Desalination of Brackish Waters Using Ion-Exchange Media

An environmentally friendly method and materials study for desalinating inland brackish waters (i.e., coal bed methane produced waters) using a set of ion-exchange materials is presented. This desalination process effectively removes anions and cations in separate steps with minimal caustic waste generation. The anion-exchange material, hydrotalcite (HTC), exhibits an ion-exchange capacity (IEC) of ~3 mequiv g^-1. The cation-exchange material, an amorphous aluminosilicate permutite-like material, (Nax+2yAlxSi1xO2+y), has an IEC of ~2.5 mequiv g-1. These ion-exchange materials were studied and optimized because of their specific ionexchange capacity for the ions of interest and their ability to function in the temperature and pH regions necessary for cost and energy effectiveness. Room temperature, minimum pressure column studies (once-pass through) on simulant brackish water (total dissolved solids (TDS) = 2222 ppm) resulted in water containing TDS = 25 ppm. A second once-pass through column study on actual produced water (TDS = ~11 000) with a high carbonate concentration used an additional lime softening step and resulted in a decreased TDS of 600 ppm.