Removal of Pb fromWater by Adsorption on Apple Pomace: Equilibrium, Kinetics, and Thermodynamics Studies

e adsorption-in�uencing factors such as pH, dose, and time were optimized by batch adsorption study. A 0.8 g dose, 4.0 pH, and 80min of contact timewere optimized formaximumadsorption of Pb onAP.e adsorption isotherms (Langmuir and Freundlich) were well �tted to the data obtained with values of qqmax (16.39mg/g; rr 2 = 0.985) and K (16.14mg/g; rr = 0.998), respectively. e kinetics study showed that lead adsorption follows the pseudo-second-order kinetics with correlation coefficient (rr) of 0.999 for all of the concentration range. FTIR spectra also showed that the major functional groups like polyphenols (–OH) and carbonyl (–CO) were responsible for Pb binding on AP. e thermodynamic parameters as ΔGG, ΔHH (33.54 J/mol), and ΔSS (1.08 J/mol/K) were also studied and indicate that the reaction is feasible, endothermic, and spontaneous in nature.


Introduction
Due to the industrialization, especially in the developing countries, the emission of the heavy metals as lead, cadmium, chromium, nickel, arsenic, and mercury are highly concerned to public and aquatic health.Lead is released with the effluent from the paint, batteries, and automobiles manufacturing units.Lead is one of the toxic metals and largely affects the central, peripheral nervous system.Besides this the other toxic effects of the lead are visual disturbances, convulsions, loss of appetite, antisocial behaviors, constipation, anemia, tenderness, nausea, vomiting, severe abdominal pain, anemia, and gradual paralysis in the muscles [1].ere are several methods for removing heavy metals from aqueous solutions, such as chemical precipitation, membrane �ltration, ion exchange, reverse osmosis, and adsorption [2].However, the methods for the removal of metal are expensive, difficult, incomplete, and generate large amount of solid waste.
Among these the adsorption process is the most demanding technique which is easily accessible and economically feasible for the removal of water contaminants [3,4].It is the most suitable process for the removal of metals due to low cost, being easily obtained, and minimizing the volume of chemical and biological sludge.Adsorption of metals involves several mechanisms that differ qualitatively and quantitatively, according to the species used, the origin of the biomass, and its processing procedure [5].e literature was reviewed and it was found that different kinds of the adsorbent material as activated carbon [6], pine cone [7] grape bagasse [8], pine needles [9], peels of banana are used for removal of particular metals from water.
In India, out of 5000 tons of apple pomace (AP) 3000 tons are produced in Himachal Pradesh [10].Its huge production in apple juice industry becomes a challenge of its utilization as well as its disposal.Presently, the apple pomace produced aer the extraction juice from its manufacturing unit is disposed off in the �eld for natural decomposition.Aer period of time the waste undergoes anaerobic decomposition during rain and cause environmental pollution by releasing signi�cant amount of methane.�lobally, about 3-19% emission of total anthprogenic methane was contributed by waste dumping site [11].is is also creating the problem for the public as well as the environment.About 25-30% of apple pomace is le of the total processed fruit, which is rich in polyphenols, polysaccharides, pectins, cellulose hemicellulose, and lignin [10].Since these contains the functional groups, -COO, -CO, -NH   highly responsible for the metals binding capacity [12].e literature reported that the polyphenols are highly efficient for the removal of lead than the others metals [13].
Since Pb ion had large binding capacity with polyphenols and AP is rich source of polyphenols, by viewing this fact, the present study investigated for removal of Pb from water by the surface adsorption method which is inexpensive, feasible, and environmental friendly.e adsorption model as Langmuir and Freundlich satis�ed the data with regression coefficient ( 2 ),  max , and  for Pb.Spontaneity of adsorption process with respect to temperature and the behavior of adsorption with the passage of time were studied using thermodynamic and kinetic studies.e adsorption parameters as pH, dose, and time were studied which affect the adsorption.

Chemicals.
All the chemicals used in the present work were of analytical grade.e �lter papers were obtained from Qualigens (125 mm), 615A, Germany.e stock solution of Pb (1000 mg/L) was prepared by dissolving appropriate amount of lead nitrate Pb(NO 3 ) 2 (Sd Fine Chemicals Ltd.Mumbai, India).e desired concentrations of lead solutions were prepared by appropriate dilution of the stock solution for adsorption studies.

