Removal Of Copper Ions By A Biosorbent Environmental Sciences Essay

Abstraction: In the present survey, Cinnamomum camphora leaves pulverization ( CLP ) was investigated as a biosorbent for the remotion of Cu ions from aqueous solutions. The biosorbents before and after surface assimilation were measured by EDS and FT-IR. Kinetic informations and sorption equilibrium isotherms were carried out in batch procedure. The surface assimilation kinetic experiments revealed that there are three phases in the whole surface assimilation procedure. It was found that Cu ( II ) surface assimilation onto CLP for different initial Cu ( II ) concentrations all followed pseudo-second order dynamicss and were chiefly controlled by the movie diffusion mechanism. Batch equilibrium consequences at different temperatures suggest that Cu ( II ) surface assimilation onto CLP can be described absolutely with Langmuir isotherm theoretical account compared to Freundlich and D-R isotherm theoretical accounts, and the characteristic parametric quantities for each surface assimilation isotherm were besides determined. Thermodynamic parametric quantities calculated show that the surface assimilation procedure has been found to be endothermal in nature. The analysis for the values of the average free energies of surface assimilation ( Ea ) , the Gibbs free energy ( ?G0 ) and the consequence of ionic strength all demonstrate that the whole surface assimilation procedure is chiefly dominated by ion-exchange mechanism, accompanied by a certain sum of surface complexation which has been verified by fluctuations in EDS and FT-IR spectra and pH value before and after surface assimilation. Regeneration surveies show CLP possesses an first-class reusability.

Cardinal words: Adsorption ; Cinnamomum camphora foliage ; Cu ( II ) ; Kinetics ; Isotherms ; Thermodynamicss

1. Introduction

Today, heavy metal pollution has become one of the most of import environmental jobs. Copper ( II ) is known to be one of the heavy metals and a widely used in many industries including metal cleansing and plating, paper board, printed circuit board, wood mush, fertiliser, pigments and pigments, etc. [ 1,2 ] . The wastewaters in these industries normally contain a considerable sum of Cu, which spreads into the environment through dirts and H2O watercourses and accumulates along the nutrient concatenation, ensuing in a high hazard to human wellness, as high concentrations of Cu will do tummy disturbance and ulcer, mental retardance, liver and encephalon harm, and so on [ 3 ] . As Cu ( II ) does non degrade biologically, the control of Cu ( II ) pollution has particular importance for both beings that live in Waterss and those that benefit from Waterss.

Different methods of handling effluents incorporating heavy metal ions have been developed over old ages which include curdling, ion-exchange, membrane separation, rearward osmosis, solvent extraction, chemical precipitation, electroflotation etc [ 4 ] . However, most of these techniques have some disadvantages such as complicated intervention procedure, high cost, and energy usage. Among these methods, surface assimilation is a much preferred technique for the remotion of heavy metals from polluted Waterss compared to others due to ease of operation and cost-efficient procedure [ 5 ] . Even though the most promising adsorbent for surface assimilation is activated C, which has a high surface country and a high surface assimilation capacity, it is really expensive, has high operation costs and there is a demand for regeneration after each surface assimilation rhythm [ 6,7 ] . Hence, it is imperative to happen alternate low-priced sorbent stuff to replace high cost activated C for H2O and effluent intervention. Over the past two decennaries, legion low-priced stuffs have been tested for their heavy metal sorption potency [ 8-14 ] . Of these stuffs, workss waste stuffs, such as peat, rice chaff, sugar Beta vulgaris mush, banana pith, saw dust, works foliages, bark, coir, etc. , are doing scientist ‘s involvement in wasterwater intervention due to wide handiness and comparative bargain rate. These wastes as heavy metal adsorbents have been extensively reviewed by Demirbas [ 12 ] , Wan Ngah and Hanafiah [ 13 ] and Sud et al [ 14 ] .

