The adsorption and dispersing mechanisms of sodium lignosulfonate on Al2O3 particles in aqueous solution

The adsorption behavior and dispersion efficiency of sodium lignosulfonate (NaLS) on Al2O3 particles at different pH values were investigated by UV-Vis spectroscopy, zeta potential measurement, X-ray photo-electron spectroscopy, and viscosity measurements. The effects of the additives urea, Na2SO4, and NaCl were tested. At low pH values, NaLS adsorbed on the Al2O3 particles in the form of aggregates and at high pH values as separated single molecules. At pH 3-11, the adsorption was not affected through addition of urea, ruling out hydrogen bond as a controlling factor. By adding Na2SO4 and NaCl, the main driving force was the synergistic effect of the electrostatic interaction and the metal cation-pi interaction at pH < pH(IEP) (IEP, isoelectric point), whereas the metal cation-pi interaction was dominant at pH > pH(IEP). The dispersing mechanism was mainly attributed to the steric hindrance (at pH < pH(IEP)) and the electrostatic repulsive force (at pH > pH(IEP)) owing to the differences in the aggregation state of the adsorbed molecules.