Selective lithium extraction from brines

A process for extraction of lithium from a brine comprising Li+, Na+, K+, Mg2+, Ca2+, SO42− and a boron salt, the process comprising:

• clarifying and heating the brine to remove suspended solids to provide a heated clarified brine at a temperature of up to about 65° C.;
• in a lithium extraction step, exposing the heated clarified brine to a particulate ferric phosphate solid in the presence of a reducing agent with the addition of an acid or a base at a controlled lithium extraction pH, to extract lithium from the heated clarified brine by reductive topotactic insertion into the particulate ferric phosphate to form a loaded lithium ferrous phosphate solid admixed with a hot spent brine;
• performing a lithium-extraction solid/liquid separation to separate the loaded lithium ferrous phosphate solid from the hot spent brine;
• in a lithium elution step, exposing the lithium ferrous phosphate solid to an oxidizing agent with the addition of an acid or a base at a controlled acidic lithium elution pH to elute lithium into a liquid lithium eluate and to provide regenerated ferric phosphate solids, the lithium elution step being carried out at a controlled elution solid/liquid ratio of the lithium ferrous phosphate solid to the liquid lithium eluate of at least 2%, wherein the lithium extraction step and the lithium elution step are carried out so as to provide a lithium concentration of at least 20 g/L, optionally at least 30 g/L or optionally at least 40 g/L in a concentrated liquid lithium eluate;
• in one or more impurity removal steps, in any order, providing a purified lithium chloride solution by:
• removing dissolved calcium and magnesium from the concentrated liquid lithium eluate, by one or both of:
• precipitation of calcium solids and magnesium solids, and one or more steps of impurity-removal solid/liquid separation to separate alkaline earth impurity solids;
• and/or,
• ion exchange separation of divalent cations from the liquid lithium eluate;
• and/or,
• removing dissolved boron from the concentrated liquid lithium eluate by exposure to a boron-specific ion exchange resin;
• precipitating a solid lithium carbonate from the purified lithium chloride solution by addition of an alkali metal carbonate with heating to at least 80° C., optionally at least 85° C., optionally at least 90° C. or above, at atmospheric pressure or above, to produce a solid lithium carbonate product comprising at least 99.5 wt % or optionally at least 99.8 wt % Li2CO3.