Selective arsenic removal from enargite by alkaline digestion and water leaching

• Arsenic was removed from enargite by digestion in Na2S–NaOH solution.
• In alkaline digestion of enargite, copper remains in the solids as digenite.
• Arsenic dissolution is extremely rapid in the digestion of enargite with mass transfer control.

Copper concentrates with elevated enargite content are not apt to be treated by the current technology of smelting/converting because of the high risk of pollution with toxic arsenic compounds. Therefore, these copper–high arsenic concentrates must be pretreated to remove the arsenic before smelting and the traditional method of pretreatment is roasting. In this work, an alternative hydrometallurgical method for selective removal of arsenic from enargite is presented. The process consists of alkaline digestion with a concentrated Na2S–NaOH solution followed by water leaching. The experimental results obtained using high grade enargite showed that the alkaline digestion is very effective for rapid and selective removal of arsenic from enargite. The copper in the solid residues remains as digenite (Cu9S5). More than 97% of the arsenic was removed in 12 min of digestion at 80 °C, 100% excess of Na2S and 2 M of NaOH. The kinetics of the digestion reaction was analyzed by a shrinking particle kinetic model and the determined activation energy was 22.1 kJ/mol for the temperature range of 70–90 °C. This activation energy is consistent with a mass transfer kinetic control.