Method for preparing semi-hydrated / anhydrous calcium sulfate and synchronously recovering hydrochloric acid from epoxy chloropropane saponification wastewater

Abstract

The invention discloses a method for preparing semi-hydrated / anhydrous calcium sulfate and synchronously recovering hydrochloric acid from epoxy chloropropane saponification wastewater, which comprises the following steps: adding a sulfuric acid solution into the epoxy chloropropane saponification wastewater according to the SO4 < 2-> / Ca < 2 + > molar ratio of 0.5-2.0 to obtain mixed slurry of calcium sulfate dihydrate and hydrochloric acid; carrying out a hydrothermal reaction on the mixed slurry of calcium sulfate dihydrate and hydrochloric acid at the temperature of 30-150 DEG C to obtain a mixed slurry of hemihydrate / anhydrous calcium sulfate and hydrochloric acid, and keeping the temperature for 0.5-10 hours; filtering the mixed slurry of the semi-hydrated / anhydrous calcium sulfate and hydrochloric acid to obtain a filtrate which is a hydrochloric acid solution and filter residues which are semi-hydrated / anhydrous calcium sulfate; and drying the semi-hydrated / anhydrous calcium sulfate filter residue to obtain a semi-hydrated / anhydrous calcium sulfate powder product. By utilizing the method, the epoxy chloropropane saponification wastewater can be efficiently utilized, the hemihydrate / anhydrous calcium sulfate is extracted from the epoxy chloropropane saponification wastewater, and the relatively pure hydrochloric acid solution is filtered out.

Description

Technical Field

[0001] The invention belongs to a method for preparing semi-aqueous / anhydrous calcium sulfate from epichlorohydrin saponification wastewater and simultaneously recovering hydrochloric acid. Background Art

[0002] Epichlorohydrin is an important organic chemical raw material, widely used as a solvent and surfactant for medicines, coatings, adhesives, resins and other products. At present, there are three main production processes for epichlorohydrin: propylene high-temperature chlorination method, propylene acetate method and glycerol method. All three processes require saponification treatment to produce epichlorohydrin products. Most saponification processes use lime milk as a saponifying agent. For every ton of epichlorohydrin product produced, the propylene high-temperature chlorination method, propylene acetate method and glycerol method will produce ≥40 tons, ≥10 tons and 4 to 6 tons of calcium chloride saponification wastewater respectively. The calcium chloride saponification wastewater has a high salt content and COD value, resulting in a high cost for its treatment as wastewater.

[0003] In order to solve the problem of high treatment cost of calcium chloride saponification wastewater produced by the epichlorohydrin process, a Chinese patent document with publication number CN105712520A discloses a method of introducing CO2 gas into calcium chloride saponification wastewater and then adding ammonium sulfate to precipitate Ca in the wastewater. 2+ The precipitate and wastewater after ammonium sulfate treatment are biochemically treated to meet the discharge standards.

[0004] The Chinese patent document with publication number CN107686209 A discloses obtaining saponified wastewater in the process of preparing epichlorohydrin by high-temperature chlorination of propylene; mixing the saponified wastewater with an acid to obtain a mixed solution, wherein the pH value of the mixed solution is 8 to 9; mixing the mixed solution with a flocculant, stirring, and settling to obtain a clear solution and a sediment; centrifuging the sediment to obtain lime water and lime slag; and returning the lime water for repeated flocculation and sedimentation. The patent document discloses adding acid to the calcium chloride saponified wastewater to adjust the pH value to 8 to 9, and then adding a flocculant to precipitate Ca 2+ , reduce the Ca in calcium chloride saponification wastewater 2+ concentration to reduce the subsequent biochemical treatment costs.

[0005] The methods disclosed in the above two patent documents start from the harmless disposal of epichlorohydrin saponification wastewater, first precipitate Ca 2+ , reduce the salt content of wastewater, regenerate and treat it, and make the wastewater meet the discharge standards. However, the calcium chloride saponification wastewater produced by the epichlorohydrin process has a large amount of water and high salinity, and the wastewater treatment is difficult and expensive. If the calcium chloride contained in it can be converted into useful products, it can not only reduce the cost of wastewater treatment, but also turn waste into treasure, promote the comprehensive utilization of epichlorohydrin saponification wastewater and reduce wastewater discharge.

