Evaluation of heavy metals in hazardous automobile shredder residue thermal residue and immobilization with novel nano-size calcium dispersed reagent

다국어 초록 (Multilingual Abstract)

<P><B>Abstract</B></P> <P>This study was conducted to synthesize and apply a nano-size calcium dispersed reagent as an immobilization material for heavy metal-contaminated automobile shredder residues (ASR) dust/thermal residues in dry condition. Simple mixing with a nanometallic Ca/CaO/PO<SUB>4</SUB> dispersion mixture immobilized 95–100% of heavy metals in ASR dust/thermal residues (including bottom ash, cavity ash, boiler and bag filter ash). The quantity of heavy metals leached from thermal residues after treatment by nanometallic Ca/CaO/PO<SUB>4</SUB> was lower than the Korean standard regulatory limit for hazardous waste landfills. The morphology and elemental composition of the nanometallic Ca/CaO-treated ASR residue were characterized by field emission scanning election microscopy combined with electron dispersive spectroscopy (FE-SEM/EDS). The results indicated that the amounts of heavy metals detectable on the ASR thermal residue surface decreased and the Ca/PO<SUB>4</SUB> mass percent increased. X-ray diffraction (XRD) pattern analysis indicated that the main fraction of enclosed/bound materials on ASR residue included Ca/PO<SUB>4</SUB>− associated crystalline complexes, and that immobile Ca/PO<SUB>4</SUB> salts remarkably inhibited the desorption of heavy metals from ASR residues. These results support the potential use of nanometallic Ca/CaO/PO<SUB>4</SUB> as a simple, suitable and highly efficient material for the gentle immobilization of heavy metals in hazardous ASR thermal residue in dry condition.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Nanometallic Ca/CaO/PO<SUB>4</SUB> for heavy metals immobilization in ASR residue. </LI> <LI> Heavy metals immobilization in dry condition attained about 95–100%. </LI> <LI> Remaining heavy metals were lower than the Korean standard regulatory limit. </LI> <LI> The amounts of heavy metals detectable on the ASR dust surface decreased. </LI> <LI> Nanometallic Ca/CaO/PO<SUB>4</SUB> has a promising potential for heavy metal remediation. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Schematic representation of possible mechanisms determining the heavy metals immobilization efficiencyof ASR dust/thermal residues after treatment with nanometallic Ca/CaO/PO<SUB>4</SUB>.</P> <P>[DISPLAY OMISSION]</P>