Adsorption of Dextrin and Guar Gum onto Talc. A Comparative Study

Abstract

The interaction of guar gum and dextrin with talc has been investigated through adsorption, flotation, and electrokinetic measurements. The adsorption densities are independent of pH and the isotherms exhibit Langmuirian behavior. Higher adsorption density of guar gum onto talc is observed vis-à-vis that of dextrin. Pretreatment of talc with a complexing agent such as ethylenediaminetetraacetate results in a decrease in the adsorption density, highlighting the importance of metallic magnesium sites for the adsorption process. The adsorption density of guar gum is decreased when the talc sample is subjected to leaching and/or calcination attesting to the contribution of metallic sites and brucite structure in enhancing the adsorption process. An increase in the surface face-to-edge ratio leads to increase in adsorption density. The flotation recoveries are independent of pH, with the guar gum exhibiting better depressant ability compared to dextrin, complementing the adsorption results. However, polymer depressant ability is reduced in the case of leached or calcined talc sample in comparison to that on talc. Electrokinetic measurements portray conformational rearrangements of macromolecules with the loading, resulting in the shift of the shear plane, further away from the interface. Coprecipitation, conductance, and viscosity tests confirm polymer−magnesium ion interaction in the bulk solution. The adsorption process is governed by hydrogen bonding as well as chemical interaction between the polysaccharides and the surface metal hydroxide groups of talc. The better depressant activity of guar gum may be attributed to its more favorable cis-configuration of the hydroxyl groups as opposed to the trans-hydroxyl groups of dextrin, apart from its higher molecular weight.