Method for preparing anhydrous lithium chloride from salt lake brine with low magnesium-lithium ratio

Abstract

The invention belongs to the technical field of inorganic salt chemical industry. The invention provides a method for preparing anhydrous lithium chloride by using salt lake brine with low magnesium-lithium ratio, which comprises the following steps: pumping clear salt lake brine with low magnesium-lithium ratio into a plate-and-frame filter press for filtration, and sequentially performing microporous filtration and ultrafiltration on filtrate to obtain primary refined brine; filtering the primary refined brine through a nanofiltration membrane device to obtain secondary refined brine; allowing the secondary refined brine to pass through chelating resin to obtain magnesium-removed brine; mixing the magnesium-removed brine with an alkali solution, adjusting the pH value of the mixed solution, and pumping the mixed solution into a continuous extraction device for solvent extraction to obtain a lithium chloride solution; and evaporating and drying the lithium chloride solution in sequence to obtain an anhydrous lithium chloride product. The anhydrous lithium chloride product is prepared by adopting a nanofiltration membrane separation and solvent extraction combined process, the recovery rate of lithium ions is higher than 80%, the fresh water consumption of 1 ton of lithium chloride product is less than 50 cubic meters, the production cost is low, the chemical units are few, and the automation degree is high.

Description

Technical Field

[0001] The invention relates to the technical field of inorganic salt chemical industry, and in particular to a method for preparing anhydrous lithium chloride by using salt lake brine with a low magnesium-to-lithium ratio. Background Art

[0002] In recent years, with the advent of new solid-state lithium-ion batteries, the new energy industry's demand for metallic lithium has expanded year by year. Lithium chloride is the basic raw material for the production of lithium fine chemicals such as metallic lithium, lithium carbonate, and lithium hydroxide.

[0003] Low magnesium-to-lithium ratio salt lakes are an important type of salt resource, mainly distributed in Tibet and the lithium triangle region of Bolivia, Argentina, and Chile in South America. The hydrochemical types include carbonate, chloride, and sulfate. The lithium reserves in low magnesium-to-lithium ratio salt lakes are extremely considerable, and have broad development prospects. Traditional processes are generally used to develop low magnesium-to-lithium ratio salt lakes internationally. For example, SQM, ALB, and Allkem use step-by-step precipitation to produce lithium carbonate from the Atacama Salt Lake in Chile and the Olaroz Salt Lake in Argentina, respectively, with an annual production of nearly 200,000 tons. However, the traditional process adds quicklime to remove magnesium and sulfate, and obtains high-concentration lithium brine by evaporating the salt pan, and then produces lithium carbonate products by step-by-step precipitation. The lithium ion recovery rate is generally less than 40%, which leads to serious waste of lithium resources. There are a large number of low magnesium-to-lithium ratio salt lakes in the Ali region of Tibet, my country. Due to the general altitude of more than 4,300 meters, there is a great engineering risk in the large-scale construction of salt pans on the permafrost layer. The use of salt pan evaporation combined with step-by-step precipitation technology also has the problem of waste of lithium resources.

[0004] In response to the above problems, the industry generally adopts the adsorption method to directly extract lithium from salt lake brine to avoid the evaporation process of salt fields, successfully increasing the lithium ion recovery rate from less than 40% to more than 80%. The scale of lithium carbonate production has been rapidly improved, especially in the salt lake area of ​​Qaidam Basin in Qinghai Province, my country and some salt lakes in South America. The adsorption method has become one of the mainstream processes for extracting lithium from salt lakes. There are many patents published in this field, such as CN111804270A, an aluminum-based lithium adsorbent and its preparation method, CN112142076A, a method for preparing lithium from brine by adsorption, CN107058735A, a continuous ion exchange device for preparing lithium and a lithium extraction process, etc. However, most of the salt lake areas in the world are generally dry and rainy, with scarce water resources. The water consumption of the adsorption method is high. Under normal circumstances, the amount of fresh water consumed to produce 1 ton of lithium chloride is as high as 240 to 350 cubic meters. The problem of "production based on water" is particularly prominent, which largely limits the large-scale use of the adsorption method. Therefore, providing a method for preparing anhydrous lithium chloride using salt lake brine with a low magnesium-to-lithium ratio, which has a high lithium ion recovery rate and low fresh water consumption, has good application prospects. Summary of the invention

[0005] In order to solve the above problems, the present invention proposes a method for preparing anhydrous lithium chloride using salt lake brine with a low magnesium-to-lithium ratio. The present invention adopts a combination of nanofiltration membrane separation and solvent extraction processes to physically remove magnesium ions and sulfate impurities in salt lake brine, selectively separate lithium ions, and realize the direct preparation of lithium chloride products from raw brine. The recovery rate of lithium ions is higher than 80%, and the fresh water consumption is reduced to less than 50 cubic meters per ton of lithium chloride. It is particularly suitable for lithium extraction from salt lake brine with a low magnesium-to-lithium ratio.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing anhydrous lithium chloride using salt lake brine with a low magnesium-to-lithium ratio, comprising the following steps:

