calculation from literature values with standard SSA and SSD at ionic strength of 1M, log K for pHzpc 8.4-8.6 in brackets for pHzpc 9-9.5 »Fe-O<1-> + NH4<1+> = »Fe-O-NH4 logK = 12.6 (12.3) »Fe-OH = »Fe-O<1-> + H<1+> pK2 = -logK = 12.3 sum »Fe-OH + NH4<1+> = »Fe-O-NH4 + H<1+> logK=12.6(12.3)-12.3 = 0.3(-0)