A semi-batch
foam-flotation in which air is continuously sparged through an emulsion, with
added surfactant, a coagulant, and a solvent, has been shown to be effective in
the treatment of steel-rolling mill effluents.
The effect of
time of flotation, effects of surfactant and alum concentrations, and effect of
the solvent volume were all experimentally explored. The oil recovery
increased with concentrations of alum and sodium lauryl sulphate of up to
around 4 g/l, and then leveled off.
Volume of the
solvent layer at the top improved the separation of oil with an optimum ratio
of 0.167 ml solvent per ml of emulsion. The oil separation was highest for the
time of flotation of about 25 minutes, and reemulsification of the separated
self-emulsifiable oil was observed beyond this time.
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