RU2347829C2 - Method of producing lithium hydroxide out of spodumene concentrate - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to method of producing lithium hydroxide out of spodumene concentrate. The method includes activation and successive sulphatisation of the concentrate, water leaching of sulphatised concentrate with transition of lithium sulphate into a solution. Further neutralisation of leaching pulp is carried out. After separation of neutralised pulp out of produced solution of lithium sulphate lithium hydroxodialuminate is settled at ambient temperature by treatment with concentrated solution of sodium aluminate at weight ratio Al:Li 11.5÷12.5 in produced pulp. Further causticization of lithium hydroxodialuminate is led with lime milk at consumption CaO 4.0÷4.5 g per 1 g in lithium hydroxodialuminate with following separation of lithium hydroxide solution from calcium aluminate final slag. Crystallisation is performed by evaporation out of solution of lithium hydroxide with successive separation of pulp of lithium hydroxide crystals into solid and liquid phases.

EFFECT: reduction of lithium losses and also reduced power consumption of process.

2 tbl, 1 ex

Description

The invention relates to metallurgy, in particular to the processing of spodumene concentrates.

Spodumene (Li ₂ O · Al ₂ O ₃ · 4SiO ₂ ) is one of the main industrial lithium minerals [Ostroushko Yu.I., Buchihin P.I., Alekseeva V.V. et al. Lithium, its chemistry and technology. M .: Atomizdat, 1960. - S.12-18]. In mining operations, spodumene is extracted from ores in the form of spodumene concentrates.

To extract lithium from spodumene concentrate, a large number of known methods can be used: sulfate, sulfuric acid, and others [Ostroushko Yu.I., Buchihin P.I., Alekseeva V.V. et al. Lithium, its chemistry and technology. M .: Atomizdat, 1960. - P.121-157; Plyushchev V.E., Stepin B.D. Chemistry and technology of compounds of lithium, rubidium and cesium. M .: Chemistry, 1970. - S.226-272].

Sulfate method [Plyushchev V.E., Stepin B.D. Chemistry and technology of compounds of lithium, rubidium and cesium. M .: Chemistry, 1970. - P.254-264], taken as an analogue, based on the interaction of spodumene and K ₂ SO ₄ (at t = 1050 ÷ 1100 ° C) with the formation of water-soluble lithium sulfate and water-insoluble potassium aluminosilicate:

.

.

Water leaching of the cake obtained in this way manages to transfer 95% of the mass. lithium in solution, leaving insoluble potassium aluminosilicate in the sediment. By filtering off the latter, a lithium sulfate solution is obtained. In order to concentrate lithium, the sulfate solution was evaporated. An aluminum impurity is removed from the solution in the form of sparingly soluble Al (OH) _{3 by} neutralization of the evaporated solution with sodium hydroxide or potash to pH≈7. The purified lithium sulfate solution is treated with soda ash at the boiling point, resulting in the precipitation of poorly soluble lithium carbonate (Li ₂ CO ₃ ), which is subjected to water washing from impurities (boiling the solution is necessary, since under these conditions lithium carbonate has minimal solubility). Due to the increased solubility of lithium carbonate in solutions of alkali metal sulfates, the deposition of lithium carbonate is not complete, the total extraction of lithium from the concentrate to carbonate is (excluding recycled lithium-containing technology products) only 50% of the mass. [Ostroushko Yu.I., Buchihin P.I., Alekseeva V.V. et al. Lithium, its chemistry and technology. M .: Atomizdat, 1960. - P.135].

The lithium carbonate washed from impurities is used to produce lithium hydroxide by causticizing lithium carbonate with lime milk [Plyushchev V.E., Stepin B.D. Chemistry and technology of compounds of lithium, rubidium and cesium. M .: Chemistry, 1970. - S.272-277]:

After separation of the calcium carbonate from the lithium hydroxide solution, this solution was evaporated to give crystals of lithium hydroxide monohydrate (LiOH · H ₂ O). The output of lithium from carbonate in hydroxide monohydrate is up to 90% of the mass.

The disadvantage of the analogue method are:

- low extraction of lithium from a sulfate solution to lithium carbonate and from lithium carbonate to lithium hydroxide;

- the use of energy-intensive evaporation of the initial solution of lithium sulfate before deposition of lithium carbonate from it;

- the use of energy-intensive deposition of lithium carbonate from a boiling sulfate solution.

