Powdered Ca-activated zeolite for phosphate removal from treated waste-water

Abstract

Background: A powdered zeolitic material synthesised from fly ash (FA) (NaP1-FA) and its calcium modified form (CaP1-NA) were studied as sorbent materials for the recovery of phosphate from treated waste-water effluents. Phosphate-sorption equilibrium experiments were performed by varying the experimental conditions, including solution pH, phosphate concentration, and the presence of competing ions. Results: The maximum phosphate-sorption capacities were 57 ± 5 and 203 ± 11 mgP–PO4g-1 for NaP1-FA and CaP1-NA, respectively. The sorption capacities of both zeolites in the pH range expected for waste-water effluents (pH 7 to 9) were slightly dependent on pH, exhibiting maxima at pH 8. Phosphate removal proceeds through two main mechanisms: (a) surface complexation with ≅AlOH and ≅FeOH groups of the zeolitic structure or unreacted minerals from the FA; and (b) the formation of Ca–phosphate phases, mainly brushite. Conclusions: The removal mechanisms were confirmed by XRD analyses and P speciation. The stabilities of the phosphate-loaded zeolite samples evaluated by the extraction experiments confirmed their potential availabilities in soil applications. Finally, the higher solubility of brushite compared with that of Hap makes this zeolitic material promising as a novel inorganic zeolite/CaP1-NA/brushite fertiliser