Study of environmental feasibility of paste and thickened tailings by life-cycle assessment

摘要

Paste and thickened tailings (P&TT) technology has important advantages not only from the safety point of view, but especially from the environmental point of view. The objective of this paper is to prove that this technology is a real sustainable alternative that can be evaluated using life-cycle analysis (LCA) methodology. P&TT has emerged in recent years as an alternative for the treatment and disposal of mine waste. It involves thickening the tailings (a mix of process water and waste solids obtained after the process of separating the gangue of an ore) to a higher solid content, recovering the water, and recycling it back to the process. The volume of the final waste once it has been thickened is smaller and requires less storage capacity. Conventional tailings disposal has some important disadvantages such as poor water recovery, high volume storage requirements, the need for containment structures like basins or dams (which can present stability and safety issues), and lower rehabilitation potential. Thickening technologies applied to tailings, in order to reach solid concentrations over 50%, are a real alternative to traditional disposal techniques. Scarcity of water and increasing demand for higher recycling rates can be partially solved, pollution and seepage problems are avoided, smaller containment facilities are required, and footprint is reduced due to smaller land needs, even allowing partial rehabilitation while the mine is still under operation. Besides these important benefits, P&TT technologies require specific equipment and important energy consumption, with associated economic costs and environmental impacts. In order to evaluate them, a standardised tool should be used. This tool is the LCA, which allows calculating the potential environmental impact of an activity such as tailings thickening process during its whole lifecycle, quantifying the use of natural resources and the impacts on the evaluated system. The International Organization for Standardization (ISO) defines LCA as a technique for assessing the potential environmental aspects and potential impacts associated with a product, process, or activity by compiling an inventory of relevant inputs and outputs, evaluating the potential environmental impacts associated with those inputs and outputs, and interpreting the results of the inventory and impact phases in relation to the objectives of the study. The selection of LCA as an evaluation methodology for this study is due to the strong presence of this kind of tool in the environmental literature in the last several years. Its implementation has been fast, and several databases and software programs adequate for the inventory and impact assessment phases have been developed.