Removal of antimony from water by iron-coated cork granulates

Abstract This study demonstrated the viability of the application of iron-coated cork granulates, previously developed for As removal, in the adsorption of Sb from water. Batch adsorption assays were carried out both for high Sb initial concentrations and typical environmental values. The ionic strength was varied in environmentally relevant scenarios by changing the concentration of NaCl as a background electrolyte. Adsorption kinetics were best described by the Elovich model at high Sb initial concentrations and the pseudo-second-order model at lower levels. Adsorption of Sb(III) was faster than Sb(V) and an increase in ionic strength decreased the rates of adsorption. Equilibrium data was modelled by the Freundlich and Langmuir isotherms and the maximum adsorption capacities were estimated as 5.8 ± 0.5 mg g−1 Sb(III) at pH 6 and 12 ± 2 mg g−1 Sb(V) at pH 3. Sb(III) adsorption was unaffected by pH and positively or neutrally affected by ionic strength, indicating that the adsorption mechanism was the formation of inner-sphere complexes. Sb(V) adsorption, however, was higher at acidic values and decreased with increasing pH, and was negatively affected by ionic strength. The surface charge of the adsorbent was also influenced by the presence of Sb(V), suggesting that Sb(V) is adsorbed by electrostatic interactions and outer-sphere complexation. Speciation studies were carried out with analysis of Sb(III) and no evidence was found of oxidation-reduction reactions occurring parallel to Sb uptake. Iron-coated cork granulates showed good potential to be used as adsorbents of both Sb(III) and Sb(V), with possible economical and environmental benefits.