Effect of thermal pretreatment on grindability and upgradation of bauxite for refractory applications

Abstract

Iron is a detrimental element in bauxite used for refractory applications. A process has been developed in the laboratory on removal of iron and improvement in alumina recovery of bauxite by reduction/calcination roasting followed by magnetic separation, For effective liberation of mineral, the ore is to be comminuted to the desired fineness. As the comminution process is energy intensive, a study has been undertaken on determination of overall energy requirement for grinding of ore as well as ore samples undergone various pretreatments (reduction roasting with coke/calcination quenching in water at room temperature) for effective liberation of minerals, The ground samples were subjected to different magnetic intensity for maximum removal of iron with highest recovery of alumina. The reduction using 5-10% coke in the mixture or calcination was effected at 850degreesC temperature. The crude, reduced and calcine-quenched ores were subjected to grinding for liberation of minerals suitable for magnetic separation. There has been considerable savings in grinding time for heat treated samples over crude ore. The ground samples were subjected to magnetic separation of different intensities. The relative savings in grinding time for reduced and calcined quenched ores over crude ore were 36% and 57%. Around 28% overall savings in energy was achieved for grinding of calcined quenched ore over crude ore. The magnetic intensity required for obtaining a refractory grade bauxite (Fe2O3 : <2.5%) is 14 Tesla for crude ore whereas for calcine ore it is 7.1 T and for reduced ore 1.4 T. The alumina recoveries in the non-magnetic fraction (product) were 60%, 56% and 36% for reduced, calcined and crude ore respectively. Thus he thermal pretreatment method has shown several advantages in the upgradation process including grindability aspect of bauxite used for refractory applications. This paper highlights these aspects in details.