Method for selectively and efficiently removing impurities from desulfurized gypsum and preparing high-quality alpha-semi-hydrated gypsum

Abstract

The invention discloses a method for selectively and efficiently removing impurities in desulfurized gypsum and preparing high-quality alpha-semi-hydrated gypsum, which comprises the following steps: (1) removing organic impurities in the desulfurized gypsum by utilizing flotation, then removing soluble impurities by washing, and aerating air to oxidize calcium sulfite into calcium sulfate dihydrate while washing, then carrying out acid leaching in a hydrochloric acid solution to remove insoluble impurities, taking out and drying to obtain treated desulfurized gypsum; and (2) adding the desulfurized gypsum treated in the step (1) into a carboxylic acid aqueous solution to carry out solution crystallization reaction, adding potassium carboxylate into the carboxylic acid aqueous solution to regulate and control the crystallization rate and crystal morphology, carrying out solid-liquid separation after the reaction is finished, and washing, drying and ball-milling the solid to obtain the high-quality alpha-semi-hydrated gypsum powder. The alpha-semi-hydrated gypsum product obtained by the invention is high in purity, and the hydrated body has high absolute dry compressive and flexural strength.

Description

Technical Field

[0001] The present invention relates to the technical field of solid waste resource utilization, and specifically relates to a method for selectively and efficiently removing impurities from desulfurized gypsum and preparing high-quality α - Hemihydrate plaster method. Background Art

[0002] Desulfurization gypsum is a byproduct produced during the calcium-based wet flue gas desulfurization process. Its primary component is calcium sulfate dihydrate, with a purity of 90% to 95% and a moisture content of 10% to 15%. Impurities in desulfurization gypsum primarily include fly ash, organic carbon, calcium carbonate, calcium sulfite, and soluble salts composed of sodium, potassium, and magnesium sulfates or chlorides. These impurities are a key factor affecting the quality of desulfurization gypsum and restricting its high-value-added utilization.

[0003] Desulfurized gypsum does not have gelling properties and is currently mainly used as a soil conditioner, cement additive, and roadbed base material, etc., with low market value; the intermediate utilization process of desulfurized gypsum is calcination preparation. β - Hemihydrate gypsum is mainly used to make gypsum boards, plaster, etc. Its powder requires a lot of water for hydration, and the compressive and flexural strength of the hardened body is low; the high-value utilization of desulfurized gypsum is through conversion preparation α - Hemihydrate gypsum has complete crystal surface, low hydration water requirement and high hardened body strength. It can be widely used in the manufacture of high-strength gypsum board, thermal insulation and waterproof gypsum board, gypsum-based self-leveling materials, high-strength gypsum blocks, precision casting molds, ceramic molds, etc.

[0004] Current desulfurization gypsum conversion preparation α The main method for hemihydrate gypsum is the normal pressure hydrothermal method. This method has mild reaction conditions, does not require high-pressure equipment, is suitable for micron-sized powdered gypsum raw materials, and the crystallization process is easy to control. At present, the normal pressure hydrothermal method can be divided into salt solution crystallization method and alcohol solution crystallization method according to the crystallization medium. For example, the patent specification with publication number CN102992375A discloses a α The preparation method of ultra-high-strength gypsum comprises the following steps: a) dissolving a soluble inorganic salt in water to obtain a brine solution; b) adding desulfurized gypsum, natural gypsum or a mixture thereof to the brine solution to obtain a premixed liquid; c) adding a crystallization agent to the premixed liquid to obtain a reaction liquid; and d) heating the reaction liquid to 60-100° C. and performing crystallization at a constant temperature and normal pressure, filtering the reaction liquid after crystallization, and obtaining α For example, the patent specification with publication number CN108411369A discloses a method for preparing ultra-high strength gypsum by using desulfurized gypsum in an alcohol-water system. αThe method for preparing hemihydrate gypsum whiskers comprises: (1) preparing a mother liquor: mixing an inorganic salt, a cationic surfactant and an alcohol aqueous solution to prepare a mother liquor; (2) feeding and crystallizing: mixing desulfurized gypsum with the mother liquor to form a suspension, and performing a crystallization reaction under normal pressure hydrothermal conditions; (3) collecting the product: separating the suspension after the crystallization reaction into solid and liquid, recycling the mother liquor, and obtaining the product through post-treatment of the solid phase. α - Hemihydrate gypsum whiskers.