Camphor tree ( Cinnamomum camphora ) is an everygreen tree indigen to China, distributed in the states South of the Yangtze River and Japan, India, Malaysia country. Its wood, bark and foliages can be used to pull out camphor oil, which has an of import fungicide activity [ 15,16 ] . In southwesterly China, many metropoliss have planted Cinnamomum camphora tree in chief roads, Parkss and schools. The Cinnamomum camphora tree on a regular basis sheds its foliages during spring, which become waste. To day of the month, some types of tree foliages were used as Cu ions biosorbents [ 17-19 ] . Kumar et Al. [ 17 ] have studied the surface assimilation of Cu ( II ) ion from aqueous solution by Tectona grandis L.f. ( teak leaves pulverization ) . Sawalha et Al. [ 18 ] have investigated the thermodynamic and isotherm of Cu ( II ) onto foliages of saltbush ( Atriplex canescens ) and compared biosorption features of Cu ( II ) with those of Pb ( II ) and Zn ( II ) . Wan Ngah and Hanafiah [ 19 ] have studied dynamicss, isotherm, and biosorption mechanisms of Cu ions from dilute aqueous solutions on base treated gum elastic ( Hevea brasiliensis ) leaves pulverization. However, to our best cognition, there is still no reported about the usage of Cinnamomum camphora leaves as heavy metals biosorbent.

In the present survey, finely land pulverization prepared from Cinnamomum camphora foliages ( CLP ) , a bio-based waste stuff, was used as biosorbent for the remotion of Cu ( II ) from an aqueous solution. The surface assimilation dynamicss, isotherm and thermodynamics under assorted experimental conditions ( i.e. , pH, ionic strength of the solution, contact clip, concentration and temperature ) were investigated. Pseudo-first order, pseudo-second order, and intra-particle diffusion theoretical accounts [ 20-22 ] were used to analyse the surface assimilation dynamicss. The Langmuir, Freundlich and Dubinin- Radushkevich isotherms theoretical accounts [ 23-25 ] were used to suit the surface assimilation equilibrium informations. The thermodynamic parametric quantities were determined utilizing Va n’t Hoff equation. The equations matching to these theoretical accounts are given in Appendix A. The public presentation of the repeated usage of the biosorbent was besides studied. The surface assimilation mechanism is discussed comprehensively based on the consequences.

2. Experimental

2.1. Materials and chemicals

The Cinnamomum camphora tree ‘s foliages used in the present probe were collected in spring 2009 from campus of Taizhou University, China. A stock solution of Cu ( II ) was prepared by fade outing CuSO4·5H2O in double distilled H2O. Other agents used, such as HCl, NaOH, were all of analytical class and all solutions were prepared with dual distilled H2O.

2.2. Preparation of the biosorbent

The gathered foliages were washed repeatedly with distilled H2O for several times to take soil atoms and soluble drosss and were allowed to dry in an air oven at 353 K for a period of 24 H when the foliages became sharp. These were crushed into a all right pulverization in a mechanical bomber to obtain the foliages pulverization. The pulverization was sieved to obtain particle size of & A ; gt ; 200 mesh. The obtained stuff was washed repeatedly with distilled H2O till the lavations were free of coloring material and turbidness. Finally, the obtained stuff was so wholly dried in an air go arounding oven at 353 K for 2 yearss and preserved in glass bottles for usage as a biosorbent.

2.3. Adsorption surveies

Adsorption experiments were evaluated in batch equilibrium manner. All experiments were conducted by blending 25 milliliter of aqueous Cu ( II ) solutions with 0.05 g of the biosorbent. The pH values of solutions were adjusted with dilute HCl or NaOH solution by utilizing a Mettler Toledo 320 pH metre. The mixtures of the biosorbent and Cu ( II ) solution were shaken in a thermostatic shaker bath ( THZ-98A mechanical shaker ) at 120 revolutions per minute at coveted temperature and contact clip, and so the suspensions were centrifuged at 5000 revolutions per minute for 10 min.

To analyze the consequence of pH, surface assimilation experiments were conducted at different pH runing from 2 to 5 at 150 mg L-1 of Cu ( II ) solution. Concentrations of Cu ( II ) solutions before and after surface assimilation were measured with an atomic soaking up spectrophotometer ( Perkin-Elmer SIMAA 6000 ) . The surface assimilation capacity of the biosorbent at equilibrium was calculated utilizing the equation:

( 1 )

For kinetic surveies a series of different initial concentrations ( 25, 50, 100 mg L-1 ) of Cu ( II ) solution with seting pH of 4.0 were chosen as the initial concentration of Cu ( II ) solution. The surface assimilation capacity of the biosorbent at any clip was calculated by:

( 2 )

Adsorption experiments were besides carried out to obtain isotherms at different temperatures. This was done at 303.2, 313.2, 323.2 and 333.2 K, severally. The mixture of the biosorbent and Cu ( II ) solution was shaken for 1 Hs to make equilibrium at different temperatures. In this group of experiments Cu ( II ) solutions with different initial concentration, in the scope of 12.5-150 milligram L-1, were selected.

