In an industry that is consistently trying to minimize its risk exposure while simultaneously driving down unit costs, the management of mine tailings has provided an ongoing concern to mine managers and owners. The current resource boom is seeing lower and lower grade deposits becoming economically viable, with the inevitable consequence that greater volumes of tailings are produced per unit of commodity recovered.
Conventional tailings management methods rely on transporting the tailings to the tailings storage facility (TSF) at a low-solids content, with more than three parts water to one part solid not being unusual. The consequence of this approach has sometimes been catastrophic failures resulting in significant economic and environmental damage and even fatalities. (The most recent failure of this type of storage resulted in fatalities in China in April 2006.) However, more common and immediate concerns include the enormous wastage of water that results, difficulties with post-closure rehabilitation, and high operational costs that result from having to frequently undertake earthworks to raise the height of the TSF.
In the 1970s an alternative approach was advocated by Eli Robinsky of Canada. He suggested thickening the tailings to a consistency such that no segregation of particles occurred upon deposition and no free water bled to the surface of the TSF, significantly reducing the need for water retention and management. His idea was received with interest but also scepticism and for decades was considered largely impractical.
Despite this apparent lack of support, Robinsky persevered with the idea and was responsible for implementation of the first thickened tailings surface disposal site at the Kidd Creek mine in Timmins, Ont. The project encountered many difficulties with achieving the required underflow densities consistently, but despite this, the perseverance of the mine management paid off and today the site seems to be operating as planned. More importantly, it showed that the technology was workable, if only the equipment was available to reliably and economically prepare and transport the thickened tailings. Industry developments over the past two decades have provided this equipment, and many of the problems encountered by the Kidd Creek team have since been overcome.
Only seven or eight years ago, most tailings operators and managers were interested but sceptical about thickened tailings, commonly asking questions such as, “But where is it working?” and there were very few examples available. Things are different today. There are many instances around the world where the technology has been implemented and thoroughly evaluated, from diamond, mineral sands, gold, alumina, lead-zinc and nickel operations. There are upwards of a dozen sites in Australia alone that are now using some form of thickened tailings disposal on surface and at least a similar number of underground operations using even higher consistency material (paste tailings) for backfilling mined voids underground.
We now have the opportunity to learn from many of these operations, providing sound arguments for future projects that are considering thickened tailings as an alternative solution to site-specific problems.
There is now sufficient experience of operating thickened tailings sites available to begin validating some of the claimed benefits of the technology, such as reduced water and reagent usage, decreased operational costs and reduced seepage to the subsurface. Interesting experiences with the management of storm water runoff are also available. Comparing the problems of closing a facility built using thickened tailings (such as a central thickened discharge) with those of a conventional facility provide for interesting debate.
All of these issues will be aired at the Australian Centre for Geomechanics’ 10th International Seminar on Paste and Thickened Tailings that will take place in Fremantle, Western Australia in March 2007. The seminar will provide an opportunity to share successful experiences with thickened tailings, as well as the problems that have been encountered. This will help indicate the direction that future research and development should focus on, as the industry tries to drive down unit costs of tailings management as well as reduce the risks to potentially affected communities and the environment.
For further information about Paste 07, please visit www.paste07.com.
(Dr. Fourie is principal, environmental geomechanics at the Australian Centre for Geomechanics. He may be contacted at email@example.com.)