LITHIUM CARBONATE RECOVERY PROCESS

Abstract

A process for the recovery of lithium carbonate from a solution (1) containing a mixture of lithium sulfate and lithium hydroxide, the process comprising the precipitation of lithium carbonate (3) from the solution (1) containing a mixture of lithium sulfate and lithium hydroxide through the addition of carbon dioxide (2).

Claims

1-19. (canceled)

20. A process for the recovery of lithium carbonate from a solution containing a mixture of lithium sulfate and lithium hydroxide, the process comprising the precipitation of lithium carbonate from the solution containing a mixture of lithium sulfate and lithium hydroxide through the addition of carbon dioxide.

21. The process of claim 20, wherein a slurry resulting from the precipitation of lithium carbonate is passed to solid liquid separation, and optionally subsequent washing, to remove entrained liquor from the lithium carbonate.

22. The process of claim 21, wherein the liquor from solid liquid separation and/or washing contains lithium sulfate and some minor impurities.

23. The process of claim 21, wherein the liquor from solid liquid separation and/or washing contains lithium sulfate and some minor impurities, and that liquor is directed to a process to convert lithium sulfate to lithium hydroxide and thereby improving the recovery of lithium.

24. The process of claim 20, wherein lithium carbonate is precipitated at atmospheric pressure.

25. The process of claim 20, wherein lithium carbonate is precipitated at a temperature of: a. between ambient to about 100° C.; b. greater than about 50° C.

26. The process of claim 20, wherein the lithium precipitation occurs over a residence time of about 2 hours.

27. The process of claim 20, wherein the lithium precipitation achieves a precipitation extent of about 90% of the stoichiometric mass of lithium hydroxide contained in the solution containing both lithium sulfate and lithium hydroxide.

28. The process of claim 20, wherein lithium carbonate is precipitated with the addition of in excess of stoichiometric carbon dioxide addition.

29. The process of claim 20, wherein the process comprises the method steps of: a) Precipitation of lithium carbonate from a solution containing lithium sulfate and lithium hydroxide through the addition of carbon dioxide; b) Solid liquid separation and optionally washing of the precipitated lithium carbonate to recover a liquor containing lithium sulfate; c) Recycle of the liquor to a subsequent step to convert lithium sulfate to lithium hydroxide; d) Purification of the lithium carbonate by pulping in water and addition of carbon dioxide to produce lithium bicarbonate solution; e) Solid liquid separation of the lithium bicarbonate solution to remove insoluble impurities; f) Heating the lithium bicarbonate solution to strip carbon dioxide and re-precipitate lithium carbonate; and g) Solid liquid separation, drying and packing of the purified lithium carbonate product.

30. The process of claim 29, wherein the lithium carbonate precipitation step a) is operated at atmospheric pressure.

31. The process of claim 29, wherein the lithium carbonate precipitation step a) is operated in a temperature range of: a. between ambient to about 100° C.; b. greater than about 50° C.; or c. between about 50° C. to 100° C.

32. The process of claim 29, wherein the lithium carbonate precipitation step a) occurs over a residence time of about 2 hours.

33. The process of claim 29, wherein the lithium carbonate precipitation step a) achieves a precipitation extent of about 90% of the stoichiometric mass of lithium hydroxide contained in the solution containing both lithium sulfate and lithium hydroxide.

34. The process of claim 29, wherein the lithium carbonate precipitation step a) comprises the addition of in excess of stoichiometric carbon dioxide addition.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The process of the present invention will now be described, by way of example only, with reference to one embodiment thereof and the accompanying drawings, in which:—

[0036] FIG. 1 is a flow sheet depicting a process for the recovery of lithium carbonate from a solution containing lithium hydroxide and lithium sulfate containing liquor in accordance with the present invention.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

[0037] The present invention provides a process for the recovery of lithium carbonate from a solution containing a mixture of lithium sulfate and lithium hydroxide, the process comprising the precipitation of lithium carbonate from the solution containing a mixture of lithium sulfate and lithium hydroxide through the addition of carbon dioxide.

[0038] The addition of carbon dioxide to the solution containing both lithium sulfate and lithium hydroxide enables the separation of lithium from sulfate, and provides corresponding higher separation efficiency than the prior art.

[0039] The precipitation chemistry for lithium carbonate is shown as follows:

2LiOH.sub.(aq)+CO.sub.2(g).fwdarw.Li.sub.2CO.sub.3(g)+H.sub.2O.sub.(aq)

[0040] The slurry resulting from the precipitation of lithium carbonate is subject to solid liquid separation, and washing, to remove entrained liquor from the lithium carbonate.