The consequence of ionic strength was studied utilizing NaCl as the ionic medium. The concentration of this salt was varied within the scope 0.001-0.5 mol L-1. The concluding pH values of solutions at equilibrium were measured in order to more in-depth apprehension of surface assimilation mechanism.

Normally, pH 4.0 ; ionic strength of about 0 and 303.2 K were selected as surface assimilation conditions unless otherwise stated in the whole survey. Each experiment was triplicated under indistinguishable conditions and merely intend values were presented. To measure the cogency of kinetic and isotherm theoretical accounts to stand for the experimental information, statistical analyses for the standard mistakes ( S.E. ) and F values of F-test were performed at a 95 % assurance interval ( CI ) utilizing statistical package ( SPSS 13.0 for Windows ; SPSS Inc. , Chicago, Illinois, USA ) .

2.4. Desorption and regeneration surveies

The biosorbent utilized for the surface assimilation of an initial metal concentration of 150 mg L-1 was separated from the Cu ( II ) solution by centrifugation. The Cu ( II ) -loaded biosorbent was gently washed with 25 milliliters double distilled H2O to take any un-adsorbed Cu ( II ) and so carried out by agitating with 25 milliliters of 0.1 mol L-1 HCl solution at 303.2 K for 4 h. After this, the biosorbent was washed three times with dual distilled H2O, and so dried and reused for surface assimilation surveies. The adsorption-desorption procedure was performed in five times. Desorption capacity and desorption efficiency were defined in Equations ( 3 ) and ( 4 ) , severally.

( 3 )

( 4 )

2.5. Word picture of samples

Energy diffusing spectrometry ( EDS ) analyses of CLP before and after Cu surface assimilation were done in a Jeol JSM-5600LV with samples fixed in an aluminium stub. In order to avoid the intervention of Au component, is carried out on samples without gold spray.

In order to look into the consequence of pH on spectral alterations of the functional groups, control sample, CLPblank ( non including metal bearing solution but the biosorbent and distilled H2O, whose pH was adjusted to 4.0 ) were besides tested at the same time in metal uptake experiments. FT-IR spectra measurings of CLP, CLPblank and Cu ( II ) -loaded CLP were done on a Thermo Nicolet NEXUS TM spectrophotometer utilizing the KBr pellets. The spectrum was collected 32 times in the scope of 4000-400 cm-1 with a declaration of 4 cm-1 and corrected for the background noise. CLPblank and Cu ( II ) -loaded CLP used for FT-IR survey were obtained by pull outing the biosorbent from the liquid stage after centrifugation and drying in an oven at 60 oC for 2 H.

The pH at point zero charge ( pHPZC ) of the biosorbent was determined by the solid add-on method [ 26 ] .

Terminology

CLP

Cinnamomum camphoraleaves powder

C0

the initial concentration of the adsorbate in solution ( mg L-1 )

Cerium

the equilibrium concentration of the adsorbate in solution ( mg L-1 )

Connecticut

the concentration of the adsorbate in solution at any clip T ( mg L-1 )

Volt

the volume of the solution added ( L )

m

the mass of the biosorbentused ( g )

phi

The initial pH value of solution

pHf

The concluding pH value of solution

qd

desorption capacity of the biosorbent ( mg g-1 )

Erectile dysfunction

desorption efficiencyof the biosorbent

Qd

sum of metal desorbed in one rhythm ( milligram )

Qe

sum of metal loaded in one rhythm ( milligram )

T

surface assimilation clip ( min )

k1

pseudo-first order rate invariable of surface assimilation ( min-1 )

