A method for comprehensively recovering calcium and arsenic from calcium arsenic slag

Abstract

The application provides a method for comprehensively recovering calcium and arsenic from calcium-arsenic slag, comprising the following steps: S1: mixing and reacting calcium-arsenic slag and a sodium carbonate solution, and then filtering to obtain filtrate and filter residue containing calcium carbonate; washing the filter residue and collecting washing liquid A; the pH value of the mixing and reaction is 10-11; the temperature of the mixing and reaction is 25-60 DEG C; S2: mixing the filtrate and the washing liquid to obtain a sodium arsenate solution, adding ferrous sulfate, and controlling the oxidation-reduction potential to 400-550 mv by using hydrogen peroxide to precipitate arsenic. The application provides a method for comprehensively recovering calcium and arsenic from calcium-arsenic slag, the sodium-calcium replacement efficiency is improved by jointly controlling pH, temperature and liquid-solid ratio, the purity of the sodium arsenate solution is improved, then the pH-potential-iron-arsenic molar ratio is jointly controlled, under the conditions of relatively high pH, high potential and high iron-arsenic molar ratio, the tobermorite with a wheat grain shape is generated, and the leaching stability is good.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of resource utilization and harmless disposal of arsenic-containing hazardous waste, and particularly relates to a method for comprehensively recovering calcium and arsenic from calcium-arsenic slag. BACKGROUND

[0002] Resource utilization and harmless disposal of arsenic-containing hazardous waste has been an environmental protection problem, and the arsenic-containing hazardous waste includes arsenic-containing waste liquid and arsenic-containing waste slag. Calcium-arsenic slag is a kind of arsenic-containing sludge produced by traditional lime-iron salt method for treating waste acid, and accounts for a large proportion in arsenic-containing waste slag. The calcium-arsenic slag has low arsenic content and large slag quantity, and the only disposal method is safe landfill, thus occupying a large amount of land resources. Most of the researches on calcium-arsenic slag focus on harmless stabilization, and how to realize resource reduction of calcium-arsenic slag is a meaningful environmental protection project, and relevant researches are less. At present, the resource recovery direction of calcium-arsenic slag mainly is to prepare arsenic products, such as copper arsenate, diarsenic trioxide and elemental arsenic, etc. However, due to the high production cost of arsenic products, and the demand market tends to be saturated, the arsenic products can only be temporarily stored, and cannot bring economic benefits, and is a huge safety hazard to the surrounding ecological environment. In the existing research, a comprehensive treatment method of calcium-arsenic slag is provided, which adjusts the slurry of calcium-arsenic slag, uses carbon dioxide to replace arsenate in calcium arsenate to form calcium carbonate and arsenic acid solution, and concentrates and crystallizes the arsenic acid solution to obtain arsenic oxide, and the arsenic oxide and hot carbon are reduced to obtain elemental arsenic, so as to realize the separation and recovery of calcium and arsenic. The above method adopts wet method and fire method in combination, and finally realizes the separation and recovery of calcium and arsenic and the reduction of arsenic slag. However, the efficiency of carbon dioxide gas dissolved in water to replace arsenate with carbonate is low, and the energy consumption of high-temperature carbon reduction is high, the elemental arsenic needs to be sealed and treated and stored, the management difficulty is large, and the secondary pollution hidden danger is large.

[0003] In summary, it is urgent to provide a method for comprehensively recovering calcium and arsenic from calcium-arsenic slag with low energy consumption. SUMMARY

[0004] The present application aims at at least solving one of the above technical problems in the prior art. To this end, the present application provides a method for comprehensively recovering calcium and arsenic from calcium-arsenic slag, which uses sodium carbonate to provide high-concentration carbonate, and improves the sodium-calcium replacement efficiency by jointly controlling pH, temperature and liquid-solid ratio, and improves the purity of sodium arsenate solution, and then adopts pH-potential-iron-arsenic molar ratio joint control to generate malachite with a grain-like morphology under the conditions of relatively high pH, high potential and high iron-arsenic molar ratio, which has good leaching stability, and at the same time ensures that the arsenic concentration of the post-arsenic precipitation solution is at a low level, and guarantees the purity of the subsequent evaporation and concentration crystallization product.

