Method for preparing potassium sulfate by using underground native sulfur-rich potassium-containing minerals

Abstract

A method for preparing potassium sulfate by using underground native sulfur-rich potassium-containing minerals comprises the following steps: mixing and stirring a potassium chloride raw material and a potassium-magnesium-vanadium raw material, adding water with TDS / mg / L less than 45000 and SOP mother liquor, stirring, and filtering slurry to obtain washing mother liquor LLeo and a filter cake S2; the filter cake S2 is conveyed into a crystallizer, water with TDS / mg / L smaller than 45000 and SOP mother liquor are added, crystallization is carried out in the crystallizer, the temperature in the crystallizer is kept at 40-65 DEG C, crystallized slurry is filtered, a potassium sulfate wet material and filtrate are obtained, the filtrate is returned to act on the SOP mother liquor for utilization, and the product obtained through the scheme is high in yield and low in cost.

Description

Technical Field

[0001] The present invention relates to the field of a preparation method of potassium sulfate, and particularly to a method for preparing potassium sulfate by using underground primary sulfur-rich potassium-containing minerals. Background Art

[0002] At present, potassium sulfate is an important chlorine-free potassium fertilizer, which is widely used in agriculture and has a large market demand. In the current technology, CN108349743A discloses a method for producing potassium sulfate from potassium-containing ore at high ambient temperature. The method includes contacting an aqueous potassium- and sulfate-containing composition with magnesium chloride to obtain a composition containing langbeinite; concentrating the langbeinite from the composition; reacting the langbeinite with magnesium sulfate and potassium sulfate to convert the langbeinite into polyhalite; contacting the polyhalite with water to remove the excess; and contacting the polyhalite with water to leach out the magnesium sulfate contained in the polyhalite and at least substantially selectively precipitate potassium sulfate. This method can operate at a relatively high temperature, especially at a temperature higher than 35°C, but the total recovery rate of the product obtained by this method in laboratory-scale experiments is about 48%.

[0003] CN111533140B discloses a method for preparing potassium sulfate magnesium fertilizer, potassium chloride and potassium sulfate from sulfate carnallite. The method first performs flotation treatment on the sulfate carnallite ore with an anionic flotation agent to obtain a potassium-sulfur mixed salt concentrate and a chloride-type tailing; then performs reverse flotation treatment on the chloride-type tailing with a reverse flotation agent to obtain a magnesium chloride-type tailing and sodium chloride; finally, performs washing, refining and decomposition treatment on the magnesium chloride-type tailing to obtain potassium chloride. The present invention adopts a double flotation separation technology to provide a raw material basis for simultaneously and efficiently preparing potassium chloride and potassium sulfate magnesium fertilizer products; at the same time, adopts the "reverse flotation - washing bischofite - decomposition" technology to remove sodium chloride and magnesium chloride in the chloride-type tailing successively, which is beneficial to obtaining carnallite concentrate and efficiently preparing high-grade potassium chloride products. This method requires flotation agents and reverse flotation agents, and a large amount of water is required in the process, resulting in a high cost. Summary of the Invention

[0004] (1) Technical Problems to be Solved

[0005] In view of the above-mentioned disadvantages and deficiencies of the prior art, the present invention provides a method for preparing potassium sulfate by using underground primary sulfur-rich potassium-containing minerals, which can obtain a higher yield and lower cost under high-temperature conditions.

[0006] Technical Solution

[0007] In order to achieve the above object, an embodiment of the present invention provides a method for preparing potassium sulfate by using underground primary sulfur-rich potassium-containing minerals, including the steps:

[0008] Mix the potassium chloride raw material and the langbeinite raw material, add the SOP mother liquor and stir, filter the slurry to obtain the washing mother liquor L Leo and the filter cake S2;

[0009] Transport the filter cake S2 to a crystallizer, add water with TDS / mg / L < 45000 and the SOP mother liquor, carry out crystallization in the crystallizer, keep the temperature in the crystallizer at 40 - 65°C, filter the crystallized slurry to obtain wet potassium sulfate and filtrate, and return the filtrate for utilization as the SOP mother liquor.

[0010] In one embodiment, the potassium chloride raw material is obtained by the following method:

[0011] Mix carnallite and potash ore concentrate, and after the first crushing, obtain a mixed raw material of carnallite and potash ore, with the proportion of the mixed raw material having a particle size ≤ 20mm being ≥ 90%;

[0012] Add the mixed raw material to the saturated mother liquor for pulp adjustment. The saturated mother liquor consists of the mother liquor composition at the triple co-saturation point D of the metastable phase diagram of the pentasystem of Na + , K + , Mg 2+ / / Cl - , SO 4 2- —H 2 O at 35°C, KCl, and carnallite;

[0013] The material after pulp adjustment is subjected to a second crushing, and the material after the second crushing is decomposed;

[0014] The decomposed slurry is subjected to a third crushing, and the material after the third crushing is used for flotation; among them, the particle size after each crushing is smaller than that of the previous crushing;

[0015] Add a flotation collector and carry out rough potassium flotation to obtain a rough potassium slurry S1 and tailings T1. After filtering the rough potassium slurry S1, obtain a rough potassium filter cake K1 and mother liquor L1. After filtering the tailings T1, obtain T2 and mother liquor L1. The obtained K1 is washed, filtered, and dried and dehydrated to obtain the potassium chloride product;

[0016] Preferably, before the first crushing, mix carnallite and potash ore concentrate and carry out a first screening, and combine the oversize and undersize after crushing to obtain the mixed raw material of carnallite and potash ore;

[0017] Before the second crushing, carry out a second screening on the material after pulp adjustment. The oversize is subjected to a second crushing, and the undersize of the second screening and the material after the second crushing are used for decomposition;

[0018] Before the third crushing, the slurry after decomposition is subjected to the third screening. The oversize material is subjected to the third crushing, and the undersize material from the third screening and the material after the third crushing are used for flotation. Among them, the particle size of the current screening in the three - stage screening is smaller than that of the previous screening.

