Beneficiation of Calcite from Sankaridurg, Madras

Abstract

A sample of low grade limestone assaying 43.05% CaO, 35.9% CO2,1.80% MgO,15.40% SiO2, 2.14% Al2O3,0.66% Fe2O3, 0.09% S, 0.19% P2O3 was received in National Metallurgical Laboratory from the Government of Madras, for beneficiation studies. Calcite was well liberated from the quartz even at 35 mesh . Soap flotation using oleic acid emulsion as collector for calcite and sodium as gangue depressant, yielded a rougher float assaying 52.90% CaO, 2.0% insolubles with a recovery of 97.1% CaO. Single reflotation of the rougher float improved the grade of concentrate to 53.34% CaO, 0.8% insolubles and 0.26% P2O5 with recovery of 94.7% CaO. Apatite flotation of the refloat conc, using Katha as a calcite depressant yielded a tailing (limestone concentrate)assaying 52.95% CaO, 1.08% insolubles, 0.10% P2O5. This product fulfills the grade requirements laid for its use in steel making. Pelletization studies undertaken on the above low-phosphorous limestone concentrate without further grinding indicated that good green pellets could be produced by using 4.0% molasses, 8.1% moisture. Heat hardening at 110° C yielded pellets having a compressive strength of 60.45 Kgs /pellets. Calcination studies on the green pellets in a stationary gas fired kiln as well as in a rotary kiln at 1000°-1050°C showed that the calcined pellets retained their shape and strength well, though the original limestone lumps crumbled to 6.00 mm and finer, even at 550°-600°C.