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The Formation of Silicate-Stabilized Passivating Layers on Pyrite for Reduced Acid Rock Drainage
journal contribution
posted on 2017-08-23, 00:00 authored by Rong Fan, Michael D. Short, Sheng-Jia Zeng, Gujie Qian, Jun Li, Russell C. Schumann, Nobuyuki Kawashima, Roger St. C. Smart, Andrea R. GersonAcid and metalliferous release occurring
when sulfide (principally
pyrite)-containing rock from mining activities and from natural environments
is exposed to the elements is acknowledged as a major environmental
problem. Acid rock drainage (ARD) management is both challenging and
costly for operating and legacy mine sites. Current technological
solutions are expensive and focused on treating ARD on release rather
than preventing it at source. We describe here a viable, practical
mechanism for reduced ARD through the formation of silicate-stabilized
iron oxyhydroxide surface layers. Without silicate, oxidized pyrite
particles form an overlayer of crystalline goethite or lepidocrocite
with porous structure. With silicate addition, a smooth, continuous,
coherent and apparently amorphous iron oxyhydroxide surface layer
is observed, with consequent pyrite dissolution rates reduced by more
than 90% at neutral pH. Silicate is structurally incorporated within
this layer and inhibits the phase transformation from amorphous iron
(oxy)hydroxide to goethite, resulting in pyrite surface passivation.
This is confirmed by computational simulation, suggesting that silicate-doping
of a pseudoamorphous iron oxyhydroxide (ferrihydrite structure) is
thermodynamically more stable than the equivalent undoped structure.
This mechanism and its controlling factors are described. As a consequence
of the greatly reduced acid generation rate, neutralization from on-site
available reactive silicate minerals may be used to maintain neutral
pH, after initial limestone addition to achieve neutral pH, thus maintaining
the integrity of these layers for effective ARD management.
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pseudoamorphous iron oxyhydroxideequivalent undoped structuremetalliferous releasepyrite dissolution ratesreactive silicate mineralslegacy mine sitesgoethiteSilicate-Stabilized Passivating LayersARD managementacid generation ratelimestone additionAcid rock drainagepyrite particles formpHferrihydrite structurepyrite surface passivationsilicate additioniron oxyhydroxide surface layermining activitiesmechanismRock Drainagesilicate-stabilized iron oxyhydroxide surface layersphase transformation
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