K2

pseudo-second order rate invariable of surface assimilation ( g mg-1min-1 )

qi

intra-particle diffusion rate invariable ( mg g-1min-1/2 )

qe

surface assimilation capacity of the biosorbentat equilibrium ( mg g-1 )

qt

surface assimilation capacity at any clip T ( mg g-1 )

qmax

the monolayer capacity of the biosorbent ( mg g-1 )

B

the Langmuir invariable ( L mg-1 )

Kf

the Freundlich invariable ( mg1-1/nL1/ng-1 )

N

experimental changeless declarative mood of the surface assimilation strength of the biosorbent

?

a changeless related to the average free energy of surface assimilation ( mol2kJ-2 )

qm

the theoretical impregnation capacity ( mg g-1 )

?

the Polanyi potency, which is equal to RT ln ( 1+ ( 1/Ce ) )

Thymine

the absolute temperature ( K )

?G0

alteration in the Gibbs free energy ( kJ mol-1 )

?H0

alteration in the heat content ( kJ mol-1 )

?S0

alteration in the information ( kJ mol-1 K-1 )

3. Consequences and treatment

3.1. Word picture of the biosorbent

In this survey, EDS is used to examine the alteration in element composings of CLP and Cu ( II ) loaded-CLP ( Fig. 1 ) . It is clearly observed in Fig. 1 that the CLP consist of chiefly C and O, and little sums of Si, Ca, Na, K, P and S. After surface assimilation, Ca, Na, K, P and S peaks about diminished and the Cu extremums in the spectra are seeable, proposing ion-exchange might be one of the mechanisms involved in Cu remotion [ 19 ] .

Fourier transform infrared spectral analysis is of import to place some characteristic functional groups, which are responsible for adsorbing metal ions [ 19,27-29 ] . Taking into history wavenumber of extremums may alter before Cu ( II ) surface assimilation by the influence of solution pH, a clean sample was added in FT-IR analysis. The FT-IR spectra of CLP, CLPblank and Cu ( II ) -loaded CLP and matching alterations in extremums are presented in Fig. 2 and summarized in Table 1. The declaration of the setup used was 4 cm-1, which means any displacement of equal to or less than 4 cm-1 may be caused by the instrument itself. So the displacements of more than 4 cm-1 were chiefly focused in this survey. In general, the relevant functional groups on the CLP could be determined based on the FT-IR surface assimilation set. Based on the ascription of extremums in the tabular array, it can be known that CLP contains a figure of functional groups such as -OH, -NH2, -COOH, -POH, etc. The comparing of the spectral alterations of CLP and CLPblank showed that there are really similar infrared spectra, bespeaking solution pH did non do an apparent structural alteration on biomass surface. However, the wavenumber imputing to -OH blueshifted from 3415 to 3394 cm-1, which might be caused by acidic solution. H+ ions in solution as givers can adhere to the sites on the surface of CLP and organize impersonal functional groups ( -OH, -NH2 and -COOH, etc. ) , which result in the stretching quivers of a lower frequence in FT-IR spectra [ 34,35 ] .

After Cu ( II ) binding, the most of characteristic extremums matching to these groups changed. The wavenumber of -OH group redshifted from 3394 to 3413 cm-1 compared with that of CLPblank, bespeaking complexation occurred sing the formation of surface composites can impact the peak place of -OH. The extremums at 1441 and 1375 cm-1 show a singular addition in wavenumbers, and the peak strength decreased to some extent after surface assimilation, bespeaking that hydroxyl involved in surface assimilation to a big extent. In add-on, important alterations have besides taken topographic point for the characteristic extremums matching to amino after surface assimilation. Specifically, the extremum at 1613 cm-1 redshifted of 6 cm-1 and the extremum at 1318 cm-1, was non changed, but strength of the extremum dramatically weakened. This indicates that amino has an of import part to the surface assimilation. Compared to the hydroxyl and amino, the sum of carboxyl groups involved in surface assimilation was significantly smaller than those of the two groups, which can be easy seen from the extent in alterations of its characteristic extremums. Overall, the above mentioned groups all participated surface assimilation procedure for Cu ( II ) , with the chief part of hydroxyl and amino. Based on the analysis, the mechanism of Cu surface assimilation on CLP could besides happen by surface complexation [ 19,28 ] .

