TW201540668A - Method for recycling ammonium sulfate to manufacture dihydrate gypsum - Google Patents

Abstract

The present creation relates to a method for recycling ammonium sulfate to manufacture dihydrate gypsum, in which ammonium sulfate is prepared into a solution for a metathetical reaction with calcium oxides and/or hydroxides to produce a mixture of ammonium and gypsum, then ammonium is separated from the mixed solution; after the unreacted is further converted into gypsum or soluble calcium salts, a gypsum hydration reaction is performed to produce a highly purified dihydrate gypsum.

Description

Method for recovering dihydrate gypsum by recovering ammonium sulfate 【0001】

The present invention relates to a method for recovering dihydrate gypsum from ammonium sulfate, especially for treating ammonia-containing wastewater in the electronics industry or general industry, and treating the obtained ammonium sulfate waste liquid to produce dihydrate gypsum with high purity to provide industry A technical method of reusing and having economic value.

【0002】

In recent years, the domestic industry has flourished, and the types and quantities of wastewater generated in the manufacturing process have increased. For example, ammonia-containing wastewater produced by the electronics industry or the petrochemical industry has to be regulated by the government's environmental regulations. deal with. There are many treatment methods for ammonia-containing wastewater, such as stripping, stripping, biochemical treatment, thin film distillation, and chlorination. One of the methods is to convert ammonia into ammonium sulfate. The main use of ammonium sulphate is in agricultural fertilizers. However, because the competent authority considers that many heavy metals or rare metals are contained in the electronics industry, the ammonium sulphate waste liquid produced in agriculture will cause unpredictable pollution problems and is not recommended for use. Agriculture, therefore, the use of ammonium sulphate is greatly limited, and the application of ammonium sulphate is rarely directly applied to industries other than agriculture, and other recycling routes must be sought.

[0003]

At present, the domestic ammonium sulfate recycling technology, in addition to the direct application of ammonium sulfate, is still in the state of exploration, most of the focus is on the recovery of ammonia water, there is no commercial technology to recover ammonia water at the same time and convert the sulfate in ammonium sulfate into economic value. High-purity, high-purity dihydrate gypsum, but treated as waste, resulting in considerable waste of resource utilization.

[0004]

Further, U.S. Patent No. 3,637,347 mentions that in the treatment of SO _X air pollution generated by a fuel boiler, ammonia water is used to absorb SO _X to form ammonium sulfate, and then calcium oxide is added to form calcium sulfate and ammonia water, and ammonia water is recycled, but calcium sulfate is used. Dispose of as waste.

[0005]

In order to solve the above problems, the present invention provides a method for recovering dihydrate gypsum from ammonium sulfate, comprising a reaction step of applying ammonium sulfate or ammonium sulfate solution at 20 ^. C~120 ^. At a temperature of C, it reacts with calcium oxides and/or hydroxides to form a mixture of ammonia and gypsum, and then physically separates ammonia from the mixed solution and collects it to obtain ammonia water and ammonia-removing gypsum. Mixing liquid, adjusting the average step, adding sulfuric acid or other acid to the ammonia-removing gypsum mixed solution, and converting the unreacted calcium oxide and/or hydroxide in the ammonia-gypsum mixed solution into gypsum or soluble calcium salt. In the hydration step, the solution will be adjusted to 20 after homogenization ^. C~120 ^. C and lower than the temperature of the reaction step, the hydration reaction of gypsum is carried out to form dihydrate gypsum with high purity, a solution containing high-purity dihydrate gypsum is further obtained, and a separation step is carried out to prepare a solution containing high-purity dihydrate gypsum. Using a separation device, high-purity dihydrate gypsum containing free water is separated.

[0006]

The creation method can recover ammonia water, and can also obtain dihydrate gypsum with high purity, and achieve the purpose of waste recycling and reuse.

