CN103466662B - Method for preparing potassium sulfate with large grain diameter by utilizing reaction crystallization - Google Patents

Abstract

The invention relates to a method for preparing potassium sulfate with a large particle size by using reaction crystallization. The method includes two processes: the double decomposition of langbeinite and potassium chloride to prepare potassium sulfate and the growth of potassium sulfate crystals in the solution. The present invention uses the balanced mother liquor of potassium sulfate as the base. When the mixed slurry of langbeinite and potassium chloride is gradually added to the mother liquor, the two react to form potassium sulfate to form a supersaturated solution, which generates driving force to make the crystals of potassium sulfate grow. At the same time, the degree of supersaturation of the solution is controlled by controlling the feeding rate, so as to prevent the nucleation rate from being too fast and the crystal grains from being too fine. The average grain size of the potassium sulfate crystal obtained in the present invention can reach more than 250 μm, and the K ₂ O in the potassium sulfate can reach more than 51%, which meets the standard requirements of the high-grade potassium sulfate used in water-salt system technology and agriculture. Moreover, the present invention has rich and easy-to-obtain raw materials, simple process and recycling of raw materials, which greatly reduces the production cost of potassium sulfate.

Description

A kind of method utilizing reaction crystallization to prepare potassium sulfate with large particle size

technical field

The technical scheme of the present invention belongs to the preparation of potassium sulfate, specifically, it is a method for preparing large particle size potassium sulfate with langbeinite and potassium chloride.

Background technique

Potassium sulfate is a high-quality chlorine-free potassium fertilizer with high active ingredients (K ₂ O ~ 50%), low salt index and low hygroscopicity. It is widely used in tobacco, sugarcane, tea tree, mulberry tree, potato, citrus, Watermelon and other economic crops that avoid chlorine. The main production methods of potassium sulfate include sulfuric acid method, double decomposition method, seawater or brine extraction of potassium sulfate, solid potassium ore extraction, etc., but the products are all powdery substances with small sizes, and the particle size is generally below 90 μm. Dust is easy to appear in the soil, and it is easy to cause the loss of potassium sulfate and the imbalance of soil nutrients when applied in the field. With the improvement of China's agricultural mechanization, sowing and fertilization is even more difficult for powdered fertilizers. Therefore, the market's demand for large particle size potassium sulfate is increasing.

At present, the production of large particle potassium sulfate mainly increases the particle size of potassium sulfate by adding hardeners, coating agents and surfactants. CN85103968 discloses a method of utilizing surfactant to compress potassium sulfate into granules, which is obtained by mixing a small amount of water containing surfactant dissolved or dispersed therein with powdered potassium sulfate, and then pressing the mixture into granules to obtain Granular potassium sulfate. CN87105366 discloses a kind of wet granulation method, is to add at least one component selected from a group of calcium hydroxide, calcium oxide, calcium carbonate, magnesium hydroxide, magnesium oxide, magnesium carbonate and ammonia to the Potassium and sulfuric acid are reacted in the anhydrous state to obtain converted potassium sulfate and contained unconverted sulfuric acid, followed by wet granulation. These methods have high energy consumption, large losses, and serious dust pollution in the workshop. Therefore, the new process of directly crystallizing potassium sulfate with large particle size from the solution without machinery and additives can not only reduce pollution and dust, but also greatly reduce production costs, which has practical significance for the production of potassium sulfate.

Contents of the invention

The object of the present invention is to prepare potassium sulfate crystals with large particle size through reaction crystallization with no pollution, low energy consumption and low cost. In the present invention, the reaction of langbeinite extracted from salt lake brine and potassium chloride is directly crystallized from the solution to produce potassium sulfate with a large particle size, which includes two processes: double decomposition of langbeinite and potassium chloride Take potassium sulfate and the growth of potassium sulfate crystals in the solution. The present invention uses the balanced mother liquor of potassium sulfate as the base. When the mixed slurry of langbeinite and potassium chloride is gradually added to the mother liquor, the two react to form potassium sulfate to form a supersaturated solution, which generates driving force to make the crystals of potassium sulfate grow. At the same time, the degree of supersaturation of the solution is controlled by controlling the feeding rate, so as to prevent the nucleation rate from being too fast and the crystal grains from being too fine. And because the recycling of the first and second stages of mother liquor is realized, the waste of raw materials is reduced and the recovery rate of K ⁺ is improved.

