Method for extracting and preparing lithium carbonate from low-concentration lithium solution

Abstract

The invention belongs to the technical field of lithium recovery, and particularly relates to a method for extracting and preparing lithium carbonate from a low-concentration lithium solution, which comprises the following steps: 1) extraction: extracting lithium ions in a water phase by using an extraction organic phase to obtain a loaded organic phase and raffinate; 2) back extraction: back-extracting the loaded organic phase by using a back-extraction water phase, and introducing CO2 gas in the back-extraction process, so that lithium ions are transferred from the loaded organic phase to the back-extraction water phase and are crystallized at the same time, and then carrying out phase separation to obtain a lithium carbonate solid; and 3) post-treatment: washing and drying the lithium carbonate solid to obtain the electronic-grade lithium carbonate ultrafine powder. According to the method, lithium-sodium separation and lithium enrichment are effectively realized by controlling extraction and back extraction conditions, meanwhile, a lithium carbonate preparation process and a back extraction process are synchronously carried out, the grain diameter of lithium carbonate is effectively regulated and controlled, a lithium carbonate product with low impurity content and fine granularity is obtained, the problem that a low-concentration lithium-containing solution is difficult to recover is solved, and the method is suitable for industrial production. The method has the advantages of high efficiency, environmental protection and low cost.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium recovery, and in particular relates to a method for preparing lithium carbonate by extraction from a low-concentration lithium solution. Background Art

[0002] Lithium is widely used in heat-resistant glass, ceramics, lithium grease lubricants, flux additives for iron, steel and aluminum production, new energy battery materials and other fields, especially in the field of new energy battery materials, which is growing year by year. At present, lithium raw materials include lithium ore, salt lake brine, geothermal springs and secondary lithium resources. Regardless of the raw material, most of them still use sodium carbonate lithium precipitation process to obtain lithium carbonate products. Since lithium carbonate has a certain solubility, the solution after precipitation still contains a certain amount of lithium (Li: 0.1~5g / L). Moreover, the solution contains a large amount of sodium and other impurities such as calcium and magnesium. The solution is alkaline, which makes it difficult to recover lithium in the solution. At present, efficient recovery of lithium from low-concentration lithium solutions has become a research hotspot.

[0003] At present, the main methods for enriching and recovering lithium from low-concentration lithium solutions and preparing lithium carbonate include adsorption, precipitation, extraction, and the like. Among them, the general process of the adsorption method is as follows: an adsorbent is used to adsorb a lithium-containing solution multiple times, and the lithium-containing acid solution obtained by multiple acid desorption is returned to the front end of the system. Therefore, the adsorption method requires multiple adsorption and desorption, and the steps are cumbersome. The precipitation method is a mature process, which mainly involves acidification and decarbonization of the lithium-containing solution, evaporation concentration, and lithium carbonate precipitation, and then continues to be used to precipitate lithium to prepare lithium carbonate, but this method consumes a lot of steam, requires a lot of raw materials, and has a complicated process. The extraction method is a method such as the method disclosed in the invention with application number 202010750006.6: an extraction phase is obtained by extraction from a higher concentration lithium-containing solution, and lithium carbonate is obtained by carbonic acid stripping and heating to above 50°C. The lithium extraction rate of this method is only 80%, and the purity of the obtained lithium carbonate is not high, and the particle size is relatively coarse, so battery-grade lithium carbonate cannot be directly obtained. Therefore, in order to shorten the process, reduce energy consumption and save costs, it is still necessary to develop a new method to recover lithium and directly prepare high-purity lithium carbonate through extraction. Summary of the invention

[0004] The present invention aims to provide a method for preparing lithium carbonate by extraction from a low-concentration lithium solution, so as to solve the problem that lithium resources in a low-concentration lithium-containing solution are difficult to enrich and recover.

[0005] In order to achieve the above object, the scheme of the present invention is: a method for extracting and preparing lithium carbonate from a low-concentration lithium solution, comprising the following steps:

[0006] S1, extraction: using an extraction organic phase to extract lithium ions in an aqueous phase to obtain a loaded organic phase and a raffinate; wherein the extraction organic phase comprises an extractant, a modifier and a diluent, and the extractant is a diketone extractant;

[0007] S2, stripping: using stripping water to strip the loaded organic phase, and introducing CO2 gas during the stripping process, so that lithium ions are transferred from the loaded organic phase to the stripping water phase and crystallized at the same time, and then phase separated to obtain lithium carbonate solid; wherein the stripping water phase includes a stripping agent and a surfactant;

[0008] S3. Post-treatment: After washing and drying the lithium carbonate solid, electronic grade lithium carbonate ultrafine powder is obtained.

