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The Australian Centre for Geomechanics held the 14th International Seminar on Paste and Thickened Tailings, 5 - 7 April 2011, in Perth, Western Australia.
A Paste Seminar is held annually in different locations around the world and is recognised as the main vehicle to disseminate P & TT technologies internationally. This seminar was the fourteenth in the series and reflected the developing maturity of the technology and management of P &TT. Paste 2011 explored the considerations needed to raise the awareness of mining industry leaders to how important environmental stewardship is to their tailings facilities in terms of long-term industry sustainability.
More than 260 paste and thickened tailings practitioners attended the Paste 2011 seminar that featured state-of-the-art technical presentations and case studies concentrating not only on the traditional disciplines of P&TT (namely, thickening, transportation and disposal), but other key considerations such as the rheology of slurries and mine backfill. Additionally, special attention was given to beach slope prediction which remains the major area of uncertainty in TSF design.
Prior to the seminar, the ACG hosted two workshops. Professor Paul Simms, Carleton University, Canada facilitated a highly interactive Prediction of Beach Slopes Workshop that was attended by 65 delegates. Professor Paul Slatter, RMIT University, Australia led a Rheology Workshop attended by almost 80 delegates.
Professor David V. Boger, Monash University; and The University of Melbourne, Australia, a world expert in rheology and recipient of the 2005 Prime Minister’s Prize for Science, opened the Paste 2011 seminar with an excellent overview, “A personal perspective on paste and thickened tailings - a decade on”. Professor Boger noted the positive impact that the P&TT seminar series have had on the development of this “designer waste”. He also concluded and recommended that traditional tailings “dams” can and should be eliminated for flocculated fine particle suspensions by producing and stacking a designer paste. Reclamation can and should then occur concurrently with the paste stacking.
“In paste and thickened tailings we are not talking about rocket science; we are talking about accounting practices which encourage degradation of the environment and regulators (governments) who do not have the courage to implement the latest technology. There are two groups of people here - the public servants and the elected representatives. Elected representatives are the ones who lack the political fortitude while the public servants lack resources in quality and quantity. Realising that each case can be different, the author believes that most tailings dams could be eliminated for flocculated fine particle wastes by the implementation of paste thickening. Producing and stacking a designer paste would allow the concurrent reclamation. Wouldn’t that be a major step forward? Maybe the industry will take the initiative!"
Day two was opened with a keynote address by Fred Schoenbrunn, FLSmidth Inc., USA, “Dewatering to higher densities - an industry review”. Schoenbrunn’s paper noted that “the development of high density and paste thickened technologies has changed the economics used in evaluating the benefits of increased thickener underflow density. This comes at a time of increasing competition for scarce water resources and a tightening regulatory framework in both water use and impoundment. These and other factors have led to more and more plants using high density and paste thickening technologies together with optimised tailings disposal schemes to recover water, minimise tailings impoundment areas and comply with regulations. High density and paste thickening have allowed these plants to take advantage of tailings disposal options that weren’t previously possible. The technology has significant benefits and has been proven in applications such as leach feed, CCD circuits, underground backfill, and filter feed and tailings disposal. "
Seminar chairs Richard Jewell and Andy Fourie were delighted to commission a keynote presentation from Dr Gavin Mudd, Monash University, Australia that addressed the potential for thickening to ameliorate the degradation of the environment by acid and metalliferous drainage from TSFs. Jewell observed “many leaders of the mining industry pay lip service to the ‘sustainability’ of their operations but appear to pay scant regard to the effects on the environment of the tailings produced from mining in the outcome of their high level meetings."
In his keynote address, Mudd, an active researcher and advocate on the environmental impacts and management of mining for over a decade, presented a unique and timely view of another potential advantage in P & TT.
