Supercritical CO2 extraction method refers to a method that utilizes the good dissolution and mass transfer properties of CO2 fluid in a supercritical state to effectively separate the extract. CO2 in the supercritical state has dual characteristics of liquid and gas. Its density is similar to that of liquid and has strong dissolving ability; its viscosity is close to that of gas and its diffusion ability is strong, so it can effectively enter the interior of the waste clay pores. The dual characteristics of supercritical CO2 are used to first dissolve the remaining oil in the waste clay into CO2, and then cool down and reduce the pressure to become a gas in a normal state, which is automatically precipitated from the clay to achieve the purpose of oil recovery. When Jerry . W. King et al. used supercritical CO to extract waste clay produced from edible oil refining, they added a certain amount of diatom dispersant. The experimental results showed that the oil content of the clay after oil removal was almost zero . The supercritical CO2 extraction method has the advantages of being clean, combining extraction and separation into one, being safe and non-toxic, and having adjustable and controllable extraction pressure and temperature. It has very promising application prospects in waste clay treatment.

In addition, solvent methods, extraction methods, transesterification methods, centrifugal separation methods, etc. are also used in the waste clay recovery process. However, these methods also have certain limitations and cannot completely recover waste clay. of oil without damaging the structure of the clay. The pollution-free treatment of waste clay requires not only the recovery of the oil in the waste clay, but also the complete recovery of the adsorption capacity of the waste clay without causing secondary pollution.

At present, various refineries are actively developing waste clay regeneration methods suitable for their own production. However, all regeneration methods at this stage have not achieved the full recovery of waste clay oil and the complete recovery of waste clay adsorption capacity, and cannot be reused. As environmental protection regulations become increasingly stringent, refining waste clay regeneration technology will surely become a research hotspot.