Remarkable enrichment of heavy metals in baghouse filter dust during direct-fired thermal desorption of contaminated soil.

This study focuses on the widely applied technology of direct-fired thermal desorption, taking a site contaminated by polycyclic aromatic hydrocarbons (PAHs) as a typical test case. The entire thermal desorption process of contaminated soil is considered in the analysis. The concentration levels and occurrence characteristics of heavy metals in dust traditionally considered to be clean are evaluated, and possible secondary pollution and environmental impacts are explored. The results indicate that, compared with the thermal desorption soil, the dust samples generated in the baghouse filter during the ex situ direct-fired thermal desorption process have higher amounts of heavy metal accumulation as well as altered speciation. In addition, the enrichment characteristics and origins of the heavy metals are analyzed according to the process flow and particle size composition as well as the results of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron probe microanalysis (EPMA), and other microscopic research methods. Phenomenon further reveals enrichment of arsenic (As), nickel (Ni), and chromium (Cr). The findings of this study can provide a scientific basis for the proper disposal and risk management of the dust collected after direct-fired thermal desorption treatment of contaminated soil.