title: Phosphorus immobilization in micropores of drinking-water treatment residuals: implications for long-term stability.
abstract: Drinking-water treatment residuals (WTRs) can immobilize excess soil phosphorus (P), but little is known about the long-term P retention by WTRs. To evaluate the long-term P sorption characteristics of one Fe- and one Al-based WTR, physicochemical properties pertinent to time-dependency and hysteresis of P sorption were assessed. This study also investigated the P sorption mechanisms that could affect the long-term stability of sorbed P by WTRs. Phosphorus sorption kinetics by the WTRs exhibited a slow phase that followed an initial rapid phase, as typically occurs with metal hydroxides. Phosphorus sorption maxima for both Fe- and Al-based WTRs exceeded 9100 mg of P kg(-1) and required a greater specific surface area (SSA) than would be available based on BET-N2 calculations. Electron microprobe analyses of cross-sectional, P-treated particles showed three-dimensional P sorption by WTRs. Carbon dioxide gas sorption was greater than N2, suggesting steric restriction of N2 diffusion by narrow micropore openings. Phosphorus-treated Co2 SSAs were reduced by P treatment, suggesting P sorption by micropores (5-20 A). Mercury intrusion porosimetry indicated negligible macroporosity (pores > 500 A). Slow P sorption kinetics by WTRs may be explained by intraparticle P diffusion in micropores. Micropore-bound P should be stable and immobilized over long periods.
authors.affiliation: Soil and Water Science Department, University of Florida, G163 McCarty Hall, P.O. Box 110290, University of Florida, Gainesville, Florida 32611, USA.
authors.forename: Konstantinos C
authors.initials: KC
authors.lastname: Makris
authors.forename: Willie G
authors.initials: WG
authors.lastname: Harris
authors.forename: George A
authors.initials: GA
authors.lastname: O'Connor
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Obreza
mesh_terms: D000327:Adsorption; D004058:Diffusion; D004784:Environmental Monitoring; D007700:Kinetics; D010758:Phosphorus / Q000032:analysis* / Q000737:chemistry*; D016062:Porosity; D014865:Waste Disposal, Fluid / Q000379:methods*; D014881:Water Supply
chemical_list: D010758:Phosphorus