Effect of pH and Dissolved Silicate on the Formation of Surface Passivation Layers for Reducing Pyrite Oxidation

摘要

Acid mine drainage (AMD)and toxic metal release generated by oxidation of sulphide minerals, particularly pyrite, in mine wastes,are a critical environmental issue worldwide.Currently, there are many options to diminish sulphide oxidation including barrier methods that isolate pyrite from oxygen or water, chemical additives and inhibition of iron-oxidizing bacteria. This study focuses on understanding the rolethatsilicate and pH conditions play in the formation and stabilisation ofpyrite surface passivation layers found in lab and field studies.The results from pyrite dissolution tests under various conditions showed that the pyrite oxidation rate has been reduced by up to 60% under neutral pH with additional soluble silicate. Solution speciation calculation predicted that crystalline goethite is formed in the experiment without silicate additionbutan amorphous iron hydroxide surface layer is stabilizedby the addition of the silicate, inhibiting goethite formation and continuing pyrite oxidation.This coherent, continuous amorphous layer has been verified in SEM.