Using life cycle assessment to evaluate some environmental impacts of gold production

Abstract The environmental profile of gold production with regards to embodied energy, greenhouse gas emissions, embodied water and solid waste burden has been assessed using life cycle assessment methodology. Both refractory and non-refractory ores were considered, with cyanidation extraction followed by carbon in pulp (CIP) recovery assumed for non-refractory ore processing. Flotation and pressure oxidation were included prior to cyanidation for processing refractory ores. For a base case ore grade of 3.5 g Au/t ore, the life cycle-based environmental footprint of gold production was estimated to be approximately 200,000 GJ/t Au, 18,000 t CO 2 e/t Au, 260,000 t water/t Au and 1,270,000 t waste solids/t Au for non-refractory ore. The embodied energy and greenhouse gas footprints were approximately 50% higher with refractory ore due to the additional material and energy inputs and gold and silver losses associated with the additional processing steps required with this ore. The solid waste burden was based on an assumed strip ratio of 3 t waste rock/t ore, but this ratio varies considerably between mines, significantly influencing the estimated value of this impact. The environmental footprint of gold production (per tonne of gold produced) was shown to be several orders of magnitude greater than that for a number of other metals, largely due to the low grades of ore used for the production of gold compared to other metals. The mining and comminution stages made the greatest contribution to the greenhouse gas footprint of gold production, with electricity being the major factor, and being responsible for just over half of the greenhouse gas footprint. This result emphasises the need to focus on these stages in any endeavours to reduce the embodied energy and greenhouse gas footprints of gold production. However, the significance of the contribution of the mining and comminution stages to the environmental footprint also means that falling gold ore grades will have a major impact on the environmental profile, and this issue is examined in the paper. Some technological developments in gold ore processing that have the potential to reduce the environmental footprint of gold production are also discussed.

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