Author: J. Arrueste
International Conference Water in Mining WIM 2008, July 10, 2008
Abstract
Despite that most of Chilean mining facilities are located in the driest area of the world, business has developed strongly and actively for more than a century. However, the negative effect on the water reservoirs and the environment is, lately, resulting in growing social pressures, and the reduction of the authorized Water Rights. Holding Water Rights for any given volume does not guarantee that the resource will be available when needed.
A number of projects, beyond the mining sector, could remain on paper only due to fresh water availability limitations. Water overexploitation is affecting the replenishing of the underground water reservoirs in the lower parts of the valleys, where most of the extraction of the resource takes place. This problem would be aggravated with the implementation of new projects, and the potential future impacts of climatic changes. Mining water consumption during year 2000, according to DGA (Chilean Water Authority), was 1,238,356 m3/day, with an average usage estimation given by 0.75 m3/ton of ore, and 97.3 lt/kg Cu.
Water scarcity has significantly climbed the Water Rights costs Recent published data on Water Rights transactions emphasizes the cost of US$ 135 million for 630 l/s, equivalent to US$ 215,000 lt/s (Escondida water purchasing to Zaldivar, 2000), and other recent costs in the range of US$ 75,000 – US$ 225,000 lt/s (Tarapaca and Antofagasta regions). Caserones project has recently acquired 239.5 lt/s Water Rights for their future mining facilities in the IV Region (costs involved N/A).
Mining facilities shall be designed to reduce potential environmental and social effects to be generated by water consumption, using proven technologies, and considering the best practices available. These measures shall constitute a complete structural framework for the environmental impact assessment (EIA) of the Project. The measures to prevent and mitigate the impacts on the water resources shall be considered in-deep during the design stage of any mining project.
Current and future mining projects in Chile are conscious that the increasing pressure on the limited water resources is becoming unsustainable. Additionally, water scarcity has climbed significantly Water Rights costs, impelling and justifying the implementation of non-conventional technical solutions to increase water recovery and the use sea water. The technological solutions being adopted to overcome the present and future water limitations problem are linked, mainly, to optimized water recovery and/or sea water desalination projects or, even the direct use of sea water. Depending on availability, treated effluent from municipal sewage treatment plants would be also a suitable water source for mining projects in the future.
Existing and new projects show a growing interest in implementing thickened tailing dam facilities, due to the increased water recovery compared with the conventional solutions. Regarding desalination, membrane sea water desalination by reverse osmosis is the preferred technology, coupled with pumping and long pipelines to the plant facilities, implying a total desalinated water supply cost of about 1.8 - 2.0 US$/m3. These high water costs are not representing a limitation to mining projects development and operation, being sustained in the high metal prices.
