Utilization of Waste Leaves Biomass of Myrica esculenta for the Removal of Pb ( II ) , Cd ( II ) and Zn ( II ) ions from Waste Waters

In the present study, we have used the waste leaves of Myrica esculenta for the removal of Pb2+, Cd2+ and Zn2+ ions from the synthetically prepared waste water. The adsorption based removal process has been carried out under the batch system. The batch system was included pH, contact time, dosage, concentration and temperature. The maximum removal efficiency was achieved at optimized conditions i.e. higher contact time, higher pH, lower metal ion concentrations and moderate temperatures. The presence of various organic binding groups was characterized by FTIR spectroscopy. The percentage adsorption of Pb2+, Cd2+ and Zn2+ ions was found 97.02%, 92.52% and 81.99% at pH 6 after contact time 25 minutes. The data of adsorption were tested with Langmuir, Freundlich and Temkin isotherm models. The adsorption capacity of Pb2+, Cd2+ and Zn2+ ions was evaluated as 8.264, 5.617 and 7.751mgg-1 by Langmuir isotherm model.


INTROdUCTION
Since from last two or three decades, the exposure of heavy metals in the aquatic bodies has increased very rapidly 1 .The presence of heavy metals in the water or waste water causes life threatening problems to all living organisms 2,3 .These contaminants are non biodegradable and remain persistent in the environment.The common heavy metals are copper, lead, cadmium, zinc, chromium, nickel, arsenic, iron and cobalt.Biologically, they play an important role in the different physiological activities under the limits.In excess, they are definitely harmful to human and other life forms and some of them are very harmful even at very low concentrations [4][5] .The conventional methods used for the removal of heavy metals such as chemical precipitation, electro winning, reverse osmosis, ultrafiltration, ion exchange are suffering from poor performances, less applicability in large scale operations, high cost and generation of harmful chemical sludge.The adsorption process using any local abundant adsorbent is better alternative over conventional methods.It minimizes the use of chemicals, requires very low cost, efficient and can be applicable in large scale waste water treatment methods without any harmful sludge 6,7 .This process is depending on the physico-chemical pathways of uptake or as the property of certain biomass to bind and concentrate selected metal ions or other contaminants from aqueous solutions [8][9][10][11] .Lead is a very common heavy metal and released through leaded gasoline, smelting, combustion, battery recycling, lead containing pipes etc.It causes some very harmful effects on reproductive, nervous and urinary systems in the humans.Lead is also a carcinogenic agent and it retards the rate of photosynthesis in plants [12][13][14][15][16] .The exposure of cadmium (Cd) in the fresh or saline waters is from the industries like ceramics, metal finishing, alloying, mining etc.It is harmful to human beings and can cause hypertension, renal dysfunction, hepatic injury, lung damage etc [17][18][19][20][21][22][23] .Zinc is biologically very important in human and other life forms but its extra doses through contaminated water or food causes abdominal pain, dizziness, poor performances of muscles and acute renal failures in human.It releases in water bodies through electroplating, mineral processing, galvanizing plants, paint formulation, porcelain enameling, and vegetable fat producing industries 24,25 .The plant Myrica esculenta is abundantly found in the hills of Kumaun and Garhwals, Himanchal Pradesh, Jammu -Kashmir, Sikkim, Arunachal Pradesh, Assam, Meghalaya, Nagaland, Manipur and western Nepal.It is an evergreen gymnospermic plant and has many medicinal properties and is used in the treatment of treating wounds, musculoskeletal disorder and disease of oral cavity.The waste leaves of the plant have been collected from the Kumaun hills of India in the month of June.

MATERIAL ANd METHOdS
All plastics and borosil reagent bottles were used for preserving adsorbent, stock and working solutions soaked for 12 h in 10% nitric acid solution and then washed with deionised water.The chemicals used in the present work were of analytical grade and double distilled water used for washing of glasswares and preparation of all solutions.
Preparation of adsorbent: The waste leaves of Myrica esculenta were collected in the month of June from the Kumaun hills of Uttarakhand, India.The collected leaves were then washed 3-4 times with deionized water and then dried in the laboratory.The moisture contents of the leaves removed by the drying of leaves in tray dryer between the temperature 60-65 0 C under controlled conditions.After that, these leaves have been grinded and sieved into the particle size 0.125 mm (BSS120).The prepared leaf powder then preserved in sealed bottles and 0.1 g was used for FTIR studies.

