In the last three decades, the economic conditions and the increasingly stringent environmental legislation worldwide have led metallurgical industry more difficult to develop. In addition, copper resources become increasingly depleted and the number of low-grade refractory copper ore grows day after day. Therefore, more attention must be paid to develop a low-cost, environment-friendly and high economic benefits process of recovering copper from ore. The extraction of copper from ore has commonly been performed using mainly pyrometallurgical, hydrometallurgical, and biochemical processes [1] -[3] . In traditional pyrometallurgical process, various gases released produced unacceptable air pollution, and metallurgy equipments always suffered serious erosion, leading to high production cost. Biochemical processes are mostly popular in processing the low-grade tailings or abandoned ore. While the use of this process is restricted by the strict growth environment such as temperature, pH, oxygen concentrate and light condition of microorganism and the long leaching period. However, hydrometallurgical process does not have the problems mentioned before. Therefore, hydrometallurgical process becomes the most viable and promising approach to treat copper sulfide ore in metallurgy fields. In hydrometallurgical process, the most widely used pretreatment process is roasting before leaching. There are three common roasting methods: oxidation roasting, chlorination roasting and sulfation roasting. Oxidation roasting needs high roasting temperature and copper will suffer a loss by generating copper ferrite. Chlorination roasting process is an environmental threat to the exhaust gas (SO₂, Cl₂, HCl) from the furnace. In sulfation roasting, copper was mainly formed to soluble sulfate by water or dilute acid after roasting. Mostly this method is applied to pretreatment of copper concentrate with high percentage of sulfur. A sulfate promoter can change the roasting atmosphere from oxidation to reduction, with releasing sulfur dioxide, turning metal oxides and sulfides to soluble metal sulfate [4] . Pyrite, sulfur, and sulfuric acid are the sulfate promoters normally used to produce the reductive atmosphere [5] -[8] . Prasad and Pandey studied the sulfation roasting of the mixture of copper-iron sulfides and copper sulfide formed copper sulfate, whereas iron sulfide converted mostly to hematite at 500˚C [9] .

In the present work, a sulfation roasting-acid leaching process that associated pyrometallurgical and hydrometallurgical methods has been used for the recovery of copper from a copper sulfide concentrate. The reactions investigated show an enhanced recovery of copper from its concentrate into a leachate which is almost devoid of iron. Suitable roasting temperatures, roasting time and a proper amount of addition have been explored in this study.

During sulfate roasting, copper extraction is mainly affected by roasting temperature, roasting time and Na₂SO₃ addition amount. The optimum roasting temperature and time were 500˚C - 550˚C and 2 h, respectively. At the optimum conditions, there was about 96% of copper leached out. The sulfation promoter Na₂SO₃ only improved the copper extraction at high roasting temperature. It couldn’t improve the sulfation effect when the roasting temperature was below 550˚C.

The author gratefully acknowledges the financial support of Jilin Province Wan Guo Gold Co. Ltd. (Ji’an, China).