Abstract
The issue of poor aeration efficiency and low oxygen transfer in the heap leaching of gold has gained considerable attention. In this study, ozone ice was studied as an oxygen release reagent in the cyanide heap leaching of gold at a low temperature of approximately 5 °C, owing to its effective oxidation and clean and green properties. Quartz Crystal Microbalance with Dissipation (QCM-D) was used to monitor the effect of different ratios of cyanide and oxygen concentrations on the gold leaching rate. The results showed that the leaching rate doubled when the dissolved oxygen (DO) was increased from 8.2 mg/L to 12 mg/L at a relatively high cyanide concentration of 60 mg/L. The release of oxygen during the process of ozone ice melting was analyzed by simulating the oxygen-deficient condition of the ore heap in column leaching. In the first stage of ice melting, the DO in the solution increased dramatically, and the rate of increase improved with increased initial ozone concentration in the ice. In the second stage of ice melting, the rate of increase in the DO of the solution was not significantly affected by the initial ozone concentration in the ice; this was consistent with the decomposition rate of ozone. The addition of ozone ice containing 300 mg/L ozone increased the gold extraction by 4.1% in the ore column leaching experiment, compared to a column with no ozone ice. However, continuously increasing the ozone concentration up to 600 mg/L had no further significant effect, because the dissolved oxygen in the leaching solution reached saturation. The results facilitate a better understanding of the decomposition law of ozone in the melting process of ozone ice and help to improve the oxygen deficit state in gold leaching heaps.
Highlights
Heap leaching is a process extensively used by the mining industry to recover valuable metals from low-grade ores, owing to its low cost and operational advantages [1,2]
Since 2002, cyanide heap leaching of gold ore has been practiced in more than 100 operations worldwide [4]
A cyanide heap leaching system consisting of solid–liquid–gas phases is a series of transport and kinetic processes, which begins with the transport of substances, including cyanide, lime, water, and oxygen, from the heap surface to the particles [5]
Summary
Heap leaching is a process extensively used by the mining industry to recover valuable metals (especially gold) from low-grade ores, owing to its low cost and operational advantages [1,2]. In the cyanide heap leaching of gold ore, associated minerals, such as copper sulfide and pyrite, consume abundant oxygen [8]. Increasing the concentration of oxygen at the bottom of the gold heap is an effective method for improving leaching extraction. Inorganic peroxides act as effective oxidants in the reaction and provide oxygen for the cyanide leaching of gold under certain oxygen deficiency conditions [15,16]. The ore heap temperature must be maintained at 1–8 ◦C for the slow melting of ice. In this study, an aqueous solution containing ozone was made into ice as an oxygen release reagent to supply DO to the leaching solution inside the ore heap to improve gold extraction (Figure 1). We measured the concentration of ozone in the ice and found that the ozone retention rate during the icemaking process was approximately 45–65%, and this increased as the ozone concentration in the initial aqueous solution increased
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