抄録
The adsorption of sulfate and nitrate on two allophane samples, with high and low Si/Al ratio, was found to decrease with increasing pH. The highest adsorption of sulfate and nitrate was obtained at initial pH 3 for both the allophane samples. No adsorption of nitrate was observed at equilibrium pH above 7, however, sulfate was still adsorbed. The strong adsorption of sulfate at pH about below 7 could be attributed to ligand exchange reaction, whereas nitrate was non-specifically adsorbed throughout the pH examined. Allophane sample with low Si/Al ratio or KyP adsorbed more sulfate and nitrate than with the high Si/Al ratio sample or KnP. This is because KyP has high aluminol groups (Al-OH, Al-OH2) per unit mass than KnP. The aluminol groups are believed to be responsible for the adsorption of sulfate and nitrate on nano-ball allophane. Both sulfate and nitrate adsorption results showed a better fitness with the Freundlich adsorption equation with sulfate having a higher k and n values as compared to nitrate which implies that sulfate was strongly adsorbed on nano-ball allophane as compared to nitrate.
