Methods of Determining Lead Speciation in Fly Ash by X-ray Absorption Fine-Structure Spectroscopy and a Sequential Extraction Procedure

Abstract

Understanding the chemical state of lead in fly ash generated from a waste thermal treatment is important, since the toxicity and solubility of the element depends on its chemical state. This study identified three potential methods for obtaining quantitative information regarding the chemical state of lead in fly ash: X-ray absorption near edge structure (XANES) analysis, extended X-ray absorption fine structure (EXAFS) analysis, and the sequential extraction procedure. The result of this procedure was strongly affected by the pH and sample matrix, and did not necessarily accurately reflect the chemical state. It was difficult to quantitatively examine the chemical species using only EXAFS. However, an XANES fitting enabled direct quantification of the chemical species. An XANES analysis showed that PbSiO3, PbCl2, or Pb2O(OH)2 was the predominant chemical species in fly ash. We concluded that multiple analyses should be compared multilaterally to improve the accuracy of the final analysis.