[0005] The salt solution crystallization method is regulated by changing the salt solution concentration, pH value and adding additives (such as organic salts, organic acids and metal ions). α - Morphology and size of hemihydrate gypsum, but salt ions can easily enter α - Hemihydrate gypsum lattice and adsorption on the crystal surface, affecting α -The purity of hemihydrate gypsum products. Compared with salt solutions, alcohol-water solutions have lower dielectric constants and higher solvating power, which can be α - Hemihydrate gypsum granules provide a cleaner crystallization medium and the prepared α - Hemihydrate gypsum products have higher purity, but the amount of alcohol solution required and the high cost limit its large-scale industrial application.

[0006] In summary, desulfurization gypsum conversion preparation α - Hemihydrate gypsum is an important direction for its high value utilization. The key lies in how to efficiently remove impurities in desulfurized gypsum and how to convert it into high-quality α - Hemihydrate gypsum products. Summary of the Invention

[0007] In view of the above technical problems and the shortcomings in the field, the present invention provides a desulfurization gypsum selective and efficient impurity removal and preparation of high-quality α - hemihydrate gypsum method, the resulting α -The semi-hydrated gypsum product has high purity and the hardened body has high absolute dry compressive and flexural strength.

[0008] A method for selectively and efficiently removing impurities from desulfurized gypsum and preparing high-quality α - A method for hemihydrate gypsum plastering comprising the steps of: (1) First, the organic impurities in the desulfurization gypsum are removed by flotation, and then the soluble impurities are removed by water washing. During the water washing, the calcium sulfite is oxidized into calcium sulfate dihydrate by exposure to air. Then, the insoluble impurities are removed by acid leaching in a hydrochloric acid solution, and the treated desulfurization gypsum is taken out and dried; (2) adding the desulfurized gypsum treated in step (1) into a carboxylic acid aqueous solution to carry out a solution crystallization reaction, wherein potassium carboxylate is also added into the carboxylic acid aqueous solution to regulate the crystallization rate and crystal morphology. After the reaction is completed, the solid and liquid are separated, and the solid is washed, dried, and ball-milled to obtain high-quality α - Hemihydrate gypsum powder.

[0009] The characteristics of the method of the present invention are: First, flotation is used to remove organic impurities in the desulfurization gypsum; then, soluble salt impurities in the desulfurization gypsum are removed by water washing, and air is introduced into the aqueous solution to oxidize the incompletely oxidized calcium sulfite in the desulfurization gypsum into calcium sulfate dihydrate; then, hydrochloric acid leaching is used to dissolve the insoluble impurities in the desulfurization gypsum, such as incompletely reacted calcium carbonate, to further improve the purity of the desulfurization gypsum.

[0010] After the desulfurized gypsum is fully decontaminated, a carboxylic acid aqueous solution is used to carry out the desulfurized gypsum phase transformation reaction. The rate of this transformation reaction is controlled by the water activity of the solution. The lower the water activity, the greater the driving force for the phase transformation. Carboxylic acids can effectively reduce the water activity of the aqueous solution through solute effects, dissociation, and hydrogen bonding, thereby promoting the desulfurized gypsum phase transformation reaction. First, as a soluble solute, carboxylic acid will occupy the position of some solvent molecules in the aqueous solution, reducing the number of free water molecules and thus reducing the water activity. At the same time, carboxylic acid partially dissociates into hydrogen ions and carboxylate ions in water. The ions produced by dissociation further increase the total number of ions in the solution, enhancing the solute effect, thereby more significantly reducing the water activity. Furthermore, the carboxyl groups in the carboxylic acid molecules partially bind water molecules by forming hydrogen bonds with water molecules, reducing the availability of free water.

