The chemistry of heavy metals in digested sewage sludge i. copper ii complexation with soluble organic matter
Fletcher, P.; Beckett, P.H.T.
Water Research 21(10): 1153-1162
Characteristics of copper-binding, in the soluble fraction of a digested sewage sludge, were determined using ion-selective electrodes. Results showed that ion exchange with protons is a principal component in copper binding and that the soluble organic matter has a cation exchange capacity of 8.86 m-equiv g-1 at pH 6.5. A pH-dependent exchange constant, defined in terms of mole fractions of exchange components, describes the data in the pH range 2-8 and is independent of both pH and the extent of exchange in the range 5.5-8. Supplementary data include acid/base titration curves and simple kinetic measurements. Anion uptake is insignificant in the pH range 2.5-7. A model of the aqueous phase of a sewage sludge, containing soluble organic matter with only copper and protons as competing ions, predicts that at pH 7 over 99% of the copper present will be bound to the soluble organic matter.