A method for reducing the sodium content of calcium arsenate in a causticization process

Abstract

The application discloses a method for reducing sodium content of calcium arsenate in a causticization process, and belongs to the technical field of solid waste treatment in smelting and selection. Arsenic-containing smelting waste liquid and an oxidizing agent are injected into a micro-channel reactor, and after the reaction is completed, sodium antimonate precipitate and filtrate A are obtained by filtration; the filtrate A is heated, and lime milk is added to perform a causticization arsenic precipitation operation; after the causticization arsenic precipitation operation is completed, a heat preservation and thickening operation is performed in a thickener, to obtain underflow products and overflow products, the underflow products are filtered to obtain calcium arsenate filter residue and filtrate B, and the filtrate B is returned to the system for reuse as liquid alkali; hot water and the calcium arsenate filter residue are stirred in a stirring barrel, and after the stirring is completed, calcium arsenate and filtrate C are obtained by filtration, and the filtrate C is returned to the causticization arsenic precipitation operation. The application effectively reduces the sodium content of calcium arsenate in the causticization arsenic precipitation process based on the properties of different materials, and regulates the dissolution and crystallization behavior of the materials through a combination of multiple methods, and has the advantages of simple process, environmental friendliness, and low sodium content of calcium arsenate residue.

Description

Technical Field

[0001] This invention belongs to the field of solid waste treatment technology, specifically relating to a method for reducing the sodium content of calcium arsenate during causticization. Background Technology

[0002] Currently, the causticization method is a commonly used method for treating arsenic-containing smelting wastewater. The principle of this method is to utilize the reaction of calcium hydroxide, the main component of lime slurry, with soluble arsenic to form a sparingly soluble calcium arsenate precipitate, and simultaneously generate caustic alkali sodium hydroxide. The generated sodium hydroxide is then recycled.

[0003] However, due to the very similar properties of arsenic and antimony, antimony is often present in arsenic-containing wastewater. Furthermore, the addition of lime slurry during causticization results in an exceptionally complex composition of the causticization arsenic precipitation system, including sodium antimonate, sodium antimonite, sodium arsenate, disodium hydrogen arsenate, calcium arsenate, and calcium hydroxide. The dissolution and crystallization equilibrium of these individual components are closely related to the system's pH and temperature. When other components are present, the supersaturation of each individual material gradually increases, significantly impacting the overall causticization arsenic precipitation efficiency and the quality of the calcium arsenate slag. This also causes many sodium salts to be lost as precipitates in the calcium arsenate slag. Arsenic and antimony are both variable-valence elements, commonly exhibiting +3 and +5 oxidation states. Arsenic and antimony circulate throughout the smelting process, starting from the mineral processing concentrate, further complicating the system composition. Summary of the Invention

[0004] The purpose of this invention is to address the problem of sodium content in calcium arsenate during the causticization precipitation of arsenic-containing smelting wastewater. Based on the characteristics of different components in the causticization precipitation process, a method for reducing the sodium content in calcium arsenate during the causticization process is proposed.

[0005] To achieve the above objectives, the following technical solution is adopted:

[0006] A method for reducing the sodium content of calcium arsenate during causticizing process, the specific steps of which are as follows:

[0007] S1. Arsenic-containing smelting waste liquid and oxidant are injected into a microchannel reactor. After the reaction is completed, the mixture is filtered to obtain sodium antimonate precipitate and filtrate A respectively.

[0008] S2. Heat the filtrate A, and then add lime milk to the filtrate A to carry out causticization and arsenic precipitation.

[0009] S3. After the causticization precipitation of arsenic is completed, the thickener is kept at a constant temperature to thicken the product and obtain the underflow product and the overflow product. The underflow product is filtered to obtain calcium arsenate filter residue and filtrate B. Filtrate B is returned to the system as liquid alkali for reuse.

[0010] S4. Place hot water and calcium arsenate filter residue in a mixing tank and stir. After stirring, filter to obtain high-quality calcium arsenate and filtrate C. Filtrate C is returned to the causticization precipitation process.

