Hydroxy-interlayers in expansible layer silicates and their relation to potassium fixation

Hydroxyaluminosilicate (HAS) and hydroxyaluminum (HyA) ionic solutions havi ng final Al concentrations ranging from 3.74 to 4.00 mM; NaOH/Al molar rati os of 1.0, 2.0 and 2.5; and Si/Al molar ratios of 0.00, 0.27-0.30, 0.51-0.5 6 and 0.95-1.01 were prepared through the interaction of AICl(3), orthosili cic acid and NaOH solutions. When these solutions reacted with <2 mu m size d vermiculite (Vt) and montmorillonite (Mt), varying amounts of Al and Si w ere fixed on Vt and Mt flays. Potassium fixation and exchange capacities of HyA/HAS (OH/Al = 1.0, 2.0 and 2.5)-Vt and HyA/HAS (OH/Al = 2.0)-Mt complex es were compared with those of untreated Vt and Mt at added K levels rangin g from 21 to 319 cmol(c) kg(-1). The untreated Vt clay showed K fixation as high as 94 cmol(c) kg(-1), in contrast to only 16 cmol(c) kg(-1) exchangea ble K. The unheated Mt fixed a maximum of 9 cmol(c) K kg(-1) out of a total K adsorption capacity of 67 cmol(c) kg(-1). In the HyA/HAS-Vt complexes, K fixation reduced drastically in comparison to unheated Vt, and ranged from 9 to 24 cmol(c) kg(-1) out of their total K adsorption capacities of 61 to 81 cmol(c) kg(-1). In the HyA/HAS-Mt complexes, too, the amount of K fixed reduced to a great extent in comparison to Mt and ranged from 1.48 to 1.84 cmol(c) kg(-1). Potassium became more exchangeable due to the presence of hydroxy-interlayers in the clays. The reduction in CEC and the well-known p ropping effects of hydroxy-cations' islands in the interlayers might have h indered K fixation by the complexes. The relationships of maximum K fixing capacities of the HyA/HAS-Vt complexes with the amounts of Al, Si and Al Si fixed on Vt were all exponential and negative. However, the amount of Al + Si or only Al fixed on Vt appeared to be the best indicator of K fixatio n capacities of hydroxy-interlayered Vt clay.