ADSORPTION OF Cu(II) BY ALLOPHANE AS AFFECTED BY PHOSPHATE

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Abstract
The influence of orthophosphate on chemisorption of copper by natural and synthetic allophanes has been studied at several levels of copper and phosphate adsorption. Though Cu adsorption on allophane was found to have no apparent effect on simultaneous or subsequent adsorption of PO4 and was ineffective in desorbing PO4, phosphate adsorption at moderately high levels (500 mmole/kg) enhanced Cu retention regardless of the sequence of Cu and PO4 adsorption. Phosphate was incapable of desorbing surface-bound Cu, and higher PO4 concentrations actually reduced the exchangeability of Cu. Electron spin resonance (ESR) studies of Cu retained by allophanes suggested that Cu remained bonded to surface AlOH groups whether or not phosphate was present. Comparative ESR studies with Cu adsorbed on and coprecipitated in pure solid phosphates indicated that PO4 may not coordinate strongly with Cu. A mechanism for enhanced Cu retention on allophanes and oxides is proposed in which phosphate coordinates to the axial position of a surface-bound Cu ion, thereby producing a ternary surface complex. © Williams & Wilkins 1985. All Rights Reserved.