[0005] The first aspect of the present application provides a method for comprehensively recovering calcium and arsenic from calcium-arsenic slag, comprising the following steps:

[0006] S1: mixing and reacting calcium arsenic slag and sodium carbonate solution to obtain filtrate and filter residue containing calcium carbonate;

[0007] collecting washing liquid A after washing the filter residue;

[0008] The pH value of the mixing reaction is 10-11.

[0009] The temperature of the mixing reaction is 25-60℃.

[0010] S2: mixing the filtrate and the washing liquid to obtain a sodium arsenate solution, then adding ferrous sulfate and controlling the oxidation-reduction potential to 400-550mv by using hydrogen peroxide to precipitate arsenic.

[0011] The mechanism of the method is as follows:

[0012] The sodium carbonate is prepared into a solution, uniformly stirred with the calcium arsenic slag to obtain a mixed slurry, the liquid-solid ratio, pH value and temperature are regulated, and after a period of displacement reaction, the filter residue is washed and dried to obtain calcium carbonate; the filtrate and the washing liquid in step S2 are mixed to obtain a sodium arsenate solution, the pH value is regulated by using sulfuric acid, ferrous sulfate is added according to the iron-arsenic molar ratio, the potential is regulated by using hydrogen peroxide, and the arsenic precipitation reaction is carried out at a certain temperature, and then filtration and washing are carried out to obtain a long-term stable alunite, and the filtrate is an acidic sodium sulfate and ferrous sulfate mixed solution.

[0013] According to the embodiments of the first aspect of the application, at least the following beneficial effects are achieved:

[0014] In step S1, the application uses sodium carbonate to provide high-concentration carbonate, and regulates the pH value and temperature in combination to improve the sodium-calcium replacement efficiency, improve the purity of the sodium arsenate solution, and avoid the influence of too high calcium ions on the subsequent arsenic precipitation effect. By regulating the suitable liquid-solid ratio, pH value and temperature of the mixed slurry, the sodium-calcium replacement efficiency is ensured. When the temperature is 25-60℃, the solubility of sodium carbonate is at a relatively high value, the carbonate concentration is high, and a higher sodium-calcium replacement driving force is provided. The temperature should not be too high, because too high temperature will cause arsenic volatilization and secondary pollution. The pH value is controlled between 10 and 11, which not only ensures the generation of sodium arsenate from arsenic alkali solution and improves the replacement efficiency, but also is beneficial to the subsequent pH reduction. The liquid-solid ratio is greater than 1:1, which avoids the influence of too high arsenic concentration on the sodium-calcium replacement efficiency.

[0015] In step S2, the application uses pH-potential-iron-arsenic molar ratio joint regulation to generate a kind of alunite with a grain-like morphology under the conditions of relatively high pH, high potential and high iron-arsenic molar ratio, which has good leaching stability, and at the same time ensures that the arsenic concentration in the solution after arsenic precipitation is at a relatively low level, which guarantees the purity of the subsequent evaporation and concentration of the crystalline product. The acidic sodium sulfate and ferrous sulfate mixed solution can be used to adjust the initial pH value of the sodium arsenate solution, and the enriched sodium sulfate can be recycled.

[0016] According to some embodiments of the present application, in step S1, the liquid-solid ratio in the mixing reaction is not less than 1:1.

[0017] Under the above liquid-solid ratio, the reaction efficiency is improved, ensuring that the calcium arsenic slag and the sodium carbonate solution are in sufficient contact, thereby accelerating the chemical reaction and improving the conversion rate of the reaction; improving the filtration performance helps to obtain better separation effect of filtrate and filter residue, reduces the residual impurities in the filter residue, and improves the efficiency of subsequent treatment; in the washing process, the soluble impurities in the filter residue can be more effectively removed, ensuring that the purity of the collected washing liquid is higher; the stability of the reaction environment is maintained, thereby improving the controllability of the reaction.

[0018] According to some embodiments of the present application, the calcium arsenic slag is an arsenic-containing slag mainly containing calcium arsenate generated by lime-iron salt neutralization method, and the arsenic content is 2-10%.

