Mineralogical and chemical characterization of Joule heated soil contaminated by ceramics industry sludge with high Pb contents

Abstract

This research deals with the first attempt to vitrify by a Joule heating process soils contaminated by Pb (2.85 wt.%) from ceramic industry sludges.Physical, mineralogical, and chemical characterization of the glasses were obtained by using several imaging and analytical techniques, namely Scanning Electron Microscopy (SEM) with coupled Energy Dispersive Spectroscopy (EDS), X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF) and by a specifically built-in sensor for “in-situ” temperature measurements of the melt. The chemical stability of the glass produced by the process was determined by leaching tests.The progressive heating and successive melting of the soil led to decomposition of organic compounds and removal of volatile metals. The cooling of the melt formed a monolithic glass with the aim of immobilizing the heavy metals and inorganic contaminants.All the glasses were found, on a macroscopic scale, mineralogically, chemically and morphologically homogeneous independent of the starting composition. However, on a microscopic scale an inhomogeneous glass matrix was observed. SEM-EDS and XRD revealed the presence of micro-sized Pb particles and Zr2SiO4 (zircon) crystals. In agreement with the microscopical observations, leaching tests indicated high leaching behaviour for Pb.These results should be considered as a general study of the technological effectiveness of vitrification by Joule heating technology with a view to scaling up the process on a field scale and to the treatment of large amount of inorganic industrial wastes containing high amounts of Pb.