Method for recovering bischofite

Abstract

The invention relates to the field of bischofite recovery, and discloses a method for recovering bischofite. The method comprises the following steps: (1) collecting nanofiltration concentrated water separated from a magnesium-lithium separation process in a lithium carbonate production process, and controlling the pH value of the nanofiltration concentrated water within a range of 5-6; (2) dissolving bischofite in the nanofiltration concentrated water to obtain mineral dissolving water; (3) concentrating the ore dissolving water to obtain a high-magnesium mother solution with the magnesium ion content of 108-120g / L and the potassium ion content of 1.4-1.6 g / L; and (4) mixing the high-magnesium mother liquor with original halogen according to the volume ratio of 1: (0.9-1.3), concentrating, and crystallizing carnallite. By means of the method, magnesium salt in the salt pan system can be effectively recycled, and efficient and environment-friendly recycling of bischofite in the salt pan system is achieved.

Description

Technical Field

[0001] The present invention relates to the field of recovery of bischofite, and particularly to a method for recovering bischofite. Background Art

[0002] Bischofite, with the chemical formula MgC1 2 ·6H 2 O, is an important magnesium compound with wide industrial application value. Bischofite contains 11.96% magnesium and 34.87% chlorine. It belongs to the monoclinic system. The crystal is short columnar, and the aggregates are plate-shaped, granular, scaly, fibrous, etc. The color is transparent colorless or white, with vitreous luster, spicy and bitter taste. It has strong hygroscopicity, is extremely easy to deliquesce, and is easily soluble in water and alcohol. The Yiliping mining area is rich in salt lake resources. However, due to only focusing on extracting potassium chloride and lithium carbonate products in the initial stage of development, a large amount of bischofite is formed after the old brine concentration stage and the by-product waste brine is discharged and evaporated by sunlight. At present, most of the bischofite is directly precipitated in the salt pond or discharged to the salt field after simple treatment, which not only causes waste of magnesium resources but also has a negative impact on the salt lake ecological environment. Therefore, the comprehensive utilization of bischofite resources needs to be solved urgently. The bischofite produced in the salt field system during the production process is an important industrial by-product containing magnesium and chlorine elements, with a magnesium chloride content as high as 40% and high recycling value. Currently, many salt lake enterprises fail to effectively treat and utilize this bischofite, resulting in waste of resources and a decrease in the utilization rate of salt field ore ponds. Therefore, researching and developing the recycling technology of bischofite is of great significance for improving the resource recovery rate and the utilization rate of ore ponds. Summary of the Invention

[0003] The purpose of the present invention is to overcome the problems such as serious waste of bischofite in the salt lake of the Yiliping mining area existing in the prior art, and provide a method for recovering bischofite, which can effectively recycle the magnesium salt in the salt field system and realize the efficient and environmental protection recovery of bischofite in the salt field system.

[0004] To achieve the above purpose, on the one hand, the present invention provides a method for recovering bischofite, the method comprising the following steps:

[0005] (1) Collect the nanofiltration concentrated water separated in the magnesium-lithium separation process during the production of lithium carbonate, and control the pH value of the nanofiltration concentrated water within the range of 5-6;

[0006] (2) Dissolve bischofite in the nanofiltration concentrated water to obtain ore-dissolving water;

[0007] (3) Concentrate the ore-dissolving water to obtain a high-magnesium mother liquor with a magnesium ion concentration of 108-120 g / L and a potassium ion concentration of 1.4-1.6 g / L;

[0008] (4) Mix the high-magnesium mother liquor and the raw brine at a volume ratio of 1:0.8 - 1.5, then concentrate the carnallite-forming water obtained after mixing, and then carry out carnallite crystallization;

[0009] In the raw brine, the concentration of magnesium ions is 25 - 35 g / L, the concentration of potassium ions is 10 - 15 g / L, and the concentration of lithium element is 0.1 - 0.4 g / L.

[0010] Preferably, in the raw brine, the concentration of sulfate ions is 25 - 30 g / L.

[0011] Preferably, in the raw brine, the concentration of magnesium ions is 28 - 32 g / L, the concentration of potassium ions is 11 - 13 g / L, and the concentration of lithium element is 0.2 - 0.3 g / L.

[0012] Preferably, in the ore-dissolving water, the concentration of magnesium ions is 90 - 100 g / L.

[0013] Preferably, the nanofiltration concentrated water contains magnesium ions with a concentration of 10 - 15 g / L, potassium ions with a concentration of 0.05 - 0.1 g / L, and lithium element with a concentration of 0.08 - 0.2 g / L.

