Reduction, mineralization, and magnetic removal of chromium from soil by using a natural mineral composite.

Reductive immobilization has been a commonly used technique to detoxify Cr(VI) from soil; however, it's challenging to remove the reduced Cr from soil to prevent its re-oxidation. This work explored a natural magnetic composite for the remediation, mineralization, and magnetic removal of Cr(VI) from the soil. It consists of 77% magnetite and 23% pyrrhotite with strong magnetic properties. A series of characterization tests show that composites of magnetite and pyrrhotite are interlaced and closely bonded, and contain no other heavy metals. The Cr(VI) removal rate increases with the decrease in composite particle size. A kinetics study shows that removing Cr(VI) by the composite is likely through both adsorption and reduction. Acidic conditions are more favorable for the immobilization of Cr(VI), at 45.8 mg Cr(VI) removal per g of composite at pH 2. After 100 days of in-situ treatment by the composite, the leaching concentration (TCLP) of Cr(VI)-contaminated soil was 1.95 mg L-1, which was below the EPA limit (5 mg L-1) for hazardous waste. After reduction, the composite was separated from soil by magnetic characteristics, and 58.2% of Cr was found mineralized. The post-treatment Cr-containing composite was analyzed by SEM-EDS, Raman spectra, and XPS. It was found that Cr was mineralized on the surface of the composite in the form of Cr(OH)3, Cr2O3, and FeCr2O4. This indicates that reduction and mineralization of Cr(VI) in the soil can be accomplished through natural magnetic mineral composites and easily separated and removed from the soil, achieving a complete soil cleanup.

Selective catalytic degradation of a lignin model compound into phenol over transition metal sulfates.

Transition metal salts were employed as the catalysts to improve the selective degradation of the α-O-4 lignin model compound (benzyl phenyl ether (BPE)) in the solvothermal system. The results concluded that most of the transition metal salts could enhance BPE degradation. Among which, NiSO4·6H2O exhibited the highest performance on BPE degradation (90.8%) for 5 h and phenol selectivity (53%) for 4 h at 200 °C. In addition, the GC-MS analysis indicated that the intermediates during BPE degradation included a series of aromatic compounds, such as phenol, benzyl methyl ether and benzyl alcohol. Furthermore, the mechanisms for BPE degradation and phenol selectivity in the NiSO4·6H2O system involved the synergetic effects between the acid catalysis and coordination catalysis, which caused the effective and selective cleavage of the C-O bonds.