Preparation of waste water and adsorption study
The waste water containing Pb 2+ , Cd 2+ and Zn 2+ ions was prepared by dissolving the salts lead nitrated Pb (NO 3 ) 2 , cadmium nitrate Cd (NO 3 ) 2 and zinc sulphate Zn (SO 4 )2.7 H 2 O in double distilled water, separately.For making 1000 mgl -1 stock solutions, 1.598 g Pb (NO 3 ) 2 , 2.103 g Cd (NO 3 ) 2 and 4.397 g Zn (SO 4 ) 2 .7H 2 O were dissolved separately in deionized waters.The pH of stock solutions was adjusted 4 by digital pH meter (Model: Teshcon Sr No 15J520).The pH of all stock and working solutions was adjusted by using 0.1 M HCl or 0.1 M NaOH solutions.A required amount of adsorbent (0.1 to 1g) was treated with 100 ml of desired working solutions containing 10 to 50 mg/L of Pb 2+ , Cd 2+ and Zn 2+ ions in a 250 ml of Erlenmeyer flask at constant rpm 170 and pH 1 to 6.The contact times 10 to 70 min.and temperatures 10 to 70 0 C have been used in the overall removal process.After completion the reaction, the solutions were filtered and metal ion concentrations measured in filtrate using Atomic Absorption Spectroscopy (Thermo Scientific: iCE 3000 Series).The percentage adsorption of metal ios onto the adsorbent is calculated by following formula: Where, C i and Cf are initial and final concentration of metal ions in the aqueous solution.

RESULTS ANd dISCUSSION
Characterizations: Fourier transform infrared spectroscopy (FTIR) is depending on the interference of the electromagnetic radiation and the absorption spectra obtained by the techniques of interference.The FTIR spectra explain the presence of organic binding groups that are responsible for the interactions with metal ions.The FTIR spectra of adsorbent prepared from the waste leave biomass of Myrica esculenta in the range of 4000-400 cm -1 are represented in Fig. 2. The sharp peaks at 3425 cm -1 , 3401 cm -1 , 3371 cm -1 , 2923 cm -1 , 2853 cm -1 , 1621 cm -1 , 1541 cm -1 , 1368 cm -1 and 1231 cm -1 have been found due to presence of different organic groups.The sharp adsorption bands at 3425 cm -1 , 3401 cm -1 , 3371 cm -1 , 2923 cm -1 and 2853 cm -1 are indicating that the presence of -OH, -NH, and C-H (aliphatic) groups on the surface of adsorbent.The peaks 1621 cm -1 , 1541 cm -1 , 1368 cm -1 , 1231 cm -1 are assigned to C=O, C=C, C-N, C-O, C-C etc on the surface of unloaded leaf powder [26][27][28][29] .
Initially, the adsorption of lead, cadmium and zinc was found to be 4.48, 1.39 and 12.48% and that recorded 10.79, 8.79 and 20.81% at the dosage 0.4 g.The highest removal was achieved at 1 g after 25 minutes.At this amount, 31.08% lead, 18.99% cadmium and 5.601% zinc have been removed at pH 4 (Fig. 5).In general, the number of active sites increases with the increase of the amount of adsorbent and that results maximum adsorption 33 .
The experimental data of adsorption of all these metal ions indicate that the removal efficiency decreases with the increase in the concentrations of solution but the amount of adsorbate metal ions (mg/g) increases.This can be explained as the generation of motive force of concentration gradient as the initial metal ion concentration 34,35 .At initial metal ion concentration (10 mg/L), the removal efficiency for Pb(II), Cd(II) and Zn(II) ions was found to be 27.09,15.69 and 40.75% and that decreases to 11.75, 7.92 and 13.99% (Figure 6).

Effect of pH and contact time:
The pH of solution is very important parameter in the adsorption phenomenon.At pH 3, the removal efficiencies of lead, cadmium and zinc has been recorded 10.79, 10.11 and 26.75% and increases to 26.79, 14.71 and 48.03% at pH 4. The maximum adsorption was found at pH 6; that has been found to be 97.02,92.52 and 81.99% for lead, cadmium and zinc.It is due to the factor that all the binding organic groups undergo protolysis and become positively charged at lower pH.It is therefore, repulsion occurs between metal ions and binding groups that result poor adsorption [30][31][32] (Fig. 3).A minimum time is required for the interactions of metal ions and adsorbent.The percentage adsorption was found to be 29.88,13.97 and 52.81% for Pb (II), Cd (II) and Zn (II) at contact time 30 min.and after 60 min.it increases to 47.65, 39.88 and 68.90% at pH 4 and 10 mg/L concentration of metal ions (Fig. 4).After that, the adsorption becomes constant due to the occupation of all the active sites by the metal ions 24,25 .

