Recovery of fine-size coal from impounded wastes

Abstract

Over the years, Alabama’s coal industry has generated, during mining and cleaning operations, about 150 million st of fine waste coal, with this total increasing at a rate of 2 million stpy. Reclamation of the fine-size wastes (containing 20%–60% clean coal by weight) provides, free of charge, mined and crushed feed stocks for coal recovery. Also, the removal or recovery of pyrite from the tailings should eliminate a major source of acid-water pollution. Tests were made on the impounded wastes and current plant discharges to recover the coal fraction by sizing, gravity and flotation techniques. Gravity separation of the +100-mesh material produced commercial-grade coal averaging 7.6% ash, 0.8% sulfur and 13,471 Btu/lb. However, thecoalyield, at about 31%–56%, was relatively low. Froth flotation, using mechanical and froth column methods, gave similar coal products at much higher coal recovery rates of 87%–93%. This coal analyzed 10% ash and 1.1% sulfur.