[0019] In one embodiment, the potassium chloride raw material is obtained by the following method:

[0020] The collected underground primary sulfur - rich potassium - containing ore is subjected to multi - stage crushing to obtain sulfur - rich potassium - containing minerals with the required particle size;

[0021] The sulfur - rich potassium - containing minerals and seawater are mixed and stirred for conversion at a temperature of 35°C to 50°C to obtain a solid - liquid mixed slurry;

[0022] The solid - liquid mixed slurry is adjusted with the mother liquor of carnallite flotation. After adding flotation reagents and mixing evenly, carnallite flotation is carried out. The flotation reagent is an aqueous solution of organic sodium salt produced by chlorination, sulfonation and saponification of heavy oil;

[0023] The flotation foam obtained in flotation is filtered and separated. The obtained solid is the carnallite concentrate, and part of the flotation mother liquor generated by flotation is returned to the previous slurry - adjusting step.

[0024] In one embodiment, the particle size of the first screening is 20 - 12.5 mm. The oversize material is sent for crushing, and the crushing particle size P90 is between 20 - 12.5 mm; the particle size of the second screening is 5 - 2 mm. The oversize material is sent for secondary crushing, and the crushing particle size P90 is between 5 - 2 mm. The particle size of the third screening is 1 - 0.85 mm. The oversize material is sent for crushing, and the crushing particle size P90 is between 1 - 0.85 mm.

[0025] In one embodiment, the carnallite ore is a natural solid carnallite ore containing sodium chloride and epsomite minerals; the sylvite ore is a natural solid sylvite ore containing sodium chloride, kieserite and gypsum minerals. The main components of the underground primary sulfur - rich potassium - containing ore are K + 8.0% - 13.0%, Na + 8.0% - 21.0%, Mg 2+ 5.0% - 8.0%, Cl - 23.0% - 35.0%, SO 4 2- 20.0% - 31.0%.

[0026] In one embodiment, the effective components of the aqueous solution of organic sodium salt are sodium petroleum sulfonate with a carbon chain length of 12 - 16 and sodium chloride. The mass percentage content of sodium petroleum sulfonate in the flotation reagent is 24% - 25%, and the mass percentage content of sodium chloride ≤ 8%.

[0027] In one embodiment, the decomposition is carried out in a decomposition tank which is provided with a draft tube. Under the action of a stirrer, the slurry flows in a closed-loop circulation state from bottom to top inside the draft tube, and the carnallite decomposition occurs during the upward stroke of the flow state. The residence time of the slurry in the decomposition tank is 30 min - 120 min;

[0028] Preferably, when carrying out the decomposition in the decomposition tank, washing mother liquor is added into the decomposition tank, and the addition amount of the washing mother liquor is 30% - 45% of the total mass of the raw ore.

[0029] In one embodiment, the mass contents of the main chemical components of the washing mother liquor are as follows: K + : 4.2 - 6.863%, Na + 0.36 - 3.96%, Mg 2+ 0.1 - 2.74%, SO 4 2- 2: 2.189 - 5.542%, Cl - 13.05 - 15.405%;

[0030] The mass contents of the main components of the saturated mother liquor at point D are K + 1.40 - 2.069%, Na + 0.14 - 1.67%, Mg 2+ 0.1 - 7.20%, Cl - 19.74 - 21.46%, SO 4 2- 2.21 - 4.189%.

[0031] In one embodiment, the flotation of kainite is a closed-circuit process with one roughing and one cleaning, and the middlings from the cleaning are returned to the roughing. The solid-phase mass content in the roughing is 25% - 35%, and the solid-phase mass content in the cleaning is 10% - 15%.

[0032] In one embodiment, the third crushing is carried out by a rod mill for grinding, and the oversize materials are collected through a chute. Mother liquor L1 is added into the chute, and the addition amount of mother liquor L1 satisfies that the discharge concentration of the rod mill is 45 - 60%, and the grinding time is 1.0 - 6.0 minutes.

[0033] (III) Beneficial effects

[0034] The beneficial effects of the present invention are as follows: In the present invention, the potassium chloride raw material and the kainite raw material are mixed and stirred. During crystallization, the use of a mixed solution of water with TDS / mg / L < 45000 and SOP mother liquor can improve the yield. And because the subsequent generated SOP mother liquor is returned to the system for utilization, the purity of potassium sulfate obtained by adopting this solution, K 2 O is higher than 50%, and the yield is higher than 52.9%. Description of the drawings

[0035] Figure 1 It is a process flow diagram of a method for producing potassium sulfate by using underground native sulfur-rich potassium minerals in an embodiment. Specific embodiments

[0036] In order to better explain the present invention for easy understanding, the present invention will be described in detail below through specific embodiments.

[0037] Please refer to Figure 1 , an embodiment of the present invention provides a method for producing potassium sulfate by using underground native sulfur-rich potassium minerals, including the steps of:

[0038] Mix and stir the potassium chloride raw material and the langbeinite raw material, add the SOP mother liquor (potassium sulfate synthesis mother liquor) and stir, and filter the slurry to obtain the washing mother liquor L Leo and the filter cake S2;

[0039] Transport the filter cake S2 to a crystallizer, add water with TDS / mg / L < 45000 and the SOP mother liquor, conduct crystallization in the crystallizer, keep the temperature in the crystallizer at 40 - 65 °C, filter the crystallized slurry to obtain wet potassium sulfate and filtrate, and the filtrate is returned for utilization as the SOP mother liquor.

[0040] The water in this application refers to water with TDS / mg / L < 45000.

[0041] Specifically, a method for producing potassium sulfate by using underground native sulfur-rich potassium minerals includes the steps of:

[0042] S1. Mix carnallite and potash ore raw ore, and conduct the first crushing to obtain a mixed raw material of carnallite and potash ore, and the proportion of the mixed raw material with a particle size ≤ 20 mm is ≥ 90%.

[0043] Preferably, the crushing particle size P90 is between 20 and 12.5 mm.

[0044] In one embodiment, specifically, the carnallite ore is a natural solid carnallite ore containing sodium chloride and epsomite minerals; the sylvite ore is a natural solid sylvite ore containing sodium chloride, kieserite and gypsum minerals. The ratio of carnallite to sylvite is 6-8:2-4. The control of the ratio of carnallite to sylvite generally needs to be considered according to the actual ratio of carnallite to sylvite in the ore source. In the prior art, the ratio of carnallite to sylvite can only be limited to a relatively small range, such as 6:4, which has an adverse effect on the effective application rate of the raw ore in actual production and will cause waste of resources. In this application, since the actual mass ratio of carnallite to sylvite in the ore source is about 7.2:2.8, the ratio of carnallite to sylvite of 6:4 in the prior art will cause the raw carnallite ore to not be fully utilized. By adopting the process of this application, the mass ratio range of carnallite to sylvite can be expanded, the raw ore can be fully utilized, and the requirements for the actual ratio of the raw ore and the mining method of the raw ore are lower.

