Abstract:

The presence of arsenic (As) in copper sulfide concentrates (CSC) represents a major environmental and economic challenge. Due to its toxicity and the difficulties associated with managing potential As emissions during pyrometallurgical processing, mining companies face significant penalties from smelters. This highlights the importance of developing pre‑treatment solutions capable of selectively removing As from CSC through hydrometallurgical processes such as alkaline-sulfide leaching (ASL), while keeping copper sulfides in their solid form. Although this approach efficiently solubilizes As, it also generates highly alkaline and reducing effluents contaminated with As. This study focuses on the evaluation of the performance of As (co-)precipitation from ASL effluents using lime under alkaline conditions as a first treatment approach. The influence of operating parameters, including pH, Ca/As ratio, initial As concentration, reaction time and temperature, was investigated to identify optimal conditions for As removal and the stability of the newly formed precipitate. To do so, treatability tests using lime as a neutralizing agent were conducted on synthetic effluents with a chemical composition similar to that of ASL effluents using a parametric approach (one operating condition tested at a time). After the precipitation, solid/liquid (S/L) separation was performed by filtration and the supernatant was analyzed using ICP-OES to determine the efficiency of As removal. Experimental results demonstrated that lime (co‑)precipitation achieved up to 85% As removal efficiency under the following conditions: oxidation of As using hydrogen peroxide (H₂O₂), pH of 10, an initial As concentration of 500 ppm, a Ca/As molar ratio of 6/1, a temperature of 80°C, and a reaction time of 17 h. The resulting precipitates contained approximately 23% As and 22% Ca, suggesting the possible formation of calcium arsenate phases. These findings indicate the potential of lime (co‑)precipitation as a promising treatment strategy for alkaline As-bearing effluents. Future work will include the evaluation of precipitate stability through leaching tests and the comparison of lime precipitation with other treatment approaches, such as iron (co‑)precipitation, adsorption on different materials, and ion exchange processes. Ultimately, this project aims to develop optimized and sustainable treatment strategies capable of reducing the environmental impact of mining effluents.

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Prof. Mehrez Hermassi