Özet:

The natural sepiolite clay mineral was obtained from General Directorate of Mineral Research and Exploration (MTA) of Turkey and modified with 2.5 M of NaOH. The natural (SP) and modified (Na-SP) sepiolite samples were characterized by XRD, N2 adsorption-desorption, FTIR, SEM-EDS and NH3-TPD. The treatment of the sepiolite with NaOH led to a significant desilication and decationization of the SP. The alkali treatment with NaOH caused solution of silicon and cations, resulting in an increase in its average pore diameter and a decrease in its surface area from 187. 8 m2 g-1 to 7.1  m2 g-1. In addition, a number of weak and medium acid centres of SP was  decreased while a number of strong acid centres was increased.    The maximum As(III) and As(V) removal with the SP was achieved at an initial pH of 1.5, respectively; ca. 8.9 mg g-1  and 26.8 mg g-1.  The maximum removal of As(III) and As(V) with Na-SP was achieved at an initial pH of 5.0; ca. 46.7 mg g-1 and   35.9 mg g-1, respectively. The maximum Mn(II) removal with SP was 5.2 mg g-1. Treatment of SP with NaOH increased its the arsenic adsorption capacity up to four times, which is comparable to iron-containing sepiolite samples and bimetallic oxides. While the Langmuir isotherm fitted well with results obtained from the As(V) with SP and As(III) with Na-SP, the Freundlich isotherm model was more appropriate for the results obtained from As(V) with  Na-SP and from Mn(II) of SP. The pseudo-second-order kinetic model for the adsorption of arsenic and manganese on natural and modified sepiolite fitted well.

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