or more of sodium nitrate, potassium nitrate, magnesium nitrate, and ammonium nitrate; the nitrite is provided by nitrite and / or nitrites, wherein the nitrites are one or more of sodium nitrite, potassium nitrite, magnesium nitrite, and ammonium nitrite; the iron salt is one or two of ferrous sulfate and ferric sulfate. The concentration of the sulfuric acid is 0.2~2 mol / L; the overall concentration of the nitrate and / or nitrite is 0.02~0.5 mol / L; and the overall concentration of the iron salt is 0.1~0.5 mol / L.

[0031] The specific procedure for this step is as follows: The first leaching residue solution and arsenic sulfide slag are mixed and slurried at a liquid-to-solid volume-to-mass ratio of (3~10):1 (i.e., the ratio of liquid volume to solid mass, in ml / g). The slurry is then added to a sealed reactor, oxygen is introduced, and the oxygen pressure inside the reactor is maintained at 0.1~0.5 MPa. The temperature is raised to 70-95 ℃, and the mixture is stirred to carry out a catalytic oxidation reaction for 1~5 h, preferably 1~3 h. After the reaction is completed, the mixture is filtered, and the filtrate obtained is the first leaching solution, and the filter residue is the first leaching residue.

[0032] The first leachate contains catalytic substances (sulfuric acid, nitric acid, nitrates and / or nitrites, iron salts) from the first leaching residue solution, arsenic acid, and arsenic acid formed by the further oxidation of a small portion of arsenic acid. The first leaching residue mainly consists of elemental sulfur, arsenic trioxide precipitated from saturated arsenic acid, and a small amount of lead sulfate and residual arsenic sulfide generated from lead impurities in the original arsenic sulfide residue.

[0033] Step SA2: Cool the first leachate to crystallize and obtain arsenic trioxide product and first arsenic precipitation solution.

[0034] The specific procedure is as follows: The first leaching solution from step SA1 is added to a cooling crystallization tank and cooled to 0-30 ℃. The reaction time is controlled at 0.5-5 h. After the reaction is completed, the solution is filtered. The filter residue is arsenic trioxide product, and the filtrate is the first arsenic precipitation solution. The first arsenic precipitation solution contains impurity ions that cannot be precipitated by freezing, such as copper and zinc impurity ions from primary arsenic sulfide slag. These impurity ions are separated from the arsenic trioxide product through filtration.

[0035] In this way, the target product can be prepared using environmentally friendly oxygen. Furthermore, since the catalytic components in the first leaching solution are lost as catalysts with minimal loss, they can be continuously recycled as catalysts after the first arsenic precipitation solution is formed without special regeneration steps, making it greener, more cost-effective, and more efficient.

[0036] Furthermore, this invention takes into account that arsenic acid also exists in the first leachate, and its solubility is much greater than that of arsenous acid, so it remains soluble in the first arsenic precipitation solution even after cooling. It also considers that arsenic in arsenic acid has a high valence, giving it a certain oxidizing property, enabling it to undergo a redox reaction with arsenic sulfide to produce elemental sulfur and arsenic trioxide. Furthermore, it considers that saturated precipitated arsenic trioxide and a small amount of unreacted arsenic sulfide remain in the first leaching residue; simultaneously, the first arsenic precipitation solution still contains the catalysts such as sulfuric acid, nitric acid, nitrate / nitrite, and iron salts added in step S1.

[0037] Therefore, this invention adds step SA3: using the first arsenic precipitation solution to perform secondary catalytic oxidation on the first leaching residue to obtain the second leaching residue and the second leachate. The specific steps are as follows: The first arsenic precipitation solution from step SA2 and the first leaching residue from step SA1 are mixed and slurried at a liquid-to-solid volume ratio of (10~20):1. The slurry is then added to a sealed reactor, oxygen is introduced, and the oxygen pressure inside the reactor is maintained at 0.1~0.5 MPa. The temperature is raised to 60~100 ℃, and the reaction is stirred for 3~5 h. After the reaction is completed, the mixture is filtered to obtain the second leaching solution and the second leaching residue. By increasing the liquid-to-solid volume ratio and extending the reaction time, more complete catalytic oxidation is achieved. At this point, the second leaching residue mainly consists of elemental sulfur, and the second leaching solution mainly contains the components of the first leaching residue solution and dissolved arsenic acid.