[0034]

20‧‧‧Ammonium sulphate solution storage tank 22‧‧‧ Calcium oxide or calcium hydroxide slurry tank 24‧‧• Alkali metal hydroxide storage tank 25‧‧‧Reaction tank 26‧‧‧Ammonia-depleted gypsum mixed solution 28‧‧‧ Ammonia vapor 28‧‧A ammonia water storage tank 30‧‧ ‧After mixing mixture 32‧‧‧Water 33‧‧‧ Adjusting trough 34‧‧‧Sulfuric acid or other acid 35‧‧‧ Hydration tank 36‧‧‧2 Water gypsum seed crystal 38‧‧‧Solid containing high-purity dihydrate gypsum 39‧‧‧Separation equipment 40‧‧‧Development 42‧‧‧High-purity dihydrate gypsum containing free water 43‧‧‧ Drying equipment 44‧‧‧ Dihydrate gypsum
R1‧‧‧ reaction steps
R2‧‧‧ adjustment steps
R3‧‧‧Hydration step
S1‧‧‧ separation step
D1‧‧‧ drying step

【0007】

Figure 1 shows a simplified flow chart for the production of dihydrate gypsum by the present authoring method.

[0008]

Figure 2 shows a flow chart of the apparatus for manufacturing dihydrate gypsum by the present method.

【0009】

The following description is only for the convenience of explaining the basic teachings of the present invention. The description of the components, the amount of use, the operating concentration, the temperature and other related extensions constituting the preferred embodiment will be explained in reading and understanding of the creation. Post-related changes are implemented in industry skills. In addition, after reading and understanding the creative guidelines, changes in specific equipment, concentration, temperature and similar requirements are also industry skills.

[0010]

According to the schematic display, the present invention provides a method 10 for producing dihydrate gypsum from industrial ammonium sulfate (as shown in Fig. 1), the procedure comprising the reaction step R1, the adjustment step R2, the hydration step R3, and the separation. Step S1 and drying step D1, wherein:

[0011]

Reaction step R1 is carried out from an industrially recovered ammonium sulfate or ammonium sulfate solution at 20 ^. C~120 ^. a metathesis reaction with any of at least one of calcium oxides, hydroxides or alkali metal hydroxides at a temperature of C to form a mixture of ammonia and gypsum, and then physically separating the ammonia from the mixture of gypsum, A mixed solution of ammonia water and ammonia-removing gypsum is obtained.

[0012]

Adjusting the average step R2, adding sulfuric acid or other acid to the ammonia-removing gypsum mixed solution, and converting the unreacted calcium oxide and/or hydroxide in the ammonia-gypsum mixed solution into gypsum or soluble calcium salt, thereby obtaining Adjust the mixture after mixing.

[0013]

The hydration step R3, after adjusting the average solution, is at 20 ^. C~120 ^. The hydration reaction of gypsum is carried out under the conditions of the temperature of C and lower than the temperature of the reaction section to form a solution containing high-purity dihydrate gypsum.

[0014]

In the separation step S1, the solution containing the high-purity dihydrate gypsum is separated by a separation device to obtain high-purity dihydrate gypsum containing free water.

[0015]

In addition, in order to make the dihydrate gypsum into other crystallized gypsum products, the high-purity dihydrate gypsum containing the free water can be further separated by a drying step D1, and the free water or the crystal water can be removed by using a drying device to produce different crystals. The type of gypsum, that is to say, the dihydrate, semi-aqueous or anhydrous gypsum product can be produced according to the degree of removal of free water or crystal water.

[0016]

The equipment used in the above paragraphs may be carried out independently according to the manufacturing process, for example, by continuous or batch operation, or by combining several stages of equipment in one or more equipment, such as batch reaction, reaction steps. The adjustment step, and the hydration step can be performed using a single seat, two seat, or pedestal device.

