Fluxing of South African chromite ore with colemanite

Abstract

South African chromite ores are smelted using SiO2- and CaO-containing fluxes, normally as quartz and limestone respectively. The purpose of SiO2 is to lower the melting point of the ore, while CaO is added to ensure that the slag that forms on smelting is fluid enough to enable slag/alloy separation and tapping from the furnace. Colemanite is a borate mineral originating primarily from Turkey, and has the nominal, ideal composition CaB3O4(OH)3.H2O. B2O3 readily fluxes chromite, and low amounts of this compound can yield a lowering of the melting temperature similar to that obtained using SiO2. In addition, colemanite already contains CaO, which AIDS in making the resulting slag more fluid. Laboratory-scale smelting tests were conducted at Mintek over the course of 18 months. The work included evaluation of a variety of boroncontaining materials to replace conventional fluxes. The results of the tests and modelling work are presented in this paper.