WO2011138389A9 - Method for decreasing magnesium and increasing lithium in chloridic salt solutions - Google Patents

Abstract

The invention relates to a method for increasing lithium content while at the same time decreasing magnesium content from chloridic solutions which have high magnesium contents in relation to the lithium content. In accordance with the invention this is achieved by metering KCl into the solution intended for further evaporation, this solution containing at least 4 g/l Li+ and 60 g/l Mg2+, this KCl reacting with the MgCl2 in the solution, at least partially, to form potassium carnallite and is deposited in the form of potassium carnallite, the amount of KCl added being calculated such that the composition of the mother solution is close to saturation with carnallite (potassium carnallite) and KCl and hence the formation of lithium carnallite is prevented.

Description

 Process for depletion of magnesium and enrichment of lithium in chloridically imprinted salt solutions

The present invention relates to a process for the enrichment of lithium with simultaneous depletion of magnesium from solutions of chloridic nature, which have high magnesium contents in relation to the lithium content.

The currently known, largest resources of lithium are in the form of aqueous solutions (brines) in dried or partially dried salt lakes in South America, Asia and Africa. The solutions are mostly saturated NaCl solutions with varying concentrations of the ions K ⁺ , Mg ⁺⁺ , Li ⁺ and SO ₄ ^~~ as well as borate. The concentration for Li ⁺ is usually in a range between 200-4000 ppm. For K ⁺ , Mg ⁺⁺ and SO ₄ ^~~ the concentrations reach into the tens of gram range.

For the enrichment of lithium, the solutions are z. In evaporation basins or other technical equipment for fermentation (as in DE 10 2009 006 668.3). Initially, most of the salts are usually separated in the approximate sequence NaCl, KCl and, depending on the specific composition of the brine, various sulfates of the alkali metal magnesium sulfates. The most soluble salts LiCl and MgCl _{2 continue to} accumulate in the solution. The last parts of K + are crystallized on further evaporation as carnallite until finally bischofite, MgCl2 ^* 6H ₂ O is deposited. However, depending on the Li ⁺ concentration, the crystallization of lithium carnallite, LiCl * MgCl2 ^* 7H ₂ O, then starts, which means loss of lithium. At this point in time, it is common practice [DE Garrett, "Handbook of Lithium and Natural Calcium Chlorides - their deposit, proces- ses, uses and properties", Elsevier Academic Press, (2004); US 6,143,260] the magnesium by adding appropriate amounts of slaked lime, Ca (OH) ₂ , after the basic reaction

MgCl _{2 (} aq) + Ca (OH) ₂ -> Mg (OH) ₂ | + CaCl _{2 (a} q) as magnesium hydroxide, Mg (OH) ₂ , these magnesium hydroxide precipitates occurring both partially in the evaporation basins and in the processing tanks. could be done in the factory. As described in US Pat. No. 7,157,065 B2, the solution for precipitating the magnesium hydroxide may also contain sodium carbonate.

Since magnesium hydroxide precipitates have a large specific surface area and are only slowly reduced by aging, there is always a tendency for adsorption of Li ⁺ on these precipitates, so that washing processes are necessary to minimize Li losses. This basic procedure has z. For example, at the Salar de Atacama (Chile) and Clayton Valley (Nevada) production sites, where the mass ratios of Li: Mg in the Brines go up to about 1: 6. However, in the much larger amounts of lithium in the Salar de Uyuni (Bolivia) and the salt lakes in the Qaidam Basin (China), the Li: Mg ratios reach values of 1: 25 to 1: 100. For such Li: Mg Conditions, the precipitation of most of the magnesium as hydroxide is no longer economical, since the Li losses would be too large or the cost of washing processes increases too much. In addition, the consumption of slaked lime, the accumulation of CaCl ₂ impingement solution and Mg (OH) ₂ sludge would increase enormously.

