Field experiments previously conducted to assess organic carbon (OC) amendments for in situ biological treatment of tailings porewater at the Greens Creek Mine (Alaska, USA) showed sulfate reduction, metal-sulfide precipitation, and decreased fluxes of sulfate and dissolved metals. Here, we develop two reactive transport models using the reactive transport code MIN3P to simulate hydrogeochemical processes and $\mathrm{\delta }$³⁴S–SO₄ isotope fractionation over four years in test cells containing unamended (control) and amended (5 vol % OC) tailings. These models successfully simulate observed data including pH, SO₄, $\mathrm{\delta }$³⁴S–SO₄, Ca, Fe, K, Mg, Mn, Si, and Zn. The models also indicate that dissolution of carbonate and, to a lesser extent, aluminosilicate minerals neutralize acidic porewater generated from sulfide mineral oxidation and sulfate reduction reactions. Application of a constant kinetic fractionation factor of 0.9820 to simulate measured $\mathrm{\delta }$³⁴S–SO₄ trends confirms that sulfate removal principally results from microbially-mediated sulfate reduction in conjunction with OC oxidation and subsequent metal-sulfide precipitation. Gypsum precipitation/dissolution and thiosulfate disproportionation have negligible effects on modelled porewater $\mathrm{\delta }$³⁴S–SO₄ signatures. Our simulations are consistent with the previous findings that metal-sulfide precipitation controls Fe and Zn attenuation in amended tailings and that coprecipitation reactions contribute to metal removal. Overall, these simulations demonstrate that coupled reactive transport modelling incorporating stable isotope fractionation can improve the understanding of hydrogeochemical and biogeochemical controls within in situ treatment systems, further illustrating the benefits and limitations of this technique for improving water quality of mine drainage.

先前进行的现场实验，用于评估Greens Creek矿（美国阿拉斯加）尾矿孔隙水的原位生物处理中的有机碳（OC）修正，结果表明硫酸盐还原，金属硫化物沉淀以及硫酸盐和溶解金属的通量降低。在这里，我们使用反应运输代码MIN3P开发了两个反应运输模型，以模拟水文地球化学过程和$\mathrm{\delta }$在含有未修正（对照）和修正（5体积％OC）尾矿的测试池中，四年内进行了³⁴ S–SO ₄同位素分级分离。这些模型成功模拟了观察到的数据，包括pH值，SO ₄，$\mathrm{\delta }$³⁴ S–SO ₄，Ca，Fe，K，Mg，Mn，Si和Zn。这些模型还表明，碳酸盐的溶解以及较小程度的铝硅酸盐矿物的溶解会中和硫化物矿物氧化和硫酸盐还原反应产生的酸性孔隙水。应用0.9820的恒定动力学分馏因子模拟测得的值$\mathrm{\delta }$³⁴ S–SO ₄趋势证实，硫酸盐的去除主要是由于微生物介导的硫酸盐还原以及OC氧化和随后的金属硫化物沉淀所致。石膏的沉淀/溶解和硫代硫酸盐的歧化对模拟的孔隙水的影响可以忽略不计$\mathrm{\delta }$^34个S–SO ₄签名。我们的模拟与先前的发现一致，即硫化物的沉淀控制了尾矿中Fe和Zn的衰减，共沉淀反应有助于去除金属。总体而言，这些模拟表明，结合了稳定同位素分馏的耦合反应输运模型可以改善对原位处理系统中水文地球化学和生物地球化学控制方法的了解，进一步说明了该技术对改善矿井排水水质的好处和局限性。