Simultaneous removal of Cd(II) and Sb(V) by Fe-Mn binary oxide: Positive effects of Cd(II) on Sb(V) adsorption

The coexistence of cadmium ion (Cd(II)) and antimonate (Sb(V)) creates the need for their simultaneous removal. This study aims to investigate the effects of positively-charged Cd(II) on the removal of negative Sb(V) ions by Fe-Mn binary oxide (FMBO) and associated mechanisms. The maximum Sb(V) adsorption density (Q(max,Sb(V))) increased from 1.02 to 1.32 and 2.01 mmol/g in the presence of Cd(II) at 0.25 and 0.50 mmol/L. Cd2+ exhibited a more significant positive effect than both calcium ion (Ca2+) and manganese ion (Mn2+). Cd2+ showed higher affinity towards FMBO and increased its zeta-potential more significantly compared to Ca2+ and Mn2+. The simultaneous adsorption of Sb(V) and Cd(II) onto FMBO can be achieved over a wide initial pH (pH(i)) range from 2 to 9, and Q(Sb(V)) decreases whereas Q(Cd(II)) increases with elevated pH(i). Their combined values, as expressed by Q(Sb(V)+Cd(II)), amount to about 2 mmol/g and vary slightly in the pH(i) range 4-9. FTIR and XPS spectra indicate the significant synergistic effect of Cd(II) on Sb(V) adsorption onto FMBO, and that little chemical valence transformation occurs. These results may be valuable for the treatment of wastewater with coexisting heavy metals such as Cd(II) and Sb(V). (C) 2015 Elsevier B.V. All rights reserved.