Process Metallurgy

Metallurgical Transactions

, Volume 2, Issue 4, pp 979-986

First online:

Equilibria in the silicothermic reduction of calcined dolomite

  • J. R. WynnyckyjAffiliated withDepartment of Chemical Engineering, University of Waterloo
  • , L. M. PidgeonAffiliated withDepartment of Metallurgy and Materials Science, University of Toronto

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When a mixture of calcium oxide and silicon is heated to above 1000°C a liquid Ca-Si alloy is formed. When magnesium metal is produced by reacting calcined dolomite with silicon, the alloy still forms and is the effective reducing agent for magnesium oxide. In this investigation the thermodynamic data on the Ca-Si alloys have been related to the magnesiumproducing reaction, the calcium pressures over mixtures CaO + Si were measured using a Knudsen cell, and the magnesiumand calcium pressures over the mixtures CaO + MgO + Si were measured using the transportation method. The magnesium content of the equilibrium alloy was determined isopiestically and the identity of the silicate was established. The results constitute a complete and consistent definition of the equilibria in the magnesium production reaction, and have also yielded an improved value of thefree energy of formation of calcium orthosilicate.