Method for removing arsenic from arsenic-containing industrial gypsum and simultaneously preparing alpha calcium sulfate hemihydrate

Abstract

The invention discloses a method for removing arsenic from arsenic-containing industrial gypsum and simultaneously preparing alpha calcium sulfate hemihydrate. The method specifically comprises the following steps: drying, crushing and sieving the arsenic-containing industrial gypsum; the method comprises the following steps: mixing arsenic-containing industrial gypsum powder with a sulfuric acid solution with the mass concentration of 5-7% to obtain gypsum suspension slurry, adding the gypsum suspension slurry into a reaction kettle, carrying out stirring reaction at 110-150 DEG C for 60-180 minutes, cooling to 100 DEG C, carrying out suction filtration on the slurry while the slurry is hot, sequentially washing with boiling water and absolute ethyl alcohol for 2-4 times respectively, and drying to obtain the alpha calcium sulfate hemihydrate. According to the method, deep removal of arsenic in the arsenic gypsum can be realized, and the removal rate of arsenic is gt; according to the method disclosed by the invention, the product obtained under the condition that no crystal modifier is added has a relatively good crystal form and a relatively small length-diameter ratio, and the method disclosed by the invention realizes arsenic removal of the arsenic-containing industrial gypsum and preparation of a gypsum product with a high additional value.

Description

Technical Field

[0001] The invention belongs to the technical field of industrial solid waste recovery, and in particular relates to a method for removing arsenic from arsenic-containing industrial gypsum and preparing alpha-calcium sulfate hemihydrate. Background Art

[0002] Arsenic often exists in the form of arsenic-containing minerals in nature. With the large-scale mining of non-ferrous metal minerals, a large amount of metallurgical flue gas will be produced. In order to purify the flue gas containing arsenic and sulfur and eliminate secondary pollution, most domestic enterprises use the limestone-gypsum process to absorb the sulfur and arsenic compounds in the waste gas and store them in the environment in the form of arsenic-containing industrial gypsum. However, with the annual increase in the stockpile of arsenic-containing industrial gypsum, simple stockpiling cannot solve the problem and will pose a certain threat to the surrounding environment. The presence of impurities in it limits the resource-based high-value utilization of arsenic-containing industrial gypsum.

[0003] At present, most of the arsenic-containing waste residues in my country are disposed of by the hoarding storage method to convert the arsenic in the waste into a compound with a stable valence state or to wrap the waste in an inert material, thereby reducing the leaching toxicity of arsenic. Patent CN11035882A discloses a method for the coordinated disposal of arsenic-containing waste and barium-containing waste by stabilization and solidification, but the final product only obtains a solidified body that meets the requirements of landfill disposal but cannot meet the high-value application of waste. Patent CN106011475B discloses a method for harmless treatment and arsenic recovery of low-concentration arsenic-containing waste residues. Arsenic-containing waste residues are dearsenified by alkaline leaching, but this method is only effective for arsenic-containing wastes with low arsenic content, and Fe and Al impurities in the raw materials will also affect the leaching effect. At present, it is difficult to dearsenify hazardous wastes with an arsenic content of less than 10% using a relatively simple process flow and to utilize the products as resources. Therefore, dearsenification of arsenic-containing industrial gypsum and preparation of α-calcium sulfate hemihydrate is an extremely important way to harmlessly and highly value-added application of hazardous solid wastes. Summary of the invention

[0004] In view of the problem that low-concentration arsenic-containing gypsum is difficult to handle and recycle at present, the present invention provides a method for removing arsenic from arsenic-containing industrial gypsum and preparing α-calcium sulfate hemihydrate at the same time. The method of the present invention fully utilizes the characteristics of arsenic-containing industrial gypsum itself, completes the phase transition of calcium sulfate dihydrate to α-calcium sulfate hemihydrate while removing arsenic, and has significant economic, social and environmental benefits.

[0005] The method for removing arsenic from arsenic-containing industrial gypsum and preparing α-calcium sulfate hemihydrate at the same time is as follows: (1) Dry the arsenic-containing industrial gypsum in a 40-50°C oven for 24 hours and then grind it through a 100 mesh; (2) The arsenic-containing industrial gypsum powder is mixed with a sulfuric acid solution having a mass concentration of 5%-7% to prepare a gypsum suspension slurry, wherein the mass percentage of solids in the gypsum suspension slurry is 5%-30%. The gypsum suspension slurry is added to a reaction kettle, and the reaction is stirred at 110°C-150°C for 60min-180min in a sealed state. After the temperature is reduced to 100°C, the slurry is filtered while hot, and washed with boiling water and anhydrous ethanol in turn, 2-4 times each, and dried at 40-50°C for 24h to obtain α calcium sulfate hemihydrate.

