The Adsorptive Removal of Arsenic And Manganese from Aqueous Solution by Natural and Modified Sepiolite

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