[0045] S2. Add the mixed raw materials to the saturated mother liquor for pulp mixing. The saturated mother liquor is composed of the mother liquor composition at the triple co-saturation point D of epsomite, KCl, and carnallite in the 35°C metastable phase diagram of the Na + 、K + 、Mg 2+ / / Cl - 、SO 4 2- —H 2 O five-component system at 35°C.

[0046] In one embodiment, specifically, the mass content of the main components of the saturated mother liquor at point D is K + 1.40-2.069%, Na + 0.14-1.67%, Mg 2+ 0.1-7.20%, Cl - 19.74-21.46%, SO4 2- 2.21-4.189%.

[0047] S3. The pulp after pulp mixing is subjected to a second crushing, and the material after the second crushing is decomposed.

[0048] In one embodiment, specifically, the crushing particle size is such that P90 is between 5 and 2 mm. This particle size range is beneficial to the decomposition of carnallite.

[0049] Specifically, the decomposition is carried out in a decomposition tank. The decomposition tank is provided with a draft tube. Under the action of a stirrer, the slurry flows in a closed-loop circulation state from bottom to top in the draft tube, and the decomposition of carnallite is carried out during the upward stroke of the flow state. The residence time of the slurry in the decomposition tank is 30 min - 120 min.

[0050] When decomposition is carried out in the decomposition tank, washing mother liquor is added to the decomposition tank. The addition amount of the washing mother liquor is 30-45% of the total mass of the original ore. The addition amount of the washing mother liquor needs to be strictly controlled. Excessive mother liquor points at 35 °C K + 、Na + 、Mg 2+ / / Cl - 、SO 4 2- —H 2 O five-component hydrated salt system phase diagram is located in the kainite phase region, close to the carnallite phase region. This causes kainite to appear during decomposition. The KCl collector cannot collect kainite, which will lead to a high content of K + in the tailings. To avoid this phenomenon, it is necessary to reduce the amount of mother liquor after mixing potassium washing. When the mother liquor after mixing potassium washing is reduced to 30-45%, the flotation mother liquor point moves away from the kainite phase region and approaches the carnallite phase region. However, if the amount of mother liquor after mixing potassium washing is further reduced, the content of Mg 2+ in the solid phase is too high, and the carnallite decomposition is insufficient, which will reduce the concentrate yield and grade and increase the content of K+ in the tailings.

[0051] S4. The slurry after decomposition is subjected to a third crushing, and the material after the third crushing is used for flotation; among them, the particle size after each crushing is smaller than that of the previous crushing.

[0052] In one embodiment, specifically, the particle size of the third screening is 1-0.85 mm. Since the particle size of this crushing is 1-0.85 mm, and it is difficult for general crushers in actual production to meet this particle size requirement, a rod mill is used to achieve this function.

[0053] Preferably, before the first crushing, carnallite and sylvinite original ore are mixed and then subjected to a first screening, and the oversize and undersize after crushing are combined to obtain a mixed raw material of carnallite and sylvinite;

[0054] Before the second crushing, the slurried material is subjected to a second screening. The oversize is subjected to a second crushing, and the undersize of the second screening and the material after the second crushing are used for decomposition;

[0055] Before the third crushing, the slurry after decomposition is subjected to a third screening. The oversize is subjected to a third crushing, and the undersize of the third screening and the material after the third crushing are used for flotation; among them, the particle size of each screening is smaller than that of the previous screening.

[0056] Screening before each crushing can screen out the materials that meet the particle size requirements, so that the amount of materials to be crushed is reduced, thereby reducing costs and time and reducing the wear of equipment.

[0057] Specifically, the particle size of the first screening is 20 - 12.5 mm. The oversize materials are sent for crushing, and the crushed particle size has a P90 value between 20 - 12.5 mm. As a result, most of the materials after the first screening + crushing have a P90 particle size between 20 - 12.5 mm. That is to say, the minimum particle size requirement for the first screening and crushing can be 12.5 mm. Through screening + crushing, the particle size of most of the materials can reach 12.5 mm, and this proportion can reach over 90%. The first screening and crushing perform rough screening and crushing on large pieces of raw ore, and the particle size is relatively large compared to the subsequent screening and crushing. However, if the ore is crushed into very small particles at one time, it will cause a significant increase in crushing energy consumption and time, thus increasing costs and being unfavorable for industrial production. The control of the above particle size not only helps save crushing energy consumption and time but also ensures the smooth progress of the next steps of pulp mixing and pumping.

[0058] The particle size of the second screening is 5 - 2 mm. The oversize materials are sent for secondary crushing, and the crushed particle size has a P90 value between 5 - 2 mm. Through the second screening + crushing, the particle size of most of the materials is controlled between 5 - 2 mm. Within this range, the material can be efficiently decomposed.

[0059] Through three screenings and three crushings, and gradually reducing the particle size each time, the particle size is finally controlled below 1 - 0.85 mm. Under this particle size range, sylvite can be flotation-extracted. If single-stage crushing is used, it is impossible to achieve this particle size. With three-stage crushing, the particle size of the raw materials after the first crushing can be smoothly pumped after pulp mixing without causing blockage. And this particle size control can save costs and time to the greatest extent. The particle size control of the second crushing can achieve the most effective decomposition, and the third crushing can help achieve efficient flotation.

[0060] Specifically, the third crushing uses a rod mill for grinding. Before grinding, the oversize materials of the screening machine are collected through a chute, and mother liquor L1 is added to the chute. The addition amount of mother liquor L1 satisfies that the discharge concentration of the rod mill (solid-liquid mass percentage) is 45 - 60%, and the grinding time is 1.0 - 6.0 minutes.

[0061] S5. Add a flotation collector and conduct rough potassium flotation to obtain a crude potassium slurry S1 and tailings T1. After filtering the crude potassium slurry S1, a crude potassium filter cake K1 and mother liquor L1 are obtained. After filtering the tailings T1, T2 and mother liquor L1 are obtained.

