IM 2020 May 20 | Page 16

REPROCESSING AND TAILINGS REDUCTION Gouveia, VP, Tailings Management Systems for the company. The machine, equipped with the same advanced control system, sensors and functionality the commercial units have, was installed in March, in Brazil, and is now ready to perform all tests on an industrial scale, according to Gouveia. “At least four customers have already scheduled their tests, while others in Chile, Peru and Australia should start sending samples to Brazil in the coming weeks,” he told IM in early April. Gouveia expects these test results to be available in the near term. They will provide data on how the VPX unit can treat material from iron ore, copper and gold operations. “There is big interest in those tests in Brazil right now,” he explained. “The main point of the tests for these companies is to understand how the VPX processes the material, but they also want to use the results to dimension their circuits for tailings.” Metso has built the VPX filter to manage varied input materials with pressure up to 25 bar (and perhaps even higher). The company eliminated the use of hydraulics on this new filter, instead using electromechanical screws to achieve the high-pressure closing that turns wet material into dried cakes with as low as 7% moisture content in some applications. The modular design allows the filter to be scaled to any size, plus fit it into a container for easy logistics. The fast opening and closing mechanism, meanwhile, means the units can provide the high- capacity dewatering large mines require. Lars Gustavsson, Director, Filtration, Metso, said there has been lots of interest in the VPX filter since launch in June 2019 and the company has many units in negotiation with companies in South America, Australia, Europe and Asia. Despite both Gouveia and Gustavsson explaining the majority of this demand has come from miners looking to process fresh tailings as they made moves away from wet tailings operations, Metso’s most advanced discussions have been with a miner in Latin America looking to treat a high tonnage and difficult to dewater copper concentrate. The miner in question is also interested, longer term, in applying the VPX filter to its tailings operations, Gouveia clarified. Gustavsson explained: “The VPX, as we designed it, is not only for high pressure capacity filtering of tailings; we can also use the air blowing to reduce the cake moisture of a concentrate.” He said Metso is also starting to include details of the VPX unit in filter press quotes it sends to hematite miners in India. “We see a big potential for the VPX25 filter in India for Indian hematite,” he said. “This material can be as difficult to dewater as tailings and we are also talking about high tonnage applications.” Tailings will continue to remain the focus for Metso going forward, according to Gouveia. “With the reduction of ore head grades and the increased demand for metals, we have seen increases in the volumes of material produced,” he said. “This has seen the volume of tailings also increase. Waste to paste Faced with a significant and potentially costly challenge relating to tailings disposal, The Ural Mining Metallurgical Company (UMMC) mining and processing plant in Uchaly, Russia, turned to Outotec and its thickened tailings and paste expertise. The existing disposal pond at the plant was close to capacity, and constructing a new facility would be costly, time consuming and significantly expand the mine’s environmental footprint. The plant used the traditional impoundment method to dispose of tailings and, by 2014, the existing pond was almost full. With the mine continuing to operate underground, there were two options: either build a new tailings pond, or use the depleted open pit to store tailings. UMMC chose to implement an Outotec HCT paste thickening plant to turn concentrator waste into an environmentally friendly paste product that can be used to restore the depleted crater of the site’s open pit. The existing mine was at a depth of 400-600 m under the open pit, meaning safety was of utmost importance. To ensure safety, several factors had to be considered, according to Outotec: n Reducing the amount of water in the tailings to minimise mine drainage; n Increasing the solids content from 20% to 68-70%; and n Finding a sustainable solution for managing tailings. 14 International Mining | MAY 2020 Metso’s pilot VPX filter press unit is installed in Brazil and is ready to perform all tests on an industrial scale, according to Rodrigo Gouveia “After the most recent tailings dam accidents, there has been more concern about using dam capacity. Authorities are paying a lot more attention to this and, in many cases, are not providing authorisation to increase dam capacities. “Water scarcity in some areas is another issue. When we talk about recovering or dewatering the tailings, it also becomes a source of water that can be reused in the mining process or returned to nature.” He concluded: “These factors, plus the more cost-effective nature of new filtered tailings technology; the high cost of – and cover restrictions associated with – insuring tailings dams; and the increased risk associated with operating wet tailings dams, has made dry stack tailings a much more viable solution,” Gouveia says. Yet, it should be remembered that, with Metso’s ability to offer a complete processing offering through its expertise in comminution and beneficiation, the VPX could be used in The Outotec Thickened Tailings and Paste Plant not only reduces the area occupied by the tailings pond and the risk of environmental pollution, but also allows efficient recovery of process water for reuse and reduces the energy consumption of slurry and water pumping, the company said. In addition, by moving away from the traditional method of disposal, the operating life of the tailings pond was increased from 20 years to 50 years. Together with its partner, the Institute of the Urals Branch of the Russian Academy of Sciences in Yekaterinburg, Outotec developed an approach that would meet all project requirements and avoid the underflow flooding into the underground space, it said. Work began in 2010 when the first laboratory tailings thickening tests were performed. Pilot tests were carried out in the autumn of 2011 and the first technical and commercial quotation was prepared in 2012. In 2014, the joint engineering solution successfully passed state expert appraisal. In 2017, the plant successfully passed all the tests, with the desired solids content of 70% achieved almost immediately after start-up of the paste tailings plant, Outotec said. When mixed with cement, the paste from the thickening plant can be used for backfilling the depleted open pit or underground mine space, both decreasing the area of the tailings pond and increasing safety by improving the stability of the mine.