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, (Na x +2 y Al x Si1 - x O2+ y ), has an IEC of ∼2.5 mequiv g-1. These ion-exchange materials were studied and optimized because of their specific ion-exchange 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.

A series of amorphous silicate materials with the general formula Na x+2y M 3+x Si 1-x O 2+y (M 3+ ) Al, Mn, Fe, Y) were studied. Samples were synthesized by a precipitation reaction at room temperature. The results indicate that the ion-exchange capacity (IEC) decreases as follows: Al > Fe > Mn > Y. Additionally, the IEC increases with increasing aluminum concentration. Structural studies show that the relative amount of octahedrally coordinated aluminum increases with increasing Al content, as does the total amount of AlO 4 species increases. The data suggest that the IEC value of these amorphous aluminosilicates is dependent on the tetrahedrally coordinated aluminum. Regeneration of the Al-silicate with acetic acid does not decrease the IEC significantly.

2005 Ion exchange V 1350Structure-Property Relationship of Permutite-Like Amorphous Silicates, Nax+2y Si1-xO2+y (M 3+ : Al, Mn, Fe, Y), for Ion-Exchange Reactions. -The title compounds are synthesized by simple precipitation at room temperature. The ion-exchange capacity of the compounds decreases in the order Al > Fe >Mn > Y. Additionally, the ion-exchange capacity increases with increasing Al concentration. It is suggested that the ion-exchange capacity value of these aluminosilicates depends on the amount of tetrahedrally coordinated Al. The high ion-exchange capacity and ability to regenerate exhibited by the 22.8% Al-permutite sample makes permutite an attractive material for the desalination of brackish waters. -(PLESS, J. D.; MAXWELL, R. S.; PHILIPS, M. L. F.; HELEAN, K. B.; AXNESS, M. Y.; NENOFF*, T. M.; Chem.