[0009] Optionally, in step S1, the concentration of the extractant is 5-60 vol%, the concentration of the modifier is 0-30 vol%, and the concentration of the modifier is not zero.

[0010] Optionally, in step S1, the extractant includes at least one of β-diketone, benzoyltrifluoroacetone and nonyltrifluoroacetone, and the modifier includes at least two of tributyl phosphate, dibutyl phosphate, isooctyl alcohol, tridecanol, diisobutyl ketone, methyl isobutyl ketone, acetophenone and 2-heptanone.

[0011] Optionally, in step S1, the volume ratio of the extracted organic phase to the aqueous phase is 1 to 5:1, and the pH value during the extraction process is 12.5 to 14.0.

[0012] Optionally, in step S1, the lithium ion concentration in the aqueous phase is 0.1 to 5 g / L, and the lithium ion concentration in the loaded organic phase is 0.1 to 25 g / L.

[0013] Optionally, in step S2, the concentration of the stripping agent is 10-60 g / L, and the concentration of the surfactant is 400-600 ppm.

[0014] Optionally, in step S2, the stripping agent includes at least one of lithium carbonate and lithium bicarbonate, and the surfactant includes at least one of ethylene glycol, butanediol, pentanediol and 2-hexyl-1,3-hexanediol.

[0015] Optionally, in step S2, the volume ratio of the loaded organic phase to the stripping aqueous phase is 1 to 10:1, and the stripping time is 3 to 30 min.

[0016] Optionally, there is a washing step between step S1 and step S2: washing the loaded organic phase with washing water.

[0017] Optionally, in the washing step, the volume ratio of the loaded organic phase to the washing water is 1 to 3:1, and the pH value during the washing process is 10.5 to 12.0.

[0018] The working principle and beneficial effects of this scheme are as follows: This scheme first extracts lithium from a low-concentration lithium-containing solution by extraction to obtain an organic phase loaded with lithium containing a specific mass fraction after enrichment, fully mixes the loaded organic phase with the stripping water phase and introduces CO2 gas, and controls the stripping conditions so that the stripping process of lithium and the crystallization process of lithium carbonate proceed synchronously, so that the formation and growth of lithium carbonate nuclei are confined to the ultrafine droplets formed during the stripping process, thereby achieving effective control of the crystal form, growth rate and grain size. After stripping, the lithium carbonate solid is separated and washed and dried to obtain electronic grade lithium carbonate ultrafine powder. Therefore, this scheme provides an efficient, environmentally friendly, and low-cost method for preparing lithium carbonate from a low-concentration lithium solution. By controlling the extraction and stripping conditions, lithium-sodium separation and lithium enrichment are effectively achieved. At the same time, the lithium carbonate preparation process and the stripping process are carried out simultaneously. The ultrafine droplets formed during the stripping process can limit the growth of sodium carbonate crystal nuclei, thereby achieving effective regulation of the diameter of lithium carbonate grains. The obtained lithium carbonate has the characteristics of low impurity content, fine particle size and good controllability, narrow particle size distribution range, and good product crystallinity and morphology. In this way, this scheme solves the current industrial problem that a large amount of low-concentration lithium-containing wash water and low-concentration lithium in lithium precipitation mother liquor are difficult to recover, as well as the problems of poor lithium-sodium separation effect, low lithium recovery rate, and serious lithium loss in the traditional process of lithium precipitation using sodium carbonate, and has the advantages of stable product quality, high production efficiency, and low cost.

[0019] In summary, the advantages of this solution are:

[0020] 1. High-purity ultrafine lithium carbonate solid particles can be directly prepared through extraction and stripping, with short production process and high efficiency.

[0021] 2. The lithium in the low-concentration lithium solution is enriched and recovered through extraction technology. At the same time, it has the characteristics of complete lithium and sodium separation, low impurity content in the product and high lithium recovery rate.