[0008] 1) The low magnesium-lithium ratio salt lake brine is introduced into a sedimentation tank, and after clarification, it is pumped into a plate and frame filter press for filtration, and the filtrate is sequentially subjected to microfiltration and ultrafiltration to obtain a primary refined brine;

[0009] 2) filtering the primary refined brine through a nanofiltration membrane device to obtain secondary refined brine and nanofiltration concentrated water;

[0010] 3) The secondary refined brine is passed through a chelating resin to obtain a demagnesized brine;

[0011] 4) Mixing the demagnesized brine with the alkaline solution, adjusting the pH value of the mixed solution and then pumping it into a continuous extraction device for solvent extraction; washing the lithium-loaded organic phase with a dilute lithium chloride solution and then back-extracting with a strong acid solution to obtain a lithium chloride solution; mixing the raffinate with the nanofiltration concentrated water and pumping it back into the salt lake;

[0012] 5) Evaporating the lithium chloride solution to obtain lithium chloride solid and distilled water; the distilled water is used to prepare a strong acid solution, and the lithium chloride solid is dried to obtain anhydrous lithium chloride.

[0013] Preferably, the low magnesium-lithium ratio salt lake brine in step 1) contains the following components in concentration: [Mg 2+ ]≤5g·L -1 、[Na + ]≥50g·L -1 、[Li + ]≥0.3g·L -1 , [K + ]≥2g·L -1 , [Cl - ] is 150~190g·L -1 、[SO 4 2- ] is 0~19g·L -1 , [B 2 O 3 ] is 0~2g·L -1 , [CO3 2- ] is 0~15g·L -1 , [Mg 2+ ] / [Li + ]≤5.

[0014] Preferably, after the filtration in step 1), the turbidity of the low magnesium-lithium ratio salt lake brine is ≤15NTU; the pore size of the filter element of the microfiltration is 1-5μm, and the pore size of the filter element of the ultrafiltration is 0.05-0.5μm.

[0015] Preferably, the turbidity of the first refined brine in step 1) is ≤1NTU, and the total organic carbon is 8-30mg·L -1 .

[0016] Preferably, the nanofiltration membrane device in step 2) is a three-stage or four-stage nanofiltration membrane device, which is connected in series, wherein the operating pressure of the first stage nanofiltration is 7.5-8.0 MPa, the operating pressure of the second stage nanofiltration is 5.0-5.4 MPa, and the operating pressures of the third and fourth stage nanofiltration are independently 3.8-4.0 MPa.

[0017] Preferably, the concentration of magnesium ions in the secondary refined brine in step 2) is ≤50 mg·L -1 .

[0018] Preferably, the concentration of magnesium ions in the demagnesizing brine in step 3) is ≤1 mg·L -1 .

[0019] Preferably, the alkaline solution in step 4) is a sodium hydroxide solution, the mass fraction of the alkaline solution is 10-15%, the pH value of the mixed solution is ≥12, and the concentration of the dilute lithium chloride solution is 1-3 g·L -1 , the concentration of lithium ions in the lithium chloride solution is ≥20g / L.

[0020] Preferably, the extraction solvent used in the extraction process of step 4) is composed of an extractant, a synergist and a diluent, wherein the extractant is a β-diketone solvent, the synergist is composed of an organic phosphine and a water-insoluble ketone, and the diluent is an alkane and / or an aromatic hydrocarbon;

[0021] In the extraction solvent, the mass ratio of the extractant to the synergistic extractant is 1:0.5-1, and the total mass of the extractant and the synergistic extractant is 25-30% of the mass of the extraction solvent;

[0022] In the synergistic extractant, the mass ratio of organic phosphine to water-insoluble ketone is 1:2-4;

[0023] When the diluent is a mixture of alkanes and aromatics, the mass ratio of alkanes to aromatics is 1:0.5-1.5.

[0024] Preferably, the extraction operation in step 4) is a multi-stage countercurrent extraction, wherein the extraction section is 3 to 4 stages, the washing section is 2 to 3 stages, and the stripping section is 2 to 3 stages;

[0025] The stripping agent is a strong acid, and the concentration of the strong acid is 2 to 6 mol / L.

[0026] Compared with the prior art, the beneficial effects of the present invention include the following points:

[0027] 1) The present invention uses low magnesium-to-lithium ratio salt lake brine as raw material, and adopts nanofiltration membrane separation technology to physically remove divalent magnesium ions and sulfate impurities, thereby avoiding the high operating cost and solid waste environmental impact of chemical magnesium-lithium separation, without any waste residue discharge, and is environmentally friendly.

[0028] 2) The present invention adopts a nanofiltration membrane separation and solvent extraction combined process to directly prepare lithium chloride products from low magnesium-to-lithium ratio salt lake brine, avoiding evaporation losses in salt pans. The recovery rate of lithium ions is higher than 80%, while significantly reducing the use of chemicals such as caustic soda and soda ash. The amount of fresh water consumed for 1 ton of lithium chloride products is less than 50 cubic meters. It has the advantages of low production cost, few chemical units, and high degree of automation, especially in remote, arid, water-scarce, and sparsely populated high-altitude areas where lithium is directly extracted from salt lakes, and has great application value.