[0011] Coordinated regulation by adding potassium carboxylate α -Nucleation rate and crystal morphology of hemihydrate gypsum. In terms of crystal morphology control, carboxylate ions will be preferentially adsorbed on α -The high energy crystal plane

[111] of hemihydrate gypsum inhibits the growth in the c-axis direction and promotes the growth of short columnar α -The formation of hemihydrate gypsum; at the same time, the presence of potassium ions will promote α -The radial growth of hemihydrate gypsum, thereby reducing the aspect ratio. In terms of nucleation rate, carboxylate ions will chelate calcium ions in the solution, reducing the concentration of free calcium ions in the solution, thereby reducing α -Supersaturation of hemihydrate gypsum, slowing down α -The nucleation rate of hemihydrate gypsum, but potassium ions promote the formation of ion pairs with sulfate α -hemihydrate gypsum nucleates, thereby compensating for the inhibitory effect of carboxylate ions on the nucleation rate.

[0012] Finally, the prepared α - Hemihydrate gypsum crystals are crushed by ball milling to obtain high quality α - Hemihydrate gypsum powder. Ball milling can significantly improve α -The homogenization degree of hemihydrate gypsum powder provides a more uniform material basis for the subsequent hydration reaction, so that the water added during the hydration process is gradually and evenly distributed in the α -Around the hemihydrate gypsum molecules. At the same time, ball milling can changeα -The physical properties of hemihydrate gypsum (such as fineness and specific surface area) enhance its reactivity, which is conducive to the formation of a denser dihydrate gypsum network structure in the subsequent hydration process. α The actual water usage of hemihydrate gypsum (40%-80%) is much higher than the theoretical water-to-paste ratio (18.61%), resulting in high porosity and low strength in the hardened material. However, due to the even distribution of moisture in the milled material, the addition of water can be reduced or even eliminated during the molding stage, thereby reducing porosity and improving compressive and flexural strength.

[0013] In some preferred examples, in step (1), the flotation is reverse flotation, the flotation pulp concentration is 50-100 g / L, the flotation collector used is dodecylamine, the amount of which is 100-300 g / t desulfurized gypsum, and the foaming agent is methyl isobutyl carbinol, the amount of which is 50-150 g / t desulfurized gypsum. With respect to the special object of desulfurized gypsum, the present invention preferably adds a specific liquid collector, dodecylamine, and performs slurry adjustment so that dodecylamine is fully adsorbed on the surface of organic impurities, thereby improving the hydrophobicity of the organic impurities. Then, by adding a specific foaming agent, methyl isobutyl carbinol, a hydrophobic foam layer is generated in the pulp to carry the organic impurities to the upper layer of the pulp. The foam layer is scraped off by a scraper, thereby removing the organic impurities and improving the purity of the desulfurized gypsum.

[0014] In some preferred examples, during the water washing process in step (1), the ratio of the mass of desulfurized gypsum to the volume of water is 1:1.0-3.5, for example, 1:3, etc., the water washing temperature is 30-60°C, and the water washing time is 0.5-3 h.

[0015] In some preferred embodiments, in step (1), the air aeration rate is 0.5-5 L / min, and the aeration time is 0.5-3 h.

[0016] In some preferred examples, in step (1), the concentration of the hydrochloric acid solution is 0.3-3 mol / L, the ratio of the mass of desulfurized gypsum to the volume of the hydrochloric acid solution is 1:1.0-3.0, and the acid leaching time is 0.5-3 h.

[0017] In some preferred examples, in step (2), the carboxylic acid in the carboxylic acid aqueous solution includes at least one of citric acid, lactic acid, salicylic acid, acetic acid, benzoic acid, malic acid, tartaric acid, oxalic acid, and succinic acid.

[0018] In some preferred examples, in step (2), the volume ratio of carboxylic acid to water in the carboxylic acid aqueous solution is 1 to 5:1, for example, 1.5:1, 13:7, 2:1, 71:29, 2.5:1, 3:1, etc.

[0019] In some preferred embodiments, in step (2), the temperature of the solution crystallization reaction is 90-100°C, such as 95°C.

[0020] In some preferred examples, in step (2), the initial mass percentage of desulfurized gypsum in the reaction solution is 9% to 20%, such as 10%.

[0021] In some preferred examples, in step (2), the potassium carboxylate includes at least one of potassium citrate, potassium lactate, potassium salicylate, potassium acetate, potassium benzoate, potassium malate, potassium tartrate, potassium oxalate, and potassium succinate.