[0022] 3. The crystallization process of lithium carbonate is completed simultaneously in the stripping process. By controlling the extraction and stripping conditions, the stripping water phase can be broken into countless independent and dispersed small droplets. The mass transfer effect between the droplets is greatly weakened, and the growth of lithium carbonate grains is restricted in ultrafine droplets (stripping water phase), thereby achieving effective control of the product crystal form, growth rate and grain diameter. The product particle size can be adjusted to micron, submicron or even nanometer level as needed, and the particle size distribution range is narrow.

[0023] 4. By controlling the appropriate stripping agent concentration, stripping phase ratio (volume ratio of the loaded organic phase to the stripping water phase) and metal ion concentration of the loaded organic phase, spherical or quasi-spherical lithium carbonate particles with good crystallinity can be obtained.

[0024] 5. This solution generates less waste liquid, and the washing water can be recycled after washing. The organic phase obtained after phase separation can be recycled as an extraction organic phase, and the aqueous phase can be recycled as a stripping aqueous phase, with low environmental pressure and low cost.

[0025] 6. The various parameters in this scheme are easy to control, and the product quality fluctuates little, which is very conducive to industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention is a schematic flow chart of a method for preparing lithium carbonate by extraction from a low-concentration lithium solution according to an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0028] The present invention provides a method for preparing lithium carbonate by extraction from a low-concentration lithium solution. The method is directed to a low-concentration lithium solution of 0.1 to 5 g / L. The method comprises the following steps:

[0029] S1, extraction: use the extraction organic phase to extract lithium ions in the aqueous phase to obtain a loaded organic phase and a raffinate. Wherein, the extraction organic phase includes an extractant, a modifier and a diluent; the extractant is a diketone extractant, including at least one of β-diketone, benzoyltrifluoroacetone and nonyltrifluoroacetone, and the concentration of the extractant is 5-60vol%, preferably 10-50vol%; the modifier includes at least two of tributyl phosphate, dibutyl phosphate, isooctyl alcohol, tridecanol, diisobutyl ketone, methyl isobutyl ketone, acetophenone and 2-heptanone, and the concentration of the modifier is 0-30vol%, and the concentration of the modifier is not 0, preferably 5-30vol%; the diluent is kerosene. In addition, the volume ratio of the extraction organic phase to the aqueous phase is 1-5:1, the pH value during the extraction process is 12.5-14.0, preferably 13.0-13.5, the extraction time is 2-10min, and the extraction temperature is 10-40℃. The extraction can be a single-stage extraction or a multi-stage extraction. After the extraction is completed, phase separation (phase separation time is 1 to 10 minutes) is performed to obtain a loaded organic phase and a raffinate. The lithium ion concentration in the loaded organic phase is 0.1 to 25 g / L.

[0030] S2, washing: washing the loaded organic phase with washing water, the washing water is pure water or deionized water or tap water, the volume ratio of the loaded organic phase to the washing water is 1 to 3:1, the pH value during the washing process is 10.5 to 12.0, the washing time is 2 to 10 minutes, and the washing temperature is 10 to 40°C. The washing can be a single-stage washing or a multi-stage washing. After the washing is completed, the washed loaded organic phase and the washed water are obtained by phase separation (phase separation time is 1 to 10 minutes), and the washed water can be returned to the extraction section.

[0031] S3, stripping: Use stripping water to strip the organic phase after washing, and introduce CO2 gas during the stripping process, with a CO2 gas flow rate of 0.1-0.5L / min, to achieve the transfer of lithium from the organic phase after washing to the water phase and complete the lithium carbonate crystallization process at the same time. The stripping water phase includes a stripping agent, a surfactant and water; the stripping agent includes at least one of lithium carbonate and lithium bicarbonate, and the concentration of the stripping agent is 10-60g / L; the surfactant includes at least one of ethylene glycol, butanediol, pentanediol and 2-hexyl-1,3-hexanediol, and the concentration of the surfactant is 400-600ppm. In addition, the volume ratio of the organic phase after washing to the stripping water phase is 1-10:1, the stripping time is 3-30min, and the stripping temperature is 10-40℃. After the stripping is completed, the phases are separated and then centrifuged to obtain lithium carbonate solid.

[0032] S4. Post-treatment: The lithium carbonate solid is washed with pure water and anhydrous ethanol, filtered and then dried at 80-100° C. to obtain a lithium carbonate product.

