Method for preparing picromerite-containing mixed salt from sulfate type salt lake polyhalite

Abstract

The invention discloses a method for preparing picromerite-containing mixed salt from sulfate type salt lake polyhalite, which comprises the following steps: step 1, dissolving NaCl + MgSO4 mixed salt obtained in a salt pan evaporation process of sulfate type salt lake brine in water to obtain a leaching agent; step 2, crushing and crushing the sulfate type salt lake shallow polyhalite ore; 3, the crushed polyhalite ore and a leaching agent are stirred and leached, and slurry is obtained; step 4, filtering the infiltrated slurry to obtain an infiltrating solution; and 5, the leaching solution obtained in the step 4 is naturally evaporated, the leaching solution is subjected to three evaporative crystallization stages of NaCl + CaSO4, NaCl and picromerite-containing mixed salt, the picromerite-containing mixed salt is finally obtained, the picromerite-containing mixed salt comprises NaCl and picromerite, the content of the picromerite is 25.0-40.0 wt%, and the content of the NaCl is 50.0-65.0 wt%. According to the method, potassium and magnesium resources in the polyhalite ore are fully utilized, sources of raw materials of the leaching agent are increased, and the yield of potassium and magnesium valuable elements in the polyhalite ore is increased.

Description

Technical Field

[0001] The present invention relates to the technical field of salt lake chemical industry, and particularly relates to a method for preparing a mixed salt containing picromerite from polyhalite in a sulfate-type salt lake. Background Art

[0002] The currently studied polyhalite development processes in China include the "roasting - hot leaching" potassium dissolution method for the polyhalite ore in the Quntai Salt Lake, and a new process for preparing potassium sulfate from low-grade polyhalite ore by washing flotation - roasting hot leaching method has been studied. By roasting polyhalite at 300 - 500 °C and then performing hydrothermal leaching of the roasted product with water at 90 °C, almost all potassium is leached. The leaching solution is evaporated to obtain high-grade picromerite ore, and potassium sulfate products are obtained by the method of returning all mother liquors for conversion. However, the above process has the problem of high energy consumption.

[0003] Patent CN106276980B discloses a process for preparing potassium sulfate and potassium magnesium fertilizer from polyhalite. The process includes the following steps:

[0004] (1) Grinding: Grinding polyhalite to more than 85 wt% of -120 mesh; (2) Washing: Washing with water to remove sodium chloride in polyhalite; (3) Roasting: Roasting the washed mineral at high temperature; (4) Leaching: Leaching potassium and magnesium in polyhalite; (5) Solid-liquid separation: Performing solid-liquid separation on the leached pulp to obtain a mother liquor containing potassium sulfate and magnesium sulfate; (6) Evaporation: Evaporating the mother liquor to precipitate potassium sulfate, filtering and separating to obtain potassium sulfate products, and continuing to evaporate the mother liquor to a certain concentration, filtering and separating to obtain potassium magnesium fertilizer products. This invention washes polyhalite, and the washed mineral still uses the roasting process, which also has the problem of high energy consumption.

[0005] Polyhalite (K 2 Ca 2 Mg[SO 4 4 ·6H 2 O) contains three elements of potassium, sulfur, and magnesium. Potassium is a major nutrient element required by crops, and sulfur and magnesium are medium nutrient elements. If only considering extracting the potassium resources contained in polyhalite, the magnesium and sulfur resources in the polyhalite ore cannot be efficiently utilized, and a large amount of waste residue will be generated, causing difficulties in later treatment.

[0006] Potassium magnesium sulfate fertilizer (K 2 Mg[SO 4 2 ·6H 2 O), as a chemically synthesized compound fertilizer, is currently mainly made from picromerite ore precipitated by evaporating salt lake brine through a flotation process. Potassium magnesium sulfate fertilizer generally contains K 2 O ≧ 21%, S ≧ 14%, Mg ≧ 5%, and contains both the major nutrient element potassium required by crops and two medium nutrient elements of sulfur and magnesium.​​

[0007] The prior art mainly focuses on the production of potassium sulfate from polyhalite, and does not pay attention to the utilization of magnesium resources.

[0008] During the staged evaporation process of sulfate-type salt lake brine in the salt pan, mixed salts of sodium chloride and magnesium sulfate will precipitate.

