Uptake of Zn , Pb , Cu and Fe Ions from Spent and Unspent Engine Oil Using Termite Soil

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. gmin) 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. gmin). 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 (mggmin) 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.


Introduction
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).Some major pollutants found in spent lubricating oil include polynuclear aromatic hydrocarbons (PAHs) and high levels of heavy metals.Considerable quantities of heavy metals, such as Pb, Zn, Cu, Cr, Ni, and Cd, are contained in used crankcase oil (Vwioko and Fashemi, 2005).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.Although some heavy metals at low concentrations are essential micro nutrients for plants, at high concentrations they could cause high metabolic disorder and growth inhibition for most plant species.Spent engine oils are particularly dangerous to the environment due to their contamination with products of thermal decomposition and mechanical impurities.These pollutants become hardly biodegradable and have carcinogenic properties (Grzegorz et al., 2015).
Contaminations of soil with engine oil are rampant in the Nigerian environment and have adversely affected seasonal crops such as maize (Kelechi et al., 2012;Agbogidi et al., 2007).
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.In recent times, termites soils have been investigated and reported to have high porosity and water infiltration due to buildup of have galleries (Schaefer, 2001;Dangerfield et al., 1998) which makes it a suitable adsorbent for metal removal (Agbozu and Bassey, 2016).Also, pH of termite soil tends to be higher than that of adjacent soils thereby causing an increase in adsorption sites (Holt et al., 1998).
Adsorption kinetics is important in the evaluation of the performance of a given adsorbent and underlying mechanisms of sorption.From the kinetic analysis, the solute uptake rate, which determines the residence time required for completion of adsorption reaction, may be established.Also, one can know the scale of an adsorption apparatus based on the kinetic information.Generally speaking, adsorption kinetics is the base to determine the performance of fixed-bed or any other flow-through systems (Dabrowski, 2001).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).

Lagergren Pseudo-first Order Model
The pseudo first-order kinetic model (Lagergren's equation) describes adsorption in solid-liquid systems based on the sorption capacity of solids.It assumes that one metal ion (adsorbate) is adsorbed onto one sorption site on the adsorbent surface:

Pseudo-second Order Model
The pseudo second-order rate expression has been applied for analyzing chemisorption kinetics from liquid solutions.The model assumes that one metal ion (adsorbate) is sorbed onto two sorption sites on the adsorbent surface:

Elovich Model
Elovich equation is also used successfully to describe second order kinetic assuming that the actual solid surfaces are energetically heterogeneous, but the equation does not propose any definite mechanism for adsorbate-adsorbent relationship.
In order to avert the problem of soil pollution caused by used engine oil, there is need to study the adsorption kinetics of termite soil for the removal of heavy metals (Pb, Fe, Zn, and Cu) from spent and unspent engine oil through adsorption process.

Sampling
Termite soil was collected from Ugbomro Community in Uwvie Local Government Area of Delta State, Nigeria at Latitude N 05 o 34' 09.8" and Longitude E 005 o 50' 23.0".

Pretreatment
The termite soil was air dried at room temperature for 72 hours and crushed in a mortar.The sample was pretreated to remove non clay material such as carbonate and quartz minerals.A 2M Hydrochloric acid (HCl) was added to 0.6mm particle sized adsorbent to remove heavy metals present in the adsorbent and improve the sorption property of the absorbent.The mixture was stirred for 1 hour and allowed to remain in a plastic for 24hours and then thoroughly washed with distilled water and air dried for 2days.Virgin (unspent engine) oil with Society of Automotive Engineers (SAE) Grade of 20W-50 was used in a generator running at 6 hours daily for one week.Residual engine oil was collected after 42 hours of usage in the generator and labeled as spent engine oil.

Initial Concentration of Heavy Metals in Adsorbent and Adsorbate
A 0.5g of the termite soil was weighed into a 100ml beaker, and then 20ml of an aqua regia mixture (15ml conc.HCl, 5ml conc.HNO 3 in the ratio of 3:1) was added to the soil sample in the beaker.The sample was then digested using a block digester under fume hood for 15 minutes.The solution was allowed to cool, and then filtered into a 100 ml Pyrex and immediately transferred into 120ml plastic container.Concentrations of heavy metals were determined using atomic absorption spectrophotometer (spectral 220 FX).similarly, 5ml of the spent engine oil sample was measured, and added to a mixture of 20ml HNO 3 and HCl (5ml HCl +15ml HNO 3 ) (Yong et al., 2016).Results from the analysis were used as initial concentration of metal ions.Same process was used for digestion of unspent engine oil.

Adsorption Techniques
A glass separating funnel was fitted with cotton wool and held firmly in a vertical position with the aid of a retort stand.Atmospheric pressure helped to push the sample through the adsorbent.Adsorption process was carried out at room temperature.Process parameters such as contact time and adsorbent dosage were varied.