[0029] 3) The lithium chloride product obtained by the present invention can be used as a basic chemical raw material to produce a variety of lithium fine chemicals such as metallic lithium, lithium hydroxide and lithium carbonate products, and has a strong ability to resist market risks. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0031] Figure 1 The present invention is a process flow chart for preparing anhydrous lithium chloride using salt lake brine with a low magnesium-to-lithium ratio. DETAILED DESCRIPTION

[0032] The present invention provides a method for preparing anhydrous lithium chloride using salt lake brine with a low magnesium-to-lithium ratio, comprising the following steps:

[0033] 1) The low magnesium-lithium ratio salt lake brine is introduced into a sedimentation tank, and after clarification, it is pumped into a plate and frame filter press for filtration, and the filtrate is sequentially subjected to microfiltration and ultrafiltration to obtain a primary refined brine;

[0034] 2) filtering the primary refined brine through a nanofiltration membrane device to obtain secondary refined brine and nanofiltration concentrated water;

[0035] 3) The secondary refined brine is passed through a chelating resin to obtain a demagnesized brine;

[0036] 4) Mixing the demagnesized brine with the alkaline solution, adjusting the pH value of the mixed solution and then pumping it into a continuous extraction device for solvent extraction; washing the lithium-loaded organic phase with a dilute lithium chloride solution and then back-extracting with a strong acid solution to obtain a lithium chloride solution; mixing the raffinate with the nanofiltration concentrated water and pumping it back into the salt lake;

[0037] 5) Evaporating the lithium chloride solution to obtain lithium chloride solid and distilled water; the distilled water is used to prepare a strong acid solution, and the lithium chloride solid is dried to obtain anhydrous lithium chloride.

[0038] In the present invention, the low magnesium-lithium ratio salt lake brine in step 1) preferably contains the following concentrations of components: [Mg 2+ ]≤5g·L -1 、[Na + ]≥50g·L -1 、[Li + ]≥0.3g·L -1 , [K + ]≥2g·L -1 , [Cl - ] is 150~190g·L -1 、[SO 4 2- ] is 0~19g·L -1 , [B 2 O 3 ] is 0~2g·L -1 , [CO 3 2- ] is 0~15g·L -1 , [Mg 2+ ] / [Li + ]≤5.

[0039] In the present invention, after the filtration in step 1), the turbidity of the low magnesium-lithium ratio salt lake brine is preferably ≤15NTU, more preferably ≤13NTU, and more preferably ≤10NTU; the pore size of the filter element of the microfiltration is preferably 1-5μm, more preferably 2-4μm, and more preferably 3μm; the pore size of the filter element of the ultrafiltration is preferably 0.05-0.5μm, more preferably 0.2-0.4μm, and more preferably 0.3μm.

[0040] In the present invention, the filtration in the plate and frame filter press in step 1) is to remove solid impurities in the brine of the salt lake with a low magnesium-lithium ratio.

[0041] In the present invention, step 1) filtering the low magnesium-lithium ratio salt lake brine step by step is to remove particulate matter suspended in the brine to meet the water inlet requirements of the nanofiltration membrane.

[0042] In the present invention, the turbidity of the primary refined brine in step 1) is preferably ≤1NTU, more preferably ≤0.8NTU, and more preferably ≤0.5NTU; the total organic carbon is preferably 8-30mg·L -1 , more preferably 10 to 25 mg·L -1 , more preferably 15 mg·L -1 .

[0043] In the present invention, the nanofiltration membrane device in step 2) is preferably a three-stage or four-stage nanofiltration membrane device, which is connected in series, wherein the operating pressure of the first stage nanofiltration is preferably 7.5-8.0 MPa, further preferably 7.6-7.8 MPa, and more preferably 7.7 MPa, the operating pressure of the second stage nanofiltration is preferably 5.0-5.4 MPa, further preferably 5.1-5.3 MPa, and more preferably 5.2 MPa, and the operating pressures of the third and fourth stage nanofiltration are independently preferably 3.8-4.0 MPa, further preferably 3.85-3.95 MPa, and more preferably 3.9 MPa.

[0044] In the present invention, since the salt lake brine with a low magnesium-lithium ratio is often a solution saturated or nearly saturated with sodium chloride, the Mg in the brine during the membrane separation process is 2+ Gradual enrichment increases the membrane separation osmotic pressure, so high-pressure nanofiltration is required to obtain a more ideal lithium ion recovery rate while removing magnesium ions.

[0045] In the present invention, the brine system Li after magnesium removal by nanofiltration membrane + ,Na + ,K + ,Cl - -H 2 O quaternary water-salt system, the extraction process is mainly to achieve the separation of lithium and potassium and sodium. Since the brine basically does not contain particulate matter and organic matter, the extraction-strip extraction process does not form a "third phase", ensuring the stable operation of the production process.

[0046] In the present invention, step 2) filtering the primary refined brine through a nanofiltration membrane device is to remove magnesium salts in the primary refined brine.