[0062] Since the washing mother liquor generated after washing in S5 is returned to the decomposition step, the single-pass yield of KCl is greatly improved. In the prior art, generally, the washing mother liquor is transported to a salt pan for salt pan spreading and drying, and the decomposition yield of the obtained KCl is only about 70%. Through the reflux control of this application, the decomposition yield of KCl can be increased to 119% (relative to the raw ore). This is because of the K +Recycling has been carried out. At the same time, the liquid used for decomposition in this application is the washing mother liquor generated in the process. Water is not used in this decomposition step, greatly reducing the water consumption of the system and lowering the cost.

[0063] S6. Multistage crushing is performed on the mined underground primary sulfur-rich potassium-containing raw ore to obtain sulfur-rich potassium-containing minerals with the required particle size.

[0064] Specifically, in one embodiment, two-stage crushing or more than two-stage crushing can be adopted. The particle size of the previous crushing is smaller than that of the subsequent crushing, and the final particle size of the last-stage crushing is 1 mm to 2 mm. Compared with single-stage crushing, multiple crushing can effectively save energy consumption and crushing time. In addition, controlling the particle size within 1 mm to 2 mm can achieve better subsequent conversion and control the cost within a reasonable range.

[0065] Specifically, the main components of the underground primary sulfur-rich potassium-containing raw ore are K + 8.0% - 13.0%, Na + 8.0% - 21.0%, Mg 2+ 5.0% - 8.0%, Cl - 23.0% - 35.0%, SO 4 2- 20.0% - 31.0%.

[0066] S7. The sulfur-rich potassium-containing minerals and seawater are mixed and stirred. The stirring time is 40 min to 150 min, and the conversion temperature is controlled at 35°C to 50°C to obtain a solid-liquid mixed pulp.

[0067] Specifically, in one embodiment, the mass ratio of the primary sulfur-rich potassium-containing raw ore to seawater is 1:0.45 - 0.75. When the K + concentration is higher, a higher amount of seawater is required. When the K + concentration is lower, the required amount of seawater can be appropriately reduced. In short, the mass ratio is controlled within the range of 1:0.45 - 0.75.

[0068] S8: The solid-liquid mixed pulp is adjusted with schoenite flotation mother liquor to control the flotation concentration. After adding flotation reagents and mixing evenly, schoenite flotation is carried out. The dosage of the flotation reagent is 250 g / ton of raw ore to 500 g / ton of raw ore, and the flotation reagent is an aqueous solution of organic sodium salt produced by chlorination, sulfonation, and saponification of heavy oil.

[0069] Specifically, the flotation is a closed-circuit process of one rough selection and one fine selection, and the middlings in the fine selection are returned to the rough selection. Among them, the solid-phase mass content in the rough selection is 25% - 35%, and the solid-phase mass content in the fine selection is 10% - 15%.

[0070] Specifically, the active ingredients of the aqueous solution of organic sodium salt are sodium petroleum sulfonate with a carbon chain length of 12 to 16 and sodium chloride. The mass percentage content of sodium petroleum sulfonate in the flotation reagent is 24% - 25%, and the mass percentage content of sodium chloride ≤ 8%.

[0071] In this application, the flotation reagent is an aqueous solution of organic sodium salt produced by chlorination, sulfonation, and saponification of heavy oil. The active ingredients of the aqueous solution of organic sodium salt are sodium petroleum sulfonate with a carbon chain length of 12 to 16 and sodium chloride. The mass percentage content of sodium petroleum sulfonate in the flotation reagent is 24% - 25%, and the mass percentage content of sodium chloride ≤ 8%. Compared with directly using pure substances of sodium petroleum sulfonate with a carbon chain length of 12 to 16 and sodium chloride to prepare the flotation reagent or other flotation reagents, their effects cannot reach the flotation effect of this application.

[0072] S9. Filter and separate the flotation foam obtained in the flotation. The obtained solid is the langbeinite concentrate. After the obtained tailings are concentrated, the high-concentration tailings are discharged. Part of the flotation mother liquor generated by flotation filtration or concentration is returned to step S8 for pulp adjustment, and the excess part enters the salt field for evaporation, concentration, and graded sun drying of potassium-containing minerals and then returns to the processing system.

[0073] Specifically, through the above process and the selected reagents, the langbeinite flotation concentrate K + recovery rate is about 70%, and the flotation concentrate yield is between 42 - 51%.

[0074] S10. Mix and stir the crude potassium filter cake K1 and the langbeinite concentrate, add the SOP mother liquor and stir. Filter the slurry to obtain the washing mother liquor L Leo and the filter cake S2. The washing mother liquor L Leo is returned to the previous steps of decomposing carnallite and potassium rock.

[0075] Specifically, in one embodiment, the mass ratio of the crude potassium filter cake K1 to the langbeinite concentrate is 1.0 - 1.6:1, which is transported to a stirring tank, and the SOP mother liquor obtained from the subsequent system is added. The amount of the SOP mother liquor is 2.2 - 3.2 times the mass of K1. After staying in the stirring tank for 30 - 60 minutes, a slurry is obtained.

[0076] S11. Transport the filter cake S2 into the crystallizer, along with water with TDS / mg / L < 45000 and SOP mother liquor, and maintain the temperature in the crystallizer at 40 - 65°C. Filter the slurry after crystallization to obtain wet potassium sulfate and SOP mother liquor, and the SOP mother liquor is recycled. Preferably, the water with TDS / mg / L < 45000 can be seawater. In areas lacking fresh water resources, using seawater directly as process water can save the investment cost of seawater desalination devices. The main use of the SOP mother liquor is for slurry preparation. Using only water will significantly reduce the yield. Therefore, adding seawater and SOP mother liquor for crystallization can not only save water costs but also increase the yield. The mass ratio of seawater to SOP mother liquor is 4:6 - 7:3. Preferably, it is 5:5.

[0077] Preferably, in one embodiment, add seawater or the subsequently obtained SOP mother liquor to adjust the slurry concentration (mass percentage) to 35 - 45%. The addition amount of seawater and the subsequently obtained SOP mother liquor is 0.45 - 0.55 times that of S2 (calculated by mass).

[0078] After the slurry stays in the crystallizer for 1.5 - 2.5 hours, filter the slurry in the crystallizer to obtain wet potassium sulfate and SOP mother liquor. The composition of the SOP mother liquor is K + 6.54 - 8.78%, Na + 1.33 - 3.71%, Mg 2+ 2.0 - 2.46%, Cl - 13.38 - 14.07%, SO 4 2- 4.34 - 5.61%.

