Abstract— The re-refining of waste lubricating oil using activated Ukpor clay as an adsorbent was investigated. Clay activation was performed using sulphuric acid (H2SO4) with equivalent concentrations varying between 0.5 – 2 mol/L at a constant temperature of 90oC for 3.5 hours. The adsorption process was studied over a fixed amount of adsorbent at ambient conditions. Adsorbent performance was determined by its effectiveness in enhancing the properties of the waste oil and in removing trace metal ions contained in them. Furthermore, the effect of contact time and the adsorption performance of the adsorbent in the recycling treatment of the lubricating oil were evaluated. The kinetic data were modelled using the Pseudo-first order, the Pseudo-second order, the intra particle diffusion and the Elovich kinetic models. Analysis carried out on the lubricating oil showed the presence of many heavy metal ions and trace elements. Ca, Pb and Zn had the highest concentrations of 804, 398 and 222 mg/L respectively, while Ba had the least concentration of 0.1 mg/L. However, with treatment using this adsorbent, the concentrations of Ca, Pb and Zn were found to considerably reduce to 3.6, 5.6 and 0.01 mg/L respectively. The concentration of Ba was equally found to reduce to 0.01 mg/L, wherein the clay sample treated with 2 mol/L H2SO4 gave the best result in terms of improvement in the properties of the lubricating oil as well as on the percentage removal of these heavy metals and trace elements. For best describing the process within the adsorbent and with a high correlation coefficient (R2 value > 0.999), kinetic data were best fitted by the Pseudo-second order kinetic model and this result indicates that this adsorbent provides a good medium for the re-refining of waste lubricating oil.
Keywords— Clay; recycling; adsorption; lubricating oil; kinetic models.
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