Reprocessing Tailings Dams – A systematic Approach (Part 1)

This is the first of two blogs examining the reprocessing of tailings dams.

Millions of tonnes of sulphide tailings are produced each year from base metal and gold flotation operations. Of these tailings a substantial amount is stored in tailings dams of which an example is shown in Figure 1. These tailings invariably contain sulphides which have potential to cause acid mine drainage (AMD). Sustainable environmental management of tailings is required to mitigate acid mine drainage and to ensure potential future liability at mine closure is obviated. If the sulphide component of tailings could be separated out relatively simply into a low volume fraction that could be separately stored and managed it would represent a major step forward in the environmental management of sulphide tailings (Bruckard and McCallum, 2007).

Fig 1. Ernest Henry Mine – Tailings Dam

In addition to environmental benefits of removing sulphide components from tailings there is the potential of additional economic benefit through retreatment. Reprocessing is most appropriate for mine sites still in current operation, where reprocessing can be integrated with existing mine planning and management strategies. The essential requirements of an orebody characterisation require quantification of process properties such as hardness, comminution energy, size reduction, liberation potential and product recovery. It is critical to characterise the tailings in detail in terms of mineralogy, chemical and physical properties. This step is often not completed with the thoroughness required (Bruckard and McCallum, 2007).

This is where geometallurgy steps in, as the processes involved in a thorough geometallurgical characterisation will provide the required data to properly plan for tailings reprocessing. The traditional approach to tailings evaluation would seem to have been predominantly based on assays and limited metallurgical testwork. No published evidence of any 3D block modelling of tailings has been found that incorporates non-additive variables like metallurgical recovery. It also seems that limited sampling is done on tailings dams, and variations in tailings mineralisation (and thus grade and recovery potential) are not taken into account.

A broad view of geometallurgy encompasses all activities that utilise improved understanding of the rock properties of the resource and other mined material which impact (positively or negatively) on the final value of the saleable product, and hence project value (Dunham et al., 2011). Tailings reprocessing based on a proper geometallurgical evaluation will be able to:

– Potentially allow conversion of currently uneconomic deposits (and tailings are future ore) into viable economic operations.
– Allow optimisation of the project from the viewpoint of energy consumption, carbon footprint and final project value.
– Enhance the environmental impact model through thorough geochemical characterisation.
– Reduce the technical and financial risk.

In the second part of this blog a suggested approach to structured tailings dam characterisation will be discussed. This approach forms the basis of a PhD study in progress at the JKMRC, University of Queensland, Australia.

References

Bruckard, W.J. and McCallum, D.A. (2007). Treatment of Sulfide Tailings from Base Metal and Gold Operations – A Source of saleable By-Products and Sustainable Waste Management. World Gold Conference, Cairns, QLD, p85-91

Dunham, S., Vann, J., and Coward, S. (2011). Beyond Geometallurgy – Gaining Competitive Advantage by Exploiting the Broad View of Geometallurgy. The First AusIMM International Geometallurgy Conference, Brisbane, Australia