Technical scheme of the present invention is:

A kind of method utilizing reactive crystallization to produce potassium sulfate of large particle size comprises the following steps:

The first step: a stage of crystallization - the reaction crystallization of potassium sulfate

According to the mass ratio of langbeinite: potassium chloride=1:0.6～0.75, mix langbeinite and potassium chloride evenly, and then use it directly as a material or add mother liquor A as a material for use , wherein, the quality of the added mother liquor A is less than or equal to 2 times of the sum of the quality of langbeinite and potassium chloride; and then additionally weigh mother liquor B of 0.1 to 5 times the quality of langbeinite, and place it in the seedless Or add the previous material under the condition of adding the seed crystal to the mother liquor B. The materials are gradually added to the mother liquor B under the condition of stirring for 0.5 to 2 hours, and the temperature is kept at 45 ° C to 60 ° C;

Stir directly for 0-2 hours after feeding, or continue stirring for 0-2 hours after adding water, wherein the amount of water added is less than or equal to 2 times the mass of langbeinite, and water is gradually added to the above slurry in 0.1-2 hours while stirring In the feed, finally obtain crude potassium and a section of mother liquor after solid-liquid separation, crude potassium is used as the raw material of the next step, and one section of mother liquor can be recycled as the mother liquor A of the first step in the next cycle reaction;

The second step: Second stage crystallization - the growth of potassium sulfate

Weigh 0.1 to 3 times the mass of langbeinite in the first step, mix half of the water with the crude potassium obtained in the first step, and maintain the temperature at 45°C to 60°C, and then mix it under constant stirring. Gradually add the remaining water in 0.1-2 hours, let it stand for 0-30 minutes, and separate the solid and liquid again to obtain the solid and the second-stage mother liquor. The second-stage mother liquor obtained can be recycled as the mother liquor B of the first step in the next cycle reaction ; The obtained solid is centrifuged and dried to obtain large-diameter potassium sulfate with an average particle diameter of more than 250 μm.

The mass percent of the mother liquor A component is: K ⁺ =9.03-10.33%, Mg ²⁺ =2.03-3.17%, Cl ^- =13.48-15.76%, SO ₄ ^2- =3.01-6.23%, and Na ⁺ =0.10 ~1.10%, the rest is water;

The source of the mother liquor A is any one of the following three schemes: scheme one: it is directly prepared by selecting raw materials according to the composition of the mother liquor A; or, scheme two: when the composition of a section of the mother liquor meets the composition of the mother liquor A above, it can be Direct use to achieve recycling; or, scheme three: If the composition of the obtained first-stage mother liquor does not meet the composition of mother liquor A, add raw materials to the first-stage mother liquor to make the composition within the composition range of mother liquor A to realize recycling.

The mass percentages of the components of mother liquor B are: K ⁺ =6.34-9.10%, Mg ²⁺ =0-1.02%, Cl ^- =0-7.83%, SO ₄ ^2- =5.06-8.49%, and Na ⁺ =0 ~1.40%, the rest is water;

The source of the mother liquor B is any one of the following three schemes: scheme one: it is directly prepared from raw materials selected according to the composition of the mother liquor B; It can be used directly to realize recycling; or scheme three, when the composition of the second-stage mother liquor exceeds the composition of mother liquor B or the quality is insufficient, add raw materials so that the composition of the second-stage mother liquor is within the composition and dosage range of mother liquor B. Meet the dosage and realize its recycling.

The raw material is one or more of MgSO ₄ , MgSO ₄ 7H ₂ O, K ₂ SO ₄ , KCl, MgCl ₂ , MgCl ₂ 6H ₂ O, Na ₂ SO ₄ , NaCl and H ₂ O, The dosage and the ratio of the materials are obtained according to the composition and dosage of mother liquor A or mother liquor B, and are obtained by adopting conventional material balance methods well known in the art.

The seed crystal is potassium sulfate with an average particle size of 125-150um, and the amount of the seed crystal added is 0.007-0.07 times the mass of langbeinite.

The invention has the advantages that: ① the lenbeinite used in the raw material is extracted from salt lake brine with abundant potassium resources, and has abundant resources and low price. ② The recycling of raw materials, including the recycling of the first-stage mother liquor and the second-stage mother liquor, improves the recovery rate of potassium ions and reduces the waste of raw materials. ③ The present invention adopts reactive crystallization to prepare potassium sulfate and directly obtains crystals with large particle diameters from the solution. This process is clean and pollution-free, easy to operate, and convenient for industrialized production.

