PROCESS FOR THE RECOVERY OF LITHIUM

Abstract

The present invention relates to an enhanced process for the recovery of lithium from compositions also containing aluminum. An example of such a metallurgical compositions is the metallurgical slag that is obtained when recycling lithium-ion batteries or their derived products using a pyrometallurgical smelting process. Acid leaching of such a slag, followed by neutralization to precipitate aluminum leads to poor lithium yields as lithium tends to co-precipitate with aluminum. A process is presented wherein aluminum is selectively precipitated using a source of phosphate at a controlled pH preferably between 3 and 4.

Claims

1-5. (canceled)

6. A process for recovering lithium from a lithium- and aluminum-bearing metallurgical composition, comprising the steps of: leaching the metallurgical composition by contacting the composition with a sulfuric acid aqueous solution at a pH of 3 or less, thereby obtaining a residue comprising insoluble compounds and a first leachate comprising lithium and aluminum; optionally, neutralizing the first leachate comprising lithium and aluminum to a pH of 2 to 4, thereby precipitating a residue comprising a first part of the aluminum, and obtaining a second leachate comprising lithium; adding a source of phosphate ions to the first leachate comprising lithium and aluminum, or, with the proviso that the optional neutralizing of the first leachate is performed, to the second leachate comprising lithium and aluminum, thereby precipitating a residue comprising a second part of the aluminum, and obtaining a third leachate comprising lithium; optionally neutralizing the third leachate comprising lithium and aluminum to a pH of 3 to 4, thereby precipitating a residue comprising a third part of the aluminum, and obtaining a fourth leachate comprising lithium; and separating the residue comprising the second part of the aluminum from the third leachate by filtration, or, with the proviso that the optional neutralizing of the third leachate is performed, separating the residue comprising the third part of the aluminum from the fourth leachate by filtration.

7. The process according to claim 6, further comprising, after the step of leaching and before the step of adding a source of phosphate, separating the first leachate comprising lithium and aluminum by filtration.

8. The process according to claim 6, further comprising, after the optional step of neutralizing the first leachate and before the step of adding a source of phosphate, separating the second leachate comprising lithium and aluminum by filtration.

9. The process according to claim 6, further comprising precipitating lithium from the fourth leachate, and separating the lithium by filtration.

10. The process according to claim 6, wherein the metallurgical composition is a metallurgical slag.

Description

[0025] Example 1 illustrates the co-dissolution of aluminum during the leaching of lithium slag.

[0026] A slag containing approximately 2.5% Li was submitted to a leaching test in order to assess the leachability of lithium. Approximately 300 g of slag was repulped in 1.0 L water, and the slurry was heated to 70° C. Upon reaching this temperature, H.sub.2SO.sub.4 was slowly added to acidify the pulp and dissolve the lithium. The H.sub.2SO.sub.4 dosing was performed in such a way that the acidity of the pulp reached a pH of 4. After equilibration for a period of 12 hours at pH 4, a first slurry sample was taken. Subsequently, the pH of the slurry was further decreased in a stepwise fashion and after each pH adjustment, the slurry was equilibrated for at least 12 hours before taking a sample.

[0027] The samples taken at pH 3, 2.5, 2, and 1, were all filtered and washed. Both the filtrates, wash waters and residues were analyzed for Li as well as for the typical slag formers being Ca, Si and Al. An overview of the filtrate compositions and the calculated metal leach yields is shown in Table 1.

[0028] The results reveal that the majority of the lithium can be dissolved already at pH 2.5. Unfortunately, the co-dissolution of Al is already significant at this pH. As a result of this unfavorable behavior of Al, the filtrates that are obtained in the lower pH region contain considerably more Al than Li.

[0029] The conclusion can be drawn that with this type of slag, it is not possible to combine good Li leach yields with a good selectivity towards Al. This means that high Li leach yields will necessarily result in the presence of large amounts of unwanted Al in solution.

TABLE-US-00001 TABLE 1 Compositions and yields in function of the pH when leaching a slag Filtrate (g/L) Leaching yield (%) pH of sampling Li Ca Si Al Li Ca Si Al 4.0 2.6 0.62 0.29 0.07 30 1 1  0 3.0 3.7 0.72 0.28 3.5 46 1 1  7 2.5 5.8 0.73 0.29 27 96 1 1 60 2.0 5.5 0.62 0.38 31 97 1 1 73 1.0 5.3 0.59 0.53 26 98 1 2 86

[0030] Example 2 shows how Al can be precipitated from solution selectively when phosphates are used.