[0019] According to some embodiments of the present application, in step S1, the molar ratio of sodium carbonate to arsenic is 1.1-1.3:1.

[0020] Under the above molar ratio, it can ensure that there is enough sodium carbonate in the reaction system to undergo double decomposition reaction with calcium arsenate, which helps to improve the dissolution efficiency of arsenic.

[0021] According to some embodiments of the present application, in step S2, the molar ratio of calcium to arsenic in the sodium arsenate solution is not higher than 0.05.

[0022] In the arsenic precipitation process, a high concentration of calcium ions will affect the nucleation and growth process of scorodite crystals, leading to incomplete precipitation or abnormal crystal morphology, thereby reducing the arsenic precipitation efficiency and producing irregular or unstable solid forms. Under the above molar ratio, it helps to effectively precipitate arsenic and ensure a high arsenic precipitation rate.

[0023] According to some embodiments of the present application, in step S2, the pH value of the sodium arsenate solution is 1-3.

[0024] Under the above conditions, it helps to dissolve metal ions in the liquid phase and maintain their activity, avoiding the formation of precipitates or other insoluble substances. It can prevent other metals (such as calcium, magnesium, etc.) from generating insoluble metal salts in the arsenic precipitation reaction, which may interfere with the arsenic precipitation reaction. It helps to form iron ions with better solubility, and then the iron ions react with arsenate to form insoluble arsenic-iron compounds (such as scorodite), thereby effectively precipitating arsenic. When the pH is close to 1.5, the oxidation state of iron ions (such as Fe 3+ ) is more stable, which can react with arsenate to form a precipitate, thereby improving the removal efficiency of arsenic.

[0025] According to some embodiments of the present application, in step S2, the temperature for precipitating arsenic is 75-95℃.

[0026] Within the above temperature range, it can be more effective to combine with arsenate to form insoluble arsenic-iron precipitate (such as scorodite), thereby improving the removal efficiency of arsenic. At the same time, this helps to generate a more compact and stable crystal structure, reducing the risk of arsenic release in subsequent processing or long-term storage.

[0027] According to some embodiments of the present application, in step S2, the molar ratio of iron to arsenic is 1.1-1.5:1.

[0028] According to some embodiments of the present application, in step S2, the reduction potential is 500-550mv.

[0029] Under the above conditions, the excess supply of iron ions ensures that the combination reaction with arsenate can be carried out sufficiently, and at the same time, during the arsenic precipitation reaction, part of the iron ions reacts with other substances or participates in side reactions, resulting in a decrease in effective iron ions. By adjusting the potential to 500-550mv, it is helpful to oxidize the divalent iron (Fe 2+ ) in the reaction system to trivalent iron (Fe 3+ ), so that Fe 3+ is continuously generated, thereby making it easier for arsenate (AsO4 3- ) to combine with Fe 3+ to generate stable insoluble arsenic-iron compounds.

[0030] Under the premise that the above pH, iron-arsenic molar ratio and temperature meet the basic requirements, the most critical parameter is the potential. At a higher potential, the arsenic precipitation in the solution is more complete, the generation efficiency of scorodite is higher, and the scorodite crystal morphology is in the shape of a grain. In a preferred scheme, the pH of the sodium arsenate solution is 1-3, the hydrogen peroxide is adjusted to a potential of 400-550mv, the temperature is controlled at 75-95℃, and the scorodite obtained after arsenic precipitation is a crystal in the shape of a grain, with an arsenic leaching toxicity of less than 1mg / L, and an arsenic concentration in the solution after arsenic precipitation of 1-2mg / L. The scorodite crystal in the shape of a grain has a stable structure during the arsenic precipitation reaction, a lower arsenic leaching toxicity, and long-term environmental safety.

[0031] According to some embodiments of the present application, in step S2, the arsenic precipitation further includes washing the arsenic residue obtained after the arsenic precipitation to obtain a washing liquid B.

[0032] According to some embodiments of the present application, in step S2, it further includes concentrating the washing liquid B to obtain a concentrated liquid B.

[0033] The concentrated liquid B and the washing liquid B are returned to prepare a sodium carbonate solution, without secondary wastewater being generated.

