Pyrite and calcite are mineral phases that play a major role in acid and neutral mine drainage processes. However, the prediction of acid mine drainage (AMD) or contaminated neutral drainage (CND) requires knowledge of the mineral composition of mining waste and the related potential for element release. This paper studies the combination of acid–base neutralizing capacity (ANC–BNC) with geochemical modeling for the characterization of mining waste and prediction of AMD and CND. The proposed approach is validated with three synthetic mineral assemblages: (1) siliceous sand with pyrite only, representing mining waste responsible for AMD, (2) siliceous sand with calcite and pyrite, representing calcareous waste responsible for CND, and (3) siliceous sand with calcite only, simulating calcareous matrices without any pyrite. The geochemical modeling approach using PHREEQC software was used to model pH evolution and main element release as a function of the added amount of acid or base over the entire pH range: 1 < pH < 13. For calcareous matrices (sand with calcite), the results are typical of a carbonated environment, the geochemistry of which is well known. For matrices containing pyrite, the results identify different pH values favoring the dissolution of pyrite: pH = 2 in a pyrite-only environment and pH = 6 where pyrite coexists with calcite. The neutral conditions can be explained by the buffering capacity of calcite, which allows iron oxyhydroxide precipitation. Major element release is then related to the dissolution and precipitation of the mineral assemblages. The geochemical modeling allows the prediction of element speciation in the solid and liquid phases. Our findings clearly prove the potential of combined ANC–BNC experiments along with geochemical modeling for the characterization of mining waste and the assessment of risk of AMD and CND.

中文翻译：

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ANC–BNC滴定法和地球化学模型用于表征钙质和硅质采矿废料

黄铁矿和方解石是矿物相，在酸性和中性矿山排水过程中起主要作用。但是，对酸性矿山排水（AMD）或受污染的中性排水（CND）的预测需要了解采矿废料的矿物成分以及相关的元素释放潜力。本文研究了酸碱中和能力（ANC–BNC）与地球化学模型的结合，用于表征采矿废料以及预测AMD和CND。所提出的方法已通过三种合成矿物组合进行了验证：（1）仅含黄铁矿的硅砂，代表造成AMD的采矿废物；（2）具有方解石和黄铁矿的硅砂，代表造成CND的钙质废物，以及（3）硅砂仅含方解石，模拟不含黄铁矿的钙质基质。使用PHREEQC软件进行地球化学建模的方法是在整个pH范围内（1 <pH <13），根据酸或碱的添加量来模拟pH的演变和主要元素的释放。对于钙质基质（方解石砂），结果是典型的碳酸盐化环境，其地球化学是众所周知的。对于含有黄铁矿的基质，结果确定了有利于黄铁矿溶解的不同pH值：仅在黄铁矿环境中pH = 2，在黄铁矿与方解石共存的pH = 6的情况下。中性条件可以通过方解石的缓冲能力来解释，方解石可以使羟基氧化铁沉淀。然后，主要元素的释放与矿物组合的溶解和沉淀有关。地球化学模型可以预测固相和液相中的元素形态。我们的发现清楚地证明了结合ANC-BNC实验以及地球化学建模来表征采矿废物以及评估AMD和CND风险的潜力。