[0017]

In the reaction step R1, the ammonium sulfate or ammonium sulfate solution recovered from the industry does not need to be restricted to a specific saturation concentration to carry out the metathesis reaction, but it is recommended to add water to adjust the concentration of the ammonium sulfate solution to be 5%. 40%, the optimum concentration is 10% to 30%, because if the concentration of ammonium sulfate solution is too low, the space required for the reaction equipment is large. If the concentration of ammonium sulfate solution is too high, exceeds the saturation solubility, the metathesis reaction efficiency becomes low, and The gypsum crystals become fine, which makes it difficult to obtain high-purity dihydrate gypsum containing free water in the separation step (S1).

[0018]

Further, calcium oxide is preferably calcium oxide (CaO), and hydroxide is preferably calcium hydroxide (Ca(OH) ₂ ). The higher the purity, the better, calcium oxide (CaO) or calcium hydroxide (Ca ( OH) ₂ ) the purity is better than 90%, because if the purity of calcium oxide (CaO) or calcium hydroxide (Ca(OH) ₂ ) is too low, the purity of the produced gypsum will decrease, calcium oxide (CaO) or hydroxide Calcium (Ca(OH) ₂ ) may be used singly or in combination, and may be used in a solid form or in a slurry form, and a preferred option is to formulate calcium oxide (CaO) or calcium hydroxide (Ca(OH) ₂ ). It is slurried, so that calcium oxide can be digested to form calcium hydroxide, and it is easy to use pump delivery. The concentration of calcium oxide (CaO) or calcium hydroxide (Ca(OH) ₂ ) is not particularly limited, and the concentration is generally 10%. ~40%, the best concentration is 20%~30%.

[0019]

The theoretical molar ratio of the metathesis reaction in the reaction step R1 is 1:1, and the molar ratio at the time of the reaction is not particularly limited, but the efficiency of converting ammonium sulfate into ammonia is improved, and ammonium sulfate and calcium oxide or calcium hydroxide are used. The molar ratio is generally set between 1:1 and 1:1.2. If the molar ratio is too high, the ammonium sulfate is excessive, and the unreacted ammonium sulfate is increased. The soluble ammonium content in the solution increases after the reaction, which is unfavorable for the ammonium-nitrogen emission control. If the ratio is too low, the calcium oxide and/or hydroxide is excessive, and the unreacted calcium oxide and/or hydroxide is increased. For the subsequent hydration step, the amount of acid during neutralization must be increased. The cost is unfavorable.

[0020]

In the reaction step R1, in order to increase the metathesis reaction rate, an appropriate amount of an alkali metal hydroxide may be further added, and the alkali metal hydroxide is any one of sodium hydroxide and potassium hydroxide, and the alkali metal hydroxide may be When the alkali metal hydroxide is formulated into a liquid state, the liquid alkali metal hydroxide concentration is not particularly limited, and is set at about 45% to 55%, and the optimum saturation concentration is in the liquid state or the solid state. 50%, the amount can be used in combination with the amount of calcium oxide (CaO) or calcium hydroxide (Ca(OH) ₂ ) to add at least one of ammonium sulfate and calcium oxides and hydroxides to the hydroxide. The molar ratio after sodium or potassium hydroxide is maintained between 1:1 and 1:1.2. Further, the reaction temperature in the reaction step is not particularly limited and is usually from 20 ° C to 120 ° C, preferably from 50 ° C to 110 ° C. The reaction time is not particularly limited, the temperature is low, the reaction time is increased, the opposite temperature is high, and the reaction time is decreased, and is usually 0.5 to 4 hours, preferably 1-3 hours. The reaction pressure is generally normal pressure (1 atmosphere), but in order to make the reaction temperature higher, the pressure can be increased to a normal pressure (1 atmosphere) or more.

[0021]

The present method performs a metathesis reaction in the reaction step R1 to form a mixture of ammonia and gypsum. For further separation of ammonia and gypsum, the ammonia vapor can be removed by a known physical method such as distillation, stripping (gas stripping), and the like. The aqueous ammonia solution is obtained by separating it from the mixed solution and then using water to absorb the ammonia vapor.