[0011] Furthermore, in S1, the pH value of the arsenic-containing smelting waste liquid is 10-12.5, the volume ratio of the arsenic-containing smelting waste liquid to the oxidant is 300:1-500:1, the reaction temperature in the microchannel reactor is 5-35℃, the flow rate of the arsenic-containing smelting waste liquid and the oxidant through the microchannel reactor is 15-30L / min, and the structure of the microchannel reactor is a flow focusing structure or a T-shaped structure.

[0012] In S1, the oxidant is one of liquid oxygen, liquid ozone, or hydrogen peroxide.

[0013] In S2, the temperature of filtrate A after heating is 80-95℃, the pH value of causticization precipitation of arsenic is 10-12.5, and the molar ratio of arsenic to calcium is 1:0.5-1:0.8.

[0014] In S3, the heat preservation and thickening operation time is 30-60 minutes, and the temperature is 81-86℃.

[0015] In S4, the hot water temperature is >90℃, the stirring speed is 550-600r / min, the mass concentration of the material is 50-65%, and steam needs to be injected into the filter cake during filtration, with a steam temperature of 92-95℃.

[0016] The calcium arsenate obtained from S4 contains less than 0.8 wt% sodium.

[0017] This method utilizes the properties of pentavalent antimony salts being sparingly soluble in water and pentavalent arsenic salts being readily soluble in water. Arsenic-containing waste liquid is reacted with an oxidant, causing trivalent antimony in the waste liquid to oxidize to pentavalent antimony, thus separating sodium antimonate precipitation from the arsenic-containing waste liquid. Sodium is recovered before causticization precipitation, significantly reducing the sodium content in calcium arsenate. The rapid mass transfer of the microchannel reactor improves the conversion efficiency of antimony-containing sodium salts and offers low energy consumption. Since the solubility of Na3AsO4 is much lower than that of Na2HAsO4, this method controls the pH and temperature of causticization precipitation to ensure that the arsenic-containing sodium salt exists in the more water-soluble form of Na2HAsO4, effectively reducing the sodium content in the calcium arsenate slag. By controlling the ion types, ionic strength, and temperature of the sparingly soluble sodium salt, its supersaturation is reduced, disrupting the formation of sodium salt crystals and further reducing the sodium content in calcium arsenate, while achieving efficient reuse of the alkaline solution.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) In this invention, arsenic-containing waste liquid and oxidant are oxidized in a microchannel reactor. The high mass transfer efficiency of the microchannel reactor not only effectively improves the valence state transformation of antimony, but also greatly promotes the pre-removal of antimony sodium salt, which has the advantages of high efficiency and low energy consumption.

[0020] (2) This invention further reduces the sodium content in calcium arsenate by controlling the generation of products during the causticization arsenic removal process in multiple dimensions. Furthermore, after the causticization arsenic precipitation operation, by controlling the environment of the generated calcium arsenate slag, the supersaturation effect of the sparingly soluble sodium salt system is selectively destroyed, thereby reducing the sodium content in calcium arsenate and realizing the reuse of alkali solution. It has the advantages of good product quality and high resource utilization.

[0021] (3) This invention uses different methods to remove sodium from arsenic-containing materials at different stages from multiple dimensions. It can not only selectively remove sodium salt from calcium arsenate slag, but also has the advantage of thorough sodium removal. The overall process equipment configuration is simple and suitable for large-scale promotion and application. Attached Figure Description

[0022] Figure 1 The flowchart illustrates a method for reducing the sodium content of calcium arsenate during the causticizing process, as provided by this invention. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings. It should be noted that this embodiment is based on the present technical solution and provides detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to this embodiment.

[0024] Example 1

[0025] The material described in this embodiment is arsenic-containing waste liquid from a smelter in Fujian Province, with arsenic and antimony contents of 64.45 g / L and 21.7 g / L, respectively. The material is treated using the method proposed in this invention as follows:

[0026] S1. The arsenic-containing smelting waste liquid and oxidant are injected into a microchannel reactor. The microchannel reactor has a T-shaped structure, the pH of the material is 11.5, the volume ratio of the arsenic-containing waste liquid to the oxidant (liquid ozone) is 400:1, the reaction temperature is 5℃, and the flow rate of the arsenic-containing waste liquid and oxidant through the microchannel reactor is 30L / min. After the reaction is completed, the mixture is filtered to obtain sodium antimonate precipitate and filtrate A.

