Kinetic and Thermodynamic Studies of Zinc Removal from a Metal-Plating Wastewater Using Firouzkouh Zeolite

Document Type : Research Paper


1 Assistant Professor, Department of Soil Science, College of Agriculture, Shahid Chamran University of Ahvaz, Khuzestan, Iran

2 Associate Professor, Department of Soil Science, College of Agriculture, Shahid Chamran University of Ahvaz, Khuzestan, Iran


With the rapid development of industries such as metal plating facilities, mining, fertilizer producing industries, tanneries and paper industries heavy metals enriched wastewaters are directly or indirectly discharged into the environment. Zinc is a trace element that is essential for human health. It is important for the physiological functions of living tissues and regulates many biochemical processes. However, too much zinc can cause eminent health problems, such as stomach cramps, skin irritations, vomiting, nausea and anemia. It is present in effluents from various industries such as galvanization and metal-plating facilities, manufacture of batteries and other metallurgical industries.
The most commonly used methods for the removal of metal ions from industrial effluents include chemical precipitation, solvent extraction, reverse osmosis, ultra filtration, adsorption and ion exchange. Adsorption has been proven to be an excellent and cheap method to remove hazardous materials such as heavy metals and organic dyes from waste effluents.
A good understanding of adsorption equilibrium and thermodynamics is required to design and operate an adsorption process. Natural zeolites are widely distributed in arid and semiarid regions of the world. They are low cost aluminosilicates, with a cage-like structure suitable for ion exchange due to isomorphous substitution of Al3+ with Si4+ in the structure, giving rise to a deficiency of positive charge in the framework. Due to the above structural characteristics as well as the chemical and mechanical stability, they have received a great attention for the removal of heavy metals from wastewaters. Therefore, this study was conducted to identify the suitability of this mineral for removal of zinc ions from a metal plating wastewater through a series of batch experiments. Accordingly, the influence of contact time, solution temperature, size and dose of zeolite particles were investigated.
Methods and Materials
Wastewater sample
The wastewater sample used in this study was taken from a zinc metal-plating facility in Tehran, northern Iran. The wastewater sample was analyzed for pH, electrical conductivity (EC), the total concentration of dissolved solids, turbidity, and the total concentration of Zn, Fe, Mg, Pb, and Cd ions. The concentration of Zn and other heavy metals was determined using a Savant GBC Atomic Absorption Spectrophotometer (AAS).
Kinetic experiments
All sorption studies were performed using the batch technique because of its simplicity and reliability. The experiments were conducted at pH = 5, sorbent concentration of 2 g l-1, sorbent size of 20-50 µm and at the temperature of 20±1ºC.
To investigate the effect of contact time on the adsorption processes a constant mass of zeolite (adsorbent) (0.1 g) and 50 ml of known concentration of wastewater were added to 80 ml polypropylene centrifuge tubes. The mixtures were shaken vigorously on an orbital shaker (175 rpm) and at specified times (5, 10, 15, 20, 30, 60, 120, 240, 480, 720, 1440, and 2880 minutes). Tubes were then removed from the shaker and centrifuged at 2,500 rpm for 25 min and the Zn concentration in the supernatant was measured using AAS.
In order to investigate the effects of suspension pH and temperature, adsorbent dose and particle size of adsorbents on the percentage removal of Zn, the above experiments were also run by varying initial temperature (20 and 40 ° C using a thermostatic shaker bath) adsorbent dose (2, 4, 8, 12, 16, and 20 g l-1), and particle size of adsorbent (<2, 2-20, and 20-50 µm) while keeping all other parameters constant. All the experiments were carried out using the largest size and lowest amount of sorbents to identify how removal efficiency is affected if smaller size of particles and higher doses of zeolite particles are applied.
