Cutting fluid is an industrial liquid used in metal processing and manufacturing to cool and lubricate cutting tools and machined parts. It has good cooling performance, lubrication performance, rust prevention performance, oil removal and cleaning function, and anti-corrosion function. Cutting fluids can be divided into oil-based cutting fluids and water-based cutting fluids.

Cutting fluid may fail and deteriorate during use due to impurities, temperature rise, and bacterial and microbial growth. The components of the scrapped cutting fluid are complex and difficult to treat. Generally, demulsification pretreatment is performed first, and then harmless or resource recovery treatment processes are reasonably selected based on the actual situation to effectively treat the waste cutting fluid, improving the environmental and economic benefits of metal processing enterprises.

Reason for scrapping of cutting fluid

There are various reasons for cutting fluid failure and scrapping, and the most common ones are three:

（1）The introduction of impurities leads to the deterioration of metal cutting fluid. During the metal machining process, a large amount of metal debris is generated. Under the cleaning of the cutting fluid, these debris will be mixed into it. If not treated in a timely manner, the debris will continue to accumulate, causing the lubrication performance of the cutting fluid to gradually decrease or even lose its effectiveness.

（2）The increase in temperature leads to the failure of metal cutting fluid. In the process of metal mechanical machining, when the tool is cutting the workpiece, the temperature increases due to frictional motion; Moreover, metal chips are prone to chemical reactions with certain additives in the metal cutting fluid to release heat, leading to an increase in the temperature of the cutting fluid. These heat will accelerate the deterioration of the cutting fluid, ultimately leading to failure and deterioration.

（3）Due to the growth of microorganisms, metal cutting fluids become ineffective. Improper storage of cutting fluids can easily lead to the growth and reproduction of bacteria and other microorganisms, leading to the biochemical decomposition and deterioration of oil substances, resulting in a foul odor. According to statistics, the proliferation of bacteria and microorganisms greatly affects the recycling of cutting fluid, resulting in a shortened service life of about 65% -85%. Oil substances are an important cause of bacterial and microbial growth, and in the process of metal machining, there are a large amount of guide rail oil, hydraulic oil, spindle oil, etc. in machine tools and equipment. When mixed with cutting fluid, it is easy to cause a large number of bacterial and microbial proliferation.

Pretreatment method for waste cutting fluid

（1） Pretreatment method for waste cutting fluid

Due to its complex composition and good chemical stability, the direct treatment of cutting waste liquid is difficult and generally requires pre-treatment. Pre treatment mainly involves demulsifying the waste liquid to remove oil in water or oil in water from the waste liquid. Comparison of several demulsification methods, including acid precipitation, salt precipitation, and coagulation precipitation

（2）Harmless treatment method for waste cutting fluid

After demulsification pretreatment, cutting fluid wastewater must undergo advanced treatment before being discharged. Advanced treatment mainly involves removing some oil substances, dissolved organic matter, suspended solids, ammonia nitrogen, etc. from the wastewater. Comparison of several harmless treatment methods, including hydrocyclone method, air flotation method, adsorption method, biochemical treatment method, and advanced oxidation method

（3）Resource utilization treatment method for waste cutting fluid

Several resource utilization treatment methods, including soil high-temperature contact acid free regeneration process, distillation solvent extraction clay refining process, and high-temperature distillation method

Cutting fluid may fail and deteriorate during use due to impurities, temperature rise, and bacterial and microbial growth. The components of the scrapped cutting fluid are complex and difficult to treat. Generally, demulsification pretreatment is performed first, and then harmless or resource recovery treatment processes are reasonably selected based on the actual situation to effectively treat the waste cutting fluid, improving the environmental and economic benefits of metal processing enterprises.