3.2 Effect of pH

The pH of the aqueous solution is an of import variable in the surface assimilation of metals on the biosorbents. So the influence of the initial pH of solution on the surface assimilation of Cu ( II ) onto CLP was examined in the pH scope of 2 to 5 ( Fig. 3 ) . As can be seen, the surface assimilation capacity of Cu ( II ) tended to increase with increasing pH value. The qe increases quickly with increasing pH from 2 to 3, and so increases easy with farther addition in pH. Similar fluctuations of qe V pH have been earlier recorded in survey on heavy metals surface assimilation onto some leaf biosorbents [ 19,29,31 ] .

The influence of the solution pH on the metal ions uptake can be explained on the footing of the pH at point zero charge ( pHPZC ) of the biosorbent [ 36 ] . This is a convenient index when the surface of biosorbent becomes either positively or negatively charged as a map of pH. When pH of mixture of the biosorbent and solution is lower than pHPZC, which means that the biosorbent surface nowadayss positively charged as a whole. Otherwise it would demo negatively charged. The pHPZC of CLP determined by the solid add-on method was about 5.9 ( Fig. 3 ) . For the clean experiment without adding Cu ions or the surface assimilation experiments, pH values after solid-liquid interactions are both significantly lower than the pH at point zero charge ( pHPZC ) of the biosorbent ( See inside informations in 2nd paragraph of subdivision 3.6 ) . So, it is clear that the surface of the biosorbent is positively charged as a whole in this survey. Consequently, electrostatic attractive force mechanism can be easy excluded. In fact, the fluctuation in qe V pH can be interpreted by following facts. In a extremely acidic solution ( pH of 2 ) , a high concentration of H+ ions compete with Cu ( II ) for exchangeable cations on the surface of biosorbent, ensuing in the suppression of Cu ( II ) surface assimilation on CLP surface and a low qe was observed. As pH value is higher, more exchangeable cations contained in the biosorbent can be exchanged with Cu ( II ) due to weak competitory surface assimilation of H+ ions. Furthermore, an addition in solution pH would do protonation of more ligands such as amino, hydroxyl, and carboxyl groups, which could profit for the remotion of Cu ions. So, a rapid addition in surface assimilation capacity occurred at pH scope of 2-3. The slow addition in qe after pH 3 might be related to the fact that surface assimilation mechanisms above mentioned is affected indistinctively by a alteration of pH here. In order to increase the surface assimilation capacity as possible and maintain Cu ( II ) as a simple signifier, i.e. Cu2+ in the solutions, pH of 4.0 was selected for the remainder of the batch experiments.

3.3. Adsorption dynamicss

Fig. 4 shows the consequence of contact clip on the surface assimilation capacity of CLP for Cu ( II ) at different initial concentrations. As can be seen in Fig. 4, the surface assimilation of Cu ( II ) is rapid from the beginning of the experiment and thereafter it proceeds at a slower rate and eventually reaches to equilibrium. With the addition in concentration, the tendency becomes more obvious. It is besides observed from the graphs that Cu ( II ) surface assimilation on CLP was a really fast procedure, where & A ; gt ; 90 % of the surface assimilation took topographic point within the first 10 min and equilibrium was attained within 30 min. Similar findings for Cu ( II ) surface assimilation onto bio-waste stuffs have been reported by other research workers [ 19,27 ] .

In order to look into the surface assimilation dynamicss of Cu ( II ) on CLP, three different kinetic theoretical accounts, pseudo-first order, pseudo-second order, and intra-particle diffusion, have been used to suit experimental informations obtained from batch Cu ( II ) remotion experiments. Table 2 lists the consequences of the rate changeless surveies for different initial Cu concentrations by the three kinetic theoretical accounts. At all studied initial Cu concentrations, the highly high correlativity coefficients ( & A ; gt ; 0.999 ) were obtained by ciphering with pseudo-second order kinetic equation. In add-on, the deliberate qe values besides agree with the experimental information in the instance of pseudo-second order dynamicss. These suggest that the surface assimilation informations are good represented by pseudo-second order dynamicss in comparing to the other two dynamicss, which can be farther validated by F values. It is besides observed from Table 2 that the value of the rate changeless K2 decreases with increasing initial Cu concentration for CLP. The ground for this behavior can be attributed to the lower competition for the sorption surface sites at lower concentration. At higher concentrations, the competition for the surface active sites will be high and accordingly lower sorption rates are obtained. Similar phenomena have been observed in the surface assimilation of Cu ( II ) on other natural adsorbent stuffs [ 3,17,19,27 ] .

