A process for extracting sulfur and producing arsenic from copper smelting arsenic-containing slag

Abstract

This invention discloses a process for sulfur extraction and arsenic production from arsenic-containing slag in copper smelting, relating to the field of non-ferrous metal smelting technology. The process includes: wet grinding and pulping of the arsenic-containing slag; three-stage acid leaching of the slurry under atmospheric pressure: the first stage involves iron removal through acidification; the second stage introduces oxygen-containing microbubbles to oxidize trivalent arsenic to pentavalent arsenic; and the third stage introduces a persulfate and hydrogen peroxide complex system for deep oxidation of insoluble sulfides, yielding a leachate containing arsenic and valuable metals, and a sulfur-containing leaching slag; the sulfur-containing leaching slag is first subjected to anaerobic heating and sublimation to extract sulfur, and then heated under a reducing atmosphere with a carbonaceous reducing agent to extract residual sulfur; the leachate is sent to subsequent processes for the recovery of arsenic and valuable metals. This invention utilizes a dual-oxidant stepwise enhancement of arsenic leaching ("microbubble oxidation + persulfate free radical oxidation") and a two-step stepwise extraction of sulfur directly from the slag ("anaerobic sublimation + carbothermic reduction"), achieving efficient arsenic leaching and resource recovery of sulfur under atmospheric pressure wet conditions, forming a closed-loop process for the synergistic recovery of arsenic, sulfur, and valuable metals.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal smelting technology, specifically a process for sulfur extraction and arsenic production from arsenic-containing slag in copper smelting. Background Technology

[0002] Arsenic-containing slag generated during copper smelting is a typical complex hazardous waste characterized by high arsenic, high sulfur, and multiple metals. This type of slag has a high arsenic content, mainly existing in the forms of arsenic sulfide and ferric arsenate, and is also associated with valuable metals such as copper, rhenium, molybdenum, and cadmium. Sulfur content is also generally high. Direct stockpiling or simple landfilling of this waste not only occupies a large amount of land resources, but the arsenic and heavy metal ions within it will also migrate and leach with rainwater, causing serious pollution to surrounding soil and water bodies.

[0003] Currently, the main technologies for treating arsenic-containing waste residue include pyrometallurgical roasting and volatilization of arsenic, and wet acid / alkali leaching for arsenic removal. While pyrometallurgical processes have a large processing capacity, they suffer from high energy consumption, difficulty in recovering As2O3 from flue gas, and the emission of sulfur resources primarily as SO2, making it difficult to meet increasingly stringent environmental protection requirements. Although wet processes can achieve selective leaching of arsenic to some extent, existing wet processes generally suffer from the following technical drawbacks: First, existing wet leaching methods mostly use a single oxidant system, such as hydrogen peroxide, sodium hypochlorite, or air oxidation alone. The oxidation capacity is limited, making it difficult to simultaneously achieve deep oxidation of arsenic and effective dissociation of insoluble rhenium sulfide, resulting in a low leaching rate of rare and precious metals such as rhenium.

[0004] Secondly, existing processes do not pay enough attention to sulfur resource recovery. During the leaching process, sulfur is either oxidized into sulfuric acid and enters the liquid phase, increasing the load on subsequent treatments, or it remains in the leaching residue as sulfides and is discarded. The few technologies involving sulfur recovery mainly capture SO2 from the gas phase and then perform catalytic reduction, with few effective means to directly recover elemental sulfur from the solid phase leaching residue.

[0005] Third, existing processes mostly focus on a single objective—either arsenic removal, copper extraction, or recovery of rare and precious metals—lacking a systematic solution that integrates arsenic valence state regulation, sulfur resource recovery, and multi-metal synergistic extraction into a closed-loop process.

[0006] Therefore, there is an urgent need to develop a closed-loop process that can efficiently extract arsenic under normal pressure, directly recover elemental sulfur from leaching residue, and also take into account the deep leaching of rare and precious metals such as rhenium.

[0007] Based on this, a process for sulfur extraction and arsenic production from arsenic-containing slag in copper smelting is provided, which can eliminate the drawbacks of existing equipment. Summary of the Invention

[0008] The purpose of this invention is to provide a process for sulfur extraction and arsenic production from arsenic-containing slag in copper smelting, so as to solve the problems in the background art.

