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.
The equipment selection for a fine coal tailings dewatering application is filled with numerous challenges and complications. There are known technologies operating in the Australian coal industry such as belt press filters and, recently, solid bowl centrifuges. This paper looks at three known technologies, namely belt press filters, plate and frame filters, and solid bowl centrifuges to dewater thickened fine coal tailings. A comparison of recovery, moisture, reagent addition, solids and volumetric throughput is presented. Some pros and cons of each application will also be provided. Specialised technical information on each application including the major factors that have the greatest dewatering impact on the technologies will be highlighted. Information from an installation from South Africa is shared. The paper assists with the selection process and explains important information that must be brought to light when considering a change from wet disposal to dry disposal. Elements of this paper were previously published in Meiring (2021).
Explore the following case studies for examples of current and past projects undertaken through COSIA
In 2012, SIMEC Mining commenced a detailed investigation into changing the way the magnetite tailings storage facility (Mag TSF) operates at the South Middleback Ranges (SMR) to increase water recovery and provide a sustainable cost-base for tailings management. Changes were also necessary to support the Magnetite Expansion Project (MEP) that was destined to be commissioned in October 2013. A feasibility study was performed with Golder Associates to understand the technical and commercial influences and provide a capital estimate for several options. The selected option from the study was a redesign of the current dual discharge TSF to a perimeter discharge, central decant (PDCD) design. Application of Nalco WaterShed polymer at the Big Baron Pit (Verdoornet al. 2018) revealed the technology would greatly assist in the successful conversion of the TSF to a PDCD configuration. Expectation was high that WaterShed polymer treatment would allow greater beach angle control, improved water recovery, and a reduction in surface water pooling across the TSF with water pooling concentrated around the central decant allowing for efficient removal prior to loss via evaporation or seepage. A conceptual design for the polymer tailings dewatering application was developed in collaboration with Nalco Water and dosing commenced in October 2013. Due to unknown risks associated with dewatering magnetite tailings, the project was split into two stages, namely, phase 1: a proof of concept trial to establish the applicability of Watershed on the magnetite tailings prior to commissioning of MEP; and phase 2: fully operationalise the PDCD configuration. Golder was engaged to develop a life-of-mine plan for the TSF at SMR that could be safely operated to a planned final height of RL 199 m. Throughout 2013 and 2014, design and construction occurred to convert the Mag TSF to a PDCD facility. A master plan was developed to manage tailings storage for five years from March 2014, referred to as the First 5 Year Plan. This involved six wall raises that would eventually fill the three voids near the western embankment and bring the height of the TSF to RL 172 m. The civil concept selected was based on an alternatives assessment that presented three options. SIMEC Mining chose the lowest cost approach of filling the voids with WaterShed polymer treated tailings to provide a base for 3 m wall raises upstream. Strict deposition and water recovery models were followed to ensure sufficient dewatering and the subsequent drying of the tailings layers. There was also extensive test work completed prior to each of the individual embankment raises to ensure that the dewatered tailings had the appropriate density and strength properties to support the raises before commencing with the lifts. During the first five years of operation, water recovery was around 60% and the volume utilisation was in line with the deposition model. The high percentage of water recovered enabled the processing plant to reach its new design capability, reduce significant downtime due to water availability and provide the mining operations with sufficient water for dust suppression. The second five-year plan is currently being finalised and progress is consistent with the tailings deposition and the dewatering model.
At present, most tailings are dewatered by static settling in tailings dams. The environmental impact of these large settlings ponds is very dramatic, not to mention the space requirements and the potential risk of dam failure. This method of disposal also results in the loss of process water due to evaporation. This can be significant in areas where the supply of fresh water is limited. The high centrifugal force in a decanter centrifuge drastically increases dewatering efficiency, as centrifugal separation happens at up to 29,430 m/s² (3,000 × gravitational acceleration or g). Depending on the material, more than 90% of the process water can be recovered using centrifuge technology. It can be reused in the mineral processing operation and will increase the water efficiency of the whole mining community. This paper presents the results of actual projects in Brazil and Peru.