[0079] The SOP mother liquor is stored in a storage tank and recycled to the previous system (for the mixture of the S10 crude potassium filter cake and potassium alum concentrate, and for supplementing the crystallization liquid in S11). The excess mother liquor is transported to the salt field for solar evaporation of minerals. The composition of the wet potassium sulfate is K + 41.03% - 42.74%, Na + 0.15% - 1.14%, Mg 2+ 1.22% - 2.08%, Cl - 1.06 - 3.97%, SO 4 2- 46.43% - 51.83%, and the remaining material is water.

[0080] The following further illustrates the present invention with reference to embodiments. The raw materials used in the embodiments of the present invention are the underground primary carnallite ore from a potassium salt mine in Africa.

[0081] Embodiment number Ion composition of the raw ore (mass percentage %)

[0082]

[0083] Example 1

[0084] (1) Collect the underground primary potassium-containing ore (carnallite ore) and S ore (potassium rock ore) of a certain potassium salt mine, and mix them according to the mass ratio of 6:4 to obtain a mixed raw material.

[0085] (2) Pass the mixed raw material through the first screening, with the screening particle size of 12.5 mm. The oversize material is subjected to the first crushing until P90 is -12.5 mm.

[0086] (3) Add the crushed mixture into a stirring tank filled with a saturated solution for pulp mixing. The saturated mother liquor is composed of the mother liquor composition near the triple co-saturation point D of the metastable phase diagram of the five-component aqueous salt of Na + , K + , Mg 2+ / / Cl - , SO4 2- —H2O, carnallite, and KCl. The mass contents of the main components are Na + 1.591%, K + 2.069%, Mg 2+ 6.342%, SO4 2- 4.189%, Cl - 19.740%.

[0087] (4) The pulped material is subjected to the second screening, with the screening particle size of 2 mm. The oversize material is subjected to the second crushing until P90 is -2 mm. The material after the second crushing and the undersize material after the second screening are transported to the decomposition tank.

[0088] (5) Add the washing mother liquor L Leo into the decomposition tank. The liquid addition amount is 35% of the raw material amount, and the deficiency is supplemented with water. The decomposition tank is equipped with a draft tube. Under the action of the stirrer, the slurry flows in a closed-loop upward flow P90 shape in the draft tube, and carnallite decomposition occurs during the upward stroke of the flow state.

[0089] (6) After the slurry stays in the decomposition tank for 30 minutes until the carnallite is fully decomposed, the slurry is transported to a sieve with a screen hole size of 0.85 mm for the third screening. The oversize material of the rod mill is subjected to the third crushing, with the grinding time of 5 minutes and the grinding concentration (solid-liquid mass percentage) of 55%. The material after the third crushing and the undersize material are transported to the flotation pulp mixing tank together.

[0090] (7) Add a flotation collector into the flotation pulp mixing tank. The slurry is transported to a flotation machine. Through flotation, a crude potassium slurry S1 and tailings T1 are obtained. The tailings T1 are transported to the tail salt yard and naturally filtered to obtain T2 and mother liquor L1. After filtration of S1, a crude potassium filter cake K1 and mother liquor L1 are obtained.

[0091] (8) Collect the underground primary potassium-bearing ore (sulfur-rich potassium-bearing raw ore) of a certain potassium salt mine, and crush it by screening multiple times to a P90 of -2 mm.

[0092] (9) Mix the crushed raw ore and seawater in a mass ratio of 1:0.55, stir for 150 min, and control the conversion temperature at 35 °C to obtain a decomposed solid-liquid mixed ore pulp.

[0093] (10) Adjust the concentration of the solid-liquid mixed ore pulp with the mother liquor of langbeinite flotation, add flotation reagents and mix well, then enter the flotation machine for flotation. The flotation process is a closed-circuit process of one rough selection and one fine selection, with the middlings of the fine selection returned to the rough selection. Among them, the mass concentration of the rough selection is 35%, and the concentration of the fine selection is 15%. The flotation reagent is an aqueous solution of organic sodium salt produced by chlorination, sulfonation and saponification of heavy oil, which is only added in the rough selection, and the dosage is 375 g / t of raw ore.

[0094] (11) Filter and separate the flotation foam obtained in the flotation. The obtained solid is the langbeinite concentrate, and its chemical composition is K + 17.13%, Na + 1.320%, Mg 2+ 5.629%, Cl - 3.920%, SO 4 2- 40.74%, reserved for use; after the tailings are concentrated, the high-concentration tailings are discharged. Part of the flotation mother liquor generated from the filtration of the concentrate and the concentration of the tailings in the flotation is returned to step (10) for recycling; the excess part enters the salt pan for evaporation, concentration, and graded sun-drying of potassium-containing minerals, and then returns to the processing system.

[0095] (12) Mix the crude potassium filter cake K1 obtained in step (7) and the langbeinite concentrate obtained in step (11) in a ratio of 1.44:1, transport them to a stirring tank, add the SOP mother liquor from the subsequent system, and the amount of the SOP mother liquor is 2.78 times the mass of K1. After staying in the stirring tank for 45 minutes, a slurry is obtained. Filter the slurry to obtain the washing mother liquor L Leo and the filter cake S2. Store the washing mother liquor L Leo in a storage tank for standby.

[0096] (13) Transport the filter cake S2 to a crystallizer, add seawater to the crystallizer, and the addition amount is 0.55 times the mass of S2. Add the subsequent SOP mother liquor to adjust the concentration of the mixed slurry to 42.05% for the insufficient part. Keep the temperature in the crystallizer at 45 °C. After staying in the crystallizer for 2 hours, filter the slurry in the crystallizer to obtain wet potassium sulfate and the SOP mother liquor. The composition of the SOP mother liquor is K + 7.78%, Na + 1.83%, Mg 2+2.46%, Cl - 13.88%, SO 4 2- 4.34%.

[0097] The SOP mother liquor is stored in a storage tank and returned for use in the previous system. The excess mother liquor is transported to the salt pan for ore drying. The composition of the wet potassium sulfate material is K + 41.03%, Na + 0.15%, Mg 2+ 2.08%, Cl - 3.97%, SO 4 2- 46.43%.

