Exploiting the ion-exchange ability of titanate nanotubes in a model water softening process

Titanate nanotubes were utilized in Ca2+ and Mg2+ removal in a continuous ion-exchange unit. Three consecutive water softening-regeneration cycles were performed. The highest measured value of the total ion-exchange capacity was 1.2 mmol g (1) which decreased to 0.66 mmol g (1) in the third cycle. The capacity loss was due to the irreversible binding of Ca2+ ions to very strong adsorption sites, while the Mg2+/Na+ exchange was reversible. A relatively fast initial adsorption step and a subsequent slower concentration decrease were the two processes that governed the kinetics of the ion exchange reaction. (C) 2013 Elsevier B.V. All rights reserved.