[0033] Example 1

[0034] This embodiment provides a method for extracting lithium carbonate from a low-concentration lithium solution. The process of the method is as follows: Figure 1 As shown, and carried out at room temperature, the method specifically comprises the following steps:

[0035] (1) Extraction: Prepared Li-containing + 5g / L sulfate solution (feed liquid) is the treatment object, the extraction organic phase is β-diketone-tributyl phosphate-kerosene system, and in the extraction organic phase, the concentration of β-diketone is 30vol%, and the concentration of tributyl phosphate is 10vol%. The extraction organic phase and the feed liquid (aqueous phase) are mixed in a volume ratio of 1:1, and the extraction equilibrium pH value is adjusted to 12.5 with sodium hydroxide solution. After 3-stage extraction (single-stage extraction time is 5min), phase separation is 2min, and the loaded organic phase is collected. The lithium extraction rate is 99.9%.

[0036] (2) Washing: Use pure water to wash the loaded organic phase, the volume ratio of the loaded organic phase to pure water is 2:1, and the washing equilibrium pH value is adjusted to 11.0 with sodium hydroxide solution. After two-stage washing (single-stage washing time is 3 minutes), the phases are separated for 1 minute to obtain the washed loaded organic phase. The impurity elution rate is 99.9%, and there is no lithium loss.

[0037] (3) Stripping: Use 30g / L lithium carbonate solution (containing 500ppm of ethylene glycol) to strip the washed loaded organic phase, and introduce CO2 gas during the stripping process, and the CO2 gas flow rate is 0.3L / min. The volume ratio of the washed loaded organic phase to the lithium carbonate solution is 4:1, the stripping stirring speed is 1000rpm, and the stripping time is 3min. After 3-stage stripping (single-stage stripping time is 3min), centrifugation is performed to obtain lithium carbonate precipitate. The lithium stripping rate is 99.9%, and the lithium stripped into the water phase is almost completely precipitated, with a precipitation rate greater than 99.9%.

[0038] (4) Post-treatment: The lithium carbonate precipitate was washed twice with pure water and once with anhydrous ethanol, filtered and dried at 80°C. The obtained lithium carbonate crystal was cubic, with a growth rate of 0.376 g / min, an average particle size of 1.5 μm, a lithium carbonate content of 99.7%, and Na + The content is 0.015%, Mg + The content is 0.008%, Ca 2+ Content is 0.002%, SO4 2- The content is 0.05%, which meets the requirements of YS / T582-2013 "Battery Grade Lithium Carbonate" and is battery grade lithium carbonate.

[0039] Example 2

[0040] This embodiment provides a method for extracting and preparing lithium carbonate from a low-concentration lithium solution. The method is carried out at room temperature and specifically comprises the following steps:

[0041] (1) Extraction: Based on the Li content of a certain factory + 3.5g / L lithium precipitation mother liquor (feed liquid) is the treatment object, the extraction organic phase is benzoyl trifluoroacetone-dibutyl phosphate-hexanophenone-kerosene system, and in the extraction organic phase, the concentration of benzoyl trifluoroacetone is 40vol%, the concentration of dibutyl phosphate is 5vol%, and the concentration of hexanophenone is 15vol%. The extraction organic phase and the feed liquid (aqueous phase) are mixed in a volume ratio of 2:1, and the extraction equilibrium pH value is adjusted to 13.0 with sodium hydroxide solution. After 4-stage extraction (single-stage extraction time is 5min), phase separation is 2min, and the loaded organic phase is collected. The lithium extraction rate is 99.8%.

[0042] (2) Washing: Use pure water to wash the loaded organic phase, the volume ratio of the loaded organic phase to pure water is 1:1, and the washing equilibrium pH value is adjusted to 10.5 with sodium hydroxide solution. After one stage of washing (single stage washing time is 3 minutes), the phases are separated for 1 minute to obtain the washed loaded organic phase. The impurity elution rate is 99.9%, and there is no lithium loss.

[0043] (3) Stripping: Use 20g / L lithium carbonate solution (containing 400ppm of 2-hexyl-1,3-hexanediol) to strip the washed loaded organic phase, and introduce CO2 gas during the stripping process, and the CO2 gas flow rate is 0.5L / min. The volume ratio of the washed loaded organic phase to the lithium carbonate solution is 3:1, the stripping stirring speed is 1000rpm, and the stripping time is 3min. After 4 stages of stripping (single-stage stripping time is 3min), the same stripping water phase is used for 4 cycles of enrichment and then centrifuged to obtain lithium carbonate precipitate. The lithium stripping rate is 99.4%, and the lithium that enters the water phase through stripping is almost completely precipitated, with a precipitation rate greater than 99.7%.

