Process for the production of lithium sulfate monohydrate in ponds

Abstract

Process for obtaining lithium sulfate that involves generating salts from sulfated brines to be subsequently processed and generate finished products such as lithium carbonate and / or lithium hydroxide monohydrate. The process includes optimizing the precipitation of Li2SO4*H2O in ponds, for which it includes adding magnesium chloride or calcium chloride to the natural brine, decreasing the SO4 / Mg ratio, avoiding the precipitation of other sulfated salts that later concentrate together with the lithium sulfate in a flotation stage, minimizing the performance of the collector in the plant and increasing the impurities in the final product.

Description

[0001] PRODUCTION PROCESS OF LITHIUM SULFATE MONOHYDRATE IN PONDS PREVIOUS ARTE

[0002] Lithium production in salt flats generally considers two deposits, one where the predominant anion is Chloride and another that has a large amount of Sulfate, thus affecting the required production and / or refining process.

[0003] The production of Li2C3 and subsequently LiOH hO is carried out from the first deposit, which has a low sulfate concentration. However, there was no technically viable alternative for processing the brines with high sulfate content.

[0004] Previously, this high-sulfate brine was used for potassium salt production and then reinjected, without yielding lithium products despite its high content. Currently, all the brine produces both potassium and lithium.

[0005] US Patent 20140301922 describes a method comprising supplying a lithium chloride-containing solution to a silica removal stage to produce a silica-free lithium chloride-containing solution; wherein the silica removal stage can remove at least a portion of the silica present in the lithium chloride-containing stream. The method includes the step of supplying said silica-free lithium chloride-containing solution to a lithium chloride capture step, wherein the lithium chloride capture step is operable to capture lithium chloride from the silica-free lithium chloride-containing stream. The lithium chloride is recovered from the lithium capture stage to produce a lithium chloride-rich stream.The method also includes contacting the lithium chloride-rich current with a base and adding a carbonate so that at least some of the calcium, magnesium, manganese, or zinc present precipitates as a solid.

[0006] The method involves adding a carbonate so that at least some of the calcium, magnesium, manganese, or zinc present precipitates as a solid; separating the precipitate from the lithium chloride-rich stream to produce a precipitated solid residue and a purified lithium chloride-rich stream, said purified lithium chloride-rich stream having a lower concentration of at least one of the following elements: calcium, magnesium, manganese, or zinc.

[0007] This document describes precipitating magnesium and calcium, but through the addition of a carbonate and not a chloride as the object of the invention.

[0008] Document EP3589763 describes a method for producing high-purity lithium hydroxide for use in batteries and / or accumulators from lithium-containing ore and / or minerals using a chlor-alkali process, which increases the recovery rate of high-purity lithium hydroxide. This is achieved by using calcination and leaching stages, extracting lithium from the lithium-containing ores and / or minerals and / or soils using one or more metal chlorides and / or a mixture of metal chlorides, and then leaching them, particularly with water, generating a lithium chloride solution. This solution is then subjected to a purification stage to remove impurities, particularly cations such as sodium, potassium, calcium, magnesium, and / or iron, which are removed from the lithium chloride solution, yielding high-purity lithium hydroxide.

[0009] The method stipulates that one or more metal chlorides or the mixture of metal chlorides used in the calcination and leaching stage comprise at least potassium chloride and / or lithium chloride and / or magnesium chloride and / or calcium chloride.

[0010] This document discloses the use of calcium chloride or magnesium chloride, but to a leaching solution from the processing of pegmatites and not to the brine prior to the precipitation of lithium sulfate.