[0047] In the present invention, the concentration of magnesium ions in the secondary refined brine in step 2) is preferably ≤50 mg·L -1 , more preferably ≤45mg·L -1 , more preferably ≤40mg·L -1 .

[0048] In the present invention, step 3) is to pass the secondary refined brine through a chelating resin in order to further remove the remaining magnesium ions.

[0049] In the present invention, the concentration of magnesium ions in the demagnesizing brine in step 3) is preferably ≤1 mg·L -1 , more preferably ≤0.8mg·L -1 , more preferably ≤0.5mg·L -1 .

[0050] In the present invention, since the β-diketone extractant has a strong selectivity for magnesium ions, magnesium ions will be enriched in the reverse liquid during the extraction process. Therefore, a chelating resin is required to further adsorb and remove the magnesium ions to reduce the magnesium ion concentration to 1 mg·L -1 The following is to meet the extraction water inlet conditions.

[0051] In the present invention, the alkaline solution in step 4) is preferably a sodium hydroxide solution, the mass fraction of the alkaline solution is preferably 10-15%, more preferably 15%, the pH value of the mixed solution is preferably ≥12, more preferably ≥13, and the concentration of the dilute lithium chloride solution is preferably 1-3 g·L -1 , more preferably 1.5 to 2.5 g·L -1 , more preferably 2 g·L -1 The concentration of lithium ions in the lithium chloride solution is preferably ≥20 g / L, more preferably ≥25 g / L, and more preferably ≥30 g / L.

[0052] In the present invention, the extraction solvent used in the extraction process of step 4) is preferably composed of an extractant, a synergist and a diluent, wherein the extractant is preferably a β-diketone solvent, further preferably one or more of ethyl benzoyl acetate, α-acetyl-m-dodecyl acetophenone (trade name LIX54, ZD54-100, AD108), dibenzoylmethane, stearoylbenzoylmethane, 1,1,1-trifluoro-5,5-dimethyl-2,4-hexanedione, 2-thenoyltrifluoroacetone and benzoyltrifluoroacetone, the synergist is preferably composed of an organic phosphine and a water-insoluble ketone, the organic phosphine is preferably a trialkylphosphine oxide or trioctyl phosphate, the water-insoluble ketone is preferably one or more of 4-methyl-2-pentanone, acetophenone and methyl nonyl ketone, the diluent is preferably an alkane and / or an aromatic hydrocarbon, the alkane is preferably an alkane solvent oil 260# and / or Exxsol D80, and the aromatic hydrocarbon is preferably an aromatic hydrocarbon solvent oil S150.

[0053] In the present invention, the β-diketone solvent has an "enol tautomerization" structure, and its carbonyl carbon active hydrogen can undergo ion exchange reaction with aqueous lithium ions in an alkaline solution environment, thereby realizing the transfer of lithium ions from the aqueous phase to the organic phase. Lithium ions are hydrated ions in aqueous solution, and their tetrahedral structure is highly hydrophilic. Therefore, the extraction process requires the coordination of a co-extractant to further improve the hydrophobicity of lithium ions, thereby improving the extraction efficiency and reducing the emulsification of the extractant. Therefore, the extraction solvent is composed of an extractant, a co-extractant and a diluent.

[0054] In the present invention, in the extraction solvent, the mass ratio of the extractant to the synergistic agent is preferably 1:0.5-1, more preferably 1:0.6-0.8, and more preferably 1:0.7; the total mass of the extractant and the synergistic agent is preferably 25-30% of the mass of the extraction solvent, more preferably 26-28%, and more preferably 27%;

[0055] In the synergistic extractant, the mass ratio of the organic phosphine to the water-insoluble ketone is preferably 1:2-4, more preferably 1:2.5-3.5, and more preferably 1:3;

[0056] When the diluent is preferably a mixture of alkanes and aromatics, the mass ratio of alkanes to aromatics is preferably 1:0.5 to 1.5, more preferably 1:0.8 to 1.2, and even more preferably 1:1.

[0057] In the present invention, the lithium-loaded organic phase in step 4) is washed with a dilute lithium chloride solution in order to remove the sodium salt.

[0058] In the present invention, a dilute lithium chloride solution is used in the washing process to elute the sodium chloride entrained in the organic phase and replace the sodium ions entering the organic phase, so that the sodium impurities in the reverse liquid are reduced to 200 mg·L -1 Next, to ensure the quality of the lithium chloride product, since the replaced sodium eluent still contains lithium, the washing water is returned to step 3) and mixed with the magnesium removal brine for recycling to further recover the lithium ions therein.

[0059] In the present invention, the extraction operation in step 4) is preferably a multi-stage countercurrent extraction, wherein the extraction section is preferably 3 to 4 stages, more preferably 3 stages, the washing section is preferably 2 to 3 stages, more preferably 3 stages, and the stripping section is preferably 2 to 3 stages, more preferably 2 stages;

[0060] The stripping agent is preferably a strong acid, more preferably hydrochloric acid, sulfuric acid or nitric acid, and the concentration of the strong acid is preferably 2 to 6 mol / L, more preferably 3 to 5 mol / L, and more preferably 4 mol / L.

