A method for producing super-grade anhydrite by decomposing calcium chloride and producing hydrochloric acid as a by-product

Abstract

The present invention discloses a method for producing super-grade anhydrite by decomposing calcium chloride and producing hydrochloric acid as a byproduct. The method comprises heating a calcium chloride solution to above 102°C, adding concentrated sulfuric acid for stirring reaction, obtaining a reaction solution containing calcium sulfate precipitation and hydrogen chloride gas; the reaction solution containing calcium sulfate precipitation is subjected to solid-liquid separation to obtain an anhydrous calcium sulfate product and a filtrate containing calcium chloride; the hydrogen chloride gas is absorbed by water to obtain hydrochloric acid. The anhydrous calcium sulfate obtained by the method has high grade and good quality, meets the quality standard of super-grade anhydrite specified in GB / T 5483‑2008, and has a complete crystal structure, no cracks, low surface activity, and is suitable for use as a filler in industries such as plastics, rubber, paint, textiles, and papermaking. The method is simple, easy to operate, and has low production cost, and is suitable for large-scale industrial production of super-grade anhydrite.

Description

Technical Field

[0001] The invention relates to a method for preparing gypsum, in particular to a method for producing super-grade anhydrite by decomposing calcium chloride and producing hydrochloric acid as a by-product, and belongs to the field of chemical metallurgy. Background Art

[0002] Gypsum material has many excellent properties. It is widely used in cement, new binders, painting materials, self-leveling materials, plastics, rubber, paint, textiles, papermaking, chalk, toothpaste, cosmetics, medical treatment, arts and crafts and other fields.

[0003] As is known to all, gypsum has 5 phases and 7 variants, among which anhydrous gypsum (hard gypsum) has 4 variants, namely α-III type anhydrous gypsum, β-III type anhydrous gypsum, II type anhydrous gypsum, and I type anhydrous gypsum. Since type III anhydrous gypsum is formed by heating and dehydrating hemihydrate gypsum or dihydrate gypsum at a temperature below 360°C, it is a soluble hard gypsum and a metastable anhydrous gypsum. Because many cracks are generated on the surface during the heating and dehydration process, it is very easy to absorb water molecules in the air and hydrate into hemihydrate gypsum, so type III anhydrous gypsum is limited in use. Type I anhydrous gypsum is transformed from Type II hard gypsum at a temperature higher than 1180°C. It can only exist at a temperature higher than 1180°C. Below this temperature, it will turn into Type II anhydrite. Therefore, the anhydrite usually used in industry refers to Type II anhydrous gypsum, which mainly comes from natural anhydrite, anhydrous fluorinated gypsum which is a by-product of hydrogen fluoride production, and anhydrous gypsum obtained by calcining dihydrate gypsum at 360-1180°C.

[0004] Pure anhydrite is transparent, colorless or white, and contains impurities to become dark gray, sometimes with a slight red or blue tint. Therefore, only the impurity-free super-grade anhydrite can be used as filler in industries such as plastics, rubber, paint, textiles, and papermaking. However, with the depletion of natural high-quality anhydrite mines, most of the super-grade anhydrite currently sold on the market is made from high-quality precipitated calcium sulfate dihydrate as raw material, which is prepared by high-temperature calcination. The resulting product is not only expensive in raw material price, but also has high processing costs. Summary of the invention

[0005] In view of the defects of the existing anhydrite preparation technology such as poor product quality and high production cost, the present invention aims to provide a method for producing special grade anhydrite by decomposing calcium chloride and producing hydrochloric acid as a by-product. The method has simple process, easy operation, low production cost, good product quality, and is economical and environmentally friendly.

[0006] In order to achieve the above technical purpose, the present invention provides a method for producing special-grade anhydrite by decomposing calcium chloride and producing hydrochloric acid as a by-product, wherein the method comprises heating a calcium chloride solution to above 102°C, adding concentrated sulfuric acid for stirring reaction, and obtaining a reaction liquid containing calcium sulfate precipitates and hydrogen chloride gas; the reaction liquid containing calcium sulfate precipitates is subjected to solid-liquid separation to obtain an anhydrous calcium sulfate product and a filtrate containing calcium chloride; and the hydrogen chloride gas is absorbed by water to obtain hydrochloric acid.

[0007] As a preferred solution, the filtrate containing calcium chloride is circulated for preparing a calcium chloride solution.

[0008] In the present invention, calcium chloride solution is used as the raw material liquid and concentrated sulfuric acid is used as the decomposition agent. Since calcium chloride solution and concentrated sulfuric acid have strong water absorption and dehydration properties under the condition of temperature>102°C, the Ca 2+ and SO4 2- At a temperature not lower than 102°C, it can be assembled in situ to form anhydrous CaSO4 crystals. - The common ion effect generated forces the HCl gas in the reaction liquid to volatilize, avoiding the formation of calcium sulfate dihydrate, calcium sulfate hemihydrate and calcium hydrogen sulfate, and releasing HCl gas. The slurry after the reaction is separated into solid and liquid to obtain special hard gypsum and filtrate containing CaCl2. The filtrate containing CaCl2 is returned to prepare the raw material liquid for recycling, realizing its clean and environmentally friendly recycling process. The generated HCl gas can be absorbed by water to obtain hydrochloric acid. The basic reaction principle in the process of the present invention is as follows:

[0009] CaCl2+H2SO4=Δ=CaSO4↓+2HCl↑.

