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µ-XANES AND µ-XRF INVESTIGATIONS OF METAL BINDING MECHANISMS IN BIOSOLIDS
Citation:
Hettiarachchi**, G. M., K G. Scheckel*, J A. Ryan, S. R. Sutton, AND M. Newville. µ-XANES AND µ-XRF INVESTIGATIONS OF METAL BINDING MECHANISMS IN BIOSOLIDS. G. M. Pierzynski (ed.), JOURNAL OF ENVIRONMENTAL QUALITY. ASA, CSSA, SSSA, Madison, WI, 35(1):342-351, (2006).
Description:
Micro-X-ray fluorescence (µ-XRF) microprobe analysis and micro-X-ray absorption near edge spectroscopy (µ-XANES) were employed to identify Fe and Mn phases and their association with selected toxic elements in two biosolids (limed composted and Nu-Earth) containing low and very high levels of Cd, before (intact) and after OC removal treatment. Elemental correlations derived from elemental mapping showed strong correlations between Fe with Cd, Cr, Pb, or Zn (r2 from 0.65 to 0.92) before and after removal of OC. Observed strong correlation between Fe and Cu disappeared after OC removal suggesting that Cu was possibly associated with OC coatings that may have been present on Fe compounds. Lack of correlations observed between Mn and other elements (except for Fe and Cr) in the intact sample was possibly due to the low concentration of Mn in the tested samples. Correlations of other elements with Mn were improved after removal of OC from the system indicating that OC removal treatment has had some effects on Mn as well as on some other elements. The Fe µ-XANES spectra of the intact biosolids sample showed that every point had varying mixtures of Fe (II and III) species and no two points were identical. This lack of uniformity in Fe species in the biosolids sample illustrates the complexity of these materials and the futility of studying them using conventional analytical tools and/or chemical extraction techniques. Moreover, these microscopic observations support previous laboratory and field data and provide direct evidence to support the hypothesis that Fe (and possibly Mn) plays a major role in retention of environmentally important trace elements in biosolids. This could be due to coprecipitation of these elements with Fe, adsorption of these elements onto Fe compounds, or combination of both of those mechanisms.