[0014] Preferably, in step (2), concentrate the carnallite-forming water until the concentration of magnesium ions in the carnallite-forming water is 80 - 90 g / L and the concentration of potassium ions is 18 - 20 g / L, and then carry out carnallite crystallization.

[0015] Preferably, when the temperature ≥ 25 °C, concentrate the carnallite-forming water until the concentration of magnesium ions in the carnallite-forming water is 85 - 90 g / L and the concentration of potassium ions is 18 - 20 g / L, and then carry out carnallite crystallization.

[0016] Preferably, when the temperature ≤ 0 °C, concentrate the carnallite-forming water until the concentration of magnesium ions in the carnallite-forming water is 80 - 85 g / L and the concentration of potassium ions is 18 - 20 g / L, and then carry out carnallite crystallization.

[0017] Preferably, the volume ratio of the high-magnesium mother liquor to the raw brine is 1:0.9 - 1.3.

[0018] Preferably, in the carnallite, the content of potassium element ≥ 6.5 wt%.

[0019] The method described in the present invention dissolves bischofite with the nanofiltration concentrated water of specific components, then concentrates the solution after ore dissolution to obtain a high-magnesium mother liquor with a specific magnesium ion content. Then, the raw bittern with a specific composition is blended with the high-magnesium mother liquor, and then concentrated to increase the magnesium ion content in the mixed solution, shorten the ore-sunning time, and quickly reach the carnallite mineralization point. Then, potassium chloride is crystallized out from the carnallite, thereby realizing the recovery of bischofite. At the same time, the potassium, lithium, and magnesium elements in the nanofiltration concentrated water are also recycled and utilized.

[0020] Meanwhile, the method described in the present invention uses the nanofiltration concentrated water to dissolve the solid ore of bischofite in the potassium ore pond, further recovers and utilizes the potassium and lithium resources entrained between the crystals of the bischofite solid while recycling the nanofiltration concentrated water, and realizes the ore pond cleaning work by dissolving bischofite with the nanofiltration concentrated water, which can save the ore extraction cost of bischofite, save costs and improve the utilization rate of the salt pan ore pond.

[0021] The method described in the present invention provides a complete method for the recovery and utilization of bischofite, realizes the efficient and environmental protection recovery of bischofite in the salt pan system, and the recovery process described in the present invention can significantly improve the utilization rate of bischofite and the recovery rates of potassium and lithium resources, and provide technical support and theoretical basis for the sustainable development of the salt pan system. Description of the Drawings

[0022] Figure 1 is the solubility change curve of bischofite in water at different temperatures;

[0023] Figure 2 is the change relationship curve of the beach drying and concentration time of the solution after bittern blending and the contents of potassium ions, magnesium ions, and lithium ions in the solution obtained after bittern blending;

[0024] Figure 3 is the change relationship curve of the beach drying and concentration time of the solution after bittern blending and the specific gravity of the solution obtained after bittern blending. Detailed Embodiments

[0025] The following details the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.

[0026] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0027] The present invention provides a method for recovering bischofite, which comprises the following steps:

[0028] (1) collecting nanofiltration concentrated water separated from the magnesium-lithium separation step in the lithium carbonate production process, and controlling the pH value of the nanofiltration concentrated water within the range of 5-6;

[0029] (2) dissolving bischofite in the nanofiltration concentrated water to obtain molten mineral water;

[0030] (3) concentrating the molten mineral water to obtain a high-magnesium mother liquor having a magnesium ion concentration of 108-120 g / L and a potassium ion concentration of 1.4-1.6 g / L;

[0031] (4) The high-magnesium mother liquor is mixed with the raw brine in a volume ratio of 1:0.8-1.5, and then the carnallite ore-forming water obtained after the mixing is concentrated, and then the carnallite is crystallized.

[0032] In the prior art, nanofiltration concentrated water is water produced after a pressure-driven membrane separation process between reverse osmosis and ultrafiltration through membrane separation technology. The nanofiltration concentrated water produced after different raw materials pass through the nanofiltration membrane contains different substances. In the method of the present invention, the nanofiltration concentrated water is the nanofiltration concentrated water separated from the magnesium-lithium separation process in the lithium carbonate production process, and the nanofiltration concentrated water contains a part of lithium and magnesium elements. Direct discharge will not only waste the lithium resources therein, but also be unfavorable for the recycling of resources. By using the nanofiltration concentrated water to dissolve bischofite, it is possible to achieve the reuse of nanofiltration concentrated water and bischofite, and at the same time, the lithium element, magnesium element in the nanofiltration concentrated water and the potassium element and lithium element resources originally lost by the solid intercrystalline entrainment of bischofite can be further recycled and reused, further realizing the resource recovery of metal resources, and improving the resource recovery rate of potassium, lithium and magnesium elements.

