Adsorption behavior of hexavalent chromium on synthesized ethylenediamine modified starch

The starch-based material, ethylenediamine modified cross-linked starch (CAS) was synthesized and employed to remove hexavalent chromium from aqueous solution. Maximum adsorption of total chromium was observed at reaction pH of 4.0 and adsorption equilibrium achieved within 4h. The adsorption process can be described by pseudo-second-order adsorption model and the best-fit isotherm is Freudlich equation. The mechanism is predominately based on electrostatic attraction. The FT-IR spectra indicate that the amino groups of CAS are protonated and the hexavalent chromium ions were effectively adsorbed. Furthermore, studies on chromium release by using inorganic electrolytes confirm the mechanism observed by sorption experiments, which HCrO4- ion plays an important role interacting with CAS. Chromium release increases with increasing negative charge of electrolyte following the sequence PO43- > SO42- > B4O72- > NO3-.