1.0 Introduction
Lubricant is an oil or grease that is applied as a surface coating to moving parts to protect and reduce friction of two surfaces in relative motion, eliminate temperature build up and keep the engine clean (Toolingu, 2013; Udonne 2011; Ogbeide, 2010). It also serves the purpose of transportation of foreign particles, heat transfer, corrosion prevention, cutting of metal and protection against wear (Udonne 2011; Ogbeide, 2010). The lubricating oils are either bio or petroleum based and the petroleum base feedstock are mainly complex mixtures of hydrocarbon molecules (Udonne, 2011; Hamad et al., 2005) ranging from low viscosity oils to high viscosity lubricating oil. T.Y chemicals (1990) analysis shows that the presence of impurities depends on the petroleum process and production method but concluded that lube oil contains aromatics in the range 4 to 12 % free, sulphur and other impurities.
Machineries / engines that make use of oil lubricant include all vehicles, motor bikes, generating plants and it is also used in various industries/factories equipments. Spent oil is any petroleum-based or synthetic oil that has been used and as a result, is contaminated and has lost nearly all its physical or chemical properties but do not wear out and the contaminant present in it can be removed to the point that it can be reused as engine or machine oil (Garthe, 2005). Contaminants or impure lubricants are drained off from cars and disposed off as used or waste oil containing undesirable oxidation product, sediments, metallic wear particles, water, degraded additives and lead hazardous substances (James, 1967; Kamal and Khan, 2009; Durrani et al., 2011; Emam and Shoaib, 2012; Abdulkareem et al., 2014).
Disposal of used oil into the environment, used as weed killers, pouring into ditches or dumping illegally is dangerous to life. It contaminates water as research shows that a gallon of used oil can contaminate one million gallons of water. Used oil can also affect plant life if poured on the ground and it sinks down into the water table (EPA 530-F-94-008). It is therefore obvious that indiscriminate disposal of used lubricating oil into the environment constitutes hazards to both fauna and flora. Hence, the need to recycle used lubricating oil. There have been several approaches in an attempt to regenerate used lubricants (Isah et al., 2013; Abdulkareem et al., 2014; Durrani et al., 2011 Jhanani and Joseph, 2011; Ogbeide, 2010; Josiah and Ikiensikimama, 2010; Abdul-Jebbar et al., 2010; Kamal and Khan, 2009; Rahman et al., 2008; Gorman, 2005).
Industries and private users of lubricating oils demand necessitates the need to find ways of regenerating the oil after use due to the rapid depletion of fossil fuel reserve which is the source of oil feedstock, shortage of fresh oil, price increase and high demand (Zambiri, 1988). The increased use of lubricating oil globally for which Nigeria produces 364 166 000 litres of used oil annually disposed as a common practice into gutters, water drains, open plots and farms which led to streams, ground water, lakes and oceans pollution (Isah et al., 2013; EPA 530-F-94-008). The frequent disposal of waste lubricating oils globally is alarming and requires serious attention.
Presently, many countries in the world are presently giving serious attention to the problems of environmental degradation and hazards caused by the disposal of waste lubricating oils (Hamad et al., 2005; Jilner, 1997). T.Y Chemicals (1990) referred regeneration of used lubricating oil as the means of removal of contaminants or impurities by sulphonating agents such as sulphuric acid, oleum or sulphur trioxide and concluded that the process is made up of two cycles, the removal of about 80 % aromatics and other impurities in the first cycle and other 20% impurities in the second operation cycle. However, Isah et al. (2013) carried out regeneration of used engine oil treated with sulphuric acid and bleached using industrial bleaching earth and activated carbon for different formulated grades.
The results obtained by the group showed that the best grade in comparison with fresh oil in terms of viscosity, specific gravity and total acid number was obtained using industrial bleaching earth. Abdulkareem et al. (2014) compared the performance efficiency of used lubricating oil treatment methods and concluded from their findings that acid and acid/clay treatment methods were the most attractive with consequences of environmental pollution resulting from acid sludge. Emam and Shoaib (2012) also made comparison between acid/clay percolation and solvent/clay methods of recycling lubricating oils and concluded that the used of acid treatment method was the most attractive interms of quality while solvent method gave the highest yield.
The used of sulphonating agents specifically sulphuric acid to treat used lubricant has been fully established by many researchers (Abdulkareem et al., 2014; Isah et al., 2013; Emam and Shoaib, 2012) and its performance has been very competitive but environmental consequences are part of its major limitations. In addition to environmental consequences, there is a dare need to quantitatively and qualitatively analyze the effect of other acids which suggest in this study the investigation of nitric, sulphuric and hydrochloric acids suitability and effects in the treatment stage of used lubricating oil recycling.
