Adsorption of Pb(II) and Zn(II) in the presence and absence of CO2
Description
Adsorption data on goethite vs. pH of Pb(II) and Zn(II) under different conditions especially in the presence and absence of CO2. Aqueous chemical speciation expected of both vs. pH in the absence of adsorption. The data shows that there is no distinction between adsorption on two goethites of different particle sizes in the presence and in the absence of CO2, for Pb(II) up to a pH of 6.4, and for Zn(II) up to a pH of 7.0. This confirms that dissolved carbonate does not affect the adsorption behavior of these and other heavy metal cations, and thus, that laboratory experiments may be performed in open atmosphere, but modeled in the absence of CO2. The model shows a contribution of a bidentate surface complex with the unhydrolyzed metal(II), and a monodentate complex with the hydroxylated metal(II).
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Steps to reproduce
Adsorption reaction were performed in duplicate or triplicate in 60 mL high-density polyethylene (HDPE) bottles with a total volume of 50.0 mL, with a goethite concentration of 1 g/L and an ionic strength of 0.01 mol/L (NaNO3 – Sigma >99%). For Pb(II), the pH adsorption edges were generated in the pH range from 3.7 to 6.5, and additional samples in triplicate were adjusted to pH 6.4 for the 86 m2/g goethite, and to 6.2 for the 42 m2/g goethite. For Zn(II) the pH range used from a previous work was 4 to 7 on a 95 m2/g goethite, and triplicates were performed on 86 and 42 m2/g goethites at pH 7.0. The procedure for the CO2-free systems was performed inside a glove bag (AtmosBag, Sigma-Aldrich) under a nitrogen atmosphere to prevent potential adsorption of CO2 as carbonates on the mineral surface, as well as potential metal cation-carbonate interactions.
Institutions
- Universidad Nacional Autónoma de MéxicoMexico City, Mexico City