[0006] The Chinese patent document with publication number CN111777091A discloses a method for preparing calcium sulfate and hydrogen chloride using pivalic acid waste acid and epichlorohydrin waste water. The epichlorohydrin waste water is first diluted, a reaction aid is added, and preheated, and then pivalic acid byproduct waste acid is added for reaction. The product is filtered, washed and dried to obtain a calcium sulfate product, and the filtrate is analyzed to obtain hydrogen chloride gas. This method realizes the resource utilization of epichlorohydrin saponification waste water and has high economic and environmental benefits. However, this method dilutes the epichlorohydrin saponification waste water, which will reduce the concentration of the hydrochloric acid solution and increase the cost of hydrochloric acid analysis; adding reaction aids such as aluminum chloride, polyacrylic acid, and tartaric acid will introduce impurities into the reaction system, increase costs, and reduce the added value of the product. Summary of the invention

[0007] The invention provides a method for preparing semi-aqueous / anhydrous calcium sulfate from epichlorohydrin saponification wastewater and simultaneously recovering hydrochloric acid. The method can efficiently utilize epichlorohydrin saponification wastewater, extract semi-aqueous / anhydrous calcium sulfate from the epichlorohydrin saponification wastewater, and filter out a relatively pure hydrochloric acid solution.

[0008] The present invention provides a method for preparing semi-aqueous / anhydrous calcium sulfate from epichlorohydrin saponification wastewater and simultaneously recovering hydrochloric acid, comprising:

[0009] S1, according to SO4 2- / Ca 2+ The molar ratio is 0.5 to 2.0, sulfuric acid solution is added to the epichlorohydrin saponification wastewater to obtain a mixed slurry of calcium sulfate dihydrate and hydrochloric acid;

[0010] S2, subjecting the mixed slurry of calcium sulfate dihydrate and hydrochloric acid to a hydrothermal reaction to obtain a mixed slurry of hemihydrate / anhydrous calcium sulfate and hydrochloric acid, wherein the temperature of the hydrothermal reaction is 30-150° C. and the temperature is kept for 0.5-10 h;

[0011] S3, filtering the mixed slurry of semi-hydrated / anhydrous calcium sulfate and hydrochloric acid, the filtrate is a hydrochloric acid solution, and the filter residue is semi-hydrated / anhydrous calcium sulfate;

[0012] S4, drying the semi-hydrated / anhydrous calcium sulfate residue to obtain a semi-hydrated / anhydrous calcium sulfate powder product.

[0013] Preferably, SO4 2- / Ca 2+ The molar ratio is 0.8 to 1.0.

[0014] Preferably, the mass percentage concentration of the sulfuric acid is 10-90%.

[0015] The present invention controls the concentration of sulfuric acid so that the morphology of the obtained calcium sulfate is better, that is, the aspect ratio is larger, and the sulfuric acid concentration in the hydrochloric acid is appropriate, so as to avoid the sulfuric acid concentration in the hydrochloric acid being too high, which is not conducive to the recovery of the hydrochloric acid. Further preferably, the mass percentage concentration of the sulfuric acid is 30-60%.

[0016] The epichlorohydrin saponification wastewater used comes from the saponification process in the epichlorohydrin production process. The CaCl2 concentration of the saponification wastewater produced by different epichlorohydrin production processes is different, and the mass percentage concentration of CaCl2 is 20-40%.

[0017] Preferably, the HCl concentration of the hydrochloric acid solution is 1.0 to 5.0 mol / L. For the epichlorohydrin saponification wastewater with a stable source, its CaCl2 concentration remains almost unchanged. The HCl concentration of the obtained hydrochloric acid solution mainly depends on the concentration of the sulfuric acid used. Under the condition that the preferred sulfuric acid concentration is 30 to 60%, the HCl concentration of the obtained hydrochloric acid solution is 3.0 to 4.5 mol / L.

[0018] The hydrochloric acid solution can be directly returned to the epichlorohydrin production process for utilization, or returned to the epichlorohydrin production process for utilization after analysis. The specific method of hydrochloric acid recovery and utilization depends on the production process of epichlorohydrin.

