With the number of high-profile tailings storage facility incidents over recent years, filtration and dry stacking has received unprecedented attention as a viable option for the management of tailings. Due to regulatory pressures, both new and existing operations are at the very least evaluating or re-evaluating the cost-benefit balance offered by tailings filtration. Consequently, there has been a significant increase in the amount of evaluative test and design programmes in the area. However, the quality of this work may not always meet a level of technical rigour commensurate with the higher cost and associated risk of the filtration approach.One key risk in the filtered tailings design process lies in the interface between the tailings processing and materials handling/geotechnical disciplines, which typically operate in isolation of each other. This risk is in part due to different terminologies and technical bases used for describing similar properties, but more so is due to this divide preventing development of a holistic picture of the behaviour of the material (e.g. dewatering rates, achievable versus target moistures, rheological behaviour, material variability) across thickening, pumping, filtration, cake handling and ultimate placement. If available as early as possible in the design process, this information can save money and reduce risk by allowing well-informed decisions around design criteria, equipment choices (type, size, dewatering pressure, operational targets) and ongoing detailed test programmes.Using indicative data (Compressibility/permeability, rheology, filter sizing, Atterberg limits, unconfined compressive strength, flow moisture point) this paper illustrates how a testing and evaluative approach integrating both process and geotechnical considerations can assist in clearly and quickly identifying critical flow sheet design information, operational windows, design and operational risks and highlight avenues for optimisation. Importantly much of this information can be obtained with relatively small sample sizes, early in the evaluation process and at lower cost. The strong interlinkage between material properties is also discussed. Whilst the focus of this paper is on filtration, this approach is equally valuable across all methods of tailings dewatering and disposal, and in particular assists with the early identification of the most suitable approach for an operation.
The potential processing risks associated with the presence of dispersive, swelling clays in mineral orebodies are well known. Uncontrolled dispersion of such clays on contact with water results in problems including poor tailings dewatering and consolidation, increased reagent demand, dirty process water and reduced mineral recoveries and increased plant maintenance with associated economic, environmental and safety implications.Dispersive clays are typically managed via approaches including high dosages of both polymer coagulant and flocculants in thickening, high-pressure secondary dewatering steps such as pressure filtration, belt press filtration or centrifugation, or inline flocculation and deposition of thickened tailings. Commonly, the secondary dewatering step requires re-dosing of additional coagulant and/or flocculant to regenerate a flocculated structure to develop acceptable dewatering rates.An alternative, more proactive approach to managing tailings containing dispersive clays is to promote controlled dispersion of the clays by conditioning the process water circuit to induce a coagulative state in the clays on first contact, reducing clay breakup and ultra-fines generation during initial wetting of the ore on entry to the plant. Clay dispersion control via process water conditioning involves reagent dosing into the process water at only a single location, however, this delivers benefits at every stage of dewatering across the tailings management flow sheet.The potential site-wide benefits of this approach are demonstrated for the ClariVie44®process water conditioner, using a combination of flocculation and settling test results, compression-permeability testwork and pressure filtration model simulations from a range of different tailings samples.The benefits demonstrated include step changes in thickener fines capture and overflow clarity, material improvements in process plant operability and reduced down time due lower fines recirculation, elimination of coagulant dosing in the thickener and downstream secondary dewatering operations, increases in pressure filtration throughputs of up to 300%, improvements in any process technology employing secondary flocculation due to more homogenous structure development, and improved tailings storage facility (TSF) operability and lower risk due to less segregation, faster consolidation and operational dry densities and improved decant water management. Test data from the Jagersfontein kimberlite tailings are also discussed in the context of the recent TSF failure and the potential role of dispersive clays as a risk factor at this site.
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