Separation of sillimanite from beach sands contaminated with shell

Sillimanite is a very important raw material for the manufacture of refractory bricks used in iron and steel,
cement and glass industries. In some coastal stretches of
south India, the beach sand is contaminated with shell. After recovering heavy minerals like ilmenite, rutile, zircon and garnet by various physical separation techniques, the final sand containing sillimanite, quartz and shell is presently dumped as waste. Separation of sillimanite from these rejects was studied by flotation process using oleic acid and octylhydroxamate as collectors for selective flotation of sillimanite. Starch and tannin were tried as depressants for shell and sodium silicate as dispersant for quartz. Though the quartz could be depressed effectively, the shell was found to float along with sillimanite both in the presence of oleic acid and octylhydroxamate. When starch or tannin was added to suppress the shell flotation, the floatability of
sillimanite and in turn its recovery was drastically affected. Alternatively shell was totally removed by treating with dilute hydrochloric acid and sillimanite was separated from quartz using oleic acid and sodium silicate. The concentrate analyzing 97% sillimanite free from shell were achieved from the initial sand assaying 48 % sillimanite, 46 % quartz and 3.3% shell.