[0009] Taking the data of the natural evaporation process of a certain sulfate-type salt lake brine as an example:

[0010]

[0011] Evaporating 100 Kg of the original brine, from the evaporation of the original brine to the brine being saturated with magnesium chloride, it experiences five evaporation and crystallization stages of NaCl, NaCl + MgSO 4 、NaCl + MgSO 4 + Pic, NaCl + MgSO 4 + KCl, NaCl + MgSO 4 + Car.

[0012] For every 100 Kg of the original brine evaporated, 1.31 Kg of the mixed salt of NaCl + MgSO 4 can be obtained, with a small amount of potassium entrained, containing about 1.22% KCl. For the mixed salt of NaCl + MgSO 4 , current domestic potassium fertilizer production enterprises have not developed and utilized it, occupying salt pan resources. Therefore, the present invention uses the mixed salt of NaCl + MgSO 4 obtained by evaporation as a leaching agent for polyhalite, which not only solves the problem of leaching polyhalite, but also develops and utilizes the NaCl + MgSO 4 mixed salt in the idle salt pan, improving the utilization efficiency of the salt pan.

[0013] The present invention mainly aims to develop and utilize the shallow polyhalite ore in sulfate-type salt lakes, extract and separate the valuable potassium and magnesium metal elements in the polyhalite ore to obtain brine containing potassium and magnesium. The invention aims to produce potassium magnesium sulfate fertilizer, uses polyhalite as the raw material, leaches the polyhalite ore with a magnesium-containing leaching agent to obtain brine rich in potassium and magnesium, and the mixed salt containing picromerite precipitated by evaporating the brine containing potassium and magnesium can be used to produce potassium magnesium sulfate fertilizer. A regulator is added to adjust the composition of the brine containing potassium and magnesium, so that potassium and magnesium precipitate in the form of picromerite, providing high-quality raw materials for the production of potassium magnesium sulfate fertilizer. Summary of the Invention

[0014] The purpose of the present invention is to provide a method for preparing a mixed salt containing picromerite from polyhalite in sulfate-type salt lakes, aiming at the fact that the utilization of magnesium resources in polyhalite in the prior art has not been taken seriously.

[0015] The technical solution adopted to achieve the purpose of the present invention is:

[0016] A method for preparing a mixed salt containing picromerite from kainite in sulfate-type salt lakes, comprising the following steps:

[0017] Step 1, preparing a leaching agent: dissolving the mixed salt of NaCl + MgSO 4 obtained during the evaporation of sulfate-type salt lake brine in a salt pan in water to obtain a leaching agent;

[0018] Step 2, crushing kainite: crushing and pulverizing the shallow kainite ore in sulfate-type salt lakes;

[0019] Step 3, leaching: stirring and leaching the pulverized kainite ore in Step 2 with the leaching agent prepared in Step 1 to obtain a slurry;

[0020] Step 4, filtering: filtering the slurry after leaching in Step 3 to obtain a leaching solution;

[0021] Step 5, naturally evaporating the leaching solution obtained in Step 4. The leaching solution undergoes three evaporation and crystallization stages of NaCl + CaSO 4 , NaCl, and a mixed salt containing picromerite. Finally, a mixed salt containing picromerite is obtained. The mixed salt containing picromerite includes NaCl and picromerite, wherein the content of picromerite is 25 - 40 wt%, and the content of NaCl is 50 - 65 wt%.

[0022] In the above technical solution, when evaporating the leaching solution in Step 5, an adjusting agent is added to adjust the composition of the leaching solution until the mass ratio of potassium to magnesium in the leaching solution is close to 3.22.

[0023] In the above technical solution, in Step 5, the NaCl obtained during the evaporation process is returned to Step 1 for the preparation of the leaching agent; the tail liquid obtained after the evaporation and precipitation of the mixed salt containing picromerite is returned to the leaching solution in Step 4.

[0024] In the above technical solution, the concentration of the mixed salt of NaCl + MgSO 4 in the leaching agent in Step 1 is 5 wt% - 10 wt%.

[0025] In the above technical solution, the particle size of the kainite after crushing and pulverizing in Step 2 is 60 - 100 mesh.

[0026] In the above technical solution, the leaching time in Step 3 is 180 - 240 h.

