Isotherm, kinetic and thermodynamic studies

The 10th International Chemical Engineering Congress & Exhibition (IChEC 2018) Isfahan, Iran, 6-10 May, 2018

Removal of malachite green from aqueous solutions using chemically modified celery residue: Isotherm, kinetic and thermodynamic studies S.Mohebali, D.Bastani* School of chemical and petroleum engineering, Sharif university of technology, Tehran, Iran. Corresponding Author’s E-mail: [email protected]

Abstract Celery residue modified with H2SO4 was utilized as a low-cost adsorbent for removal of hazardous malachite green cationic dye from aqueous solution in batch adsorption process. The efficacy of dye removal of the modified celery residue (MCR) was investigated by varying adsorbent dose, contact time, pH and initial dye concentration. The isotherm models analysis shows that the experimental data can be better described by Langmuir isotherm model. The maximum monolayer adsorption capacity of MCR achieved 526.316 mg/g at 303 K. The adsorption kinetic results were well described by the pseudo-second order model. Thermodynamic studies revealed that the adsorption process is spontaneous and exothermic in nature. The values of ΔH˚ and ΔS˚ have been determined to be negative which confirm that the adsorption process in more favourable in lower temperatures. Regeneration of adsorbent was evaluated and excellent results were obtained. The results of this study indicate that MCR is an effective low-cost adsorbent for removal of malachite green from aqueous solutions. Keywords: Adsorption, low-cost adsorbent, agricultural residue, malachite green, celery residue.

Introduction In recent decades, water pollution has became one of the major environmental problems. Dyes are one of the major water pollutants. Dyes are steady to light, heat, oxidizing agents and hard to degrade by microorganisms [1]. The wastewater that contain dyes are usually poisonous, carcinogenic and teratogenic to human beings [2]. Malachite Green (MG) is a cationic dye and most generally used for the dyeing of cotton, silk, paper, leather. Among different processes for removal of dyes from wastewater, the adsorption method is an appealing approach for wastewater treatment, especially if the adsorbent is not expensive. Agricultural byproducts have been comprehensively examined for dye removal from wastewater. Celery (Apium graveolens) is a member of the parsley family. Today, celery is a popular vegetable in the world because of its excellent nutritional containments and versatility. In this study, chemically modified celery residue has been used as an adsorbent to study the decontamination of MG dye from aqueous solutions.


Experimental The celery residues (CR) were collected from a local juice production unit in Tehran, Iran, and were washed thoroughly with distilled water and dried in sunlight for 48h then converted to very small pieces and soaked with H2SO4 (1 mol/L) for 3h. Then the resulted products were washed several times with distilled water until the sample was neutralized (pH≈7). Then this modified celery residue (MCR) was dried in sunlight for 48h again then powdered and screened through 20-40 mesh. For accomplishing main tests, a certain amount of MCR (0.07 g) was mixed with 50 mL of known concentration of dye solution. The mixture was agitated at 150 rpm in a shaker at constant temperature until equilibrium was reached. Then, the mixture was filtered and the residual dye in the solution was determined using UV–vis spectrophotometer. After the completion of adsorption equilibrium, dye-loaded adsorbents were added to four 250 mL conical flask, each containing 50 mL of one of 0.01, 0.001, 0.0001 M HCl as the desorption solutions. The mixtures were agitated at 150 rpm and constant temperature (303 K) for 3h (optimum). The procedure was repeated for five cycles of adsorption–desorption. Results and discussion The effect of adsorbent dosage on MG removal was displayed in Fig. 1. It was observed that the dye removal efficiency increased and qe decreased when MCR dosage was increased which was probably due to the increased adsorbent surface area and more accessibility of active adsorption sites [4].

Fig. 1 Effect of MCR doses on MG adsorption (initial MG concentration=100 mg/L, natural pH=4, temperature 303 K).

Fig. 2 Effect of solution pH on adsorption of MG onto MCR (initial MG concentration=100 mg/L, MCR dosage=1.4 g/L, contact time=180 min, temperature=303 K).