It was found from Table 2 that the correlativity coefficients for the intra-particle diffusion theoretical account are all lower obviously than those of the pseudo-first order and the pseudo-second order theoretical accounts. This indicates that the surface assimilation of Cu ( II ) onto CLP do non follow the intra-particle diffusion dynamicss. However, the secret plans of qt versus t1/2 can be divided into a multi-linearity correlativity ( Fig. 5 ) , which indicates that three stairss occur during surface assimilation procedure. For the first sharper part i.e. from 0 to 1 min, it is postulated that Cu ( II ) was transported to the external surface of the biosorbent through movie diffusion and its rate, the values of ki1 were between 4.97 and 10.50 mg g-1 min-1/2, which shows this surface assimilation procedure is really fast. The 2nd part is the gradual surface assimilation phase where the intra-particle diffusion with ki2 ( 0.24283, 0.60277 and 0.90756 mg g-1 min-1/2 for 25, 50 and 100 milligram L-1, severally ) can be rate commanding. The 3rd part ( after 12.5 min ) is the concluding equilibrium phase where the intra-particle diffusion starts to decelerate down due to the highly low solute concentration in solution [ 37 ] . Furthermore, it can be observed that the larger incline is represented for higher initial concentration whether the first or the 2nd parts. From the above analysis, it can be concluded that both movie diffusion and intra-particle diffusion were at the same time runing during the procedure of the surface assimilation of Cu ( II ) on CLP and were both enhanced with the addition of initial concentration.

3.4. Adsorption isotherms

The equilibrium surface assimilation isotherms are one of the most of import informations to understand the mechanism of the surface assimilation systems. Hence, the surface assimilation of Cu ( II ) onto CLP at different temperatures are determined as a map of equilibrium ( residuary ) Cu ( II ) concentration ( Ce ) and the corresponding surface assimilation isotherms are plotted in Fig. 6. The parametric quantities and correlativity coefficients obtained from the secret plans of Langmuir, Freundlich and D-R ( figures non shown ) are listed in Table 3. The values of r2 and F all suggest that the Langmuir theoretical account gave closer adjustments than those of Freundlich and D-R theoretical accounts. In add-on, the surface assimilation capacity ( qmax and Kf ) increases with an addition in temperature while the opposite behaviour is presented for qm. Seen overall, the information therefore obtained specifies an endothermal nature of the bing procedure. The maximal monolayer surface assimilation capacity of CLP for Cu ( II ) ions was besides noted to be higher than the other antecedently reported adsorbents ( Table 4 ) . Differences of metal consumption are due to the belongingss of each adsorptive stuff such as construction, functional groups and surface country.

Through the treatment for isotherm invariables, it can foretell whether an surface assimilation system is favourable or unfavourable. The indispensable features of the Langmuir isotherm can be expressed by agencies of ‘RL ‘ , a dimensionless invariable referred to as separation factor or equilibrium parametric quantity, which is defined by [ 47 ]

RL = 1/ ( 1+bC0 ) ( 5 )

where C0 is the highest initial metal concentration. The parametric quantity indicates the type of isotherm to be irreversible ( RL=0 ) , favourable ( 0 & A ; lt ; RL & A ; lt ; 1 ) , additive ( RL=1 ) or unfavourable ( RL & A ; gt ; 1 ) . As seen from Table 3, at all temperatures the RL values were between 0 and 1.0, bespeaking that surface assimilation of Cu ( II ) onto CLP are all favourable.

The n values of Freundlich equation can give an indicant on the favorability of sorption. It is by and large stated that values of N in the scope 2-10 represent good, 1-2 reasonably hard, and less than 1 hapless sorption features [ 48 ] . The consequence shows that the values of Ns are all greater than 2 bespeaking that the Cu ions are favourably adsorbed by CLP. This is in great understanding with the findings sing to RL value.

