A Novel Approach for Adsorption of Lead (II) Ions from Wastewater Using Cane Papyrus

E29 A Novel Approach for Adsorption of Lead (II) Ions from Wastewater Using Cane Papyrus Mohammed Jaafar Ali Al-atabe Al-Mustansaryah University, BaghdadIraq Abstract Lead (II) ions are a very toxic element known to cause detrimental effects to human health even at very low concentrations. An adsorbent prepared using Cane Papyrus was used for the adsorption of lead (II) ion from aqueous solution. Batch experiments were performed on simulated aqueous solutions under optimized conditions of adsorbent dosage, contact time, pH and initial lead (II) ion concentration at 25C. The Freundlich isotherm model more suitably described the adsorption process than the Langmuir model with linearized coefficients of 0.986 and 0.9733, respectively. Pseudo-second order kinetic equation best described the kinetics of the reaction. Fourier transform infra-red analysis confirmed the presence of amino (–NH), carbonyl (–C=O) and hydroxyl (–OH) functional groups. Furthermore, 0.2M HCl was a better desorbing agent than 0.2 M NaOH and de-ionized water. The experimental data obtained demonstrated that Cane Papyrus can be used as a suitable adsorbent for lead (II) ions removal from wastewater.


Introduction
Heavy metal pollution has been one of the most challenging environmental problems due to their toxicity, persistence and bioaccumulation tendencies [l, 2]. Most industries produce and discharge metal-containing wastes mostly into water bodies, which affect the aesthetic

No.18 Journal of Petroleum Research & Studies
(JPR&S) E31 for simulated wastewater samples. The adsorbent showed a fluffy and highly porous and rough microstructure containing some voids and cracks which is suitable for the adsorption of Pb +2 ions . The concentration of Pb +2 ions in aqueous solution was analyzed using Atomic Absorption Spectrometer (AAS). Mechanical shaker with adjustable speed, time was used for agitation and pH meter was used for all pH measurements. The chemical composition of the adsorbent was analyzed using X-ray Fluorescence spectrometer. The chemical composition of the adsorbent is presented in Table l. Surface area of the adsorbent was l.96 m 2 /g ( Table 2). This is comparable to 2 m 2 /g reported by  gm. The optimum dosage obtained was used for subsequent processes. Similarly, the effects of pH, initial lead (II) ion concentration and equilibration time were varied between 2-l2 and l-50 mg/l and 5-l20 min, respectively. The percentage removal of Pb +2 ions from aqueous solution was estimated by using Equation (l):

(l)
Where C i and C f are the initial and final metal ion concentrations, respectively.

(2)
Where qe is the amount of metal adsorbed in mg/g, C i and C e represent initial and equilibrium concentrations of metal ions in aqueous phase. V is the volume of the solution in liters (l) and W is the weight of the adsorbent used in grams.

Studies of Desorption
One gram of adsorbent was introduced into a l00 ml Teflon container containing l0 mg/l Pb +2 ions. After equilibration for 60 min, the adsorbent was recovered. Residual Pb +2 ions on the surface of the used adsorbent were removed by washing it three times with ultra-pure water. Deionized water, 1M NaOH and 1M HNO 3 were tested as potential desorbing agents. 40ml of the desorbing agents were introduced into a l00 ml Teflon container containing the recovered adsorbent and equilibrated for 60 min at a speed of 200 rpm and T = 25C o . The aqueous solutions after equilibration were centrifuged and the supernatant were analyzed to determine the concentration of Pb +2 ions after desorption.

Infra-Red Spectroscopy Results
The results from the Fourier transform infra-red showed a broad peak at 3000 cm −l with a high transmittance frequency, which can be attributed to either -OH or -NH groups [l,l6]. As shown in Figure  Papyrus. There was a rapid uptake of pb +2 ions with a removal efficiency of 85% within five minutes of equilibration. The rapid uptake was due to fast transfer of the metal ion onto the empty adsorption sites on the surface of the adsorbent. Afterwards, there was a slow additional uptake of the metal ion from 5 min up to 60 min of equilibration, accounting for 98.5% pb +2 ions removal. There was no significant increase in the removal of pb +2 ions after 60 min indicating that equilibrium condition has been reached. This shows that the remaining empty sites on the adsorbent has been occupied leading to repulsive forces between adsorbed pb +2 ions on the adsorbent and those in the aqueous phase.