As a further method to deposit the magnesium in the form of salts, it has been proposed to separate MgSO ₄ hydrates or its double salt with Na ₂ SO ₄ by Na ₂ SO ₄ additions [US Pat. No. 3,268,289]. On the deposition of lithium sulfate monohydrate, Li ₂ SO ₄ ^* H ₂ O, with purities of> = 95%, a number of other proposals. The attempt is made to exploit the solubility of lithium sulfate, which rapidly decreases with the Li content and the MgCl ₂ content of the solution, and to exploit the differences in the temperature dependence of the solubility to magnesium sulfate. The ₄ ^* H ₂ O crystallization necessary for the Li ₂ SO sulfate contents are on the one hand by sulfate additive to solutions with relatively high Li contents and MgCl ₂ contents [US 4 287 1 63, US 4,723,962] or by mixing suitable solutions [US Pat. No. 6,547,836]. Disadvantage of all these process variants are the quite complex process steps to comply with the appropriate for the Li ₂ SO ₄ separation concentration and temperature regime, the equivalent consumption of sulfates and the limited need for Li ₂ SO ₄ , which in further steps, usually in Li ₂ CO ₃ , needs to be converted.

Finally, the precipitation of magnesium as an oxalate was proposed, which has about 100 times less solubility than the corresponding lithium compound [urinary zaoui, AH M'nif, A., Hammi, H., Rokbani, R. Desalination, 158 (2003), 221-224]. However, there are certain co-crystallization effects of lithium that are not yet understood.

In other process proposals, Li ^{+ is} tried directly from the solutions by specific adsorption or ion exchange on granules or tablets based on (Al (OH) ₃ (US Pat. No. 5,389,349, US Pat. No. 6,280,693 B1), certain types of manganese oxides, such as λ type [Sagara, F., Ning, WB, Yoshida, I., Ueno, K., Separately See Technol., 24 (1989), 1227-1243; Chitrakar, R., Kanoh, H., Miyai, Eng. Chem. Res. 40 (2001), 2054-2058] or titanic acids [Yawata, K., Res. Rep. Of the Tsuruoka Technical College 41 (2006), 53-56 The problems of these processes lie in the consumption of fresh water for the elution of lithium from the granules and in the limited number of sorption cycles for which the granules can be used, and often the selectivity for Li + im Ratio to Mg ⁺⁺ is insufficient and the behavior of the sorbents markedly pH-dependent, the latter affecting both the ion exchange behavior and the chemical S stability of the granules.

In other variants of the sorption process, the Al (OH) _{3 is} precipitated directly in the Li-containing solution and then the Li-containing solid is completely dissolved in acid again [Marcus, Y., Hydrometallurgy 6 (1981), 269-275; Hamzaoui, AH, Jamoussi, B., M'nif, A. Hydrometallurgy 9 (2008), 1-7]. For the separation of Li ⁺ from the Al ³⁺ / Li ⁺ solution, liquid-liquid extraction with organic solvents such as alcohols has been proposed.

Ion exchange resins for Li separation have also been proposed instead of the inorganic sorbents [Bauman, WC, "Structure and Operation of DOW's New Lithium Selective Ion-Exchange Resin", in "Lithium - Current Applications in Science, Medicine and Technology", J. Wiley and Sons, 1985]. Although ion exchange resins can be better cut with respect to lithium ion selectivity, they are often more expensive than the abovementioned sorbents.

The direct liquid-liquid extraction of LiCl with alcohols such as isopropanol or isoamyl alcohol from very high concentration LiCl-containing solutions [US Pat. No. 4,274,834] or lower concentration [Bukowski, H., Uhlemann, E., Separ. Be. Technol. 28 (1993), 1357-1360] has been proposed. All these methods with the use of organic solvents have the disadvantage that the economy depends on the fullest possible recovery of the solvent. This is especially true for alcohols with particularly high Li selectivity such as 2-ethyl-1 .3-hexanediol.

Furthermore, [Talanta 20 (1973), 237- 240 Rona, M., Schmuckler, G.,] or electrodialysis [WO 2003/037794] has also been attempted opposite Mg ⁺⁺ higher ionic mobility of Li ⁺ for the separation by permeation to use. With such methods, it is difficult to realize high space-time yields.

