Several alternative leaching agents for gold have been studied in recent years. These include thiourea, thiocyanate, thiosulphate and some halide/halogen systems (namely, iodine/iodide and bromide/bromine). Among these reagents thiosulphate presents some interesting features, as it operates in alkaline pH (around 10) and utilizes oxygen (air) as the oxidizing agent. This means that thiosulphate operates in pH and potential conditions, which are similar to those of the conventional cyanide process. In addition, for the thiosulphate leaching to be effective a certain amount of copper ions must be present in solution, whereas the presence of copper is detrimental to the cyanide leaching. Such characteristics suggest that ammoniacal thiosulphate may be an adequate chemical system for gold extraction from copper bearing ores or concentrates. Furthermore, thiosulphate is less toxic and harmful to the environment than cyanide. Although the thiosulphate leaching has been widely investigated in recent years, much less have been done towards the recovery of gold from the leach liquors in recent years. In the present work, the cementation of gold by zinc powder is investigated as one possible route for the removal of gold from ammoniacal thiosulphate solutions. The cementation parameters studied include thiosulphate concentration in solution; copper concentration in solution; ammonia concentration in solution; pH (range of 9 to 11); temperature and time (cementation time). Overall, zinc powder has proved to be effective in recovering gold from the investigated solutions.
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