Halloysite Composites with Fe₃O₄Particles: The Effect of Impregnation on the Removal of Aqueous Cd(II) And Pb(II)

In this study, halloysite-Fe₃O₄composites were synthesized by a chemical-precipitation method to facilitate magnetic separation of the sorbents from aqueous solution. The research focused on the effect of Fe₃O₄phase on the halloysite sorption properties. The X-ray diffraction (XRD) results confirmed successful deposition of Fe₃O₄particles on a halloysite surface. They showed that the coating with Fe₃O₄particles enhanced the halloysite adsorption affinity toward Cd(II) and Pb(II). The highest adsorption capacity was determined for the composites having 10% of the surface deposited with Fe₃O₄. In this case, the adsorption capacity for Cd(II) and Pb(II) was 33 and 112 mmol·kg^-1, respectively. The point of zero charge (pH_PZC) and desorption results indicated that the removal mechanism of metals is mainly related to chemisorption involving reaction with hydroxyls of either halloysite or Fe₃O₄phase. The ion exchange is of limited importance due to the low cation exchange capacity (CEC) of halloysite - Fe₃O₄composites.