Selection of active and passive treatment systems for AMD - flow chartsfor New Zealand conditions

摘要

Treatment of acid mine drainage (AMD) can be accomplished by either active or passive treatment systems. Choice between active and passive treatment and appropriate selection of systems within each category is critical for treatment success. In general, active treatment systems are more commonly used at active mines whereas passive treatment systems are typically used at closed and abandoned mines. Active mines often have limited space for remediation systems and have drainage chemistry and flow rates that can change as mining proceeds, factors that are addressed more easily with active treatment than passive treatment. However, if sufficient space is available, and chemistry and flow rates are not expected to change significantly with time, passive treatment can be a suitable solution at active mines. In the long term, passive treatment is more economic than active treatment. Various flow charts have been prepared by previous researchers to help select among the passive systems but little work has been done to help select between active and passive treatment or to select appropriate active treatment systems. Furthermore, the passive treatment flow charts have typically not included a variable important at New Zealand AMD sites: topography and available land area. Very steep topography, dense and often protected vegetation, and a high-rainfall climate result in AMD with high flow rates in locations with limited space for remediation. Flow charts specific to New Zealand have been prepared which accommodate topography and available land area. Parameters necessary to use the flow charts include suspended solids content, pH, selected metal concentrations (iron, aluminium, and manganese), ferrous to ferric iron ratio, acidity, dissolved oxygen concentration, flow rate, acid load, topography, and available land area.