The object of the invention is therefore a method that allows the accumulation of lithium and the separation of companion salts without lithium loss.

According to the invention the object is achieved by a process for the depletion of magnesium and enrichment of lithium in chloride salt solutions, in which the further evaporated solution is added with minimum contents of 4 g / L Li ⁺ and 60 g / L Mg ²⁺ KCl, which with the MgC of the solution is at least partially converted to carnallite (Kaliunncarnallit) and deposited in the form of Kaliunncarnallit, wherein the added KCI amount is such that the composition of the mother solution in the vicinity of the saturation of carnallite (Kaliunncarnallit) and KCl sets and thus the formation of lithium carnallite is avoided.

The fact that the composition of the mother solution sets in the vicinity of the saturation of Kaliunncarnallit and KCl, means that the mother liquor has taken up the maximum amount of KCl according to their temperature and thus the preferred deposit Kaliunncarnallit is secured against Lithiumcarnallit.

It has now been found that in solutions that z. B. from concentrated saline brines as essential constituents still LiCl and MgC, MgC depleted and LiCI can be further concentrated by always adding so much KCl that MgC in the form of carnallite (Kaliunncarnallit) is deposited and always solid KCl in suspension is available. The inventive method allows the enrichment of lithium with simultaneous depletion of magnesium from solutions of chloridic nature, which have high magnesium contents in relation to the lithium content, as z. B. in the Brines of Salar de Uyuni or the Brines (Bolivia) of the Qaidam Basin (China) is the case. This is achieved by adding as much KCl as possible to the solution starting from a minimum content of Li ⁺ and Mg ²⁺ for the further concentration of Li ⁺ so that potassium carnallite forms and a solution composition approaches approximately in the range of saturation with carnallite and KCl sets. Lithium loss through the formation of lithium carnallite is prevented in this way and the MgC discharged as potassium carnallite by solid-liquid separation. The KCl is recovered by known methods of carnallite decomposition.

The further evaporated solutions with minimum contents of 4 g / L Li ⁺ and 60 g / L Mg ²⁺ KCl is added, which is at least partially reacted with the MgC of the solution to carnallite. Thus, MgC in the form of Kaliumcarnallit at a suitable temperature by solid-liquid separation are discharged from the solution. The amount of KCI added is such that the composition of the mother liquor settles near saturation with carnallite and KCl, which is best ensured by the steady presence of solid KCl in the suspension.

The presence of crystalline KCl in the suspension, with sufficient mixing, prevents the formation of lithium carnallite, which otherwise causes lithium loss and limits the lithium chloride concentration process.

Thus, in the presence of KCl, the solution can be further evaporated until a sufficiently high Li: Mg mass ratio is achieved.

If evaporation occurs at elevated temperature, it is conveniently allowed to cool to ambient temperature and separate the potassium carnallite from the mother liquor by conventional solid-liquid separation techniques. For the mother solution, Li: Mg mass ratios of up to 7: 1 can be achieved in this way.

The KCl is fed gradually or continuously to the evaporator. The addition of the KCl can be carried out periodically or continuously, just as the carnallite can be separated off in one or more stages or can also be made continuous. The actual design depends essentially on the mass ratio of potassium carnallite to be formed and the remaining volume of mother solution resulting for a desired Li: Mg ratio.

According to an advantageous embodiment of the invention, the KCl is added in solid form, as an aqueous suspension with optionally further dissolved salts such as NaCl or MgC or as a homogeneous saturated solution.

The KCl may be in solid form, preferably fine-grained, metered or in a thick aqueous suspension, which may contain besides water also other for LiCI separation little disturbing components such as NaCl, MgC or some sulfate. A homogeneous saturated or nearly saturated aqueous solution of KCl is also applicable.

The time of KCI addition in the process can be chosen differently, but should be at least shortly before reaching saturation of lithium carnallite in the mother liquor.

According to an advantageous embodiment of the method according to the invention KCl is added after the evaporation of the desired amount of water. The evaporation can be carried out according to this variant, first at elevated temperature to the desired degree of concentration and then added KCl and cooled after a certain period of time for the Lösereaktion and as described above potassium carnallite are separated.