[0061] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0062] Example 1

[0063] The raw material was taken from a sulfate salt lake brine in Argentina, South America (density 1.196 g·L -1 ), having the chemical composition shown in Table 1. From the composition analysis, the magnesium-lithium ratio in the brine is 2.26:1.

[0064] Table 1 Chemical composition of brine from a sulfate salt lake in Argentina, South America

[0065] Element Name <![CDATA[Li + ]]> <![CDATA[Mg 2+ ]]> <![CDATA[Na + ]]> <![CDATA[K + ]]> <![CDATA[Cl - ]]> <![CDATA[SO 4 2- ]]> <![CDATA[B 2 THE 3 ]]> <![CDATA[Content (g·L -1 )]]> 0.426 0.963 98.476 4.265 153.296 13.561 0.979

[0066] 1) 500L of the above brine is introduced into a sedimentation tank. After clarification, it is pumped into a plate and frame filter press with a centrifugal pump for filtration. The filtrate is filtered through a ceramic membrane microfiltration (the pore size of the filter element is 5μm) and ultrafiltration (the pore size of the filter element is 0.05μm) in sequence. The produced water is collected, and the concentrated water is returned to the raw material tank and mixed with the raw water for further filtration to obtain 498L of primary refined brine. The turbidity of the primary refined brine is measured to be 0.4NTU, and the total organic carbon is 10mg / L.

[0067] 2) The primary refined brine was pumped into a four-stage nanofiltration membrane device in series, and the operating pressure of the first stage of nanofiltration was set to 7.8 MPa, the operating pressure of the second stage of nanofiltration was 5.2 MPa, and the operating pressures of the third and fourth stages of nanofiltration were both 3.9 MPa, to obtain 361 L of secondary refined brine and 134 L of nanofiltration concentrated water, respectively. + ]=0.536gg·L -1 , [Mg 2+ ]=0.048g·L -1 ,[SO 4 2- ]=0.102g·L -1 , [B 2 O 3 ]=0.864g·L -1 The recovery rate of lithium ions in this section is 91.21%, the removal rate of magnesium ions is 96.39%, the removal rate of sulfate ions is 99.46%, and the concentration of lithium ions in the nanofiltration concentrated water is 0.131 g·L -1 .

[0068] 3) The secondary refined brine is pumped into a chelating resin column for further de-magnesiumization to obtain 360 L of de-magnesiumized brine. 2+ ]<1mg·L -1 , the content of other elements is [Li + ]=0.536g·L -1 , [Na + ]=96.99g·L -1 , [K + ]=4.249g·L -1,[SO 4 2- ]=0.101g·L -1 , [Cl - ]=150.162g·L -1 , [B 2 O 3 ]=0.853g·L -1 , it can be seen from the data that the brine system has been converted into chloride.

[0069] 4) Mixing the demagnesized brine with a sodium hydroxide solution having a mass fraction of 15%, stirring the mixture to adjust the pH value of the mixture to 12.8, and pumping the mixture into a continuous extraction device with a pump, wherein the extraction solvent consists of an extractant, a synergist, and a diluent, wherein the extractant is α-acetyl-m-dodecylacetophenone, the synergist consists of trialkylphosphine oxide and acetophenone (the mass ratio of trialkylphosphine oxide to acetophenone is 1:3), the diluent consists of alkane solvent oil Exxsol D80 and aromatic solvent oil S150 (the mass ratio of Exxsol D80 to S150 is 1:1), the mass ratio of the extractant to the synergist is 1:1, the total mass of the extractant and the synergist is 30% of the mass of the extraction solvent, and the concentration of the lithium-loaded organic phase is 2.0 g·L -1 The diluted lithium chloride solution was washed and then stripped with a 5 mol / L hydrochloric acid solution. The extraction process was set to 4 stages of extraction, 2 stages of washing, and 2 stages of stripping. The extraction process data after stable operation are shown in Table 2. The total lithium ion concentration obtained in the extraction process was 29.62 g·L -1 6.3L of lithium chloride solution is obtained, and the raffinate is mixed with the concentrated water from the nanofiltration and pumped back into the salt lake.

[0070] Table 2 Extraction data of anhydrous lithium chloride from a sulfate salt lake brine in Argentina, South America

[0071]

[0072] 5) Place the lithium chloride solution in a rotary vacuum evaporator, open the oil bath, set the temperature to 120° C., turn on the vacuum pump to evaporate the lithium chloride solution to obtain lithium chloride solid and distilled water, and then dry the lithium chloride solid at 180° C. for 2 h to obtain anhydrous lithium chloride, totaling 1.14 kg. The detection indicators meet the national standard for anhydrous lithium chloride GB / T10575-2007.

[0073] The recovery rate of lithium ions from the raw halogen pretreatment to the anhydrous lithium chloride product was calculated to be 87.25%.

[0074] During the experiment, 46.3L of fresh water was consumed to prepare acid, alkali and washing liquid, and 5.7L of distilled water was recovered by evaporation. It was calculated that 35.6m3 of fresh water was consumed per ton of lithium chloride product. 3 .

