Abstract
Removal of Zn, Pb, Cu and Fe ions from unspent and spent engine oil was studied using Termite soil. Process parameters such as contact time and adsorbent dosage were varied. Values from contact time were used for predicting kinetics equation of their uptake. At optimum time of 40 minutes, percentage adsorption was of the order Fe>Zn>Cu>Pb for both spent and unspent engine oil. Kinetics equation such as Elovich, Intra-particle, Pseudo-first order and Pseudo-second order were tested. Results obtained shows that their sequestering pattern fit into the pseudo-second order kinetics. Initial reaction rates, h (mg/g.min) and α (mg. g-1min-1) for all metal ions obtained from Pseudo-second order and Elovich kinetic models followed the trends Zn>Fe>Cu>Pb and Zn>Fe>Pb>Cu respectively in spent engine oil while for unspent engine oil, the trend was Fe>Zn>Cu>Pb for h (mg/g.min) and Zn>Fe>Pb>Cu for α (mg. g-1min-1). Electrostatic attraction existing on the surface of the adsorbent assisted in the high initial reaction of Zn and Fe ions, implying good affinity of the ions for the adsorbent. Desorption constant ᵦ (g/mg) was of the trend Cu>Pb>Fe>Zn and Cu>Pb>Zn>Fe for spent and unspent engine oils respectively. Intra-particle diffusion constant kid (mgg-1min-1/2) followed a similar pattern, revealing strong binding between Zn and termite soil than any of the metal ion. This pilot research has been able to suggest a kinetic process for uptake of the studied ions from spent and unspent engine oil.
Highlights
Spent motor oil is an alarming environmental pollutant and is usually obtained after servicing and subsequent draining from automobile and generator engines by auto-repairers (Sharifi et al, 2007)
At optimum time of 40 minutes, percentage adsorption was of the order Fe>Zn>Cu>Pb for both spent and unspent engine oil
H and α for all metal ions obtained from Pseudo-second order and Elovich kinetic models followed the trends Zn>Fe>Cu>Pb and Zn>Fe>Pb>Cu respectively in spent engine oil while for unspent engine oil, the trend was Fe>Zn>Cu>Pb for h and Zn>Fe>Pb>Cu for α β
Summary
Spent motor oil is an alarming environmental pollutant and is usually obtained after servicing and subsequent draining from automobile and generator engines by auto-repairers (Sharifi et al, 2007). Improper disposal of spent engine oil leads to a buildup of essential inorganic nutrients such as phosphorus, calcium, and magnesium, and trace amounts of lead, zinc, iron, copper and cobalt. These elements if in excess accumulate in plant tissues. In Nigeria, the Government has not been able to monitor or control the discharge of used oils and grease from the numerous auto- repair workshops littered over the country because they have proven to be very difficult to regulate their activities by virtue of their small size (Ahamefule, 2013) Several adsorbents such as agricultural waste have been investigated for sequestering of heavy metals from various waste matrices. Adsorption kinetics is determined by the following stages: 1) diffusion of molecules from the bulk phase towards the interface space commonly called external diffusion; 2) diffusion of molecules inside the pores internal diffusion; 3) Adsorption-desorption elementary processes (Sharma, 1990)
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