Mechanism investigation and surface complexation modeling of zinc sorption on aluminum hydroxide in adsorption/coprecipitation processes

Chiharu Tokoro, Taisuke Sakakibara, Shinya Suzuki

    Research output: Contribution to journalArticle

    18 Citations (Scopus)

    Abstract

    The sorption mechanism of dilute Zn [initial Zn(II) concentration up to 40mgdm<sup>-3</sup>] on aluminum hydroxide was investigated. Adsorption and coprecipitation at pH 7 were compared. The adsorption process gave a Langmuir-type isotherm and the zeta potential of Zn(II)-adsorbed aluminum hydroxide decreased linearly with increasing sorption density of Zn on aluminum hydroxide. The adsorption mechanism is therefore mainly surface complexation. In contrast, in the coprecipitation process, a Brunauer-Emmett-Teller like isotherm was obtained; the slope of the zeta potential versus Zn(II) sorption density decreased when the initial Zn/Al molar ratio was greater than 0.5. The X-ray diffraction pattern of Zn(II)-coprecipitated aluminum hydroxide changed from that of poorly crystalline gibbsite to a Zn-Al layered double-hydroxide (LDH) when the initial Zn/Al molar ratio was greater than 0.5, showing that surface complexation was the main sorption mechanism, but surface precipitation of Zn-Al LDH was also involved when the initial Zn/Al molar ratio in the coprecipitation process was greater than 0.5. A quantitative diffuse-layer model was constructed. The aluminum hydroxide exchange capacity was set at 0.61molmol-Al<sup>-1</sup>, based on the experimentally determined surface area, 340m<sup>2</sup>g<sup>-1</sup>. Surface complexation coefficients for H<sup>+</sup>, OH<sup>-</sup>, and Zn(II) adsorption on aluminum hydroxide were determined by fitting to the experimental adsorption results. The obtained parameters were in excellent agreement with those previously reported for a database of gibbsite adsorption equilibrium constants. The pH edge for Zn(II) removal by aluminum hydroxide was successfully reproduced by the constructed model.

    Original languageEnglish
    Pages (from-to)86-92
    Number of pages7
    JournalChemical Engineering Journal
    Volume279
    DOIs
    Publication statusPublished - 2015 Nov 1

    Keywords

    • AMD
    • DLM
    • ICP-AES
    • LDH
    • Poorly crystalline gibbsite
    • Surface precipitation
    • Wastewater treatment
    • XRD
    • Zeta potential
    • Zn-Al LDH

    ASJC Scopus subject areas

    • Chemical Engineering(all)
    • Chemistry(all)
    • Industrial and Manufacturing Engineering
    • Environmental Chemistry

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