Coagulation of oil in water using sawdust, bentonite and calcium hydroxide to form floating sheets

The coagulation of oil in water is valuable for the removal of oil from water. The use of a mixture of bentonite and sawdust, with sawdust being the vast majority, is highly effective for the coagulation of oil in water, giving coagulation efficiency 92% or above. A minor amount of calcium hydroxide may be optionally added to the mixture to increase the coagulation efficiency to 94%. The use of organobentonite in place of unmodified bentonite increases the coagulation efficiency further to 95%, but increases cost. Sawdust by itself sinks in water. However, the coagulated aggregates float on water when sawdust is used with the bentonite. These aggregates are sheet-like, with the oil–bentonite–sawdust serving as a continuous matrix and apparently no upper limit to the aggregate sheet size. They contain, for example, 81 vol.% oil, 15 vol.% sawdust, 3 vol.% bentonite (with basal spacing 14.4 Å) and 1 vol.% calcium hydroxide. Upon compression, 73% of the oil in the aggregate is removed. Without sawdust, the aggregates sink in water and the coagulation efficiency is only 37%. The sawdust functions as a fibrous framework for the attachment of the coagulating oil and bentonite, thus facilitating floating aggregate formation and the subsequent removal of the aggregates. In the presence of unmodified bentonite, sawdust enhances the coagulation efficiency significantly, while calcium hydroxide enhances the coagulation efficiency by a much lower degree.