Study on Generation Processes of Used Mineral Oil and Their Heavy Metal Concentration Characteristics

The generation processes of 6 typical used mineral oils were analyzed, and their heavy metal content characteristics systematically studied. The results showed that there were obvious differences in the oil consumption and used oil production among different oil generation processes and working surroundings. Seven main heavy metals were detected in the typical used mineral oil samples, including Cr, Ni, Zn, Cu, Pb, Mo and Ba. The Zn contents were relatively high, followed by Cr, Cu, Mo and Ba contents, and Ni and Pb contents were relatively less. Among them, heavy metals Zn, Mo and Ba were mainly from oil additives, while Cr, Ni, Cu and Pb were mainly from the abrasive particles or impurities mixing in the oil using process. In condition of the 6 used oils directly dumped into the environment, the heavy metal equivalent concentrations were in the following order: used vehicle lubricating oil > used hydraulic oil > used quenching oil > used refrigeration oil > used antirust oil > used while oil, in which the potential hazards of heavy metals in the used hydraulic oil and used vehicle lubricating oil were the highest. In addition, in the used oil recycling, most of the heavy metals were transferred into residue (such as oil residue, distillation residue, waste clay, etc.), while a few remained in recycled oil; in the used oil incineration process, the final destination of heavy metals were tail gas and bottom ash. Therefore, the used oil disposal and recycling process should be managed strictly, in order to prevent and control the secondary pollution of heavy metals.