Nowadays the removal of heavy metals from wastewater is essential due to their high toxicity and impact on human health. In the present study, branches of palm trees were converted into activated carbon by chemical and physical activation. The prepared samples were used for the removal of Cr(VI) from their aqueous solution. Chemical activation was carried out using (20 and 50%) H3PO4 and K2CO3, and physical activation was performed using steam. Batch adsorption experiments were carried out to examine the removal process under factors such as pH and . The metal ion removal was pH dependent and reached maximum removal at pH 2. Experimental data were analyzed using Langmuir, Freundlich, and Flory-Huggins isotherms. The adsorption studies revealed that the removal of Cr(VI) ions was well fitted with Langmuir isotherm. The adsorption kinetics well fitted using a pseudo second-order kinetic model. Column studies revealed that the highest bed volume (60?BV) was observed for the sample activated with 50% H3PO4. The adsorption efficiency was enhanced with acid treatment (50% H3PO4) and reduced by steam. 1. Introduction The discharge of heavy metals into the environment has been increasing continuously due to rapid industrialization and has created a major global concern. The release of these heavy metals causes a significant hazard to human health and the environment because of their toxicity, accumulation in living tissues, and consequent biomagnifications in the food chain [1, 2]. Among the different heavy metals in concern is chromium. Compounds of chromium mainly occur in the environment as trivalent Cr(III) and hexavalent Cr(VI). Trivalent chromium is an essential element in human nutrition (especially in glucose metabolism) and is less toxic than the hexavalent state, which is recognized as a carcinogenic and mutagenic agent [3]. Acute exposure to high levels of Cr(VI) can produce nervous system damage and liver disorder. EPA (Environmental Protection Agency) has set the maximum level of total Cr concentration allowed in drinking water at 0.1?mg?L?1 [4]. Chromium and its compounds are widely used in electroplating, leather tanning, cement, dying, metal processing, wood preservatives, paint and pigments, textile, steel fabrication, and canning industries. In Egypt, about 2000–5000 tons of chromium pollute the environment annually from several industries in the aqueous effluent compared to the recommended permissible discharge limits of 2?mg?L?1 [5]. Conventional methods for removing dissolved heavy metal ions include chemical precipitation, chemical
References
[1]
H. K. An, B. Y. Park, and D. S. Kim, “Crab shell for the removal of heavy metals from aqueous solution,” Water Research, vol. 35, no. 15, pp. 3551–3556, 2001.
[2]
N. Febriana, S. O. Lesmana, F. Q. Soetaredjo, J. Sunarso, and S. Ismadji, “Neem leaf utilization for copper ions removal from aqueous solution,” Journal of the Taiwan Institute of Chemical Engineers, vol. 41, no. 1, pp. 111–114, 2010.
[3]
K. Mohanty, M. Jha, B. C. Meikap, and M. N. Biswas, “Removal of chromium (VI) from dilute aqueous solutions by activated carbon developed from Terminalia arjuna nuts activated with zinc chloride,” Chemical Engineering Science, vol. 60, no. 11, pp. 3049–3059, 2005.
[4]
US EPA, IRIS, Integrated Risk Information System, US Environmental Protection Agency, Washington, DC, USA, 1997.
[5]
C. Raji and T. S. Anirudhan, “Kinetics of Pb(II) adsorption by polyacrylamide grafted sawdust,” Indian Journal of Chemical Technology, vol. 4, no. 3, pp. 157–162, 1997.
[6]
S. S. Ahluwalia and D. Goyal, “Microbial and plant derived biomass for removal of heavy metals from wastewater,” Bioresource Technology, vol. 98, no. 12, pp. 2243–2257, 2007.
[7]
A. Baran, E. Bicak, S. Hamarat, and O. S. Baysal, “Comparative studies on the adsorption of Cr(VI) ions on to various sorbents,” Bioresource Technology, vol. 98, no. 3, pp. 661–665, 2006.
[8]
S. Gupta and B. V. Babu, “Adsorption of Chromium by a low cost adsorbent prepared from tamarind seeds,” in Proceedings of the International Symposium and 59th Annual Session of IIChE in Association with International Partners (CHEMCON '06), pp. 27–30, GNFC Complex, Bharuch, India, December 2006.
[9]
R. C. Bansal and M. Goyal, Activated Carbon Adsorption, Taylor & Francis, Boca Raton, Fla, USA, 2005.
[10]
H. Marsh and F. R. Reinoso, Activated Carbon, Elsevier, San Diego, Calif, USA, 2006.
[11]
H.-D. Choi, W.-S. Jung, J.-M. Cho, B.-G. Ryu, J.-S. Yang, and K. Baek, “Adsorption of Cr(VI) onto cationic surfactant-modified activated carbon,” Journal of Hazardous Materials, vol. 166, no. 2-3, pp. 642–646, 2009.