“The potential scale of acid and metalliferous drainage risks from tailings and waste rock across the global mining industry is enormous and growing exponentially as well as being cumulative in environmental terms. Due to declining ore grades and the increased use of open cut mining, combined with continually growing minerals demand, the problems of mine waste will only escalate. Although AMD risks from mine wastes can be quite complex, since many factors vary from site to site, the basic process of sulphide oxidation leads to mammoth environmental risks - such as polluted surface waters, groundwater and significantly reduced biodiversity. Once the process has begun, it can take years to develop but last decades or centuries. There has been significant growth in paste and thickened tailings technology and use over the past decade, and it certainly appears that there are indeed good technical reasons to argue that P&TT can help in addressing AMD risks from tailings and/or waste rock. Given the scale of legacy and polluting mines sites, which were much smaller than present mines but where AMD is invariably the cause of pollution, it is clear that prevention is not only better than cure but considerably cheaper. There is a clear need for more research, and especially longer term site studies, but paste and thickened tailings can indeed act as a friend against acid and metalliferous drainage, helping to make the industry more sustainable in its management of mine waste."
Presentations from major mining countries from throughout the world were also very well received. Paul Simm’s presentation gave a powerful insight into the new deposition methods being evaluated by Shell Canada for use in their Northern Alberta oils sands operations. From the paper, “Field trials of thin-lift deposition of amended mature fine tailings at the Muskeg River Mine in Northern Alberta”, and amongst the technologies currently planned for deployment, Simms outlined the development of a new and exciting deposition method - atmospheric fines drying process (AFD).
“The AFD process entails amendment of the fluid fine tailings with a flocculating polymer such that rheology and depositional characteristics are modified, water release is enhanced upon deposition and the deposits are managed to enhance the rate of dewatering such that fluid tailings have geotechnical strength properties. Shell Canada commenced large AFD trials in August 2010."
One area generating solid industry interest was the ongoing advancements in paste backfill and/or cemented backfill. As noted in Aldea et al.’s paper, the use of this technology is “particularly prevalent in Canada and the USA because of increasingly stringent environmental regulations. Its main benefits are lower operating costs and a reduction of the amount of water sent to the tailings facility for disposal. The decrease of the amount of waste reduces the environmental impact and offers significant environmental benefits for the mines."
It is interesting to note that China is looking to readily embrace this practice with the imminent forecasted growth of surface paste disposal. In his paper, Professor A-X Wu found that incomplete data showed that there are more than 1,500 tailings ponds in China and over 8 billion tonnes of tailings are stored on surface; increasing at a rate of 600 million tonnes per year. Presently, the quantity of tailings discharged each year is about 130 Mt from iron mines; 140 Mt from non-ferrous metal mines; and 24.5 Mt from gold mines. Wu believes that surface paste stacking solves the security and environmental problem of tailings dams and has many benefits, but for technical and economic reasons it is a new technology in China. Paste filling can not only make use of the whole unclassified tailings, but also, with the material’s concentration increasing to about 78% solids content and the strength of the fill body increased to 3 MPa, this will increase the safety of the mining activities.
“For paste filling technology in China, we should develop the basic theory and dedicated devices for underground disposal with unclassified tailings. It is also necessary to expand the applied range of paste stacking to higher precipitation areas. In open pit mines, we can take the advantage of good permeability in waste stacking to develop open pit waste rock co-disposal techniques."
The technology and knowledge surrounding the design and implementation of mine backfill is maturing. The ACG looks forward to hosting the 11th International Symposium on Mining with Backfill in Perth, Western Australia, in 2014. Mine fill is recognised worldwide as an integral component of most underground mining operations. The stability of and safety within underground mines are enhanced by the closely controlled placement of mine fill into stope voids. Mine Fill 2014 will explore both the theoretical and practical aspects of the application of mine fill, with many case studies expected from both underground and open pit mines. More: www.minefill2014.com
The Paste 2011 seminar concluded with a site tour to Alcoa of Australia’s Pinjarra Refinery. This operation is one of the world’s largest refineries with a capacity of 3.2 million tonnes. The ACG expresses our gratitude to the Alcoa team for generously providing their time and resources for this site visit.
The 15th International Seminar on Paste and Thickened Tailings will be hosted by The Southern African Institute of Mining and Metallurgy, 16 - 19 April 2012, Sun City, South Africa. More: www.saimm.co.za.
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