Zinc ion adsorption on montmorillonite–Al hydroxide polymer systems

Abstract

Summary Clay–Al hydroxide polymers (CAlHO) can bind heavy metals effectively and may play an important role in the adsorption behaviour and metal binding capacity of soils. We studied the dependence of Al loading and pH on the adsorption of Zn on Na‐saturated montmorillonite–Al hydroxide polymer systems. The available binding sites on Al hydroxide polymers (AlHO) had a very strong affinity for Zn ions. Zinc binding on the clay surface became important when the binding sites on the AlHO were nearly all occupied. The pH had a very strong effect on the Zn binding. At pH 6.6 much more Zn could be adsorbed to the AlHO than at pH 5.0. The effect of the Al:clay ratio on Zn binding was influenced by pH. At pH 6.6, Zn binding to the AlHO, expressed per mole AlHO, was independent of the Al:clay ratio, whereas at pH 5.0 this relation was dependent. This is related to the constant charge of the AlHO at pH 6.6, whereas at pH 5.0 the charge decreases with increasing Al:clay ratio. If clay–Al hydroxide polymers are present in the soil their Zn binding to the AlHO will strongly influence the availability of the Zn.

Soil properties controlling Zn speciation and fractionation in contaminated soils

“…Additional Zn inputs may therefore not be converted into Zn-HIM, thus favoring the formation of other Zn-species or Zn leaching to deeper soil horizons. In batch experiments, the extent of specific sorption of Zn to HIM was shown to increase with increasing pH (Lothenbach et al, 1997; Janssen et al, 2003). However, the limited number of specific sorption sites for Zn in HIM and the limited abundance of HIM in soils pose limits to the amounts of Zn that can be bound as Zn-HIM (Jacquat et al, 2009).…”

Local coordination of Zn in hydroxy-interlayered minerals and implications for Zn retention in soils

“…Differentiation between these two trends by LCF was complicated, because they both had similar effects on the shape of the EXAFS spectra (reduced second shell and higher shell signals compared to Zn incorporated into dioctahedral vacancies). According to Janssen et al (2003b), uptake of Zn by cation exchange only becomes relevant once sorption to Al-polymers approaches its maximum.…”

“…The formation of hydroxy-Al interlayers in smectites or vermiculites strongly reduces the cation exchange capacity (CEC) and affects the ion sorption properties of the clay minerals (Barnhisel and Bertsch, 1989;Janssen et al, 2003b;Meunier, 2007). Laboratory studies have shown that Cu, Cd, Ni, Pb, and Zn sorb strongly to hydroxy-Al interlayered montmorillonite under acidic conditions, while 0016-7037/$ -see front matter Ó 2008 Elsevier Ltd. All rights reserved.…”

“…doi:10. 1016/j.gca.2008.10.026 adsorption to pure montmorillonite at acidic pH is dominated by cation exchange (Lothenbach et al, 1997;Saha et al, 2001;Janssen et al, 2003b). Furthermore, hydroxyAl polymers bound to a clay surface have a higher affinity for metal sorption than pure Al hydroxides (Keizer and Bruggenwert, 1991).…”

“…The incorporation of Zn into the hydroxy-Al interlayers of HIM by specific adsorption may have a substantial impact on Zn bioavailability and mobility in acidic soils, where adsorption is otherwise mainly due to cation exchange (Scheinost et al, 2002;Janssen et al, 2003b). Using bulk-and l-EXAFS spectroscopy, Zn incorporated into HIM (Zn-HIM) has so far been detected in one contaminated (Scheinost et al, 2002) and two uncontaminated acidic soils Manceau et al, 2005).…”