Synthesis of high alumina refractories from lithomargic clay

Lithomargic clay underlying Awaso bauxite deposits consists mainly of kaolinite and minor fractions of gibbsite. Gibbsite, useful as a source of alumina, was separated from kaolinite. Gibbsite was added to lithomargic clay in various amounts, using Mfensi clay as a binder, and fired at 1350 oC for 2 h. Linear firing shrinkage, density, porosity, water absorption and cold crushing strength were used to characterize the fired bricks. The mineralogical compositions in the fired bricks were analyzed by X-ray diffraction techniques. The results showed that increasing the gibbsite amount up to 40 wt% increased the firing shrinkage and density whilst the apparent porosity and water absorption values decreased. Increasing the gibbsite amount enhanced mullite and corundum formation whilst the formation of free-silica phases was inhibited. The cold crushing strength increased linearly with increasing gibbsite content.