Investigating the effect of contact time shows the very rapid change in adsorption capacity at first 15 minutes. This may be due to the increase in the number of vacant adsorption sites available at the initial phase [5]. Thereafter, with increasing contact time from 15 to 180 min, it was slowly increased then reached equilibrium. The results of pH studies were illustrated in Fig. 2. It is noted that the adsorption capacity of MG onto MCR reached the maximum amount of 61.57 mg/g at pH 8. Since MG is a cationic dye, at higher pH values, the functional groups present on the adsorbent surface became deprotonated leading to an increase in the negative charge density on the MCR surface and enhance the binding of MG through electrostatic attraction [4,7,8]. Tests were carried out at different initial MG concentration to investigate the effect of initial dye concentration. Obtained results show that the adsorption capacities of MCR increased rapidly with increasing the initial dye concentration from 50 to 700 mg/L which can be described by the fact that a higher initial concentration leads to a larger driving force to overcome the mass transfer resistance of adsorbate from aqueous phase to solid phase until saturation is achieved [9,10]. In order to understand the mechanism of adsorption, common kinetic models were fitted to the experimental data. As can be observed from Table 1, the pseudo-second order kinetic


model is the best fit to experimental data. Referring to Fig. 3, two different regions are observed which the first part was the surface adsorption or rapid external diffusion phase and the second part is the gradual adsorption phase controlled by intra-particle diffusion [5,11]. Table 1 Kinetic parameters for MG adsorption onto MCR. qe,exp (mg/g) 52.5 qe,exp (mg/g) 52.5 Fig. 3 Intra-particle diffusion kinetic model (initial MG concentration=100 mg/L, MCR dosage=1.4 g/L, natural pH=4, contact time=180 min, temperature=303 K).

Pseudo-first order qe,calc (mg/g) k1 (min-1) 3.909 0.0268 Pseudo-second order qe,calc (mg/g) k2 (g/mg.min) 52.632 0.0246 Intra-particle diffusion kid (mg/g.min0.5) C 0.4106 48.026

R2 0.9433 R2 1.00 R2 0.7177

The experimental data were fitted using Langmuir, Freundlich, and Temkin isotherm models. The isotherm parameters at three different temperatures are shown in Table 2. Langmuir isotherm is the best fit to experimental data at each temperature. The maximum monolayer adsorption capacity of MCR was found to be 526.316 mg/g. The values of thermodynamic parameters are listed in Table 3. The obtained values of ΔG° was negative which indicates that MG adsorption on MCR is feasible and spontaneous in nature [12]. The negative value of change in enthalpy indicates that MG adsorption on MCR is exothermic. The value of ΔS° is positive which corresponds to a increase in the solid/solution interface randomness during the process of MG adsorption into MCR. Fig. 4 displays the results of reusability study of MCR in adsorbing MG. The adsorption capacity was slightly reduced which confirms excellent performance of MCR during multiple adsorption cycles. Table 2 Isotherm parameters for adsorption of MG onto MCR. Langmuir isotherm Temp. (K) qm (mg/g) KL (L/mg) R2 RL 303 313 323

Temp. (K)

526.316 555.556 588.235

0.0103 0.0085 0.0078

0.9924 0.991 0.9939

0.12-0.66 0.14-0.70 0.15-0.72

Freundlich isotherm KF ((mg/g)(L/mg)1/n)

1/n

R2

9.905 8.364 7.971

0.6954 0.7270 0.7386

0.9634 0.9908 0.9921

303 313 323

Temkin isotherm Temp. (K) 303 313 323

bT (KJ/mol)

KT (L/g)

R2

26.916 26.641 27.009

0.179 0.154 0.149

0.9634 0.9679 0.9675

Fig. 4 Desorption study of MG loaded MCR.

