It is well established that natural organic acids, which are ubiquitous in soil systems, alter the surface reactivity of metal oxides thereby modifying the ability of trace elements to adsorb onto the surface of the oxide.  Understanding the influence of organic acids on the adsorption of trace elements to oxide particles is thus key to building accurate predictive transport models.  In our research we utilize wet chemical techniques with synchrotron-based X-ray approaches, Fourier transform infrared  analysis and computational chemistry, to examine the effect a suite of organic acids have to the adsorption tendencies of lead(II) onto the surface of hematite and to characterize the bound structures.  The results indicate for structurally understood acids such as citric acid and phthalic acid that slight differences in their molecular structures are manifest in quite different adsorbed lead structures.  For example, lead adsorption to hematite in the presence of citric acid was dominated by outer-sphere coordination of citrate-chelated lead whereas lead coordination to the same surface in the presence of phthalate was only minimally perturbed.  For fulvic acid, the results suggest that the lead is predominantly held in an outer sphere complex similar to citric acid, while the humic acid complexed lead include both inner and outer sphere complexes.  The results of these studies provide needed insight into the role of organic acids on lead adsorption to oxide surfaces and can be used to develop improved parameters for reactive transport models to increase the accuracy of site characterizations and the effectiveness of the resulting remediation.

Lead (II) coordination to hematite in the presence of naturally-occurring organic acids

247th National Meeting (2014)

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