| Budget Amount *help |
¥5,500,000 (Direct Cost: ¥5,500,000)
Fiscal Year 1992: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1991: ¥4,700,000 (Direct Cost: ¥4,700,000)
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| Research Abstract |
The present project has been aimed at developing a novel method of treatment of oil-gearing water by addition of solid particles which would collect oil droplets. Oil should be removed together with the particles from the water, in the form of aggregate.
Hydrophobic particles have difficulty in mixing with water, although they are more wettable with oil. Therefore. hydrophilic CaCO_3 ( size: 10-20mum) and quartz ( size: 5-10mum) particles have been chosen for the water treatment. In addition, both of them would be easily obtained and harmless to the environment. Adhesion behavior of these particles and oil droplets was studied in detail for sufficient information of proper condition for the adhesion. Then, removal of dispersed oil droplets by these particles was examined. The results are summarized as follows :
1. Adhesion of quartz particles to oil droplets: In the aqueous phase of pH3, hydrophilic quartz particles adhered to kerosene droplets, whereas kerosene drops did not contact wit
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h quartz surfaces. It was suggested that, on this condition, the negatively charged quartz particles and the positively charged kerosene droplets coagulate across water layers. On the other hand, in CaCl_2 solution of pH 11.5, where quartz particles adhered to droplets of hydrocarbons as well as those of kerosene, oil drops were found to contact directly with quartz surfaces. In this case, water layers between quartz particles and oil droplets should be removed by specific interaction, probably due to specific adsorption of CaOH^+ on both quartz and oil surfaces.
2. Adhesion behavior of CaCO_3 particles to oil droplets : When mixed with sufficient volume of oil, CaCO_3 particles in surfactant-free solutions easily adhered to and floated with oil droplets at and above the natural pH(9.7) of the CaCO_3 aqueous suspension. In weakly alkaline solution, the adhesion was explained in terms of low potential barrier getween an oil droplet and a very weakly charged CaCO_3 particles. While at high alkaline pH, CaOH^+ from dissolved Ca^<2+> was considered to enhance the adhesion. Sodium dodecyl benzenesulfonate, a surfactant which would adsorb preferentially onto oil droplets, was found to have reverse effect on particle-droplet adhesion.
3. Considerable amount of kerosene oil was found to adhere to these hydrophilic particles under the conditions described in (1) and (2). Adhesion density was lowered with increasing addition of the particles. A correlation was implied between the residual oil concentration and the amount of oil adhesion to CaCO_3 particles of unit weight. The amount of the particles required to lower oil concentration to 5ppm ( legal for drainage ) was much decreased by stepwise addition. When oil concentration is relatively low, the total particle consumption was also able to ge lowered by reusing the particles. Coagulation was enhanced by oil adhesion for all particles used. Water content of the oil-bearing sludge was 30-40Z, which is much less than that of the sludge from a conventional flocculation method (>60Z). Less
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