Dual mechanochemical immobilization of heavy metals and decomposition of halogenated compounds in automobile shredder residue using a nano-sized metallic calcium reagent |
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Authors: | Mallampati Srinivasa Reddy Lee Byoung Ho Mitoma Yoshiharu Simion Cristian |
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Institution: | 1.Department of Civil and Environmental Engineering, University of Ulsan, Daehak-ro 93, Nam-gu, Ulsan, 680-749, Republic of Korea ;2.Department of Environmental Sciences, Prefectural University of Hiroshima, 562 Nanatsuka-Cho, Shobara City, Hiroshima, 727-0023, Japan ;3.Department of Organic Chemistry, Politehnica University of Bucharest, 060042, Bucharest, Romania ; |
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Abstract: | Simultaneous immobilization of heavy metals and decomposition of halogenated organic compounds in different fractions of automobile shredder residue (ASR) were achieved with a nano-sized metallic calcium through a 60-min ball milling treatment. Heavy metal (HM) immobilization and chlorinated/brominated compound (CBC) decomposition efficiencies both reached 90–100 %, after ball milling with nanometallic calcium/calcium oxide (Ca/CaO) dispersion, regardless of ASR particle size (1.0, 0.45–1.0, and 0.250 mm). Concentrations of leachable HMs substantially decreased to a level lower than the regulatory standard limits (Co and Cd 0.3 mg L?1; Cr 1.5 mg L?1; Fe, Pb, and Zn 3.0 mg L?1; Mn and Ni 1 mg L?1) proposed by the Korean hazardous waste elution standard regulatory threshold. Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) element maps/spectra showed that while the amounts of HMs and CBCs detectable in ASR significantly decreased, the calcium mass percentage increased. X-ray powder diffraction (XRD) patterns indicate that the main fraction of enclosed/bound materials on ASR includes Ca-associated crystalline complexes that remarkably inhibit HM desorption and simultaneously transform dangerous CBCs into harmless compounds. The use of a nanometallic Ca/CaO mixture in a mechanochemical process to treat hazardous ASR (dry conditions) is an innovative approach to remediate cross-contaminated residues with heavy metals and halogenated compounds. |
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