CARBONATE

FIELD OF THE INVENTION

The present invention relates to a method for recovering metal compounds from brines. Particularly, the present invention relates to a method for recovering lithium salts from brines.

BACKGROUND OF THE INVENTION

A significant number of commercial applications for lithium, minerals thereof and salts thereof are known at present, being used in various industries such as electronic, pharmaceutical, ceramic and lubricant industries, among others.

First, lithium, which chemical symbol is Li, was used in accumulation batteries due to its high electrochemical potential and because it is the lightest solid. Lithium batteries are rechargeable and are preferably used in portable computers, mobile telephones and digital cameras.

The first successful lithium batteries contained a metal lithium anode, but since lithium is a highly reactive metal its use raised serious safety concerns. Moreover, as the number of charge-discharge cycles that the battery might undergo was very low, the lifetime of the battery was short. This was due to the formation of dendrites in the anode during use, which modified the anode geometry and further incremented its reactivity.

These problems were solved with the appearance of Li-ion batteries, wherein the metal lithium anode was substituted by a carbon anode capable of intercalating lithium ions inside, thus becoming reversible. In this way lithium ions go back and forth between the carbon anode and a cathode formed by a cobalt-lithium double oxide.

However, Li-ion batteries with nanostructurated anode and based on lithium titanate nanoparticles (Li ₄ Ti ₅ 0i2) provide a better performance than Li- ion batteries with graphite anode. These new generation batteries allow to operate under high power conditions, are long-lasting, their recharge times are substantially shorter and have a great thermal stability, thus being safer.

Although Li-ion rechargeable batteries with graphite anode represented an important improvement as they are light, scarcely contaminant, have higher energy density and no memory effects in the charge-discharge cycles, they had some drawbacks, such as safety problems when the temperature exceeded 100°C, a limited battery lifetime, low charge rhythm and restricted power.

But the massive use of Lithium developed from military uses, mainly in lubricant greases, and a wide variety of industrial applications, among others the use as catalyst in the manufacture of synthetic rubber.

Lithium minerals and salts are used in the manufacture of glass and ceramics, the latter use being generalized to a greater scale. Also they are used in the manufacture of china, porcelains, sanitary appliances, glazing and enamels, and in the manufacture of glasses and containers. Particularly, the lithium mineral called spodumene is capable of supporting sudden temperature changes.

The most important commercial lithium minerals obtained from veins are: spodumene, lepidolite, ambligonite, trifilite, petalite, zinnwaldite and eucripte,

Among the industrial grade lithium chemical compounds, we can mention lithium carbonate which is mainly used in the manufacture of glasses, enamels for ceramics, and it is also a critical ingredient in the manufacture of television tubes.

Lithium hydroxide is used in the manufacture of lubricant greases of multiple uses, in obtaining metal lithium, as air purifier in ventilation systems by absorbing the CO ₂ produced in closed environments such as space shuttles and submarines, as a component of the electrolyte of accumulators used in submarines and telephone installations, as well as in power supplies for trains and telephones, and as starting material to obtain the ⁶ Li sotope.

On the other hand, lithium halides have various applications; lithium bromide is used as a catalyst in the manufacture of oriented polymers useful in the rubber industry, in the photography field, and due to its high hygroscopicity in the control of gas moisture and air conditioning, and also it is used in heat absorption pumps; lithium iodide is used in the photography field; lithium chloride is also highly hygroscopic and is used as a drying agent for air conditioning, in special welding and other fluxes, and also for obtaining metal lithium by electrolysis; and lithium fluoride is used in special welding and aluminum metallurgy.

Lithium hypochlorite is used in the sterilization of water for swimming pools as its quick solubility makes it ideal for shock ch!orination. Since it does not contain calcium, it does not harden water, is not flammable and does not produce dust; it is stable as it loses only 0.1% of available chlorine per month and it dissolves without clouding the water.

Lithium peroxide is used for obtaining oxygen and lithium borohydride and lithium hydride are used for obtaining hydrogen.

Aluminum and lithium hydride is used in organic chemical synthesis as a reducing agent of organic compounds at room temperature in ethereal solutions. In turn, lithium hydride is used to inflate life vests.

Lithium stearate is used as an additive in lubricant greases in the automobile and industrial fields. Perhaps the most significant commercial use of lithium compounds is the manufacture of greases capable of retaining their lubricant properties within a wide range of extreme temperatures, thus making them water and stain resistant .

Lithium niobate is an electrooptical material currently leading the manufacture of optical communication devices, where it has shown great applicability and capability.

On the other hand, ceramic materials made of lithium tantalate or lithium nitrate have been developed, which have become the most widely used piezoelectric materials. These materials show a piezoelectric character after an artificial polarization.

As regards metal lithium, it can be mentioned that it is used together with hydrogen in the manufacture of tritium bombs, and also as an ingredient of space rocket fuels.

Since it is the solid substance having the highest calorific capacity, it is commonly used in heat transfer applications. To this effect, it is used as coolant in atomic reactors wherein it behaves as a heat exchange fluid.

In the metallurgy of aluminum it is used in electrolytic cells, which allows lowering the power consumption of the process about 10%. Lithium- aluminum alloys show great resistance under high temperature conditions, and extra-light lithium-magnesium alloys are used mainly in the space industry. It is also a common component of some cadmium, copper and manganese alloys used in aeronautical manufacturing.

The use of lithium has become relevant in the steel industry, particularly in processes known as "continuous casting" in which liquid materials are solidified. Lithium steam prevents carbon dioxide and oxygen from forming a rust layer in the furnaces during the thermal treatment of steel. The advantage of using lithium is that its chemical properties provide a quicker and effortless operation during the molding process. Also, it is used as a cleaner and degreaser of stainless ductile steels, and as a deoxidant and purifier by extracting undesirable gases in copper castings and during the production of iron, nickel and copper alloys.

The key to obtain high purity metal lithium is to minimize the level of impurities such as sodium, calcium and magnesium in the lithium salt used to feed the electrolytic cells. There are, however, other impurities such as carbonate, sulfate and borate which, while not significantly affecting the purity of the obtained metal lithium, impair the performance of the electrochemical cell, thus increasing the carbon electrode consumption due to the oxidation of these species in the anode, resulting in the production of carbon dioxide and decreasing the efficiency of the metal production.

In the pharmacological field, the Li ⁺ ion is used in the form of its salts as a drug. It is believed that its action is based on its agonist effects on the serotoninergic function. Lithium salts stabilize altered states of mind, especially bipolar disorder, and are efficiently useful in the treatment of unipolar depression and mania. Particularly in cases of depression, lithium can be used to enhance the effect of other antidepressants. While lithium carbonate is the most prescribed salt, there are some alternatives such as citrate salt, lithium sulfate, lithium aspartate and orotic acid lithium salt.

In view of the importance of lithium and compounds thereof, it is highly desirable to have a low impurity lithium source, and an economically viable method for producing the same.

A substantial portion of the lithium available at present is recovered from brines, which also contain high levels of sodium, making the production of low sodium lithium salts difficult and expensive. Natural brines that contain lithium also have many impurities as illustrated by Table 1 below:

Table 1 : Composition of natural brines expressed by weight percent.

Brine sources of lithium include the salars in the Andes Mountains of South America which have been discovered to contain significant deposits of lithium salts; these comprise the Salar de Atacama, Chile, Salar de Uyuni, Bolivia, and Salar de Rincon, Province of Salta, Argentina.

Salars in the Andes Mountains are large, dry lakebeds where the brines are located just under a layer of crusted salt deposits. These types of deposits provide a viable source of concentrated natural brines which can potentially be processed to produce purified lithium salts provided that impurities are in such a ratio that exploitation is economically acceptable.