Effect of Adsorbent Dosage
The effect of adsorbent dosage on the adsorption of pb +2 ions was determined by varying the adsorbent dosage from l0-200 g. The percentage removal of pb +2 ions by the adsorbent increased sharply from 30% at adsorbent dosage of l0 g to 95% at l00 g but decreased slightly to 85% when 200 g was used. The initial rapid increase observed could be due to the increased availability of binding sites and surface area which makes the adsorption of the ions quite easy until equilibrium was reached. The subsequent decrease in the removal efficiency could be due to aggregation or overlapping of the adsorption site. Figure (4) represented these changes.
where Ce is the equilibrium concentration of the metal ion (mg/l), q e is the quantity of pb +2 ions adsorbed at equilibrium (mg/g), q max is the maximum amount adsorbed (mg/g) and b is the adsorption constant (l/mg). The plot of l/q e against l/Ce gave a straight line with a regression  Table (3). The conformity of the adsorption process to langmuir model was determined using Equation (4): Where R l is the separation factor, Co is the initial metal concentration (mg/l) and b is the langmuir constant (l/mg). R l > l indicates an unfavorable monolayer adsorption process, R l = l linear, 0 < R l < l favorable and R l = 0 irreversible. The result obtained from this study has an R l value between zero and one, indicating a favorable adsorption process. This implies that chemisorptions process duly explains the adsorption of pb +2 ions onto Cane Papyrus.  E37 where K f is the adsorption capacity (l/mg) and l/n is the intensity of the adsorption showing the heterogeneity of the adsorbent site and the energy of distribution . Equation (6) was obtained by taking the logarithm of Equation (5): logq e = log K l + logC e (6) A plot of logqe against logCe gave a linear graph with a regression coefficient of 0.9869 ( Figure   6), indicating that the adsorption also fits into Freundlich model. From the linearised coefficients obtained from both models, the langmuir model best described the adsorption process than the Freundlich model. This suggests a chemisorptions process rather than a physisorption process.
The constants obtained for the Freundlich and langmuir plot is presented in Table (3). A maximum adsorption capacity of 45.5 mg/g was obtained in this study for the adsorption of pb +2 ions. The use of Cane Papyrus is therefore a potential candidate for the removal of pb +2 ions in water and wastewater.

The Models of Adsorption Reaction :
The mechanism adsorption reactions are usually carried out using adsorption reaction models and adsorption diffusion models. Both models are used to understand the kinetics of the reaction. The linearised equations for the pseudo first and pseudo second order kinetics are presented in Equations (7) and (8), respectively. where q e and q t are the amounts of pb +2 ions adsorbed at equilibrium and at a given time t; k l and k 2 are the rate constants of pseudo first and pseudo second order models. The pseudo first order kinetic model was used to treat the experimental data obtained by plotting log(q e -q t ) vs.
equilibration time (Figure 8).  was used to ascertain whether intra-particle diffusion or film diffusion (external diffusion) is the rate-controlling step.

qt = Kd(t) 1/2 +I (9)
Where k d is the intra-particle diffusion rate constant (mg/g min −0.5 ) and I (mg/g) is a constant describing the thickness of the boundary layer. A linear plot of qt versus t 1/2 passing through the origin will suggest intra-particle diffusion as the sole rate-determining step. However, if a linear plot was obtained that is not passing through the origin; it means the adsorption process is controlled by more than one mechanism. In this study, a linear plot was obtained that did not pass through the origin (Figure 9), suggesting that the mechanism of the reaction is multi-linear and the rate-limiting reaction is controlled both through film diffusion and intra-particle diffusion.

Desorption Studies
This study was carried out to assess the most suitable desorbing agent for eluting adsorbed pb +2 ions from the surface of Cane Papyrus. The effects of de-ionized water, 0.2M NaOH and 0.2M HNO 3 solutions were tested for their ability to remove the adsorbed pb +2 ions from the surface of the adsorbent. HNO 3 was a better desorbing agent and was able to recover 50% of pb +2 ions adsorbed to the surface of the adsorbent. NaOH and de-ionized water showed desorption efficiencies of 25% and 2%, respectively. Desorption is beneficial for the separation and enrichment of pb +2 ions as well as the regeneration of the adsorbent.

Conclusions
The adsorption ability of powdered Cane Papyrus has been investigated and found effective