[0033] In the method of the present invention, the solid ore of bischofite in the mining pool is dissolved by using nanofiltration concentrated water with specific components, thereby shortening the dissolution time and further realizing the resource recovery of potassium and lithium elements. The nanofiltration concentrated water contains magnesium ions with a concentration of 10-15 g / L, potassium ions with a concentration of 0.05-0.1 g / L, and lithium elements with a concentration of 0.08-0.2 g / L.

[0034] In some specific embodiments, tail brine can also be used as a dissolving medium to dissolve bischofite, and the comprehensive application of tail brine can be further realized while recovering bischofite. The tail brine can be the tail brine discharged from the production of lithium carbonate by the raw brine lithium extraction process.

[0035] In a specific embodiment, since the dissolution of bischofite needs to be carried out in a certain acidic environment, therefore, it is necessary to limit the pH value of the nanofiltration concentrated water used for dissolution to be weakly acidic. Specifically, the pH value of the nanofiltration concentrated water is 5-6. Specifically, the pH value of the nanofiltration concentrated water can be 5, 5.5 or 6.0.

[0036] In some specific embodiments, an acidic substance or an oxidant can be used to adjust the pH value of the nanofiltration concentrated water used first, and then the nanofiltration concentrated water with the adjusted pH value is used to dissolve bischofite.

[0037] In some specific embodiments, after introducing the nanofiltration concentrated water into the ore pool containing bischofite, the dissolution of bischofite in the ore pool is accelerated under the action of wind. In addition, the ore pool is fully stirred by the way of picking fishbone ditches in the ore pool, so as to accelerate the dissolution of bischofite. When bischofite gradually dissolves in the nanofiltration concentrated water, the magnesium ions, potassium ions and chloride ions contained therein will be gradually dissolved and released. After the bischofite is completely dissolved, a leaching solution is obtained. The content of magnesium ions in the leaching solution is relatively high. Specifically, the concentration of magnesium ions in the leaching solution is 90-100 g / L, preferably 95-100 g / L.

[0038] In some specific embodiments, in step (1), the leaching solution is further evaporated and concentrated to obtain a high-magnesium mother liquor. By controlling the contents of magnesium ions and potassium ions in the obtained high-magnesium mother liquor, and then mixing the obtained high-magnesium mother liquor with the original brine, the content of magnesium ions and potassium ions in the original brine can be effectively increased, thereby accelerating the mineralization rate of the mineralization water, greatly shortening the solar evaporation time in the salt pan, and effectively increasing the mineralization yield at the same time.

[0039] In a preferred embodiment, the concentration of magnesium ions in the high-magnesium mother liquor is 108-120 g / L, and the concentration of potassium ions is 1.4-1.6 g / L. Specifically, the concentration of magnesium ions in the high-magnesium mother liquor can be 108 g / L, 109 g / L, 110 g / L, 112 g / L, 115 g / L, 116 g / L, 118 g / L or 120 g / L; the concentration of lithium ions in the high-magnesium mother liquor can be 1.4 g / L, 1.5 g / L or 1.6 g / L.

[0040] In the method of the present invention, by mixing crude bittern and high-magnesium mother liquor in a certain proportion, the content of magnesium ions in the carnallite-forming brine is increased, the ore-sunning time is shortened, and the carnallite-forming point is quickly reached. Therefore, the mixing volume of the high-magnesium mother liquor and the crude bittern is extremely crucial in the method of the present invention. When the dosage of the crude bittern is not within the range defined in the present invention, the following two results will occur: First, when the dosage of the crude bittern is too much, the best effect of bittern mixing cannot be achieved, resulting in the magnesium content in the carnallite-forming brine obtained after bittern mixing not reaching the expected index. Continuing the beach drying will extend the beach drying and concentration time, and the utilization rate of the salt pond will decrease. Second, when the dosage of the crude bittern is too little, too much high-magnesium mother liquor will cause the magnesium content in the carnallite-forming brine obtained after bittern mixing to be relatively high or even reach saturation, and the carnallite-forming brine will precipitate in the regulating pond during the bittern mixing stage, causing premature precipitation of potassium chloride and resulting in waste of resources. Preferably, the volume ratio of the high-magnesium mother liquor to the crude bittern during mixing is 1:0.8 - 1.5, and more preferably 1:0.9 - 1.3. Specifically, the volume ratio of the high-magnesium mother liquor to the crude bittern during mixing can be 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, or 1:1.5.