[0022] In some preferred examples, in step (2), the carboxylic acid groups of the carboxylic acid in the carboxylic acid aqueous solution are entirely or partially identical to the carboxylic acid groups of the potassium carboxylate.

[0023] In some preferred examples, in step (2), the amount of potassium carboxylate added to the carboxylic acid aqueous solution is 0.1-0.3 mol / L, for example, 0.11 mol / L, 0.18 mol / L, 0.2 mol / L, 0.25 mol / L, etc.

[0024] In some preferred embodiments, in step (2), the drying temperature is 55-65°C, such as 60°C, and the drying time is 2-3 h.

[0025] In some preferred embodiments, in step (2), the high quality α -The particle size distribution of hemihydrate gypsum powder is 20~30 μm. The powder with this particle size distribution has low water requirement for hydration, and the obtained hardened body has high absolute dry compressive and flexural strength.

[0026] In step (2), the high quality α -The purity of hemihydrate gypsum powder is greater than 98.5%.

[0027] The present invention also provides the desulfurization gypsum selective and efficient impurity removal and preparation of high-quality α -High quality prepared by the method of hemihydrate gypsum α - Hemihydrate gypsum powder.

[0028] The present invention also provides a high-quality α - Hemihydrate gypsum hardened body, through the high quality α -Hemihydrate gypsum powder is prepared.

[0029] The present invention also provides a high-quality α - A method for preparing a hardened hemihydrate gypsum, comprising: α - Mix hemihydrate gypsum powder with water and stir thoroughly until α - After the semi-hydrated gypsum reacts completely with water to form a fluid hydrated body, it is molded and cured until the hydrated body is completely dry to obtain the high-quality α -Hydrated hemihydrate gypsum.

[0030] The invention has high quality α -High quality of hemihydrate gypsum powder preparation α -The absolute dry compressive strength of the hardened hemihydrate gypsum is greater than 30 MPa, and the absolute dry flexural strength is not less than 10 MPa.

[0031] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention removes organic impurities, soluble impurities and insoluble impurities in desulfurized gypsum by coupling (reverse) flotation + water washing oxidation + acid leaching, which has good impurity removal effect and improves α - Purity of hemihydrate gypsum product.

[0032] 2. The present invention uses carboxylic acid aqueous solution to carry out solution crystallization reaction of desulfurized gypsum, and simultaneously uses trace amount of potassium carboxylate to coordinately regulate α -Nucleation rate and crystal morphology of hemihydrate gypsum, prepared α - Hemihydrate gypsum crystals are of high purity and their hardened bodies have high absolute dry compressive and flexural strengths.

[0033] 3. The raw material desulfurization gypsum used in the present invention is one of the bulk industrial solid wastes, which is widely available and cheap. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The invention provides a desulfurization gypsum selective and efficient impurity removal and preparation of high-quality α - Schematic diagram of the process flow of hemihydrate gypsum.

[0035] Figure 2 This is a scanning electron microscope (SEM) photograph of the original desulfurization gypsum of Example 1. DETAILED DESCRIPTION

[0036] The present invention will be further described below in conjunction with the accompanying drawings and specific examples. It should be understood that these examples are intended to illustrate the present invention and are not intended to limit the scope of the invention. The operating methods in the following examples where no specific conditions are specified are generally performed under conventional conditions or as recommended by the manufacturer.

[0037] Example 1: See also Figure 1 , a desulfurization gypsum selective and efficient impurity removal and preparation of high-quality α - A method for hemihydrate gypsum plastering comprising the steps of: (1) 100 g of desulfurized gypsum (morphology as Figure 2 The prepared slurry was mixed with 2.0 L of tap water to form a flotation pulp with a concentration of 50 g / L, and 0.01 g of dodecylamine and 0.005 g of methyl isobutyl carbinol were added. The prepared slurry was then added to a flotation machine for reverse flotation. After the flotation, the tailings of the slurry were separated by vacuum filtration.

