A Case Study On Bio-heapleaching Practice Of Zijinshan Copper Sulphide

Bioheapleaching-SX-EW process was developed for copper recovery from low grade copper sulfide including more than20mines all over the world since80's of the last century. In China, the first commercial plant of bioheapleaching-SX-EW with a capacity of10,000t Cu/a in Zijinshan Copper Mine commissioned by the end of2005. Based on mineralogy of the ore and local geography of the mine, distinct engineering operations such as multi-lift permanent stacking in coarse particle size (P80=40mm) without agglomeration and aeration were applied in Zijinshan bioheapleaching practice. Copper was leached efficiently, pyrite dissolution was inhibited and jarosite was formed in the heap by taking advantages of high acidity, high iron concentration, and elevated temperature in the leaching system. The distinct operations and excellent performance probably make Zijinshan copper bioheapleaching practice the first one in the world in which copper was recovered at high efficiency with low activity of microorganism. To reveal key factors which effected the operation in Zijinshan bioheaps, this paper focused on dissolution kinetics of copper sulfides and pyrite, bio-oxidation kinetics of ferrous and kinetics of jarosite formation. The results of kinetics may provide theoretical basis to understand distinct bioehapleaching operation of Zijinshan, and some implication for optimization of similar bioheapleaching practice.The main copper sulfides in Zijinshan were digenite and covellite. In aqueous ferric sulfate the activation energy of copper sulfide dissolution were relative high (covellite96kJ/mol and digenite72kJ/mol), thus elevated temperature was key factor to accelerate the dissolution of copper sulfides; Ferric concentration and redox potential only have a litte positive effect on the dissolution kinetics of copper sulfides. As a result, under high concentration of ferric ion, to increase temperature of the leaching system is the critical path for the copper sulfides dissolution. Relative high content of pyrite (6%) were within Zijinshan copper ores, which was the source of the excessive acid and iron in leaching system. In ferric sulfate solution, the dissolution rate of pyrite has significant correlation with redox potential in order of2.68. Under low redox potential, the dissolution of pyrite was limited even at high temperature. Thus at high leaching temperature, to keep leaching system at low redox potential was the key path for copper competitive bioleaching from pyrite by ferrous oxidation inhibition. Elevated temperature, low pH and high iron concentration could inhibit the iron bio-oxidation, thus lower the redox potential. The analysis of thermodynamics and kinetic experiments showed that temperature was the key factor for jarosite formation. In Zijinshan bioheapleaching system, hydronium jarosite could be readily formed to remove iron inside the heap. Column leaching tests indicated, proper match of temperature, iron concentration and pH, high copper recovery and acid and iron balance at low cost could be achieved.