Removal of Dyes From Aqueous Solutions by Using Residual Black Tea Papers (RBTP)

Transcription

1 Removal of Dyes From Aqueous Solutions by Using Residual Black Tea Papers (RBTP) Ayad F. Al-Kaim Aseal M. Kadhum Khalied G. * Khawla a Gani * College for Women Sciences/ Babylon university College for Sciences * / Al-Muthan a university * Abstract The removal of two dyes: methyl violet (MV) and methyl blue (MB)from aqueous solutions by adsorption on RBTP was investigated by using uv-visible technique. The adsorption of methyl violet is better than of methyl blue dye from aqueous solution at normal conditions. The Freundlich and Dubinin-Rasdushkevich (D-R) isotherm equations were applied to the data and values of parameters of these isotherm equations were calculated. The measured adsorption isotherms at the different temperatures 98 K, 308 K and 318 K were found extent of adsorption decrease as the temperature increase. Also the measured adsorption isotherms at the different phs 3, 7 and 11and it s found the adsorbed amount of MB dye decrease with increase ph, MV dye prefer the neutral media. The adsorption process was found to be exothermic with an estimated mean enthalpy change of two dyes MB and MV (-0.67 kj/mole and KJ/mole) respectively. The thermodynamic functions G o, H o and S o were calculated and were explained in the mean of the chemical structure of the adsorbate. 1

2 الخالصة: ذى اسرخذاو تما ا ورق انشاي األسىد )RBTP( إلسانح صثغر ان ث م انث فسج وصثغح ان ث م انشرلاء ي ان حان م ان ائ ح, اسرخذيد ذم ح ايرصاص األشعح ان زئ ح انفىق انث فسج ح نرمذ ز ك ح انصثغر ان رثم ح تعذ ا رهاء ع ه ح االيرشاس. وجذ ا سعح ايرشاس صثغح ان ث م انث فسج ح هى أفضم ي صثغح ان ث م انشرلاء ع ذ انظزوف انطث ع ح. ذى اسرخذاو كم ي يعادنر فز ذنج ود ث راسذوشكف ج )D-R( اال سىثزي ر نه رائج ان سرحصهح, وذى حساب انثىاتد نكهرا ان عادنر. ا سىثزياخ االيرشاس ذى حساتها ع ذ درجاخ حزار ح يخرهفح )31-9( يطهك, ووجذ ا ك ح االيرشاس ذمم يع س ادج درجاخ انحزارج. كذنك ذى حساب ا سىثزياخ االيرشاس ع ذ دوال حايض ح يخرهفح )111,13( ووجذ ا ك ح االيرشاس نصثغح ان ثم انشرلاء ذمم يع س ادج انذانح انحايض ح, ت ا صثغح ان ثم انث فسج وجذ تأ ها ذفضم األوساط ان رعادنح. وجذ ا ع ه ح االيرشاس ه ع ه ح تاعثح نهحزارج يع ذغ ز يعذل ل ى اال ثانث نكهرا انصثغر " ان ث م انشرلاء وان ث م انث فسج " ه )-1.61 و تىحذاخ كهج/يىل( عهى انرىان. ذى حساب انذوال انثزيىد اي ك ح S o, H o, G o وي خالنها ذى دراسح سهىك ح انرزك ة انك ائ نه ادج ان رشج.

3 Introduction Dyeing waste-water has a pollution problem because of its colour and organic content. A combination of several processes is generally necessary to achieve adequate removal of all contaminants. Dyeing and finishing processes are two important steps in the textile manufacturing process (1, ). The steps involve the dyeing of man-made or, natural fibers to the desired permanent colours and processing of these fibers into commercial products, subsequently discharging the waste-water. Before directing these waters away from the industry, they should be treated to remove organic wastes and colouring agents (3). For this adsorption has evolved as one of the most effective and suitable, physical; processes for de-colourization of textile waste-water. The most efficient and commonly used adsorbent is activated carbon, However, activated carbon is costly and has regeneration problems. Recent investigations have focused on the use of low-cost materials such as rice hulls (4), coconut husk (5), maize cobs (6), banana pith (7), saw dust (8), fly ash (9), hexane-extracted spent bleaching earth (10), chrome sludge (11), chitin (1) and residual black tea papers to remove dyes with varying degrees of success. In this experiment study, we have investigated the possibility of using commercial residual black tea papers, to remove pollutants dyes from aqueous solution. Materials Tea powder was prepared by taken 50 gm of commercial black tea papers [Ceylon Kuwait company Seri Lanka ] in beaker containing 50 ml of water, and heated for 3 hours in 60 o C, the mixture allow to stand for 10 minutes then filtered, aliquot solution neglected, this process is repeated about fifth to sixth times to remove all the color which result from commercial tea, until the aliquot of precipitate give base line which saw in naked eyes. The precipitate was suspended in HCl solution of 0.0 M to remove all undesired compounds such as, caffeine, alkaloid, etc., and it was washed with an excess amount of distilled water to remove the soluble material. Then it was dried in the room temperature for seven days, then kept in airtight containers. The dried material was ground well to a fine powder and sieved well for maximum particle size (100 m) The structural form of methyl basic blue and methyl violet dyes are given in figure (1) respectively (13). 3

