Sequestering of Fe and Pb ions from Wastewater by Canarium schweinfurthii after carbonization and chemical treatment : Isothermal and Kinetic Modeling

: In this paper agricultural waste; Canarium schweinfurthii was explored for the sequestering of Fe and Pb ions from wastewater solution after carbonization and chemical treatment at 400 o C. Optimum time of 30 and 150 min with percentage removal of 95 and 98% at optimum pH of 2 and 6 was obtained for Fe and Pb ions. Kinetics model followed pseudo-first order as sum of absolute error (E ABS ) between Q e and Q c greater than that of pseudo second order. Parameters evaluated from isothermal equation (Freundlich and Langmuir) showed that K L and Q O for Fe > Pb and R 2 for Langmuir> Freundlich. The study reveals the suitability of the adsorbent for sequestering of Fe and Pb ions from industrial wastewater.


Introduction
Man's activities in the environment have greatly led to an increase in concentration levels of heavy metals.These have generated a lot of interest in pollution studies.Heavy toxic metals entered into the environment through wastewater from metal plating industries and industries of lead, cadmium and nickel batteries, phosphate fertilizer, mining, pigments electroplating, Corrosion, and other industrial waste (Ahalya et al,. 2005) .Natural sources of these metals include; rock-weathering, releases from terrestrial and submarine sediments, some of these metals are often found in crude oils in small quantities and discharged into the environment during the refining process (Cutler, 2007).The discharge of heavy metals into the environment has become a matter of concern and seems to threaten the survival of living things (Zupanc et al., 2002).
Conventional methods of removing heavy metal pollutant from wastewater can be expensive, prohibitive for developing economy and most times do not effectively remove polluting metals.Thus, it becomes imperative to search for cheap and alternative means and bio-sorbents lately have become of considerable interest (Bassey et al., 2015).Adsorption by activated carbon, by far, has become a method of choice to offset this problem.Adsorption becomes a preferred choice than other physicochemical techniques of heavy metal remediation due to its simplicity, cheap, easy to scale-up and most importantly able to remove low concentration substance even at part per million levels with high efficiency.Activated carbon has been widely used in water treatments because of its high specific surface area, chemical stability and durability.Its utilization for heavy metals adsorption greatly relies upon surface acidity and special surface functionality (Sato et al., 2007) and coordination to functional groups (Jia et al., 2002).The quality of activated carbon is dependent upon the extent of its surface area, number of pores as well as its surface functional groups.Structurally, carbon is made up of tiny graphite-like platelets with a wall of open cavities that form the pore system.The presence of tiny pores on their internal and external surfaces has been attributed to be responsible for adsorption of organic materials, non-polar compounds and metals from gaseous and liquid media (Ekpete et al., 2010).Generally Activated carbons are generated using materials such as; coal, wood, coconut shell, after some form of activation process (Lartey and Acqual, 1999).Recent, agricultural waste material has been adopted for production of activated carbons at temperature range of 450-700 o C (Okieimen and Wuana, 2007;Tarawou and Horsfall, 2007).The common process involved during the production of activated carbon is based on carbonizing and activating the carbonaceous at certain furnace temperature.This can be achieved physically; a process involving carbonization of the precursor material or chemically; a process of adding a chemical agent and then subjecting it to temperature (Dilek and Oznur, 2008).Metal uptake by biosorption is reported to occur through interactions with functional groups native to the biomass cell wall *1 BASSEY UWEM, EDJERE, OGHENEKOHWIRORO OTOLO, SOLOMON EBIYE (Goksungur et al., 2005;Krishnakuman et al., 2007).It is metabolism-independent and proceeds rapidly within some minutes by any one or combination of the following metal binding mechanisms; coordination, complexation, ion exchange, physical adsorption (e.g.electrostatic) or inorganic microprecipitation Carbonaceous surfaces, typically in the form of soot particles, play an important role in the chemistry of adsorption.These carbons are characterized by a high degree of chemical and morphological heterogeneity that affects their function.These characteristics affect their interactions with molecular adsorbates and, hence, the adsorption capacity (or efficiency) and catalytic activity.According to Osu and Odoemelam (2010), modification of the adsorbent (Crasstrotrea gasar) by esterifying the carboxylic group present in the cell wall with ethanol in the presence of HCl did not improve the adsorptive capacity of the adsorbent used.Jameel (2011) reported that the presence of -OH, -CH 2 -, -CHO, -C=C-and -C-O-at 3412.01,  2926.11,2856.67,1660.77and 1095.60cm -  in duckweed enhanced binding the metals of metal ions onto the adsorbent.Therefore this work is aimed at optimizing the function and usefulness of evaluating the isothermal and kinetic model of treating Fe and Pb ions in waste water using carbonization and chemical treatement of Canarium schweinfurthii