Effect of dosage and concentration
The removal efficiency of metal ions is usually increased with the amount of adsorbents.Langmuir isotherm model explains the formation of monolayer of metal ions on the surface of adsorbents that contain a finite number of binding groups.These binding groups are arranged in a regular pattern 36,37 .
Mathematically, the Langmuir isotherm model can be represented as below: Where, C f and Q e are the equilibrium concentrations (mgl -1 ) of metal ions in aqueous solution and their amount adsorbed on the surface of adsorbent (mgg -1 ).The Langmuir constant K l and b represents adsorption capacity (mgg -1 ) and adsorption equilibrium constant (Lmg -1 ).The values of K l and b have been evaluated from the graph C f /Q e vs C f (Fig. 8).For Pb(II), Cd(II) and Zn(II), the values of K l and b are found 8.264, 5.617 and 7.751mgg -1 and 1.001, 1.002 and 1.013 Lmg -1 .The values of regression (R 2 ) indicates that zinc (R 2 = 0.977) follows Langmuir model more than cadmium (R 2 = 0.961) and lead (R 2 = 0.837).The dimensionless factor R L of Langmuir model is represented as below:

Effect of temperature
The adsorption of metal ions increases with increase in temperature of the aqueous solutions due to the escaping tendency of adsorbate metal ions to the entire space of the surface of adsorbents.After certain temperature, the adsorption becomes constant or decreases.It may be attributed to the dissolution of adsorbed metal ions in the solutions 6 .At initial temperature 10 0 C, the removal efficiency of Pb(II), Cd(II) and Zn(II) ions was recorded 25.99, 10.25 and 44.41%.It increases very smoothly to 32.90, 34.03 and 67.91% at 60 0 C.After 60 0 C, the adsorption of lead, cadmium and zinc becomes about constant (Figure 7).

Adsorption isotherms
In general, the adsorption isotherms explain the distribution of adsorbate metal ions in between two phases i.e. solid and liquid and existence of an equilibrium state.Suitable designed isotherms indicate the type of adsorption and critical optimization of the utilization of adsorbents.Where, b and C i are the Langmuir constant and the initial metal ion concentration (mgl -1 ).The value of R L determines adsorption i.e. favorable (0<R L <1), unfavorable (R L >1), linear (R L =1) or irreversible (R L =0).Here the value of R L was found to be <1 in all cases of applied batch system of concentration dependency.The Freundlich isotherm model is explained as the presence of different binding groups that involved in the interaction with metal ions varying with different energies on the heterogeneous surface of the adsorbents 38 .The Freundlich isotherm model is mathematically given as below: log Q e = log K f + 1/n log C f Where, Qe and Cf are the amount of metal ion adsorbate and final concentration of aqueous solution in mgg -1 and mgl -1 .The constants K f and 1/n are the adsorption capacity and intensity of adsorption and their values are calculated from the graph log Q e vs log C f (Fig. 9).The values of K f for lead, cadmium and zinc are evaluated as 2.691, 3.176 and 1.927 mgg -1 , respectively.From the values of R 2 , we can arrange all the metal ions for the suitability for Freundlich isotherm model as Cd(II) = Zn(II) > Pb(II) (Table 1).Temkin isotherm model is generally used for the interactions between adsorbed metal ions and a linear decrease of heat of adsorption for the coverage due to metal ions on the surface of adsorbents 6 .The Temkin isotherm model is mathematically defined as: Where C f is the equilibrium concentration of metal ions in mgl -1 , Q e is the amount of adsorbate metal ions in mgg -1 , X and Y are adsorption capacity and Temkin constant (Table 1).

CONCLUSION
The experimental data of adsorption shows that the waste leaves of Myrica esculenta are potential adsorbents for the removal of Pb(II), Cd(II) and Zn(II) ions from the waste waters.The maximum adsorption of metal ions was observed at contact time 60 min.pH 6, dosage 1 g and