[0041] The liquor from solid liquid separation and washing contains lithium sulfate and some minor impurities. The liquor, which contains lithium sulfate, is directed to a process to convert lithium sulfate to lithium hydroxide and to improve the recovery of lithium.

[0042] Lithium carbonate is precipitated at a temperature of between ambient to about 100° C., for example about 20° C. to 100° C. and at atmospheric pressure.

[0043] In one form of the present invention, lithium carbonate is precipitated at atmospheric pressure.

[0044] In one form of the present invention, lithium carbonate is precipitated at greater than about 50° C.

[0045] In a further form of the present invention, lithium carbonate is precipitated at between about 50° C. to 100° C.

[0046] In a still further form of the present invention the lithium precipitation occurs over a residence time of about 2 hours.

[0047] In a yet still further form of the present invention the lithium precipitation achieves a precipitation extent of about 90% of the stoichiometric mass of lithium hydroxide contained in the solution containing both lithium sulfate and lithium hydroxide.

[0048] Lithium carbonate is precipitated with the addition of in excess of stoichiometric carbon dioxide addition.

[0049] In one form the present invention provides a process for the recovery of lithium carbonate from a solution containing lithium sulfate and lithium hydroxide, the process comprising the method steps of: [0050] a) Precipitation of lithium carbonate from a solution containing lithium sulfate and lithium hydroxide through the addition of carbon dioxide; [0051] b) Solid liquid separation and washing of the precipitated lithium carbonate to recover a liquor containing lithium sulfate and solids containing lithium carbonate; and [0052] c) Recycle of the liquor post the solid liquid separation step (ii) to a preceding stage that converts lithium sulfate to lithium hydroxide.

[0053] The separation of the precipitated lithium carbonate from the liquor is achieved by filtration or decantation, and the resulting filtrate contains the large majority (greater than about 90%) of lithium sulfate contained in the liquor.

[0054] Washing of the lithium carbonate substantially removes entrained impurities and lithium sulfate.

[0055] In one embodiment of the process of the present invention, a lithium sulfate and lithium hydroxide containing liquor is treated in accordance with the present invention as shown in FIG. 1.

[0056] In FIG. 1 there is shown a flow sheet in accordance with the present invention and in which the embodiment depicted is particularly intended for the processing of lithium sulfate and lithium hydroxide containing liquor to recover lithium as lithium carbonate 17.

[0057] A lithium sulfate and lithium hydroxide containing solution 1 is directed to a lithium carbonate precipitation step 100 operating at 20-100° C. and atmospheric pressure. Carbon dioxide 2 is added to precipitation step 100 to precipitate lithium carbonate. The precipitation step 100 proceeds over a retention time of about 2 hours and achieves a precipitation extent of about 90% of the stoichiometric mass of lithium hydroxide contained in the solution containing both lithium sulfate and lithium hydroxide 1.

[0058] A resulting lithium carbonate slurry 3 is directed to a filtration step 110, for example a vacuum filter, which enables the lithium carbonate slurry 3 to be filtered. A filter cake is washed with water 4 to remove lithium sulfate entrained in the filter cake to the filtrate 5.

[0059] The lithium sulfate containing filtrate 5 is directed to a preceding stage that converts lithium sulfate to lithium hydroxide.

[0060] Lithium carbonate filter cake 6 is re-pulped in water 7 and carbon dioxide 8 is added in the lithium carbonate dissolution stage 120 to dissolve lithium carbonate. A resultant slurry 9 is directed to a solid liquid separation stage 130 to separate a lithium bicarbonate solution 10, or filtrate, from insoluble impurities 11.

[0061] The lithium bicarbonate solution 10 is directed to a lithium carbonate re-precipitation stage 140, in which the liquor is heated to strip carbon dioxide 12 and lithium carbonate subsequently precipitates. A precipitation slurry 13 is directed to a filtration step 150 utilising, for example, as a centrifuge. A centrifuge cake is washed with water 14 to remove impurities. A lithium carbonate filter cake 15 is removed from the centrifuge and directed to a drying and packaging step 160.

[0062] The filtrate 16 from the filtration step 150 contains lithium carbonate in solution. This filtrate 16, or liquor, is recycled upstream to enable a high recovery of lithium to the lithium carbonate product 17.

[0063] As can be seen from the above description, the process of the present invention provides a process in which carbon dioxide is added to a solution containing both lithium sulfate and lithium hydroxide, thereby enabling the separation of lithium from sulfate, and in turn providing corresponding higher separation efficiency than the prior art.

[0064] Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention.