GLYCINE-CYANIDE SYNERGIES IN THE LEACHING OF COPPER-GOLD ORES AND CONCENTRATES

摘要

The presence of reactive copper minerals in the cyanidation of copper-gold ores intensively increases the cyanide consumption and deceases the extraction of gold. There are also increasing environmental concerns and restrictions on the discharge copper-cyanide complexes to tailings dams. In addition to that, additional cyanide recovery or cyanide detoxification/destruction processes are required. This research study introduces a new process to extract gold and silver from copper-gold ores and concentrate using glycine-cyanide mixture. The effect of glycine/copper and cyanide/copper molar ratio addition on gold leaching kinetics and recovery was studied. The results show that, in the presence of glycine, gold and silver leaches fast (in comparison to either cyanide or glycine on their own) in solutions containing copper-cyanide species at a very low, or zero, free cyanide concentration. It has been shown that the gold recovery in glycine-cyanide system is almost three times higher than the gold dissolution rate in the conventional cyanidation. Kinetic studies were conducted to evaluate the effects of glycine concentration, pH, CN/Cu ratio on the dissolution of gold and silver. It has also been shown that the gold dissolution rate increases by increasing the glycine concentration up to 7.5 g/L and any further glycine addition has no effect on the dissolution of gold. Increasing leaching pH up to 11.0 enhances gold dissolution in the copper-cyanide-glycine solutions. The main finding from this research is that the presence of glycine in solutions containing different copper(l)-cyanide species can significantly enhance the dissolution of precious metals. It appears as if the glycine is involved in dissolving the passivation layer of both Cu(OH)_2 and CuCN formed on the gold surface at low, or zero free cyanide, and re-generating free CN~- ions from CuCN which will be involved in any further gold dissolution. In addition, glycine also stabilises the cupric ion in the system which act as a stronger oxidant for gold leaching.