Surface chemical properties and selective flocculation studies on alumina and silica suspensions in the presence of xanthan gum

The changes in the surface chemical properties of alumina and silica suspensions consequent to the addition of xanthan gum were studied. The adsorption density of xanthan gum for alumina was found to be maximum at pH 2, whereas nil adsorption was found for silica throughout the pH investigated. The isoelectric points (i.e.p.) of alumina and silica were found to be located at pH 9.1 and presumably less than pH 2 respectively. The addition of xanthan gum shifted the i.e.p. of alumina towards more acidic pH values, in proportion with the concentration of xanthan gum added, with a concomitant change in the zeta potentials to more electronegative or less electropositive values. The addition of xanthan gum beyond a certain concentration (>50 ppm), increases the flocculation of alumina suspension to a higher value (∼92%), in the pH range of 2–9. The electrokinetic and flocculation characteristics of the silica were not altered much by the addition of xanthan gum, akin to the adsorption result. FTIR spectral investigations provide evidence in support of hydrogen bonding and chemical interaction forces between alumina and xanthan gum. Maximum separation efficiency of ∼93% for alumina-silica synthetic mixture was observed in selective flocculation tests.