Contact Ti
A 0.5g of term allowed to rem each contact t analysis using

Infra-red S
In other to de hexane.Two leaving a cast resulting samp

Data Anal
The following adsorbent.

Kinetic equati
Where M is the mass C 0 and C e are  V is the volume of solution in litres and q t is the quantity of metal ions adsorbed at any particular time (mg/g).ᵦ (g/mg) is desorption constant, α (mg.g -1 min -1 ) is the initial reaction rate from Elovich equation

Result and Discussion
Figure 2. FTIR spectra in the 4000-400 cm -1 wave number range for termite soil From Figure 1.0 the main bands appearing in that spectrum were due to stretching vibrations of OH groups in the range from 3750 -3000 cm -1 , which are overlapped to the stretching vibration of N-H; and C-H bond in -CH 2 (2943 cm −1 ).Bending vibrations of methyl groups occurred at 1436 cm −1 , (Mano et al., 2003).Absorption in the range of 1643-1436 cm −1 was related to the vibrations of carbonyl bonds (C=O) of the amide group CONHR (secondary amide, 1643 cm −1 ) (Marchessault et al., 2006).On the basis of interaction with functional group, hydroxide ions present in the adsorbent provide sites for chemisorptions of heavy metals.Surface reaction includes; Zn 2+ (aq) + 2OH -(aq) Zn(OH) 2 (s) Fe 2+ (aq) + H 2 O Fe 3+ (aq) + 3OH -(aq) Fe(OH) 3 (s).
Similar reaction of Cu and Pb ions give product of their hydroxides.The ease at which this bond would be destroyed by water molecules is dependent on their enthalpies of hydration.The hydration energy for the +2 oxidation states of the studied metal ions are -1946 kJ/mol for Fe (II), -1480kJ/mol for Pb (II), -2046kJ/mol for Zn (II) and -2100kJ/mol for Cu (II) respectively.According to Ayuba and Khuzaifa (2014) stronger enthalpy of hydration leads to better adsorption and reduces the tendency for desorption.Therefore Zn and Cu ions would held strongly on the adsorbent with less ease of leaching away.-0.n -1/2 ) 0 0. Graph of against t was used in determining initial reaction rate h(mg/g.min)as described by pseudo-second order kinetics.Also plot q t against Int gave elovich parameter α for initial reaction rate determination.Values obtained shows that Zn and Fe had fast uptake compared to Cu and Pb.The theoretical adsorption capacity also reveals the availability of Cu and Zn ions on the adsorbent surface.Possibly Pb and Cu ions tends to desorp away from the adsorbent upon getting to the surface as evidence from their high desorption constant as seen in the Tables 5 and 6, desorption constant is of the order Cu>Pb>Zn>Fe for spent engine oil Table 5.0 and Pb>Cu>Zn>Fe for unspent engine oil Table 6.0.Values obtained for pseudo-second order kinetics have less difference between theoretical (Q t ) and experimental adsorption (Q e ) capacity Plot of q t against √t were used in obtaining intra-diffusion parameters.Intercept C (mg/g) obtained from Tables 5 and 6 are negligible, implying insignificant restriction of boundary layer of the adsorbent for the uptake of the ions.According to Imaga and Abia (2015), for uptake of ions in a heterogeneous system to be best described by intra particle diffusivity the boundary layer C (mg/g) should be equal to zero.Values of boundary layer for the adsorbent during uptake of metal ions were not equal to zero.The observed values shows that the mode of transport is affected by more than one process such as surface adsorption, chemisorptions, ion exchange, precipitation and intra-particle diffusion are occurring concurrently (Igwe et al., 2005).Intra-particle diffusion constant (k id ) is of the order Zn>Fe>Pb>Cu.This reveals the affinity of the adsorbent (termite soil) with various metal ions.According to Itodo et al. (2010) higher values of k id illustrate an enhancement rate of adsorption, which is related to improve bonding between adsorbate and adsorbent particles.Hence Zn ions formed strong bond with the adsorbent compared to other metal ions.Desorption constant 'beta' obtained shows that Zn ions has less potential to be leached from the pores of the adsorbent.

Table 1 .
Initial concentration (mg/l) of metal ions in spent and unspent engine oil

Table 6 .
Kinetics parameters for unspent engine oilTable5and 6 gives various parameters for Pseudo-first, pseudo-second, intra-particle and elovich parameters used in describing the factors influencing the movement of metal ions onto available adsorption sites on the adsorbent.It is observed that correlation coefficient for pseudo-first order kinetics is larger compared to other kinetics model, and had theoretical adsorption capacity close to the experimental value.Hence describes the pattern of movement of metal ions to the surface of the adsorbent.Also R 2 for spent and unspent engine are 0.983, 0.905, 0.982, 0.900 and 0.982, 0.927, 0.945, 0.964 respectively is greater compared to other kinetics models.