Adsorption of Se(IV) and Se(VI) on an iron-coated sand from water

This study was aimed at developing a method for coating hydrated iron-oxide onto the surface of quartz sand. Two coating parameters were investigated: the pH at which iron-oxide was synthesized and the coating temperature. According to the results, a larger quantity of iron was coated onto quartz sand in the lower pH range (0.5-2.0). This iron-oxide-coated sand (IOCS) produced at low pH was more difficult to dissolve in acidic and basic solution and had better Se(IV) and Se(VI) adsorption efficiencies than did IOCS produced at high pH (8.0-11.0). Adsorption experiments showed that Se(IV) adsorption by IOCS was specific and Se(VI) adsorption was nonspecific. In kinetic experiments, pseudo-equilibrium of Se(IV) adsorption was attained within 10 minutes while Se(VI) adsorption needed 1.5 hours. Higher concentrations of NaOH solution could increase the desorption rate of Se(VI) but could not increase the total desorbed quantity. In addition, adsorption isotherm results indicated that the adsorption capacity of IOCS from pH 4.0 to 6.5 was 0.014-0.017 mmole Se/g sand for Se(IV) and was 0.013-0.014 mmole Se/g sand for Se(VI). (C) 1997 Elsevier Science Ltd.