[0044] (4) Post-treatment: The lithium carbonate precipitate was washed twice with pure water and once with anhydrous ethanol, filtered and dried at 80°C to obtain lithium carbonate with an average particle size of 2.5 μm and a lithium carbonate content of 99.5%. + The content is 0.023%, Mg + The content is 0.007%, Ca 2+ Content is 0.001%, SO4 2- The content is 0.06%, which meets the requirements of YS / T582-2013 "Battery Grade Lithium Carbonate" and is battery grade lithium carbonate.

[0045] Example 3

[0046] This embodiment provides a method for extracting and preparing lithium carbonate from a low-concentration lithium solution. The method is carried out at room temperature and specifically comprises the following steps:

[0047] (1) Extraction: Based on the Li content of a certain factory + 0.1g / L lithium precipitation washing water (feed liquid) is the treatment object, the extraction organic phase is β-diketone-tridecanol-methyl isobutyl ketone-diisobutyl ketone-kerosene system, and in the extraction organic phase, the concentration of β-diketone is 20vol%, the concentration of tridecanol is 15vol%, the concentration of methyl isobutyl ketone is 12vol%, and the concentration of diisobutyl ketone is 3vol%. The extraction organic phase and the feed liquid (aqueous phase) are mixed in a volume ratio of 4:1, and the extraction equilibrium pH value is adjusted to 13.5 with sodium hydroxide solution. After two-stage extraction (single-stage extraction time is 5min), phase separation is 2min, and the loaded organic phase is collected. The lithium extraction rate is 99.8%.

[0048] (2) Washing: Use pure water to wash the loaded organic phase, the volume ratio of the loaded organic phase to pure water is 3:1, and the washing equilibrium pH value is adjusted to 11.5 with sodium hydroxide solution. After 3-stage washing (single-stage washing time is 3 minutes), the phases are separated for 1 minute to obtain the washed loaded organic phase. The impurity elution rate is 99.8%, and there is no lithium loss.

[0049] (3) Stripping: Use 45g / L lithium bicarbonate solution (containing 450ppm of pentanediol) to strip the washed organic phase, and introduce CO2 gas during the stripping process, and the CO2 gas flow rate is 0.4L / min. The volume ratio of the washed organic phase to the lithium bicarbonate solution is 8:1, the stripping stirring speed is 1000rpm, and the stripping time is 3min. After 4 levels of stripping (single-stage stripping time is 3min), the same stripping water phase is used for multiple cycles of enrichment until crystals are precipitated and centrifuged to obtain lithium carbonate precipitation. The lithium stripping rate is 99.8%, and the lithium that enters the water phase through stripping is almost completely precipitated, with a precipitation rate greater than 99.3%.

[0050] (4) Post-treatment: The lithium carbonate precipitate was washed twice with pure water and once with anhydrous ethanol, filtered and dried at 80°C to obtain lithium carbonate with an average particle size of 3.1 μm and a lithium carbonate content of 99.8%. + The content is 0.035%, Mg + The content is 0.005%, Ca 2+ Content is 0.003%, SO4 2- The content is 0.06%, which meets the requirements of YS / T582-2013 "Battery Grade Lithium Carbonate" and is battery grade lithium carbonate.

[0051] Example 4

[0052] This embodiment provides a method for extracting and preparing lithium carbonate from a low-concentration lithium solution. The method is carried out at room temperature and specifically comprises the following steps:

[0053] (1) Extraction: Prepared Li-containing + The 2.8g / L lithium-containing solution (feed liquid) is the treatment object, the extraction organic phase is a nonyltrifluoroacetone-isooctanol-2-heptanone-kerosene system, and in the extraction organic phase, the concentration of nonyltrifluoroacetone is 35vol%, the concentration of isooctyl alcohol is 15vol%, and the concentration of 2-heptanone is 15vol%. The extraction organic phase and the feed liquid (aqueous phase) are mixed in a volume ratio of 1.8:1, and the extraction equilibrium pH value is adjusted to 14.0 with sodium hydroxide solution. After 3-stage extraction (single-stage extraction time is 5min), phase separation is 2min, and the loaded organic phase is collected. The lithium extraction rate is 99.7%.