[0075] Example 2

[0076] The raw material was taken from the brine of a carbonate salt lake in Ali, Tibet (density 1.206 g·L -1 ), having the chemical composition shown in Table 3. From the composition analysis, the magnesium-lithium ratio in the brine is 0.7:1.

[0077] Table 3 Chemical composition of brine from a carbonate salt lake in Ali region of Tibet

[0078] Element Name <![CDATA[Li + ]]> <![CDATA[Mg 2+ ]]> <![CDATA[Na + ]]> <![CDATA[K + ]]> <![CDATA[Cl - ]]> <![CDATA[CO 3 2- ]]> <![CDATA[SO 4 2- ]]> <![CDATA[Content (g·L -1 )]]> 0.374 0.263 95.584 9.615 151.429 11.508 9.846

[0079] 1) 500L of the above brine is introduced into a sedimentation tank. After clarification, it is pumped into a plate and frame filter press with a centrifugal pump for filtration. The filtrate is filtered through a ceramic membrane microfiltration (the pore size of the filter element is 5μm) and ultrafiltration (the pore size of the filter element is 0.1μm) in sequence. The produced water is collected, and the concentrated water is returned to the raw material tank and mixed with the raw water for further filtration to obtain 499L of refined brine. The turbidity of the refined brine is measured to be 0.6NTU, and the total organic carbon is 30mg / L.

[0080] 2) The primary refined brine was pumped into a three-stage series nanofiltration membrane device, and the operating pressure of the first stage nanofiltration was set to 7.7 MPa, the operating pressure of the second stage nanofiltration was 5.2 MPa, and the operating pressure of the third stage nanofiltration was 3.9 MPa, respectively, to obtain 351 L of secondary refined brine and 148 L of nanofiltration concentrated water. [Li + ]=0.472g·L -1 , [Mg 2+ ]=0.041g·L -1 ,[SO 4 2- ]=0.089g·L -1 , [CO 3 2- ]=0.264g·L -1 The recovery rate of lithium ions in this section is 88.77%, the removal rate of magnesium ions is 89.03%, the removal rate of sulfate ions is 99.36%, and the removal rate of carbonate ions is 98.39%. The concentration of lithium ions in the nanofiltration concentrated water is 0.142 g·L -1 .

[0081] 3) The secondary refined brine is pumped into a chelating resin column for further de-magnesiumization to obtain 350 L of de-magnesiumized brine. 2+ ]<1mg·L -1 , the content of other elements is [Li + ]=0.469g·L -1 , [Na + ]=93.621g·L -1 , [K +]=7.948g·L -1 ,[SO 4 2- ]=0.089g·L -1 , [Cl - ]=150.376g·L -1 , [CO 3 2- ]=0.264g·L -1 , it can be seen from the data that the brine system has been converted into chloride.

[0082] 4) Mixing the demagnesized brine with a sodium hydroxide solution having a mass fraction of 10%, stirring the mixture to adjust the pH value of the mixture to 13.5, and pumping the mixture into a continuous extraction device with a pump, wherein the extraction solvent consists of an extractant, a synergist, and a diluent, wherein the extractant is ethyl benzoyl acetate, the synergist consists of trialkylphosphine oxide and acetophenone (the mass ratio of trialkylphosphine oxide to acetophenone is 1:3), the diluent consists of alkane solvent oil Exxsol D80 and aromatic solvent oil S150 (the mass ratio of Exxsol D80 to S150 is 1:1), the mass ratio of the extractant to the synergist is 1:1, the total mass of the extractant and the synergist is 25% of the mass of the extraction solvent, and the concentration of the lithium-loaded organic phase is 2.0 g·L -1 The diluted lithium chloride solution was washed and then stripped with a 6 mol / L hydrochloric acid solution. The extraction process was set to extract 3 stages, wash 2 stages, and strip 2 stages. The extraction process data after stable operation are shown in Table 4. The total lithium ion concentration obtained in the extraction process was 20.39 g·L -1 7.6L of lithium chloride solution is obtained, and the raffinate is mixed with the concentrated water from the nanofiltration and pumped back into the salt lake.

[0083] Table 4 Extraction data of anhydrous lithium chloride from brine of a carbonate salt lake in Ali region of Tibet

[0084]

[0085] 5) Place the lithium chloride solution in a rotary vacuum evaporator, open the oil bath, set the temperature to 120° C., turn on the vacuum pump to evaporate the lithium chloride solution to obtain lithium chloride solid and distilled water, and then dry the lithium chloride solid at 180° C. for 2 h to obtain anhydrous lithium chloride, totaling 0.96 kg. The detection indicators meet the national standard for anhydrous lithium chloride GB / T10575-2007.

[0086] The recovery rate of lithium ions from the raw halogen pretreatment to the anhydrous lithium chloride product was calculated to be 83.39%.

[0087] During the experiment, 49.8L of fresh water was consumed to prepare acid, alkali and washing liquid, and 7.3L of distilled water was recovered by evaporation. It was calculated that 44.3m3 of fresh water was consumed per ton of lithium chloride product. 3 .

