Copy of workshop presentation. Ridlen presents the difference between tailings and water dams and the challenges of both. He then presents his client experiences and an example of a client policy and project.
Estimation of fines and solids content in tailings oil sands deposits is imperative for tailings planning as well as reporting tailings inventory to the regulator. This report reviews the development of a proper procedure for the engineering assessment of uncertainty in reported tailings mass/ volume as a function of data spacing.
Quote from main page: A Guide to the Management of Tailings Facilities (the Tailings Guide) is designed to be applied by MAC members and non-MAC members alike, anywhere in the world. The Tailings Guide, first released in 1998, provides guidance on responsible tailings management, helps companies develop and implement site-specific tailings management systems, and improves consistency of application of engineering and management principles to tailings management.
Tailings storage facility (TSF) design has long been based on deterministic limits. By extension, the TSF owner accepts a Probability of Failure (PF) associated with these deterministic limits which are assessed against industry norms with respect to investigation/analysis and design assumptions related to the operation of the facility. If the Probability of Failure of a design that is derived in this way is taken as the likelihood related to the tolerable risk limit, it follows that the same, or a lower PF, should be maintained during operations. Examples of operational controls include pond management and inspections/monitoring. Upset conditions arise when operational controls are not being implemented. Therefore, by comparing the calculated PF of the TSF complying with the design assumptions and the PF for the same TSF in an upset condition, the required PF of operational controls can be estimated. This concept assists the TSF owner in determining what is required to safely operate the facility and communicate the geotechnical risk to all stakeholders. By extension, scenarios where a TSF owner cannot achieve the required PF of operational controls can be addressed with: 1. Greater rigor applied to operational controls. 2. Addition of more operational controls. 3. A change to the design assumptions, where the timing of the project allows. This method provides a measured approach to risk management in the design and operational phases, without a TSF owner having to quantify an acceptable risk tolerance. Instead, the design is based upon widely accepted practice and industry/business accepted safety, economic and environmental risk levels. Subsequently, the design PF can be calculated and then applied as a benchmark for operations. This approach serves to reduce uncertainty through alignment of the design and operation phases. The concept is explored for three different tailings storage methods: upstream raised TSF, downstream raised TSF, and impoundment by mine waste dumps, to estimate how sensitive each storage method is to the type and effectiveness of operational controls implemented by the dam owner.
The Multiple Accounts Analysis (MAA) method presented in this paper provides a sound basis for presenting, discussing and exploring differences of opinion (between stakeholders) in the analysis and decision making for a preferred alternative (e.g. tailings impoundment site) based on an alternatives selection process.
Tailings are the materials left over after the process of separating the valuable fraction of ore from the gangue. Tailings ponds are engineered structures created using dams, berms and natural features such as valleys, hillsides or depressions. The pumping of tailings slurry into a pond allows the sedimentation of solids from the water. Tailings ponds can be highly toxic because they are used to store harmful waste made from separating minerals from rocks or the slurry produced from tar sands mining. To minimise contamination of underlying groundwater, high-density polyethylene (HDPE) liners are used. These liners are prefabricated sheets that are welded onsite to form a continuous waterproofing membrane that prevents the migration of contaminated water into the environment. Despite their widespread application, HDPE liners have inherent performance limitations, such as leakages at the location of welds, UV resistance, maintenance and repair. This paper considers a new type of sprayable reactive membrane as a waterproofing structure. Permeability tests with the Rowe cell, chemical and durability tests (interaction with water and leachates at different temperatures, oxidation and UV resistance tests) and mechanical tests (tensile strength tests, elongation tests, puncture tests) were performed and compared with conventional HDPE membranes for tailing ponds. Results showed that the new sprayable membrane has good performance comparable with the conventional HDPE membrane and it can be a very attractive solution for tailings ponds liners
Background page on tailings. From ICMM Page: Tailings is a common by-product of the metals and minerals recovery process. It usually takes the form of a liquid slurry made of fine metal or mineral particles and water created when mined ore is crushed and finely ground in a milling process.
Planning, operating, monitoring and closing a tailings storage facility (TSF) can present many challenges, especially in dynamic mining environments where site conditions vary spatially and with time. However, big impacts can be made at relatively small cost once the tailings management system, design and performance are well defined and understood. This paper presents various examples of initiatives aimed at achieving the design intent that have been adopted by Rio Tinto Iron Ore, which also reduce risks and improve tailings management performance. Examples presented include development and communication of short-term, long-term and life-of-facility deposition plans, implementation of simple deposition management tools, monitoring and managing slurry density, development and continual oversight of water balance models, and sound investment in water management infrastructure extending to safe performance in emergency situations. Regular governance was also implemented to provide assurance that these controls remain effective.
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.
Tailings dam failures have and continue to cause large-scale devastation and environmental impacts. Historically these impacts have largely been predicted using Newtonian hydrodynamic modelling principles resulting in a general overestimation of potential consequences. However, since about 2014 the collective mining industry began developing complex tools to better predict the likely impacts of these failures. The industry has focused on leveraging the latest in computational flow dynamics modelling software and computational hardware to preform non-Newtonian tailings dam break assessments. However, as our tools become more sophisticated so does the requirement on input data. This paper discusses the past modelling approaches and the development of non-Newtonian tailings dam break models. The sensitivity of the flow behaviour is presented through four case studies, showing how this selection influences the outcomes and how previous approaches assuming Newtonian characteristics may present an overly conservative result. It is noted that additional knowledge and expertise will become available as non-Newtonian tailings dam break studies become the norm. In the interim, the uncertainty of these analysis needs to be analysed.