[0011] US patent 4723962 describes a process for recovering lithium sulfate monohydrate from a complex feed brine containing chloride and sulfate, comprising:

[0012] (a) cooling the complex feed brine in a first stage to approximately 10°C but not less than approximately 4 o C to precipitate the potassium chloride recovered from the brine;

[0013] (b) further cooling said cooled, potassium chloride-reduced brine recovered from step (a) in a second step in the presence of added water, to approximately 0 o (c) to precipitate the Epsom salt recovered from the brine; (c) evaporatively concentrate the cooled brine recovered from step (b) until the lithium content of the brine is at least approximately 90% by weight of the lithium saturation concentration of the brine;

[0014] (d) recycling a portion of the evaporatively concentrated, cooled brine to mix with the complex feed brine to produce a potassium-to-lithium molar ratio in the relatively concentrated cooled brine below approximately 0.35;

[0015] (e) cooling a larger quantity of the evaporatively concentrated brine in a third stage to approximately 0 o C to precipitate carnallite;

[0016] (f) evaporatively concentrate the cooled brine recovered from step (e) to remove water from the brine without substantially precipitating solid salts from it;

[0017] (g) adding a sufficient quantity of magnesium sulfate to the brine produced in step (f) to produce a brine suspension having a lithium sulfate molar ratio of at least approximately 0.9, and a water content of less than approximately 60% by weight and thereby precipitating the lithium sulfate monohydrate;

[0018] (h) Recover the lithium sulfate monohydrate from the brine suspension. The added magnesium sulfate is Epsom salt.

[0019] This document describes the use of magnesium sulfate to precipitate lithium sulfate, but it does not describe the concept of using magnesium or calcium chloride added to the brine prior to the precipitation of lithium sulfate and carnallite. US document 6143260 describes a process for recovering lithium carbonate from a brine containing lithium and magnesium, characterized in that it comprises:

[0020] (a) preparing a feed brine by concentrating a brine comprising lithium and magnesium ions to saturate the brine with magnesium chloride and lithium chloride and precipitate LCl.MgCl2*7H2O;

[0021] (b) adding Ca(OH)2 to the recycled mother liquor from step (e) to produce lime mother liquor;

[0022] (c) mixing the mother liquor of lime with the feed brine while maintaining a pH of 8.40 to 8.80 to precipitate magnesium ions as magnesium hydroxide and to precipitate calcium carbonate,

[0023] (d) recover the brine from step (c) and add a sufficient amount of sodium carbonate to precipitate the lithium carbonate;

[0024] (e) separating the precipitated lithium carbonate from the mother liquor; and

[0025] (f) recycle the mother liquor produced in step (e) to step (b)

[0026] The concentration of lithium ions in the feed brine is approximately 5.5 to approximately 6.5% by weight

[0027] The L1Cl.MgCl2*7H2O is recovered and processed to recover the lithium contained within it.

[0028] The pH in stage (c) is between 8.55 and 8.75.

[0029] The concentration process produces the precipitated double salt of lithium magnesium chloride heptahydrate (LiCl·MgCl₂·7H₂O), which begins to precipitate once the lithium concentration reaches approximately 4%. The lithium in these salts is recovered, for example, by suspending and washing the salts using a brine saturated with magnesium chloride but not saturated with respect to the lithium chloride salts, to produce bischofite (MgCl₂·6H₂O), which can be recovered, for example, by centrifugation, filtration, or drainage. The overall lithium yield from 6% lithium brine is 97% when the lithium values ​​are recovered from the double salt. The 3% lithium loss associated with the additional bischofite produced is offset by the improved lithium carbonate yield when using the one-step 6% lithium brine process.

[0030] This document mentions the recovery of lithium from lithium and magnesium chloride salts using brines saturated in magnesium chloride, but it does not mention or outline obtaining lithium sulfate and carnallite using magnesium chloride or calcium chloride in the brine prior to precipitating said lithium sulfate and carnallite.

