Purification of sepiolite and its dissolution in hydrochloric acid and sodium Acetate-Acetic acid buffer.

Abstract

The associated impurities with sepiolite, mainly palygorskite, quartz, and dolomite, reduce the industrial quality of this mineral. The objectives of this study were to i) investigate the efficiency of particle size separation for purifying sepiolite and ii) determine the kinetic dissolution of sepiolite in HCl and sodium acetate - acetic acid buffer (SAB). Bulk sepiolite was provided from a mine located around the city of Fairman, in northeastern Iran. Three particle size fractions of 20-50, <20. and <2 µm were separated from the bulk sepiolite. The XRD results showed that the particle size separation method has a great impact on reducing the amount of quartz as well as the complete elimination of dolomite in particles <2 µm and palygorskite in 20-50 µm fractions. The <20 µm fraction composed ~70% of the sample which it’s impurities considerably decreased; Therefore, it is a cost-effective fraction for industrial use. Therefore, it is a simple and low-cost physical procedure, without applying chemical reagents to achieve suitable purified sepiolite. The results of dissolution kinetic showed that the data had the best fit with the rate equation of Kt=[(1-(1-X)1/2)2]. Increasing acid concentration, temperature, and time had a direct relation, while the solid to liquid ratio had an inverse relation with the apparent rate constant. This trend was observed for SAB, too. Dissolution of sepiolite in HCl was higher than that of SAB. Acid concentration and temperature were the most effective factors on sepiolite dissolution.

Keywords

• sepiolite dissolution
• clay purification
• kinetic dissolution
• particle size fractionation