High-pressure extraction of polychlorinated biphenyls from soils and other fine-grained solids

Four doped and three really contaminated samples were subjected to high-pressure PCB (polychlorinated biphenyl) extraction in a laboratory-scale experimental plant using CO2 (carbon dioxide) as solvent. The PCB levels (sum out of the six key substances) of the real samples were 2.6, 6.8, and 139 mg/kg. The success of the cleaning process was determined by measuring the residual PCB levels in the soil after the extraction. Parameters were varied and samples were taken selectively from various points in the bed (length 270 mm, diameter 14 mm, weighed - in soil 50-60 g) in order to gain an idea of the effects of upscaling. The following parameters were varied: extraction temperature 40-90 C; extraction pressure 200-300 bar; CO2 flow rate 3.6-14.6 g/min; CO2 quantity 0-328 g; degree of contamination (doped samples) 12-60 mg/kg; soil moisture 0-15%; particle size 0-2000 μm; entraining agent methanol, ethanol, acetone; proportion of entraining agent 0-7.5% by weight. Furthermore the influence of moisture at the time of doping on extraction was examined. (orig./ABI)