[0006] The arsenic content in the arsenic-containing industrial gypsum is less than 10wt%.

[0007] In order to ensure the complete conversion of dihydrate gypsum to α-hemihydrate gypsum and ensure the arsenic removal efficiency while controlling the cost of the treatment process, too low sulfuric acid concentration and too high solid content in the gypsum suspension slurry will reduce the removal efficiency of arsenic impurities and increase costs.

[0008] The temperature is lowered to 100°C and washed with boiling water and anhydrous ethanol to prevent the α-hemihydrate gypsum in the product from hydrating into dihydrate gypsum, which will affect the purity of the product.

[0009] Sulfuric acid can not only effectively remove arsenic impurities in the arsenic-containing industrial gypsum in its own form and adsorbed on the surface, but also release the arsenic impurities inside the gypsum into the solution during the dissolution-crystallization process of the gypsum in the solution. As the temperature rises, due to the difference in the solubility of dihydrate gypsum and hemihydrate gypsum with temperature, hemihydrate gypsum will crystallize first at a certain temperature.

[0010] Arsenic precipitated from gypsum is mainly in the form of H3AsO4 and H2AsO4 - exists in the solution and reacts with SO4 2- The structure of sulfuric acid is quite different and will not undergo eutectic substitution with sulfate. However, while sulfuric acid plays a role in removing arsenic, the presence of sulfate also promotes the crystallization of α-hemihydrate gypsum. Ultimately, not only the arsenic on the surface of gypsum and inside the crystal lattice is removed, but also the preparation of α-hemihydrate gypsum is achieved.

[0011] The present invention removes adsorbed water contained in gypsum through pretreatment such as drying and grinding, and then removes arsenic impurities in the gypsum through a pressurized hydrothermal method, thereby preparing high-purity columnar α-hemihydrate gypsum with a small aspect ratio. The present invention realizes deep removal of arsenic in arsenic gypsum, and the arsenic removal rate is greater than 93%. The product obtained by the present invention without adding any crystal inversion agent has a good crystal form and a small aspect ratio. The method of the present invention realizes the removal of arsenic from arsenic-containing industrial gypsum and the preparation of high-value-added gypsum products. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a microscopic morphology of the gypsum product obtained in Example 1; Figure 2 This is the XRD pattern of the gypsum product obtained in Example 1; Figure 3 This is a microscopic morphology of the gypsum product obtained in Example 2; Figure 4 This is the XRD pattern of the gypsum product obtained in Example 2; Figure 5 The microscopic morphology of the gypsum product obtained in Example 3 Figure 6 This is the XRD pattern of the gypsum product obtained in Example 3; Figure 7 This is a microscopic morphology of the gypsum product obtained in Example 4; Figure 8 This is the XRD spectrum of the gypsum product obtained in Example 4. DETAILED DESCRIPTION

[0013] The present invention is further described in detail below by way of examples, but the protection scope of the present invention is not limited to the contents described above. The methods in the examples are conventional methods unless otherwise specified, and the reagents used are conventional commercially available reagents or reagents prepared according to conventional methods unless otherwise specified; The arsenic-containing industrial gypsum in the embodiment comes from a tin smelter in Yunnan; Example 1

[0014] (1) After drying the arsenic-containing industrial gypsum at 45°C for 24 hours, the gypsum was ground and passed through a 100-grit sieve. The main components of the arsenic-containing industrial gypsum are shown in Table 1. Table 1 Main element composition and proportion of raw material arsenic-containing industrial gypsum ; (2) 30 g of arsenic-containing industrial gypsum powder was mixed with 210 mL of 5% sulfuric acid solution to prepare a gypsum suspension slurry. The gypsum suspension slurry was added to a reactor and reacted for 120 min at 120 °C and 180 rpm in a sealed state. After cooling to 100 °C, the slurry was filtered while hot, washed with boiling water and anhydrous ethanol three times each, and dried at 45 °C for 24 h to obtain α calcium sulfate hemihydrate. The microscopic morphology of α calcium sulfate hemihydrate is shown in the figure. Figure 1 As shown in the figure, it can be seen that the crystal form of the product is mainly columnar α-calcium sulfate hemihydrate, and the XRD spectrum is as follows Figure 2 As shown in the figure, it can be seen that the main phase of calcium sulfate is α calcium sulfate hemihydrate. The arsenic content of the product is 0.884g / kg, and the arsenic removal rate reaches 98.6%. Example 2