[0022]

In the tempering step R2, any one of sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid or the like is added to the ammonia-removing gypsum mixed solution generated from the reaction step R1, and the ammonia-free gypsum mixed solution is not reacted. The calcium oxides and/or hydroxides are converted to gypsum and/or the alkali metal hydroxide is converted to a soluble calcium salt (eg, calcium nitrate, calcium chloride, calcium phosphate, sodium sulfate, potassium sulfate, etc.). If no sulfuric acid or other acid is added, the unreacted calcium oxides and/or hydroxides reduce the hydration efficiency of the subsequent hydration step R3 and the purity of the dihydrate gypsum. The concentration of sulfuric acid or other acid used is not particularly limited. The pH of the ammonia-depleted mixed solution is generally controlled in the range of 1-10, preferably 4-6. If the pH is too low, the free acid will be too much, and the washing will not be good. If the pH is too high, the solubility of calcium oxides and/or hydroxides is not good.

[0023]

In the hydration step R3, if the solution containing high-purity dihydrate gypsum is not properly controlled, the obtained gypsum form may contain both dihydrate gypsum (CaSO ₄ 2H ₂ O) and hemihydrate gypsum (CaSO). One or more crystalline forms such as ₄ 1/2H ₂ O) or anhydrite (CaSO ₄ ). In order to obtain the crystalline form of dihydrate gypsum which is stable at room temperature, the hydration reaction of gypsum must be carried out under the appropriate operating concentration, temperature and hydration time, in order to completely convert the gypsum into high-purity dihydrate gypsum and Water crystal form. Generally, the temperature of the reaction step R1 is higher than the hydration temperature by about 5 ° C to 30 ° C, so that the gypsum in the ammonia-depleted gypsum mixed solution generates semi-aqueous or anhydrous gypsum in the reaction step R1, and then controlled in the hydration step R3. Lower than the temperature of the reaction step R1, the semi-aqueous or anhydrite is slowly hydrated to dihydrate gypsum. The temperature of the hydration step R3 is not particularly limited, and is generally 20 ° C to 120 ° C and most preferably 30 ° C to 100 ° C. However, the hydration step R 3 temperature is lower than the reaction step temperature. The reaction time of the hydration step is not particularly limited and is usually from 0.5 to 4 hours, preferably from 2 to 4 hours. When hydration, the dihydrate gypsum seed crystal can be added to promote the hydration and the formation rate of the dihydrate crystal. The amount of the dihydrate gypsum seed crystal is generally 0.1% to 5.0% of the weight of the ammonia-removing gypsum mixed solution, and the best is removed. The weight of the ammonia gypsum mixed solution is 0.5% to 2.0%.

[0024]

In the separation step S1, the high-purity dihydrate gypsum solution obtained from the hydration step R3 can be separated by using a solid-liquid separation device such as a centrifuge or a filter press to separate the gypsum. The dihydrate gypsum contains free water and may contain unreacted ammonium sulfate or soluble calcium salt. In this case, the water may be washed with water to wash off the impurities, and the product having high purity may be directly sold or dried and sold.

[0025]

In the drying step D1, the dihydrate gypsum obtained from the separation step S1, if the required specification has a limit on the content of free water or crystal water, may use drying equipment such as an oven, a gas flow dryer, a vacuum dryer. Etc., remove free water or remove crystal water to produce products of different gypsum crystalline forms, such as gypsum products containing dihydrate, semi-water, or anhydrous, and in detail, the dihydrate gypsum is quickly added to 80 ^. For a period of time above C, the dihydrate gypsum can be converted into hemihydrate gypsum, and the hemihydrate gypsum can be continued at 80 ^. After heating for a period of time above C, the hemihydrate gypsum is converted into anhydrite.

