Abstract
Mine tailings are generally disposed of by artisanal and small scale gold miners in poorly constructed containment areas and this leads to environmental risk. Gold phytomining could be a possible option for tailings management at artisanal and small-scale gold mining (ASGM) locations where plants accumulate residual gold in their above ground biomass. The value of metal recovered from plants could offset some of the costs of environmental management. Getting gold into plants has been repeatedly demonstrated by many research groups; however, a simple working technology to get gold out of plants is less well described. A field experiment to assess the relevance of the technology to artisanal miners was conducted in Central Lombok, Indonesia between April and June 2015. Tobacco was planted in cyanidation tailings (1 mg/kg gold) and grown for 2.5 months before the entire plot area was irrigated with NaCN to induce metal uptake. Biomass was then harvested (100 kg), air dried, and ashed by miners in equipment currently used to ash activated carbon at the end of a cyanide leach circuit. Borax and silver as a collector metal were added to the tobacco ash and smelted at high temperature to extract metals from the ash. The mass of the final bullion (39 g) was greater than the mass of silver used as a collector (31 g), indicating recovery of metals from the biomass through the smelt process. The gold yield of this trial was low (1.2 mg/kg dry weight biomass concentration), indicating that considerable work must still be done to optimise valuable metal recovery by plants at the field scale. However, the described method to process the biomass was technically feasible, and represents a valid technique that artisanal and small-scale gold miners are willing to adopt if the economic case is good.
Highlights
While many large-scale gold mining operations have struggled with economic viability as the gold price has dropped from historic highs in 2011, the number of artisanal and small-scale gold mining (ASGM) around the world has continued to increase
Minerals 2016, 6, 84 many locations become controlled by criminal groups who have turned to gold mining due to the potential for high profit margins [3]
The final waste product of mining, are generally disposed of in poorly constructed containment areas and this leads to transfer of contaminants to food and water, exposure pathways, and unacceptable environmental risk
Summary
While many large-scale gold mining operations have struggled with economic viability as the gold price has dropped from historic highs in 2011, the number of artisanal and small-scale gold mining (ASGM) around the world has continued to increase. A legal status for miners brings about resources to protect, remediate and rehabilitate the consequences of mining, and establishes a level of accountability for these consequences [3] This is important for the larger artisanal operations that may process as much as 5000 metric tonnes of ore per day [7]. Krisnayanti et al proposed that gold phytoextraction could be a possible option for tailings management at ASGM locations [9] This idea was based on an earlier field demonstration of gold phytoextraction technology at a mine site in Brazil, where corn and mustard plants were induced to accumulate gold from low-grade gold ore (0.6 g/t) using a one-time application of cyanide solution to the soil [10]. This work is a key step towards the eventual uptake of phytomining as a technology to manage the long-term environmental liability of ASGM mine waste
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