MATERIALS AND METHODS
Air dried endocarps of Canarium schweinfurthii were |milled and passed through 250 micron mesh screen.The sieves were kept for carbonization.

Carbonization of adsorbent:
The sieved biomass was activated by placing it in an electric furnace at 300 o C and heated for one hour.After which it was allowed to cool in an ice bath.
Chemical activation of carbonized adsorbent : 10 g of carbonized endocarp of Canarium Schweinfurthii was transferred into a beaker containing 50 cm 3 of 0.5 molar trioxonitrate (V) acid.The beaker contents were thoroughly homogenized until a paste was formed.The homogenized samples was then transferred to crucible and placed at the centre of a Gallenkamp electric muffle furnace and heated at 400 o C for 10 minutes.The chemically activated sample were cooled in an ice bath and washed with distilled water to a pH range of 6-7, and was further oven dried at a temperature of 105 o C for 20 minutes, product obtained was screened through a 250 µm mesh size sieve.This process was repeated till sustainable quantity was obtained.
Preparation of simulated wastewater: Aqueous solution containing the respective selected metals: Pb and Fe was prepared from analytical grade Pb(NO 3 ) 2 , FeSO 4 .7H 2 O. 1000 mg/L stock solutions of each of the metal salts were prepared.The solution was introduced for each metal according to the method of continuous dilution from the sample.
Preparation of reagents and standard solutions: 1000 mg/L Pb: 1.60 g of Pb (II) from Pb(NO 3 ) 2 was dissolved in 1000 cm 3 volumetric flask before being made to mark with distilled water.The solution was shaken to ensure thorough mixing.Other concentrations (10, 25, 50, 75,100 and 150 mg/L) were prepared from the stock solution by serial dilution from a formulae C 1 V 1 = C 2 V 2 ; 1000 mg/L Fe: 4.96 g of Fe (II) from FeSO 4 .7H 2 O was dissolved in 1000 cm 3 standard thorough mixing.Other concentrations (10, 25, 50, 75,100 and 150 mg/L) were obtained from this solution by serial dilution.
Sorption experiment was carried out at pH of 2, 4,6,8,9 and contact time of 30, 60, 90,120 and 150 min for their optimization.Residual metal ion concentration was determined using atomic absorption spectrophotometer AA-6300shimadzu and Accufys 211 model.
Desorption studies: Recovery of the metal ion adsorbed from the adsorbent was done using different concentrations of hydrochloric acid (0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) mol/dm 3 .The desired volume of 40 cm 3 of 5 mg/L of metal solution was poured into designated Pyrex conical flask for each concentration of desorbing agent.Solutions of metal ions were contacted using adsorbent dosage of 0.5 g for the optimum pH, contact time, stirring speed after which they were filtered.The filtrate was kept for analysis and the spent biomass contacted with the appropriate concentration of the desorbing agent for the optimum contact time, at the end of which the contents were filtered.Values are mean ±standard deviation   Percentage removal for both metal ions reduced at alkaline medium.This is due to the fact that at higher pH metal ions combines with OH - radicals present in the adsorbent and in solution forming metal hydroxide precipitate, which affect the adsorption of metal ions by the adsorbent (Bailey et al., 1999).There is high possibility of increase in repulsive forces between OH -ions with radicals such as NO 3 -and SO 4 2-generated from Pb(NO 3 ) 2 and FeSO 4 .7H 2 O used for the preparation of simulated solution which would negatively affect the adsorption of these ions.Quek et al.(1998) in their study on the application of sago waste for the adsorption of Pb (II) and Cu (II).The sorption process was examined in terms of its isotherm and kinetics for Pb (II) and Cu (II).Optimum pH range was found to be 4 to 5.5 for both metals this was because at such pH range hydrogen ions influents the surface charges of the adsorbent positively.Wong et al.