The Removal of Zinc from Aqueous Solutions Using Malvaparviflora

In this study, the adsorption of Zn (NO3)2 is carried out by using surfaces of malvaparviflora. The validity of the adsorption is evaluated by using atomic absorption Spectrophotometry through determination the amount of adsorbed Zn (NO3)2. Various parameters such as PH, adsorbent weight and contact time are studied in terms of their effect on the reaction progress. Furthermore, Lagergren’s equation is used to determine adsorption kinetics. It is observed that high removal of Zn (NO3)2 is obtained at PH=2. High removal of Zn (NO3)2 is at the time equivalent of 60 min and reaches equilibrium,where 0.25gm is the best weight of adsorbant . For kinetics the reaction onto malvaparviflora follows pseudo first order Lagergren’s equation.


Introduction
The following processes are similar to the chemical manufacturing: metal finishing and electroplating major sources of poisonous metals are industrial wastes.The increasing levels of heavy metals discharged to the environment represent a severe threat to human health, living resource and ecological system.According to the World Health Organization (WHO), the toxic metals are aluminum, chromium, magnesium, iron, nickel, cobalt, copper, cadmium, zinc, mercury and lead.Adsorption is one of the most frequent methods used to remove heavy metal ions from several aqueous solution [1].Malvaparviflora belongs to the family Malvaceae.A hot poultice prepared from leaves is used in treating wounds and swellings.Moreover, it is incorporated into a lotion to treat bruised and broken limbs [2].Xhosa people of South Africa have used the leaves of M. for drawing swollen, inflamed purulent wounds [3].The methanolic segment of polyphenols plant is an antioxidant potential for containing different quantities of phenols, flavonoid, saponin, alkaloid, resin and tannin [ 4].The removal of Zn(II) from aqueous solutions by studying the optimization variables include: contact time, PH and temperature .The adsorption process can be evaluated by freundlich isotherms.The order of adsorption is evaluated from the kinetic study.

Materials and Methods:
Apparatus:

The different influences of PH(3,7 and 10) on adsorption of Zn(NO 3 ) 2 on malvaperviflora
The PH is adjusted by using 0.1M( HCl or NaOH) solution before the adsorption process.The final PH is recorded by the PH meter .Three samples are shaken for 1 hour, samples are centrifuged for 20 min at 3300 rpm than the concentration of Zn +2 ions remaining in solution is measured by using Atomic Absorption Spectrophotometer.

Results and Discussion
The effect of Contacton Time: Adsorption equilibrium studies are performed with an adsorbent quantity of (0.25 gm) by 25 ml of Zn(NO 3 ) 2 (25 ppm).The experimental results of adsorption of Zn(NO 3 ) 2 on malvaperviflora at different times (15, 30, 45, 60, 75 and 90)min are illustrated in Fig. 1.and Table (1).They show that the adsorption process exhibit an immediate rapid adsorption and reaches equilibrium within a short period of 60 min [5].

Effect of PH
The PH solutionaffect the charge of surface, the adsorbent, the degree of ionization.The new types of the adsorbate .The adsorption of metal ions from aqueous solution depends on the PH solution [8].The removal of metal ions when pH varies from 3-10 by adsorption experiments use different PH methods.PH affects the adsorption of Zn (II) on adsorbent are shown in Figure ( 4) and Table (4).From Figure 5 it can be seen clearly that the maximum adsorption occurs at lower PH value namely (3).This may be due to the presence of a large number of H + ions which in turn neutralize the negatively charged adsorbent thereby reducing hindrance to the diffusion of Znic ions.The decrease at high PH may belong to abundance of OH -ions causing hindrance to diffusion Znic [9].The thermodynamic functions Δ H o , ΔG o , and ΔS o have been calculated by using the following formulas ΔG o =-RT ln K - -----------------------( --------------------(4) According to Eq.(2,3 and 4)the Δ H o and ΔS o parameters for Zn(NO 3 ) 2 can be calculated from the slope and intercepts of the plot of In(K) versus 1/T (Fig. 5)where K is the thermodynamic equilibrium constant of adsorption process.K, can be calculated form intercept of linear equation log Qve.log C e The calculated values of Δ H o , ΔS o , and ΔG o are listed in Table 5.The obtained values for Gibbs free energy change (ΔG o ) ranging from 7.606 to -2.252) KJ/mole for Zn(NO 3 ) 2 adsorption on malvaperviflora ranging from (298-318) K.The negative ΔG o values indicate the thermodynamically spontaneous nature of the adsorption.The reduction in ΔG o values with increasing temperature shows a decrease in feasibility of adsorption in higher temperatures.The value of the parameter Δ H o is -0.08721KJ/mole for Zn(NO 3 ) 2 adsorption on malvaperviflora.The positive Δ H o is an indicator of exothermic nature of the adsorption and also its magnitude gives information on the type of adsorption, which can be either physical or chemical.The enthalpy of adsorption, ranging from 7.356to 25.816 J/mole corresponds to a physical sorption.The adsorption heat of Zn(NO 3 ) 2 is in range of physisorption.Therefore, the Δ H o values show that the Zn(NO 3 ) 2 adsorption on adsorbent is takes place via physisorption [10].

Adsorption Kinetics
The adsorption kinetics of Zn(NO 3 ) 2 on malvaperviflora adsorbents is investigated to determine the order of reaction.The bkinetic equations applied can be expressed as follows [11]: 1-Langergren model Pseudo first order Lagergren's is as follows log (q eq t ) = log qe -k 1 / 2.303 t----(5) where qe and qt (mg/g) are the sum of adsorbed Zn(NO 3 ) 2 at equilibrium and time t.k 1 is the first order rate constant (min -1 ).The plot of log (q e -q t ) versus t for the adsorption of Zn(NO 3 ) 2 onto malvaperviflora is drawn in Figure ( 6) and Table (6), while the values of k 1 and qe are calculated from the slope and then intercept.The resulted R 2 value is high (0.953) which signifies that the adsorption of Zn(NO 3 ) 2 perfectly complies with pseudo first order reaction.Similar kinetic results have also been reported for the adsorption of certain dyes onto Aspergillusniger and onto Peat [5].determined by the following relationship [12]: q t = k D t 1/2 (6) Where k D is the diffusion rate constant(mg/g min), which can be determined from the slope of the linear plot of qt versus t 1/2 .Fig. (7) presents a linear fit of this model for adsorption of Zn(NO 3 ) 2 .

Fig
Fig.(1)The Variation of Qe with the Contact Time for 25 ppm of Zn(NO 3 ) 2 Solution at 298K.

Figure ( 3 )
Figure (3) give the relationship Q e vs.C e for the adsorption a series of Zn(NO 3 ) 2 solution at different temperatures .According to Giles classification ,the shape of adsorption isotherms obtained in this work is like L-type isotherm.This could be explained, as the concentration of Zn(NO 3 ) 2 whish increases the vacant sites on the surface that are filled with the Zn(NO 3 ) 2 molecules in completion with the water

Fig
Fig. (4)The Quantity of Adsorption at Different PH value Using Malvaparviflora at 318K for 25ppm Zn (NO 3 ) 2 Solution

Fig.( 5 )
Fig.(5)The Plot of ln K vs.the Reciprocal of Temperature .