Abstract: A method was established for the determination of iron species in residue by inductively coupled plasma optical emission spectrometry (ICP-OES). Four representative iron compounds: ferric chloride, iron naphthenate, iron 2-ethlhexannoate, and iron meso-tetraphenylporphine chloride were employed as model chemicals to investigate the extraction efficiency and conditions. The results showed that the extraction rate of ferric chloride reaches 100% by pure water. In the case of dilute acid is used as the extraction agent, the irons in residue can be divided into acid extracted iron, residual iron in oil and other iron irons. The acid extracted iron includes water soluble iron, majority of oil acid iron and a small amount of ferroporphyrins. Hydrochloric acid solution(5%) was found to be the best extraction solvent for iron naphthenates. The spiked recoveries of iron naphthenates and iron 2-ethlhexannoate in residue are 100.5% and 93.2%, respectively after extraction for 3h with the HCL solution. It is found that the other iron compounds disappear after hydrogenation, indicating they are easy to remove by hydrogenation. However, the removal rate of the residue iron in oil is far lower than the total iron removal rate.

Key words: iron, species, residue, ICP-OES