[0010] As a preferred solution, the mass concentration of calcium chloride in the mixed solution during the stirring reaction is not less than 14%. Too low mass concentration of calcium chloride solution in the reaction system will lead to a decrease in the boiling point of the solution, and the HCl gas generated by the reaction will be difficult to volatilize if the solution temperature is not high, thereby affecting the quality of the calcium sulfate product.

[0011] As a preferred solution, the mass concentration of the concentrated sulfuric acid is not less than 64%.

[0012] As a preferred solution, the calcium chloride solution is reacted with concentrated sulfuric acid at a molar ratio of Ca / S>1.5.

[0013] As a preferred solution, the conditions of the stirring reaction are: temperature of 102-165° C., time of 0.5-3.5 h. Controlling the reaction temperature of the mixed solution in a suitable range is conducive to obtaining high-quality calcium sulfate products. When the reaction temperature is lower than 102° C., the HCl gas generated by the reaction of adding concentrated sulfuric acid is difficult to evaporate from the solution, and the failure of the HCl gas to evaporate in time will lead to an increase in the acidity of the solution, resulting in a colloidal precipitation of calcium hydrogen sulfate. In addition, too high a reaction temperature will cause a large amount of evaporation of water in the solution, and the slurry will become viscous, which is not conducive to the rapid volatilization of the HCl gas generated by the reaction, affecting the reaction efficiency.

[0014] As a preferred solution, the calcium chloride solution is a solution formed by mixing calcium chloride with water, or a solution formed by mixing a filtrate containing calcium chloride with calcium chloride at a solid-liquid ratio of 1:1 to 10 g / mL. The filtrate containing calcium chloride produced during the reaction can be configured to form a new raw material solution (calcium chloride solution) by adding a certain amount of calcium chloride, thereby realizing the recycling of calcium chloride.

[0015] As a preferred embodiment, the calcium chloride includes at least one of anhydrous calcium chloride, dihydrate calcium chloride and hexahydrate calcium chloride.

[0016] As a preferred solution, the grade of the anhydrous calcium sulfate product is ≥99.5%.

[0017] The invention discloses a method for producing super-grade anhydrite by decomposing calcium chloride and producing hydrochloric acid as a by-product. The grade of anhydrous calcium sulfate precipitated in the process is ≥99.5%, which meets the quality standard of super-grade anhydrite specified in GB / T 5483-2008. The hydrochloric acid obtained by absorbing HCl gas released in the process meets the quality standard of superior products in synthetic hydrochloric acid specified in national standard GB320-2006.

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

[0019] (1) The prepared anhydrous calcium sulfate has high grade and good quality, meeting the quality standard of special-grade anhydrite specified in GB / T 5483-2008, and the hydrochloric acid obtained as a by-product meets the quality standard of superior products in synthetic hydrochloric acid specified in the national standard GB 320-2006;

[0020] (2) The anhydrous calcium sulfate has a complete crystal structure, no cracks, and low surface activity, and is suitable for use as a filler in industries such as plastics, rubber, paint, textiles, and papermaking;

[0021] (3) The method is simple, easy to operate, and has low production cost. The calcium chloride product produced can be recycled, which is green and environmentally friendly and very suitable for large-scale industrial production of special-grade anhydrite. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the XRD pattern of the anhydrous CaSO4 product obtained in Example 3.

[0023] Figure 2 This is the SEM image of the anhydrous CaSO4 product obtained in Example 3. DETAILED DESCRIPTION

[0024] The present invention will be further described below in conjunction with examples. The following examples are intended to illustrate the present invention rather than to further limit the present invention.

[0025] Example 1

[0026] Take 650mL of liquid calcium chloride with a mass concentration of 40% and add it to the three-necked biscuit, stir and heat it, and when the solution temperature rises to 105°C, slowly immerse and drip 112g of 98% concentrated sulfuric acid. After the concentrated sulfuric acid is added, continue heating and stirring for 1h to allow the HCl produced by the reaction to completely evaporate. Filter to obtain 131g of anhydrous CaSO4 with a purity of 99.8% and a CaCl2 solution with a mass concentration of 33% and a pH of 2.3. The volatilized HCl gas is absorbed by three-stage countercurrent water, and the obtained hydrochloric acid meets the quality standard of superior products in synthetic hydrochloric acid specified in the national standard GB 320-2006.

[0027] Example 2

[0028] First, the mass concentration obtained in Example 1 is 33% CaCl2 solution 586mL is added to the three-necked sesame seed cake, then 141g of calcium chloride dihydrate is added, and stirring and heating is performed until the solution temperature rises to 109°C, 112g of 98% concentrated sulfuric acid is slowly immersed and added dropwise, and after the concentrated sulfuric acid has been added dropwise, heating and stirring are continued for 0.5h to allow the HCl produced by the reaction to volatilize completely, heating is stopped, stirring and cooling to~80°C, and 135g of anhydrous CaSO4 with a purity of 99.6% and a mass concentration of 29% CaCl2 solution 597mL is obtained, and the volatilized HCl gas is absorbed by three-stage countercurrent water, and the hydrochloric acid obtained reaches the quality standard of the superior product in the synthetic hydrochloric acid specified in national standard GB 320-2006.