In these natural lithium containing brines, the impurities of the matrix, such as magnesium, calcium, sodium, sulfate and boron, must be minimized in order to obtain a lithium saline product suitable for the intended use.

Alkali metals, such as sodium, and alkali-earth metals, such as calcium and especially magnesium, must be substantially removed. The simple technical means to remove them from lithium alkali metal are not profitable. The individual applications require that these ionic impurities be reduced to maximum specific levels and a number of processes have been described to eliminate such impurities.

For example, United States Patent No. 4,207,297 describes an integrated continuous process for producing lithium hydroxide monohydrate and high purity lithium carbonate with a high average particle size, that comprises: converting technical grade impure lithium carbonate into lithium hydroxide by a basification step with a suspension of calcium hydroxide; separating the precipitated calcium carbonate of the resulting lithium hydroxide solution; dividing the resulting lithium hydroxide solution in two: a major portion and a minor portion at a volume of said major portion to said minor portion ratio from about 10:1 to about 2:1; precipitating the lithium hydroxide monohydrate from the major portion of the lithium hydroxide solution and recovering the same; introducing carbon dioxide or lithium carbonate to the minor portion of the lithium hydroxide solution for further precipitation of calcium as calcium carbonate; separating the calcium carbonate from the lithium hydroxide solution; introducing carbon dioxide to the hydroxide lithium solution to precipitate high purity lithium carbonate with high average particle size; separating said lithium carbonate from the resulting solution of diluted lithium carbonate and recycling said diluted solution of lithium carbonate to said basification step.

This process is impaired by an extremely slow filtration step, thus rendering it unsuitable for commercial practice.

US 4.980.136 discloses a process for producing lithium chloride substantially free from boron having a purity higher than 99% from a natural or waste brine of other processes that contains a sufficient amount of lithium substantially free from sulfate, comprising the steps of: contacting said brine containing lithium chloride that comprises from 2% to 7% by weight of lithium obtained by solar evaporation, by heating or any other conventional means, saturated in hydrated metal salts present in the brine and substantially devoid of free water, with an organic solution comprising from 5% to 40% by volume of a fatty alcohol that contains from 6 to 16 carbon atoms in kerosene in a volume ratio of organic solution to brine that ranges from about 1 :1 to 5:1 to extract the boron from the brine to the organic solution phase; separating said organic solution phase from said brine; evaporating the aqueous phase at a temperature higher than about 100,5°C under vacuum of about 590 mm Hg to about 760 mm Hg to crystallize lithium chloride anhydrous; and separating the lithium chloride anhydrous from the remaining aqueous phase. Optionally, this process is followed by washing and/or extraction with a low molecular weight alcohol of the resulting lithium chloride to remove the residual boron together with other contaminants present below 1% in the lithium chloride thus solubilizing the same. The alcohol solution containing lithium chloride is then filtered and evaporated to form lithium chloride crystals with a high degree of purity greater than 99.9%. The obtained anhydrous lithium chloride is particularly useful for producing lithium metal by electrolysis.

This process comprises the steps of extracting with a mixture of alcohol-kerosene solvents that are potentially economically unviable at the requested industry scales, let alone the negative impact on the environment because of the use of alcohol-kerosene as solvents.

US 5.219.550 describes a process for producing lithium carbonate having a low content of boron from a lithium containing natural brine, comprising essentially the steps of: contacting a lithium chloride containing brine substantially free from sulfate, that has a lithium content from about 2% to about 7% by weight obtained by solar evaporation or other conventional means, said brine saturated in hydrated metal salts present in the same and substantially devoid of free water, having a pH that ranges from about 1 - 2 measured when diluted with 10 volumes of water, with an organic solution comprising from about 5% to about 50% by volume of a fatty alcohol containing from 6 to 16 carbon atoms in kerosene in a volume ratio of organic solution to brine ranging from about 1:1 to 5:1 , to extract the boron present in the brine to the organic phase; separating said organic solution phase from said brine; removing magnesium and calcium from said brine by conventional means; adding sodium carbonate to precipitate lithium carbonate from said brine; and separating the resulting lithium carbonate from same. The obtained lithium carbonate is particularly useful for conversion into high purity lithium chloride for the production of lithium metal by electrolysis. This kind of multi-step process involving extraction with solvents is unsuitable at a commercial scale, while also producing a negative impact on the environment.

As can be inferred from the prior art described above, a significant research and development effort has been invested in the search for economic means of commercially exploiting lithium-containing brines at an industrial scale and to produce lithium salts such as chloride and carbonate of sufficient purity to produce high-purity lithium metal.

However, a process that allows treating a brine in an aqueous medium for obtaining high purity lithium carbonate without using extraction solvents, and easy to implement near the salars has not been disclosed. Therefore, there remained the need for improving known methods in order to attain the object.

To this end, in the PCT patent published as WO2010/006366A1 a process for recovering lithium from an impure natural or industrial brine was proposed, the process comprising adjusting the pH of a feed brine containing lithium to a value of no less than 11.3 and separating the waste solids and a solution containing lithium values. The solution may be further concentrated and treated to obtain lithium carbonate and a lithium chloride solution suitable for obtaining electrolytic grade lithium chloride.

It should be taken into account, however, that most natural lithium- bearing brines originate in internal continental deposits which lay on endorreic basins which once worked as the natural receptacle of insoluble clastic supplies and liquids of the tectono-volcanic setting. These supplies accumulated as evaporitic chemical sediments, mainly salts such as chlorides, sulfates, borates, carbonates, etc., and as insoluble clastic sediments, free silica, silicates, decomposed or crushed organic matter, soaked with interstitial brine bearing a great variety of ions. The ion concentration of these brines results from the balance between the influxes received by the basin and the water it loses as a consequence of evapotranspiration. This balance strongly depends on the weather conditions of the laying area of the basin. This is one of the reasons accounting for the fact that saline bodies have a different chemism and, therefore, a different economic potential. Among the cations present in the brines imbibing the above mentioned saline bodies, lithium is presently the most interesting one and, generally, potassium comes second in importance. Magnesium is a penalty and should be removed either by natural crystallization during a pre-concentration process, by chemical treatment or by natural crystallization during a pre- concentration process followed by chemical treatment.

In order to carry out a comparative analysts among different brines, Table 2 below shows in detail the lithium, potassium and magnesium contents and the content ratios for the main saline bodies in the Argentine Puna and the Atacama Salt Deposit.

Table 2

Compiled from the following bibliographic sources: I. Recursos minerales de la Republica Argentina - Volumen II - SEGEMAR - Buenos Aires - 1999. Value corresponding to weight percent of magnesium corrected by the Mining Department, Salta.

II. Recursos minerales de la Republica Argentina - Volumen II - SEGEMAR - Buenos Aires - 1999.

III. Dr. Daniel Ernesto Galli's files.

IV. Soriano J.M., Nicolli M.B., Abril E.G., Gomez Pera M.A. y Martinez D.E.- Geoquimica de los metales alcalinos en las salmueras del Salar del Rincon, Provincia de Salta, Republica Argentina - Correlacion Geologica, 1989, No 3: 133 - 148.

V. US Patent 2006/0115396 A1

The above Table 2 shows that while the lithium, potassium and magnesium contents in the brine imbibing the saline bodies of the listed salt deposits have a great dispersion (about 250%), the same is not true with the potassium/magnesium ratio which has a dispersion not greater than 75%, as shown in the chart of Figure .

This means that in many cases a high potassium content is accompanied by a high magnesium content. Thus, it is clear that for such cases the advantage associated with potassium vanishes if there is not a process available having low environmental impact, maximum resource recovery and reasonable cost for eliminating magnesium.

