Abstract Arsenic (As) release related to gold mining activity can alter surface water and sediment chemistry. However, the toxicity of As in mine wastes, which is controlled by the speciation, concentration, and bioavailability of As, depends on the geochemical conditions of the impacted environment (e.g., pH, Eh, climate, mineralogy, etc). This study investigates the mechanisms of As partitioning into, or out of, streambed sediments downstream of the Porgera Gold Mine in Papua New Guinea. Mine tailings at this site are treated with lime and discharged directly into the watershed, thus making them susceptible to interaction with rain water, reducing groundwaters, or acid rock drainage if it were to develop post mine-closure. Although lime treatment increases pH and effectively triggers the precipitation of most mining-derived trace metals from wastewaters, As can become more soluble at elevated pH. We conducted batch reactor experiments to simulate the effects of changing pH (4-10) and wetting/drying cycles on As interactions with lime-treated tailings and to understand potential As behavior following mine closure. Across the pH range investigated, lime-treated waste sediments and streambed sediments located downstream of the open pit mine effectively scavenged As from the water column. Specifically, the lime-treated tailings buffered the pH and enhanced interactions between dissolved As and sediment surfaces via surface complexation reactions on amorphous iron oxides, as suggested by surface complexation modeling and batch reactor experimental results. This As scavenging mechanism further counteracted the increased solubility of As at high pH. Based on wetting/drying cycle experiments, we inferred that lime-treated tailings subjected to repeated wetting/drying cycles rapidly desorbed As during the onset of rewetting, but sorbed As via an aluminum-bridging mechanism in subsequent wetting/drying cycles. These results highlight the importance of continued lime treatment to reduce As mobility in mine wastes following mine closure, particularly for mine sites where wastes are released directly into watersheds with no containment infrastructure.

中文翻译：

---

改变 pH 值和实验再润湿循环下金矿废料中的砷封存

摘要 与金矿开采活动相关的砷 (As) 释放会改变地表水和沉积物的化学性质。然而，由砷的形态、浓度和生物利用度控制的矿山废物中砷的毒性取决于受影响环境的地球化学条件（例如，pH、Eh、气候、矿物学等）。本研究调查了 As 在巴布亚新几内亚 Porgera 金矿下游的河床沉积物中或从河床沉积物中分离出来的机制。该地点的矿山尾矿经过石灰处理后直接排入流域，因此很容易与雨水相互作用，减少地下水，如果在矿山关闭后形成酸性岩排水。尽管石灰处理会提高 pH 值并有效地引发废水中大多数源自采矿的痕量金属的沉淀，但 As 在升高的 pH 值下会变得更易溶解。我们进行了间歇式反应器实验，以模拟改变 pH (4-10) 和润湿/干燥循环对 As 与石灰处理尾矿相互作用的影响，并了解矿山关闭后潜在的 As 行为。在调查的 pH 值范围内，位于露天矿下游的石灰处理废物沉积物和河床沉积物有效地从水体中清除了砷。具体而言，如表面络合模型和间歇反应器实验结果所表明的，石灰处理的尾矿通过无定形氧化铁的表面络合反应缓冲了 pH 值并增强了溶解的 As 和沉积物表面之间的相互作用。这种 As 清除机制进一步抵消了 As 在高 pH 值下溶解度的增加。基于润湿/干燥循环实验，我们推断经过反复润湿/干燥循环的石灰处理尾矿在再润湿开始期间迅速解吸砷，但在随后的润湿/干燥循环中通过铝桥接机制吸附砷。这些结果强调了继续石灰处理以减少矿山关闭后矿山废物中 As 流动性的重要性，特别是对于废物直接排放到没有围堵基础设施的流域的矿场。但在随后的润湿/干燥循环中通过铝桥接机制吸附砷。这些结果强调了继续石灰处理以减少矿山关闭后矿山废物中 As 流动性的重要性，特别是对于废物直接排放到没有围堵基础设施的流域的矿场。但在随后的润湿/干燥循环中通过铝桥接机制吸附砷。这些结果强调了继续石灰处理以减少矿山关闭后矿山废物中 As 流动性的重要性，特别是对于废物直接排放到没有围堵基础设施的流域的矿场。