Oxidation Of Arsenic Sulfide Copper Concentrate Roasting

Arsenic content of a copper sulfide concentrate has a negative effect on its selling price. The copper sulfide concentrate from Puer' contains 7.10% As and thus it becomes necessary and significant to treat the concentrate for its price promotion.The copper sulfide concentrate from Puer', being of high arsenic content is a typical tennantite. With the actual requirement of the enterprise to leach copper oxide ore in ammonia solutions, a roasting (get free coppers)-ammonia leaching for copper sulfide concentrate was proposed. During determining the operating parameters in the roasting process, the conversion ratio of the free copper oxide, as well as the As and S stabilization effect, were particularly focused on.Laboratory tests are carried out in a box-type resistance furnace. From the experimental results, the optical conditions in the absence of calcium oxide are as follows: roasting temperature at 500℃, roasting time of 3 h and a stirring per 30 minutes. Under such a condition, a total proportion 85.87% of the free copper oxide of is achievable. The ratios of As and S stabilizations are 79.98% and 48.47%, respectively; this is mainly due to the presence of calcium carbonate or calcium oxide contained in the copper sulifide concentrate, which can stabilize most of the As and S. Therefore, in order to explore the possibility of increasing As and S stabilizations ratios, further tests are performed. However, it was found that after adding the calcium oxide or calcium carbonate in the concentrate, the As and S fixation ratios increased and the conversion ratio of the free copper oxide decreased, due to the compaction phenomenon.While keeping the operating parameters in the ammonia leaching process changeless, i.e., the total ammonia content of 3.5 mol/L, the mol ration of c[NHs] to c[(NH4)2CO3] of 8:1 and the stirring speed of 400 rad/min, leaching tests are carried out in the roasted concentrate. Under such a condition, it was found that a copper leaching efficiency of 75.99% is achievable when the liquid-solid ratios is 6:1 at a leaching time of 2 h, in the first ammonia leaching stage. On the basis of the first leaching stage, the second leaching test is performed to increase the copper leaching ratio and the total copper recovery increased from 75.99% to 83.67%, by optimizing the leaching conditions, i.e., the mol ration of c[NH3J to c[(NH4)2CO3J of 8:1, the stirring speed of 400 rad/min, the total ammonia content of 1.5 mol/L, leaching time of 1.5 h and liquid-solid ratio of 2:1; A copper leaching efficiency of 7.68% is achieved in the second leaching stage.Therefore, the total copper leaching efficiency is 83.67% after two stages ammonia leaching in the concentrate, approaching to that of the free copper oxide in the roasting tests.Furthermore, the thermodynamic mechanism in the roasting stage is theoretically discussed. Based on the phase diagram and Gibbs free energy function, the following conclusions are drawn:the roasting products are copper oxide and copper sulfate at a low roasting temperature and such products can be leached out in ammonia solutions; and the roasting product is copper ferrite at a high roasting temperature and this product can not be leached out in ammonia solutions. The oxidation mechanism for the sulfide minerals, which is consistent with the test phenomenon, is also discussed in the present study.