Based on D-R isotherm equation, Ea can be calculated utilizing the equation, Ea = ( 2? ) -1/2 [ 49 ] . The isotherm invariables, Ea and correlativity coefficients are calculated and presented in Table 3. As seen in the tabular array, the values of Ea at different temperatures are found to lie between 9.97 and 11.58 kJ mol-1 in the whole scope of investigated Cu concentrations. The average energy of surface assimilation is the free energy alteration when one mole of the ion is transferred to the surface of the solid from eternity in the solution. The value of this parametric quantity can give information about surface assimilation mechanism. When one mole of ions is transferred, its value in the scope of 1-8 kJ mol-1 indicates physical surface assimilation [ 50 ] , the value of Ea is between 8 and 16 kJ mol-1, which indicates the surface assimilation procedure follows by ion-exchange [ 51 ] , while its value in the scope of 20-40 kJ mol-1 is declarative of chemosorption [ 52 ] . Combination of the predating analysis for EDS and FT-IR, it is likely that the whole surface assimilation procedure were predominated by ion-exchange mechanism, accompanied by a certain grade of surface complexation.

3.5. Thermodynamic parametric quantities

Harmonizing to values of thermodynamic parametric quantities, what procedure will happen spontaneously can be determined. ?G0 can be calculated utilizing the relation:

?G0 = -RTlnb ( 6 )

?H0 and ?S0 were calculated from the incline and intercept of the additive secret plan of ln B versus 1/T ( Fig. 7 ) harmonizing to the Va n’t Hoff equation. Obtained thermodynamic parametric quantities are given in Table 5. As shown in the tabular array, ?H0 was positive value, proposing endothermal reaction. The positive value of ?S0 suggests the increased entropy at the solid/solution interface during the surface assimilation of Cu ( II ) onto CLP. The negative values of ?G0 imply the self-generated nature of the surface assimilation procedure. Further, the lessening in the values of ?G0 with the increasing temperature indicates the surface assimilation was more self-generated at higher temperatures [ 53 ] . By and large, the alteration in free energy for physisorption is between -20 and 0 kJ mol-1, but chemosorption is a scope of -80 to -400 kJ mol-1 [ 54 ] . The values of ?G0 obtained in this survey are within the scopes of neither the physisorption nor chemosorption, bespeaking that the other surface assimilation such as ion-exchange and/or surface complexation is likely the chief mechanism.

3.6 Effect of ionic strength

Heavy metal effluents from many industries contain assorted types of suspended solids and salts. The presence of ions leads to high ionic strength, which may significantly impact the public presentation of the surface assimilation procedure. Fig. 8 presents the consequence of ionic strength on the remotion of Cu ( II ) . It was observed that the surface assimilation capacity fluctuates insignificantly in the scope of ionic strength from 0 to 0.1 mol L-1, and so somewhat decreases with a larger concentration of NaCl. Compared with informations related to lower ionic strength, the surface assimilation capacity is merely a bead of 7 % even if the ionic strength has reached 0.5 mol L?1. The consequence indicates that the presence of external electrolyte, such as Na chloride, has a limited consequence on the surface assimilation capacity between CLP and Cu ions.

The pH value of concluding Cu ( II ) solution is declarative of the belongings of liquid system because it is the consequence of interaction between biosorbent and Cu ( II ) solution. Hence, the fluctuation of the pH of the Cu ( II ) solution before and after surface assimilation in the conditions of different ionic strengths were investigated. As seen in Fig. 8, pH of concluding solution decreases somewhat from 4.60 to 4.55 with the addition of NaCl concentration. In the clean experiment without adding Cu ions, pH value after surface assimilation is 4.35, which is lower than the above values of 4.55-4.60. Based on the old kinetic and isothermal surveies, it is considered that the ion-exchange and surface complexation occurred at the same time during the surface assimilation procedure. Ion-exchange would bring on the addition in pH value of solution due to the lower hydrolyse invariable of Cu ( II ) compared to cations such as Na+ , K+ , Ca2+ , etc. on CLP. In contrast to the former, surface complexation on the CLP can convey a lessening in concluding pH because H ions will travel into the solution after surface assimilation. Harmonizing to the consequences of pH values above, it can be concluded that the whole surface assimilation procedure is chiefly dominated by ion-exchange mechanism, accompanied by a certain grade of surface complexation. The consequence good corroborates the old guess in subdivision 3.4.