[0041] In a specific embodiment, due to the "common ion effect" during the bittern mixing process, part of the sodium chloride will quickly precipitate in the regulating pond. After the carnallite has precipitated relatively completely, the upper-layer brine is uniformly collected into the old brine pond for concentration to obtain lithium-rich old brine. After reaching the old brine feeding index, it is supplied to the lithium business unit for the production of lithium salt products, and at the same time, the resource recycling of the remaining components in the old brine is further realized.

[0042] In the method of the present invention, in the crude bittern, the concentration of magnesium ions is 25 - 35 g / L, the concentration of potassium ions is 10 - 15 g / L, and the concentration of lithium element is 0.1 - 0.4 g / L. By limiting the content of potassium ions in the crude bittern, the potassium content in the carnallite-forming brine obtained after mixing can be increased, thereby reducing the ore-sunning time, quickly reaching the carnallite-forming point, accelerating the formation of carnallite, and shortening the overall recovery time of bischofite. In addition, by limiting the content of lithium element in the crude bittern, the lithium element content in the subsequent obtained lithium-rich old brine can be further increased. Thus, during the process of preparing lithium carbonate using the recycled lithium-rich old brine, the subsequent lithium element adsorption and recovery time can be shortened, the production quality and output of lithium carbonate can be improved, the process time of lithium carbonate can be shortened, and the production efficiency can be enhanced. Further preferably, in the crude bittern, the concentration of magnesium ions is 28 - 32 g / L, the concentration of potassium ions is 11 - 13 g / L, and the concentration of lithium element is 0.2 - 0.3 g / L.

[0043] In a further preferred embodiment, the raw brine further contains sulfate ions, and the concentration of the sulfate ions is 25-30 g / L. By limiting the content of sulfate ions in the raw brine, the carnallite ore grade can be further improved. If the content of sulfate ions in the raw brine is too high, a large amount of mirabilite (Na 2 SO 4 ) will precipitate during the ore-forming process in winter. At the same time, sulfate will form double salts with magnesium ions, potassium ions, etc., such as kainite. These double salts will co-crystallize with carnallite, affecting the purity and crystal form of the carnallite ore, resulting in impurities being mixed into the carnallite crystals and reducing its quality. If the content of sulfate in the raw brine is too low, it will lead to insufficient raw materials and unable to effectively carry out the production of potassium sulfate and magnesium sulfate products, restricting the diversified development of the salt lake industry. In addition, too high or too low sulfate content will change the phase diagram of the salt lake brine system and change the crystallization sequence of various salt minerals.

[0044] In some preferred embodiments, the carnallite ore-forming water is evaporated and concentrated. When the concentration of magnesium ions in the carnallite ore-forming water is concentrated to 80-90 g / L and the potassium ion concentration is 18-20 g / L, it is introduced into the ore-forming pool until carnallite crystallizes out.

[0045] In a more preferred embodiment, since the solubility of carnallite ore-forming water changes at different temperatures, the content of magnesium ions in the concentrated solution is adjusted according to the change of environmental temperature. Specifically, when the temperature ≥ 25 °C (i.e., in summer), the carnallite ore-forming water is concentrated until the concentration of magnesium ions in the carnallite ore-forming water is 85-90 g / L and the potassium ion concentration is 18-20 g / L, and then carnallite crystallization is carried out. When the temperature ≤ 0 °C (i.e., in winter), the carnallite ore-forming water is concentrated until the concentration of magnesium ions in the carnallite ore-forming water is 80-85 g / L and the potassium ion concentration is 18-20 g / L, and then carnallite crystallization is carried out.

[0046] In a specific embodiment, the content of potassium element in the obtained finished carnallite is ≥ 6.5 wt%, meeting the production standard of potassium chloride in Yiliping; the content of lithium element in the rich lithium old brine obtained by concentrating the upper brine after carnallite crystallization is ≥ 3 g / L, meeting the production standard of lithium carbonate in Yiliping.

[0047] The method of the present invention can realize the recycling of bischofite, achieve the efficient and environmental protection recycling of bischofite in the salt pan system, and can also significantly improve the utilization rate of bischofite and the recovery rate of potassium and lithium resources, and provide support and theoretical basis for the sustainable development of the salt pan system.

[0048] The present invention will be described in detail below through examples, but the protection scope of the present invention is not limited thereto.

[0049] In the following examples and comparative examples, the calculation formula for the recovery rate of bischofite is as follows: Recovery rate of bischofite = (Amount of water in carnallite ore formation × Magnesium ion content in concentrated carnallite ore formation water) / (Amount of water in high-magnesium mother liquor × Magnesium ion content in high-magnesium mother liquor + Amount of original brine × Magnesium ion content in original brine).