Control treatments with no addition of adsorbent were also run to test the possible adsorption and/or precipitation of Zn onto the container walls. Preliminary experiments showed that metal losses due to the adsorption onto the container walls were negligible.
The amount of Zn2+ adsorbed by zeolite, CS (mg g-1), was obtained as follow:
Where, C0 and Ce(mg l-1) are the initial and final (equilibrium) concentrations of Zn, respectively; V (ml) is the volume of solution and M is the mass of sorbent (mg). All measurements were carried out with three replications.
Thermodynamic studies
The activation energy of Zn adsorption on zeolite was calculated using Arrehenius equation which is expressed as below:
k2 = k exp (-Ea/RT)                                                                                         (6)
Where k is the temperature-independent factor (g mg -1 min-1), Ea the activation energy of sorption (KJ mol-1), R the universal gas constant (8.314 J mol-1 K) and T is the solution temperature (K).
Thermodynamic parameters of sorption including Gibbs free energy (ΔG0), change in enthalpy (ΔH0) and change in entropy (ΔS0) were also calculated using the following equations (7&8):
ΔG0 = -RT ln K0                                                                                                 (7)
Ln K0 = ΔS0/R- ΔH0/RT                                                                                     (8)
K0 can be defined as:
K0 = Csolid/Cliquid                                                                                                 (9)
Where, Csolid is the amount of Zn2+ adsorbed by zeolite at equilibrium and Cliquid is the equilibrium concentration of Zn2+ in solution. The values of ΔH0, ΔS0 and ΔG0 calculated from the slope and intercept of the plot of Ln K0 versus 1/T, respectively.
Results and Discussion
Contact time is an important parameter because it can reflect the adsorption kinetics of an adsorbent for a given initial concentration of adsorbate. The results showed an increasing trend on sorption of zinc ions onto zeolite particles. Based on this, the maximum adsorption capacity of zeolite for zinc ions was 17.9 mg g-1 and more than 80 percent of the total amounts of zinc ions were absorbed on zeolite particles within first 2 hours of experiments. The initial rapid phase may be due to the increase in the number of vacant sites and also the high concentration gradient between adsorbate in solution and that in the adsorbent.
As the temperature increases from 20 to 40 C, the adsorption capacity of sepiolite for Zn2+ decreases from 17.9.1 to 14.9 mg g-1. The decrease in removal capacity of Zn2+ ion with the rise in temperature is probably due to an increase in desorption of Zn2+ ion from the minerals interface to the solution. Results obtained from thermodynamic studies illustrated that sorption of zinc on zeolite particles is a reversible exothermic and physical process.
As compared to the pseudo-first-order kinetic model, a very good correlation coefficient (r2) was obtained for the pseudo-second-order kinetic model. 
As expected, the percent removal of Zn2+ ions increases as the amount of sepiolite increases. This can be attributed to an increase in the number of sorbent sites after the addition of more mineral particles to the suspension.
The results of the effect of zeolite particle size on the removal efficiency of Zn2+ ions from wastewater  indicates that as the particle size decreases, the metal diffusion is induced. This increases the accessibility of Zn2+ ions by the mineral. This suggests that the most suitable particle size of sepiolite for the removal of Zn2+ ions from wastewater studied is < 2µm.
The results also indicated that under similar conditions (T= 40C), increasing dose of zeolite particles to more than 12 g l-1 with sizes less than 2 µm is a good way to reach to the maximum efficiency for the removal of zinc ions from the studied wastewater.