The closest set of features to the proposed method is a sulfuric acid method for extracting lithium from spodumene concentrates [Plyushchev V.E., Stepin B.D. Chemistry and technology of compounds of lithium, rubidium and cesium. M .: Chemistry, 1970. - S.234-242]. In the sulfuric acid process, lithium is selectively extracted by preliminary activating roasting (decryptation) of spodumene at 1100 ° C and subsequent processing of the activated feed with sulfuric acid at 250-300 ° C. Firing spodumene leads to a change in the crystal lattice of the mineral and makes it possible to transfer 99-100% of the mass. lithium to water-soluble sulfate by the action of sulfuric acid:

.

.

The second reaction product is H ₂ O · Al ₂ O ₃ · 4SiO ₂ , during the subsequent water leaching of the sulfated feed, it remains in an insoluble residue, filtering which gives a solution of lithium sulfate. Loss of water-soluble lithium with an insoluble residue is << 1% of the mass. from its content in spodumene concentrate. In order to concentrate lithium, a sulfate solution containing 100 g / l of Li ₂ SO ₄ was evaporated to a content of Li ₂ SO ₄ in it of 200 g / l. An aluminum impurity is removed from the solution in the form of sparingly soluble Al (OH) _{3 by} neutralization of the evaporated solution with calcium carbonate to pH = 6.0–6.5. The purified lithium sulfate solution is treated with soda ash at the boiling point, resulting in the precipitation of poorly soluble lithium carbonate, which is washed with water from impurities. Due to the noticeable solubility of lithium carbonate, its precipitation from a solution of lithium sulfate is not complete enough even under conditions of boiling the solution.

The lithium carbonate washed from impurities is used to produce lithium hydroxide by causticizing lithium carbonate with lime milk [Plyushchev V.E., Stepin B.D. Chemistry and technology of compounds of lithium, rubidium and cesium. M .: Chemistry, 1970. - S.272-277] according to the reaction equation (2). After separation of the calcium carbonate from the lithium hydroxide solution, the solution was evaporated to give crystals of lithium hydroxide monohydrate. The output of lithium from carbonate in hydroxide monohydrate is up to 90% of the mass.

The disadvantage of the prototype method are:

- low extraction of lithium from a sulfate solution to lithium carbonate and from lithium carbonate to lithium hydroxide;

- the use of energy-intensive double (by volume) evaporation of the initial solution of lithium sulfate before deposition of lithium carbonate from it;

- the use of energy-intensive deposition of lithium carbonate from a boiling sulfate solution.

The problem to which the claimed invention is directed, is to develop a method for producing lithium hydroxide from spodumene concentrate, which reduces lithium losses from the mother liquor from the stage of lithium extraction from the sulfate solution to the primary technical lithium compound and reduces lithium losses with causticization cake of the indicated compound, and also reducing the energy intensity of the process.

The essence of the proposed method for producing lithium hydroxide from spodumene concentrate is that, in contrast to the known prototype method, which includes activation and subsequent sulfatization of the concentrate, water leaching of the sulfated concentrate with the conversion of lithium sulfate into solution, neutralization of the leaching pulp, separation of the neutralized leaching pulp into a solution lithium sulfate and dump cake, deposition of lithium compounds from a sulfate solution, separation of precipitated lithium compounds from the dump of the mother liquor, caustification of the separated lithium compound with lime milk to produce a lithium hydroxide solution, separation of the lithium hydroxide solution from the waste sludge, crystallization of lithium hydroxide by evaporation of its solution, followed by separation of the pulp of lithium hydroxide crystals into solid and liquid phases, according to the invention after separation of the neutralized pulp leaching of the obtained lithium sulfate solution at ambient temperature precipitates lithium hydroxodialuminate a concentrated solution of sodium aluminate with a mass ratio of Al: Li in the resulting pulp of 11.5 ÷ 12.5, and the caustification of lithium hydroxodialuminate is carried out at a CaO consumption of 4.0 ÷ 4.5 g per 1 g of lithium in its hydroxodialuminate, followed by separation of the lithium hydroxide solution from dump calcium aluminate.

