抄録
Waste lubricating oils generally contain metallic compound impurities, which result from various additives mixed into fresh lubricating oils and wear grits generated during machine operations. To remove these metallic compounds and other impurities from waste lubricating oils for recycling as base oil, refining process with brown coal has been studied. Several steps, such as water addition, heating, adsorption with brown coal particles and solid-liquid separation (centrifugation) are included in this process for removal of impurities in various chemical forms. Then, to improve the removal performance with this process, exact chemical forms of metallic compounds and their removal mechanisms should be specified. In this study, experimental investigations were conducted to determine what mechanism happens to metallic impurities in each step and then which step would be effective to remove these impurities. Elemental composition analyses of oil samples after several processing described above showed that many kinds of elements could exist in close relation with moisture in waste lubricating oil. Some of metallic impurities separated out as depositions by a dehydration of waste oils during heat treatment. Water addition showed a stimulating effect on coal adsorption of some metallic impurities.