4 Figure 1: A: Structure of the MB adsorbate B: Structure of the MV adsorbate Chemicals: Chemicals used for this work are listed in table (1) together with the purity and sources. All chemicals were used without further purification. Table (1) chemical and their purity and manufactured used in this study. Chemical Source Conc. % Methyl violet dye BDH 93 Basic methyl blue Merch 97 Hydrochloric acid BDH 35 Instruments: The following instruments were used in this study: 1. Uv-Visible Spectrophotometer, Single Beam, Pye Unicam Shaker Bath, SB. 4, Tecam. 3. Digital ph-meter,hanaa, Roman Method Adsorption experiments were carried out by shaking 0.03 g RBTP samples with 30 ml aqueous solution of dyes of desired concentration at various phs (3, 7 and 10), temperatures (98, 308 and 318 K) for 1 h (the required time for methyl blue "MB" and Methyl violet "MV" to reach the equilibrium concentrations). A thermostated shaker bath was used maintains the temperature to be constant. The initial concentrations of dyes solutes, C 0, were in the range of [-16 ppm]. All adsorption experiments were performed at 98 K and ph 7.0 except those in which the effects of temperature and ph of the solution were investigated. The ph of the solution was adjusted with NaOH or HCl solution by using ph meter equipped with a combined electrode. At the end of the adsorption period, the solution was centrifuged for min at 000 rpm 4

5 and then the concentration of the residual [Ce,] of MB or MV, was determined with by using uv- visible Spectrophotometer at a maximum absorbency λ max for methyl blue 660 nm and methyl violet 580 nm. The adsorbed amounts of two dyes were calculated from the concentrations in solutions before and after adsorption according to the equation (1) Q e ( C o C e ) V W...(1) where C 0 and C e are the initial and equilibrium liquid phase concentrations of dye solution (mg/l), respectively; Qe is equilibrium dye concentration on adsorbent (mg.gm -1 ), V is the volume of dye solution (L), and W is the mass of CBTP sample used (g). All solutions were prepared using distilled water. Adsorption Isotherms Adsorption at equilibrium conditions were determined for methyl basic blue and methyl violet on CBTP adsorbent. Plots of the Q e (mg.g -1 ) against equilibrium concentration C e (mg/l) for MB and MV onto CBTP, the data are listed in table () and Figure () which showed multilayer adsorption at relatively high concentration concerning the heterogeneity of the surface S type of Gilles classification (14). Also the adsorption capacity of methyl violet dye is better than methyl basic blue at different temperatures. Table () adsorption isotherms values of two dyes (MB and MV) on the CRBTP surface at 98 K. C o (mg/l) C e (mg/l) Q e (mg/gm) Basic methyl blue ln C e ln Q e C e (mg/l) Q e (mg/gm) Methyl violet ln C e ln Q e , ,9 1., , , ,

6 Adsorption Capacity (mg/gm) 10 8 CRBTP Methyl Blue Methyl Violet Concentration Equilibrium (mg/l) Figure. Adsorption isotherm of MV and MB on CRBTP surface at 98 K at ph of 7. It is obvious from Figure that the adsorption isotherms of dyes on CRBTP surface is indicates that a large amount of dye is adsorbed at a lower concentration as more active sites of CBTP are available. As the concentration increases, it becomes difficult for a dye molecule to find vacant sites, and so monolayer formation occurs. Effect of temperature on the adsorption isotherms The effect of temperature variation on the adsorption extent of MB dye and MV dye on the CBTP surface has been studied at neutral media ph= 7. Figures 3 and 4 illustrate the general shapes of MB dye and MV dye adsorption isotherm at 98, 308 and 318 K. it can be seen that as the temperature increased, the adsorption quantity decreased. 6