[0019] Preferably, a mixed slurry of calcium sulfate dihydrate and hydrochloric acid is subjected to a hydrothermal reaction to obtain calcium sulfate hemihydrate, and the temperature of the hydrothermal reaction is 60 to 90° C. and the temperature is kept for 1 to 3 hours.

[0020] Preferably, a mixed slurry of calcium sulfate dihydrate and hydrochloric acid is subjected to a hydrothermal reaction to obtain anhydrous calcium sulfate, and the temperature of the hydrothermal reaction is 80 to 120° C. and the temperature is kept for 5 to 8 hours.

[0021] The process of sulfuric acid and epichlorohydrin saponification wastewater mixing to form calcium sulfate dihydrate is SO4 2- With Ca 2+ The combined precipitation reaction, however, has a large solubility in hydrochloric acid solution, and increasing the reaction temperature will further increase the solubility of calcium sulfate dihydrate in hydrochloric acid solution. Therefore, by increasing the reaction temperature and extending the reaction time, the calcium sulfate dihydrate formed by the mixture of sulfuric acid and epichlorohydrin saponification wastewater can be gradually dissolved and converted into hemihydrate calcium sulfate and anhydrous calcium sulfate with lower solubility and better stability.

[0022] Preferably, the sulfuric acid solution is added to the oxychloropropane saponification wastewater and then stirred, and the stirring rate is 300-1200rp.

[0023] The epichlorohydrin saponification wastewater is directly reacted with sulfuric acid to obtain a mixed slurry of calcium sulfate dihydrate and hydrochloric acid. The mixed slurry has a relatively high viscosity and requires a relatively high stirring rate to ensure uniform heat and mass transfer of the materials.

[0024] Preferably, the drying temperature of step S4 is 80-300°C.

[0025] When the drying temperature exceeds 300°C, calcium sulfate hemihydrate or anhydrous calcium sulfate gradually transforms into dead-burned anhydrous calcium sulfate which is insoluble in water and has low activity. At a temperature exceeding 200°C, calcium sulfate hemihydrate gradually dehydrates and transforms into anhydrous calcium sulfate. Preferably, the drying temperature is 100-200°C. At this temperature, the obtained calcium sulfate hemihydrate or anhydrous calcium sulfate has high activity and is partially soluble in water.

[0026] Preferably, the semi-hydrated / anhydrous calcium sulfate powder product is calcined to obtain dead-burned anhydrous calcium sulfate, and the calcination temperature is 500-1000°C.

[0027] At higher temperatures, the semi-hydrated / anhydrous calcium sulfate powder product can be converted into dead-burned anhydrous calcium sulfate with a more stable structure.

[0028] More preferably, the calcination temperature is 600-800°C.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] By controlling SO4 2- / Ca 2+ The molar ratio makes the SO4 in the hydrochloric acid solution 2- and Ca 2+ The content is appropriate, so as to obtain hydrochloric acid with higher purity, which is conducive to the reuse of hydrochloric acid. At the same time, if SO4 2- Too high or Ca 2+ If the content is too high, it will inhibit the dissolution of calcium sulfate dihydrate in hydrochloric acid solution, which is not conducive to the preparation of hemihydrate / anhydrous calcium sulfate with regular structure and morphology, resulting in the obtained hemihydrate / anhydrous calcium sulfate having a composite morphology of granules, short rods and needles, and poor activity.

[0031] The invention increases the hydrothermal reaction temperature and prolongs the heat preservation time, so that the calcium sulfate dihydrate formed by the mixture of sulfuric acid and epichlorohydrin saponification wastewater is dissolved in a hydrochloric acid solution and converted into hemihydrate / anhydrous calcium sulfate with higher stability. In the prior art, after the calcium sulfate dihydrate is obtained, it is generally taken out to evaporate the water to obtain the hemihydrate / anhydrous calcium sulfate. However, in actual application, the epichlorohydrin saponification wastewater to which sulfuric acid has been added in the reactor is taken out and dried, which has a complicated process and high energy consumption. The innovation of the invention is to convert the calcium sulfate dihydrate into hemihydrate / anhydrous calcium sulfate with higher activity directly in the reactor by a method of regulating crystallization through a hydrothermal reaction, which has a simple process, a short flow and a high product added value. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the XRD diagram of the calcium sulfate product obtained in Comparative Example 1 of the present invention;

