Catalytic degradation of PNP and stabilization/solidification of Cd simultaneously in soil using microwave-assisted Fe-bearing attapulgite

A novel Fe-bearing attapulgite (Fe/ATP) as microwave (MW) absorber, cadmium (Cd) stabilizer and active catalyst to simultaneously stabilize/solidify Cd and oxidize p-nitrophenol (PNP) in soil was reported. The toxicity characteristic leaching procedure tests showed 80% of Cd was successfully stabilized in soil with Fe/ATP addition, whereas Cd stabilization efficiency of 99.3% was successfully achieved in MW-assisted Fe/ATP system. In addition, the long-term stabilization efficiency of Cd (180-day of curing) increased about 2-fold in MW-assisted Fe/ATP system compared with Fe/ATP system. XRD, FTIR, and XPS studies showed that Cd was more mineral-integrated than surface-bound with Fe/ATP, and a part of the stabilized Cd in Fe/ATP transformed into ferrite or encapsulated in vitrification with MW irradiation. Fe/ATP also showed extremely high catalytic performance for PNP oxidation, achieving complete PNP removal from soil within 20 min of MW irradiation. The enhancements of Cd stabilization and PNP removal were attributed to the “hot spots” effect on the Fe/ATP surface with MW excitation. In addition, active species (holes, OH, and O2−) generated from the redox of Fe2+-Fe3+ species were responsible for the PNP degradation. The use of Fe/ATP to catalytic oxidize PNP and stabilize/solidify Cd under MW irradiation was demonstrated to be an effective method for rapid remediation of organic-heavy metal co-contaminated soil.