[0015] (1) The arsenic-containing industrial gypsum was dried at 40° C. for 24 hours and then ground through a 100 mesh sieve. The main components of the arsenic-containing industrial gypsum were the same as those in Example 1. (2) 30 g of arsenic-containing industrial gypsum powder was mixed with 210 mL of 6% sulfuric acid solution to prepare a gypsum suspension slurry. The gypsum suspension slurry was added to a reactor and reacted for 120 min at 140 °C and 180 rpm in a sealed state. After cooling to 100 °C, the slurry was filtered while hot, washed with boiling water and anhydrous ethanol in turn, 4 times each, and dried at 50 °C for 24 h to obtain α calcium sulfate hemihydrate. The microscopic morphology of the product is shown in the figure below. Figure 3 As shown, the XRD spectrum is Figure 4 As shown, the conversion of α-calcium sulfate hemihydrate is very complete, and the crystal shape is columnar with an aspect ratio of 4.1. The arsenic content in α-calcium sulfate hemihydrate is 3.08 g / kg, and the arsenic removal rate reaches 95%. Example 3

[0016] (1) The arsenic-containing industrial gypsum was dried at 40° C. for 24 hours and then ground through a 100 mesh sieve. The main components of the arsenic-containing industrial gypsum were the same as those in Example 1. (2) 30 g of arsenic-containing industrial gypsum powder was mixed with 210 mL of 6% sulfuric acid solution to prepare a gypsum suspension slurry. The gypsum suspension slurry was added to a reactor and reacted for 60 min at 140 °C and 180 rpm in a sealed state. After cooling to 100 °C, the slurry was filtered while hot, washed with boiling water and anhydrous ethanol in turn, 4 times each, and dried at 50 °C for 24 h to obtain α calcium sulfate hemihydrate. The microscopic morphology of the product is shown in the figure below. Figure 5 As shown, the XRD spectrum is Figure 6 As shown, the conversion of α-calcium sulfate hemihydrate is very complete, and the crystal shape is columnar with an aspect ratio of 8.4. The arsenic content in α-calcium sulfate hemihydrate is 4.44 g / kg, and the arsenic removal rate reaches 93.2%. Example 4

[0017] (1) The arsenic-containing industrial gypsum was dried at 50° C. for 24 hours and then ground to pass through a 100-mesh sieve. The main components of the arsenic-containing industrial gypsum were the same as those in Example 1. (2) 30 g of arsenic-containing industrial gypsum powder was mixed with 210 mL of 7% sulfuric acid solution to prepare a gypsum suspension slurry. The gypsum suspension slurry was added to a reactor and reacted for 60 min at 150 °C and 180 rpm in a sealed state. After cooling to 100 °C, the slurry was filtered while hot, washed with boiling water and anhydrous ethanol in turn, 4 times each, and dried at 40 °C for 24 h to obtain α-calcium sulfate hemihydrate. The microscopic morphology of the product is shown in the figure below. Figure 7 As shown, the XRD spectrum is Figure 8 As shown, the conversion of α-calcium sulfate hemihydrate is very complete, and the crystal shape is columnar with an aspect ratio of 9.2. The arsenic content in α-calcium sulfate hemihydrate is 2.72 g / kg, and the arsenic removal rate reaches 95.8%.

Claims

1. A method for removing arsenic from arsenic-containing industrial gypsum and preparing α-calcium sulfate hemihydrate, characterized in that: Here are the steps: (1) Drying, crushing and screening the arsenic-containing industrial gypsum; (2) The arsenic-containing industrial gypsum powder is mixed with a sulfuric acid solution with a mass concentration of 5%-7% to obtain a gypsum suspension slurry, which is added to a reactor and stirred at 110°C-150°C for 60min-180min. After cooling to 100°C, the slurry is filtered while hot, washed with boiling water and anhydrous ethanol in turn, 2-4 times each, and dried to obtain α-calcium sulfate hemihydrate.

2. The method for removing arsenic from arsenic-containing industrial gypsum and preparing α-calcium sulfate hemihydrate according to claim 1, characterized in that: The solid mass percentage in the gypsum suspension slurry is 5%-30%.

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