DISSOLUTION KINETICS OF SEPIOL ITE FROM ESK ISEHIR (TURKEY) IN HYDROCHLORIC AND NITRIC ACIDS

various temperatures and particle sizes using dilute hydrochloric and nitric acids. Dissolution reaction rate constants were calculated and apparent activation energies were dependent on acid concentration. For both acids, apparent activation energy values reached a minimum of ~11 kcal/mol at an acid concentration f 0.75 u. For the second-order reaction which is independent of the acid concentration, the activation energy was 14.5 kcal/mol for both acids. The reaction rate constants were proportional to the acid concentrations, and inversely proportional to the square-root fthe initial particle radii of the sepiolite. The activation of natural clay surfaces by acid treatment has been studied extensively. Dissolution of Mg from sepiolite mined at Eskisehir (Turkey) using dilute acids was first attempted by Abdul-Lat i f & Weaver (1969) who found that dissolution of palygorskite and sepiolite in excess hydrochloric acid was a first order reaction in terms of concentrations of A1, Fe and Mg. They also noticed that the dissolution reaction rate constant of Mg in sepiolite was 240 times that for Mg in palygorskite. Several studies of the acid activation of Spanish sepiolite have been carried out to improve the surface area and porosity (J imenez-Lopez et al., 1978; Rodr iguez-Reinos