Adsorptive Interaction Studies of Aqueous Carboxylic Acids with Smectites, Kaolin and their Li-Exchanged Forms

Commercial smectites (montmorillonite, hectorite and bentonite) and kaolin clays were purified by fractionated sedimentation with fraction 2 μm particle size and their Li-exchanged forms were prepared by cation exchange method and characterized by XRD and SEM techniques. The XRD Patterns confirmed the purity and crystalline nature and SEM images indicated the particle sizes and morphologies of the materials investigated. Gels of smectites are formed when concentrations are greater than ~ 2 % by weight in deionized water. The effects of adsorptive interactions of aqueous carboxylic acids (HCOOH, CH3COOH and CH3CH2COOH) 20 % (V/ V, 10mL) were examined refractometrically using 0.05g of each clay sample in 14mL vials at room temperature. The experimental results proved that hectorite i.e., trioctahedral magnesium smectite showed preferential adsorption of water from aqueous phase of carboxylic acids. Smectites (0.5 %)expanded and changed into jelly-like forms and kaolin formed a swollen paste in the aqueouscarboxylic acids in vials. The sizes of the cylindrical shaped jells of smectites formed depend on thelayer charge density, location of charge, size of carboxylic acid and nature of the interlayer cationand its hydration properties, were in the following order. Li-montmorillonite Na, Ca-montmorillonite Na-bentonite Li-bentonite ≥ Na-hectorite ≈ Lihectorite. It was also observed that the cylindrical shaped jells of the clays formed were largest in the aqueous propionic acid. The 0.5 % by weight of commercial clays formed slurries while pure clays changed to suspensions in deionized water in vials under similar conditions. The interactions of the water and carboxylic acids with the interlayer cations and the exposed smectite clay surface are responsible for the swelling due to the expansions of the interlayers from its dry state.