Abstract: Pure water and hydrochloric acid solution were used to extract the aged oils of different depths in the oil tank, respectively. The metal contents in extracted oils were determined by inductively coupled plasma emission spectrometry (ICP-OES). Meanwhile, sodium benzoate, calcium naphthenate, nickel meso-tetraphenylporphine, nickel octaethylporphine, vanadyl meso-tetraphenylporphine, and vanadyl octaethylporphine were employed as model chemicals to study the metal species in the aged oils. The results showed that the contents of iron, sodium, calcium, and other metal elements in each phase were high and followed the rule of additivity after extraction and separation, respectively. The composition of the aged oil was complicated, and the iron in aged oil should be +2 valences according to the color of acid extract. It is expected that the aged oil can be recovered by means of washing and centrifugation to remove most of the metals in it. If further removal is required, acid reagent treatment should be considered.

Key words: metal, speciation analysis, aged oil, ICP-OES