抄録
The amount of negative charge (CEC) of allophane increased markedly after the organic compounds adsorption (in NaCl with total [Na+] =10mM), except for acetate, while the positive charge decreased significantly for all cases. The CEC of allophane treated by oxalate at initial pH4 was higher than that treated by citrate and acetate. At higher pH, citrate caused increase in CEC more than oxalate and acetate. Because the oxalate adsorbed in binuclear form, increase in the CEC was just through creating the new negative charge on silanol groups. Whereas, citrate adsorbed on allophane in bidendate form, so increase in CEC of allophane-citrate complex may includes negative charge carried by citrate itself. The change in surface charges was divided into two factors: effect of increase in pH and net effect of the organic compounds adsorption. The value of net CEC change tended to decrease with increasing the equilibrium pH. This resulted from decrease in the amount of the OC adsorption with increasing the pH. Based on the H (heat of formation) value, the inductive power of the three organic anions in accelerating deprotonation on silanol groups was estimated as oxalate>citrate>acetate.
