Calorimetric and other interaction studies on mineral-starch adsorption systems

Abstract

Studies have been made on adsorbabilities of starch, phosphorylated starch and starch constituents - amylose and amylopectin - on hematite and also calcite. The adsorption process is slow, partially irreversible, non-physical and appreciably exothermic. For a small starch concentration, ΔH on hematite reaches a maximum of 314 J/g starch adsorbed, and then falls off at higher concentration, probably due to partial deanchorage and reorientation of adsorbed molecules initially lying flat on the surface. Adsorption isotherm patterns, including pH-dependence behaviour, are similar for starch and amylopectin. The magnitude of adsorption of amylose, compared to that of amylopectin (nearly 20 times bulkier), is larger on a molar basis but smaller on a g/cm² basis. Thus, interpretation of calcite-starch adsorption data should be made in terms of amylose as well as amylopectin. For the hematite-starch system, adsorption of amylopectin is of crucial importance. Conductometric data and IR spectrograms point to specific chemical interactions between starch constituents and ions such as Fe²⁺ and Ca²⁺. These are evidence of the existence of chemisorption bonds of amylose as well as of amylopectin interacting on calcite and hematite surfaces.