An application of acetonitrile leaching and disproportionation.: Refining segregated copper from roasted concentrates and ores

Pure copper with > 99% recovery has been obtained on a laboratory scale from a variety of copper sulfide concentrates by the following steps. An oxidative roast at 800–900°C to remove sulfur; reduction of the calcine, preferably but not necessarily under segregation roasting conditions at 650–750°C, to generate particulate copper; screening, in the case of segregation roasting, to partially separate from magnetite the over-size carbon which is coated with copper, gold and silver; selective dissolution in acetonitrile-water of the copper from both fractions; then thermal disproportionation of the copper(I) sulfate solution to remover pure copper powder. At least 80% of the silver and > 98% of the copper is recovered by this new concept. Cyanidation of leach residues recovers > 99% of the copper, > 90% of the silver and 80% of the gold, without interference from the iron in the residue. The method has been applied to the product of a segregation roast of refractory copper ores (TORCO process), to the product of a double roast of copper concentrates (Opie-Coffin process) and to the product of a non-segregation reductive roast of a dead roasted concentrate (USBM process). It is also applicable to calcines reduced in a blast furnace.Successful scale up could result in a low cost process for producing copper from copper concentrates. The energy requirements promise to be less than 6000 kJ as 25 psig steam per kg copper, if effective use of steam from the exothermic roasts can be achieved.