The high grade of copper in the Igarapé Bahia (Brazil) gold-copper ore prevents the direct application of the classic cyanidation process. Copper oxides and sulfides react with cyanides in solution, causing a high consumption of leach reagent and thereby raising processing costs and decreasing recovery of gold. Studies have showm that a feasible route for this ore would be a pretreatment for copper minerals removal prior to the cyanidation stage. The goal of this experimental work was to study the experimental conditions required for copper removal from Igarapé Bahia gold-copper ore by sulfuric acid leaching by applying a statistical approach to the experimental design. By using the Plackett Burman method, it was possible to select the variables that had the largest influence on the percentage of copper extracted at the sulfuric acid leaching stage. These were temperature of leach solution, stirring speed, concentration of sulfuric acid in the leach solution and particle size of the ore. The influence of the individual effects of these variables and their interactions on the experimental response were analyzed by applying the replicated full factorial design method. Finally, the selected variables were optimized by the ascending path statistical method, which determined the best experimental conditions for leaching to achieve the highest percentage of copper extracted. Using the optimized conditions, the best leaching results showed a copper extraction of 75.5%.

This experimental work presents the optimization results of obtaining a high indium concentration solution and minimum iron poisoning by solvent extraction with D2EHPA solubilized in isoparaffin and exxsol. The variables studied in the extraction step were D2EHPA concentration, acidity of the aqueous phase and time of contact between phases. Different hydrochloric and sulfuric acid concentrations were studied for the stripping step. The optimum experimental conditions resulted in a solution with 99% indium extraction and less than 4% iron. The construction of a McCabe-Thiele diagram indicated two theoretical countercurrent stages for indium extraction and at least six stages for indium stripping. Finally, the influence of associated metals found in typical sulfate leach liquors from zinc plants was studied. Under the experimental conditions for maximum indium extraction, 96% indium extraction was obtained, iron extraction was about 4% and no Ga, Cu and Zn were co-extracted.

The galvanic stripping technique for metal recovery uses commercial organic extractants containing a metal to be recovered. The organic phase is placed in contact with a solid metal reducer that allows electrochemical reactions to occur. One product of these reactions is a metal layer deposited on the surface of the reducer consisting of reduced species desorbed from the organic phase. Another product is metal ions from the reducer adsorbed onto the organic phase. This work presents results for gold recovery by galvanic stripping of strong-base anionic extractants of a quaternary amine salt, ALIQUAT336®, in xylene using solid zinc as the metal reducer. The parameters studied were contact time for the organic phase containing gold and the samples of the reducing zinc metal, temperature of the system, gold concentration in the organic phase and type of stirring used in the galvanic stripping system. Experiments showed results higher than 28% of gold recovery and an adherent film of gold on the zinc surface. The Arrhenius plot for gold recovery from the organic extractant suggests a change in the rate- controlling step from mixed control to diffusion control with increasing temperature in the range of 20 to 50ºC.