Purification of Lithium Carbonate

Submitted by E. R. Caley and P. J. Elving Checked by William D. Stillwell  

Since lithium salts obtainable by purchase, even of so-called c.p. or reagent quality, frequently contain impurities totaling about 1 per cent, it is desirable to have a rapid method for obtaining such salts in a reasonably pure state. The following simple procedure for the purification of c.p. or reagent grade lithium carbonate provides such a method, since the resulting pure carbonate may be readily converted by treatment with the proper pure acid into practically any lithium salt desired. The procedure is based upon the fact that lithium carbonate, in contrast to the salts that contaminate it, is much less soluble in hot than in cold water. J In other words, simple recrystallization is employed, but the process is carried out in the reverse direction. 

Twenty-five grams of lithium carbonate is dissolved in 2 1. of water in a 3-1. beaker at room temperature. This operation requires about half an hour if stirred by a motor stirrer. Suspended impurities and any small residue of undissolved carbonate are then removed by filtering the solution, preferably through a large folded filter. The 

The yield, based on the amount of lithium carbonate taken, is about 40 per cent. The filtrate from the second filtration may, after cooling, be again saturated with lithium carbonate to give a second crop almost as pure as the first. In this way, the total yield can be considerably increased. 

For special purposes, where a product of higher purity is required, a double recrystallization from hot water may be employed but in this case, of course, the yield is considerably reduced. 

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The purification of lithium carbonate by taking advantage of its negative coefficient of solubility has been described by E. R. Caley and P. J. Elving, Inorganic Syntheses, 1, 1 (1939). 

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