REMOVAL OF HEAVY METALS FROM WASTE WATER BY USING A NATURAL AND BIODEGRADABLE ADSORBENT BASED ON PRUNUS AVIUM L. STEMS AS ADSORBENTS

Ali Mcheik, Wassef El Khatib, Akram Hijazi*, Kamal Hariri, Mohamad Reda, Hassan Rammal Doctoral School of Science and Technology, Research Platform for Environmental Science (PRASE), Lebanese University, Lebanon. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History


Experimental methods
Batch experiments were carried out using a series of Erlenmeyer flask of 50 mL capacity. Batch experiments were prepared to study the effect of initial Cu (II) concentration, pH, contact time, adsorbent dose and temperature on adsorption of the Cu (II) ions from its solution. All the adsorption experiments were carried out at room temperature except where the effect of temperature was being investigated. The initial pH was adjusted with HNO 3 (1 M) or NaOH (1 M) solutions.

Biosorption isotherms
Adsorption isotherms are essential for understanding the mechanism of an adsorption system. Since they represent the amount of compounds adsorbed on a surface as a function of concentration at a constant temperature [ xvi ]. Two isotherms models were tested: 1.
Freundlich isotherm: is the well-known earliest relationship which describes the adsorption process. It can be applied to non-ideal sorption on heterogeneous surfaces as well as multilayer sorption [ xvii ]. This isotherm is expressed by the following linear equation: Log qe = log kF + 1 log Ce (3) Where KF is the Freundlich constant related to the bonding energy (L/mg), 1/n is the heterogeneity factor and n (g/L) is a measure of the deviation from linearity of adsorption. Freundlich equilibrium constants were determined from the plot of log qe versus log Ce (Figure 1), basis on the linear of Freundlich equation (3). Where the n value indicates the degree of non-linearity between solution concentration and adsorption as follows: if n=1, the adsorption is linear. If n<1, the adsorption is a chemical process. If n>1, the adsorption is a physical process. The n value in Freundlich equation was found to be 0.983 for P. avium. Since n is greater than 1, this indicates the physical biosorption of Cu (II) onto P. avium. The values of correlation coefficients R 2 are done as a measure of goodness of fit of the experimental data to the isotherm models [ xviii ]. adsorption of the surface will be achieved. The linear form of the Langmuir isotherm model is described as: Where q max is the maximum adsorption capacity (mg/g) and KL is the Langmuir constant related to the energy of adsorption (l/g). Values of Langmuir parameters q max and KL were calculated from the slope and intercept of the linear plot of Ce/qe versus Ce as shown in Figure 2. Values of q max , K L and correlation coefficient R 2 are listed in Table 1. These values for P. avium biosorbent indicated that Langmuir model describes the biosorption phenomena favorable. The essential characteristics of the Langmuir isotherm parameters can be used to predict the affinity between the sorbate and sorbent using separation factor or dimensionless equilibrium parameter, RL expressed as in the following equation: Where Co is the initial concentration of sorbate (mg/l) and KL is the Langmuir constant (L/mg). There are four possible values for R L : to be irreversible ( The R L was found to be 0.9937 for concentration of 25-600 mg/L of Cu (II). They are in the range of 0-1 which indicates the favorable biosorption.

Results and Discussion:-
When P. avium stems powder was tested for its ability to adsorb Cu (II) ion from aqueous solution, initial pH 6 was used for most experiments. The effects of the following experimental parameters (pH, initial concentration, contact time, temperature and the adsorbent dosage) on adsorption were studied. The percentage of the uptake or adsorption of Cu (II) was calculated using the following equation: Where Ci = initial concentration (mg/l); Cf = final concentration (mg/l). The adsorption capacity of Cu (II) is the concentration of Cu (II) over the adsorbent mass and it was calculated based on the mass balance principle according to the following equation:

FT-IR and XRF analysis of adsorbent:-
The FT-IR spectrum presented in the figure 3 was used to investigate the functional groups present on the P. avium stems that could be responsible for the removal of heavy metal species [ xxi ]. The spectrum of the adsorbent was measured within the range of 4000-400 cm -1 wave number. The comparison of the FT-IR spectra has been done before and after loading with Cu (II). The P. avium stems show a number of absorption peaks that reflects its complex nature. Two peaks at 3513 cm -1 and 3436 cm -1 are due to the presence of N-H bond stretching (primary amine). A broad peak at 3292 cm -1 is due to the existence of OH group. The absorption peak at 2924 cm -1 could be assigned to C-H stretching vibration, 1736 cm -1 to ester carbonyl, 1608 cm-1 to C=C, 1520 cm -1 to N-H, 1066 cm -1 to C-O. After adsorption, a broad peak at 3466 cm -1 corresponds to the overlapping of OH and NH peak. This phenomenon may be attributed to the water molecule directly interacting with amide.
After  The mixture was continuously agitated at 25 ± 2 °C with a shaker at 400 rpm. The pH of the solution was adjusted to a pH 6. After the established contact time (1 hour) was reached, the suspension was filtered in 2 steps: first by Buchner filtration then by 0.45 μm filter. After that, the final concentration of Cu (II) in the filtrate was determined using AAS. The adsorbed amount was determined from the difference between the initial and residual concentrations of Cu (II) in the liquid phase.

The effect of pH on adsorption of Cu (II) ions
The pH of the aqueous solution is an important parameter which controls the Cu (II) adsorption process, as it affects the surface charge of the adsorbents and the degree of ionization [ xxiii ]. Figure 5 shows clearly that P. avium stems exhibit maximum Cu (II) removal at pH 4, which were rather acidic. At low pH (below 3), the increased number of protons in solution on this biosorbent often refuses the formation of links between Cu (II) ions and the active site.        The values of correlation coefficient R 2 are regarded as a measure of goodness of fit of experimental data to isotherm model. Therefore, from table 1 for Cr (IV) and Pb (II) we can see that Langmuir gave a better fit than Freundlich isotherm, while for Cu (II) and Cd (II) Freundlich gave a better fit than Langmuir isotherm.

Conclusion:-
This study investigated the adsorption of Cu (II) ions from aqueous solutions onto dried Prunus avium stems that is dependent on biosorption process such as initial metal ions concentration, pH, adsorbent dose, and temperature and contact time. To provide best correlation for biosorption of Cu (II) ions onto P. avium stems, Freundlich and Langmuir biosorption isotherm were demonstrated. From this study, it was observed that stems of P. avium stems can be used as an alternative low cost, eco-friendly and effective adsorbent for treatment of waste water containing Cu (II) ions. Other heavy metals adsorbed by stems of P. avium are under study. 15