[0054] (2) Washing: The loaded organic phase was washed with deionized water, the volume ratio of the loaded organic phase to pure water was 2.5:1, and the washing equilibrium pH value was adjusted to 11.1 with sodium hydroxide solution. After two-stage washing (single-stage washing time was 3 minutes), the phases were separated for 1 minute to obtain the washed loaded organic phase, the impurity elution rate was 99.8%, and no lithium was lost. In addition, part of the washed water was refluxed to the extraction section.

[0055] (3) Stripping: Use 55g / L lithium bicarbonate solution (containing 550ppm of butanediol) to strip the washed loaded organic phase, and introduce CO2 gas during the stripping process, and the CO2 gas flow rate is 0.2L / min. The volume ratio of the washed loaded organic phase to the lithium bicarbonate solution is 5:1, the stripping stirring speed is 1000rpm, and the stripping time is 3min. After 3 levels of stripping (single-stage stripping time is 3min), use the same stripping water phase to circulate and enrich for multiple cycles until crystals are precipitated and then centrifuged to obtain lithium carbonate precipitate. The lithium stripping rate is 99.5%, and the lithium that enters the water phase through stripping is almost completely precipitated, with a precipitation rate greater than 99.8%.

[0056] (4) Post-treatment: The lithium carbonate precipitate was washed twice with pure water and once with anhydrous ethanol, filtered and dried at 80°C to obtain lithium carbonate with an average particle size of 1.9 μm and a lithium carbonate content of 99.6%. + The content is 0.019%, Mg + The content is 0.006%, Ca 2+ Content is 0.001%, SO4 2- The content is 0.05%, which meets the requirements of YS / T582-2013 "Battery Grade Lithium Carbonate" and is battery grade lithium carbonate.

[0057] Example 5

[0058] This embodiment provides a method for extracting and preparing lithium carbonate from a low-concentration lithium solution. The method is carried out at room temperature and specifically comprises the following steps:

[0059] (1) Extraction: Prepared Li-containing + The 1.2 g / L lithium-containing solution (feed liquid) is the treatment object, the extraction organic phase is a β-diketone-isooctanol-tridecanol-hexanophenone-kerosene system, and in the extraction organic phase, the concentration of β-diketone is 43 vol%, the concentration of isooctyl alcohol is 25 vol%, the concentration of tridecanol is 15 vol%, and the concentration of hexanophenone is 5 vol%. The extraction organic phase and the feed liquid (aqueous phase) are mixed in a volume ratio of 1.2:1, and the extraction equilibrium pH value is adjusted to 13.5 with sodium hydroxide solution. After 5-stage extraction (single-stage extraction time is 5 min), the phase is separated for 2 min, and the loaded organic phase is collected. The lithium extraction rate is 99.9%.

[0060] (2) Washing: The loaded organic phase was washed with pure water, the volume ratio of the loaded organic phase to pure water was 1.2:1, and the washing equilibrium pH value was adjusted to 10.6 with sodium hydroxide solution. After two-stage washing (single-stage washing time was 3 minutes), the phases were separated for 1 minute to obtain the washed loaded organic phase, the impurity elution rate was 99.8%, and no lithium was lost. In addition, all the washed water was refluxed to the extraction section.

[0061] (3) Stripping: Use 10g / L lithium bicarbonate solution (containing 420ppm of ethylene glycol) to strip the washed loaded organic phase, and introduce CO2 gas during the stripping process, and the CO2 gas flow rate is 0.1L / min. The volume ratio of the washed loaded organic phase to the lithium bicarbonate solution is 4:1, the stripping stirring speed is 1000rpm, and the stripping time is 3min. After 2-stage stripping (single-stage stripping time is 3min), the same stripping water phase is used for multiple cycles of enrichment until crystals are precipitated and then centrifuged to obtain lithium carbonate precipitate. The lithium stripping rate is 99.7%, and the lithium that enters the water phase through stripping is almost completely precipitated, with a precipitation rate greater than 99.5%.

[0062] (4) Post-treatment: The lithium carbonate precipitate was washed twice with pure water and once with anhydrous ethanol, filtered and dried at 80°C to obtain lithium carbonate with an average particle size of 1.6 μm and a lithium carbonate content of 99.5%. + The content is 0.017%, Mg + The content is 0.005%, Ca 2+ Content is 0.004%, SO4 2- The content is 0.04%, which meets the requirements of YS / T582-2013 "Battery Grade Lithium Carbonate" and is battery grade lithium carbonate.

