SORPTION OF NONIONIC, HYDROPHOBIC ORGANIC-CHEMICALS TO MINERAL SURFACES

Equilibrium sorption coefficients (K-d) Of a series of polycyclic arom atic hydrocarbons (PAHs) and chlorobenzenes were measured on the pure mineral oxides alpha-Al2O3 and alpha-Fe2O3 using column chromatography . Sorbent surface area did not account for differences in the measured distribution coefficients (K-d) for a given compound on alpha-Fe2O3 a nd alpha-Al2O3. This observation indicates that the type of mineral su rface is important in the sorption of nonionic, hydrophobic organic ch emicals (HOCs). On both minerals, sorption was reversible as sorption isotherms of the PAHs were linear to at least 50% of solute aqueous so lubility and the measured enthalpy of sorption similar to the compound s negative enthalpy of dissolution. Solution pH and the sign and magni tude of sorbent surface charge did not affect sorption, nor did a fact or 50 change in ionic strength. The relationship between K-d and the a queous activity coefficient, gamma(sat)(w), was log K-d = 0.70 log gam ma(sat)(w) + -10.68R(2) = 0.94 on alpha-Al2O3 and log K-d = 0.98 log g amma(sat)(w) + -11.39R(2) = 0.92 on alpha-Fe2O3 for the PAHs, chlorobe nzenes, and biphenyl. Our observations support the hypothesis that non ionic, HOCs interact weakly and nonspecifically with mineral surfaces. For the sorption of PAHs to mineral surfaces containing organic matte r, the mineral contribution to K-d should become significant at values below log f(oc) = -4.43 to -4.00 for alpha-Al2O3 and log f(oc) = -4.3 3 to -3.46 on alpha-Fe2O3.