Leaching properties of zinc from hazardous zinc leach residues under simulated environmental conditions

Mining operations have been a significant source of environmental pollution due to their excessive water usage during ore processing and the subsequent discharge of tailings into the environment. It is imperative to assess the extent of toxic metal release resulting from these activities at any given time. In this investigation, we explore the environmental risks and the release patterns of zinc (Zn) from zinc leach residues (ZLRs) originating from the Angoran mine in the Zanjan province of Iran. A series of batch experiments were conducted on two distinct ZLR samples (S₁ and S₂) to analyze the influence of factors such as particle size, contact duration, liquid-to-solid ratio, and pH of the leach solution on the leaching behavior of Zn. The primary constituents in the ZLR samples were found to be SiO₂ and CaSO₄. It was observed that the release of Zn was contingent on pH, with increased acidity leading to higher Zn release. Even after 360 min of contact, equilibrium was not achieved, and the release exhibited an upward trajectory. Heterogeneous behavior was noted in the particle size distribution, with the greatest Zn release observed in particles within the 0.3–0.5 mm size range. The solubility of Zn was identified as the dominant factor influencing its release from the residues, raising environmental concerns as a significant portion of Zn is present in a soluble fraction. Based on the mobility index and leaching limits defined in Decision 2003/33/EC, the tested ZLR samples were classified as highly hazardous.