Effect of Al hydroxide polymers on cation exchange of montmorillonite

Abstract

Summary Al hydroxide polymers (AlHO) can significantly influence the cation exchange behaviour of clays. We have determined the effect of synthesized AlHO on Ca–Na, Zn–Na and Pb–Na exchange for a series of exchanger compositions and two Al loadings at pH 6.0 and an ionic strength of 0.01 m. The preference for Ca on the siloxane surface of the clay–AlHO system (CAlHO) was greater than for the pure clay, and the average KV (Vanselow selectivity coefficient) was determined to be 2.16 and 1.24, respectively. The selectivity coefficients for the exchange reactions Zn–Na and Pb–Na were not directly determined in CAlHO systems, because heavy‐metal ions bind as well to the clay surface as to the AlHO over a wide range of pH. We have estimated the effect of the presence of AlHO on the selectivity coefficients of Zn–Na and Pb–Na exchange by extrapolation of the experimental results of Ca–Na, Zn–Na and Pb–Na exchange for pure clay and Ca–Na exchange for CAlHO. The average KV was increased by the presence of the AlHO from 1.23 to 2.16 for Zn–Na exchange and from 1.59 to 2.77 for Pb–Na exchange. The increase in the preference for the divalent cations is probably caused by parallel alignment of clay platelets by sorption of AlHO. Increasing the amount of AlHO did not change the selectivity for Ca–Na exchange, and probably the structure of the system or the arrangement of the clay platelets and AlHO particles was not substantially changed. This was supported by the linear reduction of the cation exchange capacity with amount of AlHO present at pH 6.6. It seems likely that the selectivity coefficients for Ca–Na, Zn–Na and Pb–Na exchange that we found apply in naturally occurring montmorillonite–AlHO systems.

A study of potassium dynamics and mineralogy in soils from subtropical Brazilian lowlands

“…The lowest Kne values were detected in the soils with the lowest clay contents due to the predominance of kaolinite and HIV in the clay fraction. Although the HIV is a 2:1 clay mineral with functional groups of permanent charges, the interlayers are partially or totally blocked by the Al polymers, preventing their interaction with the ions of the soil solution (Dixon and Weed 1989;Janssen et al 2003).…”

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

“…The sorption of Zn to HIS as a function of hydroxy-Al loading, solution pH, and Zn concentration has previously been studied by Janssen and coworkers (Janssen et al, 2003a;Janssen et al, 2003 b). They found that the formation of hydroxy-Al interlayers reduces the cation exchange capacity, but provides high-affinity sorption sites for Zn.…”

“…It has a N 2 -BET surface are of $31 m 2 /g similar to the Wyoming montmorillonite SWy-2 ( van Olphen and Fripiat, 1979;Bradbury and Baeyens, 1998), which has been used in the current study and the work by Scheinost et al (2002). Thus, the results from Zn uptake studies by Janssen et al (2003a) can be compared to the local coordination of Zn derived from EXAFS data obtained with a similar clay mineral.…”

Adsorption of phosphate on hydroxyaluminum- and hydroxyiron-montmorillonite complexes

“…Their surface properties and stability have been extensively studied [11][12][13]. Interactions between polymeric cations and clays may significantly influence surface properties of the pristine clays [11,12,14,15]. Given the high reactivity, large surface areas and high positive charges of HyAl and HyFe cations, Mt-complexes may play a significant role in regulating the mobility of P and some potential anionic pollutants such as arsenate and selenite.…”