(2003) using rice husk modified with tartaric acid as adsorbent for the removal of Pb (II) ions and reported that reported that as pH increased from 2 to 4 and gradually increased above 5. exhausted.An increase in optimum time for the uptake of Pb ions was not surprising as plot obtained for intra particle diffusion gave high boundary layer of 0.005 for Pb compared to that of Fe having 0.001 as shown in table 3 and 2. Kannan and Sundaram (2001) reported that In adsorption process, the metal ions from the bulk solution travels to the thin film surrounding the adsorbent, during the process is either the thin film in the liquid generates a impermeable membrane (boundary layer) for the metal ions to pass through or the impermeable membrane may be negligible, if the former occurs the time profile of the metal ions uptake by the adsorbent may eventually increase.Simulated Pb ion solution repelled the travel of the ion to the surface of the adsorbent.Boundary effect is an important parameter that comes into to play during metal ion adsorption.Metal ions travels across the boundary layer of the adsorbent before diffusing onto the adsorbent surface, followed by movement into the porous surface of the adsorbent.According to Kannan and Sundaram (2001) they reported that the larger the boundary layer, the more difficult for metal ions to diffuse onto the surface of the adsorbent.This explain the fact that adsorption under the same experimental condition depends upon the substrate and the metal ions.Enthalpies of hydration for studied metal ions are -1946 kJ/mol for Fe (II), -1480kJ/mol for Pb (II).This pattern shows that less negative enthalpy of hydration leads to better adsorption (Ayuba and Khuzaifa, 2014).It was observed that the trend in percentage removal of metal ion was of the order Pb (98%) > Fe (95%) > at various optimum time.Ademiluyi and Ujile (2013) studied on adsorption of Fe (II) from simulated aqueous solution.Bamboo biomass was carbonized and modified with trioxonitrate (V) acid.It was reported that there was significant increase in the adsorption of Fe (II) ions from the aqueous Pseudo-First order equation and Pseudo-second order equation: Tables 3 and 4 give parameters for pseudo-first and pseudo-second order kinetics of Fe and Pb adsorption.The slopes and intercepts of plots of log (Q e -Q t ) versus were used to determine the firstorder rate constant K 1 and equilibrium adsorption capacity (theoretical adsorption capacity) Q c .values obtained showed the closeness of experimental adsorption capacity of value 0.360mg/g for Fe and 0.364 mg/g for Pb to theoretical adsorption capacity Q c of values 0.360mg/g for both metals.Intercept from the plot of t/Q t versus t is use for estimating the value of h (initial reaction rate).A comparison of the results, showed high correlation coefficients for pseudo first order kinetics, hence it applied as a kinetic model for the order of the reaction.

RESULT AND DISCUSSION
Intra-particle diffusion: Tables 3 and 4 give parameters for intra-particle diffusion of metal ions.It is observed that there was an interference of boundary layer for both metal ions.Itodo et al. (2009) reported that deviation of the plot of q t against t 0.5 shows that intra-particle transport is not the only rate limiting step, possibly adsorption occurred on the surface of the adsorbent or there was movement of metal ions through the particle-sample interface onto the pores of the adsorbent.Similar results were reported by Badmus et al.(2007).
Intra-particle diffusion kinetics gives an idea of the penetrating capacity and movement of metal ions into the microspores structure of the adsorbent.The process involves series of stages. The first stage signifies movement of ions to the external surface of the adsorbent  The second involves rapid flow of ions into the microspores structure of the adsorbent  The last stage the microspores structure of the adsorbent becomes exhausted, making diffusion of metal ions to remain constant.