Compared with the prior art, the present invention utilizes langbeinite to prepare the significant progress of the method for large particle diameter potassium sulfate is, the average particle size of general powdery potassium sulfate on the market is below 90um, the product potassium sulfate crystal of the present invention's gained The average particle size can reach more than 250μm, and the K ₂ O in potassium sulfate can reach more than 51%, which meets the standard requirements of the superior product of potassium sulfate for water-salt system technology and agriculture. Moreover, the present invention has rich and easy-to-obtain raw materials, simple process and recycling of raw materials, which greatly reduces the production cost of potassium sulfate.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Fig. 1 is the metastable phase diagram of 50°C K ⁺ , Mg ^2- //Cl ^- , SO ₄ ^2- -H ₂ O referred to in the present invention

Fig. 2 is the particle size distribution figure of potassium sulfate in embodiment 1

Fig. 3 is the particle size distribution figure of potassium sulfate in embodiment 2

Fig. 4 is the particle size distribution figure of potassium sulfate in embodiment 3

Fig. 5 is the particle size distribution figure of potassium sulfate in embodiment 4

Fig. 6 is the particle size distribution figure of potassium sulfate in embodiment 5

Detailed ways

Figure 1 is the reference metastable phase diagram of K ⁺ , Mg ^2- //Cl ^- , SO ₄ ^2- -H ₂ O at 50°C, where:

At the eutectic point E ₁ , the equilibrium solid phase is K ₂ SO ₄ +KCl+K ₂ SO ₄ ·MgSO ₄ ·4H ₂ O, and the equilibrium liquid phase composition is: w(K ⁺ )8.27%, w(Mg ²⁺ )3.82 %, w(Cl ^- )14.94%, w(SO ₄ ^2- )0.16%;

The eutectic point E ₂ , the equilibrium solid phase is KCl+KCl·MgSO ₄ ·6H ₂ O+K ₂ SO ₄ ·MgSO ₄ ·4H ₂ O, the equilibrium liquid phase composition is: w(K ⁺ )4.45%, w(Mg ²⁺ )6.04%, w(Cl ^- )16.65%, w(SO ₄ ^2- )0.30%;

The eutectic point E ₃ , the equilibrium solid phase is MgSO ₄ ·4H ₂ O+MgSO ₄ ·6H ₂ O+K ₂ SO ₄ ·MgSO ₄ ·4H ₂ O, the equilibrium liquid phase composition is: w(K ⁺ )1.99%, w(Mg ²⁺ )6.82%, w(Cl ^- )11.38%, w(SO ₄ ^2- )0.45%;

At the eutectic point E ₄ , the equilibrium solid phase is MgSO ₄ ·4H ₂ O+KCl·MgSO ₄ ·6H ₂ O+K ₂ SO ₄ ·MgSO ₄ ·4H ₂ O, and the equilibrium liquid phase composition is: w(K ⁺ )1.85 %, w(Mg ²⁺ )7.49%, w(Cl ^- )16.95%, w(SO ₄ ^2- )0.40%;

Co-saturation point E ₅ , the equilibrium solid phase is KCl+KCl·MgSO ₄ ·6H ₂ O+KCl·MgCl ₂ ·6H ₂ O, the equilibrium liquid phase composition is: w(K ⁺ )2.24%, w(Mg ²⁺ ) 7.65%, w (Cl ^- ) 21.73%, w (SO ₄ ^2- ) 0.15%;

Co-saturation point E ₆ , the equilibrium solid phase is KCl+MgSO ₄ ·4H ₂ O+KCl·MgCl ₂ ·6H ₂ O, the equilibrium liquid phase composition is: w(K ⁺ )0.10%, w(Mg ²⁺ )9.56% , w(Cl ^- )26.56%, w(SO ₄ ^2- )0.05%;

Ar, K ₂ SO ₄ ; Syl, KCl; Hex, MgSO ₄ .6H ₂ O; Tet, MgSO ₄ .4H ₂ O; Bis, MgCl ₂ .6H ₂ O;

Leo, _K2SO4 · _MgSO4 · _4H2O ; Kai, KCl· _{MgSO4 · 6H2O} ; Car, KCl· _MgCl2 · _6H2O

The conversion of langbeinite and potassium chloride is essentially a water-salt dissolution equilibrium process, and its theoretical basis is the phase diagram of the water-salt system of K ⁺ , Mg ^2- //Cl ^- , SO ₄ ^2- -H ₂ O, as shown in As shown in Figure 1, it can be seen from the analysis in the figure that at 50°C, the point M of langbeinite reacts with potassium chloride A. According to the principle of leverage, when the point of material is point P, the recovery rate of potassium sulfate is the highest. Based on the principle of balance, the material relationship of conversion can be obtained through simultaneous equations. as table 1