[0050] Example 1

[0051] The nanofiltration concentrated water (pH value is 5) separated in the magnesium-lithium separation stage during the lithium carbonate production process is introduced into the bischofite deposition pond. This nanofiltration concentrated water contains 12.479 g / L of magnesium ions, 0.12 g / L of lithium ions, and 0.078 g / L of potassium ions. The solid bischofite is dissolved using the nanofiltration concentrated water to obtain ore-dissolving water. The concentration of magnesium ions in the ore-dissolving water is 92.1 g / L. The ore-dissolving water is accelerated in dissolution under the action of wind, and then subjected to evaporation and concentration. When the concentration of magnesium ions in the ore-dissolving water reaches 110 g / L and the concentration of potassium ions reaches 1.514 g / L, a high-magnesium mother liquor is obtained;

[0052] The high-magnesium mother liquor and the original brine (potassium ion concentration is 12.132 g / L, magnesium ion concentration is 25.123 g / L, lithium ion content is 0.289 g / L, sulfate ion concentration is 26.317 g / L) are mixed in a volume ratio of 1:1 for brine mixing, so that the magnesium content in the solution is increased to 75 g / L to obtain carnallite ore formation water. Then, it is subjected to beach drying and concentration. In the adjustment pond, it is evaporated and concentrated until the magnesium ion concentration in the carnallite ore formation water reaches 85 g / L and the potassium ion concentration is 20 g / L, and then it is introduced into the ore formation pond until carnallite crystallizes out.

[0053] According to the test, in the obtained carnallite, the content of magnesium element is 8.59%, the content of potassium element is 6.74%, and the content of chlorine element is 32.46%; at the same time, the calculated recovery rate of bischofite is 91.21%, and the calculation method is: 85×145 / (110×100 + 25.123×100)×100% = 91.21%.

[0054] Example 2

[0055] The nanofiltration concentrated water (pH value is 5.5) separated in the magnesium-lithium separation stage during the lithium carbonate production process is introduced into the bischofite deposition pond. This nanofiltration concentrated water contains 13.728 g / L of magnesium ions, 0.128 g / L of lithium ions, and 0.084 g / L of potassium ions. The solid bischofite is dissolved using the nanofiltration concentrated water to obtain ore-dissolving water. The concentration of magnesium ions in the ore-dissolving water is 90.3 g / L. The ore-dissolving water is accelerated in dissolution under the action of wind, and then subjected to evaporation and concentration. When the concentration of magnesium ions in the ore-dissolving water reaches 108 g / L and the content of potassium ions reaches 1.436 g / L, a high-magnesium mother liquor is obtained;

[0056] After mixing high-magnesium mother liquor with raw brine (potassium ion content is 14.443 g / L, magnesium ion content is 29.007 g / L, lithium ion content is 0.348 g / L, and sulfate ion concentration is 28.541 g / L) at a volume ratio of 1:1.1, the magnesium content in the solution is increased to 73 g / L to obtain carnallite-forming water, and then beach drying and concentration are carried out. The solution is evaporated and concentrated in the adjustment tank until the magnesium ion concentration in the carnallite-forming water reaches 85 g / L and the potassium ion concentration is 19.1 g / L, and then it is introduced into the ore-forming tank until carnallite crystallizes out.

[0057] According to the test, in the obtained carnallite, the magnesium content is 8.97%, the potassium content is 6.51%, and the chlorine content is 34.19%; at the same time, the recovery rate of bischofite is calculated to be 89.91%, and the calculation method is: 85×148 / (108×100 + 29.007×110)×100% = 89.91%.

[0058] Example 3

[0059] The nanofiltration concentrated water (pH value is 6) separated in the magnesium-lithium separation stage during the lithium carbonate production process is introduced into the bischofite sedimentation tank. This nanofiltration concentrated water contains 12.479 g / L of magnesium ions, 0.12 g / L of lithium ions, and 0.078 g / L of potassium ions. The solid bischofite is dissolved by using this nanofiltration concentrated water to obtain ore-dissolving water. The magnesium ion concentration in the ore-dissolving water is 98.1 g / L. The ore-dissolving water is accelerated to dissolve under the action of wind, and then evaporation and concentration are carried out. When the magnesium ion concentration in the ore-dissolving water reaches 108 g / L and the potassium ion concentration reaches 1.417 g / L, high-magnesium mother liquor is obtained;

[0060] After mixing the high-magnesium mother liquor with raw brine (potassium ion concentration is 12.132 g / L, magnesium ion concentration is 25.123 g / L, lithium ion concentration is 0.289 g / L, and sulfate ion concentration is 26.317 g / L) at a volume ratio of 1:0.9, the magnesium ion concentration in the solution is increased to 75 g / L to obtain carnallite-forming water, and then beach drying and concentration are carried out. The solution is evaporated and concentrated in the adjustment tank until the magnesium content in the carnallite-forming water reaches 85 g / L and the potassium ion concentration is 20 g / L, and then it is introduced into the ore-forming tank until carnallite crystallizes out.