[0029] Example 3

[0030] First, the mass concentration of 29% CaCl2 solution 597mL obtained by Example 2 is added to the three-necked sesame seed cake, and then 111g of anhydrous calcium chloride is added, stirred and heated, until the solution temperature rises to 115°C, 130g of 85% concentrated sulfuric acid is slowly immersed and added dropwise, after the concentrated sulfuric acid is added dropwise, heated and stirred for 1h, the HCl produced by the reaction is allowed to volatilize completely, heating is stopped, stirring and cooling to~80°C, and 132g of anhydrous CaSO4 with a purity of 99.6% and a mass concentration of 31% CaCl2 solution 573mL is obtained, and the volatilized HCl gas is absorbed by three-stage countercurrent water, and the hydrochloric acid obtained reaches the quality standard of the superior product in the synthetic hydrochloric acid specified in national standard GB 320-2006.

[0031] from Figure 1 It can be seen that the precipitate formed by sulfuric acid and calcium chloride in hot CaCl2 solution is anhydrite, which does not contain calcium sulfate dihydrate, calcium sulfate hemihydrate and calcium hydrogen sulfate, and meets the quality requirements of special grade anhydrite; Figure 2 It can be seen that the obtained anhydrous CaSO4 has a complete crystal structure, no cracks on the surface, and a small and uniform particle size, making it suitable for use as a filler in plastics, rubber, paint, textiles, papermaking and other industries.

[0032] Comparative Example 1

[0033] Take 650mL of liquid calcium chloride with a mass concentration of 40% and add it to the three-necked biscuit, stir and heat it, wait until the solution temperature rises to 45°C, slowly immerse and drip 112g of 98% concentrated sulfuric acid, after the concentrated sulfuric acid is added, heat the solution to 115°C, stir at a constant temperature for 1h, let the HCl produced by the reaction volatilize, filter, the filter residue has poor filtration performance, contains a large amount of colloidal calcium hydrogen sulfate precipitate, and cannot be used as filler in industries such as plastics, rubber, paint, textiles, and papermaking. In addition, the production of calcium hydrogen sulfate makes the slurry viscous, which seriously hinders the volatilization of HCl, and the pH of the 591mL CaCl2 solution obtained by filtration is <0.1.

[0034] Comparative Example 2

[0035] Take 650mL of liquid calcium chloride with a mass concentration of 10% and add it to the three-necked biscuit, stir and heat the solution to 101°C, slowly immerse and drip 62g of 98% concentrated sulfuric acid, after the concentrated sulfuric acid is added, heat the solution to boiling and stir for 1h, let the HCl produced by the reaction volatilize, filter, the filter residue has good filtration performance, but the obtained filter residue contains a large amount of dihydrate calcium sulfate and hemihydrate calcium sulfate, which cannot be directly used as filler in plastics, rubber, paint, textile, papermaking and other industries.

Claims

1. A method for producing super-grade anhydrite by decomposing calcium chloride and producing hydrochloric acid as a by-product, characterized in that: The calcium chloride solution is heated to above 102°C, and concentrated sulfuric acid is added to react by stirring to allow HCl generated by the reaction to completely volatilize, thereby obtaining a reaction solution containing calcium sulfate precipitates and hydrogen chloride gas; the reaction solution containing calcium sulfate precipitates is subjected to solid-liquid separation to obtain an anhydrous calcium sulfate product and a filtrate containing calcium chloride, wherein the anhydrous calcium sulfate product is special-grade anhydrite; the hydrogen chloride gas is absorbed by water to obtain hydrochloric acid; The mass concentration of the concentrated sulfuric acid is not less than 85%; The calcium chloride solution is reacted with concentrated sulfuric acid at a molar ratio of Ca / S>1.5; The mass concentration of calcium chloride in the mixed solution during the stirring reaction is not less than 14%; The stirring reaction conditions are: temperature of 102-115° C. and time of 0.5-3.5 h.

2. The method for producing super-grade anhydrite by decomposing calcium chloride and producing hydrochloric acid as a by-product according to claim 1, characterized in that: The calcium chloride solution is a solution formed by mixing calcium chloride and water, or a solution formed by mixing a filtrate containing calcium chloride and calcium chloride at a solid-liquid ratio of 1:1 to 10 g / mL.

3. A method for producing super-grade anhydrite by decomposing calcium chloride and producing hydrochloric acid as a by-product according to claim 2, characterized in that: The calcium chloride includes at least one of anhydrous calcium chloride, dihydrate calcium chloride and hexahydrate calcium chloride.

4. The method for producing super-grade anhydrite by decomposing calcium chloride and producing hydrochloric acid as a by-product according to claim 1, characterized in that: The grade of the anhydrous calcium sulfate product is ≥99.5%.

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