Ion‐exchange properties of some brown seaweeds from the indian coast

Abstract

Ion‐exchange properties of five marine algal species, viz. Sargassum tenerrimum J. Ag., S. swartzii (Turner) C. Ag., Cystoseira indica (Thivy et Doshi) Mairh, Tur‐binaria conoides (Kuetz) and Padina pavonica (L) (Thivy et Taylor) have been studied and compared with those of alginic acid. The ion‐exchange property of these samples is found to be due mainly to their alginic acid and fucoidin content. Uptake of calcium ions from different solutions and pH titration studies have revealed that the ionogenic groups present in the samples are dissociated to the extent of 35–50% even in neutral media. When subjected to continuous use, the ion‐exchange capacity of the weeds at first decreases but attains a constant value after a few cycles. The rate of exchange (H+→Na+ and H+→Ca2+) on these samples has also been investigated. Distribution coefficients (Kd) of some of the metal ions for the said species have also been determined and the affinity sequence of the metal ions for each of the samples has been given. Na+→Ca2+ and Na+→Mg2+ exchange equilibria gave abnornal exchange isotherms. However the separation factor 7alpha;Ca2+ is found to be an exponential function of the concentration ratio of the Na+/Ca2+ in the solution.