Retention of organic molecule ‘‘quinalizarin’’ by bentonitic clay saturated with different cations Original Research Article

The adsorption of organic molecule to clay mineral has been reported by several investigators. The purpose of this investigation was to removal quinalizarin, witch is a toxic molecule used to dye cotton, from aqueous solution by smectite clay modified by different exchangeable cations: monovalent, divalent and trivalent cations. A group of isotherm tests were performed to clarify specific sorption behaviors due to exchangeable cations and the quinalizarin concentration. Adsorption of the clay was essentially immediate and was correlated with the cation exchange-capacity, the type of exchangeable cations, indicating that adsorption was primary to negatively charged sites on the clay. Adsorption was greater, equal to cation-exchange capacity with 2.210−3M than 2.210−4M of quinalizarin solution concentration. Potassium ions suppressed quinalizarin adsorption to smectite, probably by collapsing the clay lattices and preventing the expression of the interlayer-derived cation-exchange capacity. More quinalizarin was adsorbed by smectite made homoionic to various mono, di and trivalent cation (except by smectite homionic to potassium). The sequence of the amount of adsorption to homoionic smectite was Al3+ > NH4+ > Na+ > Fe3+ > Li+ > Ca2+ > Mg2+ > K+. Plateau in isotherms was observed when the quinalizarin concentration was equal to the value of cation exchange capacity of clay used indicated that a fixed proportion of the added quinalizarin was adsorbed regardless of the cation exhange capacity.