[0031] Document WO2019002653 (equivalent to Chilean patent application 201902916) describes a procedure with minimal environmental impact and maximum lithium recovery for obtaining concentrated brines with minimal impurity content from brines that saturate natural salt flats and salt pans, comprising the following stages:

[0032] a) construct fractional crystallization ponds by solar evaporation;

[0033] b) fill the ponds with natural brine; c) initially pre-concentrate the natural brine to the maximum possible lithium concentration in the liquid phase without precipitating lithium-containing salts;

[0034] d) cooling the pre-concentrated brine obtained in c) ensuring maximum precipitation of salts containing the sulfate anion;

[0035] e) chemically pretreating the liquid phase of the brine separated from the salts precipitated by cooling to minimize sulfate anions in the post-cooling liquid phase;

[0036] f) finally pre-concentrate the pre-treated liquid phase to the maximum possible lithium concentration without precipitating lithium-containing salts;

[0037] g) chemically treat the liquid phase of the brine separated from the salts precipitated in step f) to minimize the concentration of magnesium, calcium, boron and sulfate in the liquid phase; and

[0038] h) Concentrate the liquid phase obtained in step g).

[0039] High purity sodium chloride is obtained in stage c) of initial pre-concentration.

[0040] The cooling stage (d) is carried out taking advantage of the low temperatures that characterize the climate where the salt flat is located, when the amount of heat that has to be extracted from the liquid phase delivered by the pre-concentration stage (c) is high, making the alternative of using refrigeration equipment that employs mechanical energy economically unfeasible. In the cooling stage (d), selected salts are separated from the group consisting of sodium sulfate, potassium chloride, potassium sulfate and their mixtures, according to the chemical composition of the brine.

[0041] In the pretreatment stage e), the use of reagents such as calcium chloride or barium chloride is minimized by significantly reducing the sulfate / lithium ratio naturally using favorable climatic conditions or mechanical crystallizers by cooling in the pre-cooling stage d).

[0042] In the pretreatment stage e), calcium sulfate is obtained from the sludge produced when calcium chloride is used as a reagent.

[0043] This document describes the use of calcium chloride in brine to obtain calcium sulfate and does not mention the production of lithium sulfate or carnallite.

[0044] The invention presents a process for generating Li₂SO₄·H₂O salts from sulfate brines for subsequent processing to produce finished products such as lithium carbonate and / or lithium hydroxide, using lithium sulfate and carnallite as raw materials. Furthermore, none of the prior art documents mention a specific procedure for obtaining lithium sulfate and carnallite that uses magnesium chloride or calcium chloride in the brine prior to precipitating said sulfate and carnallite. BRIEF DESCRIPTION OF THE FIGURES

[0045] Figure 1: represents a diagram of the prior art process for obtaining lithium carbonate L2C3.

[0046] Figure 2: represents a diagram of the current process (Previous Art) for the production of lithium products.

[0047] Figure 3: represents a diagram of the stages considered in the invention process.

[0048] DESCRIPTION OF THE INVENTION

[0049] The invention consists of a process for obtaining lithium sulfate that comprises generating salts containing lithium sulfate (Li2SO4*H2O) from sulfated brines to be subsequently processed and generate finished products such as lithium carbonate and / or lithium hydroxide monohydrate.

[0050] The process involves optimizing the precipitation of Li₂SO₄*H₂O in ponds. This is achieved by adding magnesium chloride or calcium chloride to the natural brine, decreasing the SCM / Mg ratio and preventing the precipitation of other sulfate salts that subsequently concentrate with the lithium sulfate in a flotation stage. This reduces the collector's yield at the plant and increases impurities in the final product. Initially, the process consisted of precipitating sulfate salts from the evaporation of brines high in sulfate, and then concentrating the lithium sulfate present in the salts through flotation, generating an intermediate lithium sulfate product that could be processed to produce lithium carbonate and / or lithium hydroxide.Depending on the sulfate concentration in the brine, different types of salts can be generated, such as lithium sulfate, magnesium and potassium double sulfates, and / or lithium and potassium double sulfates, which precipitate along with potassium carnallite. To maximize lithium sulfate precipitation and avoid or reduce double sulfate precipitation, the process involves using magnesium chloride in the form of bischofite to decrease the SCU / Mg ratio. The magnesium chloride is fed to the brine at a brine / magnesium chloride ratio ranging from 7:1 to 4:1. Alternatively, calcium chloride can be added to the brine at a brine / calcium chloride ratio ranging from 60:1 to 30:1 to force sulfate precipitation as calcium sulfate in the upstream ponds, thus reducing the amount of sulfate entering the carnallite and lithium sulfate ponds.Both processes decrease the precipitation of other sulfate-containing salts along with Lithium Sulfate.