[0088] Example 3

[0089] The raw material was taken from a chloride-type salt lake brine in Bolivia, South America (density 1.1636 g·L -1 ), has the chemical composition shown in Table 5. From the composition analysis, the magnesium-lithium ratio in the brine is 3.06:1.

[0090] Table 5 Chemical composition of brine from a chloride-type salt lake in Bolivia, South America

[0091] Element Name <![CDATA[Li + ]]> <![CDATA[Mg 2+ ]]> <![CDATA[Na + ]]> <![CDATA[K + ]]> <![CDATA[Cl - ]]> <![CDATA[SO 4 2- ]]> <![CDATA[B 2 THE 3 ]]> <![CDATA[Content (g·L -1 )]]> 1.327 4.059 85.087 8.215 159.295 3.419 1.474

[0092] 1) 500L of the above brine is introduced into a sedimentation tank. After clarification, it is pumped into a plate and frame filter press with a centrifugal pump for filtration. The filtrate is filtered through a ceramic membrane microfiltration (the pore size of the filter element is 5μm) and ultrafiltration (the pore size of the filter element is 0.3μm) in sequence. The produced water is collected, and the concentrated water is returned to the raw material tank and mixed with the raw water for further filtration to obtain 499L of primary refined brine. The turbidity of the primary refined brine is measured to be 0.2NTU, and the total organic carbon is 8mg / L.

[0093] 2) The primary refined brine was pumped into a four-stage series nanofiltration membrane device, and the operating pressure of the first stage of nanofiltration was set to 8.0 MPa, the operating pressure of the second stage of nanofiltration was 5.4 MPa, and the operating pressures of the third and fourth stages of nanofiltration were both 4.0 MPa, to obtain 341 L of secondary refined brine and 158 L of nanofiltration concentrated water, respectively. [Li + ]=1.835g·L -1 , [Mg 2+ ]=0.086g·L -1 ,[SO 4 2- ]=0.109g·L -1 , [B 2 O 3 ]=1.322g·L -1 The recovery rate of lithium ions in this section is 94.46%, the removal rate of magnesium ions is 98.55%, the removal rate of sulfate ions is 97.82%, and the concentration of lithium ions in the nanofiltration concentrated water is 0.233 g·L -1 .

[0094] 3) The secondary refined brine was pumped into a chelating resin column for further de-magnesiumization to obtain 340 L of de-magnesiumized brine. 2+ ]<1mg·L -1 , the content of other elements is [Li + ]=1.833g·L -1 , [Na + ]=84.096g·L -1 , [K+ ]=8.222g·L -1 ,[SO 4 2- ]=0.107g·L -1 , [Cl - ]=157.760g·L -1 , [B 2 O 3 ]=1.319g·L -1 , it can be seen from the data that the brine system has been converted into chloride.

[0095] 4) Mixing the demagnesized brine with a sodium hydroxide solution having a mass fraction of 15%, stirring the mixture to adjust the pH value of the mixture to 12.0, and pumping the mixture into a continuous extraction device with a pump, wherein the extraction solvent consists of an extractant, a synergist, and a diluent, wherein the extractant is 2-thenoyltrifluoroacetone, the synergist consists of trialkylphosphine oxide and acetophenone (the mass ratio of trialkylphosphine oxide to acetophenone is 1:3), the diluent consists of alkane solvent oil Exxsol D80 and aromatic solvent oil S150 (the mass ratio of Exxsol D80 to S150 is 1:1), the mass ratio of the extractant to the synergist is 1:1, the total mass of the extractant and the synergist is 30% of the mass of the extraction solvent, and the concentration of the lithium-loaded organic phase is 2.0 g·L -1 The diluted lithium chloride solution was washed and then stripped with a 6 mol / L hydrochloric acid solution. The extraction process was set to extract 3 stages, wash 2 stages, and strip 2 stages. The extraction process data after stable operation are shown in Table 6. The total lithium ion concentration obtained in the extraction process was 32.39 g·L -1 18.9L of lithium chloride solution is obtained, and the raffinate is mixed with the concentrated water from the nanofiltration and pumped back into the salt lake.

[0096] Table 6 Extraction data of anhydrous lithium chloride from brine of a chloride-type salt lake in Bolivia, South America

[0097]

[0098]

[0099] 5) Place the lithium chloride solution in a rotary vacuum evaporator, open the oil bath, set the temperature to 120° C., turn on the vacuum pump to evaporate the lithium chloride solution to obtain lithium chloride solid and distilled water, and then dry the lithium chloride solid at 180° C. for 2 h to obtain anhydrous lithium chloride, totaling 3.76 kg. The detection indicators meet the national standard for anhydrous lithium chloride GB / T10575-2007.

[0100] The recovery rate of lithium ions from the raw halogen pretreatment to the anhydrous lithium chloride product was calculated to be 92.42%.

[0101] During the experiment, 138.2L of fresh water was consumed to prepare acid, alkali and washing liquid, and 17.6L of distilled water was recovered by evaporation. It was calculated that 32.1m3 of fresh water was consumed per ton of lithium chloride product. 3 .