Main Subjects

شایگان، ج. و افشاری، ع. 1383. «بررسی وضعیت فاضلاب‌های شهری و صنعتی در ایران»، مجلۀ آب و فاضلاب، شمارۀ 49، ص 58 تا 69.
اسماعیلی‌ساری، ع. 1381. آلاینده‌ها، بهداشت و استاندارد در محیط‌زیست، انتشارات نقش مهر، 767 صفحه.
Alinnor, I. J. 2007. Adsorption of heavy metal ions from aqueous solution by fly ash. Fuel, 86: 853–857.
Al-Jariri, J. S., and Khalili, F. 2010. Adsorption of Zn(II), BP(II), Cr(III) and Mn(II) from water by Jordanian bentonite. Desalination and Water Treatment, 21: 308-322.
Alvarez-Ayuso, E., and Garcia-Sanchez, A. 2003. Palygorskite as a feasible amendment to stabilize heavy metal polluted soils. Environmental Pollution, 125: 337-344.
Aytas, S., Yurtlu, M., and Donat, R. 2009. Adsorption characteristics of U(IV) ion onto thermally activated bentonite. Journal of Hazardous Material, 172: 667-674.
Bektas, N., Akmen, B., and Kara, S. 2004. Kinetic and equilibrium studies in removing lead ions from aqueous solutions by natural sepiolite. Journal of Hazardous Materials, 112: 115-122.
Boparai, H., Joseph, M., and O’Carroll, D. M. 2011. Kinetics and thermodynamics of cadmium ion removal by adsorption onto nano zerovalent iron particles. Journal of Hazardous Material, 186: 458-465.
Carter, D.L., Mortland, M. M., and Kemper, W.D. 1996. Specific surface. In Klute, A. (ed.), Methods of Soil Analysis Part 1: Physical and Mineralogical Methods. Soil Science Society of America and American Society of Agronomy, Madison, WI, USA, 413-423.
Gupta, S. S., and Bhattacharyya, K. G. 2008. Immobilization of Pb(II), Cd(II) and Ni(II) ions on kaolinite and montmorillonite surfaces from aqueous medium, Journal of Environmental Management, 87 (1): 46- 58.
Hamidpour, M., Kalbasi, M., Afyuni, M., and Shariatmadari, H. 2010. Kinetic and isothermal studies of cadmium sorption onto bentonite and zeolite. International Agrophysics, 24: 253-259.
Ho, Y.S., and McKay, G. 1999. Comparative sorption kinetic studies of dye and aromatic compounds onto fly ash. Journal Environmental Sciences and Health, 34: 1179-1204.
Hojati, S., and Khademi, H. 2013. Cadmium sorption from aqueous solutions onto an Iranian sepiolite: Kinetics and isotherms. Journal of Central-South University, 20: 3627-3632.
Kara, M., Yuzer, H., Sabah, E., and Celik, M. E. 2003. Adsorption of cobalt from aqueous solutions onto sepiolite. Water Research, 37: 224-232.
Kubilay, S., Gurkan, R., Savran A., and Sahan, T. 2007. Removal of Cu(II), Zn(II) and Co(II) ions from aqueous solutions by adsorption onto natural bentonite. Adsorption, 13: 41-51.
Kul, A. R., and Koyunco, H. 2010. Adsorption of Pb(II) ions from aqueous solution by native and activated bentonite: Kinetic, equilibrium and thermodynamic study. Journal of Hazardous Material, 179: 332-339.
Lagergren, S. 1898. Zur theorie der Sogenannten: Adsorption Gelöster Stoffe. Kungliga Svenska Vetenskaps akademiens Handlingar, 24: 1-39.
Potgieter, J. H., Potgieter-Vermaak, S. S., and Kalibantonga, P.D. 2006. Heavy metals removal from solution by palygorskite clay, Mineral Engineering, 19: 463-470.
Purna Chndra Rao, G., Satyaveni, S., Ramesh, A., Seshaiah, K., Murthy, K. S. N., and Choudary, N. V. 2006. Sorption of cadmium and zinc from aqueous solutions by zeolite 4A, zeolite 13X and bentonite. Journal of Environmental Management, 81 (3): 265-272.
 Sari, A. Tuzen, M. and Soylak, M. 2007. Adsorption of Pb (II), and Cr (III) from aqueous solution on Celtek clay. Journal of Hazardous Materials, 144: 41-46.
Sharma, Y.C. 2008. Thermodynamics of removal of cadmium by adsorption on an indigenous clay. Chemical Engineering Journal, 145: 64-68.
Summer, M.E., and Miller, W.P. 1996. Cation exchange capacity and exchange coefficients. In Bartels, J.M., Bigham, J.M. (eds.), Methods of Soil Analysis Part 3: Chemical Methods. Soil Science Society of America and America Society of Agronomy, Madison, WI, USA, 1201-1231.
Unuabonah, E. I., Olu-Owolabi, B. I., Adebowale, K.O., and Ofomaja, A. E. 2007. Adsorption of lead and cadmium ions from aqueous solutions by tripolyphosphate-impregnated kaolinite clay. Colloids and Surfaces A: Physicochemcal Engineering, 292: 202-211.
Wang, W., Chen, H., and Wang, A. 2007. Adsorption characteristics of Cd(II) from aqueous solution onto activated palygorskite. Separation and Purification Technology, 55: 157-164.
Wang, Y. H., Lin, S. H., and Juang, R.S. 2003. Removal of heavy metal ions from aqueous solutions using various low-cost adsorbents. Journal of Hazardous Materials, 102: 291-302.