[0034] The washing liquid B is concentrated and crystallized to obtain mirabilite, and sodium and sulfur are recovered. The concentrated liquid and the washing liquid can realize the resourceization, reduction and long-term stable treatment of calcium arsenic residue. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is a chive stone morphology prepared by recycling of Example 1;

[0036] Figure 2 is a chive stone morphology prepared by recycling of Comparative Example 2. DETAILED DESCRIPTION

[0037] The concept and the technical effects of the present application will be described in detail below in combination with examples, so as to fully understand the purpose, features and effects of the present application. Obviously, the described examples are only some of the examples of the present application, but not all the examples. Based on the examples of the present application, other examples obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0038] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in combination with the embodiment or example are contained in at least one embodiment or example of the present application. In the present specification, the exemplary description of the above terms does not necessarily mean the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0039] Unless otherwise specified, "room temperature" in the present application means 25℃±5℃.

[0040] Unless otherwise specified, "about" in the present application means that the allowable error is within ±2%.

[0041] Unless otherwise specified, the specific conditions in the examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not marked with the manufacturer, which are all conventional products that can be purchased on the market.

[0042] The first aspect of the present application provides a method for comprehensive recovery of calcium and arsenic from calcium arsenic slag, comprising the following steps:

[0043] S1: mixing and reacting the calcium arsenic slag and sodium carbonate solution to obtain filtrate and filter residue containing calcium carbonate after filtration;

[0044] The filter residue is washed to collect washing liquid A;

[0045] The pH value of the mixing reaction is 10-11;

[0046] The temperature of the mixing reaction is 25℃-60℃;

[0047] S2: After mixing the filtrate and the washing liquid to obtain a sodium arsenate solution, ferrous sulfate is added, and hydrogen peroxide is used to control the oxidation-reduction potential to be 400-550 mv to carry out arsenic precipitation.

[0048] It should be noted that, in order to solve the problems of high energy consumption of high-temperature carbon reduction, the need for sealed treatment and storage of arsenic single element, the difficulty in management, and the high risk of secondary pollution in the prior art, sodium carbonate is prepared into a solution, and is uniformly stirred with calcium arsenic slag to obtain a mixed slurry. The liquid-solid ratio, pH value and temperature are regulated, the slurry is filtered after a period of displacement reaction, the filter residue is washed and dried to obtain calcium carbonate. The filtrate and the washing liquid in step S2 are mixed to obtain a sodium arsenate solution, the pH value is regulated by sulfuric acid, ferrous sulfate is added according to the iron-arsenic molar ratio, the potential is regulated by hydrogen peroxide, and the arsenic precipitation reaction is carried out at a certain temperature. Then, the arsenic precipitation reaction is filtered and washed to obtain smoky onion stone with long-term stability, and the filtrate is an acidic sodium sulfate and sulfuric acid mixed solution.

[0049] Example 1

[0050] The embodiment provides a method for comprehensively recovering calcium and arsenic from calcium arsenic slag, and specifically comprises the following steps:

[0051] S1: 500 g of calcium arsenic slag generated by an enterprise is weighed by wet weight, containing 53.5% of water, 3.5% of arsenic, and 15% of calcium, and is put into a 2L container. Sodium carbonate is prepared into a solution with a mass concentration of 5%, and the sodium carbonate solution is added to the container according to the carbon-arsenic molar ratio of 1.2:1. The container is placed in a water bath kettle, and the temperature is raised to 55℃. The mixture is continuously stirred, the pH value is adjusted to 10.5 by 2% sulfuric acid, and the displacement reaction is carried out for 4h. Then, the mixed slurry is filtered, washed, and the filter residue is dried to measure the arsenic content and arsenic leaching toxicity.

[0052] S2: The filtrate is diluted to 1000 mL, the pH value is adjusted to 1.5 by 10% sulfuric acid, ferrous sulfate is added according to the iron-arsenic molar ratio of 1.5, the potential is regulated by hydrogen peroxide, the water bath heating temperature is controlled at 75℃, the arsenic precipitation reaction is carried out for 4h, and the arsenic precipitation reaction is filtered and washed to obtain smoky onion stone with long-term stability, as shown in Figure 1 .

