Cadia tailings dam failure in March 2018. Image: University of Queensland
Recent high-profile tailings dam failures are threatening the mining industry’s financial and social licences to operate.
The average tailings dam failure rate over the last 100 years is 1.2 per cent, or 2.2 a year, which is higher than that for water retention dams of 0.01 per cent.
While it is difficult to decide whether the above risk level for tailings dam failure is acceptable, it does not ignore the fact that the ongoing rate of its failures is unacceptable, according to the director of the geotechnical engineering centre at the University of Queensland, David Williams.
Market capitalisation of all iron ore producers, except Vale, still remained about the same since the Brumadinho tailings dam failure.
BHP shares went up 15.1 per cent, Rio Tinto 18.2 per cent and Fortescue 34.4 per cent, while Vale was recovering to a 16.3 per cent dip (in contrast to 25.9 per cent initially) since January 25 2019.
“Approaches to tailings management need to improve,” Williams said at a tailings management workshop in Dubbo, New South Wales.
“Commonly held perception, supported by a net present value (NPV) approach, is that transporting tailings as a slurry to a dam is most economic.
“[But] few tailings storage facilities have been rehabilitated due to difficulty and expense of capping ‘slurry-like’ tailings, particularly at a time when mine is no longer producing revenue.”
Williams urged mining companies to question their conventional ‘what we have always done’ approach and treat mining and processing wastes as potential rehabilitation or construction materials.
The industry should move toward tailings minimisation, dewatering and integrated disposal with waste rock.