Chromium recovery from skin tanning

Chromium recovery was carried out, based on a reliable character ization of the tanning waste. A three stage scheme to recover chromium was proposed ; a primary treatment to removal solids, together with chemical precipitation of chromium with a magnesium oxide - calcium hydroxide mixture and then aluminium sulphate as coagulant. These compounds allow a reduction of chromium concentration to 20 mg/l, with minimal sludge production. Finally, using ionic exchange is possible to reduce chromium concentration obtaining a waste ready to final disposal. After the first stage a reduction of 50% of suspended solids and the totality of the sedimentable solids was achieved. With the chemical treatment stage, 80% of suspended solid, 60% of COD and 99% of chromium were removed.