[0098] Example 2

[0099] (1) Collect the underground primary potassium-containing ores Car ore and S ore of a certain potassium salt mine, and mix them in a mass ratio of 7:3 to obtain a mixed raw material.

[0100] (2) Pass the mixed raw material through the first screening, with a screening particle size of 20 mm. The oversize material is subjected to the first crushing until it is crushed to P95 - 20 m.

[0101] (3) Add the crushed mixture into a stirring tank filled with a saturated solution for pulp mixing. The saturated mother liquor is composed of Na + , K + , Mg 2+ / / Cl - , SO4 2- — the mother liquor composition near the triple co-saturation point D of the metastable phase diagram of the five-component water salt of epsomite, KCl, and carnallite. The mass content of the main components is Na + 1.591%, K + 2.069%, Mg 2+ 6.342%, SO4 2- 4.189%, Cl - 19.740%.

[0102] (4) The pulped material is subjected to the second screening, with a screening particle size of 5 mm. The oversize material is subjected to the second crushing until it is crushed to P95 - 5 mm. The material after the second crushing and the undersize material after the second screening are transported to the decomposition tank.

[0103] (5) Add the washing mother liquor L Leo to the decomposition tank. The liquid addition amount is 35% of the raw material amount, and the deficiency is supplemented with water. The decomposition tank is equipped with a draft tube. Under the action of the stirrer, the slurry circulates in a closed loop from bottom to top in the draft tube, and carnallite decomposition occurs during the upward stroke of the flow state.

[0104] (6) The residence time of the slurry in the decomposition tank is 60 minutes until the carnallite is fully decomposed. Then the slurry is transported to a sieve with a screen size of 0.85 mm for the third screening. The oversize material from the sieve is crushed for the third time using a rod mill. The grinding time is 5 minutes, and the grinding concentration (solid-liquid mass percentage) is 55%. After the third crushing, the material and the undersize are transported together to the flotation conditioning tank.

[0105] (7) A flotation collector is added to the flotation conditioning tank. The slurry is transported to the flotation machine. Through flotation, a crude potassium slurry S1 and tailings T1 are obtained. The tailings T1 are transported to the tail salt yard and naturally filtered to obtain T2 and mother liquor L1. After filtration of S1, a crude potassium filter cake K1 and mother liquor L1 are obtained.

[0106] (8) The underground primary potassium-containing ore of a certain potassium salt mine is collected and crushed to -2 mm through multiple screenings.

[0107] (9) The crushed raw ore and seawater are mixed at a mass ratio of 1:0.75 and stirred for 120 min. The conversion temperature is controlled at 40 °C to obtain a decomposed solid-liquid mixed slurry.

[0108] (10) The solid-liquid mixed slurry is adjusted in concentration using the carnallite flotation mother liquor. After adding flotation reagents and mixing evenly, it enters the flotation machine for flotation. The flotation process is a closed-circuit process of one roughing and one cleaning, with the middlings from the cleaning returned to the roughing. Among them, the roughing mass concentration is 30%, and the cleaning concentration is 12%. The flotation reagent is an aqueous solution of organic sodium salt produced by chlorination, sulfonation, and saponification of heavy oil, which is added only in the roughing, and the reagent dosage is 500 g / ton of raw ore.

[0109] (11) Concentration and filtration: The flotation foam obtained in the flotation is filtered and separated. The resulting solid is the carnallite concentrate, and its chemical composition is K + 16.65%, Na + 2.01%, Mg 2+ 5.240%, Cl - 2.555%, SO 4 2- 41.90%, for retention; after concentration of the tailings, the high-concentration tailings are discharged. Part of the flotation mother liquor generated from the filtration of the concentrate and the concentration of the tailings in the flotation is recycled to step (10); the excess part enters the salt field for evaporation, concentration, and graded sun-drying of potassium-containing minerals and then returns to the processing system.

[0110] (12) The S1 obtained in step (7) and the carnallite concentrate obtained in step (11) are mixed in a ratio of 1.54:1 and transported to a stirring tank. The SOP mother liquor is added from the subsequent system. The amount of the SOP mother liquor is 2.78 times the mass of K1. After staying in the stirring tank for 45 minutes, a slurry is obtained. The slurry is filtered to obtain the washing mother liquor L Leo and the filter cake S2. The washing mother liquor LLeo Stored in a storage tank for standby.

[0111] (13) Transport the filter cake S2 to the crystallizer, add seawater to the crystallizer, the addition amount of seawater is 0.66 times the mass of S2, and the insufficient part is supplemented with the subsequent SOP mother liquor to adjust the concentration of the mixed slurry to 42.05%. Keep the temperature in the crystallizer at 40 °C. After staying in the crystallizer for 2 hours, filter the slurry in the crystallizer to obtain wet potassium sulfate and SOP mother liquor. The composition of the SOP mother liquor is: K + 7.96%, Na + 1.62%, Mg 2+ 2.41%, Cl - 13.66%, SO 4 2- 4.48%. The SOP mother liquor is stored in a storage tank and returned to the previous system for use. The excess mother liquor is transported to the salt field for ore drying. The composition of the wet potassium sulfate is K + 42.74%, Na + 0.41%, Mg 2+ 1.86%, Cl - 1.41%, SO 4 2- 49.76%.

[0112] Example 3

[0113] (1) Collect the underground primary potassium-containing ores Car ore and S ore of a certain potassium salt mine, and mix them in a mass ratio of 8:2 to obtain a mixed raw material.

[0114] (2) Pass the mixed raw material through the first screening, the screening particle size is 12.5 mm, and the oversize material is subjected to the first crushing until P95 is -12.5 mm.

[0115] (3) Add the crushed mixture to a stirring tank containing a saturated solution for pulp adjustment. The saturated mother liquor is composed of Na at 35 °C + , K + , Mg 2+ / / Cl - , SO4 2- —The mother liquor composition near the triple co-saturation point D of the metastable phase diagram of the five-component water salt of H2O, kainite, KCl, and carnallite. The mass content of the main components is Na + 1.591%, K + 2.069%, Mg 2+ 6.342%, SO4 2- 4.189%, Cl - 19.740%.

[0116] (4) The sized material after sizing is subjected to a second screening, with the screening particle size being 5 mm. The oversize material is subjected to a second crushing until it reaches P95 - 2 mm. The material after the second crushing and the undersize material after the second screening are transported to the decomposition tank.