[0038] (2) The desulfurized gypsum after flotation was added to 300 mL of tap water at 30°C and stirred for 2.8 h. At the same time, air was introduced at a flow rate of 2.5 L / min for 2.8 h. After the cleaning was completed, vacuum filtration was performed for separation.

[0039] (3) The washed desulfurized gypsum was added to 250 mL of 0.4 mol / L hydrochloric acid solution for acid leaching for 3.0 h. After the acid leaching, it was separated by vacuum filtration and placed in a 60°C forced air drying oven to obtain the desulfurized gypsum after impurities were removed.

[0040] (4) After 500 mL of citric acid and 500 mL of deionized water are mixed evenly, 76.57 g of potassium citrate is added, and after stirring and heating to 95 °C, the desulfurized gypsum obtained in step (3) is added. α - hemihydrate gypsum, the entire reaction solution was separated by vacuum filtration, rinsed with hot water, poured into acetone solution for rinsing, and then placed in a 60 ° C forced air drying oven for 2 h to obtain α - Hemihydrate gypsum crystals.

[0041] (5) α - Hemihydrate gypsum crystals are placed in a ball mill and milled to a particle size of 20-30 μm to obtain high-quality α - Hemihydrate gypsum powder, the powder α -The purity of hemihydrate gypsum is 98.6%.

[0042] (6) High quality α - Add water to the semi-hydrated gypsum powder according to the water-to-paste ratio and stir thoroughly until α - After the semi-hydrated gypsum reacts completely with water to form a fluid hydrated body, it is poured into the mold for molding. After demoulding, it is placed in a constant temperature and humidity incubator for curing until the hydrated body is completely dry to obtain high-quality α -The dry compressive strength and dry flexural strength of the hardened hemihydrate gypsum are 31 MPa and 10 MPa respectively.

[0043] Example 2: See also Figure 1 , a desulfurization gypsum selective and efficient impurity removal and preparation of high-quality α - A method for hemihydrate gypsum plastering comprising the steps of: (1) 100 g of desulfurized gypsum was mixed with 1.6 L of tap water to prepare a flotation pulp with a concentration of 62.5 g / L. 0.015 g of dodecylamine and 0.008 g of methyl isobutyl carbinol were added. The prepared pulp was then added to the flotation machine for reverse flotation. After the flotation was completed, the pulp tail liquid was separated by vacuum filtration.

[0044] (2) The desulfurized gypsum after flotation was added to 300 mL of tap water at 40°C and stirred for 2.5 h. At the same time, it was exposed to air at a flow rate of 3.5 L / min for 2.5 h. After the cleaning was completed, vacuum filtration was performed for separation.

[0045] (3) The washed desulfurized gypsum was added to 200 mL of 1.0 mol / L hydrochloric acid solution for acid leaching for 2.5 h. After the acid leaching, it was separated by vacuum filtration and placed in a 60°C forced air drying oven to obtain the desulfurized gypsum after impurities were removed.

[0046] (4) After 600 mL of salicylic acid and 400 mL of deionized water are mixed evenly, 35.65 g of potassium salicylate are added, and after stirring and heating to 95 °C, the desulfurized gypsum obtained in step (3) is added. α - hemihydrate gypsum, the entire reaction solution was separated by vacuum filtration, rinsed with hot water, poured into acetone solution for rinsing, and then placed in a 60 ° C forced air drying oven for 2 h to obtain α - Hemihydrate gypsum crystals.

[0047] (5) α - Hemihydrate gypsum crystals are placed in a ball mill and milled to a particle size of 20-30 μm to obtain high-quality α - Hemihydrate gypsum powder, the powder α -The purity of hemihydrate gypsum is 98.9%.

[0048] (6) High quality α - Add water to the semi-hydrated gypsum powder according to the water-to-paste ratio and stir thoroughly until α - After the semi-hydrated gypsum reacts completely with water to form a fluid hydrated body, it is poured into the mold for molding. After demoulding, it is placed in a constant temperature and humidity incubator for curing until the hydrated body is completely dry to obtain high-quality α -The dry compressive strength and dry flexural strength of the hardened hemihydrate gypsum are 33 MPa and 12 MPa respectively.

