?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.
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.
?There has been an increasing move towards high-density thickened tailings systems over the last decade, mainly driven by the need to save water, meet environmental regulations and project specific demands. A typical tailings distribution system on a Tailings Storage Facility (TSF) consists of a main pipe with multiple discharges operating simultaneously, to distribute the slurry across an extended length over a specific area of the TSF at a time. A potential limitation of these systems is an uneven distribution of slurry flow rate and solids concentration between multiple spigot discharges, where an inadequate design can lead to laminar pipeline flow conditions resulting in particle segregation, and an increased risk of pipeline blockage. An operation with unbalanced flow rates could result in an uneven distribution of solids that could impact the formation of beach slopes and/or cause difficulties for the dam construction. Paterson & Cooke (P&C) has previously developed several thickened tailings distributed systems, where the discharge points are located on a distribution pipeline which branch off a main pipeline. This previous experience has allowed P&C to develop a methodology for the hydraulic modelling and implementation of these types of systems. This paper presents the methodology for distribution system deposition design review and its implementation of a TSF located in Southern Europe.
Evaluation of highly thickened tailings technologies requires that during early design stages an understanding is developed for the range of feasible beach slopes to be achieved during deposition. A comprehensive evaluation of the whole range of factors that influence the beach formation process is paramount to ensure that expected performance during design stages is met throughout operations. This paper presents an integral approach for beach slope estimation, considering a broader range of aspects affecting the beach formation process than those commonly used in current models (rheology and discharge rate of the deposited tailings). The additional aspects considered by this approach are site conditions (site morphology and climate), the rate of rise of the tailings impounded (the relationship between the tailings production rate and the available area for tailings spreading) and the deposition sequence (the configuration of the deposition system and its operation, e.g. thin layer deposition with drying cycles). The approach is supported by a beach slope model based on a dimensionless parameter for non-Newtonian flows, associated with sheet flows on an inclined plane, which directly relates to the tailings beach slope expected to be formed due to sub-aerial disposal. This dimensionless parameter provides a closed expression for estimating tailings beach slopes based on rheological properties and discharge rates, but with the integration of site conditions, rate of rise and deposition sequence. High thickened tailings management facility (TMF) design is well supported by this approach, providing key input as the configuration of the distribution system and the minimum area required to achieve expected performance with respect to desired beach slope, density, degree of saturation and strength.
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 technology behind industrial applications such as fluids with high percentage solids continues to evolve, as do the corresponding regulations and specifications that ensure the safety of workers and the environment. Valves make up key aspects of this technology and often represent the single point of failure for entire operations. More often than not, the valves being used in high percentage solids applications are known as severe service valves (SSVs) due to their ability to withstand extreme conditions. Most experts agree that SSVs are identified by applications, and that these applications are challenging to the valves ability to provide a minimum acceptable level of performance over a minimum acceptable duration. This paper serves to determine what the minimum requirements are for SSVs in high percentage solids applications specifically concentrating on paste and thickened tailings.
While it is trivial to pour a thickened slurry into various forms of moulds or vessels to prepare for element testing, questions remain over whether the density that is reproduced will be relevant to in situ conditions. In particular, preparation of triaxial samples from thick slurries is particularly challenging as a number of steps are required to enable such samples to be free-standing, with each one of these steps potentially leading to slight disturbance and thus densification of the sample. Where such densification occurs, it would result in the element test results being non-conservative. This could have important implications with respect to expectations of the contractive (and potentially liquefiable) or dilative response of the tailings in situ. To investigate these issues, a series of slurry-deposited triaxial tests was carried out using a non-segregating slurry. As test methods were refined during the program, the amount of disturbance applied to the specimen was reduced. However, comparison of the triaxial tests to slurry consolidometer tests indicated that, regardless of efforts made, the triaxial tests achieved denser states at a given amount of consolidation stress. This was found to be the case using any conceivable range of assumed geostatic stress ratio to interpret the slurry consolidometer results. This outcome is speculated to be a result of the quiescent conditions used in the preparation of a slurry consolidometer specimen, which only requires pouring and then application of vertical load, first using weights, then a load frame. The implications of the increased density seen in triaxial tests compared to the likely more realistic value seen from the slurry consolidometer are discussed. Alternative preparation methods to target this looser density range are briefly discussed.
The overall objective of thickened and paste tailings disposal has been stated many times: it is to thicken a tailings slurry to the point where it is non-segregating, and will beach to form a sloping, sub-aerial deposit. The advantages of this type of scheme have been stated to include higher density, higher strength (including avoidance of a slimes pond), improved seismic resistance, and better closure and rehabilitation prospects (including lower compressibility). The aim of this paper is to show how these outcomes are a product of the interaction of fundamental tailings properties, site management practices, and climatic conditions of the site. A typical set of test results is presented and discussed in the context of unsaturated soil mechanics. The absence of segregation in thickened and paste tailings is an important factor, but it is often overlooked. The paper addresses the influence of evaporative drying on the sub-aerial beach. The induced suction stresses, combined with compressibility (consolidation) largely influence the rate and extent of density and strength gain that is attributable to the thickened discharge method. Finally, the influence of overall site management practices (e.g. filling rate), together with climatic conditions, are discussed to illustrate how these may act as constraints on the potential to achieve optimum results.