[0027] In the above technical solution, the adjusting agent is a magnesium salt or a potassium salt. If the mass ratio of potassium to magnesium in the leaching solution in Step 3 = 3.22, there is no need to add an adjusting agent; if the mass ratio of potassium to magnesium in the leaching solution in Step 3 < 3.22, a potassium salt adjusting agent is added; if the mass ratio of potassium to magnesium in the leaching solution > 3.22, a magnesium salt adjusting agent is added.

[0028] In the above technical solution, the magnesium salt is selected from magnesium sulfate heptahydrate, magnesium sulfate hexahydrate, anhydrous magnesium sulfate or a mixed salt containing magnesium sulfate and sodium chloride produced by sulfate-type salt lake salt fields.

[0029] In the above technical solution, the potassium salt is selected from potassium chloride, potassium sulfate or a mixed salt containing potassium chloride and sodium chloride produced by sulfate-type salt lake salt fields, or a mixed salt containing carnallite and sodium chloride.

[0030] In the above technical solution, the adjusting agent is added at the beginning stage of natural evaporation of the leachate in step 3, or is added before the leachate evaporates naturally to the potassium saturation stage and the soft potassium magnesium alum mixed salt is precipitated, preferably before the leachate evaporates naturally to the potassium saturation stage and the soft potassium magnesium alum mixed salt is precipitated.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. The present invention utilizes NaCl+MgSO precipitated during the natural evaporation of sulfate salt lake brine 4 The resources are used as a leaching agent for polyhalite leaching to obtain brine containing potassium and magnesium, and the magnesium content in the brine containing potassium and magnesium is increased, which is convenient for obtaining soft potassium magnesium alum during the evaporation process. At the same time, a small amount of potassium is entrained in the mixed salt of sodium chloride + magnesium sulfate, which is not fully utilized and is idle in the salt fields of the salt lake. This part of potassium resources can be developed through the leaching process.

[0033] 2. The present invention is based on the actual situation and makes full use of the mixed salt of sodium chloride and magnesium sulfate in the existing salt pan to prepare the leaching agent. The leaching agent is leached with the crushed polyhalite, and the slurry in the leaching tank after the leaching is completed is filtered to obtain the brine containing potassium and magnesium.

[0034] 3. The present invention improves the dissolution performance of denser polyhalite ore by crushing, thereby increasing the extraction yield of potassium and magnesium.

[0035] 4. The present invention adopts a filtering method for the leaching solution to efficiently obtain the leaching solution, so that the leaching solution mixed in the tailings after the polyhalite ore is dissolved can be recovered. Compared with only collecting the leaching solution in the upper layer, the yield is improved.

[0036] 5. The present invention evaporates the potassium-magnesium-containing leaching solution obtained by filtration, and adds a regulator before the leaching solution naturally evaporates to the potassium saturation stage and the soft levetonite-containing mixed salt is precipitated. The main function of adding the regulator is to adjust the composition of the leaching solution so that potassium and magnesium are precipitated in the form of mixed salt containing soft levetonite, thereby avoiding the precipitation of magnesium sulfate from the leaching solution during the evaporation process, or the precipitation of potassium salt in the form of non-soft levetonite ore, such as potassium chloride, carnallite, etc., so that the potassium, magnesium and sulfur resources in the polyhalite ore can be developed and utilized, avoiding the existence of magnesium and sulfur resources in the form of magnesium sulfate salts, and reducing the development and utilization costs.

[0037] 6. The leaching solution of the present invention obtains sodium chloride through staged evaporation during natural evaporation. The sodium chloride can be used to prepare the leaching agent, realizing the recycling of resources without external purchased raw materials.

[0038] 7. The present invention returns the tail liquid obtained after the leaching solution evaporates and precipitates mixed salts containing picromerite to the leaching solution, causing potassium to precipitate in the form of picromerite, facilitating the production of potassium magnesium sulfate fertilizer, and avoiding the continuous evaporation and precipitation of other potassium salt minerals from the tail liquid after the precipitation of mixed salts containing picromerite. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The following shows the evaporation process route of the leaching solution of the present invention.

[0040] Figure 2 The following shows the corresponding positions of the leaching solution of the present invention marked on the 25 °C phase diagram of the Na, K, Mg\Cl, SO 4 —H 2 O five-component water-salt system.

