Mechanochemical approach to remove phenanthrene from a contaminated soil.

Soil samples collected from a cultivated soil of Southern Italy after artificial contamination with phenanthrene (PHE) were ground in a ball mill and compared with spiked (via acetone) sample as control. The mechanochemical treatment was also applied to a simple binary system birnessite (delta-MnO(2))-PHE and to soil added with birnessite to evaluate the oxide role in removing the contaminant. Different extraction methods, such as Soxhlet, sonication, and desorption from resin beads were adopted to estimate the residual PHE analysed with HPLC. X-ray diffraction and TG-DTA analyses were performed to quantify mineralogical phases in soil and their possible modifications after grinding. The results showed that the grinding was more efficient in removal of PHE when the pollutant was in solid phase ( approximately 50% of removal) than when it was spiked via acetone in the same soil ( approximately 20% of removal). Addition of birnessite to soil did not change significantly the removal of PHE through time. Independently of the extraction methods used, the PHE recovered after the mechanochemical treatment in the presence of solid PHE was always lower, suggesting a higher efficiency of such a treatment in degrading PHE or forming bound residues in its original or transformed form. X-ray powder diffraction of milled solid PHE showed that order-disorder phase transition occurred in solid phenanthrene as consequence of the mechanochemical treatment. X-ray diffractometry and TG-DTA analyses were crucial in evidencing that interaction between PHE and birnessite occurred.

Mechanochemical removal of organo-chlorinated compounds by inorganic components of soil.

The purpose of this work is to evaluate the catalytic efficiency of two metal oxides, ferrihydrite and birnessite and of a ferruginous smectite, towards organic molecules such as 4-chloroaniline (4-CA), pentachlorophenol (PCP), and five polychlorinated biphenyls (PCBs) characterised by different number and position of chlorine atoms. Mechanochemical dry contacts with light grinding between catalytic surfaces and pollutants have been carried out. The efficiency of the mechanochemical removal was compared with batch experiments for the soluble compounds (PCP and 4-CA). The removal of 4-CA and PCP by the mechanochemical procedure resulted more effective than by batch contact in the presence of birnessite and ferrihydrite, particularly at higher pH (100% removal of 4-CA by birnessite in 30 min at pH 8.6 after the mechanochemical contact compared to 20% removal using the batch interaction at the same pH). The mechanochemical contact of PCBs and birnessite produced a removal of pollutant that was a function of the number of chlorine atoms (complete removal of 2,2'-dichlorobiphenyl in 10 days and a removal of 30% and 20% of 2',3,4-trichlorobiphenyl and 3,3',4,4'-tetrachlorobiphenyl, respectively in 90 days) and of the position of chlorine atoms about the biphenyl rings (100% of 2,2'-dichlorobiphenyl in 10 days, 84% of 3,3'-dichlorobiphenyl in 15 days and 40% of 4,4'-dichlorobiphenyl in 27 days).