[0026]

Referring to Fig. 2, the method for producing dihydrate gypsum from ammonium sulfate recovered from the industry is carried out in an ammonium sulfate storage tank 20 from an industrially recovered ammonium sulfate or ammonium sulfate solution, and in one Calcium oxide or calcium hydroxide slurry stored in the calcium oxide or calcium hydroxide slurry storage tank 22, and alkali metal hydroxide stored in an alkali metal hydroxide storage tank 24, and sulfuric acid in the ammonium sulfate liquid storage tank 20 The ammonium or ammonium sulfate solution is adjusted to a concentration of between 5% and 40%, and the calcium oxide or calcium oxide slurry concentration in the calcium oxide or calcium oxide slurry tank 22 is adjusted to 10% to 40%, and the alkali metal hydroxide is used. The saturation concentration of the storage tank 24 is adjusted to about 50%, and the ammonium sulfate and the calcium oxide or calcium hydroxide slurry are mixed in a molar ratio of 1:1 to 1:1.2 into a reaction tank 25 for metathesis reaction, or ammonium sulfate and Calcium oxide or calcium hydroxide slurry is added to the reaction tank 25 at a molar ratio of 1:1 to 1:1.2 after adding an alkali metal hydroxide, thereby forming a mixed solution of ammonia and gypsum in the reaction tank 25, and reacting The concentration of water 32 is maintained between 5% and 40%. After the reaction is completed, ammonia is removed by distillation or stripping (gas stripping), and ammonia vapor 28 is separated from the reaction tank and then made by water absorption. The ammonia water is sent to an ammonia water storage tank 28A to obtain a mixed solution of the ammonia-removing gypsum, and then the ammonia-removing gypsum mixed solution 26 is sent to the uniform tank 33, and sulfuric acid or other acid is added to the adjusting tank 33. 34, the ammonia removal gypsum mixed solution is adjusted to a pH between 1 and 10, and after the adjusted average mixed solution is obtained in the equalization tank 33, the adjusted mixed liquid 30 is sent to the hydration tank 35. And adding the dihydrate gypsum seed crystal 36 for hydration, thereby obtaining a solution containing high-purity dihydrate gypsum in the hydration tank 35, and further feeding the solution 38 containing high-purity dihydrate gypsum to a centrifuge or a filter press, for example. In a separating device 39, a high-purity dihydrate gypsum 42 containing free water and a filtrate 40 are separated, and the filtrate 40 is treated in a waste water zone, and the dihydrate gypsum 42 containing free water is sent to, for example, baked. , Air dryer, a vacuum dryer drying apparatus 43 constitutes one of the dried gypsum 44 to obtain dried products.

[0027]

This creation is based on the above examples of the method for manufacturing dihydrate gypsum and its equipment, assuming that the method is in accordance with the method described, but it is understood that the creation is not limited by the conditions and contents described in the specific examples:

[0028]

Example 1: Ammonium sulfate waste liquid (NH ₄ ) ₂ SO ₄ produced from the semiconductor industry, the concentration was adjusted to 30%, and 1000 g of ammonium sulfate waste liquid having a concentration of 30% was weighed into a reaction tank having a capacity of 1.5 L. Then, 190 g of calcium hydroxide having a purity of 95% is added to carry out a metathesis reaction, the reaction temperature is controlled between 95 and 100 ° C, and the reaction is carried out for about 2 hours. The ammonia vapor generated during the reaction is collected by using a condenser during the reaction. In addition, the supplementary water enters the reactor to maintain the volume of the solution in the reaction tank. On the one hand, the ammonia generated in the reactor is driven out, and after the ammonia generated is completely driven out, a saturated concentration of 98% sulfuric acid solution is added to the reaction tank to adjust the reaction. The pH of the solution in the tank is about 6, then the temperature is lowered to between 50 ° C and 60 ° C in the hydration tank 35, and 5 g of dihydrate gypsum is added as a seed crystal, and the dihydrate gypsum is maintained at 50-60 ° C. After the hydration reaction and the hydration reaction, the mixture was filtered and washed with water to obtain white dihydrate gypsum. The crystal form of the dihydrate gypsum in the shape of a column was observed by a 600-fold optical microscope, and the purity of CaSO _4. 2H ₂ O was measured _. It is 95.1%.

