EFFECT OF HYDROLYSIS OF ALUMINUM ON COMPETITIVE ADSORPTION OF POTASSIUM AND ALUMINUM BY EXPANSIBLE PHYLLOSILICATES

Abstract

ABSTRACT The competitive adsorption of K and Al on montmorillonite and vermiculite as influenced by the degree of hydrolysis and polymerization of solution Al was examined. The Na-saturated minerals (0.2–2μ) were suspended in the hydroxy-Al solutions of basicites (OH/Al molar ratios) of 0, 0.5, 1.0, 1.5, 2.0, and 2.5 in the presence of a fixed concentration of K, and the suspensions were then equilibrated at 25 ± 0.2°C. Compared to Al, K became more competitive for the exchange sites in vermiculite with the increase in initial basicity of solution Al, and the reverse trend was true for montmorillonite. The more unrestricted Z-axis expansibility of montmorillonite favors the diffusion of a given size polymer in the interlayer space; thus the hydroxy-Al ions with higher charge are more competitive than K. In the case of vermiculite, the limited expansibility, the presence of wedge zones, the charge and size of the hydroxy-Al ions, and the presence of strongly competing K ions greatly hinder the adsorption of Al over K as the degree of hydrolysis of Al increases. The products of adsorption were found to vary significantly with the mineral and initial basicity. With the increase in the initial basicity, an increasingly ordered micalike mineral was formed from vermiculite. It is evident that the degree of hydrolysis and polymerization of solution Al greatly affects the adsorption of K and Al by 2:1 expansible phyllosilicates, and would thus affect the competitive formation of micalike minerals and Al interlayers of expansible phyllosilicates in soils and sediments.