Reduction of preg-robbing activity of carbonaceous gold ores with the utilization of surface blinding additives

Abstract

The carbonaceous matter present in some gold ores adsorbs the gold cyanide complexes from the leached solution and transport them to tailings, resulting in loses and preventing the recovery of the metal – a phenomenon known as preg-robbing. The present work aims at evaluating the capacity of 8blinding additives to deactivate/passivate the carbonaceous matter present in mineral coals and in gold ores. Initially, adsorption experiments with 3 mineral coals at different levels of maturation (anthracite, bituminous and lignite) were carried out to simulate the complex carbonaceous matrix of the gold ores. The coal presenting the best adsorptive capacity was selected for the experiments with the blinding additives. Different concentrations of additives (562–28,125 g/tcoal) and conditioning times (5, 30 and 120 min) were investigated. The blinding additives presenting satisfactory results were used in the deactivation/passivation carbonaceous gold ore experiments. Adsorption experiments showed that the anthracite coal adsorbed gold cyanide while bituminous and lignite coal failed to do so. It is believed that the difference in the adsorptive capacity presented by the mineral coals owes to the structure of the carbonaceous material, and also that the anthracite coal structure is similar to what is found in the carbonaceous gold ores presenting preg-robbing activity. The deactivation/passivation experiments indicated that the additives A1, A2, A3, A4 and A5 suppressed the adsorptive capacity of the anthracite by 60–85% in concentrations varying from 562 to 28,125 g/tcoal respectively. The additive presenting the best performance was A2. Experiments with a carbonaceous gold ore indicated that the use of 350 and 1000 g/tgold ore of additive A1 presented the best recoveries, 90.12 and 90.69%, resulting in the lowest presence of gold contents in the tailings, 1.17 and 1.25 g/t respectively. These values are very close to what was reported for CIL leaching (89.89% and 1.30 g/t) and considerably higher than values observed in the conventional leaching (83.79% and 2.10 g/t). Despite presenting the best deactivation/passivation performance when used with the anthracite coal, additive A2 did not reduce the preg-robbing activity of the carbonaceous matter of the ore, resulting in an increase in gold content in the tailing. The use of additives in the industrial process will demand a simpler and less expensive operational facility and the performance will be similar to the CIL technique.