[0009] To achieve the above objectives, the present invention provides the following technical solution: A process for sulfur extraction and arsenic production from arsenic-containing slag in copper smelting includes the following steps: S1: The arsenic-containing slag raw material is pretreated by wet grinding to obtain a slurry of a predetermined fineness; S2: The slurry obtained in step S1 is subjected to three stages of acid leaching under normal pressure, wherein... The first stage of acid leaching dissolves soluble iron under acidic conditions and causes it to hydrolyze and precipitate, thus achieving the initial separation of iron. The second stage of acid leaching introduces oxygen-containing gas microbubbles as the primary oxidant, oxidizing the trivalent arsenic in the leachate to pentavalent arsenic. The third stage of acid leaching introduces a compound system of persulfate and hydrogen peroxide as a second oxidant. The free radicals generated by transition metal catalysis are used to deeply oxidize and leach insoluble sulfides, resulting in a leachate containing pentavalent arsenic and valuable metals, and a sulfur-containing leachate residue. S3: The sulfur-containing leaching residue obtained in step S2 is subjected to two-stage thermal separation treatment: first, under anaerobic conditions, the elemental sulfur is heated to sublimate and volatilize and then condensed and recovered; then, under a reducing atmosphere, a carbonaceous reducing agent is added and heated to volatilize the sulfur in the residual sulfide in the form of elemental sulfur and condense and recover it, thus obtaining the residue after sulfur extraction. S4: The leachate containing pentavalent arsenic and valuable metals obtained in step S2 is further processed to recover arsenic and valuable metals.

[0010] Based on the above technical solutions, the present invention also provides the following optional technical solutions: In one alternative: the proportion of slurry with a particle size of less than or equal to 80 mesh after wet grinding pretreatment in step S1 is not less than 90%.

[0011] In one alternative approach: the conditions for the first stage of acid leaching in step S2 are: initial sulfuric acid concentration of 50-80 g / L, and the final pH value of the reaction controlled at 1.8-2.6.

[0012] In one alternative: the oxygen-containing gas microbubbles in the second stage of acid leaching in step S2 are ozone microbubbles, which are introduced by generating microbubbles with a diameter of 10-150μm through a microbubble generator, and the reaction temperature is controlled at 70-90℃.

[0013] In one alternative: the persulfate used in the third stage of acid leaching in step S2 is ammonium persulfate or sodium persulfate, and the molar ratio of persulfate to hydrogen peroxide is 1:1.2-1:1.5.

[0014] In one alternative: the heating temperature under anaerobic conditions in step S3 is 400-450℃, and the holding time is 1.5-3h.

[0015] In one alternative: in step S3, the carbonaceous reducing agent is added under a reducing atmosphere and heated to a temperature of 420-480℃. The carbonaceous reducing agent is anthracite powder, and the addition ratio is 5-15% of the slag mass.

[0016] In one alternative: the residue after sulfur extraction in step S3 is returned to the third stage of acid leaching in step S2 for secondary leaching.

[0017] In one alternative: between the second and third acid leaching stages in step S2, there is also a step of returning the unreacted solid material to the first or second acid leaching stage for cyclic leaching.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention employs a dual-oxidant leaching system combining microbubble ozone and persulfate. Microbubble technology significantly improves the mass transfer efficiency and utilization rate of ozone in the liquid phase, thereby efficiently oxidizing trivalent arsenic to pentavalent arsenic, which then dissolves stably in the leachate as arsenate. Persulfate, catalyzed by transition metal ions such as copper and iron in the leachate, generates highly oxidizing sulfate radicals, which effectively disrupt the stable structure of insoluble rhenium sulfide, oxidizing it to soluble rhenium salts. The two oxidants act stepwise and synergistically under their respective optimized conditions, simultaneously achieving the directional conversion of arsenic to its higher valence state and the deep leaching of rhenium.

[0019] This invention pioneers a two-step, cascaded sulfur recovery process for leaching residue: "anaerobic heating sublimation – carbothermic reduction." First, under anaerobic conditions, the sublimation properties of elemental sulfur are utilized to directly recover the elemental sulfur already generated in the residue, preventing its oxidation to SO2 and subsequent secondary pollution and waste. Then, under a weakly reducing atmosphere, a carbonaceous reducing agent is added to reduce the residual sulfides in the residue back to elemental sulfur for volatilization and recovery. This two-step cascaded operation significantly improves the overall sulfur recovery rate, and the recovered elemental sulfur has high purity, allowing it to be directly sold as a chemical raw material.