Therefore, it is necessary to have a procedure which is improved with respect to what document WO2010/006366A1 describes, in which magnesium removal has a low environmental impact, having a high lithium recovery and . a reasonable cost, and such that said procedure can be associated to a low cost procedure for purifying crude lithium carbonate as obtained with the new treatment proposed for magnesium removal.

SUMMARY OF THE INVENTION

Therefore, it is the object of the present invention a process for the recovery of lithium from a natural or industrial impure brine comprising:

(a) treating a feed brine containing lithium with Na ₂ C0 ₃ (sodium carbonate) solution in order to precipitate magnesium and separate the precipitated MgC0 ₃ (magnesium carbonate); (b) adjusting the feed brine pH treated in step (a) with NaOH (sodium hydroxide) solution up to a value not lower than 11.3 and separating the precipitated solid waste.

Additionally, the process comprises the previous step (a.0) pre- concentrating the feed brine thus increasing the Li ⁺ ion concentration up to a maximum value wherein no lithium salt crystallization occurs.

Preferably, the process comprises pre-concentration of the feed brine up to a value not lower than approximately 2,500 mg of Li ⁺ /liter.

More preferably, the process comprises pre-concentration of the feed brine up to a value ranging from approximately 2,500 mg of Li ⁺ /liter to approximately 3,000 mg of LiVliter.

Still more preferably, the process comprises pre-concentration of the feed brine up to a value not greater than approximately 5,000 mg of LiVliter.

Even more preferably, the process comprises pre-concentration of the feed brine up to a value ranging from approximately 10,000 mg of Li ⁺ /liter to approximately 15,000 mg of Li ⁺ /liter.

Optionally, step (a) of the process comprises adding a flocculant solution to the feed brine in order to facilitate the separation of precipitated solids from the pre-treated brine solution; and separating the precipitated solids from the pre-treated brine to make a solution of pre-treated brine and precipitated MgCO ₃ .

Also optionally, step (b) of the process comprises adding a flocculant solution to the brine pre-treated in step (a) in order to facilitate the separation of the precipitated solids from the treated brine solution; and separating the precipitated solids from the treated brine to make a solution of treated brine and a precipitated waste sludge.

Additionally, the process comprises the previous step (b.0) concentrating the feed brine pre-treated in step (a) thus increasing the Li ⁺ ion concentration up to a maximum value wherein no lithium salt crystallization occurs.

Preferably, the process comprises concentration of the feed brine pre- treated in step (a) up to a value not greater than approximately 80,000 mg of Li ⁺ /liter. Additionally, and if necessary, the process further comprises adjustment of Ca ²⁺ (calcium ions) concentration in the feed brine prior to treatment of step (a).

Also additionally, and if necessary, the process comprises precipitation of Ca ²⁺ by adding a Na ₂ S0 ₄ (sodium sulfate) solution or any other reagent at low temperature containing an anion to form a calcium salt that is insoluble in the brine, and does not alter the final product quality.

Preferably, the Na ₂ C0 ₃ used in step (a) is regenerated by means of a modified Solvay process.

Preferably, the NaOH is regenerated by means of a causticising process of Na ₂ CC>3 with Ca(HO) ₂ (calcium hydroxide) obtained by calcination of precipitated CaC0 ₃ (calcium carbonate) and hydration of CaO (calcium oxide) formed in said calcination.

More preferably, the Na ₂ C0 ₃ used in the causticising process is obtained by means of a modified Solvay process.

Still more preferably, the modified Solvay process comprises release of NH ₃ (ammonia) by means of a neutralization process of the NH ₄ Cl (ammonium chloride) formed in the production of NaHC0 ₃ (sodium bicarbonate) from carbonation of an ammoniacal brine, wherein the neutralization is conducted by using Mg(HO) ₂ (magnesium hydroxide) as a base obtained by precipitation with NaOH, or by calcination of MgC0 ₃ and subsequent hydration of the MgO (magnesium oxide) formed in said calcination process.

Even more preferably, the Mg ²⁺ (magnesium ions) content of the feed brine to be treated in step (a) by precipitation with Na2C0 ₃ ranges from approximately 0% w/w to 80% w/w of the magnesium contained in the brine.

Additionally, the process comprises step (c) precipitating borates and sulfates present in the brine treated in step (b) by adding a CaCI ₂ (calcium chloride) solution.

Preferably, the CaCl ₂ comes from the mother liquor of the NH ₃ recovery process used in a conventional Solvay process applied for obtaining Na ₂ C0 ₃ .

Preferably, the Mg ²⁺ concentration present in the brine treated after step (b) decreases to a value lower than 3 mg/l.

Also additionally, the process comprises the steps of: (d) obtaining crude Li ₂ C0 ₃ (lithium carbonate) from the treated brine precipitating Li ₂ C0 ₃ by adding a soluble carbonate solution and separating the solid product; and

(e) re-dissolving crude Li ₂ C0 ₃ obtained in step (d) and re-precipitating highly pure U2CO3 and separating the solid product from the mother liquor.

Preferably, the soluble carbonate used in step (d) is Na ₂ C0 ₃ obtained by means of a conventional Solvay process.

More preferably, the crude Li ₂ C0 ₃ obtained in step (d) is re-dissolved in cold water at a temperature lower than 25°C, wherein the cold water is distilled water, demineralized water, or water permeated by reverse osmosis.

Still more preferably, re-precipitation of highly pure Li ₂ C0 ₃ from step (e) is conducted by heating the solution or by jointly heating and evaporating the solution.

Even more preferably, re-precipitation of highly pure Li ₂ C0 ₃ from step (e) is conducted by at least one of the following sub-steps: i) crystallization in a multiple effect evaporative crystallizer, ii) crystallization in a multiple effect evaporative crystallizer with thermo-compression, iii) crystallization in an evaporative crystallizer by mechanical compression and thermo-compression, iv) crystallization by heating using only heat exchangers, v) crystallization by heating and evaporating processes using heat exchangers and any of the evaporative crystallizers indicated in i), ii), and iii).

Additionally, the mother liquor of the purification process of Li ₂ C0 ₃ is treated using ion exchange to minimize the purge and recycle the maximum amount of mother liquor into the re-crystallization process.

Also additionally, the process comprises step (f) preparing a LiCI (lithium chloride) solution from the U2CO3 obtained in step (e).

In addition, the present invention refers to a processed brine solution, lithium carbonate solution, or lithium chloride solution prepared by the above described process.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a graph providing the dispersion of the potassium/magnesium (K/Mg) ratio as a function of the main saline bodies of the Argentine Puna and the Salar de Atacama. Figure 2 shows a diagram of alternative I for pre-concentration and treatment of a natural brine with reagent regeneration according to the present invention; wherein, PN stands for Natural Pond, PN 800 stands for Natural Pond of brine with a Li ⁺ concentration of 800 mg/l, Pl-halite stands for Impermeabilized Pond of halite, SNP 800-900 stands for Preconcentrated Natural Brine with a Li ⁺ concentration of 800-900 mg/l, and SNP 2.500-3.000 stands for Preconcentrated Natural Brine with a Li ⁺ concentration of 2.500- 3.000 mg/l.

