Limestone selection criteria for EDR water remineralization

Water scarcity in Mediterranean regions has led to projects that increase water resources by desalination. In this context, it is planned to expand and improve the drinking water treatment plant of the Llobregat River near Barcelona (Catalonia, NE Spain), building the largest electrodialysis reversal (EDR) plant in the world. Llobregat River water shows high salinity due to the occurrence and exploitation of several geological formations upstream with minerals having high contents of Na, K, Cl, and Br. EDR desalinated water is highly reactive and shows a low degree of mineralization. In consequence, remineralization is necessary to equilibrate the water in order to avoid aggressiveness and corrosion in pipelines and to re-introduce some essential ions for human health. Running outlet water through limestone (CaCO3) is a simple and cheap process for remineralization. Five commercially available limestones were characterized (mineralogical and chemical composition, BET surface area, SEM analysis) and compared experimentally at both laboratory and pilot-plant scales during the EDR remineralization process. The main criteria in selecting a limestone for EDR water remineralization are its compositional purity in terms of both mineralogy and chemistry, and its textural characteristics. Texture mainly influences the suspended particulate matter (PM) generation, i.e., consumption and system performance. To minimize the negative effects of these features, an assessment, using SEM analysis and batch tests contacting limestones and desalinated water, of the capacity of PM generation is recommended.