The effect of organic cosolvent and solute–solvent interaction on the solubility of oil residue in Niger Delta soil

Abstract

The solubility of crude oil residue in contaminated soil ( $$ \log S_{\text{s}} $$ ) from six locations in the Niger Delta region of Nigeria in solvent has been determined by batch desorption technique using various fractions of water:methanol cosolvent mixtures (0, 0.2, 0.4, 0.6, and 1.0) and 100% (v/v) of four organic solvents (ethanol, dichloromethane, chloroform, and hexane). Data obtained from the experiment were applied to the solvophobic theory to evaluate the relationship between the solubility of the crude oil residue, solvent polarity, and the age of oil residue in the spilled site. Differences were observed between calculated and experimental values of solubility of oil residue in water ( $$ \log S_{\text{w}} $$ ) obtained for both old and younger oil residue, with higher values obtained for oil residue older than 5 years. Linear solvation energy relationship (LSER) using multiple-linear regression showed that the polarizability of the solvent (SP) was responsible for solute–solvent interaction. This ultimately leads to increased solubility of oil residue in the cosolvent ( $$ \log S_{\text{s}} $$ ) and dissolution of hydrophobic solute in water. Differences in Alip/Pol ratio between samples were attributed to the effect of aging on the oil residues. The correlated parameters allow an explanation of the main factors to consider when implementing the best technical option for crude oil-contaminated soil remediation by soil washing.