Waste Cutting Fluid Demulsification and Its Influencing Factors by Freeze-Thaw Method

The waste cutting fluid was treated by freeze-thaw method while the influences of freezing medium,thawing method,freezing temperature,freezing time,NaCl content and pH were investigated.On the basis of single factor test,the optimum conditions were as follows:the salt content in the waste liquid was 0-0.02 g/L and the pH was 6.0-8.0 without adding NaCl and pH adjustment,the waste cutting fluid was frozen 8 h at -8℃ and then thawed at room temperature.Under these optimum conditions,the COD removal rate of this waste water reached 85.2%.Using biological microscope to observe the microgram of waste cutting fluid before and after being frozen-thawed,the particle size of oil droplets in waste water was about 148 μm and they were significantly larger and easier to gather after freeze-thaw processing.The infrared spectra indicated that the waste cutting fluid precipitations was mainly esters.The treatment of 1 m³ waste cutting fluid can recover 7.65 kg of oil and grease,which consumes 42.90 kW·h.Freeze-thaw method is effective to recover esters from waste cutting fluid demulsification and to improve the biodegradability of waste water and to be a good application prospect.