[0038] The second leachate is returned to step SA1 as a supplement to the first leaching residue and participates in the catalytic oxidation of the arsenic sulfide slag.

[0039] The following is a specific embodiment of one of the methods.

[0040] Example 1 This embodiment prepares arsenic trioxide from sulfide slag (the main components are 37.72% As, 22.03% S, 0.14% Cu, 0.16% Pb and 0.35% Zn by weight) by the following steps.

[0041] Step SA1: Use the first leaching solution to catalytically oxidize and leach the arsenic sulfide slag to obtain the first leaching residue and the first leaching solution.

[0042] Arsenic sulfide slag, sulfuric acid, potassium nitrate, ferric sulfate, and water were mixed to prepare a first leaching solution with a sulfuric acid concentration of 1 mol / L, a potassium nitrate concentration of 0.1 mol / L, and a ferric sulfate concentration of 0.15 mol / L. This solution was then mixed and slurried at a liquid-to-solid volume ratio of 5:1. The slurry was then added to a sealed reactor, oxygen was introduced, and the oxygen pressure inside the reactor was maintained at 0.5 MPa. The temperature was raised to 95 °C, and the reaction was stirred for 1 h. After the reaction, the mixture was filtered to obtain the first leaching solution and the first leaching residue. The arsenic oxidation rate of this step was measured and calculated to be 96.47%.

[0043] The arsenic oxidation rate is calculated using the following formula.

[0044] Arsenic oxidation rate: ; In the formula: —Arsenic oxidation rate, in % m1 — Mass of arsenic sulfide slag, in grams; m2 — Mass of the first leaching residue, in grams; —The content of elemental arsenic in the form of arsenic sulfide in arsenic sulfide slag, in % —The content of elemental arsenic in the form of arsenic sulfide in the first leaching residue, in % . The methods for detecting arsenic sulfide content in both solids and liquids are all conventional methods.

[0045] Step SA2: The first leachate was added to a cooling crystallization tank and cooled to 10 °C. The reaction time was controlled at 3 h. After the reaction was completed, the mixture was filtered. The filter residue was arsenic trioxide product, and the filtrate was the first arsenic precipitation solution. The purity of the obtained arsenic trioxide product was 96.17% as determined by conventional methods.

[0046] Step SA3: Use the first arsenic precipitation solution to perform secondary catalytic oxidation on the first leaching residue to obtain the second leaching residue and the second leaching solution.

[0047] The first arsenic precipitation solution and the first leaching residue were mixed and slurried at a liquid-to-solid volume ratio of 10:1. The slurry was then added to a sealed reactor, oxygen was introduced, and the oxygen pressure inside the reactor was maintained at 0.5 MPa. The temperature was raised to 90 °C, and the reaction was stirred for 5 h. After the reaction was completed, the mixture was filtered to obtain the second leaching solution and the second leaching residue. The second leaching solution was returned to step SA1 as a supplement to the first leaching residue solution for continued use. The residual elemental arsenic content in the second leaching residue was 1.82%.

[0048] Example 2 This embodiment prepares arsenic trioxide from sulfide slag (the main components are 47.88% As, 28.25% S, 0.05% Cu, 0.12% Pb and 0.16% Zn by weight) by the following steps.

[0049] Step SA1: Use the first leaching solution to catalytically oxidize and leach the arsenic sulfide slag to obtain the first leaching residue and the first leaching solution.

[0050] Arsenic sulfide slag, sulfuric acid, nitric acid, ferrous sulfate, and water were mixed to prepare a first leaching solution with sulfuric acid concentration of 0.2 mol / L, nitric acid concentration of 0.5 mol / L, and ferrous sulfate concentration of 0.5 mol / L. The solution was mixed with arsenic sulfide slag at a liquid-to-solid volume ratio of 3:1 and slurried. The slurry was then added to a sealed reactor, oxygen was introduced, and the oxygen pressure inside the reactor was maintained at 0.3 MPa. The temperature was raised to 70 °C, and the reaction was stirred for 3 h. After the reaction was completed, the mixture was filtered to obtain the first leaching solution and the first leaching residue. The arsenic oxidation rate of this step was measured and calculated to be 95.88%.

