Waste mineral oils are the result of the use of lubricating oils: most of them are consumed during their use while the remaining part represents waste oil.
During its use, the lubricating oil undergoes chemical-physical transformations that make it no more suitable to perform the functions it was originally intended for and they require its replacement.
Lubricating oil with greater amounts of such contaminants as organic oxidation products, aging materials, soot, wear debris and other dirt may not any more fully meet the demands and thus must be replaced. They are called used, spent or waste oils and should be collected and recycled in order to prevent the environment pollution and to preserve natural resources.
QUALITY OF USED OIL
Usually the term “used oil” is understood to include only those oils which arise from the use of lubricating oils. Slop oils recovered from drainage systems, refineries, fuel storage sites, etc. are not included, although they are generally mixed in used oil collection systems and decrease the value of the material.
The largest potential source of used oils is from vehicle use, particularly engine oils. In general, the additives (particularly metals) remain in the oil after use. In addition, used engine oil contains a range of other impurities which affect the final re-refined base oil quality and cause problems to the re-refining activity. Metals from engine wear build up in the oil as does water formed from combustion of the fuel. A certain amount of unburned fuel (gasoline or diesel) also dissolves in the oil. Light hydrocarbons (HC) also arise form breakdown of the oil and heavier hydrocarbons, including PAH, from polymerisation and from incomplete combustion of the fuel.
Chlorine in used lubricating oils is a potential problem as on combustion there is the possibility of dioxin formation. Chlorine in used oils arises:
• from contamination (either accidental or deliberate) with chlorinated solvents and transformer oils, both of which are now becoming closely controlled
• from lubricating oil additives
• from the lead scavengers added to leaded gasoline.
The concentration of chlorine in used oils is reducing as the use of chlorinated solvents for industrial cleaning applications is reduced and the use of leaded petrol declines.