The interaction of montmorillonite and fulvic acid has been studied at various values of pH and 1 : 1 electrolyte concentrations. The fulvic acid was prepared from gallic acid by heterogeneous catalysis. The amounts adsorbed were determined from the decrease in solute concentration. The adsorption of fulvic acid on H-montmorillonite at pH of about 2.8 is higher than that of Na-fulvate on Na-montmorillonite at pH of about 7.5 in electrolyte-free systems. At low pH, a small amount of NaCl (10 or 20 mmol dm-3) had virtually the same effect on interaction as an amount of 200 or 500 mmol dm-3 at alkaline pH. The combined effect of the pH and NaCl was interpreted by calculating the surface charge, the potential, and the interaction energy of montmorillonite and humic substance particles by a simple model including the assumption of two widely different, intrinsic dissociation constants of the fulvic acid.
ASJC Scopus subject areas
- Geochemistry and Petrology