[0041] Figure 3 The following shows the 25 °C phase diagram of the Na, K, Mg\Cl, SO 4 —H 2 O five-component water-salt system during the evaporation process of the leaching solution of the present invention.

[0042] Figure 4 The following shows the XRD test data of the mixed salts containing picromerite of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] The present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0044] Example 1

[0045] A method for preparing mixed salts containing picromerite from polyhalite in sulfate-type salt lakes includes the following steps:

[0046] Step 1, prepare a leaching agent at a concentration of 5-10 wt%, and dissolve the NaCl + MgSO 4 mixed salts obtained during the evaporation of sulfate-type salt lake brine in a salt field in water to obtain the leaching agent.

[0047] Step 2, crush polyhalite: The polyhalite-containing minerals mined from the surface are crushed and pulverized through processes such as crushing and grinding to make the polyhalite ore reach 60 mesh, or the polyhalite-containing minerals from the surface are ground and crushed by a jaw crusher and a ball mill, and the leaching agent prepared in Step 1 is added to the ball mill.

[0048] Step 3, leaching: Stir the carnallite ore crushed to 60 mesh in Step 2 and the leaching agent prepared in Step 1 in a stirring tank, and put the slurry into a leaching tank for leaching. The leaching agent can also directly leach the surface minerals containing carnallite. The leaching solution is directly collected and used without filtration, and the leaching time is controlled at about 180 - 240 h; or discharge the slurry ground and crushed in a ball mill into a leaching tank for leaching, and the time is controlled at about 180 - 240 h.

[0049] Step 4, filtration: Filter the slurry that has completed leaching in the leaching tank. Filtering equipment such as horizontal belt filters, centrifugal filters, plate and frame filters, etc. can be used.

[0050] Step 5, utilization of leaching solution: Refer to Figure 1 , evaporate the potassium- and magnesium-containing leaching solution filtered in Step 4. The leaching solution undergoes three evaporation and crystallization stages of NaCl + CaSO 4 , NaCl, and mixed salts containing picromerite, and finally potassium and magnesium are precipitated in the form of mixed salts containing picromerite, so that the potassium and magnesium resources in the carnallite ore can be developed and utilized. Sodium chloride is obtained by fractional evaporation during the natural evaporation of the leaching solution, and sodium chloride can be used to prepare the leaching agent in Step 1, and the resources are recycled without external purchased raw materials. The tail liquid obtained after the leaching solution evaporates and precipitates the mixed salts containing picromerite is returned to the leaching solution, so that potassium is precipitated in the form of picromerite, which is convenient for the production of potassium magnesium sulfate fertilizer and avoids the continuous evaporation and precipitation of carnallite from the tail liquid.

[0051] The evaporation process of the leaching solution can use equipment such as evaporators to replace the salt field evaporation process, which is applicable to areas where it is not possible to build salt fields. When the leaching solution evaporates, a regulator is added to adjust the composition of the leaching solution. Referring to the potassium / magnesium mass ratio in picromerite = 3.22, adjust the potassium / magnesium mass ratio in the leaching solution to be close to 3.22. The main function of adding the regulator is to adjust the composition of the leaching solution so that potassium and magnesium are precipitated in the form of picromerite, avoiding the precipitation of magnesium sulfate during the evaporation process of the leaching solution, or the precipitation of potassium salts in non-picromerite ore forms such as potassium chloride and carnallite, providing high-quality raw materials for the production of potassium magnesium sulfate fertilizer. The regulator can be added to the leaching solution at the beginning of the natural evaporation of the leaching solution, or added before the potassium salt saturation stage of the natural evaporation of the leaching solution and before the precipitation of the mixed salts containing picromerite. Adding the regulator at the beginning of the natural evaporation of the leaching solution, due to the entrainment and loss of part of the regulator during the precipitation of sodium chloride during the evaporation process, therefore, it is preferred to add the regulator before the potassium salt saturation stage of the natural evaporation of the leaching solution and before the precipitation of the mixed salts containing picromerite.

