Removal of phosphate from water by a Fe–Mn binary oxide adsorbent

Abstract

a b s t r a c tPhosphate removal is important in the control of eutrophication of water bodies and adsorption is one of the promising approaches for this purpose. A Fe-Mn binary oxide adsorbent with a Fe/Mn molar ratio of 6:1 for phosphate removal was synthesized by a simultaneous oxidation and coprecipitation process. Laboratory experiments were carried out to investigate adsorption kinetics and equilibrium, in batch mode. The effects of different experimental parameters, namely contact time, initial phosphate concentration, solution pH, and ionic strength on the phosphate adsorption were investigated. The adsorption data were analyzed by both Freundlich and Langmuir isotherm models and the data were well fit by the Freundlich isotherm model. Kinetic data correlated well with the pseudo-second-order kinetic model, suggesting that the adsorption process might be chemical sorption. The maximal adsorption capacity was 36 mg/g at pH 5.6. The phosphate adsorption was highly pH dependent. The effects of anions such as Cl À ; SO 4 2À , and CO 3 2À on phosphate removal were also investigated. The results suggest that the presence of these ions had no significant effect on phosphate removal. The phosphate removal was mainly achieved by the replacement of surface hydroxyl groups by the phosphate species and formation of inner-sphere surface complexes at the water/oxide interface. In addition, the adsorbed phosphate ions can be effectively desorbed by dilute NaOH solutions. This adsorbent, with large adsorption capacity and high selectivity, is therefore a very promising adsorbent for the removal of phosphate ions from aqueous solutions.

Adsorption of antimony(V) onto Mn(II)-enriched surfaces of manganese-oxide and Fe Mn binary oxide

“…The elevated f-potential due to Mn 2+ enrichment benefited the adsorption of negatively-charged Sb(OH) 6 À , which was the main Sb(V) species over a wide pH range of 3-9. The positive electrostatic effect of Mn 2+ on the adsorption of arsenic and phosphate has been reported before (Zhang et al, 2007(Zhang et al, , 2009Stumm and Morgan, 1996). Mn 2+ contributed to a more significant f-potential increase for Mn-oxide, and the more remarkable effect on Sb(V) adsorption was observed thereafter.…”

“…By comparison, the adsorption of Sb(V) decreased the pH iep values, which were 3.2 for FMBO and 3.0 for Mn-oxide. The remarkable shift in pH iep indicated the occurrence of specific adsorption and the formation of surface complexes in the adsorption of Mn 2+ and Sb(V) (Zhang et al, 2009;Hsia et al, 1994). The elevated f-potential due to Mn 2+ enrichment benefited the adsorption of negatively-charged Sb(OH) 6 À , which was the main Sb(V) species over a wide pH range of 3-9.…”

Adsorptive removal of arsenic from water by an iron–zirconium binary oxide adsorbent

“…Adsorption of strong acid anions by metal oxides and hydroxides typically decreases with increasing pH [31]. Such a pH effect was observed for the sorption of As(V) onto iron oxides or iron-containing oxides [32,33]. H 2 AsO Lower pH is favorable for the protonation of the sorbent surface.…”

Adsorption of Phosphate from Aqueous Solution Using an Iron–Zirconium Binary Oxide Sorbent

“…Many of these adsorbents have shown much promise for the removal of phosphate from water. For example, Zhang et al (2009) reported that a Fe-Mn binary oxide had a high P sorption capacity of 36 mg g at pH 5.6. Harver and Rhue (2008) reported that mixed Al-Fe hydr(oxides) were effective for P removal.…”