Adsorption of Hydroxy-Al by Certain Phyllosilicates and its Relation to K/Ca Cation Exchange Selectivity

Abstract

Abstract-The adsorption of hydroxy-Al by the 2-0.2/x size fractions of muscovite, biotite, Kdepleted micas, vermiculite and montmorillonite was studied. The differences in the amounts of hydroxy-Al adsorbed were apparently related to the expansibility and layer charge of minerals, the ionic saturation and degree of K-depletion, the basicity (OH/AI ratio) of the equilibrating hydroxy-Al solution, and the solution-clay ratio. The CEC reduction was not necessarily proportional to the amount of AI adsorbed because CEC reduction may occur through occupation of cation exchange sites by hydroxy-AI, or through hindrance to the entry of the replacing cation to these sites. Aluminum interlayering generally increases the K/Ca cation exchange selectivity (CES) of Na-vermiculite and K-depleted biotite, whereas the K/Ca CES of Na-montmorillonite was little affected. The basicity of the initial hydroxy-Al solution appeared to affect the K/Ca CES of Na-vermiculite and K-depleted biotite by controlling the amount of hydroxyl-Al adsorbed. The data indicate that in addition to the "propping effect", hydroxy-Al interlayers may affect the K/Ca CES through the following mechanisms; (1) the "preferential occupation" of Ca adsorbing sites, and/or (2) the "retarding effect" on the entry of the more hydrated Ca ions.

Hydroxy-Interlayers in Expansible Layer Silicates and Their Relation to Potassium Fixation

“…It has been reported that hydroxy-cations' islands in the interlayer spaces of clays could prevent K fixation through reduction of effective cation exchange capacity (CEC) and by their propping effects (Rich and Black 1964). Consequently, in the presence of hydroxy-interlayers, an increase in K/Ca cation exchange selectivity of Vt and K-depleted biotite was observed (Kozak and Huang 1971). However, information on the relationship between the degree of HyA and HAS interlayering in Vt and Mt clays and K fixing capacities of the resultant HyA/HAS-Vt/Mt complexes is not clear.…”

K/Ca and NH4/Ca selectivity of hydroxyaluminum-interlayered vermiculite and montmorillonite: Contribution from regular and frayed edge exchange sites

“…We assumed that the Ca ions might have experienced a kind of steric hindrance to getting adsorbed by the HyA-Vt/Mt complexes. Kozak and Huang (1971) also speculated that the enhancement of the K/Ca selectivity as a result of HyA-interlayering in certain phyllosilicates could be partially attributed to such steric hindrance to Ca adsorption.…”

“…Thus, it was assumed that the HyA-Vt complexes could exhibit a wedge-shaped zone where K-sized cations may be preferentially adsorbed, whereas large hydrated cations such as Ca may be excluded. Moreover, a preferential occupancy of Caadsorbing sites by larger HyA ions may also affect K/Ca selectivity in hydroxy-interlayered Vt (Kozak and Huang 1971). Such assumptions were verified in NH 4 /Ca selectivity of hydroxy-interlayered Vt and Mt (Saha et al 1999).…”

“…Selective adsorption of K, NH 4 , and Cs by some clays has been observed in a number of investigations (Krishnamoorthy and Overstreet 1950;Marshall and Garcia 1959;Wiklander 1964;Sawhney 1970;Kozak and Huang 1971;Murdock and Rich 1972;Shen et al 1997). However, only a few authors have described the effects of hydroxyaluminum (HyA)-interlayers on the selective adsorption and exchange properties of the host clays (Sawhney 1970;Kozak and Huang 1971;Saha et al 1999).…”

“…However, only a few authors have described the effects of hydroxyaluminum (HyA)-interlayers on the selective adsorption and exchange properties of the host clays (Sawhney 1970;Kozak and Huang 1971;Saha et al 1999). Sawhney (1970) assumed that Al-interlayered vermiculite (Vt) shows a mica-like behavior due to the presence of several wedgeshaped interlayer zones (frayed edge sites; FES), active in selective adsorption and exchange of K over Ca.…”