[0117] (5) Wash mother liquor L is added to the decomposition tank. Leo The liquid addition amount is 40% of the raw material amount, and the deficiency is supplemented with water. The decomposition tank is equipped with a draft tube. Under the action of the agitator, the slurry circulates in a closed loop from bottom to top in the draft tube, and carnallite decomposition occurs during the upward stroke of the flow state.

[0118] (6) After the slurry stays in the decomposition tank for 60 minutes until the carnallite is fully decomposed, the slurry is transported to a sieve with a screen hole size of 0.85 mm for a third screening. The oversize material is subjected to a third crushing using a mill, with the grinding time being 5 minutes and the grinding concentration (solid - liquid mass percentage) being 65%. The material after the third crushing and the undersize material are transported to the flotation sizing tank together.

[0119] (7) A flotation collector is added to the flotation sizing tank, and the slurry is transported to the flotation machine. Through flotation, crude potassium slurry S1 and tailings T1 are obtained. The tailings T1 are transported to the tail salt storage yard, and T2 and mother liquor L1 are obtained through natural filtration. After filtration, S1 yields crude potassium filter cake K1 and mother liquor L1.

[0120] (8) The underground primary potassium - containing ore kai ore of a certain potassium salt mine is collected and sized and crushed to - 2 mm through multiple screenings.

[0121] (9) The crushed raw ore and seawater are mixed and stirred at a mass ratio of 1:0.45, with the stirring time being 60 min and the conversion temperature controlled at 45°C to obtain the decomposed solid - liquid mixed ore slurry.

[0122] (10) The solid - liquid mixed ore slurry is sized with potassium - magnesium vitriol flotation mother liquor to control the concentration. After adding flotation reagents and mixing evenly, it enters the flotation machine for flotation. The flotation process is a closed - circuit process of one roughing and one cleaning, with the middlings from the cleaning returned to the roughing. Among them, the roughing mass concentration is 25%, and the cleaning concentration is 10%. The flotation reagent is an aqueous solution of organic sodium salt produced by chlorination, sulfonation, and saponification of heavy oil, which is only added during roughing, and the reagent dosage is 250 g / ton of raw ore.

[0123] (11) The flotation foam obtained from flotation is filtered and separated, and the resulting solid is potassium - magnesium vitriol concentrate, with its chemical composition being K + 16.74%, Na + 1.965%, Mg 2+ 5.247%, Cl - 2.139%, SO 4 2-42.51%, to be retained; after the tailings are concentrated, the high-concentration tailings are discharged. Part of the flotation mother liquor generated from the filtration of the concentrate and the concentration of the tailings in flotation is returned to step (10) for recycling; the excess part enters the salt pan for evaporation, concentration, and graded sun drying of potassium-containing minerals, and then returns to the processing system.

[0124] (12) Mix the S1 obtained in step (7) and the langbeinite concentrate obtained in step (11) in a ratio of 1.54:1, transport it to a stirring tank, add the SOP mother liquor from the subsequent system, and the amount of the SOP mother liquor is 2.78 times the mass of K1. After staying in the stirring tank for 45 minutes, a slurry is obtained. Filter the slurry to obtain the washing mother liquor L Leo and the filter cake S2. Store the washing mother liquor L Leo in a storage tank for standby.

[0125] (13) Transport the filter cake S2 to a crystallizer, add seawater to the crystallizer, and the addition amount of seawater is 0.80 times the mass of S2. Add the subsequent SOP mother liquor to adjust the concentration of the mixed slurry to 45% for the insufficient part. Keep the temperature in the crystallizer at 65°C. After staying in the crystallizer for 2 hours, filter the slurry in the crystallizer to obtain wet potassium sulfate and the SOP mother liquor. The composition of the SOP mother liquor is K + 8.08%, Na + 1.61%, Mg 2+ 2.26%, Cl - 13.33%, SO 4 2- 4.20%. Store the SOP mother liquor in a storage tank and return it to the previous system for use. Transport the excess mother liquor to the salt pan for ore drying. The composition of the wet potassium sulfate is K + 41.37%, Na + 1.14%, Mg 2+ 1.22%, Cl - 1.06%, SO 4 2- 51.83%.

[0126] In the method for preparing potassium sulfate from underground native sulfur-rich potassium minerals in the present invention, KCl with relatively high purity and yield is first obtained. Through the open-circuit crushing process of three-stage screening and three-stage crushing and the combined process of cold decomposition-flotation-washing, high-quality coarse-grained potassium chloride products are extracted, reducing the grinding treatment volume and improving the grinding efficiency. In addition, by gradually reducing the grinding particle size and combining with the cold decomposition-flotation-washing process, the system yield is increased, changing the defects of the traditional grinding-decomposition-flotation process for producing potassium chloride products, such as high washing and grinding energy consumption. The purity of the obtained KCl is greater than or equal to 90%, and the decomposition yield of KCl reaches 119% (relative to the original ore). Then, potassium schoenite products can be obtained through crushing-conversion-flotation and concentration filtration, and the energy consumption and cost of the process are relatively low, while the product yield and quality are very good. The removal rates of Na + and Cl - in the obtained potassium schoenite rough concentrate reach more than 88%, and the conversion rates of K + , Mg 2+ and SO 4 2- reach 90%. Then, potassium chloride and potassium schoenite are reacted and crystallized to obtain potassium sulfate products. The purity of the obtained potassium sulfate, K 2 O, is higher than 50%, and the yield is higher than 52.9%.

[0127] In the description of this specification, the descriptions of terms such as "one embodiment", "some embodiments", "embodiment", "example", "specific example", or "some examples" mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0128] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for producing potassium sulfate using underground native sulfur-rich potassium minerals, characterized in that: include: The potassium chloride raw material and the potassium magnesium vanadium raw material are mixed and stirred, and the SOP mother liquor is added and stirred. The slurry is filtered to obtain the washing mother liquor L Leo and filter cake S2; The filter cake S2 ​​is transported to the crystallizer, and water with TDS / mg / L < 45000 and SOP mother liquor are added to carry out crystallization in the crystallizer. The temperature in the crystallizer is maintained at 40-65°C. The slurry after crystallization is filtered to obtain potassium sulfate wet material and filtrate, and the filtrate is returned to be used as SOP mother liquor.