[0052] The regulator can be a magnesium salt. Adding the magnesium salt can increase the magnesium content in the leaching solution and promote the precipitation of potassium and magnesium in the form of schoenite. The magnesium salt can be magnesium sulfate heptahydrate, magnesium sulfate hexahydrate, anhydrous magnesium sulfate and other magnesium salt products, or the mixed salt containing magnesium sulfate and sodium chloride produced from the sulfate-type salt lake salt field. The regulator can also be a potassium salt. Adding the potassium salt can increase the potassium content in the leaching solution and promote the precipitation of potassium and magnesium in the form of schoenite, and avoid the precipitation of the mixed salt containing magnesium sulfate. The potassium salt can be potassium chloride, potassium sulfate and other potassium salt products, or the mixed salt containing potassium chloride and sodium chloride, the mixed salt containing carnallite and sodium chloride produced from the sulfate-type salt lake salt field.

[0053] The basis for selecting the magnesium salt or potassium salt as the regulator lies in the comparison of the composition of the leaching solution and the composition of schoenite. In the composition of schoenite, the mass ratio of potassium / magnesium = 3.22. Judge the mass ratio of potassium / magnesium in the leaching solution. If the mass ratio of potassium / magnesium in the leaching solution = 3.22, then the mass ratio of potassium / magnesium is suitable for the precipitation of schoenite, and there is no need to add a regulator. If the mass ratio of potassium / magnesium in the leaching solution < 3.22, then a potassium salt regulator needs to be added to appropriately increase the potassium content in the leaching solution. If the mass ratio of potassium / magnesium in the leaching solution > 3.22, then a magnesium salt regulator needs to be added to appropriately increase the magnesium content in the leaching solution.

[0054] Example 2

[0055] The leaching raw material uses the mixed salt of magnesium sulfate precipitated by the natural evaporation of brine in stages, and the main components are NaCl and MgSO 4 ·7H 2 O.

[0056] Table 1 Main chemical components and contents of the leaching raw material (mixed salt of magnesium sulfate)

[0057] Component <![CDATA[K + > <![CDATA[Mg 2+ > <![CDATA[Cl - > <![CDATA[SO 2- > Mass percentage wt% 0.59 1.58 56.87 4.72

[0058] Prepare a leaching agent of 10wt% MgSO 4 +NaCl. The main chemical components and contents are shown in Table 2.

[0059] Table 2 Main chemical components and contents of the prepared leaching agent (10wt% MgSO 4 +NaCl)

[0060] Component <![CDATA[Mg 2+ > <![CDATA[K + > <![CDATA[Cl - > <![CDATA[SO 2- <!-- 4 -->]]> Mass percentage wt% 0.52 0.12 2.81 1.9

[0061] The raw material containing polyhalite is ground and screened through a 60-mesh Tyler sieve.

[0062] Weigh 1500 g of the raw material sample containing polyhalite with an electronic balance, add 4500 g of the 10wt% NaCl + MgSO 4 leaching agent and mix them in a container. The leaching time is 216 h.

[0063] After leaching, a circulating water type vacuum pump is used to separate the solid and liquid of the leached slurry to obtain a leaching solution containing potassium and magnesium.

[0064] Table 3 Main chemical components and contents of the leaching solution

[0065] Component <![CDATA[Mg 2+ > <![CDATA[K + > <![CDATA[Cl - > <![CDATA[SO 2- > Mass percentage wt% 1.06 0.86 9.45 2.99

[0066] Before the leaching solution evaporates naturally to the potassium salt saturation stage and before the mixed salt of picromerite precipitates, a regulator is added. The regulator is potassium chloride. For the main chemical components and contents of the leached solution after adjustment, see Table 4.

[0067] Table 4 Main chemical components and contents of the leaching solution after adjustment

[0068] Component <![CDATA[Mg 2+ > <![CDATA[K + > <![CDATA[Cl - > <![CDATA[SO 2- > Mass percentage wt% 1.44 2.58 13.64 6.47

[0069] After evaporation, the leaching solution obtains a mixed salt containing picromerite. For the main chemical components of the mixed salt containing picromerite, see Table 5.

[0070] Table 5 Main chemical components of the mixed salt containing picromerite

[0071]

[0072] Example 3

[0073] The leaching raw material uses the mixed salt of magnesium sulfate separated by the staged evaporation of brine naturally, and the main components are NaCl and MgSO 4 ·7H 2 O. For the main chemical components and contents of the leaching raw material, see Table 6.