[0033] Figure 2 This is the XRD pattern of the calcium sulfate product obtained in Example 3 of the present invention;

[0034] Figure 3 This is the XRD pattern of the calcium sulfate product obtained in Example 9 of the present invention;

[0035] Figure 4 This is a SEM image of the calcium sulfate product obtained in Comparative Example 1 of the present invention;

[0036] Figure 5 This is a SEM image of the calcium sulfate product obtained in Example 3 of the present invention;

[0037] Figure 6 This is a SEM image of the calcium sulfate product obtained in Example 9 of the present invention. DETAILED DESCRIPTION

[0038] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0039] Comparative Example 1

[0040] Step (1): Under the condition of stirring speed of 800 rpm, SO4 2- / Ca 2+ The molar ratio is 0.8, adding 20% ​​sulfuric acid solution into the epichlorohydrin saponification wastewater with a CaCl2 concentration of 30%;

[0041] Step (2): keeping the mixed slurry obtained in step (1) at 80° C. for 0.1 h;

[0042] Step (3): filtering the mixed slurry obtained in step (2), and collecting the filtrate and filter residue;

[0043] Step (4): Dry the filter residue obtained in step (3) at 80° C. to constant weight to obtain a powder product.

[0044] The hydrochloric acid concentration of the filtrate in step (3) and the microstructure of the powder in step (4) were detected respectively. The results showed that the hydrochloric acid concentration of the obtained filtrate was 2.6 mol / L, Ca 2+ The concentration is 8g / L and the powder product is calcium sulfate dihydrate.

[0045] Example 1

[0046] Step (1): Under the condition of stirring speed of 300 rpm, SO4 2- / Ca 2+ The molar ratio is 0.5. 10% sulfuric acid solution is added to the epichlorohydrin saponification wastewater with a CaCl2 concentration of 20%;

[0047] Step (2): keeping the mixed slurry obtained in step (1) at 30° C. for 10 hours;

[0048] Step (3): filtering the mixed slurry obtained in step (2), and collecting the filtrate and filter residue;

[0049] Step (4): Dry the filter residue obtained in step (3) at 120° C. to constant weight to obtain a powder product.

[0050] The hydrochloric acid concentration of the filtrate in step (3) and the microstructure of the powder in step (4) were detected respectively. The results showed that the hydrochloric acid concentration of the obtained filtrate was 1.0 mol / L, Ca 2+ The concentration is 20 g / L, and the powder product is calcium sulfate dihydrate; due to the low stirring rate in step (1), the homogeneity of the obtained calcium sulfate dihydrate product is poor.

[0051] Example 2

[0052] Step (1): Under the condition of stirring speed of 500 rpm, according to SO4 2- / Ca 2+ The molar ratio is 0.7. 20% sulfuric acid solution is added to the epichlorohydrin saponification wastewater with a CaCl2 concentration of 30%;

[0053] Step (2): keeping the mixed slurry obtained in step (1) at 60° C. for 5 hours;

[0054] Step (3): filtering the mixed slurry obtained in step (2), and collecting the filtrate and filter residue;

[0055] Step (4): Dry the filter residue obtained in step (3) at 120° C. to constant weight to obtain a powder product.

[0056] The hydrochloric acid concentration of the filtrate in step (3) and the microstructure of the powder in step (4) were detected respectively. The results showed that the hydrochloric acid concentration of the obtained filtrate was 3.6 mol / L, Ca 2+ The concentration is 15g / L and the powder product is calcium sulfate hemihydrate.

[0057] Example 3

[0058] Step (1): Under the condition of stirring speed of 700 rpm, SO4 2- / Ca 2+ The molar ratio is 0.9. 30% sulfuric acid solution is added to the epichlorohydrin saponification wastewater with a CaCl2 concentration of 40%;

[0059] Step (2): keeping the mixed slurry obtained in step (1) at 90° C. for 2 h;

[0060] Step (3): filtering the mixed slurry obtained in step (2), and collecting the filtrate and filter residue;

[0061] Step (4): Dry the filter residue obtained in step (3) at 150° C. to constant weight to obtain a powder product.

[0062] The hydrochloric acid concentration of the filtrate in step (3) and the microstructure of the powder in step (4) were detected respectively. The results showed that the hydrochloric acid concentration of the obtained filtrate was 4.1 mol / L, Ca 2+ The concentration is 6g / L and the powder product is calcium sulfate hemihydrate.

