Coagulation of oil in water using sawdust and bentonite and the formation of a floating coagulated material

The coagulation of oil in water is potentially cost-effective for removing oil from water. A coagulant consisting of sawdust (79.6% by volume), bentonite (15.8% by volume), and calcium hydroxide (4.7% by volume) gives coagulation efficiency of ≥94% and coagulation time of ≤45 s. The resulting coagulated material (a semisolid) floats on water. Its oil (liquid) content, which decreases with a decreasing amount of oil originally present in the water, ranges from 69-81% by volume. This paper provides the first identification of multiple forms of oil in a coagulated material that is made from a single form of oil. The oil consists of strongly bonded oil (16% by volume, with relative dielectric constant 32) and weakly bonded oil (84% by volume, with the same relative dielectric constant of 2.0 as the original oil). The maximum and minimum volumes of oil per unit area that can be coagulated by 0.022 cm3/cm2 of coagulant volume per unit area are 0.116 and 0.052 cm3/cm2, respectively. Below the minimum amount of oil, the coagulated material sinks in water, thus hindering oil removal.