Acid 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.

中文翻译：

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黄铁矿上稳定硅酸盐的钝化层的形成，以减少酸性岩层的排水

当采矿活动和自然环境中的含硫化物（主要是黄铁矿）的岩石暴露于这些元素时，会发生酸和金属含量的释放，这被认为是一个主要的环境问题。酸岩排水（ARD）管理对于运营中的矿场和遗留的矿场而言既具有挑战性，又成本高昂。当前的技术解决方案是昂贵的，并且侧重于在释放时治疗ARD，而不是从源头上防止它。我们在这里描述了一种可行的，实用的机制，可通过形成硅酸盐稳定的羟基氧化铁表面层来减少ARD。没有硅酸盐，氧化的黄铁矿颗粒会形成具有多孔结构的针铁矿或纤铁矿晶体的覆盖层。加入硅酸盐后，可以观察到光滑，连续，连贯且明显为非晶态的羟基氧化铁表面层，在中性pH值下，黄铁矿的溶解率降低了90％以上。硅酸盐在结构上并入该层内，并抑制了从无定形的（羟基）氢氧化铁向针铁矿的相变，从而导致黄铁矿表面钝化。通过计算仿真证实了这一点，这表明伪非晶羟基氧化铁（三水铁矿结构）的硅酸盐掺杂在热力学上比等效的未掺杂结构更稳定。描述了该机制及其控制因素。由于大大降低了酸的产生速率，在最初添加石灰石以达到中性pH后，可以使用现场可利用的反应性硅酸盐矿物的中和作用来保持中性pH，从而保持这些层的完整性以进行有效的ARD管理。