Geoprofessional Business Associations (GBA) Tailings Engineer-of-Record (EOR) Task Force published a Business Brief to inform and educate Member-Firms of the ever-increasing levels of risk associated with tailings dams.
?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.
The filtering of sandy tailings from the reverse cationic flotation processes and the subsequent stacking of these tailings has shown to be a very strong trend in Brazilian iron ore mining, especially after accidents involving geotechnical structures known as tailings dams, but also due to concern of mining companies to develop a disposal technique that is more complacent with the environment and the surrounding society. In order to develop the sandy tailings filtration project, a fundamental requirement was the correct choice of filtration technology among the many existing ones. For the material object of this study, the filter with vertical discs presented itself as the most productive due to factors such as granulometry, specific surface of the material and the humidity required in the filtration product. Several exploratory and material characterization tests were carried out for this purpose. Disc filters have the principle of operation linked to the difference in atmospheric pressure and the vacuum pressure induced by pumps. The vacuum must act on the filtering screens next to the filter heads and, in order not to drop the yield, the system must be sealed hydraulically. As previously mentioned, there are basically two ways to hydraulic seal the system. The first and most common in Brazilian iron ore filtration is carried out through barometric columns and the other is using filtrate pumps installed directly in the vacuum receiver of the filtration facilities. The decision of which method to use has major implications for the design of the filtering installation and the comparison between the two conditions mentioned is the objective of the present work.
With the intention of trying to determine the causes of major tailings dam incidents, 221 case records have been collected. Examples are given of accidents and failures, together with some examples of effective remedial measures. This Bulletin is addressed to all those involved in the design, construction, operation and closure of tailings dams.
For the alternative disposal method of dry disposal of tailings, two aspects of the process have to be evaluated, namely the maximum dryness of the separated solids and the maximum liquid recovery. For most mining operation, dry disposal is a new concept. Presenting these companies with examples of operations where this processing option has been successfully applied and proven, will help them to adapt to the changing requirements in the future. Focus has been placed on adapting decanter centrifuges to the mining environment. Modern decanters stand out in terms of their small footprint, low water demand, high availability and their high degree of automation, combined with the excellent cost / performance ratio. Decanter centrifuges have started to play a key role in applications such as tailing dewatering, drilling and tunneling muds processing, hydrometallurgical processes of gold, nickel or zinc and separating SX crud in copper refineries. This paper will present advantages of decanter centrifuges compared to the traditional technology and corroborate these advantages by case studies, especially from South America.
?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.
?Hindustan Zincs Rampura Agucha Mine is a world class orebody that has successfully transitioned from an open pit operation to an underground sublevel open stoping with paste backfill operation. The mine currently has two identical paste plants that each can produce between 160-185 m3/hr of cemented paste backfill. Plant #1 was commissioned in 2014 and plant #2 was commissioned in 2019. The two plants are equipped with Putzmeister piston pumps that pump from the plant to the edge of the pit, down a borehole to the North and South main ramps and then down the ramps to the top of the underground orebody approximately 500 m below surface. Each plant was designed with an operating and standby paste pump. Most of the orebody can be reached from these main lines, however, at the extreme north end of the pit, there is portion of the underground orebody that is above the uppermost underground delivery level and at a significant horizontal distance from the main paste trunk lines. Because of the location of these northern stopes, an overland pipeline to the north of the pit is required before entering a borehole down to the stoping levels. This lateral distance on surface and underground would have resulted in very high pressure on the paste pumps, and a decision was made to temporarily install the standby pump from plant 2 at a booster station that would allow the northern stopes to be reached with a 2 stage pumping system instead of a single stage pumping system. The booster station was installed and commissioned in 2019 and this paper discusses the design principles regarding booster stations in general as well as the specific design, commissioning, and operational experiences with the booster station at Rampura Agucha Mine.
?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.
A good dam surveillance program is the foundation of an overall tailings dam safety program. Tailings dams are dynamic and continually evolving structures, under construction on a regular, and often near-continuous, basis, and have a closure phase that lasts "forever". This is in contrast to conventional, water-retaining dams, which are built in a single stage at the onset of the project, have a finite operating life and are not required to last "forever". Tailings dams also can undergo environmental as well as physical failure, unlike conventional water-retaining dams that can only undergo physical failure. Accordingly, requirements for tailings dam surveillance, contrary to common perception, can be and frequently are more stringent, requiring frequent review and modification, than is the case for conventional waterretaining dams of equivalent hazard rating. Case history experience has repeatedly demonstrated that a great many tailings dam failure modes give warning signs that, if properly monitored and interpreted, give advance warning of problems, affording the opportunity to take preventative measures. Such a program involves much more than simply specification of instrumentation, reading those instruments, and filing of data reports. It requires understanding and management of risk, commitment, adequate resources and support, awareness, interpretive imagination, and clarity of communication among all responsible parties.