Gastropod shell as a precursor for the synthesis of binary alkali-earth and transition metal oxide for Cr(VI) Abstraction from Aqua System

Abstract

The synergies of binary metal oxides, habitual in natural system, in sequestrating metal ions were the premise on the synthesis of binary alkali earth and transition metal oxides (ATM) for possible environmental remediation. Gastropod shell (GS) was used as a precursor for alkali earth metal generation in the perspective of wastes recycling and cost minimization in material synthesis. ATM of different combination ratios of Ca: Fe, were synthesized and characterized (XRD, SEM, EDAX, TGA and PZC) and the potential for Cr(VI) attenuation in aqua system was appraised. The Langmuir sorption capacities (mg/g) of the ATM (112.36–117.65) were higher than that of the respective metal ion constituents (101.01–105.26). Kinetic modeling showed that the pseudo second order gave the best description of the process. pH had nominal effect on the extent of Cr(VI) sorption while the magnitude of Cr(VI) sorbed reduced with increase in molar concentrations of anions and ionic strength. The spent ATM stability, determined via the toxicity characteristic leaching procedure (TCLP), was higher in acidic medium than the alkaline medium. SEM and EDAX elucidation, confirmed the presence of Cr(VI) on the sorbent while the formation of complexes of Cr ions with metal-O functional groups was confirmed via FTIR analysis.