Abstract
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.
Highlights
Acid mine drainage (AMD) is a critical global environmental issue from many mine wastes
This study focuses on understanding the role that silicate and pH conditions play in the formation and stabilisation of pyrite surface passivation layers found in lab and field studies
It was reported from some of fund amental studies that silicate in hibits the trans formation ofamorphous iron hydroxide Fe(OH)3 to crystalline goethite (FeOOH) in synthesis processes [4,15,16]
Summary
Acid mine drainage (AMD) is a critical global environmental issue from many mine wastes. Smart et al [13] and Miller et al [14] found from their long term column leaching and field studies at the Grasberg mine Indonesia that silicate may be responsible for stabilising the iron oxy-hydroxide passivation layer on pyrite surfaces. It was reported from some of fund amental studies that silicate in hibits the trans formation ofamorphous iron hydroxide Fe(OH) to crystalline goethite (FeOOH) in synthesis processes [4,15,16]. Pyrite dissolution tests under various pH conditions in the presence of low concentrations of Na2SiO3(10 and 20 mg/Lsilicate as Si),were performedto investigate the influence of pH and dissolved silicate on the stability of iron oxyhydroxide surface layers formed during oxidative dissolution of pyrite at circum-neutral pH
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