Removal of Cr(VI) from water using Fe(II)-modified natural zeolite

• Adsorption and retention of Cr(VI) greatly enhanced by zeolite modified with Fe(II).
• An increase in Cr(VI) adsorption capacity to 700 mg/kg achieved with 0.3% Fe(II).
• A Cr(VI) retardation factor of 6 was obtained from column study.
• Lower cost compared to surfactant-modified zeolite for groundwater remediation.

In this study, natural zeolite aggregates with the particle size of 1.4–2.4 mm were modified by Fe(II). The unmodified zeolite and Fe(II)-modified zeolite (Fe-eZ) were subjected to batch and column tests to study the Cr(VI) sorption, transport, and retardation. Modification of the natural zeolite with Fe(II) resulted in an increase in Cr(VI) sorption to 6 mmol/kg. The Cr(VI) sorption followed a pseudo-second-order kinetics with a rate of 17 mmol/g h and a rate constant of 0.7 g/mmol h. Cr(VI) removal from solution increased with an increase in ionic strength, but decreased as the solution pH increased. At a Cr(VI) input concentration of 100 mg/L, unmodified zeolite did not show any Cr(VI) retardation at all. In contrast, the observed retardation factor of Fe-eZ for Cr(VI) increased by a factor of 6. The hydraulic conductivity of the zeolite showed little change before and after Fe(II) modification and before and after Cr(VI) sorption, suggesting its good mechanical stability to be used as packing materials for permeable reactive barriers in groundwater remediation.

A 6-fold increase in Cr(VI) retardation factor for Fe-eZ, at a residence time of 1 h.Figure optionsDownload high-quality image (204 K)Download as PowerPoint slide