Engineering & Mining Journal

SEP 2018

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Page 48 of 75

TAILINGS MANAGEMENT SEPTEMBER 2018 • E&MJ 47 at curbing acid rock drainage, directed by a committee with members from the min- ing industry, federal and provincial govern- ments, and nongovernmental organizations. The study describes the use of con- ventional dewatering tailings technolo- gies as well as associated facility types alternative to conventional practice in Canada (or in other locations with simi- lar climates), evaluates the applicability and efficacy of the alternatives at reduc- ing physical and geochemical risk com- pared to conventional tailings facilities, and identifies opportunities for further research and development. The study echoes others in noting that although there is a menu of choices for tailings handling and storage, the global industry suffers from a distinct knowledge gap regarding planning, costs and consid- eration of alternatives in tailings manage- ment, caused mainly by a lack of infor- mation sharing among operators and the absence of structured, useful collections of tailings management-related data. Tailings Tech Options Expand As industry and external concerns grow about the location, size, method and over- all safety of both existing and proposed TSFs, industry consultants and suppliers are offering solutions that range from sim- ple to complex, spanning a cost curve that starts with conventional tailings-as-a-slur- ry methods and equipment, and stretches into the higher-cost realms of thickened, filtered or paste systems. As will be seen later in this article, the growing list of op- tions for storing tailings and monitoring them include approaches that employ components as diverse as giant geofabric bladders, colossal filters and tiny boats. The key to lasting tailings manage- ment success, of course, is to pick the right management solution at the start. Equipment supplier McLanahan Corp. offers this advice: "The best way for pro- ducers to deal with tailings is to answer the question: What do you envision as the long-term solution? Most short-term fixes don't fix the problem and create more downtime and loss of profits." Because most tailings treatment pro- cesses begin with thickening, a basic un- derstanding of the types and costs of thick- eners typically used in tailings processing is an essential starting point. McLanahan explained that high-rate thickeners sep- arate liquids from solids using hindered settling. Rotating rake arms collect settled sludge and move it toward the center dis- charge cone. They use minimal amounts of polymers/chemicals in order to drop the solids, making it environmentally friendly. Deep cone, or paste, thickeners are meant to achieve the highest solids con- centrations possible through gravity sepa- ration. The resulting mud, or paste, is often so dense that no further separation of water and solids can be achieved. Pastes are then moved to impoundment structures or pro- cessed further through filter presses. Fed from the top, deep cone thickeners initially rely on the process of free-settling. After the fines reach a certain point in the process, they continue to thicken through hindered settling. Depending on the characteristics of the material, a deep cone thickener can be designed with no moving parts or with pickets (rakes) that rotate slowly to create channels in the mud, releasing water. When filtration is needed to reduce tailings water content beyond what thick- eners can achieve, the options include belt and plate and frame units as well as newer-generation disc filters, available in sizes to accommodate most throughput re- quirements. With some mining operations producing more than 100,000 dry tons of tailings per day, the trend among major suppliers is to provide larger units. Exam- ples of these include Diemme Filtration's GHT2500 overhead beam filter press, which measures 26 m long, 4.5 m wide and 5.5 m high. The GHT2500 can host up to 230 plates for a maximum filtration area of 2,000 m 2 (43 m 3 ), producing up to 200 t/h of high-filtration-rate tailings. According to Diemme, a distinguishing feature of the GHT filter press is the plate pack closing system: the four hydraulic cylinders in a pull-to-close configuration that maximizes the sealing of the plate pack and minimizes the stress transmitted to the frame and support structure even in the demanding conditions of the mining industry. The plates and the moving head are hung on one or two overhead beams sliding along it for opening/closing. De- pending on the type of material (high or low filtration rate) a plate-by-plate or an accordion opening system can be used to bring the highest benefit to the process. Another jumbo-sized filtration unit is FLSmidth's AFP-IV Colossal filter, capa- ble of discharging 20,000 mt/d of filter cake and recovering 600 m 3 of process water per hour. This beam filter press, ac- cording to the company, enables effective dewatering of large volumes of tailings with less than half the number of filters required by competing large filters. The Colossal filter is a key element in FLSmidth's EcoTails concept, a system it has developed in collaboration with Gold- corp that blends highly filtered tailings with waste rock to create a geotechnically sta- ble material called GeoWaste. The system is aimed at demonstrating that dry-stack tailings technology, which has typically been used at smaller tonnage mines be- cause of its higher cost, can be applied to larger-tonnage mines as well. The company believes this approach will be of interest to high-volume customers due to its claimed benefits of less risk from tailings dam fail- ures and higher water recovery rates. Tenova TAKRAF, which offers a complete dry-stack tailings solution, says the technology provides benefits ranging from reduced TSF footprint and improved safety to higher water recovery.

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