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Improvement of the treatment and recovery of waste oil emulsions in the steel industry

Oil refining and metal finishing industries, such as rolling mills and mechanical workshops, produce large quantities of oil-emulsion wastewaters that need to be treated before disposal. The requirements for the discharge of wastewaters have become more stringent in recent years in the course of the implementation of the environmental protection policy of the European Union. The present treatment of these waste oil emulsions, which consisted mainly on the retention of the oily phase, no longer meets the actual regulations, and further treatments are necessary.

The research showed that it was not possible to develop a general procedure to treat the spent cutting-oil emulsions, as it depended on the nature of the oil and its formulation. In this way each emulsion would require and specific treatment. Regarding emulsions stabilized by electrostatic interactions or by steric hindrance (due to macromolecules adsorbed at the oil/water interface) the following two treatment procedures are proposed. If the spent water-based coolant is stabilized only by electrostatic interactions, it is possible to remove a 90 % of the emulsified oil by adding an amount of an inorganic coagulant calcium clichloride above the critical coagulation concentration. The resulting aqueous phase of this treatment is a secondary emulsion that can be finally broken down in a filter coalescer or by ultrafiltration. When the emulsion is stabilized by macromolecules (steric hindrance) the utilization of batch holding tanks, in which the emulsion is heated to 60-80 C, and further addition of calcium clichloride is recommend, in this way a aqueous effluent which can be ultrafiltrated is obtained. It would be feasible to treat these emulsions with and inorganic flocculant, such as prehydrolized aluminium chloride salts, at room temperature and then employ further membrane treatment. The design and construction of a modular semi-pilot plant, that allows the application of the aforementioned possible treatments, will be carried out in order to treat spent cutting-oil emulsions generated at different workshops. Preliminary studies on the use of a peat filter as a pretreatment of an ultrafiltration of these emulsions have led to the study of composed beds (peat plus inorganic salts) that could be a feasible alternative to the treatment of these wastes.

Reported by

University of Oviedo
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