Engineering & Mining Journal

JUL 2019

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Page 35 of 67

TAILINGS FILTRATION 34 E&MJ • JULY 2019 The challenge of how to process and store tailings for optimal safety and environmental protection while main- taining operational efficiency and rea- sonable cost per ton continues to loom large over the mining landscape. The in- dustry is under intensifying pressure to develop better methods of tailings treat- ment, storage and facility monitoring. Although the cost-per-ton scale tilts heavily toward the use of convention- al tailings storage using upstream or downstream embankment methods, the weight of actual and potential financial liabilities inherent in this approach, coupled with stockholder uneasiness, appears to be powerful enough to push industry attention and investment to other tailings technologies such as high-density thickened tailings, paste or dry-stack/filtered tailings. Dry-stack or filtered tailings systems offer a number of advantages ranging from better process-water recovery and less risk of catastrophic failures, to re- duced storage-facility footprint and the ability to progressively rehabilitate areas over the course of mine life. But existing dry-stack technology hasn't been widely implemented because it's too slow, too expensive and too management-inten- sive for use at operations processing 30,000 tons per day (t/d) or more. Engineering for EcoTails Four years ago, process equipment man - ufacturer FLSmidth began collaborating with gold producer Goldcorp to develop an improved method of tailings man- agement. Goldcorp had been using FLS- midth's conventional filter presses to de- water tailings at its Éléonore mine with good results, but it wanted even better performance for its Peñasquito opera- tion and future mines without having to install an inordinate number of filtration machines. The two companies traded knowledge — FLSmidth's expertise in equipment design and Goldcorp's famil- iarity with mine operational requirements — and came up with a concept called EcoTails. This involves high-volume "fast filtering" of tailings that are then commin - gled with mine waste to form GeoWaste, a conveyor-transportable, stackable and geotechnically stable end product. A crucial step in advancing the EcoTails technology is development of filtration equipment with sufficient speed and capacity to handle the tail- ings volume of large-scale mines such as Peñasquito, which has a throughput rate of 130,000 t/d. None of the stan- dard filter press models offered by FLS- midth was able to provide that capacity or speed, and the company set its sights on designing a machine that could. In early June, FLSmidth invited potential customers from mining op- erations around the world to attend a demonstration of its progress to date in building an unprecedently high-capac- ity hydraulic filter press. The demon- stration, held at the company's Tucson, Arizona, manufacturing facility, was accompanied by a seminar focused on the potential value of the EcoTails/Geo- waste concept, the technical challenges involved in bringing it to the commer- cial market, and the results of full-scale model filtration testing at Peñasquito. Peter Flanagan, FLSmidth's senior vice president–executive accounts, said the decision to focus on EcoTails and commingling of waste and tailings meant the company's engineers didn't have to design for a final filter cake moisture content of 15%. Instead, the cake could be filtered to 18% or even 20%. "So, if we don't have to dry as much, we could get more capacity out of the filter," Flanagan explained. "Then, we looked back at all the various types of machines that we developed over the years. Generally for smaller-scale opera- tions, but we were now designing for a typical 100,000-t/d operation." Pressure filters — of which FLSmidth has delivered thousands — seemed to offer the best all-around flexibility, but there was still a problem: "Pressure fil- ters can have many plates, and those plates all have filter media, and the FLSmidth Demonstrates Fast-filter EcoTails Concept A jumbo-size pressure filter with 5 x 3-m plate dimensions makes a strong argument that bigger is indeed better for high-volume tailings dewatering By Russell A. Carter, Contributing Editor Attendees at FLSmidth's fast-fill filter demonstration are dwarfed by the 5 x 3-m filter plate prototype that will be a key component in the company's EcoTails tailings filtration program.

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