[0061] According to the test, in the obtained carnallite, the magnesium content is 8.22%, the potassium content is 6.41%, and the chlorine content is 30.17%; at the same time, the recovery rate of bischofite is calculated to be 88.50%, and the calculation method is: 85×136 / (108×100 + 25.123×90)×100% = 88.50%.

[0062] Comparative Example 1

[0063] It was implemented according to the method of Example 1, except that the potassium ion content in the raw brine was 9.652 g / L, the magnesium ion content was 14.001 g / L, the lithium ion content was 0.132 g / L, and the sulfate ion content was 21.821 g / L.

[0064] According to the tests, in the carnallite obtained, the magnesium element content was 7.47%, the potassium element content was 6.17%, and the chlorine element content was 27.96%; at the same time, the recovery rate of bischofite was calculated to be 85.68%, and the calculation method was: 85×125 / (110×100 + 14.001×100)×100% = 85.68%. Since the potassium ion content in the raw brine was low and the potassium content in the recovered bischofite was small, the potassium content did not reach the expected standard value during the ore-forming process, and the produced carnallite product did not meet the production requirements of the Yiliping area.

[0065] Comparative Example 2

[0066] It was implemented according to the method of Example 1, except that the potassium ion content in the raw brine was 17.610 g / L, the magnesium ion content was 55.674 g / L, the lithium ion content was 0.482 g / L, and the sulfate ion content was 38.670 g / L.

[0067] According to the tests, in the carnallite obtained, the magnesium content was 8.29%, the potassium content was 6.53%, and the chlorine content was 29.99%; at the same time, the recovery rate of bischofite was calculated to be 64.13%, and the calculation method was: 85×125 / (110×100 + 55.674×100)×100% = 64.13%. Since the raw brine beach drying enrichment time was long, approaching the ore-forming brine, the influence of mixing with the high-magnesium mother liquor was not obvious, so the recovery rate of bischofite was low.

[0068] Comparative Example 3

[0069] It was implemented according to the method of Example 1, except that the volume ratio of the high-magnesium mother liquor to the raw brine during mixing was 1:0.5;

[0070] According to the tests, in the carnallite obtained, the magnesium content was 8.22%, the potassium content was 6.3%, and the chlorine content was 30.17%; at the same time, the recovery rate of bischofite was calculated to be 70.05%, and the calculation method was: 85×101 / (110×100 + 25.123×50)×100% = 70.05%. Since the amount of raw brine used during the brine mixing process was small and the potassium content in the recovered bischofite was small, the potassium content did not reach the expected standard value during the ore-forming process, and the produced carnallite product did not meet the production requirements of the Yiliping area.

[0071] Comparative Example 4

[0072] It was implemented according to the method of Example 1, except that the volume ratio of the high-magnesium mother liquor to the raw brine was 1:1.8 when they were mixed.

[0073] According to the test, in the carnallite obtained, the magnesium content was 7.72%, the potassium content was 6.50%, and the chlorine content was 31.29%; at the same time, the recovery rate of bischofite was calculated to be 80.49%, and the calculation method was: 85×147 / (110×100 + 25.123×180)×100% = 80.49%.

[0074] Test Example

[0075] Test Example 1

[0076] The solubility of bischofite in water at different temperatures was tested, and the results were as Figure 1 shown;

[0077] According to Figure 1 it can be known that the solubility of bischofite in water increases with the increase of temperature.

[0078] Test Example 2

[0079] Using nanofiltration concentrated water (the magnesium ion content in the nanofiltration concentrated water was 14.10 g / L, the potassium ion content was 0.092 g / L, and the lithium ion content was 0.184 g / L) as the ore-dissolving medium, the change relationship between the potassium ion, magnesium ion, and lithium ion contents in the solution obtained after mixing the high-magnesium mother liquor formed by concentrating the ore-dissolving water with the raw brine (the same as the raw brine used in Example 1) at a ratio of 1:1 and the sun-drying and concentration time of the solution was tested, and the results were as Figure 2 shown;

[0080] The change relationship between the sun-drying and concentration time of the solution after mixing the brines and the specific gravity of the solution obtained after mixing the brines was tested, and the results were as Figure 3 shown.

