Adsorption of selenium (iv) oxoanions on calcined layered double hydroxides of Mg-Al-CO3 from aqueous solution. Effect of calcination and reconstruction of lamellar structure Article uri icon

abstract

  • The Se(IV) oxoanions adsorption in water solutions onto calcined layered double hydroxide (LDH) was analyzed detailly. The effects of calcination and reconstruction of the LDH lamellar structure upon the adsorbing capacity were also argued. The Mg/Al-CO3 LDH was fixed by a co-precipitation method, was calcinated at 550 °C (LDH550), and was rehydrated in deionized water (LDH550Reh). The characterization revealed that the LDHs were mesoporous. The XRD analysis confirmed the LDH layered structure and the destruction of the lamellar structure in the LDH550, as well as the formation of mixed metal oxides. Furthermore, the reconstruction of the layered structure in LDH550Reh and LDH550 loaded with Se(IV) was corroborated by XRD. The interlaminar carbonates were removed in the calcination, resulting in a higher positive zeta potential (ZP) on the LDH550 surface and favoring the Se(IV) oxoanions adsorption onto LDH550. At pH = 5 and T = 25 °C, the maximum adsorption capacity of LDH550 towards Se(IV) was 134.4 mg/g and 5.3-fold bigger than that of uncalcined LDH, attributed to the increment in basal sites available for adsorbing Se(IV) oxoanions. The adsorbing capacity of LDH550 towards Se(IV) oxoanions increased by reducing the solution pH from 11 to 5 because of the enhancement of the electrostatic attraction between the Se(IV) oxoanions in water solutions and the positively charged surface of LDH550. The temperature effect showed that Se(IV) adsorption on LDH550 was exothermic for uptakes of Se(IV) adsorbed higher than 90 mg/g. The adsorption of Se(IV) on LDH550 occurred by anion exchange and electrostatic attractions. The ZP of the LDH was reduced by the Se(IV) adsorption, and the reduction of ZP was incremented almost linearly with the mass of Se(IV) adsorbed, demonstrating that Se(IV) was predominantly adsorbed by electrostatic attraction. © 2021 Elsevier B.V.

publication date

  • 2021-01-01