7 Adsorption Capacity [mg/gm] Adsorption Capacity (Qe[mg/gm]) Adsorption of MB dye on CRBTP surface 98 K 308 K 318 K Concentration Equilibrium (Ce[mg/L]) Figure 3. Temperature dependence of the adsorption of MB dye on the CRBTP surface at ph of Adsorption of M V dye on CRBTP surface T = 98 K T = 308 K T = 318 K Concentration Equilibrtium [mg/l] Figure 4. Temperature dependence of the adsorption of MV dye on the CRBTP surface at ph of 7.,

8 The adsorption capacity of the CRBTP decrease with increase in the temperature of the system from 5 o C to 45 o C the thermodynamic parameters such as change in free energy G o (KJ/mole), enthalpy H o (KJ/mole) and entropy S o (J/mole.K) are determined using the following equations (15) : Qe 0.03gm Ke *...() Ce 0.03L o G RT ln Ke...(3) Here Ke is the equilibrium constant, Qe is the adsorption capacity (mg/gm), Ce is the liquid phase dye concentration at equilibrium (mg/l), T is the temperature in Kelvin and R is the universal gas constant ( KJ K -1 mole -1 ). The value of H o and S o obtained from the slope and intercept of Van t Hoff s by plots ln Xm versus (1/T) should as shown in Figures (5 and 6). o o H S ln Xm...(4) RT R When Xm (mg/gm) is the maximum value of adsorption at a certain value of equilibrium concentration (Ce).

9 ln Xm ln Xm Vant Hoff's Equation Of M.B. dye at different temperature [1000 K / T] Figure 5. Plot of ln Xm versus 1000 K/T of MB dye on the CRBTP surface Vant Hoff's Equation of M.V. Dye at Different Temperature [1000 K/ T] 9 Figure 6. Plot of ln Xm versus 1000 K/T of MV dye on the CRBTP surface.

10 Adsorption Capacity [mg/gm] Values are indicating the favorability of physisorption. The value of H o shows that the adsorption is exothermic (16). The negative value of G o show that the adsorption is highly favorable for MB and MV dyes. However, it indicates that the dye adsorption is spontaneous, during the adsorption there, some structural changes in the dye and the adsorbent occur, the value of thermodynamic function as shown in table (3). Table 3. Thermodynamic function G o, S o and, H o of (MB and NR) on the adsorbent surface CRBTP at 98K. Adsorbate G o / (kj mole -1 ) S o / (J mole -1 K -1 ) H o / (kj mole -1 ) Methyl violet dye Methyl blue dye Effect of ph The effect of ph on adsorption process was studied at three different ph values (3, 7 and 11) keeping other parameters constant. The result of variation on dye adsorption at these ph values is shown in Figures (7 and 8). This indicates the strong force of interaction between dyes and CBTP that, either H + or OH - ions could influence the adsorption capacity. Here the interaction is larger at ph= 3 due to the competence of acidic H + for methyl blue dye, the methyl violet is prefer the neutral media, in general the adsorption of dyes on the CBTP involve ion exchange mechanism (17). 10 Effect of ph on M.B. dye 8 6 ph = 3 ph = 7 ph = Concentration Equilibrium [mg/l] Figure 7. The effect of ph on the adsorption of MB dye on CRBTP surface at 98 K.

11 Adsorption Capacity [mg/gm] Effect of ph on M.V dye ph = 11 ph = 7 ph = Concentration Equilibrium [mg/l] Figure 8. The effect of ph on the adsorption of MV dye on CRBTP surface at 98 K. Isotherm Analysis The experimental data are analyzed according to the linear form of the Freundlich and D-R isotherms. The Freundlich equation is employed for the adsorption of Methyl Violet (MV), and Methyl Blue (MB) dyes on the adsorbent. The Freundlich isotherm is represented as: ln Qe ln K 1/ nln Ce...(4) f Here Qe is the amount of Methyl Violet (MV), and Methyl Blue (MB) adsorbed (mg/ g), Ce is the equilibrium concentration of dye in the solution (mg/l) and K f and n are constants incorporating all factors affecting the adsorption capacity and intensity of adsorption, respectively. Linear plot of ln Qe versus ln Ce shows that the adsorption of methyl violet, and methyl blue dyes follows the Freundlich isotherm as shown in figures (9-1). The values of K f and n found and given in Table 4, shows the increase of negative charge on the surface that enhances the electrostatic force between the carbon surface and the dye ion, which increases in turn the adsorption of dyes. The values clearly show the dominance of adsorption 11