[0031] A synthetic solution containing 20 g/L Li, 10 g/L Al and 3 g/L Fe.sup.2+ was prepared using Li.sub.2CO.sub.3 and sulfate salts of Al and Fe. H.sub.2SO.sub.4 was added to obtain an acidic solution at pH 1.5. Subsequently, 145 g of solid sodium phosphate (Na.sub.3PO.sub.4.12H.sub.2O) was added to 1.0 L of the synthetic solution; this addition represented a 100% stoichiometry with respect to the amount of Al in solution.

TABLE-US-00002 TABLE 2 Compositions in function of pH when precipitating with phosphate Li Al PO.sub.4.sup.3− Fe Start solution (g/L) 20 10 0 3 pH of sampling 2.6 Filtrate (g/L) 16 8.6 31 2.6 Residue (%) <0.05 17 1 3 Filtrate (g/L) 15 0.7 3.1 2.1 Residue (%) <0.05 18 0.4 4 Filtrate (g/L) 14 0.005 <0.3 2.1 Residue (%) <0.05 19 0.5

[0032] Upon addition of the sodium phosphate, the pH slightly increased, but NaOH was used to further neutralize the solution to pH 2.6, after which a first sample was taken.

[0033] Next, the pH was further increased to pH 3 and 4 in order to investigate the behavior of the various metals of interest. Each of the three samples was filtered and washed, after which both the filtrates and the residues were analyzed. The analytical results are given in Table 2.

[0034] From these results, it becomes clear that only a limited amount of Al precipitates at pH 2.6. The removal becomes more efficient at higher pH and at pH 4.0 the residual Al concentration is as low as 5 mg/L. Chemical analysis of the residues shows that the Li content remains below the detection limit of 500 ppm in all cases. This is a clear indication that no Li is lost to the alumina-bearing cake. Finally, the various Fe analyses show that less than 10% of that metal reports to the residue.

[0035] The important conclusion that can be drawn from this test is the following: when Al is removed from solution as an AlPO.sub.4 precipitate, no Li significant losses are encountered.

[0036] Example 3 shows how Al can be selectively removed from the filtrate of a slag leaching operation when Na.sub.3PO.sub.4 is applied as phosphate source.

[0037] The first part of example 3 is performed in a way similar to that of example 1: approximately 300 g of a Li-containing slag were repulped in 1.0 L of water and the slurry was heated to 70° C. Upon reaching that temperature, H.sub.2SO.sub.4 was slowly added to acidify the pulp and dissolve the Li. The H.sub.2SO.sub.4 dosing was performed so as to stabilize the pH at 2.5. After 5 hours, no more acid was consumed and the leaching operation was stopped. The slurry was filtered and chemical analysis showed that 6.8 g/L Li and 24 g/L Al were present in the leach solution. Leach yields of 94% and 47% were calculated for Li and Al.

[0038] Approximately 500 mL of the filtrate was slightly diluted and heated to 90° C. and Na.sub.3PO.sub.4 was slowly added as a phosphate source for precipitation of Al. The stoichiometric Na.sub.3PO.sub.4 requirement was calculated to be 73 g. After this amount had been added, the pH increased to 3.9. The slurry was left to equilibrate for approximately 3 hours before it was filtered. The residue was subsequently washed and both filtrate and residue were analyzed. The filtrate was found to contain less than 10 mg/L Al. From the chemical analyses of the residue, a lithium loss of less than 1% was calculated.

[0039] The results from this example show that relatively large amounts of Al can be precipitated from a slag leaching filtrate with high selectivity towards lithium when an appropriate phosphate source is used as precipitating agent.

[0040] Example 4 is presented to show how Li-containing slags and a suitable phosphate source can be used in one process.

[0041] A synthetic solution containing 18 g/L Li and 50 g/L H.sub.2SO.sub.4 was heated to 70° C. and neutralized to pH 2.5 using milled Li-bearing slag. After the undissolved fraction was removed by means of filtration, the filtrate was analyzed to contain 19.1 g/L Li, and 6.2 g/L Al.

[0042] In order to precipitate all Al from solution, a stoichiometric amount of 38 g of Na.sub.3PO.sub.4 was added to 1.0 L of the leach solution. Subsequently, the solution was further neutralized to pH 4.1, and another filtration was performed. The filtrate was analyzed to contain less than 10 mg/L Al.

[0043] The results obtained with this experiment show that it is possible to use a combination of Li slags and a suitable phosphate source, which in this case was Na.sub.3PO.sub.4, to effectively neutralize an acidic solution that is typically encountered in spodumene processing.