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Isolation and purifications treatments change the metal binding properties of humic acids: effect of the HF/HCl treatment
We studied the changes in metal binding characteristics of the extracted humic acids induced by the HF/HCl treatment followed by dialysis, i.e. the last step of the IHSS extraction protocol. We performed metal binding experiments with both the alkaline extracted material (AE) and the fully purified humic acid (FP) using the electrochemical stripping technique (AGNES) and modeled the results using the NICA-Donnan model. The results showed an increase of free Zn, Cd and Pb concentrations of ca. 1 order of magnitude for the AE, as compared to the FP. These differences may be mostly explained by the different carbon content (51.3% FP and 36.5% AE) allied to a carboxyl ratio AE/FP of 0.5. Simulations using the NICA-Donnan model showed that the halving of the amount of carboxylic groups (Qmax,1) for the FP reduced this difference to 0.25 log units for Cd and Zn and to 0.15 log unit for Pb. There is a clear need for further research on the differences between purified vs. less disturbed natural organic material, which will contribute to improved modeling of metal binding to organic matter in soils, hence providing a basis for a more realistic risk assessment.
EN17129 Accepted 08 September 2017
© CSIRO 2017