[0020] This invention constructs a closed-loop wet process centered on sulfur resource recovery. The entire process is based on wet leaching, with arsenic valence state control and initial iron separation achieved during the leaching stage. In the slag treatment stage, elemental sulfur is recovered in stages through physical sublimation and chemical reduction. In the liquid phase treatment stage, valuable metals such as copper, rhenium, molybdenum, and cadmium are further recovered. Any unrecovered residue is returned to the leaching process for recycling. The entire process does not involve high-temperature smelting or energy-intensive pyrometallurgical equipment, thus balancing comprehensive resource utilization with environmental risk control. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0023] In one embodiment, such as Figure 1 As shown, a process for sulfur extraction and arsenic production from arsenic-containing slag in copper smelting includes the following steps: S1: wet grinding pretreatment of the arsenic-containing slag raw material to obtain a slurry of a predetermined fineness; S2: The slurry obtained in step S1 is subjected to three stages of acid leaching under normal pressure, wherein... The first stage of acid leaching dissolves soluble iron under acidic conditions and causes it to hydrolyze and precipitate, thus achieving the initial separation of iron. The second stage of acid leaching introduces oxygen-containing gas microbubbles as the primary oxidant, oxidizing the trivalent arsenic in the leachate to pentavalent arsenic. The third stage of acid leaching introduces a compound system of persulfate and hydrogen peroxide as a second oxidant. The free radicals generated by transition metal catalysis are used to deeply oxidize and leach insoluble sulfides, resulting in a leachate containing pentavalent arsenic and valuable metals, and a sulfur-containing leachate residue. S3: The sulfur-containing leaching residue obtained in step S2 is subjected to two-stage thermal separation treatment: first, under anaerobic conditions, the elemental sulfur is heated to sublimate and volatilize and then condensed and recovered; then, under a reducing atmosphere, a carbonaceous reducing agent is added and heated to volatilize the sulfur in the residual sulfide in the form of elemental sulfur and condense and recover it, thus obtaining the residue after sulfur extraction. S4: The leachate containing pentavalent arsenic and valuable metals obtained in step S2 is further processed to recover arsenic and valuable metals.

[0024] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0025] Example 1: The arsenic-containing flue dust produced by copper smelters has the following main chemical composition: As 8.5%, S 12.3%, Cu 3.2%, Fe 18.6%, Re 0.008%, Mo 0.15%, Cd 0.06%, with the balance being gangue components such as silicon and aluminum oxides. The raw material has a particle size of 10-50 mm and a moisture content of approximately 12%.

[0026] S1: Wet grinding pretreatment: Add water to the arsenic-containing slag raw material to adjust the moisture content to ≤65%, and grind it using wet grinding equipment. Control the grinding fineness to ensure that the proportion of particles less than or equal to 80 mesh (178μm) is ≥90% (i.e., D90≤178μm) to obtain slurry.

[0027] S2: Three-stage acid leaching treatment: The first stage of acid leaching involves feeding the slurry obtained in step S1 into the first-stage acid leaching reaction tank. Sulfuric acid is added to maintain an initial concentration of 50-80 g / L, with a liquid-to-solid ratio of 4-10:1 (mass ratio). The reaction is carried out at room temperature (25-30℃) with stirring for approximately 4 hours, until the final pH value is stabilized at 1.8-2.6. During this stage, arsenic sulfides (such as As2S3) initially dissolve, and iron ions gradually hydrolyze to form ferric hydroxide precipitate under pH control. The iron removal rate can reach 60%-75%, while the co-precipitation losses of copper, cadmium, and molybdenum are controlled to ≤0.5% and ≤0.2%, respectively. After filtration and separation, the iron-containing filter cake is sent to the slag treatment process, while the filtrate containing arsenic and valuable metals enters the second-stage acid leaching.