[0049] Example 3: See also Figure 1 , a desulfurization gypsum selective and efficient impurity removal and preparation of high-quality α - A method for hemihydrate gypsum plastering comprising the steps of: (1) 100 g of desulfurized gypsum was mixed with 1.4 L of tap water to prepare a flotation pulp with a concentration of 71.4 g / L. 0.02 g of dodecylamine and 0.01 g of methyl isobutyl carbinol were added. The prepared pulp was then added to the flotation machine for reverse flotation. After the flotation was completed, the pulp tail liquid was separated by vacuum filtration.

[0050] (2) The desulfurized gypsum after flotation was added to 200 mL of tap water at 50°C and stirred for 2.0 h. At the same time, air was introduced at a flow rate of 4.0 L / min for 2.0 h. After the cleaning was completed, vacuum filtration was performed for separation.

[0051] (3) The washed desulfurized gypsum was added to 180 mL of 1.5 mol / L hydrochloric acid solution and acid-leached for 2.0 h. After the acid-leaching, it was separated by vacuum filtration and dried in a 60°C forced air drying oven to obtain the desulfurized gypsum after impurities were removed.

[0052] (4) After 650 mL of malic acid and 350 mL of deionized water are mixed evenly, 31.54 g of potassium malate are added, and after stirring and heating to 95 °C, the desulfurized gypsum obtained in step (3) is added. α - hemihydrate gypsum, the entire reaction solution was separated by vacuum filtration, rinsed with hot water, poured into acetone solution for rinsing, and then placed in a 60 ° C forced air drying oven for 2 h to obtain α - Hemihydrate gypsum crystals.

[0053] (5) α - Hemihydrate gypsum crystals are placed in a ball mill and milled to a particle size of 20-30 μm to obtain high-quality α - Hemihydrate gypsum powder, the powder α -The purity of hemihydrate gypsum is 99.3%.

[0054] (6) High quality α - Add water to the semi-hydrated gypsum powder according to the water-to-paste ratio and stir thoroughly until α - After the semi-hydrated gypsum reacts completely with water to form a fluid hydrated body, it is poured into the mold for molding. After demoulding, it is placed in a constant temperature and humidity incubator for curing until the hydrated body is completely dry to obtain high-quality α -The dry compressive strength and dry flexural strength of the hardened hemihydrate gypsum are 34 MPa and 15 MPa respectively.

[0055] Example 4: See also Figure 1 , a desulfurization gypsum selective and efficient impurity removal and preparation of high-quality α - A method for hemihydrate gypsum plastering comprising the steps of: (1) 100 g of desulfurized gypsum was mixed with 1.2 L of tap water to prepare a flotation pulp with a concentration of 83.3 g / L. 0.025 g of dodecylamine and 0.012 g of methyl isobutyl carbinol were added. The prepared pulp was then added to a flotation machine for reverse flotation. After the flotation was completed, the pulp tail liquid was separated by vacuum filtration.

[0056] (2) The desulfurized gypsum after flotation was added to 200 mL of tap water at 60°C and stirred for 1.5 h. At the same time, it was exposed to air at a flow rate of 4.5 L / min for 1.5 h. After cleaning, vacuum filtration was performed.

[0057] (3) The washed desulfurized gypsum was added to 150 mL of 2.0 mol / L hydrochloric acid solution and acid-leached for 1.5 h. After acid-leaching, it was separated by vacuum filtration and dried in a 60°C forced air drying oven to obtain the desulfurized gypsum after impurities were removed.

[0058] (4) After 290 mL of deionized water and 710 mL of tartaric acid are mixed evenly, 47.04 g of potassium tartrate is added, and after stirring and heating to 95 °C, the desulfurized gypsum obtained in step (2) is added. α - hemihydrate gypsum, the entire reaction solution was separated by vacuum filtration, rinsed with hot water, poured into acetone solution for rinsing, and then placed in a 60 ° C forced air drying oven for 2 h to obtain α - Hemihydrate gypsum crystals.

[0059] (5) α - Hemihydrate gypsum crystals are placed in a ball mill and milled to a particle size of 20-30 μm to obtain high-quality α - Hemihydrate gypsum powder, the powder α -The purity of hemihydrate gypsum is 99.2%.