Fine-grained tailings (leach residue and gypsum) resulting from hydrometallurgical processes (acid leach followed by lime neutralisation) of nickel laterite ores are proving difficult to dewater using conventional dewatering methods (thickeners/vacuum filters). To generate a dense non-segregating slurry or paste that can be deposited on surface in the form of a stable stack, more innovative dewatering methods are required. The current work involves working on thickened nickel laterite tailings to produce a paste product for surface disposal. Achieving greater dewatering would offer advantages compared to conventional slurry deposition such as reducing the size of impoundments; reducing the size and costs of containment dams; and decreasing water sent to the impoundment. It also offers environmental advantages, including reduced leachate generation and decreased permeability of paste (homogeneous mass). Electrokinetic (EK) consolidation is a soil improvement technique that has been mostly used for soft fine-grained soils, such as silts and clays. The treatment involves applying a direct current across electrodes embedded into the soil. The current induces the movement of soilwater from the anode (positive pole) toward the cathode (negative pole). Dewatering and consolidation are achieved when the water is permitted to drain at the cathode and prohibited to enter the anode. The electrochemical reactions are associated with the EK process, which leads to a pH gradient in soil, generation of hydrogen and oxygen gases at electrodes and corrosion of consumable anodes, which must be addressed on a project-specific basis. The objective of this research is to study the viability of using EK to dewater tailings (leach residue and gypsum) from hydrometallurgical processes. The electroosmotic (EO) flow rate and coefficient of EO permeability (ke) are measured to assess the effectiveness of EK dewatering. The study includes comprehensive material characterisation and EK cell tests. The results of the study indicate: EO generated significant water flow in the tailings sample. The tailings have stable electrical conductivity, i.e. the applied current can be maintained relatively constant over time under a constant voltage. The ke values are in the range of 1.00 × 10-9 to 7.00 × 10-9 m2/V/sec, which is considered very favourable for EO dewatering. The electric conductivities of the saturated tailings are in the range of 2,0002,300 ?S/cm, and the tailings porewater has the electric conductivity of 8,000 ?S/cm, which is considered favourable in terms of power consumption for EK dewatering. The zeta potentials of the tailings before and after EO tests are stable in the pH range of 49, indicating EO dewatering would be effective in tailings without pre-treatment.
The mining industry is becoming more and more attracted to dry stacking as a method of mine tailings management. The development of bigger-sized plates now allows metal producers to utilize pressure filtration technology to process flow rates of up to 200,000 tonnes per day of dry solids, which was undreamed of just a few years ago. The advantages of this technology include very low cake moisture content, significant savings in water usage and the possibility to recover product (when required) without the need of CCD washers. The filter press technology combined with bigger-sized plates enables filters to be installed in remote sites with high average rainfalls, offering the mining company the possibility of a safer and more sustainable environmental impact, thanks to a stable stack of solid material that requires less room than traditional thickened residue dams. The aim of this presentation is to show the latest studies where this technology has been applied.
To better understand the inline flocculation technique for enhanced water recovery from fine-particle suspensions, this paper studied the impacts of two typical salts, NaCl and CaCl2 on the geotechnical, hydrological, hydromechanical, and chemical behaviour of polymertreated synthetic tailings slurry using a low-shear mixer for continuous flocculation under controlled conditions. The results are discussed in light of the contribution of the polymer treatment to improved rehabilitation outcomes and the role geotechnical, hydromechanical, hydrological and chemical properties play to achieve this goal.
The Tronox KZN Sands Fairbreeze Mine is located in Zululand, south of Mtunzini on the east coast of South Africa. Mining activities commenced in 2015 and the declared life of the mine is 15 years. Fairbreeze Mine is beneficiating an orebody that is part of the Berea Red dune system and the fines content is known to approach 30% in some areas of the deposit. The definition of fines in the mineral sands industry is classified as any particle passing 75 µm and consists predominantly of clays and some traces of silica particles of silt size. Historically, the mining industry has made use of sub-aerial deposition to dewater fines that do not drain freely. The only tools available to the processing facilities using the sub-aerial deposition dewatering method, has been: In order to minimise the risk and to reduce the sterilisation of large tracts of land, mining companies are being forced to consider alternative dewatering techniques. The use of amphibious vehicles, or mud-crawlers, is a well-documented alternative in the alumina industry but little is known about the performance of amphibious scrollers on mineral sands fines residue. This paper investigates the effects of mechanical scrolling performed by mud-crawlers on the dewatering and the ultimate final dry density of Fairbreeze fines. The investigation looks at ways that mud-crawlers can be applied as a financially viable alternative to sub-aerial deposition.
The objective of this report is intended to be a technology deployment roadmap for "end to end" solutions for oil sands tailings. This technology deployment roadmap and action plan that will assist regulators and industry to create and implement technology solutions that will meet the goals of Alberta Environment (AEW) Directive 047. The report is broken into 4 components that includes a review of current technologies used in the oil sands industry, evaluation of these technologies, and highlights technologies to improve upon existing methods.