[0063] Comparative Example 1

[0064] This comparative example is basically the same as Example 1, except that the extraction equilibrium pH value in step (1) of this comparative example is 9.5, and the rest is the same. In this comparative example, the components of the raffinate were analyzed, and the lithium extraction rate was only 85%. The components of the obtained lithium carbonate were analyzed, and the Na + The content is 0.016%, Mg + The content is 0.02%, Ca 2+ Content is 0.008%, SO4 2- Compared with Example 1, the lithium extraction rate in this comparative example is lower, and the Mg content in lithium carbonate is 0.08%. + As the content increases, the impurity content increases.

[0065] Comparative Example 2

[0066] This comparative example is basically the same as Example 1, except that the extraction equilibrium pH value in step (1) of this comparative example is 15, and the rest is the same. In this comparative example, the obtained lithium carbonate was analyzed for components, and the Na + The content is 0.051%, Mg + The content is 0.09%, Ca 2+ Content is 0.008%, SO4 2- Compared with Example 1, the content of Na in the lithium carbonate in this comparative example is 0.1%. + As the content increases, the impurity content increases.

[0067] Comparative Example 3

[0068] This comparative example is basically the same as Example 1, except that the organic phase for extraction in step (1) of this comparative example is a β-diketone-kerosene system, i.e., no modifier is added, and the rest is the same. In this comparative example, the extraction rate of lithium is only 50%, and a third phase appears in the organic phase during the extraction process, and there is a sign of stratification, which is not convenient for continuous production.

[0069] Comparative Example 4

[0070] This comparative example is basically the same as Example 1, except that the washing equilibrium pH value in step (2) of this comparative example is 7.5, and the rest is the same. In this comparative example, the obtained lithium carbonate was analyzed for components, and the Na + The content is 0.23%, Mg + Compared with Example 1, the content of Na in the lithium carbonate in this comparative example is 0.03%. + Mg + The contents increased and the impurity content increased.

[0071] Comparative Example 5

[0072] This comparative example is basically the same as Example 1, except that the washing equilibrium pH value in step (2) of this comparative example is 13, and the rest is the same. In this comparative example, the composition of the water after washing is analyzed, and the lithium loss rate is 10.54%.

[0073] Comparative Example 6

[0074] This comparative example is basically the same as Example 1, except that: in step (3) of this comparative example, ethylene glycol is not added to the lithium carbonate solution, that is, no surfactant is used. The lithium carbonate crystal obtained in this comparative example is an orthorhombic crystal, with a growth rate of 0.998g / min and an average particle size of 16.8μm, which does not meet the requirements of YS / T582-2013 "Battery Grade Lithium Carbonate". This comparative example shows that the use of a surfactant helps to reduce the growth rate and reduce the particle size. Normally, if you want to control the particle size at a smaller level, you need to increase the stirring speed. When using a surfactant, the speed during stripping can be appropriately reduced and the same effect can be achieved, and the corresponding energy consumption is reduced when the speed is reduced.

[0075] Comparative Example 7

[0076] This comparative example is basically the same as Example 1, except that in step (3) of this comparative example, the volume ratio of the washed loaded organic phase to the lithium carbonate solution is 15:1, and the rest is the same. The average particle size of the lithium carbonate obtained in this comparative example is 29.7 μm, which does not meet the requirements of YS / T582-2013 "Battery Grade Lithium Carbonate". This comparative example shows that an appropriate stripping ratio helps to control the particle size of the finished product within an ideal level.

[0077] Comparative Example 8

[0078] This comparative example is basically the same as Example 3, except that: in step (1) of this comparative example, the extraction organic phase is a β-diketone-trioctyl / hexylphosphine oxide Cyanex923-kerosene system, the concentration of β-diketone is 20 vol%, the concentration of trioctyl / hexylphosphine oxide Cyanex923 is 10 vol%, and the rest is the same. In this comparative example, the lithium extraction rate is only 70%, and the extraction phase separation time is 15 min, the back extraction phase separation is emulsified, and the back extraction phase separation time is 20 min. This comparative example shows that the β-diketone-trioctyl / hexylphosphine oxide Cyanex923-kerosene system has a low lithium extraction rate for a 0.1 g / L lithium content solution, and the phase separation time is too long, it is easy to emulsify, and the lithium recovery cost is high.

