Investigation to improve recovery of copper and gold from a refractory ore

Results of tests presented in this paper indicate that the Santa Maria del Oro ores might be processed by a method which should yield a gold recovery of 96 to 98 percent and a copper recovery of about 78 percent, both figures subject to an increase with further work and study of the problem. In the method of processing outlined in Figure IX, the ores, mixed as under present operating procedure, would be crushed to minus 20-mesh and roasted with ten pounds of sodium chloride per ton of feed in a multiple-hearth, down-draft roaster at temperatures varying to a maximum of 550°C in the hottest (middle) hearth. The period of roasting should be about six hours; the atmosphere in the furnace should be controlled by adjusting the air intake so that the effluent would contain about 3% sulphur dioxide. The water leaching conditions should be as follows: water to solid ratio of 6:1 in the leaching pulp, temperature of the pulp - 23-24°C, a one hour leach. The copper in the pregnant filtrate could be recovered by crystallization as copper sulfate, by precipitation as cement copper, or by electrolytic deposition; economics would determine the method to be chosen. After being reduced to minus 100-mesh, the filter cake from the water leach should be cyanided in 0.1% sodium cyanide solution for 24 hours; a slightly increased gold extraction is possible with 0.15% sodium cyanide solution and 48 hours agitation, but the increased costs of handling and cyanide consumption might make such processing non-profitable. Again economics of the established process would determine the conditions to be utilized. A satisfactory protective alkalinity may be established with six pounds of lime per ton of filter cake processed --Summary, pages 51-52