Adsorption mechanisms of Cr(VI) on the modified bauxite tailings

The main waste product generated during the bauxite flotation in China is the aluminosilicate tailings. It is desirable to develop an application of these aluminosilicate tailings for the treatment of waste streams containing dissolved heavy metals. The Cr(VI) adsorption capacity and mechanisms of the bauxite tailings modified by FeCl3 · 6H2O are investigated in the present study. A maximum removal rate of Cr(VI) by the modified bauxite flotation tailings is obtained at 99.3% in batch experiments. The IEPs of the unmodified and modified bauxite tailings are 3.6 and 5.0, respectively. The IEP of the modified bauxite tailings shifts to lower pH value in the presence of Cr(VI), which indicates that an adsorption of anionic species happens on the modified bauxite tailings. A new band of Cr2O72- appears in the FTIR determination of the modified bauxite tailings, which shows that Cr(VI) adsorbs on the modified bauxite tailings in the form of chemical adsorption. Furthermore, the adsorption data of Cr(VI) on the modified bauxite tailings are well described by both Langmuir and Freundlich models. The pseudo-second-order kinetic model also fits experimental data for the adsorption of Cr(VI).