[0051] Step SA2: The first leachate was added to a cooling crystallization tank, cooled to 2 °C, and the reaction time was controlled at 5 h. After the reaction was completed, the mixture was filtered. The filter residue was arsenic trioxide product, and the filtrate was the first arsenic precipitation solution. The purity of the obtained arsenic trioxide product was 96.34% as determined by conventional methods.

[0052] Step SA3: Use the first arsenic precipitation solution to perform secondary catalytic oxidation on the first leaching residue to obtain the second leaching residue and the second leaching solution.

[0053] The first arsenic precipitation solution and the first leaching residue were mixed and slurried at a liquid-to-solid volume ratio of 20:1. The slurry was then added to a sealed reactor, oxygen was introduced, and the oxygen pressure inside the reactor was maintained at 0.3 MPa. The temperature was raised to 80 °C, and the reaction was stirred for 4 hours. After the reaction was completed, the mixture was filtered to obtain the second leaching solution and the second leaching residue. The second leaching solution was returned to step SA1 as a supplement to the first leaching residue solution for continued use. The residual elemental arsenic content in the second leaching residue was 1.79%.

[0054] Example 3 This embodiment prepares arsenic trioxide from sulfide slag (the main components are 42.29% As, 27.14% S, 0.12% Cu, 0.19% Pb and 0.05% Zn by weight) by the following steps.

[0055] Step SA1: Use the first leaching solution to catalytically oxidize and leach the arsenic sulfide slag to obtain the first leaching residue and the first leaching solution.

[0056] Arsenic sulfide slag, sulfuric acid, sodium nitrite, ferric sulfate, and water were mixed to prepare a first leaching solution with a sulfuric acid concentration of 2 mol / L, a sodium nitrite concentration of 0.3 mol / L, and a ferric sulfate concentration of 0.3 mol / L. The solution was mixed with arsenic sulfide slag at a liquid-to-solid volume ratio of 10:1 and slurried. The slurry was then added to a sealed reactor, oxygen was introduced, and the oxygen pressure inside the reactor was maintained at 0.1 MPa. The temperature was raised to 95 °C, and the reaction was stirred for 5 h. After the reaction was completed, the mixture was filtered to obtain the first leaching solution and the first leaching residue. The arsenic oxidation rate of this step was measured and calculated to be 97.21%.

[0057] Step SA2: The first leachate was added to a cooling crystallization tank and cooled to 25 °C. The reaction time was controlled at 1 h. After the reaction was completed, the mixture was filtered. The filter residue was arsenic trioxide product, and the filtrate was the first arsenic precipitation solution. The purity of the obtained arsenic trioxide product was 97.04% as determined by conventional methods.

[0058] Step SA3: Use the first arsenic precipitation solution to perform secondary catalytic oxidation on the first leaching residue to obtain the second leaching residue and the second leaching solution.

[0059] The first arsenic precipitation solution and the first leaching residue were mixed and slurried at a liquid-to-solid volume ratio of 15:1. The slurry was then added to a sealed reactor, oxygen was introduced, and the oxygen pressure inside the reactor was maintained at 0.2 MPa. The temperature was raised to 95 °C, and the reaction was stirred for 3 hours. After the reaction was completed, the mixture was filtered to obtain the second leaching solution and the second leaching residue. The second leaching solution was returned to step SA1 as a supplement to the first leaching residue solution for continued use. The residual elemental arsenic content in the second leaching residue was 2.12%.

[0060] The following is an overview of the second method.

[0061] Step SB1: Catalytically oxidize and leach the arsenic sulfide slag using the first leaching solution to obtain the first leaching residue and the first leaching solution. The first leaching solution and the specific steps are the same as in step SA1, and will not be repeated here.

[0062] Step SB2: Use the second leaching solution to mix and leach the first leaching residue to obtain the third leaching solution and the third leaching residue.

[0063] The second leaching residue solution is water and / or the second arsenic precipitation solution from step SB3. Since the first leaching residue already contains a large amount of precipitated arsenic oxide, this step utilizes the property that arsenic trioxide is soluble in water to form arsenous acid and that its solubility increases rapidly with increasing temperature. Warm water at 60~100℃ is used to leach and dissolve the arsenic trioxide in the first leaching residue into the liquid phase (third leaching solution). Other substances in the first leaching residue remain in the third leaching residue and can be separated by filtration.