Figure 3 shows a diagram of alternative II for pre-concentration and treatment of a natural brine with reagent regeneration according to the present invention; wherein, PN stands for Natural Pond, PN 800 stands for Natural Pond of brine with a Li+ concentration of 800 mg/l, Pl-halite stands for Impermeabilized Pond of halite, SNP 800-900 stands for Preconcentrated Natural Brine with a Li ⁺ concentration of 800-900 mg/l, SNP 2.500-3.000 stands for Preconcentrated Natural Brine with a Li ⁺ concentration of 2.500- 3.000 mg/l, Pl-K salts stands for Impermeabilized Pond with K salts, Pl- sylvinite stands for Impermeabilized Pond of sylvinite, SNP 9.000 stands for Preconcentrated Natural Brine with a Li ⁺ concentration of 9.000 mg/l, Pl- g salts (or Mg salts I, or Mg salts II) stands for Impermeabilized Pond with Mg salts (or Mg salts I, or Mg salts II), SNP 11.800 stands for Preconcentrated Natural Brine with a Li ⁺ concentration of 11.800 mg/l, and SNP >14.000 stands for Preconcentrated Natural Brine with a Li+ concentration greater than 14.000 mg/l.

Figure 4 shows a diagram describing the procedure for the production of crude IkCO^ according to the present invention.

Figure 5 shows a diagram describing the procedure for the purification of U2CO3 by re-crystallization according to the present invention; wherein, the references used have the following meanings: M-401-402, Mixer (s/l); F- 401/402, Polishing filter; P401 A/B, Pump for Li ₂ C0 ₃ solution; P402 A/B, Pump for polished solution; TK401 , Buffer Tank of solution; IE401 , Ion- exchange unit; TK402, Condensate tank; P406 A/B, Condensate pump; C401 A/B, Steam compressor; P403 A/B, Magma pump; E401 , Solution pre-heater; E402, Solution heater; CR-401 , Evaporative crystallizer; Tk403, Mother liquor tank; P404 A/B, Crystallizer discharge pump; CE401 , Centrifuge; P405 A/B, Mother liquor pump; and E403, Water cooler.

Figure 6 shows a scheme for the production of sodium carbonate from brine and sludges.

Figure 7 shows the scheme of the ammonia recovery system ith MgO according to Test 1 of Example 1.

Figure 8 shows the scheme of the ammonia recovery system with sludge according to Test 2 of Example 1.

Figure 9 shows the evolution of the Mg concentration in Test 2-1 of Example 1.

Figure 10 shows the progress of the reaction using MgO in Test 2-1 of Example 1.

Figure shows the evolution of the Mg and Ca concentration in Test 2-2 of Example 1.

Figure 12 shows the progress of the reaction using sludge in Test 2-2 of Example 1.

Figure 13 shows the evolution of the conversion for Test 2-1 and Test 2-2 of Example .

Figure 14 shows a conceptual scheme of the purification process of crude lithium carbonate by dissolution and crystallization of Example 4.

Figure 15 shows a scheme of the steps of the purification process of crude lithium carbonate by dissolution and crystallization as tested at the laboratory in Example 4.

Figure 16 shows a flow chart for the purification process of crude lithium carbonate by dissolution and crystallization as tested in a pilot plant in Example 4.

DETAILED DESCRIPTION OF THE INVENTION

The term "brine" as used in this description means waters strongly impregnated with salts. Waters containing a high concentration of dissolved solids constitute at present an important source of mineral salts. Brines are an important source of common salt, potassium, bromine, boron, lithium, iodine, magnesium and sodium carbonate.

The term "salar" as used in this description is understood as an evaporite that is essentially a centripetal area that accumulated and accumulates salts of hydrothermal and/or volcanic origin, and that in past geological eras was salt lakes with a high content of salts.

As used in this description, the term "substantially" means that the form, circumstance, magnitude, measurement or any other described characteristic but syntactically associated to it, resemble as desired to said form, circumstance, magnitude, measurement or any other characteristic as unequivocally or definitively known. Specifically, this term means that the described matter is practically equivalent for the purposes of the invention or resembles to the concrete reference used for the description, without necessarily becoming identical.

Moreover, the terms "about", "of about", or similar, used in this description and the claims mean that the numerical values affected are close to the limit value specifically mentioned and within a specific range of values and comprised within 20 % of said numerical value, preferably within 10 % of said value and, more preferably within 5 % of said value. Ranges are determined by the measuring method used and the thresholds established in the corresponding determinations.

It is therefore the object of the present invention to provide improvements to the process as described in Patent Application "A PROCESS FOR RECOVERING LITHIUM FROM A BRINE" (PCT International publication number WO2010/006366A1), the contents of which document are incorporated herein in its entirety for reference, which are mainly related to a process for magnesium removal having a low environmental impact, high recovery and a reasonable cost, and a low cost process for purifying crude lithium carbonate as obtained with the new treatment proposed for magnesium removal.

The procedure object of the present invention comprises separation of the magnesium contained in the brine by means of a treatment comprising the following steps:

Step I) - Addition of a sodium carbonate aqueous solution, preferably having a concentration of about 290 g/l of water, in an amount sufficient to separate approximately 80% of the magnesium contained in the brine. By means of this procedure, magnesium is separated from the brine as solid magnesium carbonate. The reactions occurring in the process are as follows:

MgS0 ₄ + Na ₂ C0 ₃ «# MgC0 ₃ (s) + Na ₂ S0 (1)

MgCI ₂ + Na ₂ C0 ₃ MgC0 ₃ (s) + 2NaCI (2)

As indicated in the diagrams of Figures 1 and 2, the sludge obtained post-treatment following separation, washing and drying of the solid phase, contains more than 95% magnesium carbonate, expressed as w/w on a dry basis. When this solid is calcined at 900°C, it decomposes into magnesium oxide and carbon dioxide. Magnesium oxide is hydrated with permeated water and the obtained magnesium hydroxide is used for neutralizing an ammonium chloride solution produced in the reactor where sodium bicarbonate is obtained, as described below, giving off ammonia, which is recycled to the sodium bicarbonate process in order to obtain ammoniacal brine. The ammonium chloride neutralization reaction also generates a magnesium chloride aqueous solution, the only liquid effluent produced in the treatment process. Owing to the low solubility of magnesium hydroxide, the process involving neutralization and ammonia evolution is slower than when using calcium hydroxide as in the case of the conventional Solvay process. The reactions corresponding to the above mentioned calcination, hydration and neutralization processes are as follows:

MgC0 ₃ → MgO + C0 ₂ T (3)

Mg 0 + H ₂ 0→ Mg (OH} ₂ (4)

Mg (OH) ₂ + ZNH^Cl→ 2NH ₃ T +Mg Cl ₂ + 2H ₂ 0 (5)

Step II) - Addition of a sodium hydroxide aqueous solution, having a concentration of approximately 400 g/l of water, in an amount sufficient to separate the remaining magnesium contained in the brine after treatment with sodium hydroxide. By means of this procedure, magnesium is separated from the brine as solid magnesium carbonate. The reactions occurring in the process are as follows:

MgSO + 2Na(OH → Mg (OH) ₂ i +Wa ₂ S0 ₄ (6)

MgCl _z + 2Na{OH)→ Mg(OH) ₂ I +2NaCl (7) As indicated in the diagrams of Figures 1 and 2, the sludge obtained post- treatment following separation and washing of the solid phase, contains more than about 97% magnesium carbonate, expressed as w/w on a dry basis. As indicated in Figures 1 and 2, this sludge is also used directly in the neutralization reaction of ammonium chloride. The neutralization reaction is similar to reaction (5).

