Impact of mechanochemical effect on chalcopyrite leaching

• High energy stirred milling induces crystal structure distortion.
• Mechanochemical effect increases Cu dissolution by 25% after fine grinding.
• Two circuit layouts have been proposed for mechanochemical enhanced leaching.

Stirred milling is an enabling technology to process low grade finely disseminated ore bodies. Besides size reduction, stirred mill has the ability to deliver high energy to particles which facilitate crystal structure distortion. High energy stirred milling experiments (up to 300 kWh/t) were carried out on chalcopyrite concentrate. The media size, mill speed and slurry % solids were kept constant in this experiment. The only operational variable is milling time that results different levels of specific energy. The feed and ground particles were characterized for particle size distribution and mineral phase analysis (XRD). Mechanochemical effect was quantified by calculating the degree of crystallinity, crystallite size and lattice strain. The feed and ground sample undergo leaching test in five different lixiviants. The lixiviants chosen were sulphuric acid, hydrochloric acid, nitric acid, ferric sulfate and ferric chloride. The minimum particle size and degree of crystallinity obtained were 3.7 μm and 42% respectively at 113 kWh/t. Ferric chloride exhibits the highest Cu dissolution (up to 75%) when it was ground at 113 kWh/t. Based on the results, this paper has suggested two circuit layouts that may assist mechanochemical effect in order to enhance leaching. Mechanochemical effect exhibited during high energy fine grinding enhances downstream processes i.e. leaching. This is not taken into consideration when evaluating the efficiency of the milling circuit. In the future the milling circuit efficiency should take into consideration the reduction in particle size and mechanochemical effect during milling circuit efficiency evaluation.