?Mining using backfill methods has been utilized by many mines around the world. Tailings thickening, one of the ways to prepare backfill materials, has been studied worldwide and components of the process such as the thickening mechanism of the tailings tank and principles of selecting flocculants have already been worked out. The studies of hindered settling properties of tailings during this process have lagged which can restrict the precise control of tailings thickening and affect the backfill result. Using in-situ tailings from a mine, hindered and polydisperse settling experiments of tailing slurries with different concentrations and different particle size distributions have been launched to study and analyze the hindered settling features of tailing particles. The experimental results show that the R-square figure of the hindered settling rates of classified tailings between calculated values based on Richardson-Zaki model and experimental ones is over 0.87 proving the Richardson-Zaki model can be used to calculate and predict the hindered settling rates of classified tailings. Moreover, Selims theory can capture the main properties of the polydisperse settling process of the mix of sieved and silica tailings. The self-flocculation of fine particles in silica tailings has increased the hindering effect among particles, the experimental settling rates of silica tailings are less than those theoretical values calculated by Selim theory.
Since 2005, the ACG has published conference papers across the geotechnical mining spectrum, including: underground and open pit mining, paste and thickened tailings and mine closure. The repository aims to provide the mining geomechanics fraternity with open access, peer-reviewed conference proceedings that may assist readers to maintain and develop their skills, knowledge and capabilities.
This bulletin provides a framework for classifying different types of tailings based on their geotechnical properties and provides typical geotechnical parameters for the different tailings types. It also presents technologies for dewatering tailings from thickening to filtration.
?Luossavaara-Kiirunavaara AB (LKAB), an iron ore company with mines in northern Sweden is continuously considering new technologies for handling, transportation and disposal of waste rock and tailings. The mines and concentration facilities are located north of the Arctic Circle which in Scandinavia means an average temperature of about 0° C. Snow from mid-October to mid-May. In winter the temperature may reach -35 to -40° C during weeklong cold spells. At the Svappavaara mine early technical-economical feasibility considerations together with expected space limitations in the concentrator area favored location of two thickened tailings thickeners on a hill close to the disposal area about 1600 m away from the concentrating plant. In this way only short distance pumping of thickened slurry is required and warm process water is recovered directly by gravity from the thickener to the concentrating plant. A thickener of a high-density type with 18 m diameter was first installed. Four years later an additional thickener of paste type with diameter 24 m was put into operation. The design (maximum) capacities were 115 and 275 tph (tons per hour) for the 18 m and 24 m thickeners, respectively, with solids flux rates of 0.45 and 0.6 ton/m2h. Both are planned for common use for 390 tph within a few years. The tailings product is characterized by an average particle size of about 30 µm with a maximum of about 500 µm and about 40 % passing 20 µm. Solids density about 3000 kg/m3. A solids concentration by mass of 70 % was considered sufficient for deposition at a slope of up to 3 %. The objective is to present and discuss the performance of the thickening, transportation and deposition systems during the commission stages and first years of operation. The aim is also to describe how initial conditions related to changes in the tailings production rate together with climatic conditions called for robust by-pass arrangements. Furthermore, complicating factors related to the choice of auxiliary equipment and instrumentation for central functions are discussed.
?As is well known, the availability of water for mining processes in Chile is limited. In addition, it should be considered that the vast majority of mining plants are located in the northern part of the country, which is for the most part desert, and mainly at a high altitude. Given the low availability of water, various alternatives have emerged such as thickening tailings to high concentrations by weight (recovering more water in the thickeners) or using desalinated seawater. The present study aims to define the optimum thickening concentration for copper tailings, applied to a case study of representative Chilean mine tailings, from a rheological and energy point of view, as a function of recovered water in the thickeners and specific energy consumption (SEC), transporting one ton of Non-Newtonian thickened tailings. The specific energy consumption (SEC) should be related mostly to the solids transported than to the mixture, with thickening becoming a relevant parameter, since in slurry transport, the solids are usually the "payload", while the conveying fluid is simply the "vehicle". The result of this paper provides the industry with an additional variable to consider in the optimum grade of tailings thickening and rheological design parameters for projects, which could be considered in conceptual and pre-feasibility stages or in the optimization of existing systems.
This paper presents a case study on the design of a thickened tailings storage facility (TSF) for a proposed open pit copper mine at Dareh Alou, Iran. Dareh Alou mine is a new copper mine owned by National Iranian Copper Company (NICICO). It is located in the Kerman Province of the Islamic Republic of Iran. The nominal production rate is 7 Mtpa for a life-of-mine (LOM) of 25 years. Planning was undertaken for the accommodation of a total of 175 Mt of tailings. The Dareh Alou mine site is located on a sloping side of a valley that is surrounded by hills, grading up to steep mountainous terrain. Since this is a greenfield project the location of the concentrator was selected in conjunction with the tailings deposition options study. Five concentrator locations with various ore transportation options have been investigated together with the tailings and water management study. The result of the study indicated that the best concentrator plant location was at RL 3050 m at approximately 2.5 km from the preferred TSF location. Various tailings and water management options were evaluated, including high rate, high density/high compression, and paste thickeners. These dewatering options were studied alongside the combinations of various TSF and thickener locations. The outcome of the options study indicates that if the price of make-up water is not included in the analyses, the preferred option is utilisation of high rate thickeners. However, after inclusion of make-up water at a rate of USD 1/m3, the preferred option would be the utilisation of high density/high compression thickeners. In this case, the distance between the concentrator and the TSF is such that transportation of un-thickened tailings to thickeners located adjacent to the TSF is the most efficient option. Also, thickening the tailings will provide benefits in reducing the embankment construction cost even though relatively large embankments will be required to close off the valley site.
