Acid rock drainage (ARD) is generated when mineral sulfides, primarily pyrite (FeS₂), are exposed to weathering. Pyrite oxidation and dissolution may also result in the precipitation of secondary sulfate minerals, commonly found in weathered mine wastes, that release ‘stored acidity’ on subsequent dissolution. To better understand the release of this stored acidity, a kinetic leach column experiment using a synthetic pyritic (5 wt%) mine waste was conducted for a period of 524 weeks. The first 260 weeks watering/flushing was carried out using Milli-Q water during which the leachate pH decreased from 6.0 to 2.0, pyrite passivation layers present initially were removed and secondary sulfate minerals formed. The rate at which acidity was generated from secondary sulfate mineral dissolution was significantly greater than from pyrite oxidation after the calcite-saturated silicate water treatment during the period from 260 to 440 weeks. This suggests that in weathered pyritic wastes, both the amount of acidity and the rate at which it is released may be dominated by acid sulfate minerals rather than residual pyrite. Importantly, it was found that passivation strategies appropriate for reducing pyrite oxidation rates were not effective for reducing the rate of acid release from secondary mineralisation. Significant amounts of lime-saturated water (with high alkalinity) were required to dissolve the secondary sulfate minerals containing the stored acidity before circum-neutral conditions necessary for pyrite passivation could be achieved. It follows therefore that it is necessary to quantify the amount of stored acidity in secondary minerals so that appropriate remediation and acid management strategies can be designed and implemented to achieve long-term sustainable ARD control and mine closure.

当矿物硫化物，主要是黄铁矿 (FeS ₂), 暴露在风化中。黄铁矿氧化和溶解也可能导致二次硫酸盐矿物的沉淀，常见于风化的矿山废料中，在随后的溶解中释放“储存的酸度”。为了更好地了解这种储存酸度的释放，使用合成黄铁矿 (5 wt%) 矿山废料进行了一项为期 524 周的动态浸出柱实验。前 260 周浇水/冲洗是使用 Milli-Q 水进行的，在此期间，渗滤液的 pH 值从 6.0 降至 2.0，去除最初存在的黄铁矿钝化层并形成次生硫酸盐矿物。在方解石饱和硅酸盐水处理后 260 至 440 周期间，二次硫酸盐矿物溶解产生酸度的速率显着大于黄铁矿氧化。这表明在风化的黄铁矿废物中，酸度的量和它的释放速度可能由酸性硫酸盐矿物而不是残留的黄铁矿支配。重要的是，发现适用于降低黄铁矿氧化速率的钝化策略对于降低二次矿化的酸释放速率无效。在达到黄铁矿钝化所需的环中性条件之前，需要大量的石灰饱和水（具有高碱度）来溶解含有储存酸度的次生硫酸盐矿物。