[0102] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing anhydrous lithium chloride using salt lake brine with a low magnesium-to-lithium ratio, characterized in that: The following steps are involved: 1) The low magnesium-lithium ratio salt lake brine is introduced into a sedimentation tank, and after clarification, it is pumped into a plate and frame filter press for filtration, and the filtrate is sequentially subjected to microfiltration and ultrafiltration to obtain a primary refined brine; 2) filtering the primary refined brine through a nanofiltration membrane device to obtain secondary refined brine and nanofiltration concentrated water; 3) The secondary refined brine is passed through a chelating resin to obtain a demagnesized brine; 4) Mixing the demagnesized brine with the alkaline solution, adjusting the pH value of the mixed solution and then pumping it into a continuous extraction device for solvent extraction; washing the lithium-loaded organic phase with a dilute lithium chloride solution and then back-extracting with a strong acid solution to obtain a lithium chloride solution; mixing the raffinate with the nanofiltration concentrated water and pumping it back into the salt lake; 5) Evaporating the lithium chloride solution to obtain lithium chloride solid and distilled water; the distilled water is used to prepare a strong acid solution, and the lithium chloride solid is dried to obtain anhydrous lithium chloride.

2. The method for preparing anhydrous lithium chloride using salt lake brine with a low magnesium-to-lithium ratio according to claim 1, characterized in that: Step 1) The low magnesium-lithium ratio salt lake brine contains the following components in concentration: [Mg 2+ ]≤5g·L -1 、[Na + ]≥50g·L -1 、[Li + ]≥0.3g·L -1 , [K + ]≥2g·L -1 , [Cl - ] is 150~190g·L -1 、[SO4 2- ] is 0~19g·L -1 , [B2O3]: 0~2g·L -1 、[CO3 2- ] is 0~15g·L -1 , [Mg 2+ ] / [Li + ]≤5.

3. The method for preparing anhydrous lithium chloride using salt lake brine with a low magnesium-to-lithium ratio according to claim 1 or 2, characterized in that: After step 1) filtration, the turbidity of the low magnesium-lithium ratio salt lake brine is ≤15NTU; the pore size of the filter element of the microfiltration is 1-5μm, and the pore size of the filter element of the ultrafiltration is 0.05-0.5μm.

4. The method for preparing anhydrous lithium chloride using salt lake brine with a low magnesium-to-lithium ratio according to claim 3, characterized in that: Step 1) The turbidity of the primary refined brine is ≤1NTU, and the total organic carbon is 8-30mg·L -1 .

5. The method for preparing anhydrous lithium chloride using salt lake brine with a low magnesium-to-lithium ratio according to claim 4, characterized in that: Step 2) The nanofiltration membrane device is a three-stage or four-stage nanofiltration membrane device, which is connected in series, wherein the operating pressure of the first stage nanofiltration is 7.5-8.0 MPa, the operating pressure of the second stage nanofiltration is 5.0-5.4 MPa, and the operating pressures of the third and fourth stage nanofiltration are independently 3.8-4.0 MPa.

6. The method for preparing anhydrous lithium chloride using salt lake brine with a low magnesium-to-lithium ratio according to claim 4 or 5, characterized in that: Step 2) The concentration of magnesium ions in the secondary refined brine is ≤50 mg·L -1 .

7. The method for preparing anhydrous lithium chloride using salt lake brine with a low magnesium-to-lithium ratio according to claim 6, characterized in that: Step 3) The concentration of magnesium ions in the demagnesized brine is ≤1 mg·L -1 .

8. The method for preparing anhydrous lithium chloride using salt lake brine with a low magnesium-to-lithium ratio according to claim 7, characterized in that: Step 4) The alkaline solution is a sodium hydroxide solution, the mass fraction of the alkaline solution is 10-15%, the pH value of the mixed solution is ≥12, and the concentration of the dilute lithium chloride solution is 1-3 g·L -1 , the concentration of lithium ions in the lithium chloride solution is ≥20g / L.

9. The method for preparing anhydrous lithium chloride using salt lake brine with a low magnesium-to-lithium ratio according to claim 7 or 8, characterized in that: Step 4) The extraction solvent used in the extraction process is composed of an extractant, a co-extractant and a diluent, wherein the extractant is a β-diketone solvent, the co-extractant is composed of an organic phosphine and a water-insoluble ketone, and the diluent is an alkane and / or an aromatic hydrocarbon; In the extraction solvent, the mass ratio of the extractant to the synergistic extractant is 1:0.5-1, and the total mass of the extractant and the synergistic extractant is 25-30% of the mass of the extraction solvent; In the synergistic extractant, the mass ratio of organic phosphine to water-insoluble ketone is 1:2-4; When the diluent is a mixture of alkanes and aromatics, the mass ratio of alkanes to aromatics is 1:0.5-1.

5.

10. The method for preparing anhydrous lithium chloride using salt lake brine with a low magnesium-to-lithium ratio according to claim 9, characterized in that: Step 4) The extraction operation is a multi-stage countercurrent extraction, wherein the extraction section is 3 to 4 stages, the washing section is 2 to 3 stages, and the stripping section is 2 to 3 stages; The stripping agent is a strong acid, and the concentration of the strong acid is 2 to 6 mol / L.

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