Abstract
Acid mine drainage (AMD) is a major cause of water contamination world-wide. Conventional treatment plants are expensive to build and operate, and application at remote sites may be impractical. Passive treatment systems may be an economical option to decontaminate these waters, but they are prone to clogging and passivation when treating water with high metal concentrations or high acidity loads.
Dispersed Alkaline Substrate (DAS) is an innovative passive treatment technology that can be implemented at sites with high metal concentrations. DAS consists of a fine-grained alkaline reagent mixed with a coarse matrix. The fine grain size of the alkaline reagent increases the dissolution rate due to the increased specific reactive surface area and therefore reduces passivation, while the coarse matrix provides a large pore space to store precipitates and retards clogging.
This technology has been trialled successfully at field pilot-scale at Cwm Rheidol and Parys Mountain in Wales, United Kingdom. At Cwm Rheidol (Aberystwyth), a two-step DAS system operated for over one year, removing Fe, Al, Zn, Pb, Cd and other contaminants at the former lead-zinc mining complex. At Parys Mountain a volcanogenic massive sulphide deposit (Anglesey), a three-step DAS system is removing iron, copper, zinc, aluminium, sulphate and other contaminants from the adit discharge, which was once the world’s largest copper mine in the 18th century. At both sites, DAS achieved very high metal removal rates.
This paper summarises the systems setup, operational performance and operational challenges that were overcome at both sites, as we consider future development to full scale.