[0081] From Figure 2 it can be known that with the continuous concentration of the carnallite ore-forming water, the contents of various ions in the solution are continuously enriched and increased, gradually reaching the potassium chloride saturation stage, approaching the crystallization (precipitation) point of carnallite. When the concentration of potassium ions in the solution reaches 20 g / L and the magnesium ion concentration reaches about 85 g / L, the ore-forming water is introduced into the ore-forming pool for potassium precipitation to produce carnallite ore for the production of potassium chloride.

[0082] From Figure 3 it can be known that with the continuous concentration of the carnallite ore-forming water, the specific gravity of the ore-forming water changes from 1.2185 g / cm 3 to 1.2464 g / cm 3 to 1.2526 g / cm 3 to 1.2609 g / cm 3, 1.2654 g / cm 3 , 1.2771 g / cm 3 , 1.2822 g / cm 3 , 1.2997 g / cm 3 , 1.3036 g / cm 3 It keeps rising and gradually approaches the crystallization (precipitation) point of carnallite. After the potassium ions in the ore-forming pond are completely precipitated and the lithium content reaches about 1.2 g / L, the upper layer of water in this part (i.e., the low-grade old brine) is introduced into the old brine pond for carnallite precipitation. After complete precipitation, rich lithium old brine (lithium content is 3.0 g / L) is produced for the production of lithium carbonate.

[0083] Test Example 3

[0084] According to the solubility of bischofite in water, the contents of potassium ions and magnesium ions in the solution were measured after different weights of solid bischofite were dissolved in the nanofiltration concentrated water.

[0085] Test method: Synchronously conduct eight groups of parallel tests. Take 4000 mL of nanofiltration concentrated water (the magnesium ion content in the nanofiltration concentrated water is 14.10 g / L, the potassium ion content is 0.092 g / L, and the lithium ion content is 0.184 g / L) and place it in eight beakers. Then, add 300 g, 600 g, 1100 g, 1500 g, 1800 g, 2000 g, 2100 g, and 2400 g of solid bischofite into the beakers in sequence. Stir and dissolve under the action of a stirrer at room temperature (20°C), and then measure the contents of potassium ions and magnesium ions in the obtained solution. The experimental results are shown in Table 1.

[0086] Table 1

[0087] Group Nanofiltration water Bischofite (g) <![CDATA[K + (g / L)]]> <![CDATA[Mg 2+ (g / L)]]> Group 1 4000 300 0.22 24.10 Group 2 4000 600 0.37 54.87 Group 3 4000 1100 0.51 66.10 Group 4 4000 1500 0.75 79.34 Group 5 4000 1800 1.02 87.85 Group 6 4000 2000 1.36 92.55 Group 7 4000 2100 1.37 95.36 Group 8 4000 2400 1.54 108.2

[0088] As can be seen from Table 1, by adding 300 g, 600 g, 1100 g, 1500 g, 1800 g, 2000 g, 2200 g, and 2400 g of solid-phase bischofite to eight groups of nanofiltration water, the potassium ion contents in the solution are successively: 0.22 g / L, 0.37 g / L, 0.51 g / L, 0.75 g / L, 1.02 g / L, 1.36 g / L, 1.37 g / L, and 1.54 g / L, showing a gradually increasing trend. When it reaches 1.54 g / L, the potassium ion content reaches the highest value; the magnesium ion contents are successively 24.10 g / L, 54.87 g / L, 66.10 g / L, 79.34 g / L, 87.85 g / L, 92.55 g / L, 95.36 g / L, and 108.2 g / L. When the magnesium content reaches 108.2 g / L, 2400 g of bischofite has been added, reaching the highest solubility of bischofite dissolution (under the condition of 20 °C). The nanofiltration concentrated water no longer dissolves bischofite, and bischofite reaches a saturated state in the nanofiltration concentrated water. Thus, the solubility of bischofite in the said nanofiltration concentrated water can be obtained, avoiding problems such as supersaturation of bischofite or excessive nanofiltration concentrated water.

[0089] Test Example 4

[0090] The ore-dissolving water obtained from the 8th group of experiments in Test Example 3 was further concentrated into a high-magnesium mother liquor, and then the high-magnesium mother liquor was mixed with raw brine (with the same composition as the raw brine used in Example 1) in a 1:1 ratio to form carnallite ore-forming water. The carnallite ore-forming water was further evaporated and concentrated in a salt pond. The evaporation and concentration data of the carnallite ore-forming water after mixing are shown in Table 2.

