Quantification of metals in sewage sludges by X-ray spectrometry

Abstract
The application of sewage sludge on soils is a common practice, but the heavy metals should be determined before disposal. Sewage sludges composition is mainly organic and the amount of heavy metals is variable. Usual methods for heavy metals determination are based on dissolution of the sample. The results depend, partially, on the efficiency of the dissolution of the heavy metals, which may vary from sample to sample. We studied the feasibility of analyzing pressed pellets of sludges by wavelength dispersive X-ray fluorescence spectrometry (WD-XRF), with fumdamental parameters matrix effects correction. Several ways of introducing the carbon content in the corrections were tested. Accuracy was evaluated by analysis of four international certificate reference materials. Results were within or very close to the confidence interval of the available certified values for most elements (Al, As, Cr, Cu, Fe, Mn, Ni, Pb, S, Se, Si, V, Zn). Other metals, like Cd and Hg were below the detection limits (15 and 9 mg kg ^-l, respectively). Despite the limitation concerning the proper matrix correction, the uncertainty of the XRF results is probably similar to the methods normally used in sludge analysis, with the advantage that sample preparation is much faster.