Copper(II) Complexation by Fulvic Acid Extracted From Sewage Sludge as Influenced by Nitrate Versus Perchlorate Background Ionic Media

Abstract

AbstractThe possible adverse effect of CuNO3+ ion pairs on studies of the complexes formed between Cu(II) and fulvic acid extracted from sewage sludge was investigated by potentiometric titration of 2 × 10−3M K/H fulvate with Cu(NO3)2 and Cu(C104)2, at pH 5 and 25°C, in ionic media of 0.1M KNO3 or KC104, respectively. It was shown that the degree of complexation of Cu2+ in the NO3 medium was always significantly greater than that in the C104 medium for total Cu concentrations in the range 10−4M to 10−2M. This result was interpreted as evidence for significant concentrations of CuNO3+ ion pairs and mixed CuNO3‐fulvate complexes in the NO3 medium. Further support for the existence of CuNO3+ in the NO3 medium was obtained through a successful calculation of the thermodynamic stability constant for this ion pair that employed data from blank titrations with Cu(NO3)2 and Cu(ClO4)2. It was concluded that ClO4 ionic media should be used instead of NO3 ionic media in studies of Cu(II) complexation with the functional groups of fulvic acid.