Reducing sulphide oxidation in pyritic mining wastes — phosphate miningwastes stimulate biofilm formation on mineral surfaces

摘要

Sulphide oxidation rates (log r) in tailings and waste rock have been calculatedusing Eh/pH measurements in supernatants of slurries (40 g tailings: 200 mLdistilled water) from field plots on uranium (2% pyrite), pyhrrotite (85%),polymetallic concentrator spill (6-8% sulphide) tailings and effluents of wasterock drums (4-14% pyrite) to which Natural Phosphate Rock wastes (NPR) wereadded. The log rs of uranium tailings and waste rock were up to 3 orders ofmagnitude lower than controls. Oxidation rates in concentrator spill materialwere up to 4 orders of magnitude lower. In pyhrrotite tailings slurries, NPRaddition showed no reductions in log r but great reductions in acidity. Dissolution of phosphate from NPR in aqueous H_2SO_4, adjusted to pH 3, 5 and6.5, showed that appreciable [P] was released after 60 minutes at pH 3;dissolution was minimal at higher pHs. Based on the stability fields of iron-hydroxide and ferric-phosphate, iron hydroxide will precipitate preferentially inthe presence of low [P]. SEM/EDX investigations of the waste rock surfaces found only traces ofphosphate, but did show the presence of extensive biofilms. It is suggested thatthe NPR addition reduces sulphide oxidation rates primarily by initiating anddeveloping biofilms, rather than through direct precipitation of ferric phosphate.