This is to ensure perfect
mixing and at the same time preventing any losses of oil to
the sludge. After strong agitation, it was then left under a controlled
temperature of 30 C for 24 h to allow extraction–flocculation.
After that, solvent-oil solution was separated from
sludge by filtration. The sludge was dispersed twice with the
same solvent to extract any remaining oil. The sludge was then
dried till constant weight at 105 C (WDry).