[0060] (6) High quality α - Add water to the semi-hydrated gypsum powder according to the water-to-paste ratio and stir thoroughly until α - After the semi-hydrated gypsum reacts completely with water to form a fluid hydrated body, it is poured into the mold for molding. After demoulding, it is placed in a constant temperature and humidity incubator for curing until the hydrated body is completely dry to obtain high-quality α -The dry compressive strength and dry flexural strength of the hardened hemihydrate gypsum are 35 MPa and 16 MPa respectively.

[0061] Example 5: See also Figure 1 , a desulfurization gypsum selective and efficient impurity removal and preparation of high-quality α - A method for hemihydrate gypsum plastering comprising the steps of: (1) 100 g of desulfurized gypsum was mixed with 1.1 L of tap water to prepare a flotation pulp with a concentration of 90.9 g / L, and 0.03 g of dodecylamine and 0.015 g of methyl isobutyl carbinol were added. The prepared pulp was then added to the flotation machine for flotation. After flotation, the pulp tail liquid was separated by vacuum filtration.

[0062] (2) The desulfurized gypsum after flotation was added to 150 mL of tap water at 60°C, stirred and mixed, and washed for 1.5 h. At the same time, it was exposed to air at a flow rate of 5.0 L / min for 1.5 h. After washing, vacuum filtration was performed.

[0063] (3) The washed desulfurized gypsum was added to 100 mL of 2.5 mol / L hydrochloric acid solution for acid leaching for 1.5 h. After the acid leaching, it was separated by vacuum filtration and placed in a 60°C forced air drying oven to obtain the desulfurized gypsum after impurities were removed.

[0064] (4) After 400 mL of oxalic acid, 350 mL of succinic acid and 250 mL of deionized water are mixed evenly, 36.85 g of potassium oxalate is added, and after stirring and heating to 95 °C, the desulfurized gypsum obtained in step (2) is added. After the desulfurized gypsum is completely converted to α - hemihydrate gypsum, the entire reaction solution was separated by vacuum filtration, rinsed with hot water, poured into acetone solution for rinsing, and then placed in a 60 ° C forced air drying oven for 2 h to obtain α - Hemihydrate gypsum crystals.

[0065] (5) α - Hemihydrate gypsum crystals are placed in a ball mill and milled to a particle size of 20-30 μm to obtain high-quality α - Hemihydrate gypsum powder, the powder α -The purity of hemihydrate gypsum is 99.5%.

[0066] (6) High quality α - Add water to the semi-hydrated gypsum powder according to the water-to-paste ratio and stir thoroughly until α - After the semi-hydrated gypsum reacts completely with water to form a fluid hydrated body, it is poured into the mold for molding. After demoulding, it is placed in a constant temperature and humidity incubator for curing until the hydrated body is completely dry to obtain high-quality α -The dry compressive strength and dry flexural strength of the hardened hemihydrate gypsum are 32 MPa and 13 MPa respectively.

[0067] Comparative Example 1: The only difference from Example 1 is that in step (4), potassium citrate is not added to the mixed solution of 500 mL citric acid and 500 mL deionized water. The remaining steps are the same. The final product is α -The purity of hemihydrate gypsum powder is 98.5%, and the absolute dry compressive strength and absolute dry flexural strength of its hardened body are 3 MPa and 1 MPa respectively.

[0068] Comparative Example 2: The only difference from Example 1 is that in step (4), the mixed solution of 500 mL citric acid and 500 mL deionized water is changed to 1 L deionized water, and no citric acid is added. The other steps are the same, and the desulfurized gypsum does not undergo phase inversion reaction, and no α -Nucleation of hemihydrate gypsum crystals.

[0069] Comparative Example 3: The only difference from Example 1 is that there are no steps (1), (2) and (3), and the untreated desulfurized gypsum is directly added to the citric acid solution of potassium citrate to carry out solution crystallization reaction. The other steps are the same, and the final product is α The purity of the hemihydrate gypsum powder is 95.4%, and the absolute dry compressive strength and absolute dry flexural strength of its hardened body are 26 MPa and 7 MPa respectively.