[0091] Table 2

[0092]

[0093] In the above test process, the mixing of brines was carried out in an outdoor salt pond. The mixing process of brines was not completed instantaneously, but the high-magnesium mother liquor and the raw brine were gradually mixed. After being evenly mixed under the action of natural wind, it was further concentrated and enriched in the salt pond. It can be seen from the experimental results that during the mixing and concentration process, the specific gravity, Baume degree, and the contents of potassium, magnesium, lithium and other ions in the carnallite ore-forming water gradually increase. When the magnesium content reaches 88.808 g / L, it has reached the ore-forming point (in summer), and the next step is to introduce it into the ore-forming pond for potassium precipitation.

[0094] According to the data in Table 2, with the continuous concentration of carnallite ore-forming water, the contents of various ions continuously enrich and increase, gradually reaching the potassium chloride saturation stage and approaching the carnallite crystallization (precipitation) point. When the potassium content reaches 20 g / L and the magnesium content reaches about 85 g / L, the ore-forming water is introduced into the ore-forming pond for potassium precipitation, and carnallite ore is produced for the production of potassium chloride. It can be found from the above table of the beach drying cycle that the ore-forming cycle can be greatly shortened through the brine mixing process, and the beach drying time of carnallite ore-forming water in the salt pond is shortened (about 2 months shorter than the existing technology). As the specific gravity of the ore-forming water continuously increases, it gradually approaches the carnallite crystallization (precipitation) point. When the potassium ions in the ore-forming pond are completely precipitated and the lithium content reaches about 1.2 g / L, the upper layer of this part of the water (i.e., low-grade old brine) is introduced into the old brine pond for potassium and magnesium precipitation, and old brine (lithium content is 3.0 g / L) is produced for the production of lithium carbonate.

[0095] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for recovering bischofite, characterized in that: The method comprises the following steps: (1) collecting nanofiltration concentrated water separated from the magnesium-lithium separation step in the lithium carbonate production process, and controlling the pH value of the nanofiltration concentrated water within the range of 5-6; (2) dissolving bischofite in the nanofiltration concentrated water to obtain molten mineral water; (3) concentrating the molten mineral water to obtain a high-magnesium mother liquor having a magnesium ion concentration of 108-120 g / L and a potassium ion concentration of 1.4-1.6 g / L; (4) mixing the high-magnesium mother liquor with the raw brine in a volume ratio of 1:0.8-1.5, then concentrating the carnallite ore-forming water obtained after the mixing, and then performing carnallite crystallization; In the raw brine, the concentration of magnesium ions is 25-35 g / L, the concentration of potassium ions is 10-15 g / L, and the concentration of lithium elements is 0.1-0.4 g / L.

2. The method for recovering bischofite according to claim 1, wherein In the raw halide, the concentration of sulfate ions is 25-30 g / L.

3. The method for recovering bischofite according to claim 1, wherein In the raw brine, the concentration of magnesium ions is 28-32 g / L, the concentration of potassium ions is 11-13 g / L, and the concentration of lithium elements is 0.2-0.3 g / L.

4. The method for recovering bischofite according to claim 1, wherein In the molten mineral water, the concentration of magnesium ions is 90-100 g / L.

5. The method for recovering bischofite according to claim 1, wherein The nanofiltration concentrated water contains magnesium ions at a concentration of 10-15 g / L, potassium ions at a concentration of 0.05-0.1 g / L, and lithium elements at a concentration of 0.08-0.2 g / L.

6. The method for recovering bischofite according to claim 1, characterized in that In step (2), the carnallite mineralization water is concentrated to a concentration of magnesium ions of 80-90 g / L and a concentration of potassium ions of 18-20 g / L in the carnallite mineralization water, and then carnallite crystallization is performed.

7. The method for recovering bischofite according to claim 6, characterized in that: When the temperature is ≥25° C., the carnallite mineralization water is concentrated to a concentration of magnesium ions of 85-90 g / L and a concentration of potassium ions of 18-20 g / L in the carnallite mineralization water, and then the carnallite is crystallized.

8. The method for recovering bischofite according to claim 6, characterized in that When the temperature is ≤0°C, the carnallite mineralization water is concentrated until the concentration of magnesium ions in the carnallite mineralization water is 80-85 g / L and the concentration of potassium ions in the carnallite mineralization water is 18-20 g / L, and then the carnallite is crystallized.

9. The method for recovering bischofite according to claim 1, characterized in that The volume ratio of the high-magnesium mother liquor to the raw halogen is 1:0.9-1.

3.

10. The method for recovering bischofite according to claim 1, characterized in that: The content of potassium in the carnallite is ≥6.5wt%.

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