Abstract
Adsorption of zinc on two nano-ball allophane samples, namely one with low Si/ Al ratio (KyP) and one with high Si/Al ratio (KnP) was found to increase with increasing solution pH, with highest adsorption occurring at initial pH 7. The adsorption was found to be higher in the high Si/Al allophane sample (KnP) due to its relatively higher amount of silanol groups per unit mass. It seemed that the surface OH- groups bonded to Al and/or Si atoms in nano-ball allophane structure, particularly those ionised at higher pH, retain zinc very strongly. For most cases, the Langmuir and Freundlich parameters were found to increase with increasing initial solution pH. Adsorption of zinc by allophane sample (KnP) at initial pH 6-7 fi tted with Langmuir equation. All zinc adsorption data of low Si/Al ratio (KyP) sample conformed to the Freundlich model. From the observed changes in solution pH after zinc adsorption, reaction mechanism was proposed as release of H+into the bulk solutio
