Turning water pollution sources into assets: Exploring innovative options of using abandoned mines for generating and storing renewable energy

Abstract

Through moving large volumes of rock for decades or even centuries from geological underground to surface, industrial scale mining invariably alters the natural local and regional hydrological conditions. Consequences include irreversible changes of flow gradients and water quality in aquifers and streams effected through dewatering, ground subsidence, acid mine drainage, etc. During their lifetime mines spent significant resources and energy on maintaining an ever-increasing diversion from natural hydraulic equilibria through pumping rising volumes of ingress water from ever greater depths, especially if operating below water-rich formations (karst) or in humid climates. Associated pumping costs may even lead to premature mine closure. In cases where complete flooding of closed mines is not an option (e.g. to protect water resources or infrastructure) such costs remain well after mines closed for as long as flooding restrictions apply. In large and densely populated regions in South Africa or Germany, for example, where mining succeeded in triggering urbanisation and self-sustaining economic development it is (currently) assumed that pumping will be needed forever. Accordingly, post-closure water management is no longer only a long-term liability but indeed a perpetual burden placed on future generations that had little direct benefits from earlier mining. This paper focuses specifically on possible ways of reducing perpetual post-closure water management costs specifically of using abandoned mines for generating and storing renewable energy. It discusses successful examples already implemented, concepts investigated but not yet realised as well as technologies that received little, if any, attention to date. The latter range from using mines (included flooded ones) for the storage of electrical energy via different technologies, harvesting geothermal energy from mine water and voids to different ways of transforming chemical energy contained in mine water into electricity.