[0051] Next, the salts containing lithium sulfate undergo a concentration stage in which lithium sulfate monohydrate (L₂SC₅H₂O), approximately 97% pure, and potassium chloride (KCl) are obtained. The lithium sulfate monohydrate concentrate then proceeds to a refining stage where high-purity lithium sulfate monohydrate is obtained, exceeding a certain purity. Initially, four test results are presented in which different amounts of Bischofite are added to reduce the SO₄ / Mg ratio.

[0052] a) In a 2000 mL beaker, 1000 grams of pond brine are added, followed by 247 grams of bischofite. After 30 minutes, the precipitate is separated from the supernatant, resulting in a decrease in SO4 / Mg:

[0053]

[0054] b) In a 2000 mL beaker, 1000 grams of pond brine are added, followed by 228 grams of bischofite. After 30 minutes, the precipitate is separated from the supernatant, resulting in a decrease in SO4 / Mg:

[0055]

[0056] In a 2000 mL beaker, 1000 grams of pond brine are added, followed by 209 grams of bischofite. After 30 minutes, the precipitate is separated from the supernatant, resulting in a decrease in SO4 / Mg.

[0057]

[0058] c) In a 2000 mL beaker, 1000 grams of pond brine are added, followed by 140 grams of bischofite. After 30 minutes, the precipitate is separated from the supernatant, resulting in a decrease in SO4 / Mg:

[0059]

[0060] The following are test results where Calcium Chloride is added to a solution to precipitate Calcium Sulfate and thereby reduce the SO4 / L ratio.

[0061] d) In a drum, 60 kg of brine and 1 kg of CaCl2 are added, stirred at room temperature until dissolved, and left to stand for 10 minutes to allow crystals to form.

[0062] >

[0063]

[0064] e) In a drum, 60 kg of brine and 1.8 kg of CaCl2 are added, stirred at room temperature until dissolved, and left to stand for 10 minutes to allow crystals to form.

[0065]

Claims

RECLIN DICATION IS 1. Process for obtaining lithium sulfate (Li₂SO₄*H₂O) from sulfate ponds to generate finished products such as lithium carbonate and / or lithium hydroxide monohydrate (LiOH*H₂O), which allows processing brines with high sulfate content, CHARACTERIZED in that it comprises generating lithium sulfate salts from sulfate brines by adding magnesium chloride or calcium chloride to the natural brine, decreasing the SO₄ / Mg ratio; where: a. Add magnesium chloride or calcium chloride to the sulfate brines prior to lithium sulfate precipitation to modify the SO4 / Mg ratio, reducing the co-precipitation of other sulfate salts that cause problems in subsequent stages. b. Concentrate this brine by evaporation, causing the precipitation of lithium sulfate along with potassium carnallite and other salts. c. subject the salts containing lithium sulfate to a flotation concentration stage to obtain lithium sulfate monohydrate (Li2SO4*H2O), approximately 97% pure, and potassium chloride (KCl). d. subjecting said lithium sulfate monohydrate to a refining stage where high purity lithium sulfate monohydrate, greater than 99%, is obtained.

2. Process for obtaining lithium sulfate from sulfate ponds according to claim 1, CHARACTERIZED in that it comprises that said magnesium chloride is added in the form of Bischofite to decrease the SO4 / Mg ratio.

3. Process for obtaining lithium sulfate from sulfate ponds according to claim 1, CHARACTERIZED in that said magnesium chloride is fed to the brine in a brine / calcium chloride ratio ranging from 7:1 to 4:

1.

4. Process for obtaining lithium sulfate from sulfate ponds according to claim 1, CHARACTERIZED in that said Calcium Chloride is fed to the brine in a brine / calcium chloride ratio in a proportion that varies between 60:1 and 30:1.

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