Engineering & Mining Journal

SEP 2018

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Page 51 of 75

TAILINGS MANAGEMENT 50 E&MJ • SEPTEMBER 2018 cators with particular reference to con- tainment integrity and overtopping? • Are facilities managed in accordance with the tailings management framework and are construction, operation, maintenance and surveillance of the TSF proceeding in conformance to design intent and as- sociated plans and controls? • Is compliance and performance veri- fied at the intervals defined by the man- agement framework and are there any non-conformances that may increase risk to the point where the design intent may not be achieved? • Have the above items been indepen- dently verified by review by suitably qualified professionals • Has an emergency response plan based on a comprehensive understanding of the consequences of failure been devel- oped, maintained and tested? TAKRAF Talks Tailings Strategies Tenova TAKRAF, a leading supplier of equipment used in dry- stack tailings (DST) systems, has the resources to provide its customers with a complete DST setup suited to their specific needs. However, TAKRAF understands that not every tailings operation has the characteristics needed to support economical DST handling. Martin Kressner, senior engineer–DST Systems at the TAKRAF DST Compentence Center, answers questions about finding the "sweet spot" for optimum DST applicability. Has T -density tailings systems in the past few years following the Mount Polley and Samarco dam failures? Yes, indeed. The tailings management studies initiated by min- ing companies, review of established technical standards and efforts to evaluate environmental, social and economic losses beyond the direct costs of remedying actual damages are all part of an ongoing industry process to evaluate particular risks and develop long-term strategies to handle these risks. Investigation of technologies such as dry-stack processes for dewatering tail- ings to a level at which the material can be handled similarly to conventional waste material is one of these strategies. We have seen a significant increase in customer inquiries over the last four years, which was one of the reasons why we have reor- ganized and empowered our TAKRAF DST competence center. The center combines the global competencies of both the DELKOR and TAKRAF product brands as experts for thickening, dewatering, conveying and stacking, in order to provide efficient and compe- tent responses to the various customer requests we receiv, as well as to centralize technical development and innovation. Are there any limits on the size of operations that could poten- tially benefit from adopting DST? The old rule of "the bigger the more cost efficient" is also valid for DST operations. The aspects of equipment and infrastructure concentration, job and cost efficiency and utilization increases work for DST in the same manner as for other mining processes. However, there is no precise operation size limit since other fac- tors such as local environmental conditions also significantly af- fect the economic evaluation of a DST process. Water shortages or rising fresh-water costs, absence of topographic features that provide low-cost tailings dump areas, seismic risks and legal requirements, among others, can all be boundary conditions for an economically justified decision to employ DST technology. The type of mining operation also affects perception of DST technology and its related costs. For instance, in underground mines with typically lower production rates, the acceptance of cost-intensive DST operations, such as mechanical compaction of the dumped dry cake is greater, taking into account the sig- nificantly higher portion of mining costs. Another aspect of operational size is related to layout and design of the DST process. For instance, tailings throughput is important in calculating trade-offs between truck haulage and conveying beyond the filter plant facility. If transport distance and the condition of the dry tailings are favorable, a tailings through- put of roughly 800 t/h (dry base) can be considered as the upper limit for truck haulage. From that point upward, the use of con- veying and stacking technologies provides economic benefits that continue to increase with the throughput of the tailings facility. An additional aspect that favors using DST at large opera- tions is management's intrinsic focus on long-term assessment of investments and the reduction of operating expenditures; i.e., larger operations likely are already using conveying and stacking technologies elsewhere at the site, thus reducing possible con- cerns when it comes to considering these technologies as part of the tailings handling system. Can DST be economically incorporated into an operation that's using a conventional tailings process? DST technology often can be relatively easily incorporated into a conventional tailings facility, although it depends on a number of determining factors. For example, DST technology is often "attached" to conventional tailings operations — downstream to the conventional stages of tailings thickening, DST technology performs further thickening and dewatering techniques in or- der to provide a shear strength of tailings material that enables stable dumping conditions. Depending on the manner of the attachment, there may even be the opportunity to operate a con- ventional tailings facility, including the existing tailings pond, in parallel with a DST facility. This can provide the required opera- tional flexibility for organic growth of the DST facility and allow for ramp-up periods without unwanted interference. It's usually necessary, however, to evaluate the economic im- pact of working with different tailings consistencies. Residual water content is the "adjusting screw" that defines the over- all economics of a project. Assuming that there is no option to economically and safely store liquid tailings in a former mine pit, or in a valley structure or underground stope, the required tailings consistency is defined by its residual water content. Consequently, less investment in dewatering will result in higher residual water content in the tailings and thus higher investment in transportation and deposition of the tailings, and vice-versa. Consequently, for each tailings project there exists an opti- mum point that best balances capital and operational expendi- ture for dewatering, transport and dumping. For this reason, an extensive evaluation process involving conceptual and prefea- sibility studies must be undertaken to consider and evaluate all technical options, taking into account all relevant project parameters that include characteristics of the upstream and downstream process, material parameters, site conditions such as climate, altitude, topography, seismic activities, and social and legal requirements, in order to make an informed decision that reflects the project balance point.

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