Table 150 °C under the condition of langbeinite and potassium chloride conversion to produce potassium sulfate material relationship (g)

The components of the mother liquor A described below should reach the following composition range: mass percentage: K ⁺ =9.03～10.33%, Mg ²⁺ =2.03～3.17%, Cl ^- =13.48～15.76%, SO ₄ ^2- =3.01～6.23 % and Na ⁺ =0.10～1.10%, the rest is water;

The composition of the mother liquor B should reach the following composition range: mass percentage: K ⁺ =6.34-9.10%, Mg ²⁺ =0-1.02%, Cl ^- =0-7.83%, SO ₄ ^2- =5.06-8.49% And Na ⁺ =0～1.40%, the rest is water.

Example 1

The first step: a stage of crystallization - the reaction crystallization of potassium sulfate

First mix 150 g of langbeinite and 100.5 g of potassium chloride, and use it as a material for later use. Prepare 220g of mother liquor B and keep it at 50°C. The composition of mother liquor B is mass percentage: K ⁺ =6.34%, SO ₄ ^2- =7.81%, and the rest is water (prepared by 31.16g K ₂ SO ₄ and 188.84g H ₂ O Then under the condition of constant stirring, gradually add the mixed material in the mother liquor B in 0.5 hours, and keep the reaction temperature at 50°C. After the addition, add 52.6g of water gradually in the above slurry in 0.5 hours , continue to stir for 1 hour after adding water, and finally solid-liquid separation obtains thick potassium 141.2g and one section of mother liquor 367.1g, and thick potassium is as the raw material of the second step.Wherein, the contained ionic composition of one section of mother liquor: K ⁼ 9.95%, Mg ²⁺ =2.51, Cl ^- =14.60%, SO ₄ ^2- =4.02%, Na ⁺ =0.75%, and the rest is water.

The second step: Second stage crystallization - the growth of potassium sulfate

Weigh 112.8g of water, first mix half of the water with the crude potassium obtained in the previous step, and keep the reaction temperature at 50°C, then add the other half of the water gradually under constant stirring, and the water addition time is 0.5 hours . After the second stage of adding water, leave it still for 1min, and then separate the solid and liquid again to obtain the product and the second stage mother liquor. The product is centrifuged and dried. The product quality after drying is 111.2g, and the second stage mother liquor quality is 137.4g. Periodic mother liquor B is recycled. Among them, the composition of the second stage mother liquor: K ⁺ =8.14%, Mg ²⁺ =0.90%, Cl ^- =6.11%, SO ₄ ^2- =6.17%, Na ⁺ =0.38%, and the rest is water.

The obtained second-stage mother liquor can be used as a new mother liquor B, and the second-stage mother liquor and mother liquor B meet the following composition ranges: K ⁺ =6.34～9.10%, Mg ²⁺ =0～1.02%, Cl ^- =0～7.83%, SO ₄ ^2- =5.06～8.49% and Na ⁺ =0～1.40%, the rest is water. When recycling, if the composition of the obtained second-stage mother liquor exceeds the above-mentioned composition or the quality cannot meet the dosage of the first step reaction, it is necessary to add suitable raw materials to make the composition of the second-stage mother liquor equal to the above-mentioned composition composition and the dosage of the first step reaction. Within the range and meet the dosage, realize recycling.

In this example, the average particle size of the product potassium sulfate crystals is 277.629 μm, and the content of potassium sulfate in the product reaches 94.5%, and the purity meets the national standard requirements for superior grades of agricultural potassium sulfate. Figure 2 is the particle size distribution diagram of potassium sulfate under the experimental conditions of this example. In the figure, the size of potassium sulfate crystals is mainly distributed at about 277.629 μm, and the particle size distribution is concentrated.

