PASTE & FILTERED TAILINGS
Life cycle management and tailings development
Erik Vlot , Weir Minerals Global Product Manager , GEHO PD pumps , discussed with IM a more comprehensive approach when planning tailings projects
Thickened or paste tailings is a critical application for which Weir Minerals has supplied pumps and systems for more than five decades . Erik Vlot told IM : “ In addition to thickened tailings , a conventional and filtered tailings disposal system can also be used to transport and store mine tailings at a tailings storage facility ( TSF ). Conventional tailings typically have a solids concentration of 30-55 %, whereas thickened tailings typically range from 60-75 %. Both types of tailings can be transported to the tailings storage facility by pumps . Filtered tailings typically contain only 10- 20 % of water and cannot be transported by pumps . They require transportation via conveyor belts or trucks .”
As conventional tailings contain an excess of water , the containment structure needs to be able to store all that water safely . In recent years , there have been numerous well publicised dam failures at mine sites across the globe , even though the tailings dams were designed to account for uncertainties and variability of the design loads in many cases . Vlot : “ Thickened tailings and filtered tailings disposal would reduce the risk of dam failures considerably . However , these systems require higher initial investment costs . Although filtered tailings require the least amount of water and , therefore , appear to be the preferred method in terms of tailings storage facility safety , the requirement of mechanical spreading and compaction introduces a set of constraints that can be overcome by applying thickened tailings technology . When thickened tailings technology is applied well , identical levels of tailings storage facility safety can be obtained against reduced operating costs .”
While reducing operating costs of a tailings disposal system has been the focus for many years , Vlot points out that sustainability is now another aspect to be considered . “ If mining companies apply the concept of life cycle management , they will analyse the tailings system from cradle to grave as well as the subsequent impact of the tailings system on the environment .”
They will consider all aspects that are important for the tailings disposal system , not only the investment and operating costs , but also the impact on the environment , the land usage and the carbon footprint . “ In this way , all variables relevant for the tailings disposal system are considered and factors that can be detrimental will be recognised upfront . Total investment costs and liabilities will be considered while selecting the tailings disposal system , enabling the selection of the best techno-commercial method and system .”
Vlot completed an MBA on this very topic in 2016 , with his thesis on the life cycle
Erik Vlot , Global Product Manager , PD Pumps , Weir Minerals management of tailings , looking in a more holistic way at how a customer would benefit from an approach that is not dominated initially by a process or product focus . “ You first try to establish what the criteria are , based on the tailings storage facility options , and the desired tailings properties . You can compare the various deposition methods and look at the sustainability piece including carbon footprint . And you can consider the different environmental risks associated with the different options such as dam stability or chemicals . Can you quantify all the parameters needed at the start of a tailings project to come up with the best solution , which also takes into account any future known changes or developments ? Only then do you start looking at the products and process elements .”
He adds : “ For example , positive displacement ( PD ) pumps have a very important role to play in pumping very high density tailings . However paste or thickened tailings may not be the right solution for every project . If you are in a very arid region with very high water costs , then filtered dry stack tailings may be the best option to give the best water recovery . You won ' t have too much stability risk with the stack as you don ' t have high rainfall . Elsewhere , thickened or paste tailings may be a better option , as long as you manage the tailings deposition facility properly and have a good logistical plan in place including for drying . For another project , a conventional TSF using centrifugal pumps might still represent the best option . Weir Minerals can support all three of these options . There is no generic solution , only the one that is right for the customer ' s specific site and conditions .”
He adds : “ You need to look at the planned tailings consistency first and the transportation options for that with the associated capex and opex plus carbon footprint . Then the TSF considerations - capex , stability risk , security risk , closure plan . You want a calculation model that encompasses all of these factors .”
Vlot and Weir Minerals have already applied the approach to a copper operation in eastern Turkey , which was using a conventional tailings dam and transporting tailings using gravity by pipeline . “ They needed to relocate the TSF due to the existing one only having five years of life remaining , having originally been thought to be enough for the full LOM . Filtered tailings was looked at but would have only given an additional year of life at a high capex since it involved transport using conveyors or trucks . All the costs were taken into account including water , carbon and power costs . Weir advised the client in the end to opt for a new tailings dam about 100 m uphill and a distance of several kilometres together with a thickened tailings
approach using PD pumps .”
IM