[0064] The specific procedure for this step is as follows: the second leaching residue solution and the first leaching residue are mixed and slurried at a liquid-to-solid volume ratio of (5~20):1. The slurried material is then added to the reaction vessel, heated to 60~100 ℃, and stirred for 0.5~3 h. After the reaction is completed, the mixture is filtered, and the filtrate obtained is the third leaching solution, and the filter residue is the third leaching residue.

[0065] Step SB3: Cool the third leachate to crystallize and obtain arsenic trioxide product.

[0066] Specifically, the third leaching solution from step SB2 is added to a cooling crystallization tank and cooled to 0-30 °C. The reaction time is controlled at 0.5-5 h. After crystallization, the solution is filtered, and the filter residue is arsenic trioxide product, while the filtrate is the second arsenic precipitation solution. The second arsenic precipitation solution mainly consists of water and uncrystallized arsenic trioxide / arsenous acid, so it can be returned to step SB2 as the second leaching residue solution to continue treating the first leaching residue.

[0067] In addition, the first leachate can be returned to step SB1 as the first leaching residue for recycling.

[0068] The following is a specific implementation of the second scheme.

[0069] Example 4 This embodiment prepares arsenic trioxide from arsenic sulfide slag (the main components are 41.25% As, 24.31% S, 0.36% Cu, 0.21% Pb and 0.11% Zn by weight) by the following steps.

[0070] Step SB1: Use the first leaching solution to catalytically oxidize and leach the arsenic sulfide slag to obtain the first leaching residue.

[0071] Arsenic sulfide slag, sulfuric acid, nitric acid, ferrous sulfate, and water were mixed to prepare a first leaching solution with a sulfuric acid concentration of 0.5 mol / L, a nitric acid concentration of 0.2 mol / L, and a ferrous sulfate concentration of 0.3 mol / L. The solution was mixed with arsenic sulfide slag at a liquid-to-solid volume ratio of 3:1 and slurried. The slurry was then added to a sealed reactor, oxygen was introduced, and the oxygen pressure inside the reactor was maintained at 0.3 MPa. The temperature was raised to 95 °C, and the reaction was stirred for 2 h. After the reaction was completed, the mixture was filtered to obtain the first leaching solution and the first leaching residue. The arsenic oxidation rate of this step was measured and calculated to be 98.35%.

[0072] The arsenic oxidation rate is calculated using the following formula.

[0073] Arsenic oxidation rate: ; In the formula: —Arsenic oxidation rate, in % m1 — Mass of arsenic sulfide slag, in grams; m2 — Mass of the first leaching residue, in grams; —The content of elemental arsenic in the form of arsenic sulfide in arsenic sulfide slag, in % —The content of elemental arsenic in the form of arsenic sulfide in the first leaching residue, in % . The methods for detecting arsenic sulfide content in both solids and liquids are all conventional methods.

[0074] Step SB2: Use the second leaching solution to mix and leach the first leaching residue to obtain the third leaching solution and the third leaching residue.

[0075] The first leaching residue and water (the second leaching solution) were mixed and slurried at a liquid-to-solid volume ratio of 10:1. The slurry was then added to a reaction vessel, heated to 90 °C, and stirred for 0.5 h. After the reaction, the mixture was filtered to obtain a third leaching solution containing arsenic trioxide and a third leaching residue containing sulfur. Using conventional methods, the arsenic trioxide leaching rate of the third leaching solution was 99.15%, which is the ratio of the total arsenic in the second leaching solution to the total arsenic in the first leaching residue. The residual elemental arsenic content in the third leaching residue was 2.41%.

[0076] Step SB3: Cool the third leachate to crystallize and obtain arsenic trioxide product.

[0077] The third leaching solution containing arsenic trioxide was added to a cooling crystallization tank, cooled to 5 °C, and the reaction time was controlled at 2 h. After the reaction was completed, the solution was filtered. The filtrate was the second arsenic precipitation solution, and the filter residue was the arsenic trioxide product. The purity of the obtained arsenic trioxide product was 98.58% according to conventional methods. The second arsenic precipitation solution can be returned to step SB2 as a supplement to the second leaching residue solution for continued use.

[0078] Example 5 This embodiment prepares arsenic trioxide from sulfide slag (the main components are 35.47% As, 20.15% S, 0.56% Cu, 0.28% Pb and 0.44% Zn by weight) by the following steps.

[0079] Step SB1: Use the first leaching solution to catalytically oxidize and leach the arsenic sulfide slag to obtain a first leaching residue containing elemental sulfur and arsenic trioxide.