Reagent Regeneration

As indicated in Figures 1 and 2, in order to regenerate the employed reagents, namely sodium carbonate and sodium hydroxide, a sodium chloride aqueous solution is prepared which is similar to that used in the Solvay process for the production of sodium carbonate. This brine is the other stream coming into the ammonia absorber to obtain an ammoniacal brine that gets carbonated with carbon dioxide resulting from calcination of the magnesium obtained in the treatment reactor, from calcination of calcium carbonate obtained from the basification reaction of sodium carbonate and from the calcination of sodium bicarbonate obtained in the carbonation process of the ammoniacal brine. Calcination of the sodium bicarbonate separated as a solid in the carbonator, in addition to the carbon dioxide it generates, produces sodium carbonate, which is the reagent used to separate magnesium from the brine under process. This reagent regeneration process is similar to the Solvay process, the only difference being that magnesium carbonate is employed instead of calcium carbonate. Calcination of the sodium bicarbonate separated as a solid in the carbonator, in addition to the resulting carbon dioxide, also produces sodium carbonate. The thus obtained sodium carbonate can be used as such for separating magnesium according to reactions (1) and (2) or, by means of a basification process, it can be used to obtain sodium hydroxide which in turn can be used to separate magnesium according to reactions (6) and (7). The reactions comprised in the reagent regeneration processes for separation of magnesium from the brine are those detailed in the following schemes:

Regeneration of Sodium Hydroxide

In the above scheme, equations (6) and (7) are summarized in equation (8).

Regeneration of Sodium Carbonate

tf ₂ 0 + MgCl ₂ + 2NH ₃ <- 2Ai// ₄ C. + Μβ(0Η) ₂ φ

In the above scheme, equations (1) and (2) are summarized in equation (9). According to the present invention, approximately 80% of the magnesium contained in the brine is separated using sodium carbonate and approximately 20% is separated using sodium hydroxide. This is so because about 80% is the amount that can be separated if only sodium carbonate is used, according to experimentation performed and the solubility of magnesium carbonate in the brine. It is important to note that all of the magnesium contained in the treated brine can be separated almost thoroughly by using only sodium hydroxide. This means that, according to the need for the use of thickeners, the availability of solid-liquid separation and washing processes of the cake, and the availability of power, it is possible to apply the described reagent regeneration processes, from a proportion of approximately 80% of sodium carbonate regeneration and approximately 20% of sodium hydroxide regeneration, up to about 0% of sodium carbonate regeneration and approximately 100% of sodium hydroxide regeneration. In any of these cases, the post-treatment pH is greater than 11.3, thus assuring that the magnesium content in the liquid phase is lower than about 3 mg/L.

According to the present invention, the degree of pre-concentration of the brine to be treated has also been specified. It is important to note that, for the process of the present invention, the brine entering the treatment process can range from a natural brine without any degree of pre-concentration up to a pre-concentrated brine (with or without pre-treatment) with a lithium concentration higher than 80 g/L. This flexibility for the application of the procedure is important because the following factors depend on the degree of pre-concentration of the brine to be treated: i) the technology to be used for completion of the concentration of the treated brine before entering the lithium carbonate plant; ii) the specific consumption of reagents for the treatment; iii) the consumption of thermal energy, mechanical energy and water; iv) the time necessary to reach the steady state; v) the degree of lithium and potassium recovery; and vi) the environmental impact arising from performance of the procedure.

In any case, if the calcium content in the brine to be treated is high, it must first be treated with sodium sulfate in order to avoid crystallization and precipitation of calcium carbonate. The process according to the present invention for the separation of magnesium has a friendly logistics since the necessary reagents, namely H ₂ 0, CI ₂ Na, CO ₂ , CaCC>3, NH ₃ , indicated with a bold circle in Figures (1) and (2), are available near the salar, except for the ammonia replacement which is about 0.6% of the stoichiometrically total required amount. Furthermore, at the end of the procedure performed for reagent regeneration, the magnesium separated from the brine remains in the form of magnesium chloride, thus minimizing the environmental impact of its application.

On the other hand, the treatment described for separating magnesium does not regulate the sulfate and borate contents. For this reason, and also for another still more relevant reason— namely availability of the sodium carbonate necessary to obtain lithium carbonate - the process for obtaining sodium carbonate from calcium hydroxide is described in the schemes of Figures 1 and 2. As indicated in the schemes of Figures 1 and 2, apart from sodium chloride, water and calcium carbonate, it is also necessary in this case to replace about 0.6% of the stoichiometric amount of ammonia necessary to obtain sodium carbonate intended for the production of lithium carbonate. As indicated in the above schemes, this process produces a calcium chloride solution that is used in the treatment reactor for sulfates and borates. As described in Example 2, and while expressing the boron content as B ₄ 0 ₇ ² the reactions involving this treatment are as follows:

SO - + CaCl ₂ ~* CaS0 ₄ + ZCl ^"

B O - + CaCl ₂ → CaB ₄ 0 ₇ + 2Cl ^~

As shown in Figure 2, the pre-concentrated, treated brine can be concentrated in ponds up to a lithium concentration of about 14g/l, without any crystallization of lithium salts. As disclosed in Patent Application "A PROCESS FOR RECOVERING LITHIUM FROM A BRINE" (International publication number WO 2010/006366 A1), potassium salts are harvested in the ponds which increase lithium concentration from 2.5 - 3 g/l up to 9 g/l. These salts are washed and delivered to a plant in order to obtain potassium chloride. The washing water is recycled to the potassium salts crystallization and precipitation ponds. In Figure 3 it is shown that the treated and pre-concentrated brine can be concentrated in evaporative crystallizers. In this case there is a first step in which sodium chloride is obtained, and a second step performed in Draft- Tube-Buffer-type (DTB-type) evaporators to obtain potassium chloride. In this alternative, the production of potassium chloride is practically concurrent with the production of lithium carbonate, which means a great advantage from the economic point of view. Besides, the possibility of using evaporative crystallizers allows for: i) attaining a greater lithium concentration in the brine entering the lithium carbonate plant without loss of lithium salts due to crystallization, and ii) producing water of very high quality, thus reducing the impact on the water balance of the salar due to the use of solar evaporation ponds.

Lastly, as concerns the process described for obtaining treated and concentrated brine, it is important to point out that the quality of the obtained brine and, consequently, the quality of the crude lithium carbonate obtained therefrom, requires application of a purification process to the crude lithium carbonate. For this reason, the present invention comprises a low cost purification process that reduces the level of soluble and insoluble impurities to values that are lower than those indicated in the specifications of battery grade lithium carbonate.

The degree of concentration of lithium of the brine entering the lithium carbonate plant and the new purification procedure as proposed modify the recycle regimen indicated in the PCT Patent Application published under N° WO2010/006366A1. This modification involves approximately a 26% reduction in the consumption of the sodium carbonate used with the previous process. The scheme in Figure 4 describes the procedure to obtain crude lithium carbonate corresponding to the present invention and the scheme in Figure 5 refers to the new proposed purification procedure.

PRODUCTION OF CRUDE LITHIUM CARBONATE - Description of the scheme in Figure 4.

Since the purification process, which is also the object of the present invention, does not generate a recycle, the scheme in Figure 4 indicates that only the rinsing water of the salts precipitated in the concentration pond of the mother liquor of the crude lithium carbonate reactor is recycled into the cold treatment reactor.

The post-cold treatment separation of sludge and the production of the solution entering the crude lithium carbonate reactor are the same as indicated in the scheme in Figure 6 of PCT Patent Application published under N° WO2010/006366A1.

Going back to the description of the scheme in Figure 4, as there is no recycle from the purification section, only a brine having a lithium content of 3.000 mg/l is recycled to the crude reactor, which is obtained through concentration of a mixture containing 70% of the mother liquor of the same crude reactor and 100% of the rinsing water of the crude lithium carbonate. The remaining 30% of the mother liquor of the crude reactor is recycled to the treatment plant of the pre-concentrated brine. From the point where crude lithium carbonate is obtained following centrifugation, the procedure is the same as indicated in Figure 6 of PCT Patent Application published under N° WO2010/006366A1.

PURIFICATION OF CRUDE LITHIUM CARBONATE BY RECRYSTALLIZATION - Description of the scheme in Figure 5.