[0063] Example 4

[0064] Step (1): Under the condition of stirring speed of 800 rpm, SO4 2- / Ca 2+ The molar ratio is 1.2. 40% sulfuric acid solution is added to the epichlorohydrin saponification wastewater with a CaCl2 concentration of 25%;

[0065] Step (2): keeping the mixed slurry obtained in step (1) at 120° C. for 1 hour;

[0066] Step (3): filtering the mixed slurry obtained in step (2), and collecting the filtrate and filter residue;

[0067] Step (4): Dry the filter residue obtained in step (3) at 180° C. to constant weight to obtain a powder product.

[0068] The hydrochloric acid concentration of the filtrate in step (3) and the microstructure of the powder in step (4) were detected respectively. The results showed that the hydrochloric acid concentration of the obtained filtrate was 3.3 mol / L, SO4 2- The concentration is 25g / L and the powder product is calcium sulfate hemihydrate.

[0069] Example 5

[0070] Step (1): Under the condition of stirring speed of 1000 rpm, SO4 2- / Ca 2+ The molar ratio is 1.5, 50% sulfuric acid solution is added to the epichlorohydrin saponification wastewater with a CaCl2 concentration of 35%;

[0071] Step (2): keeping the mixed slurry obtained in step (1) at 100° C. for 2 hours;

[0072] Step (3): filtering the mixed slurry obtained in step (2), and collecting the filtrate and filter residue;

[0073] Step (4): Dry the filter residue obtained in step (3) at 200° C. to constant weight to obtain a powder product.

[0074] The hydrochloric acid concentration of the filtrate in step (3) and the microstructure of the powder in step (4) were detected respectively. The results showed that the hydrochloric acid concentration of the obtained filtrate was 4.5 mol / L, SO4 2- The concentration is 45g / L, and the powder product is a mixture of hemihydrate calcium sulfate and anhydrous calcium sulfate. Due to the high stirring rate in step (1), the homogeneity of the obtained calcium sulfate dihydrate product is good, but too high a stirring rate will increase energy consumption and reduce the life of the equipment. The powder product is calcined at 600°C to obtain a dead-burned anhydrous calcium sulfate product.

[0075] Example 6

[0076] Step (1): Under the condition of stirring speed of 1200 rpm, SO4 2- / Ca 2+ The molar ratio is 1.8. 70% sulfuric acid solution is added to the epichlorohydrin saponification wastewater with a CaCl2 concentration of 25%;

[0077] Step (2): keeping the mixed slurry obtained in step (1) at 150° C. for 0.5 h;

[0078] Step (3): filtering the mixed slurry obtained in step (2), and collecting the filtrate and filter residue;

[0079] Step (4): Dry the filter residue obtained in step (3) at 250° C. to constant weight to obtain a powder product.

[0080] The hydrochloric acid concentration of the filtrate in step (3) and the microstructure of the powder in step (4) were detected respectively. The results showed that the hydrochloric acid concentration of the obtained filtrate was 3.9 mol / L, SO4 2-The concentration is 60g / L, and the powder product is a mixture of hemihydrate calcium sulfate and anhydrous calcium sulfate. Due to the high stirring rate in step (1), the homogeneity of the obtained dihydrate calcium sulfate product is good, but too high a stirring rate will increase energy consumption and reduce the life of the equipment. The powder product is calcined at 800°C to obtain a dead-burned anhydrous calcium sulfate product.

[0081] Example 7

[0082] Step (1): Under the condition of stirring speed of 1200 rpm, SO4 2- / Ca 2+ The molar ratio is 2.0. 90% sulfuric acid solution is added to the epichlorohydrin saponification wastewater with a CaCl2 concentration of 40%;

[0083] Step (2): keeping the mixed slurry obtained in step (1) at 120° C. for 5 hours;

[0084] Step (3): filtering the mixed slurry obtained in step (2), and collecting the filtrate and filter residue;

[0085] Step (4): Dry the filter residue obtained in step (3) at 300° C. to constant weight to obtain a powder product.

