Freeze-thaw method for oil recovery from waste cutting fluid without chemical additions

The effective disposal of waste cutting fluid has received increasing attention in recent years. This study focuses on the treatment of waste cutting fluid by freeze-thaw method. The influences of freezing medium, freezing temperature, freezing time, NaCl content and pH on treatment efficiency were studied. The COD removal rate of waste cutting fluid was about 80% and oil recovery reached 3700 mg/L at the freezing temperature of −8 °C for 8 h without NaCl addition or pH adjustment. The micrograms of initial and treated waste cutting fluid showed that the particles of oil droplets in wastewater were significantly larger after freeze-thaw process and easier to gather and separation. Infrared spectroscopy studies indicated that the oil recovered from waste cutting fluid precipitation was mainly composed of esters. Up to 3.7 kg fat extract was recovered from 1 m3 of waste cutting fluid, while the required power of this freezing process is 42.90 kW h by theoretical calculation. Thus, freeze-thaw method appears to be effective and feasible for waste cutting fluid treatment.