Example 2

The first step: a stage of crystallization - the reaction crystallization of potassium sulfate

Mix 50 g of the mother liquor A, 150 g of kolinite and 100.5 g of potassium chloride to form a slurry for use (hereinafter referred to as wet slurry). The composition mass percentage of the mother liquor A prepared therein: K ⁺ =9.95%, Mg ²⁺ =2.51, Cl ^- =14.65%, SO ₄ ^2- =4.05% and Na ⁺ =0.75%, the rest is water (by 2.53gMgSO ₄ , 9.50gKCl, 6.33gMgCl ₂ ·6H ₂ O, 0.96gNaCl and 30.68gH ₂ O). Weigh 10g of potassium sulfate seed crystals (the average particle size of the seeds is 125-150μm) and add it to 220g of the prepared mother liquor B, wherein the composition mass percentage of the prepared mother liquor B: K ⁺ =8.14%, Mg ²⁺ =0.90%, Cl ^- = 6.11%, SO ₄ ^2- = 6.17% and Na ⁺ = 0.39%, _the rest is water (prepared from _9.90gMgSO4 , _10.25gK2SO4 , 25.41gKCl, 2.20gNaCl and _172.24gH2O ). Then, the wet slurry was gradually added to the mother liquor B within 1.5 hours under constant stirring, and the temperature was maintained at 50°C. Add 52.6g of water to the above-mentioned slurry gradually in 0.5 hours after the feeding is finished, continue to stir for 1 hour after adding water, and finally obtain 160.2g of crude potassium and 410.1g of a section of mother liquor after solid-liquid separation. The raw material of the second step, a section of mother liquor is recycled as mother liquor A in the next cycle. The ionic composition contained in the first stage of mother liquor: K ⁺ =9.97%, Mg ²⁺ =2.54, Cl ^- =14.60%, SO ₄ ^2- =4.02%, Na ⁺ =0.36%, and the rest is water, which conforms to the composition of mother liquor A Range: K ⁺ =9.03～10.33%, Mg ²⁺ =2.03～3.17%, Cl ^- =13.48～15.76%, SO ₄ ^2- =3.01～6.23%, Na ⁺ =0.10～1.10%, and the rest is water.

The second step: Second stage crystallization - the growth of potassium sulfate

Weigh 112.8g of water, first mix half of the water with the crude potassium obtained in the first stage of reaction, and maintain the temperature at 50°C, then gradually add the other half of the water under constant stirring, and the water addition time is 0.5 hours. After adding water in the second stage, let it stand for 5 minutes, and separate the solid and liquid again to obtain the product and the second stage mother liquor, and the product is centrifuged and dried. The product quality after drying is 119.2g, and the second-stage mother liquor is 143.8g to be recycled as the mother liquor B of the next cycle, wherein the ionic components contained in the second-stage mother liquor are: K ⁺ =8.14%, Mg ²⁺ =0.90%, Cl ^- =6.11%, SO ₄ ^2- =6.17% and Na ⁺ =0.38%, the rest is water, in line with the composition range of mother liquor B: K ⁺ =6.34～9.10%, Mg ²⁺ =0～1.02%, Cl ^- =0～7.83%, SO ₄ ^2- =5.06～8.49% and Na ⁺ =0～1.40%, and the rest is water.

In this embodiment, the average particle size of the product potassium sulfate crystals is 336.443 μm, the particle size distribution is uniform, the content of potassium sulfate in the product reaches 94.9%, and the purity meets the national standard requirements for superior grades of agricultural potassium sulfate. Figure 3 is the particle size distribution diagram of potassium sulfate under the experimental conditions of this example. In the figure, the size of potassium sulfate crystals is mainly distributed at about 336.443 μm, and the particle size distribution is concentrated.

Example 3

The first step: a stage of crystallization - the reaction crystallization of potassium sulfate

Take by weighing the one section mother liquor 50g that meets mother liquor A composition that the first step obtains in the embodiment 2, zoleinite 150g and potassium chloride 100.5g are mixed uniformly stand-by, take by weighing 10g potassium sulfate crystal seed (the average particle size of crystal seed is 125 -150μm) was added to 220g of the second-stage mother liquor obtained in the second step of Example 2 that complied with the composition of mother liquor B. Since the second-stage mother liquor obtained in Example 2 could not meet the dosage for this time, all the obtained in Example 2 On the basis of using all 143.8g of the second-stage mother liquor, 3.42gMgSO ₄ , 3.57gK ₂ SO ₄ , 8.79gKCl, 0.77gNaCl and 59.65gH ₂ O need to be added to make 220g of mother liquor B, and then the wet The slurry was gradually added to the second-stage mother liquor within 1.5 hours, and the temperature was maintained at 50°C. After the addition, 52.6g of water was gradually added to the above-mentioned slurry in 0.5 hours, and the stirring was continued for 1 hour after the addition of water. Finally, 157.0g of crude potassium and 411.8g of a section of mother liquor were obtained after solid-liquid separation. Crude potassium is used as the raw material of the second step, and a section of mother liquor is recycled as mother liquor A in the next cycle. The ionic composition contained in the first stage of mother liquor: K ⁺ =9.96%, Mg ²⁺ =2.53, Cl ^- =14.60%, SO ₄ ^2- =4.02%, Na ⁺ =0.036%, and the rest is water, which conforms to the composition of mother liquor A Range: K ⁺ =9.03～10.33%, Mg ²⁺ =2.03～3.17%, Cl ^- =13.48～15.76%, SO ₄ ^2- =3.01～6.23%, Na ⁺ =0.10～1.10%, and the rest is water.

