The effect of ammonia and chloride on the precipitation of copper sulfide using S and SO_2

摘要

The effect of chloride and ammonia on the precipitation of copper sulfide using S and SO_2 was studied. In the absence of chloride or ammonia, the precipitation reaction rate is sluggish and temperatures above 90℃ are required to obtain satisfactory copper recoveries. This is believed to stem from the fact that the precipitation reaction is energy-intensive because of the hydrophobic nature of sulfur and the strong hydration energy of the Cu(Ⅱ) ion. It was found experimentally that the presence of either chloride or ammonia has a strong effect of the mechanism because both reagents form stable Cu(Ⅰ) complexes. In the presence of ammonia in alkaline medium, copper recoveries higher than 90% were obtained at room temperature. This result was attributed to the formation of Cu(Ⅰ) amino complexes and to the acid neutralization potential of the free ammonia. The X-ray diffraction analysis showed that the reaction products are a mixture of non-stoichiometric microcrystalline copper sulfides with an average size of 30 μ and whose compositions vary from covellite (CuS) to Djurleite (Cu_(1,97)S). Their actual compositions depend on the sulfur/copper ratio.