title: Competitive sorption of Pb(II) and Zn(II) on polyacrylic acid-coated hydrated aluminum-oxide surfaces.
abstract: Natural organic matter (NOM) often forms coatings on minerals. Such coatings are expected to affect metal-ion sorption due to abundant sorption sites in NOM and potential modifications to mineral surfaces, but such effects are poorly understood in complex multicomponent systems. Using poly(acrylic acid) (PAA), a simplified analog of NOM containing only carboxylic groups, Pb(II) and Zn(II) partitioning between PAA coatings and α-Al2O3 (1-102) and (0001) surfaces was investigated using long-period X-ray standing wave-florescence yield spectroscopy. In the single-metal-ion systems, PAA was the dominant sink for Pb(II) and Zn(II) for α-Al2O3(1-102) (63% and 69%, respectively, at 0.5 μM metal ions and pH 6.0). In equi-molar mixed-Pb(II)-Zn(II) systems, partitioning of both ions onto α-Al2O3(1-102) decreased compared with the single-metal-ion systems; however, Zn(II) decreased Pb(II) sorption to a greater extent than vice versa, suggesting that Zn(II) outcompeted Pb(II) for α-Al2O3(1-102) sorption sites. In contrast, >99% of both metal ions sorbed to PAA when equi-molar Pb(II) and Zn(II) were added simultaneously to PAA/α-Al2O3(0001). PAA outcompeted both α-Al2O3 surfaces for metal sorption but did not alter their intrinsic order of reactivity. This study suggests that single-metal-ion sorption results cannot be used to predict multimetal-ion sorption at NOM/metal-oxide interfaces when NOM is dominated by carboxylic groups.
authors.affiliation: Surface & Aqueous Geochemistry Group, Department of Geological & Environmental Sciences, Stanford University , Stanford, California 94305-2115, United States.
authors.forename: Yingge
authors.initials: Y
authors.lastname: Wang
authors.forename: F Marc
authors.initials: FM
authors.lastname: Michel
authors.forename: Clement
authors.initials: C
authors.lastname: Levard
authors.forename: Yong
authors.initials: Y
authors.lastname: Choi
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Eng
authors.forename: Gordon E
authors.initials: GE
authors.lastname: Brown
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D000327:Adsorption; D000536:Aluminum Hydroxide; D000537:Aluminum Oxide / Q000737:chemistry*; D003460:Crystallization; D006863:Hydrogen-Ion Concentration; D007477:Ions / Q000737:chemistry; D007854:Lead / Q000737:chemistry*; D008670:Metals / Q000737:chemistry; D008903:Minerals / Q000737:chemistry; D009930:Organic Chemicals; D013050:Spectrometry, Fluorescence / Q000379:methods; D014965:X-Rays; D015032:Zinc / Q000737:chemistry*
chemical_list: D000180:Acrylic Resins; D007477:Ions; D008670:Metals; D008903:Minerals; D009930:Organic Chemicals; D007854:Lead; C006903:carbopol 940; D000536:Aluminum Hydroxide; D015032:Zinc; D000537:Aluminum Oxide