Recovery of Sillimanite from Beach Sands--An Operator＇s Nightmare

Sillimanite, chemically named aluminum silicate, 3Al2O3SiO2 is one of the three forms of alumino silicate polymorphs and commonly encountered in aluminous metamorphic, plutonic and volcanic rocks and their weathering products. Traditionally in India, sillimanite is upgraded by froth floatation technique using oleic acid as a collector cum frother, sodium silicate as depressant and soda ash as pH regulator. At TSPL （Trimex Sands Pvt Ltd）, conventional mechanical float cells are installed to float sillimanite. In addition to the usual problems associated with conventional cells, poor flow ability of the sillimanite concentrate is experienced in dry circuit due to the presence of sodium oleate. Fine garnet in the sillimanite concentrate contributes to high iron content in the final product, making sillimanite separation a nightmare for operators （lower recoveries coupled with inferior grades）. Various efforts were made to improve the performance of the circuit such as introduction of additional frother like MIBC （methyl ISO butyl carbinol）, optimizing the operating parameters such as pulp density, collector dosage, depressant dosage, air flow rate, pH etc., use of collector aids, stage wise addition of reagents etc.. The challenges faced to produce a sillimanite product with stringent quality norms and the efforts made to improve the grade and recovery are described in this paper.