Sulfiding of oxidized minerals of copper by sulfide solutions of ammonia at the comminution stage

Oxidized low grade copper ore minerals such as chrysocolla, atacamite and malachite are difficult to separate from the gangue by solution or flotation, but if the surface of the copper oxide can be sulfided it will become hydrophobic and can be flotated with the aid of xanthates and other chemicals. Ammonium sulfide was prepared by reacting ammonium hydroxide with hydrogen sulfide and then the sulfide was electrochemically activated to enhance the surface sensitivity by forming polysulfides. Surface analytical techniques demonstrated that sulfur adhered to the oxide particles and that covellite (a copper sulfide mineral) was present at the surface. Sulfidation was enhanced by grinding in steel ball mills and liners as contrasted to ceramic ball mills (which provided lower copper yields) as described and discussed in detail in this paper. Recovery of copper from the milled (- .074 mm) ore was 63-74%. Recycling the tailings through a closed process achieved a level of 80% copper recovery, which is 25-30% higher than direct flotation.