[0053] The arsenic content and arsenic leaching toxicity of smoky onion stone are measured, the arsenic concentration of the arsenic precipitation filtrate and washing liquid mixed and diluted to 1000 mL is measured, and the arsenic precipitation rate is calculated. According to the detection, the arsenic content in calcium carbonate is 0.006% by dry weight, the arsenic leaching toxicity is 0.05 mg / L, the carbon-arsenic displacement rate is 99.91% (calculated by arsenic, the same below), the arsenic content in smoky onion stone is 32.12%, the arsenic leaching toxicity is 0.23 mg / L, the arsenic content in the arsenic precipitation solution is 1.5 mg / L, and the arsenic precipitation rate is 99.96%.

[0054] Example 2

[0055] The embodiment provides a method for comprehensively recovering calcium and arsenic from calcium-arsenic slag, in particular to the following steps.

[0056] S1: 500g of calcium-arsenic slag generated by another enterprise is taken by wet weight, 48.2% of water, 5.2% of arsenic, and 16.8% of calcium, and is put into a 2L container; sodium carbonate is prepared into a solution with a mass concentration of 5%; the sodium carbonate solution is added into the container according to a carbon-arsenic molar ratio of 1.25:1; the container is placed in a water bath, and is heated to 55 DEG C; continuous stirring and mixing are carried out; 2% of sulfuric acid is used to adjust the pH value to 11; the displacement reaction is carried out for 4h; then, the mixed slurry is filtered and washed to obtain a filtrate and a filter residue; and the filter residue is dried to measure the arsenic content and arsenic leaching toxicity.

[0057] S2: the filtrate is diluted to 1000mL; the pH value is adjusted to 1.5 by using 10% of sulfuric acid; ferrous sulfate is added according to a ferrous-arsenic molar ratio of 1.5; the potential is controlled to 550mv by using hydrogen peroxide; the water bath heating temperature is controlled to 95 DEG C; the arsenic precipitation reaction is carried out for 2h; and the filter residue is obtained by filtering and washing, and the arsenic content and arsenic leaching toxicity are measured; the arsenic concentration of the mixed solution of the arsenic precipitation filtrate and the washing liquid is measured after being diluted to 1000mL; and the arsenic precipitation rate is calculated.

[0058] It is detected that, according to the dry weight, the arsenic content in the calcium carbonate is 0.0052%, the arsenic leaching toxicity is 0.055mg / L, the carbon-arsenic displacement rate is 99.93% (the same below), the arsenic content in the orpiment is 33.09%, the arsenic leaching toxicity is 0.11mg / L, the arsenic content in the post-arsenic precipitation solution is 0.8mg / L, and the arsenic precipitation rate is 99.97%.

[0059] Comparative Example 1

[0060] The comparative example provides a method for comprehensively recovering calcium and arsenic from calcium-arsenic slag, and the difference between the comparative example and the embodiment 1 lies in that the pH value of the sodium carbonate displacement reaction is different; in the step S1, only the pH value is adjusted to 8.5, and other conditions are the same as those in the embodiment 1.

[0061] It is detected that, according to the dry weight, the arsenic content in the calcium carbonate is 0.5%, the arsenic leaching toxicity is 5.5mg / L, the carbon-arsenic displacement rate is 92.86%, the arsenic content in the orpiment is 27.84%, the arsenic leaching toxicity is 1.13mg / L, the arsenic concentration in the post-arsenic precipitation solution is 55.8mg / L, and the arsenic precipitation rate is 98.32%. After the pH value of the displacement reaction is reduced, the calcium-sodium displacement reaction efficiency is reduced, the calcium carbonate still contains a large amount of arsenic, and due to the incomplete calcium displacement, the calcium flows into the sodium arsenate solution, so that the orpiment arsenic precipitation efficiency is also reduced.

[0062] Comparative Example 2

[0063] The comparative example provides a method for comprehensively recovering calcium and arsenic from calcium-arsenic slag, and the difference between the comparative example and the embodiment 1 lies in that the arsenic precipitation potential is 600mv, and other conditions are the same as those in the embodiment 1.