The purification procedure, which is also an object of the present invention, comprises dissolution of the crude lithium carbonate, stream 1 , in distilled water, stream 4 which is part of stream 3 obtained by mixing stream 2 [replacement lower than 3% of stream 3] and stream 35 [condensate recycle]). The amount of lithium carbonate entering mixer -401 is about 5% greater than the amount necessary to saturate stream 4 at a temperature close to room temperature, for example, about 20°C. The obtained mixture, stream 7, is pumped by means of pump P-401 A/B to polishing filter F-401 thus obtaining a saturated lithium carbonate solution in water free from water- insoluble impurities, stream 8, and a mixture of solids, stream 9, containing the excess lithium carbonate, which entered mixer M-401 , and water-insoluble impurities. Stream 9 enters mixer M-402 where it admixes with an amount of distilled water, stream 5, enough to assure complete dissolution of the lithium carbonate contained therein. The mixture obtained in mixer M-402 is pumped by means of pump P-407 A/B to polishing filter F-402 A/B, thus obtaining stream 11 which consists of the water-insoluble impurities contained in crude lithium carbonate (waste) and stream 6 which is recycled into reactor M-401.

Stream 8 enters accumulation tank TK-401 from which it is pumped by means of pump P-402 A/B, thus obtaining stream 12. This stream can totally or partly enter the ion-exchange unit IE-401 A/B as stream 13 and then enter solution pre-heater E-401 as stream 15, admixing with stream 14, a fraction of stream 12 not entering the ion-exchange unit. The stream 13 to stream 14 ratio will depend on the target product quality. Stream 15 is pre-heated with part of the condensate, stream 30, generated in solution pre-heater E-402, stream 28. Stream 31 , the condensate output of pre-heater E-401 , accumulates in tank TK-402 from which it is pumped by means of pump P- 406 A B as stream 34 to cooler E-403 in order to obtain cold distilled water stream 35. When necessary, part of the condensate is purged as stream 33. The pre-heated solution, stream 16, enters the evaporative crystallizer as stream 17. Stream 17 is the mixture of stream 16 with stream 18, which is the mother liquor from stream 24 exiting the evaporative crystallizer, and the rinsing water from stream 29 which is part of the condensate which is employed in washing the obtained lithium carbonate). The mother liquor and the rinsing water exit centrifuge CE-401 as stream 36 and accumulate in tank TK-403. From this tank it is pumped by means of pump P-405 A/B as stream 39 to the ion-exchange unit IE-402 A/B in order to eliminate calcium, magnesium and boron impurities accumulated due to concentration of the lithium carbonate solution. Output from unit IE-402 A B is stream 18. Water- soluble impurities are also purged by means of stream 38.

Stream 17 entering the evaporative crystallizer admixes with stream 19, which together with streams 20, 21 and 22 show recirculation of the solution in the evaporation equipment.

The crystallization equipment, indicated as a shaded box in Figure 5, is a mechanical compression evaporative crystallizer and comprises evaporative crystallizer CR-401 , solution heater E-402 and steam compressor C-401. This is only an embodiment example intended to explain the procedure scheme. By maintaining the scheme in Figure 5, and only changing the crystallization equipment, the purification process can also be accomplished using: i) multiple-effect evaporative crystallizers; ii) multiple-effect evaporative crystallizers with thermal compression; iii) mechanical compression evaporative crystallizers and thermal compression; iv) heat crystallization using only heat exchangers; v) heating and evaporation crystallization using heat exchangers and any of the evaporative crystallizers indicated in i), ii) and iii).

The purified lithium carbonate obtained with this procedure is of higher quality than the battery grade lithium carbonate obtained with the procedure disclosed in the Patent Application PCT published under N° WO20107006366A1. In addition, the present procedure has lower cost and permits purification of the crude lithium carbonate obtained with the procedure described in the first part of the present invention.

The procedure described in this invention comprises a set of processes among which the following are considered:

a. Solvay's reaction for obtaining sodium bicarbonate.

b. Limestone calcination for obtaining Ca(OH)2.

c. Causticising of sodium carbonate for obtaining NaOH.

All these are traditional processes well known in the previous art.

Likewise, the process for obtaining crude lithium carbonate is the one described in the PCT patent application published under number WO 2010/006366 A1.

Below, the Examples of embodiments referred to the following examples are described:

Example 1 : Examples referred to release of NH3 from an ammonium chloride solution using magnesium hydroxide.

Example 2: Example referred to the separation of g using sodium carbonate and sodium hydroxide.

Example 3: Example referred to the precipitation of sulfates and borates with calcium chloride after Mg precipitation treatment.

Example 4: Example referred to the purification of crude lithium carbonate.

EXAMPLES

EXAMPLE 1 : Ammonia recovery trials by neutralization with magnesium hydroxide Conventional Solvay process utilizes industrial lime to recover ammonia.

In order to evaluate technical feasibility of a process for the production of sodium carbonate using magnesium hydroxide contained in the sludge post-treatment with sodium hydroxide, in the NH3 recovery step, the following trials were conducted:

• Trial 1: qualitative trial to evaluate feasibility of ammonia recovery from ammonium chloride solution utilizing magnesium oxide as the reagent.

• Trial 2: quantitative trial to determine the reaction yield for ammonia recovery. The reagents to be used are magnesium oxide and sludge.

Trial description

The objective of the trials conducted according to the scheme in Figure 6 is too determine yields and operative conditions for the ammonia recovery process from a liquid solution containing ammonium chloride amongst its components. Magnesium oxide, which in the presence of water converts into magnesium hydroxide, and sludge obtained during the production process of lithium carbonate, are to be used as the reagents.

In order to perform a comparative analysis with respect to the conventional Solvay process, tests are to be conducted which use a lime slurry as the reagent for ammonia recovery.

Below, a description of each trial, their results and main conclusions are provided.

Trial 1

The object of this trial is to prove the feasibility of the reaction between magnesium oxide, one of the components of sludge, and ammonium chloride.

The reagents were: ammonium chloride, one of the components of the mother liquor obtained in the solid-liquid separation step; and magnesium oxide, a component which converts into magnesium hydroxide and replaces the lime slurry. The trial was conducted on a qualitative basis in a system shown in Figure 7.

The procedure was as follows:

Preparation of an aqueous solution of ammonium chloride. Average concentration was 4.5 M. 240 g dissolved in 1L water are used. Suspension of magnesium oxide in water and pH measurement. A 5% excess is used.

Dosing of the magnesium oxide suspension into the ammonium chloride solution.

Heating of the reaction mixture to 100°C for 6 hours. At this stage, characteristic ammonia odors were detected.

Determination of the concentration of magnesium in the reaction mixture. Samples are taken regularly, these are filtered and the magnesium content is analyzed.

When the magnesium oxide contacts water, the following chemical reaction is considered to occur.

MgO _(s) + H ₂ O _iag) ^^ ^~ ±Mg(OH) _2(a<l) (1) Magnesium hydroxide dissociates according to:

Mg(OH) _2(ail A* + 20H- _aq) (2)

Then the magnesium present in the solution reacts with ammonium chloride. The overall chemical reaction is as follows:

2NH ₄ Cl _{aL , + Mg(OH) _2{x) ^~ ^→M _g Cl _{2 ac)} + 2NH _i(gm , t ₊ 2H ₂ 0 (3)

From this test it is concluded that ammonia recovery would be possible using magnesium hydroxide. An operating temperature of 100°C is defined.

The next test aims to determine the conversion of ammonium chloride into ammonia, using sludge, and make a comparative analysis with the previous test.

Trial 2

For a comparative study of ammonia recovery from ammonium chloride, two simultaneous tests were conducted; in one of them magnesium oxide suspension was dosed and in the other one sludge was dosed.