[0086] The hydrochloric acid concentration of the filtrate in step (3) and the microstructure of the powder in step (4) were detected respectively. The results showed that the hydrochloric acid concentration of the obtained filtrate was 5.0 mol / L, SO4 2- The concentration is 175 g / L, and the powder product is anhydrous calcium sulfate. Due to the high stirring rate in step (1), the homogeneity of the obtained calcium sulfate dihydrate product is good, but too high a stirring rate will increase energy consumption and reduce the life of the equipment. The powder product is calcined at 500° C. to obtain a dead-burned anhydrous calcium sulfate product.

[0087] Example 8

[0088] Step (1): Under the condition of stirring speed of 1000 rpm, SO4 2- / Ca 2+ The molar ratio is 1.2. 60% sulfuric acid solution is added to the epichlorohydrin saponification wastewater with a CaCl2 concentration of 35%;

[0089] Step (2): keeping the mixed slurry obtained in step (1) at 100° C. for 2 hours;

[0090] Step (3): filtering the mixed slurry obtained in step (2), and collecting the filtrate and filter residue;

[0091] Step (4): Dry the filter residue obtained in step (3) at 150° C. to constant weight to obtain a powder product.

[0092] The hydrochloric acid concentration of the filtrate in step (3) and the microstructure of the powder in step (4) were detected respectively. The results showed that the hydrochloric acid concentration of the obtained filtrate was 4.6 mol / L, SO4 2- The concentration is 35 g / L, and the powder product is calcium sulfate hemihydrate; due to the high stirring rate in step (1), the homogeneity of the obtained calcium sulfate dihydrate product is good, but too high a stirring rate will increase energy consumption and reduce the life of the equipment. The powder product is calcined at 1000°C to obtain a dead-burned anhydrous calcium sulfate product.

[0093] Example 9

[0094] Step (1): Under the condition of stirring speed of 600 rpm, SO4 2- / Ca 2+ The molar ratio is 1.0, 40% sulfuric acid solution is added to the epichlorohydrin saponification wastewater with a CaCl2 concentration of 30%;

[0095] Step (2): keeping the mixed slurry obtained in step (1) at 80° C. for 6 hours;

[0096] Step (3): filtering the mixed slurry obtained in step (2), and collecting the filtrate and filter residue;

[0097] Step (4): Dry the filter residue obtained in step (3) at 200° C. to constant weight to obtain a powder product.

[0098] The hydrochloric acid concentration of the filtrate in step (3) and the microstructure of the powder in step (4) were detected respectively. The results showed that the hydrochloric acid concentration of the obtained filtrate was 4.2 mol / L, SO4 2- The concentration is 0.05g / L, Ca 2+ The concentration is 0.15g / L, and the powder product is anhydrous calcium sulfate.

[0099] Example 10

[0100] Step (1): Under the condition of stirring speed of 800 rpm, SO4 2- / Ca 2+ The molar ratio is 0.8. 30% sulfuric acid solution is added to the epichlorohydrin saponification wastewater with a CaCl2 concentration of 25%;

[0101] Step (2): keeping the mixed slurry obtained in step (1) at 120° C. for 4 hours;

[0102] Step (3): filtering the mixed slurry obtained in step (2), and collecting the filtrate and filter residue;

[0103] Step (4): Dry the filter residue obtained in step (3) at 100° C. to constant weight to obtain a powder product.

[0104] The hydrochloric acid concentration of the filtrate in step (3) and the microstructure of the powder in step (4) were detected respectively. The results showed that the hydrochloric acid concentration of the obtained filtrate was 3.8 mol / L, Ca 2+ The concentration is 9g / L and the powder product is anhydrous calcium sulfate.

[0105] from Figure 1 , Figure 2 , Figure 3 It can be seen that the sulfuric acid prepared in Comparative Example 1 reacts with calcium chloride to first form calcium sulfate dihydrate, and the short insulation time cannot form hemihydrate / anhydrous calcium sulfate. However, after a hydrothermal reaction at a suitable temperature and insulation time, the calcium sulfate dihydrate is converted into hemihydrate calcium sulfate prepared in Example 3 and anhydrous calcium sulfate prepared in Example 9. Examples 3 and 9 prepare hemihydrate calcium sulfate and anhydrous calcium sulfate products with higher purity and better crystallization.