[0064] The arsenic content in the calcium carbonate was 0.0048% by dry weight, the arsenic leaching toxicity was 0.053 mg / L, the carbon-arsenic replacement rate was 99.93%, the arsenic content in the scorodite was 32.18%, the arsenic leaching toxicity was 2.68 mg / L, the arsenic concentration in the solution after arsenic precipitation was 0.82 mg / L, and the arsenic precipitation rate was 99.97%. After the iron potential increased in the arsenic precipitation reaction, the arsenic-containing compounds produced in the arsenic precipitation increased the leaching toxicity, and the morphology of the product also changed, as shown in FIG. 1. Figure 2

[0065] Comparative Example 3

[0066] This comparative example provides a method for comprehensively recovering calcium and arsenic from calcium-arsenic slag. The difference between this comparative example and Example 2 is that the arsenic precipitation iron-arsenic molar ratio is different, and the iron-arsenic molar ratio is 1.1. The other conditions are the same as those in Example 2.

[0067] The arsenic content in the calcium carbonate was 0.0048% by dry weight, the arsenic leaching toxicity was 0.053 mg / L, the carbon-arsenic replacement rate was 99.93%, the arsenic content in the scorodite was 32.18%, the arsenic leaching toxicity was 1.13 mg / L. The arsenic concentration in the solution after arsenic precipitation was 48.8 mg / L, and the arsenic precipitation rate was 98.60%. After the iron-arsenic molar ratio decreased in the arsenic precipitation reaction, the arsenic precipitation efficiency also decreased.

[0068] Comparative Example 4

[0069] This comparative example provides a method for comprehensively recovering calcium and arsenic from calcium-arsenic slag. The difference between this comparative example and Example 2 is that the arsenic precipitation potential is different, and the arsenic precipitation potential is 220 mV. The other conditions are the same as those in Example 2.

[0070] The arsenic content in the calcium carbonate was 0.0048% by dry weight, the arsenic leaching toxicity was 0.053 mg / L, the carbon-arsenic replacement rate was 99.93%, the arsenic content in the scorodite was 32.18%, the arsenic leaching toxicity was 0.68 mg / L, the arsenic concentration in the solution after arsenic precipitation was 1500 mg / L, and the arsenic precipitation rate was 57.11%. After the potential decreased in the arsenic precipitation reaction, the arsenic precipitation efficiency decreased significantly.​

Claims

1. A method for the comprehensive recovery of calcium and arsenic from calcium-arsenic slag, characterized in that, Includes the following steps: S1: After mixing and reacting calcium arsenic residue and sodium carbonate solution, filter to obtain filtrate and filter residue containing calcium carbonate; After washing the filter residue, collect the washing liquid A; The pH value of the mixture reaction is 10-11; The temperature of the mixing reaction is 25℃-60℃; S2: After mixing the filtrate and the washing solution A to obtain a sodium arsenate solution, ferrous sulfate is added, and hydrogen peroxide is used to control the oxidation-reduction potential at 400-550mV to precipitate arsenic.

2. The method according to claim 1, characterized in that, In step S1, the liquid-to-solid ratio in the mixed reaction is not less than 1:

1.

3. The method according to claim 1, characterized in that, In step S1, the molar ratio of sodium carbonate to arsenic is 1.1 to 1.3:

1.

4. The method according to claim 1, characterized in that, In step S2, the molar ratio of calcium to arsenic in the sodium arsenate solution is not higher than 0.

05.

5. The method according to claim 1, characterized in that, In step S2, the pH value of the sodium arsenate solution is 1-3.

6. The method according to claim 1, characterized in that, In step S2, the temperature for arsenic precipitation is 75-95℃.

7. The method according to claim 1, characterized in that, In step S2, the molar ratio of iron to arsenic is 1.1 to 1.5:

1.

8. The method according to claim 1, characterized in that, In step S2, the reduction potential is 500-550mV.

9. The method according to claim 1, characterized in that, In step S2, the arsenic precipitation step further includes washing the arsenic residue obtained after arsenic precipitation to obtain washing liquid B.

10. The method according to claim 9, characterized in that, Step S2 also includes concentrating the washing solution B to obtain concentrated solution B.

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