[0028] The second stage of acid leaching involves transferring the filtrate from the first stage into the second stage reaction tank, maintaining a liquid-to-solid ratio of approximately 6:1. Ozone microbubbles, with a diameter of 10-150 μm and an ozone flow rate of approximately 400 mL / min, are introduced as the oxidant via a microbubble generator. The reaction temperature is controlled at 80℃, the stirring speed at 300-400 r / min, and the reaction time is approximately 2 hours. Under the strong oxidizing effect of the microbubble ozone, trivalent arsenic is efficiently oxidized to pentavalent arsenic (arsenate), increasing the leaching rates of copper, molybdenum, and rhenium to ≥98%, ≥97%, and ≥95%, respectively. A small amount of unreacted solid material can be returned to the first stage for recycling.

[0029] The third stage of acid leaching involves transferring the leachate from the second stage into a third-stage acid leaching reaction tank. A compound oxidant consisting of ammonium persulfate and hydrogen peroxide (25% by mass) is added, with a molar ratio of ammonium persulfate to hydrogen peroxide of 1:1.2-1:1.5 and a liquid-to-solid ratio of approximately 6:1. The reaction temperature is controlled at 70℃, the stirring speed at approximately 300 r / min, and the reaction time at approximately 2 hours. Under the catalytic action of copper ions in the leachate, persulfate decomposes to produce sulfate radicals (SO4-·), which effectively disrupt the stable structure of insoluble rhenium sulfide (ReS2), oxidizing it to soluble rhenium ion (ReO4-). The rhenium leaching rate is ≥92%; the pentavalent arsenic conversion rate is ≥98%; and the residual sulfur in the solid phase mainly exists in the form of elemental sulfur, with a sulfur ion conversion rate of ≥99.8%. After leaching, solid-liquid separation is performed to obtain a leachate containing pentavalent arsenic and valuable metals, and a sulfur-containing leachate residue. S3: Two-stage thermal separation for sulfur removal: First-stage anaerobic heating for sulfur extraction—The sulfur-containing leaching residue obtained in step S2 is fed into a vacuum rotary kiln, with the oxygen concentration inside the kiln controlled to ≤1%. Under anaerobic conditions, it is heated to 400-450℃ and held at this temperature for approximately 2 hours. At this temperature, the elemental sulfur in the residue directly sublimates and volatilizes. The sulfur vapor is then condensed and recovered by a water-cooled condenser, yielding an elemental sulfur product with a purity ≥99%.

[0030] Secondary reduction heating for residual sulfur removal—The residue after primary sulfur removal is transferred to a rotary kiln, and anthracite powder is added as a carbonaceous reducing agent at a ratio of 5-15% of the slag mass. The filling rate is 10%-15%, the rotation speed is 0.5-1.5 r / min, and the kiln inclination is 3%-5%. Heating is carried out in a weak reducing atmosphere to 420-480℃ and held for approximately 2 hours. Under these conditions, residual arsenic sulfides and other sulfides in the slag are reduced by carbon, and sulfur volatilizes as elemental sulfur, which is then recovered as elemental sulfur through condensation. The kiln temperature is strictly controlled to not exceed 480℃ (far below the critical volatilization temperature of arsenic, approximately 615℃), ensuring an arsenic volatilization rate of ≤10%.

[0031] S4: Post-treatment of leachate: The leachate containing pentavalent arsenic and valuable metals obtained in step S2 is sent to the subsequent recovery process. Conventional metallurgical methods such as reduction precipitation, extraction, ion exchange or electrolysis can be used to recover valuable components such as arsenic, copper, rhenium, molybdenum and cadmium.

[0032] S5 Material Recycling: The residue after the secondary sulfur extraction in step S3 still contains a small amount of valuable metals such as copper, molybdenum, and rhenium (contents of approximately 2.1%, 0.3%, and 0.01%, respectively). It is returned to the third stage of acid leaching in step S2 for secondary leaching to maximize the recovery of valuable metals.

[0033] In this embodiment, the total leaching rate of arsenic is ≥98%, the total leaching rate of rhenium is ≥92%, the elemental recovery rate of sulfur is ≥96%, and the leaching toxicity concentration of arsenic in the residue after sulfur extraction is ≤2.5mg / L, which meets the limit requirement of arsenic ≤5.0mg / L in GB5085.3-2007, and can be disposed of as general industrial solid waste.

