WATER MANAGEMENT
FLSmidth – taking a systems approach
FLSmidth ’ s Tailings Group was formed in 2016 – it saw a group of experts take a more system-based approach rather than just looking at individual pieces of equipment – everything from pumps & cyclones for a traditional sand dam through different thickener and filter types right through to co-mingling of tailings and coarser waste as part of its EcoTails ® solution . Paul Moore spoke to one of the founders , Ken Rahal , FLSmidth Director of Tailings Solutions , about water ’ s role in mining
Q What is driving the focus on water saving and recycling in mining ? A Both water saving and water recycling are important in mining but which is deemed first or second varies from customer to customer and really depends on their situation . There are miners we have worked with where they have a high fresh water cost , so in that case water saving does drive a lot of the financial justification of looking at filtered tailings . In Chile of course you have desalination at the cost , with water then pumped all the way up 4,000 m or more to the mines in the Atacama – and those pumping costs are significant , and they are on top of the desal cost itself . So their water costs can be $ 4- $ 5 per cubic metre . For these mines filtered tailings can make a significant difference as it allows you to recycle most of your process water . Then there are also mines such as in Australia that from time to time experience severe drought conditions – and in some cases have had to reduce throughput due to inability to access enough water . So for them filtered tailings are also attractive but for a different reason . In India we had a customer that wanted to do a plant expansion to improve the economics of the mine , but the municipality wouldn ’ t provide them with any more water . They were already doing some filtering for their paste backfill but because of the water situation they significantly expanded their filtration plants . Overall , water scarcity will become more of an issue for mines as world population continues to increase so water recycling is becoming one of the key topics in mine development for both existing and greenfield operations .
Q Is there still a reluctance in mining to go down the filtered & paste tailings route ? A I think a lot has changed since the high profile tailings dam failures in recent years , which understandably has created a lot of discussion around how you reduce the risk of TSF failures plus the creation of the Global Industry Standard on Tailings Management . That drives a lot of investigation but at some point the investigation has to reach an economic discussion . Accurate soft ( indirect ) costs have been hard to quantify – particularly risk related dollar values for different tailings management strategies , though there are consultants and others working on this . Overall miners are very focussed on becoming more environmentally and socially conscious , and the hit their social licence to operate took from tailings failures is a part of that .
Q How does water saving and the tailings approach differ between an existing mine and greenfield project ? A For greenfield sites , its about doing the detailed studies upfront and getting permitting in place for a filtered tailings route . We are working with some customers on that and they have indicated that going down this path is helping their permitting process versus going with a wet TSF . The work we are doing with brownfield sites varies . If they have an existing wet TSF and there have been no concerns , plus if its capacity is still in check with the current minelife , then they are looking more at moving from unthickened to thickened ( paste ) tailings to improve their water balance and decrease the volumes of fresh water needed . It also means they get more storage capacity in their existing TSF plus still represents a safety increase . Other brownfield sites may be extending the minelife through new reserves in the existing orebody or in a nearby satellite deposit , so they are running out of storage capacity in their existing TSF . Their options Ken Rahal , FLSmidth Director are build a new wet TSF or switch to of Tailings Solutions filtered tailings . So we are also helping customers go through those evaluations , from lab scale to pilot studies – to ascertain when is the right time to make the switch to filtered .
Q How important is water cost now in tailings management studies ? A It is definitely something being factored in very early on – we do a lot of conceptual level work for greenfield projects based on ore samples or core . We give them the different options +/ - 30 % Capex / Opex accuracy . Even without ore samples we can still do desktop studies , albeit less accurate , based on our prior experience and data from similar projects if they have a basic flowsheet design in place . It still gives an order of magnitude idea of costs for different routes .
Q How does the relative importance of thickeners versus filter presses relate to the type of tailings route chosen ? A When it comes to types of dewatering equipment , for conventional tailings , thickeners can handle pretty much any throughput and particle size distribution . They remain the cheapest way to dewater – after all gravity is free . Once you start trying to produce a filtered product with 15- 25 % moisture , at lower tonnage throughputs you have at lot more options including vacuum filters , belt presses , centrifuges and filter presses . But above a certain tonnage and certainly for the 100,000 t / d plus mines , most of these aren ’ t economic because their capacity per unit is too low so you would need too many of them . For 30,000-50,000 t / d vacuum filters and filter presses are still in the game . But for the larger mines , especially where the PSD low and the tonnages are high , the filter press is really the only option . And that ’ s why we have developed ever larger presses as you want to bring down the number to then reduce ancillary costs such as maintenance , labour and energy – fewer HPUs and compressors .
Q So why the hesitancy in mining to opt for the super large presses ? A They are still quite new for a lot of people ’ s experience levels . Filtered tailings have been around for decades but projects have been small . Once you get to huge presses , they see it as a new technology risk , though from our standpoint it is the same technology but bigger as long as the right testing has been done from the outset on the material variability throughout the mine life and the geotechnical aspects . We have a number of pilot studies either underway or being discussed with customers as well as customers that are investing in or in discussions to install demonstration plants with full scale equipment such as our Colossal filter . The miners just want to go through that derisking process to gain confidence in the full scale operation .
2020 , there were no risks associated with the lack of water resources for withdrawal and consumption . ALROSA says it takes measures for
the rational use of water resources , which contribute to the reduction of water withdrawal indicators , and also performs responsible management of wastewater . “ The company focuses on developing circulating water supply system and a tailings thickening system .” It
22 International Mining | MARCH 2022