The scheme of the system used for ammonia recovery is shown in Figure 7 and Figure 8. Trial 2-1

Ammonium chloride and pro-analysis magnesium oxide were used. This test is similar to test 1 (see Figure 7). The procedure and the chemical reactions were presented in the previous section

The progress of the reaction was monitored as a function of the amount of magnesium ions entering the solution during the reaction time. This variable is considered to be directly related to the amount of ammonia produced.

Trial 2-2

Ammonium chloride and sludge from a filter press of a lithium carbonate plant were used in an aqueous medium. The chemical composition of the sludge is shown in Table 3. The moisture content of the sludge is 24% (wet basis).

Table 3: Chemical Composition of Sludge (ppm)

From the chemical composition data, the amounts of sludge required for the transformation of 240 g of ammonium chloride into ammonia are determined. The following was assumed:

All the magnesium in the sludge is part of the magnesium hydroxide.

All the sulfate ions are combined with calcium.

Remaining calcium is part of the calcium hydroxide.

In this test, ammonium chloride reacts ith magnesium hydroxide and calcium hydroxide, both from the sludge. Another component of the sludge is calcium sulfate, which does not react in the recovery of ammonia.

The dosage of sludge is calculated based on the stoichiometric necessary hydroxyl groups for the transformation of all the ammonium chloride into ammonia, with a 5% excess. The proportions of reagents used are:

240 g of NH ₄ CI

900 ml of water

414J grams of sludge The chemical reactions taking place are:

2NH,Cl _(aq) +Mg(OH) _2(ac!) - ^→MgCl _2{atl) + 2NH _W f +2H ₂ O

2NH ₄ 0 _{{all) +} Ca(OH) _2{aq) -^→CaCl _{2(aq) +} 2NH ₎ t +2H ₂ 0

Ammonia recovery was conducted at 100°C and atmospheric pressure, with stirring of the reaction mixture.

The reaction was monitored based on the amount of magnesium and calcium ions that react and enter into solution. For such monitoring, periodic samples are taken to be analyzed for calcium and magnesium. The evolution of the concentration of these ions corresponds to the transformation of ammonium chloride into ammonia.

Results

Below are the results of Trial 2-1 and Trial 2-2.

Prior to the chemical analysis, the samples are conditioned by filtration. Trial 2-1

The evolution of the magnesium concentration during the reaction as a function of time is shown in Figure 9. The increase in the magnesium concentration is directly related to the release of ammonia.

From the results of the test the conversion is determined assuming that the only reaction taking place is reaction (3) with NH ₄ CI as reactant and that all the magnesium dissolved corresponds to the reacted MgO.

Conversion of ammonium chloride (x _{NH a} ) is calculated according to ^CI _M

Mg where:

C _M : Magnesium concentration .

V : Volume of the reaction mixture.

M _Mg : Molar mass of magnesium.

n° _{tii a} : Initial quantity of moles of ammonium chloride.

The conversion is calculated assuming that maximum conversion is when 2.24 moles of magnesium enter the liquid phase which is equal to 55.65 g of Mg .. The limiting reagent is ammonium chloride. Figure 10 shows the progress of the reaction.

With the assumptions and conditions previously mentioned, and for a test time of six hours, a maximum value of 57% conversion is estimated. This value serves as information to carry out comparative studies and to set test conditions.

Trial 2-2

The magnesium and calcium concentrations are determined to quantify the amount of ammonia released and the conversion. In Figure 1 1 the evolution of the concentration of magnesium and calcium ions is presented.

Having in mind that the experiment was carried out using the same amount of ammonium chloride (4.49 mol) and that according to reaction (4) and (5) the maximum amount of equivalents of magnesium and calcium is 2.24 moles.

For this test, conversion is calculated based on the amount of Mg and Ca dissolved. It is assumed that all the Mg and Ca dissolved are reaction products of reactions (4) and (5), and no side reactions occur. In Figure 12, the evolution of the conversion is presented.

With the hypotheses and conditions presented previously, a maximum value of 50% conversion is estimated; as with the results of the previous test, these results are used in a comparative study and to set test conditions.

In Figure 13 the evolution of conversion for Trial 2-1 and Trial 2-2 is shown. As the reaction progresses, differences in conversion can be appreciated and by the end of the test the conversion is 7% better using MgO than using sludge.

Conclusions

From the tests carried out with the purpose of understanding ammonia recovery from a liquid containing ammonium chloride, the following is concluded:

Conversion when MgO is used is 7% better than when sludge is used.

Ammonia can be recovered with sludge.

The trial time can be reduced by increasing the reaction temperature in the process of ammonia recovery. The conversion results of the tests obtained are valid for comparative purposes and for the conditions in which they were carried out.

The test that utilizes magnesium oxide (MgO) has the goal of knowing a limit value in relation to the sludge and at the same time to evaluate alternatives to produce a sludge with a better magnesium hydroxide content.

EXAMPLE 2: Chemical treatment of brine with Na ₂ C0 ₃ solution and NaOH solution

Treatment with Na2C0 ₃

This chemical treatment stage aims at precipitating the magnesium contained in the brine as magnesium carbonate using a sodium carbonate solution. The amount of magnesium that precipitates as magnesium carbonate is based on its solubility in the reaction medium.

^• The test was conducted in 70 m ³ tank reactor with a stirrer. The reactor was loaded with 50 m ³ of brine with a density of 1.256 kg/l and a total dissolved solids (TDS) of 0.372 kg/l.

Then, a 20% w/w sodium carbonate solution was dosed until the magnesium content was reduced by 80%. The processing time was 30 minutes. The density of the dosed sodium carbonate solution was 1.2 kg/l and the total dissolved solids (TDS) was 0.24 kg/l.

Table 4 shows the results of the chemical treatment:

Table 4: properties of the treatment system currents with a ₂ COa solution

I Description Unit Loaded Reagent Treated _. . Precipitated brine brine ; solid

Volume n 50 167 64

Mass kg 62,900 20,179 79,866 3,312

[Chemical ^{^}

Magnesium g/l 22.743 3.548

Calcium mg/l 0.140 4

Sulfate g/l 33.882 26.43

Borate g/l 8.852 6.905 Na ₂ C0 ₃ % w/w 20

Property

Density kg/I 1.258 1.209 1.246

TDS kg/I 0.375 0.241 0.305

TDS: Total dissolved solids.

Once the reaction was finished, the solid-liquid separation was conducted. After the solid-liquid separation, 60 m ³ of brine were obtained with the concentration shown in Table 4, which were sent to the following chemical treatment step. The solid contained wetting water with a moisture content of 45% on a wet basis.

The solid contained a mixture of magnesium carbonate and calcium carbonate. Since the moisture content was high, the washing process was conducted with water so as to minimize lithium losses. The amount of washing water depended on the amount of solids. The amount used was equivalent to a cake volume whose typical density is 1.45 kg/m ³ . The wetting water was sent to the ponds for concentration and lithium recovery. _/ Treatment with NaOH

This chemical treatment stage is aimed at precipitating the remaining magnesium contained in the brine treated with sodium carbonate solution.

The test was conducted in a 70 m ³ tank reactor with a stirrer. The reactor was loaded with 60 m ³ of brine with a density of 1.246 kg/I and a total dissolved solids (TDS) of 0.305 kg/I.

Then, a 32% w/w sodium hydroxide solution was dosed in the necessary amount for precipitating the magnesium contained in the brine. The processing time was 30 minutes. The density of the sodium hydroxide solution was 1.349 kg/I and the total dissolved solids (TDS) was 0.431 kg/I.

Table 5 shows the results of the chemical treatment.