[0027] S2. The filtrate A is heated to 90°C, the pH for causticizing arsenic precipitation is 11.5, the ratio of arsenic to calcium is 1:0.6, and then lime milk is added to the filtrate A to carry out the causticizing arsenic precipitation operation.

[0028] S3. After the causticization precipitation of arsenic is completed, the thickener is kept at a high temperature for 45 minutes and 84°C to obtain underflow product and overflow product. The underflow product is filtered to obtain calcium arsenate filter residue and filtrate B. Filtrate B is returned to the system as liquid alkali for reuse.

[0029] S4. Place hot water and calcium arsenate slag in a mixing tank and stir. The hot water temperature is 91℃, the mixing speed is 550r / min, and the mass concentration of the material is 60%. After stirring, filter (steam is sprayed during filtration, and the steam temperature is 92℃) to obtain high-quality calcium arsenate and filtrate C. Filtrate C is returned to the causticization arsenic precipitation process.

[0030] Example 2

[0031] The material described in this embodiment is arsenic-containing waste liquid from a smelter in Xinjiang, with arsenic and antimony contents of 70.68 g / L and 25.9 g / L, respectively. The material is treated using the method proposed in this invention as follows:

[0032] S1. Inject arsenic-containing smelting waste liquid and oxidant into a microchannel reactor. The pH of the material is 12.5. The microchannel reactor has a T-shaped structure. The volume ratio of arsenic-containing waste liquid to oxidant (liquid oxygen) is 500:1. The reaction temperature is 10℃. The flow rate of arsenic-containing waste liquid and oxidant through the microchannel reactor is 25L / min. After the reaction, the mixture is filtered to obtain sodium antimonate precipitate and filtrate A.

[0033] S2. The filtrate A is heated to 80°C, the pH for causticizing arsenic precipitation is 12.5, the ratio of arsenic to calcium is 1:0.8, and then lime milk is added to the filtrate A to carry out causticizing arsenic precipitation.

[0034] S3. After the causticization precipitation of arsenic is completed, the thickener is kept at a high temperature for 30 minutes and 86°C to obtain underflow product and overflow product. The underflow product is filtered to obtain calcium arsenate filter residue and filtrate B. Filtrate B is returned to the system as liquid alkali for reuse.

[0035] S4. Place hot water and calcium arsenate slag in a mixing tank and stir. The hot water temperature is 93℃, the mixing tank speed is 550r / min, and the mass concentration of the material is 65%. After stirring, filter (steam is sprayed during filtration, and the steam temperature is 94℃) to obtain high-quality calcium arsenate and filtrate C. Filtrate C is returned to the causticization arsenic precipitation process.

[0036] Example 3

[0037] The material described in this embodiment is arsenic-containing waste liquid from a smelter in Fujian Province, with arsenic and antimony contents of 53.61 g / L and 13.6 g / L, respectively. The material is treated using the method proposed in this invention as follows:

[0038] S1. The arsenic-containing smelting waste liquid and oxidant are injected into a microchannel reactor. The microchannel reactor has a flow focusing structure, the pH of the material is 10, the volume ratio of the arsenic-containing waste liquid to the oxidant (hydrogen peroxide) is 300:1, the reaction temperature is 35℃, and the flow rate of the arsenic-containing waste liquid and oxidant through the microchannel reactor is 15L / min. After the reaction is completed, the mixture is filtered to obtain sodium antimonate precipitate and filtrate A.

[0039] S2. The filtrate A is heated to 95°C, the pH for causticizing arsenic precipitation is 12, and the ratio of arsenic to calcium is 1:0.5. Then, lime milk is added to the filtrate A to carry out the causticizing arsenic precipitation operation.

[0040] S3. After the causticization precipitation of arsenic is completed, the thickener is kept at a high temperature for 60 minutes and 81°C to obtain underflow product and overflow product. The underflow product is filtered to obtain calcium arsenate filter residue and filtrate B. Filtrate B is returned to the system as liquid alkali for reuse.