The solution of this problem and the achievement of relevant technical results is ensured by the fact that in the inventive method, insoluble lithium hydroxodialuminate (Li ₂ O · Al ₂ O ₃ · 11H ₂ O) is deposited as a primary technical compound from a sulfate solution. This achieves a high extraction of lithium from a sulfate solution in comparison with the prototype method, according to which a significantly more soluble lithium carbonate is precipitated from this solution. Moreover, in the inventive method there is no need to evaporate the sulfate solution, as well as to heat it when precipitating lithium hydroxodialuminate from the specified solution, since, unlike lithium carbonate, the solubility of lithium hydroxodialuminate in water is the lower, the lower the dissolution temperature. The flow rate and concentration of the precipitant lithium hydroxodialuminate (lithium aluminate solution) is determined based on the achievement of high lithium recovery from the sulfate solution. In the process of causticizing lithium hydroxodialuminate with lime milk, a lithium hydroxide solution is obtained. Subsequent evaporation of this solution gives crystals of lithium hydroxide monohydrate, which are separated from the mother liquor by filtration. The consumption of calcium oxide for the caustification of lithium hydroxodialuminate is determined on the basis of achieving high lithium extraction in a lithium hydroxide solution.

An example implementation of the method.

The method is carried out on conventional equipment using spodumene concentrate with a lithium content of 3.28% of the mass. The concentrate is processed by the prototype method to the stage of evaporation of a lithium sulfate solution having a concentration of 100 g / l.

Further processing of the obtained solution of lithium sulfate is performed both by the prototype method and by the claimed method.

According to the claimed method, the sulfate solution at ambient temperature is treated with a concentrated solution of sodium aluminate to obtain a mass ratio of Al: Li in the pulp of the precipitated lithium hydroxodialuminate of 11.5 ÷ 12.5. Precipitation is carried out for 1 h while stirring the pulp. Then the precipitated lithium hydroxodialuminate is filtered off from the mother liquor. By the residual lithium content in the mother liquor, the completeness of the deposition of lithium from the sulfate solution into the hydroxodialuminate is estimated. The obtained lithium hydroxodialuminate is subjected to a 2-time filter-repulpative washing with water at 18 ÷ 22 ° C, T: W = 1: 4 (by wet lithium hydroxodialuminate), the duration of each washing is 30 minutes. The washed hydroxodialuminate is causticized (treated with milk of lime at the rate of 4.0 ÷ 4.5 g CaO per 1 g of lithium in its hydroxodialuminate). Caustification is carried out at 80 ° C and stirring the pulp for 1 h, after which the solution of the formed lithium hydroxide is separated from the insoluble calcium aluminate (CaO · 2Al ₂ O ₃ ) by filtration. Subsequent crystallization of lithium hydroxide by evaporation of its solution is carried out in accordance with the prototype method. The filtered calcium aluminate is subjected to filter-repulpative washing with water at 80 ° C, T: W = 1: 3 (by wet calcium aluminate) for 15 minutes. The residual lithium content in the washed calcium aluminate assesses the completeness of lithium extraction in an alkaline solution.

Table 1 shows the results of the process for producing lithium hydroxide from spodumene concentrate according to the present method and the prototype method (precipitation of hydroxodialuminate and lithium carbonate from a solution of lithium sulfate).

Table 1 Example No. Implementation Method Al: Li weight ratio in lithium hydroxodialuminate pulp The lithium content in the mother liquor after deposition of lithium hydroxodialuminate (carbonate), g Extraction of lithium in lithium hydroxodialuminate (carbonate),% wt. one The claimed
the way 8.5 0.7 93 2 11.5 0.2 98 3 12.5 0.1 99 four 14.0 0.1 99 5 Prototype method - (0.9) (91) Note: in examples 1-5, the initial loading of a solution of lithium sulfate (conc. 100 g / l) for the precipitation of hydroxodialuminate and lithium carbonate was 10 g in terms of lithium.

Table 2 shows the results of the process for producing lithium hydroxide from spodumene concentrate according to the claimed method and the prototype method (causticization of hydroxodialuminate and lithium carbonate).

table 2 Example No. Implementation Method CaO consumption, g / g lithium in lithium hydroxodialuminate (carbonate) The lithium content in the caustification sludge, g Extraction of lithium from hydroxodialuminate (carbonate) of lithium,% wt. one The claimed
the way 3,7 0.8 92 2 4.0 0.3 97 3 4,5 0.2 98 four 4.9 0.3 97 5 Prototype method (4,5) (1,0) (90) Note: 1) in examples 1-5, the initial charge of lithium hydroxodialuminate and lithium carbonate for caustification was 10 g in terms of lithium;
2) in examples 1-4, a mixture of lithium hydroxodialuminates obtained in examples 2 and 3 was used (table 1).

