Open AccessEnergy and environmental research emphasizing low-rank coal: Task 1.7, Hot-water extraction of nonpolar organic pollutants from soils
Author(s) -
S.B. Hawthorne
Publication year - 1995
Language(s) - English
Resource type - Reports
DOI - 10.2172/206858
Subject(s) - extraction (chemistry) , supercritical fluid , chemistry , bar (unit) , soil water , pollutant , supercritical fluid extraction , solubility , wastewater , environmental chemistry , analytical chemistry (journal) , chromatography , environmental engineering , organic chemistry , environmental science , soil science , physics , meteorology
Supercritical water extraction of organic pollutants from solids is extremely effective because supercritical water has a low dielectric constant and can, therefore, efficiently solvate organics. However, the decrease in the dielectric constant of water can be achieved at much milder conditions (pressures of a few bar and temperatures of ca. 200{degrees}{minus}250{degrees}C) than the conditions used for supercritical water (pressure > 221 bar and temperature > 374{degrees}C) extractions. Polycyclic aromatic hydrocarbons (PAHs) were extracted from a highly contaminated soil using using water at temperatures ranging from 50{degrees} to 400{degrees}C, and pressures from 5 to 600 bar. Most PAHs could not be extracted at 50{degrees}C but were completely removed at a temperature of 250{degrees}C. Additional increases to 300{degrees}C (still subcritical conditions) and 400{degrees}C (supercritical water) did not increase the recoveries significantly. The removal of PAHs had very little dependence on pressure when the temperature was 250{degrees}C, except that steam extraction (at 5 bar) yielded lower recoveries than the liquid water extractions (at 50, 350, and 600 bar). Therefore, the optimal conditions for extracting PAHs using water were 50 bar and 250{degrees}C (hot water). Based on the extraction rates obtained for several of the PAHs, the solubility of high molecular weight PAHs increased at least several thousandfold by increasing the water temperature to 200{degrees}{minus}300{degrees}C. Polychlorinated biphenyls (PCBs) were extracted from an industry soil and a sediment using hot-water (subcritical) extraction at 50 bar and 250{degrees}C. The high removal efficiencies of PCBs from soil and sediment agree very well with those obtained for PAHs from highly contaminated soil at the same extraction conditions, demonstrating that water is a potentially useful extraction solvent for many organics