The potassium carnallite which forms is discharged stepwise or continuously from the solution to the evaporator by means of solid-liquid separation. For solid-liquid separation, filtration with vacuum or overpressure or centrifugation or a combination of methods is used.

The potassium carnallite separation takes place at temperatures of 15 to 60 ° C, preferably at 15 to 40 ° C. The suitable temperature for carnallite separation is preferably the ambient temperature. The deposition of magnesium chloride in the form of potassium carnallite has the further advantage that the morphology of the carnallite crystals for a solid-liquid separation is more favorable than that of bishopite and less mother solution sticks to the solid-liquid separation. Moreover, solutions close to the compositions of simultaneous saturation of potassium carnallite and KCl, at a given LiCl concentration, have higher vapor pressures and lower viscosities than solutions at higher MgC.sub.x concentrations necessary for bischofite deposition.

The precipitated and discharged potassium carnallite can be broken down into KCl and a concentrated MgC ^ solution by using water or a relatively dilute MgCl solution by known methods. Preferably, this carnallite decomposition will be carried out at ambient temperature. In this way, the KCl used for MgC ^ enrichment recovered back and can be used again for the inventive method.

If potassium carnallite precipitates on the basis of corresponding potassium contents of the starting solutions in upstream process steps, it can be included in the decomposition process of KCI recovery and the excess KCl can be discharged from the process and further processed into a salable product.

According to an advantageous embodiment of the method according to the invention KCl is recovered in the process step of Carnallitzersetzung on the recovery of the KCl by including incurred from other process steps potassium carnallite and / or KCI-containing fractions.

The inventive method for depletion of magnesium and enrichment of lithium is an essential step in the production of concentrated lithium solutions of solutions of natural Li-containing salt deposits (Brines). The solutions are mostly saturated NaCl solutions with varying concentrations of the ions K ⁺ , Mg ⁺⁺ , Li ⁺ and SO ₄ ^~~ as well as borate. The concentration for Li ⁺ is usually in a range between 200-4000 ppm. For K ⁺ , Mg ⁺⁺ and SO ₄ ^~~ the concentrations reach into the tens of gram range. Concentrated lithium solutions are prepared by the process according to the invention from such solutions with the following steps: a) separation of NaCl and KCl by evaporation,

 b) if appropriate, the crystallization and separation of magnesium sulfate hydrate and its double salts,

 c) desulphating by addition of concentrated CaCl 2 solution and separation of the sulphates in a known manner,

 d) crystallization of boric acid by addition of hydrochloric acid and separation of the borates,

e) upon reaching such a concentrated solution with minimum contents of 4 g / L Li ⁺ and 60 g / L Mg ²⁺ depletion of MgC and enrichment of LiCl according to the method of the invention.

At least in process steps a) and e), a concentration is carried out by evaporation.

In a typical processing of solutions from a Salar, such as Salary de Uyuni, the content of Li ⁺ is first brought to about 4-15 g / L by solar evaporation, with typical Mg ²⁺ contents of 60-90 g / L result.

Depending on the sulphate content, complete desulphation or at least partial desulphation is carried out either on the way to this Li.sup. ⁺ Concentration or after it has been reached. Thereafter, most of the borate is removed by crystallization of boric acid, which forms after the reaction with appropriate amounts of sulfuric or hydrochloric acid.

KCl can then be added in several stages, further evaporated and the crystallizing carnallite separated from the mother liquor by a suitable solid-liquid separation method (filtration, centrifugation). The Li: Mg ratio has then typically increased to about 3: 1, with Li ⁺ concentrations in the range of 20-60 g / L. The carnallite is washed with a small amount of water or a suitable process solution in order to remove most of the LiCI adhering to the mother liquor. before being sent to KCI recovery for decomposition. The washing solution is recycled in the process stages located further up.