[0029]

Example 2: Ammonium sulfate waste liquid (NH ₄ ) ₂ SO ₄ produced from the semiconductor industry, the concentration was adjusted to 20%, and 1000 g of a 20% ammonium sulfate waste liquid was weighed into a reaction tank having a capacity of 1.5 L. Then, 125 g of calcium hydroxide having a purity of 95% is added to carry out a metathesis reaction, the reaction temperature is controlled between 95 and 100 ° C, and the reaction is carried out for about 2 hours. The ammonia vapor generated during the reaction is collected by using a condenser, and the ammonia generated is all driven out. Thereafter, a 98% sulfuric acid solution is added to the reaction tank, and the pH of the solution in the reaction tank is adjusted to about 6, and then 300 g of water is added, and then the temperature is lowered in the hydration tank 35 to between 50 ° C and 60 ° C. And adding 3 g of dihydrate gypsum as a seed crystal, maintaining the hydration reaction of dihydrate gypsum at 50-60 ° C, and after hydration reaction, washing with water to obtain white dihydrate gypsum, using a 600-fold optical microscope, The crystal form of the rhombohedral dihydrate gypsum was observed, and the purity of CaSO _4. 2H ₂ O was determined to be 96.2%.

[0030]

Example 3: Ammonium sulfate waste liquid (NH ₄ ) ₂ SO ₄ produced from the semiconductor industry was adjusted to a concentration of 20%, and 1000 g of a 20% ammonium sulfate waste liquid was weighed into a reaction tank having a capacity of 1.5 L. Then, 110 g of purity 95% calcium hydroxide and 20 g of 45% sodium hydroxide were added to carry out a metathesis reaction, the reaction temperature was controlled at 95-100 ° C, and the reaction was carried out for about 2 hours, and the ammonia vapor generated during the reaction was collected using a condenser. After all the ammonia generated is ejected, a 98% sulfuric acid solution is added to the reaction tank, and the pH of the solution in the reaction tank is adjusted to about 5, and then 250 g of water is added, and then the temperature is lowered in the hydration tank 35. Between 50 ° C and 60 ° C, and adding 3 g of dihydrate gypsum as a seed crystal, maintaining the hydration reaction of dihydrate gypsum at 50-60 ° C, after the hydration reaction is finished, filtering and washing with water to obtain white dihydrate gypsum. The crystal form of the columnar dihydrate gypsum was observed by a 600-fold optical microscope, and the purity of CaSO _4. 2H ₂ O was determined to be 95.4%.

[0031]

The method for producing dihydrate gypsum from ammonium sulfate can obtain dihydrate gypsum with high purity, and obtain gypsum (dihydrate gypsum, hemihydrate gypsum or anhydrite gypsum) of different crystal state according to the drying time, and obtain High-purity dihydrate gypsum can recover ammonia water at the same time, thus improving the economic value of recovering ammonium sulfate waste liquid.

[0032]

The basic teachings of this creation have been described, and many extensions and variations will be apparent to those of ordinary skill in the art. For example, for example, the method for producing dihydrate gypsum may not include a drying step, that is, the high-purity dihydrate gypsum containing free water obtained in the separation step can be directly applied, and the drying step is only to further remove free water. Or crystallizing water to make the water of dihydrate gypsum lower, or further to make high-purity dihydrate gypsum containing free water into hemihydrate gypsum or anhydrite gypsum.

[0033]

The disclosure of the present invention may be embodied in other specific forms without departing from the spirit and scope of the invention. The scope of the present invention is defined by the scope of the appended claims, and is not intended to be limited by the scope of the invention.

