Method for producing lithium carbonate
The present invention relates to a method for producing lithium carbonate, which is important as a raw material of a lithium ion battery and the like, from brine resources. More specifically, the invention relates to a method for producing lithium carbonate, in which carbon dioxide gas obtained by calcining limestone is introduced, in the presence of ammonia, into a concentrated brine, which is prepared from a lithium-containing brine as a raw material through an evaporative concentrating step, a desulfurizing step and an electrodialysis step, thereby depositing lithium carbonate crystals, and the crystals thus deposited are recovered through solid-liquid separation.
1. A method for producing lithium carbonate, the method comprising:
a desulfurizing step of adding a desulfurizing agent containing a calcium compound to a lithium-containing brine as a raw material, and removing sulfate ion contained in the brine as gypsum, thereby obtaining a desulfurized brine;
evaporatively concentrating the desulfurized brine, and removing crystallized matters therefrom through solid-liquid separation, thereby obtaining a primarily concentrated brine;
subjecting the primarily concentrated brine to electrodialysis by a monovalent ion-permselective ion exchange membrane, thereby obtaining a secondarily concentrated brine;
evaporatively concentrating again the secondarily concentrated brine, and removing crystallized matters therefrom through solid-liquid separation, thereby obtaining a tertiary concentrated brine;
a carbonation step of introducing carbon dioxide gas obtained by calcining limestone to the tertiary concentrated brine in the presence of ammonia, thereby depositing lithium carbonate crystals; and
recovering the lithium carbonate crystals through solid-liquid separation.
2. The method for producing lithium carbonate according to claim 1 , wherein the tertiary concentrated brine, to which carbon dioxide gas is to be introduced in the carbonation step, has a lithium concentration of from 20 to 55 g/L.
3. The method for producing lithium carbonate according to claim 1 , wherein an amount of the ammonia that is present in the carbonation step is from 0.8 to 2.0 in terms of the NH 3 /Li molar ratio.
4. The method for producing lithium carbonate according to claim 1 , wherein an amount of the carbon dioxide gas that is introduced in the carbonation step is from 0.3 to 1.5 in terms of the CO 2 /Li molar ratio.
5. The method for producing lithium carbonate according to claim 1 , wherein the ammonia that is used in the carbonation step is recovered ammonia obtained in such a manner that calcium oxide produced upon calcining limestone for obtaining carbon dioxide gas, or calcium hydroxide obtained from the calcium oxide through lime slaking is added to a separated liquid obtained through solid-liquid separation after the carbonation step, and ammonia gas formed through reaction of ammonium chloride contained in the separated liquid with the calcium oxide or calcium hydroxide is recovered and cyclically used.
6. The method for producing lithium carbonate according to claim 5 , wherein an amount of the calcium oxide or calcium hydroxide to be added upon the recovery of ammonia is from 0.3 to 1.0 in terms of the Ca/NH 3 molar ratio.
7. The method for producing lithium carbonate according to claim 5 , wherein a residual liquid containing calcium chloride, obtained after the recovery of ammonia gas is used as the desulfurizing agent containing a calcium compound, which is added in the desulfurizing step.
8. The method for producing lithium carbonate according to claim 1 , wherein the lithium carbonate crystals recovered through solid-liquid separation after the carbonation step are washed by flow-through washing.