According to Hameed et al. (2006) irrespective of large value of regression coefficient, for intra-particle diffusion kinetic model to predict the kinetics of adsorption, the following parameters must be accomplished  A linear plot for intra-particle diffusion passing through the origin must be obtained  Boundary effect should be zero as this increases the rate of diffusion(C≤0)  Freundlich isotherm model:: Log = logC e + LogK F …………. ( 5) Where and K F represent the Freundlich constant, related to the adsorption intensity and adsorption capacity.
Freundlich equation is used in investigating the nature of the adsorbent surface.1/n represents the adsorption intensity, used for predicting the effect of metal ions concentration on the surface of the adsorbent, and it is also a measure of the adsorbent strength (Hamidi et al., 2013)From Tables 5 and 6 the values of 1/n for Fe (0.946) > Pb (0.782) indicating normal adsorption as 1/n > implies cooperative processes.Chilton et al.(2002) and Goldberg (2005) reported that large values for 1/n indicates changes in adsorbent surface over different metal ion concentration and that when 1/n>1 the amount of metal ions in the adsorbent is more than that in the solution.They also reported that as 1/n tends to zero, surface of adsorbent becomes more heterogeneous the influence of the ions on the surface of the adsorbent, making it more heterogeneous.
Values of n obtained for all metal Arivoli et al. (2005) reported that adsorption intensity (n) > 1 indicates the prevalence of chemisorptions over physical adsorption.K F value obtained for Fe (9.484 mg/g) for is greater than that of Pb (7.311mg/g).K F is a measure of the capacity of the adsorbent for the metal ion of interest and gives the concentration of the metal ions per unit mass of the adsorbent.5 and 6 Q 0 obtained for Fe (7.7519mg/g) is higher than that of Pb (5.8480mg/g).

Fig 10
Fig 10 shows the concentration of metal ions recovered from both adsorbents using hydrochloric acid of different concentration.It could be seen that as the concentration of eluent increases, recovery of metal ions also increases.Matheikal et al. (1991) reported that higher concentrations of acids, increases proton availability, thereby dislodging metal ions that are bonded to the adsorbent by making adsorbentadsorbate bond weak, due to changes in bond orientation.This is not surprising as large numbers of protons are made available for protonating hydroxyl or carbonyl groups present in the adsorbent, thereby preventing attractive force between H + and carbonyl or hydroxyl groups (Horsfall and Spiff, 2003).The *1 BASSEY UWEM, EDJERE, OGHENEKOHWIRORO OTOLO, SOLOMON EBIYE order of metal ions recovery was Fe > Pb.The results obtain reveals the existence of both physical and chemical bond binding adsorbent-adsorbate in the simulated solution.Economy application of adsorbents depends on the extent of regeneration after a particular cycle of usage.The ability and ease of recovery of metal ions from adsorbent is vital if adsorption process is to be viable.Acids have the potential to elute metal ions form biosorbents, thereby important for detoxification process (Cortoras, 1992).According to Gadd (1990) adsorbent tends to deteriorate when there is prolonged exposure to higher concentration of acids.
The metal ions recovered can be concentrated into purer form.Chaney et al. (2007) proposed burning of plant biomass to further concentrate the bio-ore.These authors showed that the value of the metal recovered in the biomass was shown to offset the cost of the technology.Furthermore, Watanabe (1997) reported that Zn and Cd recovered from a typically contaminated site could have a resale value of $1,060/hectare.

