Arsenic Adsorption Behaviors of Heated Calcium-Rich Sepiolite in Water.

Calcium-rich sepiolite was taken as an object for study, in which it was modified by heating, and then analyzed for changes in composition and structure from the original with XRF, XRD, and SEM-EDS, separately. Moreover, effects of the modification on its adsorption of As³⁺ and As⁵⁺ and their influencing factors were studied. Results show that the modification significantly increased sepiolite's As adsorption capacity. Its As³⁺ and As⁵⁺ adsorption capacity in water with pH being 7 in value reached theoretically as high as 25.61 mg·g^-1 and 30.30 mg·g^-1, respectively, with adsorption isotherms fitting the Langmuir model. Fitting of its As adsorption kinetics reveals that its As³⁺ adsorption was in consistence with the pseudo-second order model, while its As⁵⁺ adsorption was with both the pseudo-first and -second order kinetics models. Besides, the study of influencing factors found that changes in particle size was not a major factor affecting As adsorption of the modified calcium-rich sepiolite and neither was pH (6-11). Among the co-existing ions, PO₄^3- was found to be the major one. The low-cost thermal treated calcium rich sepiolite was proven to be an effective arsenic remover in the wastewater.