Apple Pomace. e AP was collected from Himachal
Pradesh Horticultural Produce Marketing and Processing Corporation (HPMC), processing unit Parwanoo, District Solan, Himachal Pradesh, India.e AP was dried at room temperature, crushed in an electric grinder to make �ne particle size and sieved through 0.5 mm pore size.e sieved biosorbent was stored in a container for further adsorption study.

Batch Studies. e optimization of batch adsorption
parameters, that is, dose, pH, and time for AP, was performed in a synthetic solution of Pb metal by varying a single parameter at a time with respect to that of the others constant.Aer adsorption, the �ask was removed and �ltered through �attmann �lter paper and the �ltrate analyzed for residual metal.e effect of AP dose and favourable pH was investigated between 0.1 to 1.2 g and 2 to 9, respectively, in 50 mL synthetic solutions of lead ions.0.1 N of HCl and NaOH were used for pH adjustment.e pH was measured by Cyberscan PC510 (Eutech, Singapore).e

Adsorption Isotherm and Kinetics Study.
Nine concentration ranged from 10-200 mg/L of Pb ions were prepared from the stock solution of 1000 mg/L by appropriate dilution.e optimized parameters as dose (0.8 g), pH (4), and time (80 min) remain constant for adsorption isotherm study.e kinetic study was done to observe the behavior of adsorption with the passage of time to establish equilibrium.e concentration of Pb ions from 10-100 mg/L in 50 mL was used in all optimized condition and each �ask was removed aer regular interval of time from 5-80 min.

ermodynamics Study.
Effect of temperature on Pb adsorption was studied from 25-50 ∘ C in incubator shaker at initial concentration (50 mg/L) of Pb ion.ermodynamics study was done to con�rm the feasibility and spontaneity of adsorption process by using the Van't Hoff equation [26,27].By using the Van't Hoff equation a plot of log  versus / is drawn to found the slope and intercept which is Δ and Δ, respectively.e spectral analysis of AP before and aer adsorption of Pb ions showed that the peaks either decreases in intensity or disappear might involve in metals adsorption [28].e peaks at 3410.2, 2919.8,2850.7,1645.3,1053.7, and 570.4 cm −1 are because of polyphenols (-OH) groups, aliphatic -C-H stretching, carbonyl group (-CO), -C=O, and -C-C-groups, respectively, and were responsible for the Pb binding.e surface area of AP before and aer adsorption was found to 0.7129 m 2 /g and 0.4834 m 2 /g, respectively.It indicated that the adsorption of Pb was successfully carried out onto AP.

Effect of pH.
pH is an important variable in the ion exchange governed adsorption process than the other physicochemical parameters.In order to observe the effect of pH on adsorption of Pb, AP contacted with Pb solution at different pH (2)(3)(4)(5)(6)(7)(8)(9).e effect of pH on Pb adsorption on AP is summarized in Figure 2. At lower pH, the adsorption was found low due to sorbet lyphobic behavior [29].Aer pH 2, adsorption increased sharply up to pH 4 and thereaer no signi�cant change was observed for greater pH.As the pH increases, the lower the number of H + ion and greater number of negatively charge metal binding sites are available for metal adsorption [30].e maximum adsorption of 93% was observed at pH 4.0 for Pb ions and no signi�cant difference observed by increasing pH.is may be due to the established equilibrium between metal and hydrogen ions.Similar �nding was observed for Pb adsorption on chitosan [31].No pH values over 9.0 were studies due to the precipitation of metals ion occurs.

Effect of Adsorbent Dose
. e adsorbent dose of AP was investigated from 0.1-1.2g/50 mL of Pb ions solution (Figure 3).e result showed that as the dose () of adsorbent increased, the % removal also increases; this is due to the more availability of the adsorbent surface for complex formation with metal ions in water.e maximum removal of Pb ions was observed at 0.8 g dose of AP from water.e steady state was obtained by further increased in the dose of adsorbent towards Pb metal ion adsorption.Further decrease in adsorption may be due to the adsorbent gets aggregated and provides less effective surface area for metal binding.

