National Bureau of Standards Special Publication 556. Proceedings of A SURVEY OF METALS IN OIL: OCCURRENCE AND SIGNIFICANCE FOR T. D. Coyle and A. R. Siedle This paper summarizes the results of a literature review which was undertaken to (1) summarize and evaluate available data on the occurrence and on the chemical and physical forms of metals in used lubricating oils, and (2) evaluate the implications of the metal content of used lubricating oils to their use and disposition. A considerable body of information is available concerning the levels of metals in used oils. The principal sources of metals in these materials are: (1) metalcontaining additives incorporated in essentially metal-free base stocks, and (2) metals accumulated during use, primarily lead from gasoline additives and iron from wear processes. The most significant change in metal content during the service life of lubricating oils is the accumulation of lead, which increases in concentration by a factor of 10,000 to 1-1.4 percent (w/w). Additional metal inputs may occur during collection, handling, and storage of used oils. The specific chemical and physical forms of metals in used oils are largely unknown. It appears, however, that much of the lead (in the range of 50 percent) -- and possibly other metals--is present in the form of fine suspended particulates. Primary applications of spent lubricating oils to which metal contents are relevant are: (1) re-refining, (2) combustion, and (3) uses for road oiling. A significant fraction is currently disposed of by landfilling. Re-refining technology reduces metal levels to values substantially equivalent to those of virgin basestocks. While re-refining residues containing high metal concentrations present a disposal problem, metals per se do not appear to present a problem for the equivalency of re-refined oils to virgin materials for automotive use. Metallic contaminants probably do not affect either combustion efficiency or short-term integrity of combustor components when used oil is burned, particularly if it is used diluted with fuel oil from virgin sources. There are well-defined chemical mechanisms by which metallic impurities can adversely affect refractories and metals in combustion applications, but such effects have not generally been observed in short-term pilot studies. Long-term studies are probably required, however. The principal problems associated with the high levels of lead and metallic additives in spent lubricating oils are environmental, specifically emissions from combustion and uncontrolled release to the environment in road oiling and dispersion through landfill operations. Better characterization of the metallic contaminants in spent oils is of potential benefit to reprocessing technology, as well as to assessing environmental consequences of waste oil use and disposition. Data are needed on the distribution of metals among water-soluble, oil-soluble, and particulate constituents; on size distribution and metal distribution in particulate fractions; and on the specific chemical forms in which metals occur. Acquisition of these data presents significant measurement problems in the chemical characterization of amorphous particulates and in the speciation of soluble and metal-organic compounds occurring in spent oils. A copy of the complete survey is attached to this volume as Appendix I. 1 National Bureau of Standards Special Publication 556. Proceedings of SPECIATION OF METALS IN USED OILS: RECENT PROGRESS AND ENVIRONMENTAL F. E. Brinckman and W. R. Blair Materials Stability, Durability, and Corrosion Division Introduction The presence of many metals in used crankcase oils is well known to originate from wear processes in engines and from blow-by products in fuels consumed during engine operation. Additive "packages" introduced into new oils frequently contribute significant concentrations of several metals along with a variety of solubilizing ligands [1].' End uses of spent crankcase oils include re-refining and combustion as fuel components. Probably more significant to environmental concerns, however, are additional uses in road oiling or unregulated dumping in landfills. Re-refined oils display considerable reductions in residual metal loadings, although refining sludges associated with commercial reprocessing can also constitute a hazardous disposal problem [2]. Since road oiling and landfill discard represent widespread direct imposition of metal components on environmental cycling through leaching into the aquatic system, there exists a pressing need to evaluate which metals in what forms represent the chemically and biologically important threats to the environment. One aspect of recent work at the National Bureau of Standards (NBS) has therefore focused on developing means for characterizing the principal toxic metal components in waste oils as typically collected and comparing these results with those for "new" oils. Annual uncontrolled disposal is responsible for over 200 million gallons of such waste oils finding their way into drained soils [1]. Consequently, our initial studies have been directed to an assessment of the Typical amounts of a major waste oil component, lead, and the nature, or bioavailability, of lead chemical species presented by such a large and ubiquitous environmental stress. Potential Environmental Impacts of Metals in Waste Oils In studies dealing with hazards of technological materials or wastes to the biosphere, several fundamental considerations require priority. In table 1 are summarized such factors which underly the preliminary NBS studies on form and fate of toxic metals in waste oils or associated re-refining processes. Bioactivity or bioavailability of toxic metals. Degradation of crude and waste petroleum products by soil or marine microorganisms has been long known [3]. More recently, it was shown that heavy metal-polluted oils in marine sediments were subject to active bacterial degradation, implying that biotransformations both of oil and metals were occuring [4]. In general, we can conclude that, while forms of toxic metals present in new or spent oils are undetermined, some degree of direct chemical solubilization can occur into ground waters by leaching or by biological degradation yielding leachable substrates. A basic question remains concerning the mode (s) of dispersion of metalcontaining materials by man and the chemical pathways by which these toxic substances are transported. Pertinent to environmental issues involving waste oils, for example, is the evaluation of automotive traffic as a primary dispersal mechanism. Underlined numbers in brackets indicate the literature references at the end of this paper. |