Table 3 Thermodynamic parameters for adsorption of MG onto MCR. Temperature (K) 303 313 323

Thermodynamic parameters ke ΔG° (J/mol) 4.696 -3896.44 4.389 -3848.96 4.315 -3926.69

ΔH° (J/mol)

ΔS° (J/mol/K)

-3459.123

1.379

Conclusions Celery residue which was successfully modified by H2SO4, was found to be a highly efficient low cost adsorbent for removal of MG dye from water solutions. The effect of various


parameters such as adsorbent dose, contact time, pH, initial dye concentration and temperature have been investigated. Equilibrium data were well fitted to Langmuir adsorption isotherm while kinetic data was found to follow pseudo-second order kinetic model. The maximum monolayer adsorption capacity of modified celery residue was 526.316 mg/g. The thermodynamic study indicated that the adsorption process is feasible, spontaneous and exothermic. Desorption studies confirmed that the dye loaded adsorbent could be well regenerated using HCl acid solution. References [1] Chafai, H., Laabd, M., Elbariji, S., Bazzaoui, M., & Albourine, A. ,“Study of Congo Red Adsorption on the Polyaniline and Polypyrrole”, Journal of Dispersion Science and Technology, 38, 832-836 (2017). [2] Bhattacharyya, K. G., & Sharma, A. ,”Kinetics and thermodynamics of Methylene Blue adsorption on Neem (Azadirachta indica) leaf powder” ,Dyes and Pigments, 65, 51-59 (2005). [3] Han, R., Zhang, L., Song, C., Zhang, M., Zhu, H., & Zhang, L. ,”Characterization of modified wheat straw, kinetic and equilibrium study about copper ion and methylene blue adsorption in batch mode” ,Carbohydrate Polymers, 79, 1140–1149 (2010). [4] Akar, E., Altinisik, A., & Seki, Y. ,”Using of activated carbon produced from spent tea leaves for the removal of malachite green from aqueous solution” ,Ecological Engineering, 52, 19-27 (2013). [5] Belala, Z., Jeguirim, M., Belhachemi, M., Addoun, F., & Trouvé, G. ,”Biosorption of basic dye from aqueous solutions by Date Stones and Palm-Trees Waste: Kinetic, equilibrium and thermodynamic studies” ,Desalination, 271, 80-87 (2011). [6] Oguntimein, G. B. ,”Biosorption of dye from textile wastewater effluent onto alkali treated dried sunflower seed hull and design of a batch adsorber” ,Journal of Environmental Chemical Engineering, 790, 1-15 (2015). [7] Chowdhury, S., Mishra, R., Saha, P., & Kushwaha, P. ,”Adsorption thermodynamics, kinetics and isosteric heat of adsorption of malachite green onto chemically modified rice husk” ,Desalination, 265, 159–168 (2011). [8] Kamaru, A. A., Sani, N. S., & Malek, N. A. ,”Raw and surfactant-modified pineapple leaf as adsorbent for removal of methylene blue and methyl orange from aqueous solution” ,Desalination and Water Treatment, 57, 18836-18850 (2016). [9] Hashem, F., & Amin, M. ,”Adsorption of methylene blue by activated carbon derived from various fruit peels” ,Desalination and Water Treatment, 57, 22573-22584 (2016). [10] Ahmad, M. A., Afandi, N. S., Adegoke, K. A., & Bello, O. S. ,”Optimization and batch studies on adsorption of malachite green dye using rambutan seed activated carbon” ,Desalination and Water Treatment, 57, 21487-21511 (2016). [11] Ma, Q., & Wang, L. ,”Adsorption of Reactive blue 21 onto functionalized cellulose under ultrasonic pretreatment: Kinetic and equilibrium study” ,Journal of the Taiwan Institute of Chemical Engineers, 50, 229-235 (2015). [12] Feng, Y., Yang, F., Wanga, Y., Ma, L., & Wu, Y. ,”Basic dye adsorption onto an agrobased waste material – Sesame hull (Sesamum indicum L.)” ,Bioresource Technology, 10, 10280–10285 (2011).