Oxalic acid leaching of iron from silica sand: integrated effluent treatment and recovery of iron powder by photochemical precipitation and direct reduction

摘要

As part of a multinational EEC project, a process has been developed for the continuous treatment of effluents from heap or column leaching of silica sand with oxalic acid to remove iron-bearing impurities. Because of the particular properties of iron oxalates, the process facilitates treatment of the leachates to produce added-value products rather than the more usual jarosite wastes. The paper gives the results of upstream photochemical precipitation of iron from the leachates as iron(II) oxalate and its conversion by calcination and/or direct reduction to free-flowing iron powder suitable for use as a catalyst. Precipitation of residual iron by sulphate reduction in an upflow anaerobic sludge blanket (UASB) reactor and water recycle by reverse osmosis (RO) is also discussed. RO facilitates the simultaneous production of purified water for sand washing and concentrated bicarbonate for preneutralisation of the acidic leachate feed to the UASB system.