Column bioleaching characteristic of copper and iron from Zijinshan sulfide ores by acid mine drainage

Abstract

In Zijinshan, a commercial copper bio-heap leaching plant has been operating successfully since 2006. The plant used raffinate as irrigation solution and operated at low pH and high iron concentration from 2006 to 2010. However, high concentration of soluble iron led to crud formation and low current efficiency in subsequent solvent extraction and electro-winning (SX-EW) steps. It is important to reduce iron dissolution in bioleaching and address this low current efficiency issue. About 1500m3/h acid mine drainage (AMD) accumulated in collection pool in the Zijinshan copper mine. Not only does it cause the loss of copper, but also result in potentially secondary pollution. This paper proposes an option to use AMD as leaching solution for the recovery of copper. Column bioleaching experiments were performed with low-grade secondary copper sulfide ore from Zijinshan. To simulate leaching, several variables such as irrigation solution, leachate treatment (with or without recirculation), irrigation duration, temperature and pH were considered for the evaluation of the copper recovery and iron extraction. Results showed that 6–8h/d irrigation was needed to ensure the wetting of the ore surface, to keep sufficiently high temperature and aeration inside the column. Under optimal pH condition of 1.6–1.8, with recirculation of AMD, copper leaching reached 90%, however iron leaching was only 20% both after 240days, respectively. About 78–86% of copper extraction was observed in the first 100days and then slight increase of about 4–12% towards the end, whereas iron extraction continued with an upward trend after 100days. The results showed that AMD could be utilized for selective and efficient copper recovery in Zijinshan copper mine.