Closure planning and decommissioning of tailings storage facilities

Abstract

A major driver for improved planning in closure and decommissioning of tailing storage facilities (TSFs) is the numerous TSF legacies that exist around the world. Tailings are a combination of any remaining process water and the fine grained solid material remaining after the recoverable metals and minerals have been extracted from the treated ores and placed in a containment area. The physical and chemical composition of tailings varies with the nature of the material being processed, and the process itself. These differences, along with the location of the operation, will dictate the level of management required for the tailings and for the TSF during construction, deposition and closure. Tailings may be stored in a variety of ways, depending on their geochemical properties, the site topography, climatic conditions and the socio-economic context in which the mine and mill operations are located. TSFs are often viewed as the most difficult issue to resolve in mine closure. This can be mitigated by ensuring tailings closure planning occurs progressively throughout the life of the mine and a robust decommissioning process is followed. It is imperative that closure planning is an integral component of planning, design, construction, operations, closure and decommissioning. The development of leading practice tailings management is becoming increasingly more rigorous both nationally and internationally. The importance of designing a sustainable TSF landform and managing construction with the end in mind is recognised within the May 2011 ANCOLD Draft Guidelines on Tailings Dams – Planning, Design, Construction, Operation and Closure. The 2011 ANCOLD Guidelines highlight the important principle of designing, constructing and operating a TSF with an aim to an eventual closure strategy that will allow a safe and stable structure to remain following the completion of mining operations. Post-closure, a TSF must be able to cope with stochastic events and change likely to be encountered over an extended period determined as per the design life, potentially of 1,000 years or longer. This paper will link the 2011 ANCOLD Guidelines to the critical factors that impact on the decommissioning and final rehabilitation of a TSF, including the opportunity to use risk assessment techniques to identify (design out), and manage closure challenges and risks at the beginning. Robust decommissioning planning as a part of tailings management will be discussed, increasing the awareness that closure is a process not an event.