Separation of coal‐tar constituents from soil particles in a two‐liquid‐phase slurry system

Abstract

An evaluation has been made of the capability of rapeseed oil to dissolve polycyclic aromatic hydrocarbon (PAH) crystals in a biphasic system and of its capability to extract PAHs from polluted soil in a two‐liquid‐phase (TLP) slurry system. Up to 220 g l⁻¹ of the crystalline hydrocarbons could be dissolved in the organic phase, indicating oil/water‐partitioning coefficients of 10⁵. When soil from a former gasworks site was treated in a TLP slurry system, it was found that a certain critical amount of vegetable oil had to be added in order to form a free oil phase. Single and multiple extractions gave similar results for multiple short‐term and single long‐term treatments, with a maximum of 87% for pyrene release. Following a 30‐day bioslurry treatment, the total concentration of the 16 EPA PAHs in the soil decreased from 2740 mg kg‐¹ to 1366 mg kg⁻¹. This was followed by one of three different 12‐day post‐bioslurry treatments. Further bioslurry treatment reduced the final concentration to 1002 mg kg⁻¹. Abiotic treatment with a surfactant (Brij 30) achieved a reduction to 797 mg kg⁻¹. Treatment with rapeseed oil gave the best reduction to 343 mg kg⁻¹.

Keywords:

• PAH
• bioslurry
• vegetable oil
• gasworks site