Globally there is an upward trend by mining operations to opt for tailings dewatering technologies to reduce water consumption, minimise surface disturbance (footprint), increase the stability of tailings deposits and, overall, to operate sustainably. The properties of the mine tailings are largely dictated by the type of ore and the process necessary to liberate the metal values. In other words, it depends on the beneficiation process and the mineralogy of the gangue. Due to the importance of selecting the correct strategy for the management of mine tailings, designing a disposal strategy based solely on the requirements of ore processing may overlook opportunities to maximise the viability of the mining operation, especially when dewatering technologies are being considered. As an example, accepting a coarser grind may reduce overall metal recovery; however, the loss in revenue may be offset by improved dewatering performance and lower capital and operating cost to manage the tailings. Therefore, the design of the ore beneficiation process should consider the requirements for tailings disposal, specifically tailings dewatering and storage facility design, in order to obtain more efficient and sustainable mining operations. This paper will discuss the effects of mineralogical composition and particle size distribution of gold and copper tailings on rheological properties, which provides an indication of what can be achieved in thickener underflows. The present paper is based on laboratory tests performed by Golder Associates on mine projects around the globe.
?Chile is a country with high vulnerability associated with Climate Change, given among other factors, due to the need for development and growing social and environmental conflicts. This motivates the implementation of adaptation, transformation and mitigation measures at all aspects, to deal with climatological phenomena, which despite its future uncertainty, its development is a proven fact by robust and bulky scientific evidence. Motivated by the call from COP25 and the IPCC to assess adaptation and mitigation of effects and consequences of Climate Change, SRK Chile proposed to analyze the response of infrastructure associated with mining in northern Chile, considering General Circulation Models (GCM) downscaled for Atacama region at different elevations, based on the models considered by Chilean Water Directorate (DGA) in its Update of the National Water Balance of Chile (NWBC). This study considers Representative Concentration Pathways RCP 8.5 (most pessimistic scenario) as scenarios to evaluate, same as DGA NWBC. To observe the effects of these scenarios we applied the GCM as boundary conditions in 1D numerical infiltration models using the software Hydrus. In the simulations water fluxes in a column of thickened tailing above natural soil is analyzed for different precipitation regimes from GCMs. Standard values according to our experience for the hydraulic and geometry properties of the materials forming the columns are used. The results of this study shed light upon the future precipitations scenarios affect the available water in the infrastructures at different elevations, providing a quantitative comparison of the infiltration fluxes within the tailing for the GCMs in the Atacama region.
The objective during TSF beach development is to still maintain a slurry that is pumpable and self-distributing at the tailings storage facility (TSF), rather than having to rely on trucks or on conveyors and stacking systems to manage a cake, but one that will deposit at a steeper beach slope than can be achieved by thickening alone. The use of ultra paste has the potential to broaden the range of topographic conditions that will suit thickened tailings discharge. This paper presents a case study for a large copper mine in which underflow from a series of paste thickeners with a nominal tonnage of 3,660 tph at 59% solids concentration would be mixed with 1,363 tph of filter cake at 80% solids concentration. The combined tailings (ultra paste) would be discharged equally into two open channels (flumes) at the combined solids concentration of 63.5%. The ultimate goal of adopting an ultra paste scheme is to produce homogenous consistency tailings, hence proper mixing of the paste and filter cake has to occur. In this study based on a series of tests, the mixing requirement has been assessed. The study also covers a conceptual investigation of natural turbulent mixing (NTM) of the filtered tailings with paste thickened tailings and issues associated with the deposition of the combined tailings, the ultra paste, into the existing TSF. In the conclusion, the study indicates that NTM can possibly occur only for the case in which the total tailings are discharged into one channel, which is not practical due to limitations with regards to tailings management. Hence, mechanical mixing has been recommended in this case.
The Chinalco Toromocho copper mine uses four (4) 43-m diameter paste-type tailings thickener, each is designed to process over 1,300 dry metric tons per hour, mtph and 3,600 cubic meters per hour, m3/h of slurry. The target non-Newtonian underflow was designed to be pumped to the tailings storage facility, TSF to be surface stacked. Difficulty has been experienced achieving the target underflow causing water balance, pumping capacity and other issues. Chinalco contracted WesTech to perform an optimization study to evaluate the benefit of retrofitting their feed system and mechanism of their thickeners with the latest advances in the market. Plant trend data was analyzed over the past 1.5 years, establishing the current operation of the site. The tailings stream variation range in dry mtph, particle size distribution, PSD, and flocculant consumption, are shown. The underflow weight percent and overflow clarity operating ranges were tracked. The analysis gives the effect these critical parameters have on thickener performance. A comparison is provided of the predicted modernization performance in response to the established operating variability. This paper provides a review of the Toromocho thickeners trend data based performance, optimization study results, and the mines way forward to optimize their tailings thickeners.