Sorption Studies of Chromium(VI) onto Cerium/Ferroferric Oxide Composites

To improve the adsorption capacities of ferroferric oxide (Fe3O4) for heavy metals, cerium/ferroferric oxide composites (Ce/Fe3O4) were prepared by a chemical coprecipitation method, and the adsorption capacity of chromium (Cr) from solution by Ce/Fe3O4 was studied. According to the TEM and SEM–EDS results, Ce was successfully doped on Fe3O4, the morphology of Ce/Fe3O4 was irregular and glossy, there were no obvious pores, and distinct boundaries were apparent. According to the XRD results, Ce/Fe3O showed high crystallinity. The crystal grain size of Ce/Fe3O4 was 27.9 nm. The results showed that Ce could increase the crystallinity and crystal size of Fe3O4. The results of batch adsorption experiments, including pH dependence, coexisting ion interference, adsorption kinetics and isotherms, showed that acidic conditions are more favorable than alkaline conditions for Ce/Fe3O4 to adsorb and remove Cr(VI). However, under acidic conditions, Cr(VI) exists in the form of HCrO4−, and Cl−, NO3− and SO42− existing in the solution compete with HCrO4− for adsorption. The adsorption process is mainly physical adsorption, and it can occur spontaneously.