Effect of Time.
Time plays important role in adsorption of metal ions on adsorbent surface.e effect of time on Pb adsorption onto AP was studied in the range of 10-180 min (Figure 4).e result revealed that as the time increased the rate of adsorption increased upto 80 min and sudden decreased in adsorption rate was observed beyond 80 min from 94 to 90%.e maximum removal of 94% was found at 80 min.So the optimized time for the maximum removal of Pb was 80 min.5(a) and 5(b)) were obtained to establish the equilibrium data in concentration ranged from 10-200 mg/L at optimized condition of pH, time, and dose.e data obtained from the study of adsorption at different concentration applied to Langmuir and Freundlich isotherm by using well known adsorption isotherm equation [15].�oth the adsorption isotherms were well �tted with  max and correlation coefficient ( 2 ) for the adsorption of Pb metal ions on AP.In case of Langmuir isotherm maximum adsorption capacity ( max ) and constant  for adsorption of Pb on AP were found to be 16.39 mg/g, and 0.67 L/g with correlation coefficient of 0.985, respectively.On the other hand value of Freundlich constant () and  was found to be 16.14 mg/g, and 1.02 with correlation coefficient of 0.998, respectively.e value of  less than one indicate chemical adsorption while the value greater than one tells about the physical process [32].Since the  value was found above one, that is, 1.02 indicated that adsorption on AP surface was carried out by physical process.e  max values of other researchers studied for Pb removal was compared with present study (Table 2).

Kinetic Study.
In order to �nd the effect of time, the concentration ranged from 10-100 mg/L were studied in 250 mL of volumetric �asks at pH of 4, dose 0.8 g and time from 5-80 min.e pseudo-second order kinetics model has been used to evaluate the experimental kinetics data of AP [33,34].Linear plot was between   versus , whose intercept and slope gives the value of  and   (mg/g), respectively, (Figure 6).e pseudo second order equation of all selected concentration from 10-100 mg/L with their   ,  2  and  values were given in Table 3. e correlation coefficient of ( 2 ) for the second order of kinetics was found to be 0.999 which showed that reaction rate follows pseudo-second order kinetics.

Effect of Temperature.
In thermodynamics study, in the isolated system, energy neither be created nor destroyed and the change in entropy is the only energy source.In environment concept of the energy and entropy must calculate for the occurrence of spontaneity of the adsorption reaction.From Van't Hoff equation a plot of log  versus 1 (Figure 7) was drawn to found the slope and intercept for Δ and Δ, respectively.e value of Δ and Δ was found to be 33.51J/mol and 1.08 J/mol/K, respectively, which indicated that the adsorption was endothermic and increased entropy.e value of Δ was found to be −62.79,−64.69, −68.94, and −73.84 J/mol at temperature of 293, 303, 313 and 323 K.As the temperature increases the negative value of Δ also increased which indicate the feasibility and spontaneity of Pb adsorption onto AP. e endothermic nature of reaction was also supported by increase in adsorption when temperature increases.

Conclusions
e present study was aimed to evaluate the industrial waste AP for the Pb adsorption from synthetic water.e result revealed that 0.8 g of dose, 4 pH, and contact time of 80 min were optimized for maximum removal of Pb from water.is study also follows the Langmuir and Freudlich isotherm with  max value of 16.39 mg/g and  of 16.14 mg/g, respectively.
In case of thermodynamics study the negative value of Δ, positive value of Δ (33.54 J/mol) and Δ (1.08 J/mol/K) were indicated that the reaction is feasible, endothermic and spontaneous in nature.e kinetics study showed that the adsorption of Pb onto AP follows the pseudo second order of kinetics ( 2 = 0.999).e result revealed that the AP may prove to be good, economical, cheap, and environment friendly adsorbent for the Pb removal from water.

F 1 :
FTIR spectra of AP before and aer adsorption of Pb ions.

F 2 :
Effect of pH on adsorption of Pb ions onto AP (dose of 0.8 g, metal concentration of 50 mg/L).