R1‧‧‧ reaction steps

R2‧‧‧ adjustment steps

R3‧‧‧dihydrate gypsum hydration step

S1‧‧‧ Dihydrate gypsum separation step

D1‧‧‧ Dihydrate gypsum drying step

Claims (22)

[Item 1] A method for recovering dihydrate gypsum from ammonium sulfate, comprising:
In the reaction step, the ammonium sulfate or ammonium sulfate solution is at 20 ^. C~120 ^. At a temperature of C, it reacts with calcium oxides and/or hydroxides to form a mixture of ammonia and gypsum, and then physically separates ammonia from the mixture of ammonia and gypsum and collects it to obtain ammonia water and remove it. A mixture of ammonia gypsum;
Adjusting the average step, adding sulfuric acid or other acid in the ammonia-removing gypsum mixed solution, and removing the unreacted calcium oxides and/or hydroxides in the ammonia-gypsum mixed solution to be converted into gypsum or soluble calcium salt;
In the hydration step, the solution will be adjusted to 20 after homogenization ^. C~120 ^. And hydrating the gypsum under conditions of a temperature lower than the temperature of the reaction step to form a dihydrate gypsum having a high purity, and further obtaining a solution containing high-purity dihydrate gypsum;
In the separation step, a solution containing high-purity dihydrate gypsum is separated into high-purity dihydrate gypsum containing free water by using a separation device. [Item 2] A method for producing dihydrate gypsum by recovering ammonium sulfate as described in the first aspect of the patent application, wherein the concentration of the ammonium sulfate or ammonium sulfate solution is 5% to 40%. [Item 3] The method for recovering dihydrate gypsum from ammonium sulfate as described in the first paragraph of the patent application, wherein the concentration of the ammonium sulfate or ammonium sulfate solution is preferably 10% to 30%. [Item 4] A method for recovering dihydrate gypsum from ammonium sulfate as described in claim 1, wherein the purity of the calcium oxide and/or hydroxide is preferably 90% or more, calcium oxide and/or hydroxide The substance may be solid or slurried, and the concentration of calcium oxide and/or hydroxide is 10% to 40%. [Item 5] A method for producing dihydrate gypsum by recovering ammonium sulfate as described in claim 1, wherein the slurry concentration of calcium oxides and/or hydroxides is 20% to 30%. [Item 6] A method for recovering dihydrate gypsum from ammonium sulfate as described in claim 1, wherein the ammonium sulfate phase of the reaction step is compared with The molar ratio of the calcium oxide and/or hydroxide to the metathesis reaction is between 1:1 and 1:1.2. [Item 7] A method for recovering dihydrate gypsum from ammonium sulfate as described in claim 1, wherein an alkali metal oxide is further added in the reaction step to compare ammonium sulfate with The molar ratio of any of calcium oxides and hydroxides plus sodium hydroxide or potassium hydroxide is maintained between 1:1 and 1:1.2. [Item 8] A method for producing dihydrate gypsum by recovering ammonium sulfate as described in claim 7 wherein the alkali metal oxide is any one of sodium hydroxide or potassium hydroxide. [Item 9] The method for recovering dihydrate gypsum from ammonium sulfate as described in claim 1, wherein the reaction temperature in the reaction step is preferably 50-110 ° C, the reaction time is 0.5-4 hours, and the reaction pressure is above normal pressure. [Item 10] The method for recovering dihydrate gypsum from ammonium sulfate as described in claim 1, wherein the reaction temperature in the reaction step is preferably from 50 ° C to 110 ° C, and the reaction time is preferably from 1 hour to 3 hours. [Item 11] The method for recovering dihydrate gypsum by recovering ammonium sulfate according to claim 1, wherein the mixture of ammonia and gypsum formed by metathesis of the reaction step is self-mixing of ammonia vapor by distillation, stripping or stripping. The solution is separated and an aqueous ammonia solution is obtained by absorption. [Item 12] A method for producing dihydrate gypsum by recovering ammonium sulfate as described in claim 1, wherein the other acid added in the adjustment step is any one of nitric acid, hydrochloric acid, and phosphoric acid. [Item 13] A method for recovering dihydrate gypsum from ammonium sulfate as described in claim 1, wherein