Evaluation of Calcium Aluminate Slags and Pig Irons Produced from the Smelting-Reduction of Diasporic Bauxite

This work evaluates the characteristics of calcium aluminate slag and pig iron samples obtained from the smelting of calcined and reduced diasporic bauxite ore. The study is conducted in the Pedersen process framework, which is a method to produce alumina from low-grade resources. Parameters such as the effect of crucible type, lime addition, and atmospheric conditions are studied considering the characteristics of the product pig irons and calcium aluminate slags for further uses. The behavior of the bauxite and distribution of the species between slag and metal was assessed based on the applied analytical techniques and thermodynamic calculations. Iron was reduced and separated from the slags in the presence of carbon (graphite crucible) for both the reduced and calcined bauxite. Si and Ti were mainly concentrated in the slags. Iron was separated from the slag in the absence of carbon (alumina crucible) for the H₂-reduced bauxite. The results show that slags with increased lime additions are composed mainly of 5CaO.Al₂O₃ and CaO.Al₂O₃, that are considered highly leachable compounds. An optimum CaO/Al₂O₃ mass ratio of 1.12 was suggested. The presence of O₂ and/or OH^- in the furnace atmosphere will result in the formation of 12CaO.7Al₂O₃.