Pentachlorophenol sorption by variable-charge soils in methanol-water mixture: pH effect at the low solvent volume fraction.
Information on how cosolvents affect sorption of ionizable chemicals by soils with heterogeneous variable-charge mineral surface domains is sparse. In this study, the effect of soil-solution pH in methanol/water solutions on sorption of pentachlorophenol (PCP) by variable-charge soils with a range of hydrophilic (f Hphilic) and hydrophobic (f Hphobic) sorption domains was characterized. PCP sorption by 10 variable-charge soils was measured as a function of apparent pH (pH app) and methanol volume fraction (fc<or=0.6). Sorption data of both neutral (pH app<3) and anionic PCP (pH app>8) decreased log-linearly with increasing fc, but the slope of the relationship was less for anionic PCP. The empirical solvent-sorbent interaction term for anionic PCP (alpha i) was inversely correlated with f Hphilic (r2=0.82), which is consistent with methanol-induced increases in anion exchange. For neutral PCP, the empirical term (alpha n) was positively correlated with f Hphobic (r2=0.84), supporting methanol-induced increases in solution and sorbent hydrophobicity. Sorption of PCP by two soils with varying f Hphilic in the pH app range from 3 to 8 at fc<or=0.5 was well predicted using a cosolvency model. The model included only pH app-pK'a dependent speciation and the different intrinsic hydrophobic partitioning of neutral and anionic PCP without explicitly incorporating the contribution of f Hphilic. Therefore, although the degree to which methanol affects sorptivity of the two PCP species differs with sorption domain types, incorporating both cosolvent-enhanced solubility and cosolvent-induced speciation is sufficient to adequately predict the overall sorption on variable-charge soils.
Hyun
Seunghun
S
Division of Environmental Science and Ecological Engineering, Korea University, Seoul 136-713, Republic of Korea. soilhyun@korea.ac.kr
Lee
Linda S
LS
D000327:Adsorption; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D000432:Methanol / Q000737:chemistry*; D008956:Models, Chemical; D010416:Pentachlorophenol / Q000737:chemistry*; D012987:Soil; D012989:Soil Pollutants / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D014867:Water / Q000737:chemistry*
D012987:Soil; D012989:Soil Pollutants; D012997:Solvents; D014867:Water; D010416:Pentachlorophenol; D000432:Methanol