Abstract
This research work investigated the adsorption of some heavy metals contaminants in used lubricating oil using chemically activated carbon adsorbents produced from palm kernel and coconut shells. The adsorption mechanism was able to remove some heavy metals such as zinc, chromium, cadmium and magnesium contaminants from the used lubricating oil to appreciable levels. For instance, zinc from initial concentrations of 16.475±0.950 ppm before to 10.375±0.171 ppm after filtration processes for used lubricating oil sample A. Also, for coconut shell from an initial concentration of 14.575±0.272 ppm to 5.450±0.3000 ppm after filtration processes. It was observed that the coconut shell activated carbons was effective in the removal of lead metals while palm kernel cannot. However, the activated carbons produced from palm kernel and coconut shells are not suitable for the removal of both copper and iron metals. For example, after the filtration process with the palm kernel shell activated carbon, the mean concentration of copper metal increases for virgin (C) 0.001± 0.000 to 0.075±0.013 ppm and used lubricating oil samples (A&B) from 0.150±0.008 to 0.400±0.018 ppm and from 0.220±0.096 to 0.230±0.008 ppm respectively. Also, in the case of the coconut shell activated carbon, the mean concentration of copper in virgin lubricating oil remains the same 0.001±0.000 whereas for used lubricating oils samples (i.e. A&B) it increases from 0.150±0.008 to 0.780±0.014 and from 0.220±0.096 to 0.790±0.026 respectively. Also, the equilibrium adsorption data were analysed using the Langmuir isotherm model. The fit of this isotherm model to the equilibrium adsorption data was determined, using the linear coefficient of correlation (R<sup>2</sup>). The following R<sup>2</sup> values were obtained; Copper (0.8185), Cadmium (0.8347), Lead (0.9349), Chromium (0.9378), Iron (0.9927), Zinc (0.9953), and Magnesium (0.9997) respectively. From the results obtained and statistics point of view, it can be concluded that the Langmuir model shows a better fit due to the high coefficient of correlation (R<sup>2</sup> ≈ 1). The recovered oil could be also re-used.
Highlights
Activated carbon has been known as the most effective, efficient, reliable and useful adsorbents for the removal of pollutants from polluted gas, liquid streams, wastewater, dyes, used lubricating oils etc
The adsorption results obtained for magnesium heavy metal analysed indicated that activated carbons produced from the coconut and the palm kernel shells can be used as a high-performance adsorbent with higher adsorption capacity
In the ANOVA, the lesser the Pr > F value, the more significant the results. This revealed that magnesium metal conforms to a straight line Langmuir adsorption isotherm [34]. This result obtained for magnesium proofed that activated carbons produced from the coconut and the palm kernel shells can be used as a high-performance adsorbent with higher adsorption capacity [36]
Summary
Activated carbon has been known as the most effective, efficient, reliable and useful adsorbents for the removal of pollutants from polluted gas, liquid streams, wastewater, dyes, used lubricating oils etc. This is made possible because of the properties of activated carbons which have a large active surface area which can provide high adsorption capacity, well developed porous structures and good mechanical properties [1, 2]. The goal of this study is to prepare activated carbons from palm kernel shell and coconut shell by chemical activation with potassium carbonate (K2CO3) and sodium bicarbonate (NaHCO3) to adsorb some heavy metals from used lubricating oil samples. In other to further improve the adsorption efficiency of the activated carbons, this paper aims to use the data obtained to model the heavy metal parameters
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