Method of lithium sulfate and sodium (potassium) carbonate directly producing lithium carbonate and reducing sulfate radical content

A method for preparing lithium carbonate from lithium sulfate and sodium carbonate or potassium carbonate, comprising the following steps:

• S1:
• adding a 20 wt % lithium sulfate purified solution to a sodium carbonate or potassium carbonate purified solution at 90-95° C. to obtain crude lithium carbonate-1;
• separating the crude lithium carbonate-1 to obtain a primary hot mother liquor;
• S2:
• cooling the primary hot mother liquor to −15° C. to crystallize mirabilite;
• separating the mirabilite by centrifugation to obtain a secondary cold mother liquor;
• S3:
• concentrating the secondary cold mother liquor, to precipitate and separate crude lithium carbonate-1 again, and to obtain a tertiary hot mother liquor;
• S4:
• combining the tertiary hot mother liquor with the primary hot mother liquor, and repeating steps S2-S3 to reduce the sulfate anion content in the liquid system;
• S5:
• combining the crude lithium carbonate-1 obtained in steps S1 and S3, then transferring to deionized water which is 3 or 4 times the mass of the crude lithium carbonate-1 and has a temperature of 90-95° C.;
• heating to 115° C., stirring and washing for 15 minutes, then centrifuging and rinsing to obtain crude lithium carbonate-2;
• S6:
• adding the crude lithium carbonate-2 obtained in step S5 to deionized water which is 3-6 times the mass of the crude lithium carbonate-2 and is in a desorption reactor;
• heating to 159-188° C., desorbing sulfate anions adsorbed on the crude lithium carbonate-2 into the deionized water under stirring, and performing thermal aging for not less than 1 hour, to obtain a thermally aged slurry;
• and
• S7:
• adding the thermally aged slurry obtained in step S6 to a hydrocyclone to separate the liquid and solid phases.