The second step: Second stage crystallization - the growth of potassium sulfate

Weigh 112.8g of water, first mix half of the water with the crude potassium obtained in the first stage of reaction, and maintain the temperature at 50°C, then gradually add the other half of the water under constant stirring, and the water addition time is 0.5 hours. After adding water in the second stage, let it stand for 5 minutes, and separate the solid and liquid again to obtain the product and the second stage mother liquor, and the product is centrifuged and dried. The product quality after drying is 110.7g, and the second-stage mother liquor is 140.8g to be recycled as the mother liquor B of the next cycle, wherein the ionic components contained in the second-stage mother liquor: K ⁺ =8.15%, Mg ²⁺ =0.90%, Cl ^- =6.11%, SO ₄ ^2- =6.16% and Na ⁺ =0.38%, the rest is water. Comply with the composition range of mother liquor B: K ⁺ =6.34～9.10%, Mg ²⁺ =0～1.02%, Cl ^- =0～7.83%, SO ₄ ^2- =5.06～8.49% and Na ⁺ =0～1.40% , and the rest is water.

In this example, the average particle size of the product potassium sulfate crystals is 371.886 μm, the particle size distribution is uniform, the content of potassium sulfate in the product reaches 95.0%, and the purity meets the national standard requirements for superior grades of agricultural potassium sulfate. Figure 4 is the particle size distribution diagram of potassium sulfate under the experimental conditions of this example. In the figure, the size of potassium sulfate crystals is mainly distributed around 371.886 μm, and the particle size distribution is relatively concentrated.

Example 4

The first step: a stage of crystallization - the reaction crystallization of potassium sulfate

Mix 50 g of the mother liquor A, 150 g of kolinite and 100.5 g of potassium chloride to form a slurry for use (hereinafter referred to as wet slurry). The composition mass percentage of the mother liquor A prepared therein: K ⁺ =9.95%, Mg ²⁺ =2.51, Cl ^- =14.65%, SO ₄ ^2- =4.05% and Na ⁺ =0.75%, the rest is water (by 2.53gMgSO ₄ , 9.50gKCl, 6.33gMgCl ₂ ·6H ₂ O, 0.96gNaCl and 30.68gH ₂ O). Weigh 5g of seed crystals (the average particle size of the seeds is 125μm-150μm) and add it to 250g of the prepared mother liquor B, wherein the composition mass percentage of the prepared mother liquor B: K ⁺ =6.90%, SO ₄ ^2- =8.49%, The remainder was water (made up of 33.87g K ₂ SO ₄ and 186.13g H ₂ O). Then, under the condition of constant stirring, the wet slurry was gradually added into the second-stage mother liquor within 2 hours, and the temperature was kept at 60°C. Continue to stir for 2 hours after the feeding, and finally obtain 158.9 g of crude potassium and 380.0 g of a section of mother liquor through solid-liquid separation. The crude potassium is used as the raw material of the second step, and one section of mother liquor is recycled as the next cycle of mother liquor A. The ionic components contained in the first stage of mother liquor: K ⁺ =9.98%, Mg ²⁺ =2.54%, Cl ^- =14.56%, SO ₄ ^2- =4.02%, and Na ⁺ =0.37%, and the rest is water, which conforms to the composition of mother liquor A Composition range: K ⁺ =9.03～10.33%, Mg ²⁺ =2.03～3.17%, Cl ^- =13.48～15.76%, SO ₄ ^2- =3.01～6.23%, Na ⁺ =0.10～1.10%, and the rest is water.

