Mining acid rock passive treatment for closure of a lignite mine in Spain: Achieving necessary water quality for discharge into lakes and drinking water reservoirs

Abstract

AbstractThis study discusses the theory behind the passive treatment systems for controlling the acid drainage of the Meirama mine and illustrates how this approach can be applied to obtain the necessary water quality to allow the discharge of the drainage into the Barcés River, which is the primary tributary to the drinking water supply Cercebre Reservoir (Spain). Characterization analysis was carried out for 13 sampling sites, with a total of 52 tests and 780 determinations and analyses. Passive systems have been monitored over 27 sampling days, with a total of 186 samples taken, plus 1914 determinations and analyses. The passive tests treated a total of 415 000 m3 of water. The tests were designed based on several factors relevant to the sites, including hydrological characteristics, drainage composition, flow rate, climatic conditions and previous company technology experience. Different weather conditions were considered, including drought, flood and normal conditions. The horizontal system (Line A) produced a 55 mg L−1 increase in alkalinity, and iron, aluminium and manganese reductions of 90%, 91% and 30%, respectively. The eliminations for the vertical system (line B) were 40 g/m2 × day acidity, and iron, aluminium and manganese reductions of 71%, 80%, and 60%, respectively. The annual average precipitation was 150 mm, and annual average temperature, 12.4°C. It was found during the course of this study that the development and application of passive treatment systems have the following advantages: (i) they can substantially reduce costs during the active mining phase, being a pre‐treatment of the wastewater treatment plant, raising the pH and reducing the metal cation content and (ii) It is not feasible to actively operate wastewater treatment plants because, after mine closure, the land must be rehabilitated with the property then being used for other purposes. The acid rock drainage, which is a major concern, will continue to be generated for many years, requiring aftercare monitoring of these waters. Based on the results of this study, it was concluded that passive systems can achieve the necessary water quality to allow the drainage to be discharged into the Barcés River, and subsequently into the drinking water supply Cercebre Reservoir.