[0034] Example 2: The difference from Example 1 is that in the second stage of acid leaching in step S2, oxygen microbubbles are used instead of ozone microbubbles, the oxygen flow rate is appropriately increased to 600-800 mL / min, and the reaction temperature is appropriately increased to 85-90℃. The remaining conditions are the same as in Example 1. The technical effect of oxidizing trivalent arsenic to pentavalent arsenic can still be achieved, with an arsenic leaching rate ≥96% and a rhenium leaching rate ≥90%.

[0035] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A process for sulfur extraction and arsenic production from arsenic-containing slag in copper smelting, characterized in that, Includes the following steps: S1: The arsenic-containing slag raw material is pretreated by wet grinding to obtain a slurry of a predetermined fineness; S2: The slurry obtained in step S1 is subjected to three stages of acid leaching under normal pressure, wherein... The first stage of acid leaching dissolves soluble iron under acidic conditions and causes it to hydrolyze and precipitate, thus achieving the initial separation of iron. The second stage of acid leaching introduces oxygen-containing gas microbubbles as the primary oxidant, oxidizing the trivalent arsenic in the leachate to pentavalent arsenic. The third stage of acid leaching introduces a compound system of persulfate and hydrogen peroxide as a second oxidant. The free radicals generated by transition metal catalysis are used to deeply oxidize and leach insoluble sulfides, resulting in a leachate containing pentavalent arsenic and valuable metals, and a sulfur-containing leachate residue. S3: The sulfur-containing leaching residue obtained in step S2 is subjected to two-stage thermal separation treatment: first, under anaerobic conditions, the elemental sulfur is heated to sublimate and volatilize and then condensed and recovered; then, under a reducing atmosphere, a carbonaceous reducing agent is added and heated to volatilize the sulfur in the residual sulfide in the form of elemental sulfur and condense and recover it, thus obtaining the residue after sulfur extraction. S4: The leachate containing pentavalent arsenic and valuable metals obtained in step S2 is further processed to recover arsenic and valuable metals.

2. The process for sulfur extraction and arsenic production from arsenic-containing copper smelting slag according to claim 1, characterized in that, In step S1, the proportion of slurry with a particle size of 80 mesh or less after wet grinding pretreatment is not less than 90%.

3. The process for sulfur extraction and arsenic production from arsenic-containing copper smelting slag according to claim 1, characterized in that, The conditions for the first stage of acid leaching in step S2 are: initial sulfuric acid concentration of 50-80 g / L, and pH value controlled at the reaction endpoint of 1.8-2.

6.

4. The process for sulfur extraction and arsenic production from arsenic-containing copper smelting slag according to claim 1, characterized in that, In step S2, the oxygen-containing gas microbubbles used in the second stage of acid leaching are ozone microbubbles. They are introduced by generating microbubbles with a diameter of 10-150μm through a microbubble generator, and the reaction temperature is controlled at 70-90℃.

5. The process for sulfur extraction and arsenic production from arsenic-containing copper smelting slag according to claim 1, characterized in that, In step S2, the persulfate used in the third stage of acid leaching is ammonium persulfate or sodium persulfate, and the molar ratio of persulfate to hydrogen peroxide is 1:1.2-1:1.

5.

6. The process for sulfur extraction and arsenic production from arsenic-containing copper smelting slag according to claim 1, characterized in that, The heating temperature under anaerobic conditions described in step S3 is 400-450℃, and the holding time is 1.5-3h.

7. The process for sulfur extraction and arsenic production from arsenic-containing copper smelting slag according to claim 1, characterized in that, In step S3, the carbonaceous reducing agent is added under a reducing atmosphere and heated at a temperature of 420-480℃. The carbonaceous reducing agent is anthracite powder, and the addition ratio is 5-15% of the slag mass.

8. The process for sulfur extraction and arsenic production from arsenic-containing copper smelting slag according to claim 1, characterized in that, After sulfur extraction in step S3, the residue is returned to the third stage of acid leaching in step S2 for secondary leaching.

9. The process for sulfur extraction and arsenic production from arsenic-containing copper smelting slag according to claim 1, characterized in that, In step S2, between the second and third acid leaching stages, there is also a step of returning the unreacted solid material to the first or second acid leaching stage for cyclic leaching.

Images