the pH of the ammonia-containing gypsum mixed solution after adding sulfuric acid or other acid is controlled to be between 1 and 10. [Item 14] The method for recovering dihydrate gypsum by recovering ammonium sulfate as described in the first paragraph of the patent application, wherein the optimum pH of the ammonia-containing gypsum mixed solution after adding sulfuric acid or other acid is controlled at 4-6. [Item 15] A method for producing dihydrate gypsum by recovering ammonium sulfate as described in claim 1 wherein the temperature of the hydration step is preferably from 30 to 100 ° C, and the reaction time is from 0.5 to 4 hours, preferably from 2 to 4 hours. [Item 16] A method for recovering dihydrate gypsum from ammonium sulfate as described in claim 15 wherein the reaction time of the hydration step is preferably 2-4 hours. [Item 17] A method for producing dihydrate gypsum from industrially recovered ammonium sulfate as described in claim 1, wherein, in the hydration, a dihydrate gypsum seed crystal may be further added in an amount of 0.1% by weight of the ammonia-removing gypsum mixed solution. -5.0%. [Item 18] The method for recovering dihydrate gypsum by recovering ammonium sulfate according to claim 1, wherein, in the hydration, the dihydrate gypsum seed crystal may be further added, and the dihydrate gypsum seed crystal is added in the best amount to remove the ammonia gypsum mixed solution. 0.5% - 2.0% by weight. [Item 19] A method for producing dihydrate gypsum from industrially recovered ammonium sulfate as described in claim 1, wherein the separating step separates the dihydrate gypsum by using a centrifuge or a filter press. [Item 20] A method for producing dihydrate gypsum from industrially recovered ammonium sulfate as described in claim 1, wherein the high-purity dihydrate gypsum containing free water obtained by the separation step is further subjected to a drying step to remove free water or crystal water, and the drying step The drying device used is any one of an oven, a gas flow dryer or a vacuum dryer, and the high-purity dihydrate gypsum containing free water is used to remove free water or remove crystal water to produce, for example, dihydrate gypsum, hemihydrate gypsum or Anhydrite. [Item 21] A method for producing dihydrate gypsum from industrially recovered ammonium sulfate as described in claim 1 wherein the temperature of the reaction step is 5 ° C to 30 ° C higher than the hydration temperature. [Item 22] A method for recovering dihydrate gypsum from ammonium sulfate, comprising:
In the reaction step, the ammonium sulfate or ammonium sulfate solution is recovered and metathesized with at least one of calcium oxide, sodium hydroxide or potassium hydroxide to form a mixture of ammonia and gypsum, and then the ammonia is physically separated from the mixed solution. After obtaining a mixture of ammonia water and ammonia-removing gypsum, and adjusting the concentration of the ammonium sulfate or ammonium sulfate solution in the ammonia-removing gypsum mixture to 5%-40%, adding calcium oxide having a purity of 90% or more and/or The theoretical molar ratio of the hydroxide, ammonium sulfate phase to the metathesis reaction with any of the calcium oxide, sodium hydroxide or potassium hydroxide is 1:1 to 1:1.2 and the reaction temperature is 20 ° C to 120 ° C, the reaction time is 0.5-4 hours, the reaction pressure is generally above normal pressure;
In the adjustment step, any one of sulfuric acid, nitric acid, hydrochloric acid and phosphoric acid is added to the ammonia-removing gypsum mixture, and the pH is controlled between 1 and 10, and the unreacted calcium oxide in the solution is converted into gypsum. Or converting sodium hydroxide or potassium hydroxide into a soluble calcium salt to obtain a solution after adjustment;
The hydration step, in the temperature range of 20 ° C ~ 120 ° C and lower than the reaction step 5 ° C ~ 30 ° C, the average weight of the solution after the weight of 0.5% ~ 5% of the dihydrate gypsum seed crystals added to the solution after the adjustment, the adjustment The solution is subjected to hydration reaction of gypsum, and the hydration reaction time is 0.5-4 hours;
In the separation step, the solution containing dihydrate gypsum is separated from the gypsum containing free water by a centrifuge or a filter press.