The use of EDTA leaching method to predict arsenic and antimony Neutral Mine Drainage from the Eleonore tailings

Abstract

The prediction of neutral mine drainage (NMD) is difficult using classical kinetic techniques due to the sorption and precipitation processes that retain the contaminant within the material, hiding the actual geochemical behaviour. A method for NMD prediction using sorption experiments and modified kinetic experiments with a complexing agent such as ethylenediaminetetraacetic acid (EDTA) was developed to predict metal leaching in mine waste. The objective of this study was to assess the applicability of the leaching procedure to oxyanions such as As and Sb as well as the evolution of the risk of Eleonore mine tailings towards As and Sb leaching in the long-term. The study found that the Eleonore tailings contained 527 mg/kg of As and 59 mg/kg of Sb, mostly found within löllingite and arsenopyrite. The leaching of As and Sb through complexation with EDTA was found to be effective in kinetic experiments for prediction purposes, despite EDTA's classification as a cation complexing agent. The tailings sorption capacity for As was estimated to be between 43 and 76 mg/kg. By comparing the sorption capacity and the metalloid content, the ratio sorption/metalloid content was found to be below 1 (0.07–0.13), indicating a high risk towards NMD. Furthermore, no notable change in sorption capacity was observed over the course of the column experiments, suggesting that sorption is unlikely to influence the As leaching dynamic. However, it is probable that As retention in the tailings is not primarily driven by sorption; given the high iron (Fe) loadings, coprecipitation may be the dominant mechanism.