Tracking the magnetic carriers of heavy metals in contaminated soils based on X-ray microprobe techniques and wavelet transformation.

Technogenic magnetic particles (TMPs) from industrial activities are major contamination sources of soils and dusts because they usually carry large amounts of heavy metals. The understanding of the association between TMPs and heavy metals in contaminated soils helps to trace the polluting sources and probing into the mechanism of magnetic phases enriched with heavy metals. In this study, we tracked the magnetic carries of heavy metals from different emission sources in steel industrial regions by using the synchrotron-based probe techniques and multiscale analytical methods. The μ-XRF mapping showed that TMPs contained various heavy metals, depending on their sources. The Fe K-edge μ-XANES revealed that the ferroalloy, pyrrhotite and TMPs in steel slag and coal ash were major magnetic phases in contaminated soils. Their relative content varied differently at the microscale. The multiscale analysis revealed that the heavy metals associated with magnetic phases exhibited pronounced scale dependence, depending on the size, type, and assemblage of different magnetic phases. Multiscale source apportionment revealed that the contamination sources varied differently at multiple scales. Heatmap analysis revealed that at 8-μm scale, Co, Cr, Cu and Mn were mainly derived from ferroalloy, while Ti, Zn and As from both ferroalloy and TMPs from coal ash.