[0074] Table 6 Main chemical components and contents of the leaching raw material (mixed salt of magnesium sulfate)

[0075] Component <![CDATA[K + > <![CDATA[Mg 2+ > <![CDATA[Cl - > <![CDATA[SO 2- > Mass percentage wt% 0.59 1.58 56.87 4.72

[0076] The main chemical components and contents of the prepared 5wt% MgSO 4 +NaCl leaching agent are shown in Table 7.

[0077] Table 7 Main chemical components and contents of the leaching agent (5wt% MgSO 4 +NaCl)

[0078] Component <![CDATA[Mg 2+ > <![CDATA[K + > <![CDATA[Cl - > <![CDATA[SO 2- > Mass percentage wt% 0.25 0.07 1.39 1.12

[0079] The raw material containing polyhalite is ground and sieved through a 60-mesh Tyler sieve.

[0080] Weigh 1500 g of the raw material sample containing polyhalite with an electronic balance, add 4500 g of the 5wt% NaCl+MgSO 4 leaching agent, mix and place in a container, and the leaching time is 216 h.

[0081] After leaching, a circulating water type vacuum pump is used to separate the solid and liquid of the leached slurry to obtain a leaching solution containing potassium and magnesium. The main chemical components and contents of the leaching solution are shown in Table 8.

[0082] Table 8 Main chemical components and contents of the leaching solution

[0083] Component <![CDATA[Mg 2+ > <![CDATA[K + > <![CDATA[Cl - > <![CDATA[SO 2- > Mass percentage wt% 0.88 0.75 8.21 2.61

[0084] Before the leaching solution undergoes natural evaporation to the potassium salt saturation stage and before the mixed salt of picromerite precipitates, an adjusting agent is added. The adjusting agent is potassium chloride. The main chemical components and contents of the adjusted leaching solution are shown in Table 9.

[0085] Table 9 Main chemical components and contents of the adjusted leaching solution

[0086]

[0087]

[0088] The leaching solution obtains a mixed salt containing picromerite after natural evaporation. The main chemical components of the mixed salt containing picromerite are shown in Table 10.

[0089] Table 10 Main chemical components of the mixed salt containing picromerite

[0090]

[0091] Refer to Figure 2 , mark the corresponding positions of the leaching solution with Na, K, Mg\\Cl, SO 4 —H 2 O five - element water - salt system phase diagram at 25 °C. It can be seen from the figure that the leaching solution obtained by using a leaching agent of 5wt% MgSO 4 +NaCl and 10wt% MgSO 4 +NaCl is located in the picromerite area. During the evaporation process of the brine, it experiences evaporation and crystallization stages of precipitating NaCl, NaCl + MgSO 4 , NaCl + MgSO 4 +Pic, etc. According to the above brine evaporation data, potassium mixed salts containing picromerite will precipitate during the precipitation stage of NaCl + MgSO 4 +Pic in the leaching solution.

[0092] Refer to Figure 3 , for the Na, K, Mg\\Cl, SO 4 —H 2Phase diagram of the quinary hydrosalt system at 25 °C. It can be seen from the figure that the position marked as point 0 on the phase diagram is the starting point of the evaporation of the leaching solution, which is located in the kainite area; the position marked as point 16 on the phase diagram is the state where the leaching solution evaporates to the saturation of the kainite mixed salt, which is located in the kainite area; the position marked as point KPL-1 on the phase diagram is the leaching solution after adding the regulator, which is located in the kainite area and moves towards the sylvite area; the position marked as point KPL-3 on the phase diagram is the leaching solution after precipitating kainite, which is located in the kainite area and is close to the co-saturation area of epsomite, kainite and sylvite. The addition of the regulator enables the solution composition point to be completely controlled within the kainite phase region (the central pentagon area) from the start to the end of the evaporation and concentration of the leaching solution, avoiding the solution composition point from entering the sylvite or carnallite area. In this way, potassium in the leaching solution will precipitate in the form of kainite mixed salt.

[0093] Refer to Figure 4 , which is the XRD pattern of the kainite mixed salt. The blue peaks in the figure are the characteristic peaks of sodium chloride, and the green peaks are the characteristic peaks of kainite. The specific detection data are shown in Table 11.