The second step: Second stage crystallization - the growth of potassium sulfate

Weigh 176.3 of water, first mix half of the water with the crude potassium obtained in the first stage of reaction, and keep the temperature at 60°C, then gradually add the other half of the water under constant stirring, and the water addition time is 1 hour. After adding water in the second stage, let it stand for 5 minutes, and separate the solid and liquid again to obtain the product and the second stage mother liquor, and the product is centrifuged and dried. The product quality after drying is 116.1g, and the second-stage mother liquor is 210.2g to be recycled as the mother liquor B of the next cycle, wherein the ion components contained in the second-stage mother liquor: K ⁺ =8.15%, Mg ²⁺ =0.91%, Cl ^- =6.11%, SO ₄ ^2- =6.17% and Na ⁺ =0.37%, the rest is water, in line with the composition range of mother liquor B: K ⁺ =6.34～9.10%, Mg ²⁺ =0～1.02%, Cl ^- =0～7.83%, SO ₄ ^2- =5.06～8.49% and Na ⁺ =0～1.40%, and the rest is water.

In this embodiment, the average particle size of the product potassium sulfate crystals is 396.237 μm, the product particle size is uniform, the potassium sulfate content in the product reaches 94.5%, and the purity meets the national standard requirements for the superior grade of agricultural potassium sulfate. Figure 5 is the particle size distribution diagram of potassium sulfate under the experimental conditions of this example. In the figure, the size of potassium sulfate crystals is mainly distributed at about 396.237 μm, and the particle size distribution is concentrated.

Example 5

The first step: a stage of crystallization - the reaction crystallization of potassium sulfate

Mix 50 g of a first-stage mother liquor conforming to solution A obtained in the first step in Example 4, 150 g of langbeinite and 100.5 g of potassium chloride to prepare a slurry for use (hereinafter referred to as wet slurry). Weigh 5g of seed crystals (the average particle size of the seed crystals is 125μm-150μm) and add 250g to mother liquor B. Since the second stage mother liquor obtained in Example 4 cannot meet the dosage for this time, all the obtained in Example 4 On the basis of using all 210.2g of the second-stage mother liquor, 1.79gMgSO ₄ , 1.86gK ₂ SO ₄ , 4.59gKCl, 0.40gNaCl and 31.16gH ₂ O need to be added to make 250g of mother liquor B, and then the wet The slurry was gradually added to the second-stage mother liquor within 2 hours, and the temperature was kept at 60°C. Continue to stir for 2 hours after the feeding, and finally obtain 158.9 g of crude potassium and 380.0 g of a section of mother liquor through solid-liquid separation. The crude potassium is used as the raw material for the second step, and one section of mother liquor is used as the next cycle of mother liquor A for recycling. The ionic composition contained in the first stage mother liquor: K ⁺ =9.96%, Mg ²⁺ =2.54%, Cl ^- =14.60%, SO ₄ ^2- =4.02%, Na ⁺ =0.037%, and the rest is water, which conforms to the composition of mother liquor A Composition range: K ⁺ =9.03～10.33%, Mg ²⁺ =2.03～3.17%, Cl ^- =13.48～15.76%, SO ₄ ^2- =3.01～6.23%, Na ⁺ =0.10～1.10%, and the rest is water.

The second step: Second stage crystallization - the growth of potassium sulfate

Weigh 176.3 of water, first mix half of the water with the crude potassium obtained in the first stage of reaction, and keep the temperature at 60°C, then gradually add the other half of the water under constant stirring, and the water addition time is 1 hour. After adding water in the second stage, let it stand for 5 minutes, and separate the solid and liquid again to obtain the product and the second stage mother liquor, and the product is centrifuged and dried. The product quality after drying is 120.1g, and the second-stage mother liquor is 215.2g to be recycled as the mother liquor B of the next cycle, wherein the ionic components contained in the second-stage mother liquor are: K ⁺ =8.15%, Mg ²⁺ =0.91%, Cl ^- =6.12%, SO ₄ ^2- =6.17% and Na ⁺ =0.37%, the rest is water, in line with the composition range of mother liquor B: K ⁺ =6.34～9.10%, Mg ²⁺ =0～1.02%, Cl ^- =0～7.83%, SO ₄ ^2- =5.06～8.49% and Na ⁺ =0～1.40%, and the rest is water.

In this embodiment, the average particle size of the product potassium sulfate crystals is 400.259 μm, the product particle size is uniform, the potassium sulfate content in the product reaches 95.1%, and the purity meets the national standard requirements for the superior grade of agricultural potassium sulfate. Figure 6 is the particle size distribution diagram of potassium sulfate under the experimental conditions of this example. In the figure, the size of potassium sulfate crystals is mainly distributed around 400.259 μm, and the particle size distribution is concentrated.

Matters not covered in the present invention are known technologies.