The highly concentrated LiCl solution is then subjected to a fine cleaning, in particular to the remaining magnesium removal by adding NaOH, if appropriate also containing Na 2 CO 3, in order then to precipitate with soda U 2 CO 3. In another variant, the LiCl solution can be directly further evaporated to crystallize LiCl hydrate or LiCl.

embodiment

5 L of a Salar de Uyuni solution containing 2.8 g / L of Li ⁺ , 70 g / L of Mg ²⁺ , 31 .5 g / L of SO ^{2 ~} and 14 g / L of boric acid was concentrated with a stoichiometric amount CaCl 2 solution was desulfurized to a content of 4.6 g / L SO ₄ ^{2 "} and then 40% of the water was evaporated off, the Li ⁺ content rising to 4.5 g / L and that of Mg ²⁺ to 85 g / L. Next, most of the borate was removed by addition of 37% hydrochloric acid and crystallization of the boric acid at ambient temperature, HCl being in 20% excess with respect to the following reaction

B ₄ O ₇ ^{2 "} + 2H ⁺ + 5H ₂ O -> 4H ₃ BO _3. The reaction was carried out in the heat at 70 ° -80 ° C., while some water was expelled, and the boric acid content after separation was still present 7 g / L and that of Li + and Mg ²⁺ at 6.2 g / L and 1 10 g / L. Subsequently, finely ground KCl was added in 3 stages in each case in slight excess with respect to the amount required for carnallite formation the following contents were found in the mother liquor:

Stage Li ⁺ (g / L) Mg ²⁺ (g / L)

 I. 1 1 .2 60.0

 II 35.9 45.8

III 53.7 20.0 The borate content converted to boric acid dropped further to about 4 g / L. The solution lumen decreased from 1755 mL before Stage I to 200 mL after Stage III.

Claims

1 . Process for depletion of magnesium and enrichment of lithium in chloride salt solutions with minimum contents of 4 g / L Li ⁺ and 60 g / L Mg ²⁺ , in which the KCl solution to be further evaporated is metered in, at least partially into potassium carnallite with the MgC of the solution reacted and deposited in the form of potassium carnallite, wherein the amount of KCI added is such that the composition of the mother liquor adjusts to the saturation of carnallite and KCl.

2. The method according to claim 1, characterized in that the added KCI amount is such that always solid KCl is present in suspension.

3. The method according to claim 1 or 2, characterized in that the KCl is supplied in stages or continuously.

4. The method according to any one of claims 1 to 3, characterized in that the KCl is added in solid form, as an aqueous suspension optionally with further dissolved salts such as NaCl or MgCfe or as a homogeneous saturated or nearly saturated solution.

5. The method according to any one of claims 1 to 4, characterized in that KCl is added after the evaporation of the desired amount of water.

6. The method according to any one of claims 1 to 4, characterized in that the potassium carnallite is gradually or continuously discharged from the solution from the evaporator by means of solid-liquid separation.

7. The method according to claim 5, characterized in that for the solid-liquid separation, a filtration with vacuum or pressure or a centrifugation or a combination of methods are used.

8. The method according to claim 6 or 7, characterized in that the Carnallitabtrennung takes place at 15 to 60 ° C.

9. The method according to any one of claims 5 to 8, characterized in that the discharged potassium carnallite decomposes by known methods and that thereby recovered KCl is recycled to the process.

10. The method according to claim 9, characterized in that obtained from other process steps carnallite and / or KCI-containing fractions are used.

1 1. A process for the preparation of concentrated lithium solutions from natural chloride-containing lithium-containing salt solutions, comprising the following steps: a) separation of NaCl and KCl by evaporation,

b) desulphating by addition of concentrated CaCl ₂ solution and separation of the sulphates in a known manner,

 c) optionally crystallization and separation of magnesium sulfate hydrate and its double salts,

 d) crystallization of boric acid by addition of sulfuric acid or hydrochloric acid and separation of the borates,

e) on reaching such a concentrated solution having minimum contents of 4 g / L Li * and 60 g / L Mg ²⁺ depleting MgCl ₂ and enriching LiCl according to any one of claims 1 to 8, wherein at least in the process steps a) and e) concentration by evaporation takes place.