[0080] Arsenic sulfide slag, sulfuric acid, nitric acid, ferric sulfate, and water were mixed to prepare a first leaching solution with a sulfuric acid concentration of 2 mol / L, a nitric acid concentration of 0.5 mol / L, and a ferric sulfate concentration of 0.1 mol / L. The first leaching solution and arsenic sulfide slag were mixed and slurried at a liquid-to-solid volume ratio of 10:1. The slurry was then added to a sealed reactor, oxygen was introduced, and the oxygen pressure inside the reactor was maintained at 0.1 MPa. The temperature was raised to 70 °C, and the reaction was stirred for 3 hours. After the reaction, the mixture was filtered to obtain the first leaching solution and the first leaching residue containing arsenic trioxide. The arsenic oxidation rate in this step was measured to be 98.89%.

[0081] Step SB2: Use the second leaching solution to mix and leach the first leaching residue to obtain the third leaching solution and the third leaching residue.

[0082] The first leaching residue containing arsenic trioxide was mixed with water (the second leaching residue solution) at a liquid-to-solid volume ratio of 20:1 and slurried. The slurry was then added to a reaction vessel, heated to 60 °C, and stirred for 2 h. After the reaction was completed, the mixture was filtered to obtain the second leaching solution and the third leaching residue. The arsenic trioxide leaching rate of the third leaching solution was 99.08%, and the residual arsenic content in the third leaching residue was 2.96%.

[0083] Step SB3: Cool the third leachate to crystallize and obtain arsenic trioxide product.

[0084] The third leaching solution was added to a cooling crystallization tank and cooled to 10 °C. The reaction time was controlled at 5 h. After the reaction was completed, the solution was filtered. The filtrate was the second arsenic precipitation solution, and the filter residue was arsenic trioxide product with a purity of 98.84%. The second arsenic precipitation solution can be returned to step SB2 as a supplement to the second leaching residue solution for continued use.

[0085] Example 6 This embodiment prepares arsenic trioxide from sulfide slag (the main components are 27.48% As, 12.55% S, 2.72% Cu, 0.38% Pb and 0.42% Zn by weight) by the following steps.

[0086] Step SB1: Use the first leaching solution to catalytically oxidize and leach the arsenic sulfide slag to obtain a first leaching residue containing elemental sulfur and arsenic trioxide.

[0087] Arsenic sulfide slag, sulfuric acid, nitric acid, nitrate or nitrite, iron salt, and water were mixed to prepare a first leaching solution with a sulfuric acid concentration of 0.2 mol / L, a sodium nitrate concentration of 0.04 mol / L, and a ferrous sulfate concentration of 0.3 mol / L. The first leaching solution and arsenic sulfide slag were mixed and slurried at a liquid-to-solid volume ratio of 5:1. The slurry was then added to a sealed reactor, oxygen was introduced, and the oxygen pressure inside the reactor was maintained at 0.5 MPa. The temperature was raised to 80 °C, and the reaction was stirred for 3 hours. After the reaction was completed, the mixture was filtered to obtain the first leaching solution and the first leaching residue, with an arsenic oxidation rate of 98.75%.

[0088] Step SB2: Use the second leaching solution to mix and leach the first leaching residue to obtain the second leaching solution and the second leaching residue.

[0089] The arsenic trioxide leaching residue was mixed with water (second leaching residue solution) at a liquid-to-solid volume ratio of 6:1 and slurried. The slurry was then added to a reaction vessel, heated to 90 °C, and stirred for 3 h. After the reaction was completed, the mixture was filtered to obtain a third leaching solution containing arsenic trioxide and a third leaching residue containing sulfur. The arsenic trioxide leaching rate was 99.15%, and the residual arsenic content of the sulfur-containing filter residue was 2.41%.

[0090] Step SB3: Cool the second leachate to crystallize and obtain arsenic trioxide product.

[0091] The third leaching solution containing arsenic trioxide was added to a cooling crystallization tank and cooled to 20 °C. The reaction time was controlled at 0.5 h. After the reaction was completed, the solution was filtered. The filtrate was the second arsenic precipitation solution, and the filter residue was the arsenic trioxide product with a purity of 98.74%. The second arsenic precipitation solution could be returned to step SB2 as a supplement to the second leaching residue solution for continued use.