[0041] S4. Place hot water and calcium arsenate slag in a mixing tank and stir. The hot water temperature is 95℃, the mixing speed is 600r / min, and the mass concentration of the material is 50%. After stirring, filter (steam is sprayed during filtration, and the steam temperature is 95℃) to obtain high-quality calcium arsenate and filtrate C. Filtrate C is returned to the causticization arsenic precipitation process.

[0042] Comparative Example 1

[0043] The raw materials used were the same as those in Example 1. The temperature during the causticization process was 90°C, the pH was 11.5, and the ratio of arsenic to calcium was 1:0.6. The causticization process was then carried out. The difference was that after the causticization process, the calcium arsenate residue was obtained by direct filtration.

[0044] Comparative Example 2

[0045] The raw materials used were the same as in Example 2. The temperature during the causticization process was 80°C, the pH was 12.5, and the ratio of arsenic to calcium was 1:0.8. The causticization process was then carried out. The difference was that after the causticization process was completed, the calcium arsenate residue was obtained by direct filtration.

[0046] Comparative Example 3

[0047] The raw materials used were the same as in Example 3. The temperature during the causticization process was 95°C, the pH was 12, and the ratio of arsenic to calcium was 1:0.5. The causticization process was then carried out. The difference was that after the causticization process, the calcium arsenate residue was obtained by direct filtration.

[0048] Table 1 shows a comparison of the results of different embodiments.

[0049] Table 1 Comparison of results from different embodiments

[0050]

[0051]

[0052] As shown in Table 1, compared with the conventional causticization precipitation process, the sodium content in calcium arsenate residue decreased significantly after different arsenic-containing waste liquids were treated with the process proposed in this invention, indicating that the process proposed in this invention effectively reduced the sodium salt content in calcium arsenate.

[0053] For those skilled in the art, various corresponding changes and modifications can be made based on the above technical solutions and concepts, and all such changes and modifications should be included within the protection scope of the claims of this invention.

Claims

1. A method for reducing the sodium content of calcium arsenate during causticizing, characterized in that: The specific steps are as follows: S1. Arsenic-containing smelting waste liquid and oxidant are injected into a microchannel reactor. After the reaction is completed, the mixture is filtered to obtain sodium antimonate precipitate and filtrate A. S2. Heat filtrate A and add lime slurry to carry out causticization and arsenic precipitation. S3. After the causticization precipitation of arsenic is completed, the thickener is kept at a constant temperature to obtain underflow product and overflow product. The underflow product is filtered to obtain calcium arsenate filter residue and filtrate B. Filtrate B is returned to the system as liquid alkali for reuse. S4. Place hot water and calcium arsenate filter residue in a mixing tank and stir. Filter to obtain calcium arsenate and filtrate C. Filtrate C is returned to the causticization precipitation process.

2. The method according to claim 1, characterized in that: In S1, the pH value of the arsenic-containing smelting waste liquid is 10-12.5, the volume ratio of the arsenic-containing smelting waste liquid to the oxidant is 300:1-500:1, the reaction temperature in the microchannel reactor is 5-35 ℃, the flow rate of the arsenic-containing smelting waste liquid and the oxidant through the microchannel reactor is 15-30 L / min, and the structure of the microchannel reactor is a flow focusing structure or a T-shaped structure.

3. The method according to claim 1, characterized in that: In S1, the oxidant is one of liquid oxygen, liquid ozone, or hydrogen peroxide.

4. The method according to claim 1, characterized in that: In S2, the temperature of filtrate A after heating is 80-95 ℃, the pH value of causticization precipitation of arsenic is 10-12.5, and the molar ratio of arsenic to calcium is 1:0.5-1:0.

8.

5. The method according to claim 1, characterized in that: In S3, the heat preservation and thickening operation time is 30-60 minutes, and the temperature is 81-86℃.

6. The method according to claim 1, characterized in that: In S4, the hot water temperature is >90 ℃, the stirring tank speed is 550-600 r / min, the mass concentration of the material is 50-65%, and steam needs to be injected into the filter cake during filtration, with a steam temperature of 92-95℃.

7. The method according to claim 1, characterized in that: The calcium arsenate obtained from S4 contains less than 0.8 wt% sodium.

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