3.7. Regeneration surveies

Recovery of Cu from the laden biosorbent is necessary for disposal every bit good as for reuse of the adsorbate [ 55 ] . In this survey, 0.1 mol L-1 of HCl was used in the adsorption-desorption experiments. The consequence is shown in Fig. 9. It is observed from Fig. 9 that the surface assimilation capacity increases bit by bit with the addition of rhythm clip, which seems unreasonable. Copper ions adsorbed onto CLP could non be removed exhaustively from the foliage by desorption ( Fig. 9 ) . So, when the figure of rhythm related to the reutilization of the foliages additions, the sum of the freshly adsorbed Cu2+ should diminish under the status of an unchanged sum sum of available surface assimilation sites. Normally strong acerb intervention at high concentration and rather high temperature can increase the surface assimilation capacity of the biosorbent due to the addition of the porousness or surface country [ 13 ] . In this survey, an addition in surface assimilation capacity observed after desorption with dilute HCl, which cause protonation of biosorbent surface, may be attributed to the exchange of edge H ions with heavy metal ions. Consequently, it is believed that hydrochloric acid selected in this survey played a double function of desorption and protonation. For each adsorption-desorption rhythm, the figure of freshly active sites generated by dilute HCl intervention was higher than those of undesorbed sites, ensuing in an addition surface assimilation capacity with the addition in rhythm figure. Fig. 9 besides shows that desorption capacity did n’t alter obviously in the whole regeneration surveies. It can be easy known that desorption efficiency decreases easy with the increasing rhythm figure due to the addition of surface assimilation capacity. Even after 5 rhythms, the desorption efficiency is still every bit high as 92.7 % . In general, Cu ( II ) loaded CLP can be easy desorbed by choosing HCl as a regenerant and re-use efficiency of the biosorbent is fulfilling.

4. Decisions

The purpose of this work was to happen the possible usage of Cinnamomum camphora leaves pulverization as a sorbent for the remotion of Cu2+ from aqueous solutions. In kinetic survey, the pseudo-second order kinetic theoretical account was found to be good suited for the full surface assimilation procedure of Cu ( II ) on CLP. Adsorption kinetic surveies besides reveal that there are three phases in the whole surface assimilation procedure and movie diffusion mechanism should be a chief rate control mechanism. All equilibrium informations obtained at different temperatures fit absolutely with Langmuir isotherm theoretical account compared to Freundlich and D-R isotherm theoretical accounts, and the maximal surface assimilation capacities of Cu ( II ) adsorbed onto CLP are 16.756, 17.085, 17.434 and 17.870 mg g-1 at 303.2, 313.2, 323.2 and 333.2 K, severally. The Langmuir and Freundlich theoretical accounts coefficients both implied that the surface assimilation of Cu ( II ) onto CLP is favourable. Harmonizing to fluctuations in EDS and FT-IR spectra before and after surface assimilation, it is considered that ion-exchange was the major remotion mechanism and a certain sum of surface complexation mechanism coexisted. A conventional presentation of the surface assimilation procedure is given in Fig. 10aˆˆRegeneration surveies show Cu ( II ) loaded CLP can be easy desorbed by 0.1 mol L-1 HCl as a regenerant and high surface assimilation and desorption efficiencies were obtained in five rhythms of adsorption-desorption. The overall consequences indicated that the Cinnamomum camphora leaves is an effectual and low-priced biosorbent for the remotion of Cu ( II ) from aqueous solutions.

Appendix A

Model

Equation

Pseudo-first order dynamicss

Pseudo-second order dynamicss

Intra-particle diffusion dynamicss

Langmuir isotherm

Freundlich isotherm

Dubinin-Radushkevich isotherm

Va n’t Hoff

Recognitions

This work was financially supported by the National Natural Science Foundation of China ( No. 20903070 ) and Zhejiang Provincial Natural Science Foundation of China ( No. Y4090387 ) . The writers are thankful to the anon. referees for their insightful and constructive unfavorable judgment, which materially improved this work.