Effect of Copper Adsorption on Some Charge Characteristics of Nano-Ball Allophane
Mechanisms of change in charge characteristics after copper adsorption on one low Si/Al (KyP) and one high Si/Al (KnP) nano-ball allophane samples were investigated. The CEC values of the two nano-ball allophane samples tended to decrease while AEC increased after copper species adsorption at the initial concentration of 1.60 mM. The change in charge characteristics of the allophane samples was governed by the pH, Cu2+, CuOH+ in the solution and amounts of adsorption. The decline in the CEC values after adsorption was due to the neutralization reactions between the monomeric Cu2+ with Si-O- or Al-O- functional groups. Molecular orbital calculations indicated that Cu2+ and CuOH+ could adsorb not only on the dissociated Si-O- but also with the undissociated Si-OH groups. When copper ion reacted with undissociated Si-OH groups, dissociation reaction of silanol groups accelerated. The Cu2+ ion has a possibility to accelerate the deprotonation of undissociated Si-OH groups near the adsorption sites. The decrease in change CEC values was found to be higher in case of a higher Si/Al ratio (KnP) than that for the lower Si/Al ratio (KyP) counterpart, due to it`s a higher adsorptive capacity for copper species. The slight increase in the AEC values after zinc adsorption was probably due to in part to the initial H+ ions released into the bulk solution.
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