Separation processes for recovering alloy steels from grinding sludge: Supercritical carbon dioxide extraction and aqueous cleaning

Two separation processes have been developed to remove contaminants (cuttin g oil with trace phosphorus additive) from high-speed steel grinding sludge . One process uses an aqueous surfactant washing technique, and the second process uses supercritical carbon dioxide (SCCO2) extraction. Our bench sca le aqueous washings have shown that the required phosphorus removal is easi ly obtained, but a sufficient oil removal is more difficult. The experiment al results also indicate a strong dependence of the aqueous washing efficie ncy on the choice of a suitable surfactant. A mass transfer model is used t o simulate a semi-continuous washing process. SCCO2 extraction at 80 degree s C and 340 atm shows that approximately 80% of the oil can be removed from the sludge during a 60-minute process to produce a batch of recyclable ste el, and that the phosphorus removal also reaches the required level. A line ar desorption model is used to describe the irreversible desorption of oil from the solid phase into the CO2 phase and the simulated results agree ver y well with the experimental data.