[0070] Comparative Example 4: The only difference from Example 1 is that in step (4), potassium citrate is replaced by an equimolar amount of potassium chloride, and the remaining steps are the same. The final product is α The purity of the hemihydrate gypsum powder is 98.6%, and the absolute dry compressive strength and absolute dry flexural strength of its hardened body are 25 MPa and 6 MPa respectively.

[0071] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A method for selectively and efficiently removing impurities from desulfurized gypsum and preparing high-quality α - Method for hemihydrate gypsum, characterized in that, Including steps: (1) First, the organic impurities in the desulfurization gypsum are removed by flotation, and then the soluble impurities are removed by water washing. During the water washing, the calcium sulfite is oxidized into calcium sulfate dihydrate by exposure to air. Then, the insoluble impurities are removed by acid leaching in a hydrochloric acid solution, and the treated desulfurization gypsum is taken out and dried; (2) adding the desulfurized gypsum treated in step (1) into a carboxylic acid aqueous solution to carry out a solution crystallization reaction, wherein potassium carboxylate is also added into the carboxylic acid aqueous solution to regulate the crystallization rate and crystal morphology. After the reaction is completed, the solid and liquid are separated, and the solid is washed, dried, and ball-milled to obtain high-quality α - Hemihydrate gypsum powder.

2. The method according to claim 1, characterized in that In step (1), the flotation is reverse flotation, the flotation pulp concentration is 50-100 g / L, the flotation collector used is dodecylamine, the amount used is 100-300 g / t desulfurized gypsum, and the foaming agent is methyl isobutyl carbinol, the amount used is 50-150 g / t desulfurized gypsum.

3. The method according to claim 1, characterized in that During the water washing process of step (1), the ratio of the mass of desulfurized gypsum to the volume of water is 1:1.0~3.5, the water washing temperature is 30~60°C, and the water washing time is 0.5~3 h.

4. The method according to claim 1, wherein In step (1), the air aeration rate is 0.5~5 L / min, and the aeration time is 0.5~3 h.

5. The method according to claim 1, wherein In step (1), the concentration of the hydrochloric acid solution is 0.3-3 mol / L, the ratio of the mass of desulfurized gypsum to the volume of the hydrochloric acid solution is 1:1.0-3.0, and the acid leaching time is 0.5-3 h.

6. The method according to claim 1, characterized in that In step (2): The carboxylic acid in the carboxylic acid aqueous solution includes at least one of citric acid, lactic acid, salicylic acid, acetic acid, benzoic acid, malic acid, tartaric acid, oxalic acid, and succinic acid; The volume ratio of carboxylic acid to water in the carboxylic acid aqueous solution is 1 to 5:1; The temperature of the solution crystallization reaction is 90-100°C; The initial mass percentage of desulfurized gypsum in the reaction solution is 9%~20%; The potassium carboxylate includes at least one of potassium citrate, potassium lactate, potassium salicylate, potassium acetate, potassium benzoate, potassium malate, potassium tartrate, potassium oxalate, and potassium succinate; The carboxylic acid groups of the carboxylic acid in the carboxylic acid aqueous solution are all identical or partially identical to the carboxylic acid groups of the potassium carboxylate; The amount of potassium carboxylate added to the carboxylic acid aqueous solution is 0.1-0.3 mol / L; The drying temperature is 55-65° C., and the drying time is 2-3 h.

7. The method according to claim 1, characterized in that In step (2), the high quality α -The particle size distribution of hemihydrate gypsum powder is 20~30 μm; The high quality α -The purity of hemihydrate gypsum powder shall not be less than 98%.

8. The high-quality α - Hemihydrate gypsum powder.

9. A high quality α - Hemihydrate gypsum hardened body, characterized in that The high quality of claim 8 α -Hemihydrate gypsum powder is prepared.

10. A high quality α - A method for preparing a hardened hemihydrate gypsum, characterized in that: include: The high quality of claim 8 α - Mix hemihydrate gypsum powder with water and stir thoroughly until α - After the semi-hydrated gypsum reacts completely with water to form a fluid hydrated body, it is molded and cured until the hydrated body is completely dry to obtain the high-quality α -Hydrated hemihydrate gypsum.

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