Tailings are fine-grained wastes of the mining industry, output as slurries, due to mixing with water during mineral processing. Tailings facilities consist of tailings ponds or lagoons, tailings dams and tailings transport systems (usually pipelines). Though separate units, the mineral processing mills have great influence on the operation and safety of tailings facilities.
In the EU Draft Reference Document on "Best Available Techniques for Management of Tailings and Waste-Rock in Mining Activities" (draft version of May 2003), tailings are defined as "Ore from which as much as feasible of the desired minerals have been removed. Tailings consist mainly of gangue and may include process water, process chemicals and portions of the unrecovered minerals."
Deposits of these residues in ponds, usually confined by man-made dams, can present a serious threat, especially where there is improper handling and management. Recent accidents at tailings facilities, such as the Baia Mare (Romania) and the Aznalcóllar (Spain) disasters, resulted in major threats to the environment and human life. Serious hazards posed by failing tailings facilities (leaks, overflow, breaking dams etc.) include
Due to typically low concentrations of the useful component in mineral ores, large amounts of tailings are produced, requiring large tailings ponds to contain them. The most critical element of tailings facilities is usually the dam. The highest tailings dam today is as high as 230 m. Tailings dams fail ten times more often than conventional dams (73 failures occurred world-wide since 1960). The most common causes of failure are related to the forces of water, e.g. by internal erosion of the dam material or by overtopping of the dam. Dam integrity is thus particularly important under extreme weather conditions. Between 1928 and 1998 more than a thousand people lost their lives all over the world due to dam failure in tailings facilities.
Tailings dams are usually constructed using part of the material coming from the milling process. This is achieved by using hydrocyclones at the end of the pipelines transporting the slurry from the mill. The coarser particles (sandy fraction) are used for dam construction, while the fines are deposited in the pond. A high percentage of fines in the tailings results in long settling periods, sometimes several years. In handling large amounts of inhomogeneous wet slurries, water management is a key safety factor. Deficient water management is one of the main causes of accidents and hazards emanating from tailings facilities.
Objectives of the TAILSAFE project
TAILSAFE is a European research project. Its general objective is to develop and apply methods of parameter evaluation and measurement for the assessment and improvement of the safety state of tailings facilities, with particular attention to the stability of tailings dams and slurries, the special risks inherent when such materials include toxic or hazardous wastes, and authorisation and management procedures for tailings facilities.
To reduce the risk posed by tailings facilities, methods of parameter evaluation and measurement are being developed within TAILSAFE and applied for the detection, assessment and improvement of the safety state of tailings dams and ponds. Aspects of probabilistic stability analysis, water management involving paste technology, non-destructive (NDT) and minimally intrusive testing methods and monitoring methods, and intervention and practical remediation options are being considered. The results will be incorporated in a systematic risk reduction framework.
The investigations are focussed on the structural parameters of tailings dams stability, their measurement, and their evaluation as regards risk factors, with particular attention to:
The project aims at advancing the state of the art of tailings facilities safety in that a comprehensive parameter framework will be established to enable the systematic assembly and evaluation of parameters critical to tailings facilities safety. A wide range of parameters relating to design, materials, management, regulation and authorisation will be included in this risk reduction framework, so as to allow relevant stakeholders a better understanding and control of critical parameters for risk analysis. Special attention will be paid to pore pressure and piping, and methods for their measurement and monitoring developed further.
Scope of the TAILSAFE project
Although TAILSAFE primarily addresses European needs and priorities, and is based strongly on European case studies, the project builds on world-wide experience and scientific results, and hopes that much of its output will have world-wide applicability.
Tailings from the mining and primary processing of metals, minerals and coal are in principle included within the scope of TAILSAFE. Due to the limitations of any such research project, not all mineral tailings can be addressed in the same detail, but a representative range is intended. Industrial minerals, such as aggregates and clays, are one important group of raw materials whose tailings will not be covered so fully by this project.
For the avoidance of doubt, the TAILSAFE project does not seek to address the tailings produced by industrial processes other than mineral working and the primary extraction/refinement of minerals: e.g. it does not deal with tailings from power generation or waste incineration (including ashes, shales and flue dusts), from cement works, from chemical manufacturing processes (precipitates etc), or from food, agricultural or forestry production. However, much in the project may be relevant to such tailings too, and the TAILSAFE parameter framework, a key output, is being designed so that its use could be readily extended to a wider range of tailings.
Finally, TAILSAFE does not cover other forms of waste from mining and minerals processing: e.g. dry tips, spoil tips, stockpiles, pit-stripping waste, underground muck, or wastes and discards in temporary settling tanks within the processing plant.
|The TAILSAFE shell has been created and is maintained by Federal Institute for Materials Research and Testing (BAM)