ADSORPTION OF BENZOIC-ACID ON ALPHA-ALUMINA AND GAMMA-BOEHMITE

The adsorption of benzoic acid (BzCOOH) on alpha-alumina (alpha-Al2O3) and gamma-boehmite (gamma-AlOOH) from the aqueous phase has been studied. The adsorption experiments were carried out in 0 and 0.1 M NaCl solutions, with pH adjusted to 4 or 6. For both alpha-alumina and gamma-boehmite, increasing ionic strength decreases the maximum adsorption. Increasing the pH to 6 at the same ionic strength also reduces the maximum adsorption markedly. This suggests that both the anion and the corresponding acid participate in the adsorption process. The results show that benzoic acid has a greater affinity for alpha-alumina than for gamma-boehmite. Under the same experimental conditions (0.1 M NaCl, pH 4) the maximum adsorption capacities are 5.0 and 1.5 mumol/m2 for alpha-alumina and gamma-boehmite, respectively. This difference in adsorption capacities is probably due to the mineralogical difference. These results illustrate the importance of knowing the mineralogical composition of the solid phase. (C) 1994 Academic Press, Inc.