[0092] Example 7 This embodiment prepares arsenic trioxide from sulfide slag (whose main components, by weight percentage, are 44.54% As, 26.72% S, 0.18% Cu, 0.42% Pb, and 0.23% Zn) by the following steps: Step SB1: Use the first leaching solution to catalytically oxidize and leach the arsenic sulfide slag to obtain a first leaching residue containing elemental sulfur and arsenic trioxide.

[0093] Arsenic sulfide slag, sulfuric acid, nitric acid, nitrate or nitrite, iron salt, and water were mixed to prepare a first leaching solution with a sulfuric acid concentration of 1 mol / L, a potassium nitrite concentration of 0.1 mol / L, and a ferric sulfate concentration of 0.5 mol / L. The first leaching solution and arsenic sulfide slag were mixed and slurried at a liquid-to-solid volume ratio of 7:1. The slurry was then added to a sealed reactor, oxygen was introduced, and the oxygen pressure inside the reactor was maintained at 0.2 MPa. The temperature was raised to 95 °C, and the reaction was stirred for 1 h. After the reaction was completed, the mixture was filtered to obtain the first leaching solution and the first leaching residue containing arsenic trioxide, with an arsenic oxidation rate of 98.03%.

[0094] Step SB2: Use the second leaching solution to mix and leach the first leaching residue to obtain the second leaching solution and the second leaching residue.

[0095] Arsenic trioxide leaching residue was mixed with water (second leaching residue solution) at a liquid-to-solid volume ratio of 15:1 and slurried. The slurry was then added to a reaction vessel, heated to 80 °C, and stirred for 1 h. After the reaction was completed, the mixture was filtered to obtain third leaching solution and third leaching residue. The arsenic trioxide leaching rate in the third leaching solution was 99.58%, and the residual arsenic content in the sulfur-containing third leaching residue was 2.95%.

[0096] Step SB3: Cool the third leachate to crystallize and obtain arsenic trioxide product.

[0097] The second leaching solution containing arsenic trioxide was added to a cooling crystallization tank and cooled to 30 °C. The reaction time was controlled at 3 hours. After the reaction was completed, the solution was filtered. The filtrate was the second arsenic precipitation solution, and the filter residue was the arsenic trioxide product with a purity of 98.66%. The second arsenic precipitation solution can be returned to step SB2 as a supplement to the second leaching residue solution for continued use.

[0098] The present invention has the following advantages: (1) No wastewater or waste residue is generated, resulting in good environmental benefits. The solution is recycled in the process flow, with no wastewater discharge, and two products, arsenic trioxide and elemental sulfur, are obtained without generating waste residue.

[0099] (2) The first leaching residue as a catalyst is regenerable, with low reagent consumption and low production cost. Nitric acid, nitrate or nitrite as catalysts are regenerable in the process flow, with virtually no ammonia nitrogen waste gas emissions. Sulfuric acid only provides an acidic environment and does not participate in the reaction. Iron salts only serve as electron transfer substances and are basically not consumed.

[0100] (3) The reaction temperature is low and the equipment is simple. The catalytic oxidation temperature of arsenic sulfide slag is below 100℃, and production can be achieved without expensive pressurization equipment.

[0101] (4) High product purity. Two products were obtained: arsenic trioxide and elemental sulfur. The arsenic trioxide product had high purity, while the elemental sulfur contained less than 3% arsenic.

[0102] This invention effectively solves the problems of complex processes, difficult wastewater treatment, and high production costs in the existing resource utilization process of arsenic sulfide slag. This invention is applicable to the preparation of arsenic trioxide from arsenic sulfide slag, and realizes the green, efficient, and low-cost preparation of arsenic trioxide.

[0103] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of this application. The singular forms “a,” “the,” and “the” used in the embodiments and claims of this application are also intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that, unless otherwise stated, “a plurality” means two or more; the terms “first,” “second,” “third,” etc., are used only to distinguish and not to describe a particular order or sequence, nor should they be construed as indicating or implying relative importance. The term “and / or” as used herein refers to and includes any or all possible combinations of one or more associated listed items. In the description of this application, those skilled in the art will understand the specific meaning of the above terms in this application according to the specific circumstances.