[0094] Table 11 XRD detection results of the kainite mixed salt

[0095] Standard card number Mineral Compound name Molecular formula Match degree Semi - quantitative [%] 01-080-3939 Sodium chloride Sodium chloride NaCl 62 67 01-077-8370 Picromerite <![CDATA[(K 2 Mg[SO 4 2 6H 2 O)]]> ​ 42 33

[0096] From Figure 4 and Table 11, it can be seen that the main components of the precipitated kainite mixed salt are sodium chloride and kainite. Among them, the semi-quantitative analysis of the XRD shows that the sodium chloride content is 67% and the kainite content is 33%.

[0097] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a mixed salt containing soft potassium kaolinite from sulfate salt lake polyhalite, characterized in that: The following steps are involved: Step 1, preparing a leaching agent: dissolving a mixed salt of NaCl+MgSO4 obtained from evaporation of sulfate-type salt lake brine in water to obtain a leaching agent; Step 2, polyhalite crushing: crushing and pulverizing the shallow polyhalite ore in the sulfate salt lake; Step 3, leaching: stirring and leaching the crushed polyhalite ore in step 2 and the leaching agent prepared in step 1 to obtain a slurry; Step 4, filtering: filtering the slurry obtained by leaching in step 3 to obtain a leaching solution; Step 5, the leaching solution obtained in step 4 is naturally evaporated, and the leaching solution undergoes three evaporation and crystallization stages of NaCl+CaSO4, NaCl, and mixed salt containing soft leonite, and finally obtains mixed salt containing soft leonite, wherein the mixed salt containing soft leonite includes NaCl and soft leonite, wherein the content of soft leonite is 25-40wt%, and the content of NaCl is 50-65wt%.

2. The method for preparing a mixed salt containing kainite as claimed in claim 1, characterized in that: When the leaching solution evaporates in step 5, a regulator is added to adjust the composition of the leaching solution until the mass ratio of potassium to magnesium in the leaching solution is close to 3.

22.

3. The method for preparing a mixed salt containing kainite as claimed in claim 1, characterized in that: In step 5, the NaCl obtained during the evaporation process is returned to step 1 for the preparation of the leaching agent; the tail liquid obtained after the evaporation and precipitation of the mixed salt containing soft potassium magnesium sulfate is returned to the leaching solution in step 4.

4. The method for preparing a mixed salt containing kainite as claimed in claim 1, characterized in that: In step 1, the concentration of NaCl+MgSO4 mixed salt in the leaching agent is 5wt%-10wt%.

5. The method for preparing a mixed salt containing kainite as claimed in claim 1, characterized in that: The particle size of the polyhalite after crushing and pulverizing in step 2 is 60-100 mesh.

6. The method for preparing a mixed salt containing kainite as claimed in claim 1, characterized in that: The leaching time in step 3 is 180-240h.

7. The method for preparing a mixed salt containing kainite as claimed in claim 2, characterized in that: The adjusting agent is a magnesium salt or a potassium salt. If the potassium / magnesium mass ratio of the leaching solution in step 3 is 3.22, no adjusting agent needs to be added; if the potassium / magnesium mass ratio of the leaching solution in step 3 is <3.22, a potassium salt adjusting agent is added; if the potassium / magnesium mass ratio of the leaching solution is >3.22, a magnesium salt adjusting agent is added.

8. The method for preparing a mixed salt containing kainite as claimed in claim 7, characterized in that: The magnesium salt is selected from magnesium sulfate heptahydrate, magnesium sulfate hexahydrate, anhydrous magnesium sulfate or a mixed salt containing magnesium sulfate and sodium chloride produced in sulfate-type salt lake salt fields.

9. The method for preparing a mixed salt containing kainite as claimed in claim 7, characterized in that: The potassium salt is selected from potassium chloride, potassium sulfate, or a mixed salt containing potassium chloride and sodium chloride, or a mixed salt containing carnallite and sodium chloride produced in a sulfate-type salt lake salt pan.

10. The method for preparing a mixed salt containing kainite as claimed in claim 2, characterized in that: The adjusting agent is added at the beginning of the natural evaporation of the leachate in step 3, or before the leachate evaporates naturally to the potassium saturation stage and the soft kainite mixed salt is precipitated. It is preferably added before the leachate evaporates naturally to the potassium saturation stage and the soft kainite mixed salt is precipitated.

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