2.2. Kinetic model
Mass transfer kinetic model was used to represent the experiment
data because of there is no reaction between the oil and
the solvents, hexane and petroleum ether (Liauw et al., 2008).
Assumption is made that the main mechanism which controls
the rate of extraction of oil is mass transfer of oil from the waste
(solid) to the solvent (liquid). This assumption is in accordance
with other findings (Amin et al., 2010; Saxena et al., 2011). Mass
transfer rate can be written as (Liauw et al., 2008)