Claims (5)

1. utilize reactive crystallization to produce a method for Large stone potassium sulfate, it is characterized by and comprise the following steps:

The first step: one section of crystallization---the reactive crystallization of potassium sulfate

It is schoenite according to mass ratio: the proportioning of Repone K=1:0.6 ~ 0.75, schoenite and Repone K are mixed, then using it directly as material or stand-by as material after adding mother liquor A again, wherein, the quality of the mother liquor A added, is less than or equal to 2 times of schoenite and Repone K quality sum; Take the mother liquor B of 0.1 ~ 5 times of schoenite quality more in addition, without crystal seed or under having crystal seed to add the condition of mother liquor B, material is above being added, material be stir condition under added mother liquor B gradually in 0.5 ~ 2 hour, and make temperature remain on 45 DEG C ~ 60 DEG C constant;

Directly stir 0 ~ 2 hour after reinforced end, or continue stirring after adding water 0 ~ 2 hour, wherein amount of water is less than or equal to 2 times of schoenite quality, in situation about stirring, water was added gradually in above-mentioned slurry in 0.1 ~ 2 hour, finally by obtaining thick potassium and one section of mother liquor after solid-liquid separation, thick potassium is as next step raw material, and one section of mother liquor can as the mother liquor A recycle of the first step in next circulating reaction;

Second step: two sections of crystallizations---the growth of potassium sulfate

Take the water of 0.1 ~ 3 times of schoenite quality in the first step, first the thick potassium that half water and the first step obtain is mixed, and temperature maintains 45 DEG C ~ 60 DEG C, then more remaining water was added gradually in 0.1 ~ 2 hour under the condition constantly stirred, leave standstill 0 ~ 30min, carry out two sections of crystallizations, again solid-liquid separation, obtain solid and two sections of mother liquors, the two sections of mother liquors obtained can as the mother liquor B recycle of the first step in next circulating reaction; Gained solid is through centrifugal, dry, obtains the Large stone potassium sulfate of median size more than 250 μm;

The mass percent of described mother liquor A composition is: K ⁺=9.03 ~ 10.33%, Mg ²⁺=2.03 ~ 3.17%, Cl ^-=13.48 ~ 15.76%, SO ₄ ^2-=3.01 ~ 6.23% and Na ⁺=0.10 ~ 1.10%, all the other are water;

The mass percent of described mother liquor B component is: K ⁺=6.34 ~ 9.10%, Mg ²⁺=0 ~ 1.02%, Cl ^-=0 ~ 7.83%, SO ₄ ^2-=5.06 ~ 8.49% and Na ⁺=0 ~ 1.40%, all the other are water.

2. utilize reactive crystallization to produce the method for Large stone potassium sulfate as claimed in claim 1, the source that it is characterized by described mother liquor A is that one of following three kinds of schemes are any: scheme one: directly formulated for choosing raw material according to the composition of mother liquor A; Or, scheme two: directly can adopt when the composition of mother liquor A above the composition of one section of mother liquor meets, realize recycle; Or scheme three: if the one-tenth that the composition of obtain one section of mother liquor does not meet mother liquor A is grouped into, adds in raw material to one section of mother liquor and makes it form within the compositing range of mother liquor A, realize recycle.

3. utilize reactive crystallization to produce the method for Large stone potassium sulfate as claimed in claim 1, the source that it is characterized by described mother liquor B is that one of following three kinds of schemes are any: scheme one: directly formulated for choosing raw material according to the composition of mother liquor B; Or, scheme two: directly can adopt when the composition of mother liquor B above described two sections of mother liquor compositions meet, realize recycle; Or, scheme three, when the one-tenth that the composition of two sections of mother liquors exceeds mother liquor B be grouped into or mass deficiency time, add raw material and make the composition of two sections of mother liquors within the composition and amount ranges of mother liquor B and meet consumption, realize its recycle.

4. the reactive crystallization that utilizes as described in Claims 2 or 3 produces the method for Large stone potassium sulfate, and it is characterized by described raw material is MgSO ₄, MgSO ₄7H ₂o, K ₂sO ₄, KCl, MgCl ₂, MgCl ₂6H ₂o, Na ₂sO ₄, NaCl and H ₂one or more in O, the proportioning between its consumption and material, according to meeting composition and the consumption of mother liquor A or mother liquor B, adopting conventional materials accounting method and obtaining.

5. utilize reactive crystallization to produce the method for Large stone potassium sulfate as claimed in claim 1, it is characterized by described crystal seed is potassium sulfate, and median size is 125 ~ 150 μm, and the add-on of crystal seed is 0.007 ~ 0.07 times of schoenite quality.