Table 5: properties of the treatment system streams with NaOH solution

Loaded Reagent Treated Precliitated brine ^: . _{: :} >brine¾v ;/* _$ojj.d; ; ^■

Volume m ³ 60 1.1647 61.5

Mass kg 75,125 2,222 76,832 516 composition

Lithium g/i 1.965 1.926

Magnesium ≠ 3.548 0.010

Calcium mg/l 4 4

Sulfate g/i 26.43 25.905

Borate g/i 6.905 6.768

NaOH % w/w 32

Density kg/I 1.246 1.349 1.249

TDS kg/I 0.305 0.431 0.302

TDS: Total dissolved solids.

Once the reaction was finished, the solid-liquid separation was conducted. After the solid-liquid separation, 60.9 m ³ of brine were obtained with the concentration shown in Tabl5, which were sent to the following chemical treatment stage. The solid contained wetting water with a moisture content of 45% on a wet basis.

The solid contained magnesium hydroxide. Since the moisture content was high, the washing process was conducted with water so as to minimize lithium losses. The amount of washing water depended on the amount of solids. The amount used was equivalent to a cake volume. The wetting water was sent to the ponds for its concentration and lithium recovery.

EXAMPLE 3: Chemical treatment of brine with CaCI ₂ solution

This chemical treatment stage is aimed at precipitating the sulfates and borates contained in the brine. As precipitating reagent, a calcium chloride solution was dosed. The amount of reagent was dosed so that the calcium concentration after the reaction was 2 g/L, 5.5 g/l of sulfate (S0 ₄ ^2' ) and 6.7 g/l of borates (B ₄ 0 ₇ ^2" )-

The test was conducted in a 70 m ³ tank reactor with a stirrer. The reactor was loaded with about 60 m ³ of brine with a density of 1.249 kg/I and a STD of 0.302 kg/I.

Then, a 25% w/w calcium chloride solution was dosed. The processing time was 30 minutes.

Table 6 shows the results of the chemical treatment: Table 6: properties of the treatment system currents with CaCI ₂ solution

Mass kg 76,078 20,179 80,972 2,189

Magnesium g/i 0.010 0.009

Calcium mg/l 4 2.000

Sulfate g/i 25.905 5.500

Borate g/i 6.768 6.349

CaCI ₂ % w/w 25

Property

Density kg/I 1.249 1.2284 1.247

TDS kg/I 0.302 0.307 0.285

TDS: Total dissolved solids.

Once the reaction was finished, the solid-liquid separation was conducted. After the solid-liquid separation, 62 m ³ of brine were obtained with the concentration shown in 3, which were sent to concentration. The solid, mainly composed of dehydrated calcium sulfate (CaS0 ₄ .2H ₂ 0), contains wetting water with a moisture content of 45 % on a wet basis.

The solid contained dihydrated calcium sulfate. Since the moisture content was high, the washing process was conducted with water so as to minimize lithium losses. The amount of washing water depended on the amount of solids. The amount used was equivalent to a cake volume whose typical density is 1.45 kg/m ³ The wetting water was sent to the ponds for its concentration and lithium recovery.

EXAMPLE 4: Purification tests of crude lithium carbonate by dissolution and crystallization

The main stages of the proposed process are: Dissolution of crude lithium carbonate in water. A saturated lithium carbonate solution is obtained. The transformation can be represented by the following equation.

Li ₂ CO _{K ) <} ^L 2I¾ _>) + G¾ ₎ (1) Filtration of the lithium carbonate solution to separate insolubles. When a higher quality product is required, the solution is purified by ion exchange. Evaporative crystallization of lithium carbonate from the purified solution.

Figure 14 shows a conceptual outline of the process.

At the temperature of 10°C, the saturated solution of lithium carbonate in water has a lithium concentration of 1.41 % (w/w). Taking into account that the solubility of lithium carbonate decreases with the increase of the temperature, to achieve a good recovery, it is necessary to raise the temperature up to 85-90°C; under these conditions the solubility is 0.78% (w/w).

Table 7 shows solubility for different temperatures.

Table 7: Solubility of lithium carbonate at different temperatures.

The average composition of the product to be purified by dissolution in water is:

Table 8: Chemical composition of crude lithium carbonate.

Taking into account that energy consumption is high, it is necessary to increase the economy of the process by using different stages of crystallization and different technologies.

Trials

2 kinds of tests were conducted: Laboratory and pilot plant scale tests. Laboratory trial

Trials were performed considering the stages already mentioned above. Figure15 shows a diagram of the stages of the process. Crude lithium carbonate is used for the test as specified in Table 8. Osmosis water is used for dissolution having a conductivity lower than 4 pS/cm. The solution is filtered to remove insolubles. Filtrate is concentrated by water evaporation. During the process samples are taken from the suspension, which separates the lithium carbonate, whose quality is presented in Table 9.

Mother liquor has a lithium concentration lower than 1.8 g Li/L, which represents an advantage over the purification process by transformation in lithium bicarbonate.

Table 9: Chemical composition (% w/w) of purified lithium carbonate by dissolution.

There arises from this assay that it is necessary to use excess lithium carbonate with respect to the water necessary for dissolution. The specifications of the products (see Table 9) correspond to the process that results from evaporating 80% of the water.

Trial on pilot equipment

This trial aimed to determine the energy consumption, the quality of the product and the material test for the crystallizer. A process flow diagram is presented in Figure 16. It uses a steam jacket tube evaporator whose evaporation capacity is 50 l/h.

A saturated solution prepared with the lithium carbonate whose composition is shown in Table 8 was used for this test. The quality of the product obtained is contained in the Table 10 below.

Table 10: Chemical composition (%w/w) of the lithium carbonate purified by dissolution.

Components LJ2CO3 Mg ²⁺ Ca ²⁺ K ⁺ Na ⁺ SO4 ^2" cr B

Product 1 99.78 0.0011 0.0136 0.0014 0.0232 0.0280 0.0039 0.0043 A high quality product was obtained which corresponds to a 2/3 reduction in volume. The estimated consumption of thermal energy for crystallization is 60-64 tons of steam per ton of lithium carbonate, for which reason the economy of the process increases, which is one of the sought objectives.

To control the level of impurities affecting the quality of the product, one of the variables is the purge. In order to increase the performance of the process it is necessary to recycle, following an ion exchange treatment.

Industrial applicability of the invention

The present invention is applicable to the field of recovering metals from brines, particularly the invention relates to a high recovery process for the treatment of brines in an aqueous means to obtain high purity lithium carbonate, a solution of lithium chloride for producing electrolytic grade lithium chloride and derived products without the use of extraction solvents, which is easy to implement near salars, that will benefit mainly the mining industry related to exploitation of brines for obtaining lithium, as well as related industries, ail of which will be highly favored by having a procedure for obtaining high purity lithium carbonate, a solution of lithium chloride for producing electrolytic grade lithium chloride and derived products from brines in an aqueous means and with a low environmental impact, providing also an important economic benefit.

Final Considerations

Different modifications and variations to the process for obtaining high purity lithium carbonate, a solution of lithium chloride for producing electrolytic grade lithium chloride and products derived from brines according to the description of the present invention will be apparent to those skilled in the art without departing from the scope and the spirit of the invention. Although the invention has been described in relation with certain specific preferred embodiments and some variations, it is understood that the invention as claimed should not be unduly limited to said specific embodiments. In fact, it is intended that the different modifications to the mode for carrying out the invention which are apparent to the skilled in the art, or related art, are included within the scope of the following claims. In effect, the skilled in the art will recognize that numerous variations and/or changes can be made to the invention as shown in the specific embodiments, without departing from the scope of the invention as widely described. These embodiments are, consequently, considered in all respects merely illustrative and non-limiting.

Claims comprise the description of the invention object of this patent application.