Winning of calcium by thermal reduction of calcium - carbide with silicon or a silicon alloy

摘要

This process is more economic than the preparation of Ca from a mixture of Al and CaO, and produces beta-crystalline Si-C as a byproduct which is used as a de-oxidising agent in the production of iron. A Si-Fe, Si-Ca, Si-Mg, Si-Cr, or Si-Al alloy having a Si-content of at least 30% is used at such an amount that the proportion of Si is correspondent with 0.7-1.5 equivalents of CaC2. Thermal reduction is carried out at mb atmospheric pressure in a muffle furnace at 1100-1300 degrees C for at least 3 hours, or in an internal furnace at temp. of 1400-1500 degrees C. Suitable catalysts are the halogenides of Li, Na, K, Mg, Ca, Sr, Ba, Al, preferably CaF2. The pulverised raw materials are pelletised before thermal reduction. The produced Ca vapourises and condenses near the furnace outlet. The slag is recovered in pelletised form.