12 ln Qe capacity. The intensity of adsorption is an indication for the bond energies between dye and the adsorbent and the possibility of a slight physisorption rather than chemisorption (16). The possibility of multilayer adsorption of dyes through the percolation process cannot be ruled out. Table 4. Freundlich isotherm constants for different PHs, and temperatures of MB and MV dyes on the CRBTP surface. Temp (K) ph Freundlich constant for MV dye Freundlich constant for MB dye n K f R n K f R Effect of Temp. on M. B. dye T= 98 K T = 308 K T = 318 K ln Ce Figure 9. Linearized Freundlich plot of MB dye adsorption on CBTP surface at different temperature 1

13 ln Qe ln Qe Effect of Tem. on M. V. T = 98 K T = 308 K T = 318 K ln Ce Figure 10. Linearized Freundlich plot of MV dye adsorption on CBTP surface at different temperature Effect of ph on of M.V. dye ph = 11 ph = 7 ph = ln Ce Figure 11. Linearized Freundlich plot of MV dye adsorption on CBTP surface at different phs. 13

14 ln Qe Freundlich equation of M. B. dye ph = 3 ph = 7 ph = The purpose of the adsorption isotherms is to relate the adsorbate concentration in the bulk and the adsorbed amount at the interface (17). The analysis of the isotherm data is important to develop an equation which accurately represents the results and which could be used for design purposes (18). The adsorption data were also tested for another adsorption isotherm, the Dubinin Radushkevich (D-R) (19, 0). This isotherm is more general than the Langmuir isotherm since it does not assume a homogenous surface or constant sorption potential. The D-R equation is Q e X m exp( K )...(5) where (polanyi potential) = RT ln (1+1/C e ), Q e is the amount of dye adsorbed per unit weight of CRBTP surface (mg gm 1 ), Xm is the adsorption capacity (mg gm 1 ), C e is the equilibrium concentration of dye in solution (mg L 1 ), K is the constant related to the adsorption energy (mol kj ), R is the gas constant ( KJ K 1 mol 1 ) and T is the temperature (K). The D-R isotherm can be linearized as ln Q e ln Ce Figure 1. Linearized Freundlich plot of MB dye adsorption on CBTP surface at different phs. ln X m K...(6) The plots of lnq e against are shown in Figures (13-16) at different factors that effective on adsorption process. 14

15 ln Qe ln Qe D-R isotherm of M.B. dye T = 98 K T = 318 K T = 318 K Figure 13. D-R plot of CBTP / MB dye at different temperatures D-R isotherm on M.V.dye T = 98 K T = 308 K T = 318 K Figure 14. D-R plot of CBTP / MV dye at different temperatures. 15

16 ln Qe ln Qe D-R isotherm at different ph of M. B. dye 0.4 ph = 3 ph = 7 ph = Figure 15. D-R plot of CBTP / MB dye at different phs D-R iotherm on M.V. dye ph = 11 ph = 7 ph = Figure 16. D-R plot of CBTP / MV dye at different phs.

17 The mean energy of adsorption, E, can be calculated from the K values (1) 0. 5 using the relation E (K), values of E are presented in table 5. The calculated mean energy of adsorption, E, from the D-R isotherm, gives information about the chemical or physical properties of the sorption. The calculated mean energy values of adsorption of two dyes by CRBTP are very small and this implies that the type of adsorption is physical. Table 5. D-R isotherm parameters and mean energy of the adsorption for different PHs, and temperatures of MB and MV dyes on the CRBTP surface. Temp (K) ph D-R isotherm parameters for MV dye D-R isotherm parameters for MB dye K m (mole kj - ) E (kj.mole -1 ) K m (mole kj - ) E (kj.mole -1 ) Conclusions: 1. CRBTP as an adsorbent has a considerable potential for removing dyes in commercial systems because of its higher surface area.. The adsorption isotherms show that the quantity of adsorption for two dyes by CRBTP from their aqueous solutions increase by increased their concentration. 3. The adsorbed amount of MB dye decrease with increase ph and temperature, MV dye decrease with increase temperature but prefer the neutral media. 4. The adsorptivity of MV is high when compared with MB dye at normal conditions. 5. The adsorption of two dyes on the CRBTP surfaces is of exothermic process. 6. The order of heat of adsorption corresponds to concluded that the two dyes are physically adsorbed onto CRBTP and proved from two equations. 7. This work, shows the CRBTP is good adsorbent for remove pollutants dyes. 1,

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