Conclusion:
The results show that the sequestration was favored in 30 and 150min with percentage removal of 95 and 98% for Fe and Pb .This effect is as a result of uptake of metal ions due to availability of adsorption sites.Kinetics models of the metal ions followed the pseudo first order with correlation coefficient of 0.670 and 0.818 for Fe and Pb.Prevalence of chemisorptions over physisorption is an indication of interaction between functional group on the adsorbent surface and the studied metal ions.
Filtrates were analyzed for metal ion concentration using atomic absorption spectrophotometer AA-6300shimadzu and Accufys 211 model. .Characterization of activated carbon: Moisture content was determined by oven drying 5 g of the biomass at constant temperature of 105°C for five hours.Desiccators were used to preserve the sample from uptake of moisture.Percentage moisture content was determined according to the expression below.Percentage moisture content = x100 (1) *1 BASSEY UWEM, EDJERE, OGHENEKOHWIRORO OTOLO, SOLOMON EBIYE W 1 = Weight of crucible W 2 = Initial weight of crucible with sample W 3 = Final weight of crucible with sample Bulk density was determined by using 2 g of granular activated carbon of 10-30 mesh size carbon placed in a 25 cm 3 cylinder and tapping it for at least one to two minutes after which the volume of carbon in (g/m 3 ) signifying bulk density was derived as Weight of dry sample (g) -volume of packed dry sample (g) Conductivity (µS/cm) was determined by suspending one gram of activated carbon in distilled water for twenty minutes and conductivity measured as micro siemen (µS/cm).Determination of ash content was carried out by measuring 2 g of powdered carbon of 325 µm into a crucible and heating the content to 115 o C in an oven for 6 hours.The carbon was then heated in the centre of Gallenkamp muffle furnace at 950 o C for 1.5 hours, the crucible was removed and placed in desiccators in order to prevent moisture uptake.Ash was derived as Ash (%) = (2) Hardness of the sample was measured using wet attrition method reported by Toles et al .(2007)Into a 100 cm 3 acetate buffer made of 0.07 M sodium acetate and 0.03 M acetic acid of pH 4.8 in a 150 cm 3 beaker 1 g of the sample was added.To allow proper agitation, the solution was stirred for twenty four hours.The filtered sample was then well washed and dried in an oven for four hours at 90 o C

Fig 2 :
Fig 2: Variation of pH Effect of pH: Fig 2 show optimum pH of 2 and 6 for Fe and Pb.Percentage removal for both metal ions reduced at alkaline medium.This is due to the fact that at higher pH metal ions combines with OH - radicals present in the adsorbent and in solution forming metal hydroxide precipitate, which affect the adsorption of metal ions by the adsorbent(Bailey et al., 1999).There is high possibility of increase in repulsive forces between OH -ions with radicals such as NO 3 -and SO 4 2-generated from Pb(NO 3 ) 2 and FeSO 4 .7H 2 O used for the preparation of simulated solution which would negatively affect the adsorption

Fig 3 :Fig5:Fig 9 :
Fig 3: Variation of metal concentration Fig 4: Freundlich plot for Pb and Fe Equilibrium concentration of adsorbate in mg/g Q e = amount of metal ion adsorbed per gram of the adsorbent at equilibrium The adsorptive capacity of metal ions per unit adsorbent (mg/g) was determined the expression: Q e = X V ………….(7) Q o = Maximum monolayer coverage capacity in mg/g K L = Langmuir isotherm constant in L/mg The equation represents the equilibrium distribution of metal ions between the solid and liquid phases.The Langmuir isotherm is valid for monolayer adsorption onto a surface containing a finite number of identical sites.The model assumes uniform energies of adsorption onto the surface and no transmigration of metal ions in the plane of the surface.From Table

Table 1 :
Characterization of Activated carbon

Table 2 .
Functional groups present in the adsorbent Strong signal at 2351.30 cm -1 is due to overlap between stretching and bending vibration of molecules *1 BASSEY UWEM, EDJERE, OGHENEKOHWIRORO OTOLO, SOLOMON EBIYE

Table 4 :
Kinetic parameters for Pb

Table 6 :
Isothermal parameters for Pb sequestering