[0079] The above are only embodiments of the present invention. The invention is not limited to the fields involved in this implementation case. The common sense such as the known specific structures and characteristics in the scheme is not described in detail here. The ordinary technicians in the relevant field know all the common technical knowledge in the technical field to which the invention belongs before the application date or priority date, can obtain all the existing technologies in the field, and have the ability to apply the conventional experimental means before that date. The ordinary technicians in the relevant field can improve and implement this scheme in combination with their own abilities under the enlightenment given by this application. Some typical known structures or known methods should not become obstacles for ordinary technicians in the relevant field to implement this application. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several deformations and improvements can be made, which should also be regarded as the protection scope of the present invention, which will not affect the effect of the implementation of the present invention and the practicality of the present invention. The protection scope required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to explain the content of the claims.

Claims

1. A method for extracting lithium carbonate from a low-concentration lithium solution, characterized in that: The following steps are involved: S1, extraction: using an extraction organic phase to extract lithium ions in an aqueous phase to obtain a loaded organic phase and a raffinate; wherein the extraction organic phase comprises an extractant, a modifier and a diluent, and the extractant is a diketone extractant; S2, stripping: using stripping water to strip the loaded organic phase, and introducing CO2 gas during the stripping process, so that lithium ions are transferred from the loaded organic phase to the stripping water phase and crystallized at the same time, and then phase separated to obtain lithium carbonate solid; wherein the stripping water phase includes a stripping agent and a surfactant; S3. Post-treatment: After washing and drying the lithium carbonate solid, electronic grade lithium carbonate ultrafine powder is obtained.

2. The method for preparing lithium carbonate by extraction from a low-concentration lithium solution according to claim 1, characterized in that: In step S1, the concentration of the extractant is 5-60 vol%, the concentration of the modifier is 0-30 vol%, and the concentration of the modifier is not zero.

3. The method for preparing lithium carbonate by extraction from a low-concentration lithium solution according to claim 2, characterized in that: In step S1, the extractant includes at least one of β-diketone, benzoyltrifluoroacetone and nonyltrifluoroacetone, and the modifier includes at least two of tributyl phosphate, dibutyl phosphate, isooctyl alcohol, tridecanol, diisobutyl ketone, methyl isobutyl ketone, acetophenone and 2-heptanone.

4. The method for preparing lithium carbonate by extraction from a low-concentration lithium solution according to claim 1, characterized in that: In step S1, the volume ratio of the extracted organic phase to the aqueous phase is 1 to 5:1, and the pH value during the extraction process is 12.5 to 14.

0.

5. The method for preparing lithium carbonate by extraction from a low-concentration lithium solution according to claim 1, characterized in that: In step S1, the lithium ion concentration in the aqueous phase is 0.1-5 g / L, and the lithium ion concentration in the loaded organic phase is 0.1-25 g / L.

6. The method for preparing lithium carbonate by extraction from a low-concentration lithium solution according to claim 1, characterized in that: In step S2, the concentration of the stripping agent is 10 to 60 g / L, and the concentration of the surfactant is 400 to 600 ppm.

7. The method for preparing lithium carbonate by extraction from a low-concentration lithium solution according to claim 6, characterized in that: In step S2, the stripping agent includes at least one of lithium carbonate and lithium bicarbonate, and the surfactant includes at least one of ethylene glycol, butanediol, pentanediol and 2-hexyl-1,3-hexanediol.

8. The method for preparing lithium carbonate by extraction from a low-concentration lithium solution according to claim 1, characterized in that: In step S2, the volume ratio of the loaded organic phase to the stripping aqueous phase is 1 to 10:1, and the stripping time is 3 to 30 minutes.

9. The method for preparing lithium carbonate by extraction from a low-concentration lithium solution according to claim 1, characterized in that: There is also a washing step between step S1 and step S2: washing the loaded organic phase with washing water.

10. The method for preparing lithium carbonate by extraction from a low-concentration lithium solution according to claim 9, characterized in that: In the washing step, the volume ratio of the loaded organic phase to the washing water is 1 to 3:1, and the pH value during the washing process is 10.5 to 12.0.

Images