2. The method for producing potassium sulfate using underground primary sulfur-rich potassium-containing minerals according to claim 1, characterized in that: The potassium chloride raw material is obtained by the following method: The carnallites and sylvite ores are mixed and crushed for the first time to obtain a mixed raw material of the carnallites and sylvite, wherein the mixed raw material has a particle size of ≤20 mm and accounts for ≥90%; The mixed raw materials are added to the saturated mother liquor for slurry adjustment. The saturated mother liquor is Na + , K + Mg 2+ / / Cl - 、SO4 2- —The mother liquor composition of the three-phase saturation point D of Epsom salt, KCl and carnallite in the metastable phase diagram of the H2O quinary system at 35℃; The slurry-adjusted material is crushed for the second time, and the second crushed material is decomposed; The decomposed slurry is crushed for the third time, and the material after the third crushing is used for flotation; wherein the particle size after the third crushing is smaller than the particle size after the previous crushing; A flotation collector is added to carry out crude potassium flotation to obtain crude potassium slurry S1 and tailings T1. The crude potassium slurry S1 is filtered to obtain crude potassium filter cake K1 and mother liquor L1. The tailings T1 is filtered to obtain T2 and mother liquor L1. The obtained K1 is washed, filtered, dried and dehydrated to obtain a potassium chloride product; Preferably, before the first crushing, the carnallites and sylvite ores are mixed and then screened once, and the crushed oversize and undersize are combined to obtain a mixed raw material of carnallites and sylvite; Before the second crushing, the slurry-adjusted material is screened for the second time, the screened material is crushed for the second time, and the screened material of the second screening and the second crushed material are used for decomposition; Before the third crushing, the decomposed slurry is screened for the third time, the screened material is crushed for the third time, and the screened material of the third screening and the material after the third crushing are used for flotation; wherein the screening particle size of the third screening is smaller than the previous screening particle size.

3. The method for producing potassium sulfate using underground primary sulfur-rich potassium-containing minerals according to claim 2, characterized in that: Potassium magnesium vanadium raw materials are obtained by the following method: The collected underground original sulfur-rich potassium-containing ore is crushed in multiple stages to obtain sulfur-rich potassium-containing minerals with the required particle size; Mixing the sulfur-rich potassium-containing mineral and seawater, stirring and converting at a temperature of 35° C. to 50° C., to obtain a solid-liquid mixed slurry; The solid-liquid mixed pulp is slurried with potassium-magnesium sulfate flotation mother liquor, and potassium-magnesium sulfate flotation is performed after adding flotation reagents and mixing. The flotation reagents are organic sodium salt aqueous solutions produced by chlorination, sulfonation and saponification of heavy oil. The flotation foam obtained in the flotation is filtered and separated, and the obtained solid is the potassium magnesium sulfate concentrate. The flotation mother liquor produced by the flotation is partially returned to the previous slurry preparation step.

4. The method for producing potassium sulfate using underground primary sulfur-rich potassium-containing minerals according to claim 2, characterized in that: The particle size of the first screening is 20-12.5mm, the material on the screen is crushed, and the crushed particle size P90 is between 20-12.5mm; the particle size of the second screening is 5-2mm, the material on the screen is crushed for the second time, and the crushed particle size P90 is between 5-2mm, the particle size of the third screening is 1-0.85mm, the material on the screen is crushed, and the crushed particle size P90 is between 1-0.85mm.

5. The method for producing potassium sulfate using underground primary sulfur-rich potassium-containing minerals according to claim 3, characterized in that: The carnallite ore is a natural solid carnallite ore containing sodium chloride and epsomite minerals; the sylvite ore is a natural solid sylvite ore containing sodium chloride, kieserite and gypsum minerals. The main components of the underground primary sulfur-rich potassium ore are K + 8.0%~13.0%, Na + 8.0%~21.0%, Mg 2+ 5.0%~8.0%, Cl - 23.0%~35.0%, SO4 2- 20.0%~31.0%.

6. The method for producing potassium sulfate using underground primary sulfur-rich potassium-containing minerals according to claim 3, characterized in that: The effective components of the organic sodium salt aqueous solution are petroleum sodium sulfonate with a carbon chain length of 12 to 16 and sodium chloride. The mass percentage of the petroleum sodium sulfonate in the flotation reagent is 24%-25%, and the mass percentage of sodium chloride is ≤8%.

7. The method for producing potassium sulfate using underground primary sulfur-rich potassium-containing minerals according to claim 2, characterized in that: The decomposition is carried out in the decomposition tank, which is equipped with a guide tube. Under the action of the agitator, the slurry flows in a closed-loop circulation state from bottom to top in the guide tube, and the carnallite is decomposed in the upward stroke of the flow state. The residence time of the slurry in the decomposition tank is 30min-120min. Preferably, when the decomposition tank is performing decomposition, a washing mother liquor is added to the decomposition tank, and the amount of the washing mother liquor added is 30% to 45% of the total mass of the original ore.

8. The method for producing potassium sulfate using underground primary sulfur-rich potassium-containing minerals according to claim 7, characterized in that: The mass content of the main chemical components of the washing mother liquor is: K + :4.2~6.863%,Na + 0.36~3.96%,Mg 2+ 0.1~2.74%, SO4 2- 2.189~5.542%, Cl - 13.05~15.405%; The mass content of the main component of the saturated mother liquor at point D is K + 1.40~2.069%、Na + 0.14~1.67%、Mg 2+ 0.1~7.20%、Cl - 19.74~21.46%、SO4 2- 2.21~4.189%.

9. The method for producing potassium sulfate using underground primary sulfur-rich potassium-containing minerals according to claim 3, characterized in that: The potassium magnesium alum flotation is a closed-circuit process of one roughing and one concentrating, and the concentrating ore returns to the roughing, wherein the solid mass content in the roughing is 25% to 35%, and the solid mass content in the concentrating is 10% to 15%.

10. The method for producing potassium sulfate using underground primary sulfur-rich potassium-containing minerals according to claim 2, characterized in that: The third crushing adopts rod mill for grinding, the material on the screen is collected through a chute, and mother liquor L1 is added to the chute. The addition amount of mother liquor L1 satisfies the discharge concentration of rod mill to be 45-60%, and the grinding time is 1.0 to 6.0 minutes.

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