[0104] The above-described embodiments are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing arsenic trioxide from arsenic sulfide slag, characterized in that, Includes the following steps: Step SA1: Mix the first leaching residue with the arsenic sulfide residue and slurry, then introduce oxygen and catalytically oxidize and leach to obtain the first leaching residue and the first leaching solution; the first leaching residue is a solution containing sulfuric acid, iron salts, and nitrate and / or nitrite. Step SA2: Cool the first leachate to crystallize and obtain arsenic trioxide product and first arsenic precipitation solution.

2. The method according to claim 1, characterized in that, In the first leaching solution, the nitrate is provided by nitric acid and / or nitrate; the nitrite is provided by nitrite and / or nitrite. The concentration of the sulfuric acid is 0.2~2 mol / L; the overall concentration of the nitrate and / or nitrite is 0.02~0.5 mol / L; and the overall concentration of the iron salt is 0.1~0.5 mol / L.

3. The method according to claim 2, characterized in that, It also includes step SA3: using the first arsenic precipitation solution to perform secondary catalytic oxidation on the first leaching residue to obtain a second leaching residue and a second leaching solution; the second leaching solution is returned to step SA1 as a supplement to the first leaching residue solution to participate in the catalytic oxidation of arsenic sulfide residue.

4. The method according to claim 3, characterized in that, In step SA1, the first leaching residue solution and arsenic sulfide slag are mixed and slurried at a liquid-to-solid volume ratio of 3 to 10:

1. Then, oxygen is introduced and the oxygen pressure is maintained at 0.1 to 0.5 MPa. The temperature is raised to 70 to 95 °C and stirred to carry out a catalytic oxidation reaction for 1 to 3 hours. After the reaction is completed, the first leaching solution and the first leaching residue are obtained by filtration.

5. The method according to claim 4, characterized in that, In step SA3, the first arsenic precipitation solution from step SA2 and the first leaching residue from step SA1 are mixed and slurried at a liquid-to-solid volume ratio of 10-20:

1. The slurry is then added to a sealed reactor, oxygen is introduced, the oxygen pressure inside the reactor is maintained at 0.1-0.5 MPa, the temperature is raised to 60-100℃, and the reaction is stirred for 3-5 hours. After the reaction is completed, the mixture is filtered to obtain the second leaching solution and the second leaching residue.

6. A method for preparing arsenic trioxide from arsenic sulfide slag, characterized in that, Includes the following steps: Step SB1: Mix the first leaching residue with the arsenic sulfide residue and slurry, then introduce oxygen and catalytically oxidize and leach to obtain the first leaching residue and the first leaching solution; the first leaching residue is a solution containing sulfuric acid, iron salts, and nitrate and / or nitrite. Step SB2: Use the second leaching solution to mix and leach the first leaching residue to obtain the third leaching solution and the third leaching residue; Step SB3: Cool the second leachate to crystallize and obtain arsenic trioxide product and second arsenic precipitation solution; The second leaching solution includes water and / or the second arsenic precipitation solution.

7. The method according to claim 6, characterized in that, In the first leaching solution, the nitrate is provided by nitric acid and / or nitrate; the nitrite is provided by nitrite and / or nitrite; the concentration of the sulfuric acid is 0.2~2 mol / L; the overall concentration of the nitrate and / or nitrite is 0.02~0.5 mol / L; and the overall concentration of the iron salt is 0.1~0.5 mol / L.

8. The method according to claim 7, characterized in that, In step SB1, the first leaching residue solution and arsenic sulfide slag are mixed and slurried at a liquid-to-solid volume ratio of 3 to 10:

1. Then, oxygen is introduced and the oxygen pressure is maintained at 0.1 to 0.5 MPa. The temperature is raised to 70 to 95 °C, and the mixture is stirred to carry out a catalytic oxidation reaction for 1 to 3 hours. The mixture is then filtered to obtain the first leaching solution and the first leaching residue.

9. The method according to claim 8, characterized in that, In step SB2, the second leaching residue solution and the first leaching residue are mixed and slurried at a liquid-to-solid volume ratio of 5 to 20:1, then heated to 60 to 100°C, stirred and reacted for 0.5 to 3 hours, and filtered to obtain the third leaching solution and the third leaching residue.

10. The method according to claim 9, characterized in that, In step SB3, the third leachate is cooled to 0~30℃ for crystallization. After filtration, the filter residue is arsenic trioxide product, and the filtrate is the second arsenic precipitation solution.