Production and leaching of acid drainage from waste heaps

TL;DRAbstract

nnn This thesis concerns the acidic drainage which cannemanate from mineral, and mineral waste heaps; and in particular, acid drainage produced by oxidation of iron sulphidesncontained in rejects of a coal washery. The drainage, highnin acidity, sulphate, and dissolved iron, is a serious pollutionnhazard and must be treated before disposal. Beneficialnaspects of acid drainage include the removal of sulphurnfrom coal prior to combustion, thus eliminating the expensenof stack gas scrubbing. Metals can also be recovered fromnlow grade ores by leaching in this manner.n n nnn The mechanisms by which the metal sulphides, such asnpyrite (FeS2), contained in the waste are oxidized and thenfactors controlling the reaction are reviewed. Bacteriancatalyze the oxidation of ferrous ion to ferric, which innturn do the actual pyrite oxidation. Oxidation takes placenduring a relatively dry stage, after which the oxidationnproducts are removed by flushing when water infiltrates thenheap.n n nnn The stu

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