[0106] from Figure 4 , Figure 5 , Figure 6 It can be seen that the calcium sulfate dihydrate prepared in Comparative Example 1 has a lath-like whisker structure, the calcium sulfate hemihydrate prepared in Example 3 has a rod-like whisker structure, and the anhydrous calcium sulfate prepared in Example 9 has a fibrous whisker structure.

Claims

1. A method for preparing semi-aqueous / anhydrous calcium sulfate from epichlorohydrin saponification wastewater and simultaneously recovering hydrochloric acid, characterized in that: include: S1, according to SO4 2- / Ca 2+ The molar ratio is 0.5 to 2.0, sulfuric acid solution is added to the epichlorohydrin saponification wastewater to obtain a mixed slurry of calcium sulfate dihydrate and hydrochloric acid; S2, subjecting the mixed slurry of calcium sulfate dihydrate and hydrochloric acid to a hydrothermal reaction to obtain a mixed slurry of hemihydrate / anhydrous calcium sulfate and hydrochloric acid, wherein the temperature of the hydrothermal reaction is 30-150° C. and the temperature is kept for 0.5-10 h; S3, filtering the mixed slurry of semi-hydrated / anhydrous calcium sulfate and hydrochloric acid, the filtrate is a hydrochloric acid solution, and the filter residue is semi-hydrated / anhydrous calcium sulfate; S4, drying the semi-hydrated / anhydrous calcium sulfate residue to obtain a semi-hydrated / anhydrous calcium sulfate powder product.

2. The method for preparing semi-aqueous / anhydrous calcium sulfate and simultaneously recovering hydrochloric acid from epichlorohydrin saponification wastewater according to claim 1, characterized in that: SO4 2- / Ca 2+ The molar ratio is 0.8 to 1.

0.

3. The method for preparing semi-aqueous / anhydrous calcium sulfate and simultaneously recovering hydrochloric acid from epichlorohydrin saponification wastewater according to claim 1, characterized in that: The mass percentage concentration of the sulfuric acid is 10-90%.

4. The method for preparing semi-aqueous / anhydrous calcium sulfate and simultaneously recovering hydrochloric acid from epichlorohydrin saponification wastewater according to claim 3, characterized in that: The mass percentage concentration of the sulfuric acid is 30-60%.

5. The method for preparing semi-aqueous / anhydrous calcium sulfate and simultaneously recovering hydrochloric acid from epichlorohydrin saponification wastewater according to claim 1, characterized in that: The mass percentage concentration of CaCl2 in epichlorohydrin saponification wastewater is 20-40%.

6. The method for preparing semi-aqueous / anhydrous calcium sulfate and simultaneously recovering hydrochloric acid from epichlorohydrin saponification wastewater according to claim 1, characterized in that: The mixed slurry of calcium sulfate dihydrate and hydrochloric acid is subjected to a hydrothermal reaction to obtain calcium sulfate hemihydrate. The temperature of the hydrothermal reaction is 60-90° C. and the temperature is kept for 1-3 hours.

7. The method for preparing semi-aqueous / anhydrous calcium sulfate and simultaneously recovering hydrochloric acid from epichlorohydrin saponification wastewater according to claim 1, characterized in that: A mixed slurry of calcium sulfate dihydrate and hydrochloric acid is subjected to a hydrothermal reaction to obtain anhydrous calcium sulfate. The temperature of the hydrothermal reaction is 80 to 120° C. and the temperature is kept for 5 to 8 hours.

8. The method for preparing semi-aqueous / anhydrous calcium sulfate and simultaneously recovering hydrochloric acid from epichlorohydrin saponification wastewater according to claim 1, characterized in that: The sulfuric acid solution is added to the epichlorohydrin saponification wastewater and then stirred, and the stirring rate is 300-1200rp.

9. The method for preparing semi-aqueous / anhydrous calcium sulfate and simultaneously recovering hydrochloric acid from epichlorohydrin saponification wastewater according to claim 1, characterized in that: The drying temperature in step S4 is 80-300°C.

10. The method for preparing semi-aqueous / anhydrous calcium sulfate and simultaneously recovering hydrochloric acid from epichlorohydrin saponification wastewater according to claim 1, characterized in that: After obtaining the semi-hydrated / anhydrous calcium sulfate powder product, calcination is performed to obtain dead-burned anhydrous calcium sulfate, and the calcination temperature is 500-1000°C.

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