Removal of antimonate (Sb(V)) and antimonite (Sb(III)) from aqueous solutions by coagulation-flocculation-sedimentation (CFS): Dependence on influencing factors and insights into removal mechanisms

Influence of pH and Contaminant Redox Form on the Competitive Removal of Arsenic and Antimony from Aqueous Media by Coagulation

“…In the case of pH (5 and 7), the peaks appearing at (455, 596 and around (802-818)) cm −1 correspond to Sb(III)-O, Sb(V)-O and As(V)-O stretching vibrations, which further clarifies that these groups could be involved in complex coordination with FC precipitates during their competitive adsorption [57,59]. At pH 9, the peak at 586 cm −1 appears with higher intensity, due to the interaction between As(III) species and FC flocs under competitive environment [39]. Furthermore, the intensity of the peak at 810 cm −1 is significantly reduced, which indicates the inhibition of As(V) adsorption onto FC flocs under basic pH conditions.…”

“…The surface charge of ligands may also be responsible for the increase in Fe solubility under these conditions. As discussed above, the dominant form of As(V)/Sb(V) was HAsO 4 2− /Sb(OH) 6 − (Table S1) or ≡FeOSbO(OH) 4 − ), thus weakening the Fe-O bond and leading to detachment of the Fe-As or Fe-Sb groups [34,39,45]. The bond breaking at the interface of Fe(OH) 3 would lead to the release of Fe(III) in solution, thereby enhancing Fe solubility.…”

“…The bond breaking at the interface of Fe(OH) 3 would lead to the release of Fe(III) in solution, thereby enhancing Fe solubility. Secondly, the attachment of As(V) or Sb(V) through Fe(OH) 3 surface interaction energy would lead to the release of Fe complex [39]. The stability of Fe(III) lattice may be affected by the van der Wall (vdW) forces of attraction and electrostatic repulsive forces, as described by the Derja-Guin-Landau-Verwey-Overbeek (DLVO) theory [50].…”

“…The As(V)/Sb(V) species may act as an inorganic ligand binding to Fe(III) hydroxyl complex. Two modes of Fe(III) release in response to ligand sorption can be proposed, considering the association of Fe(III) on As(V)/Sb(V) [39]. First, either the attachment of As(V) or Sb(V) occurs through chemical bond (≡Fe-O-As≡ or ≡Fe-O-Sb≡) at the Fe(OH)3 interface, resulting in the formation of surface active species (≡FeAsO4 2− or ≡FeOSbO(OH)4 − ), thus weakening the Fe-O bond and leading to detachment of the Fe-As or Fe-Sb Figure 1B presents the removal of As and Sb species by FC coagulation over various pH ranging (4)(5)(6)(7)(8)(9)(10).…”

“…However, studies reported in the literature are limited to the competitive adsorption behavior of As and Sb on various Fe minerals. In addition, a number of studies [38][39][40][41][42] had been conducted using FC coagulant for As or Sb removal from water but all these studies were limited to removal of single contaminant that is, either As or Sb species. To the best of our knowledge, no study has been conducted so far which provide the knowledge on simultaneous removal behavior of coexisting As and Sb species from water using FC as a coagulant.…”