The U.S. Bureau of Mines developed an alternative electrochemical process for the production of calcium metal. The current industrial practice is costly, complex, and inefficient. The Bureau method involved electrowinning of a calcium-tin alloy followed by electrorefining to produce calcium metal. In the electrowinning cell, CaCl2 was fed to a KCl2-CaCl2 electrolyte. The calcium was electrowon at 650° C into the pure molten tin cathode until the cathode contained 7.5 wt pct Ca. Current efficiency for electrowinning averaged over 90 pct. The resulting calcium-tin alloy served as the anode for the electrorefining cell, which employed a CaCl2-CaF2 fused salt as the electrolyte. Calcium metal was electrorefined at 850° C with a current efficiency of 85 pct based on calcium metal recovered. The calcium metal analyzed 99.2 pct, which is purer than commercially produced calcium.
The U.S. Bureau of Mines has investigated the electrolytic production of calcium metal. The procedure has low energy requirements and may lower the cost of producing calcium. Lower cost calcium metal would promote wider use.
Before adoption of the present commercial process, calcium metal was manufactured by the direct electrolysis of CaCl2. In this batch process, a “carrot” of solid calcium was electrowon that contained a large amount