COMBINED CARBOTHERMIC PRODUCTION OF CALCIUM FROM CARBONATE Russian patent published in 2013 - IPC C22B26/00 C22B5/10 

FIELD: metallurgy.

SUBSTANCE: proposed method comprises making the charge from calcium carbonate, primarily, from chemically deposited chalk or high-quality sifting in production of limestone and carbon, primarily from reused graphite, obtained at final stage of carbothermic process. Note here that starting charge is pelletised, placed in furnace and heated in vacuum in one unit at three steps. At first step, calcium carbonate is dissociated in the presence of carbon at 600-700°C for 2-4 hours and residual pressure of 40-50 Pa to remove carbon monoxide. At second step, calcium carbide (CaC₂) is synthesized at 1400-1500°C and 100-150 Pa to remove carbon monoxide. At third step, calcium carbine is dissociated to produce elementary calcium and graphite at 1300-1400°C and < 10 Pa.

EFFECT: higher efficiency, simplified process, application of cheap reducing agent.

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