From the data of table 1 it follows that the inventive method allows to extract lithium from a sulfate solution in lithium hydroxodialuminate to 98-99% of the mass. (examples 2 and 3), while in the prototype method, the extraction of lithium from a sulfate solution in lithium carbonate is only 91% of the mass. (example 5). In addition, in the claimed method there is no energy consumption for evaporation of a solution of lithium sulfate and boiling of this solution in the process of deposition from it of the primary technical compound of lithium (lithium hydroxodialuminate). With an increase in the consumption of the precipitating agent of lithium hydroxodialuminate (sodium aluminate solution) to obtain a mass ratio of Al: Li in the pulp of lithium hydroxodialuminate of 14.0 (Table 1, Example 4), the extraction of lithium in lithium hydroxodialuminate remains at the level of 99% of the mass. At the same time, the consumption of precipitant increases, which is economically impractical. When the consumption of the precipitating agent of lithium hydroxodialuminate is reduced to obtain a mass ratio of Al: Li in the pulp of lithium hydroxodialuminate of 8.5 (Table 1, Example 1), the extraction of lithium in lithium hydroxodialuminate decreases to 93% of the mass. The inventive method allows more fully to recover lithium from a sulfate solution due to the deposition of lithium in the form of a compound significantly less soluble than lithium carbonate - lithium hydroxodialuminate.

The data of table 2 on the causticization of lithium hydroxodialuminate show that the maximum in the present method, the extraction of lithium in a solution of lithium hydroxide (97 ÷ 98% wt.) Is achieved when CaO consumption of 4.0 ÷ 4.5 g / g of lithium in hydroxodialuminate (examples 2 and 3). A further increase in the CaO consumption for the caustification of lithium hydroxodialuminate (Table 2, Example 4) is not economically feasible, since the degree of extraction of lithium from lithium hydroxodialuminate in a lithium hydroxide solution does not increase. If the CaO consumption at the causticization stage is less than 4.0 g / g of lithium in hydroxodialuminate, then the degree of lithium extraction from lithium hydroxodialuminate in the lithium hydroxide solution is reduced to 92% by weight. (table 2, example 1).

As follows from the data of table 2 (example 5), the prototype method, in contrast to the claimed one, is characterized by significantly lower lithium extraction in a lithium hydroxide solution at the stage of causticization of the primary technical lithium compound - lithium carbonate (in the prototype method, this extraction is only 90% of the mass .).

From the data of tables 1 and 2, it follows that the claimed method (prototype method) are characterized by the following indicators:

- the extraction of lithium from the concentrate in the sulfate solution is 99% of the mass. (99% of the mass.);

- the extraction of lithium from a sulfate solution in the primary technical compound of lithium (lithium hydroxodialuminate, lithium carbonate) is 99.5% of the mass. (91% of the mass.);

- the extraction of lithium from the primary technical compound of lithium in a solution of lithium hydroxide is 97.5% of the mass. (90% of the mass.).

Thus, the inventive method allows you to remove lithium from the concentrate in a solution of lithium hydroxide to 96% of the mass. (0.99 · 0.995 · 0.975 · 100 = 96), while in the prototype method, the specified extraction is only 81.1% of the mass. (0.99 · 0.91 · 0.90 · 100 = 81.1). In addition, the inventive method for producing lithium hydroxide from spodumene concentrate, in contrast to the prototype method, is characterized by lower energy consumption due to the elimination of the operation of evaporation of a solution of lithium sulfate and the exclusion of boiling of this solution at the stage of deposition of the primary technical lithium compound.

Claims (1)

A method for producing lithium hydroxide from a spodumene concentrate, including activation and subsequent sulfatization of the concentrate, water leaching of a sulfated concentrate with the conversion of lithium sulfate into a solution, neutralization of the leach pulp, separation of the neutralized leach pulp into a lithium sulfate solution and dump cake, lithium sulfate solution precipitation, separation of the sulfate compound precipitated lithium compounds from the stock mother liquor; caustification of the separated lithium compounds with milk of lime to obtain a lithium hydroxide solution, separating a lithium hydroxide solution from the waste sludge, crystallizing lithium hydroxide by evaporation of its solution, followed by separation of the pulp of lithium hydroxide crystals into solid and liquid phases, characterized in that after separation of the neutralized pulp of leaching from the obtained lithium sulfate solution at ambient temperature media precipitate the lithium compound in the form of lithium hydroxodialuminate by treatment with a concentrated solution of sodium aluminate at a mass ratio of Al: L i in the resulting pulp 11.5 ÷ 12.5, and the caustification of lithium hydroxodialuminate is carried out at a CaO consumption of 4.0 ÷ 4.5 g per 1 g of lithium in lithium hydroxodialuminate, followed by separation of the lithium hydroxide solution from the dump slurry of calcium aluminate.