[12]
K. Selvi, S. Pattabhi, and K. Kadirvelu, “Removal of Cr(VI) from aqueous solution by adsorption onto activated carbon,” Bioresource Technology, vol. 80, no. 1, pp. 87–89, 2001.
[13]
H.-D. Choi, M.-C. Shin, D.-H. Kim, C.-S. Jeon, and K. Baek, “Removal characteristics of reactive black 5 using surfactant-modified activated carbon,” Desalination, vol. 223, no. 1–3, pp. 290–298, 2008.
[14]
Y. Sudaryanto, S. B. Hartono, W. Irawaty, H. Hindarso, and S. Ismadji, “High surface area activated carbon prepared from cassava peel by chemical activation,” Bioresource Technology, vol. 97, no. 5, pp. 734–739, 2006.
[15]
L. S. Clesceri, A. E. Greenberg, and A. D. Eaton, “Standard methods for the examination of Water & Waste Water,” in Proceedings of the 20th American Public Health Association, pp. 3-65–3-68, Washington, DC, USA, 1998.
[16]
M. Gholipour and H. Hashemipour, “Hexavalent chromium removal from aqueous solution via adsorption on granular activated carbon: adsorption, desorption, modeling and simulation studies,” Journal of Engineering and Applied Sciences, vol. 6, no. 9, pp. 10–18, 2011.
[17]
A. R. Yacob, Z. A. Majid, R. S. D. Darsil, and V. A. Inderan, “Comparison of various sources of high surface area carbon prepared by different types of activation,” The Malysian Journal of Analytical Sciences, vol. 12, no. 1, pp. 264–271, 2008.
[18]
M. Imamoglu and O. Tekir, “Removal of copper (II) and lead (II) ions from aqueous solutions by adsorption on activated carbon from a new precursor hazelnut husks,” Desalination, vol. 228, no. 1–3, pp. 108–113, 2008.
[19]
B. Bayat, “Comparative study of adsorption properties of Turkish fly ashes: II. The case of chromium (VI) and cadmium (II),” Journal of Hazardous Materials, vol. 95, no. 3, pp. 275–290, 2002.
[20]
C. Namasivayam and K. Ranganathan, “Waste Fe(III)/Cr(III) hydroxide as adsorbent for the removal of Cr(VI) from aqueous solution and chromium plating industry wastewater,” Environmental Pollution, vol. 82, no. 3, pp. 255–261, 1993.
[21]
S. M. Nomanbhay and K. Palanisamy, “Removal of heavy metal from industrial wastewater using chitosan coated oil palm shell charcoal,” Electronic Journal of Biotechnology, vol. 8, no. 1, pp. 43–53, 2005.
[22]
T. S. Anirudhan and K. A. Krishnan, “Removal of cadmium(II) from aqueous solutions by steam-activated sulphurised carbon prepared from sugar-cane bagasse pith: kinetics and equilibrium studies,” Water SA, vol. 29, no. 2, pp. 147–156, 2003.
[23]
I. Langmuir, “The adsorption of gases on plane surfaces of glass, mica and platinum,” The Journal of the American Chemical Society, vol. 40, no. 9, pp. 1361–1403, 1918.
[24]
K. Baek, B.-K. Kim, H.-J. Cho, and J.-W. Yang, “Removal characteristics of anionic metals by micellar-enhanced ultrafiltration,” Journal of Hazardous Materials, vol. 99, no. 3, pp. 303–311, 2003.
[25]
K. Baek and J.-W. Yang, “Cross-flow micellar-enhanced ultrafiltration for removal of nitrate and chromate: competitive binding,” Journal of Hazardous Materials, vol. 108, no. 1-2, pp. 119–123, 2004.
[26]
I. A. W. Tan, A. L. Ahmad, and B. H. Hameed, “Enhancement of basic dye adsorption uptake from aqueous solutions using chemically modified oil palm shell activated carbon,” Colloids and Surfaces A: Physicochemical and Engineering Aspects, vol. 318, no. 1–3, pp. 88–96, 2008.
[27]
H. Teng, J.-A. Ho, Y.-F. Hsu, and C.-T. Hsieh, “Preparation of activated carbons from bituminous coals with CO2 activation. 1. Effects of oxygen content in raw coals,” Industrial and Engineering Chemistry Research, vol. 35, no. 11, pp. 4043–4049, 1996.
[28]
H. M. F. Freundlich, “Over the adsorption in the solution,” The Journal of Physical Chemistry, vol. 57, pp. 358–470, 1906.
[29]
A. Ergene, K. Ada, S. Tan, and H. Katircioglu, “Removal of Remazol Brilliant Blue R dye from aqueous solutions by adsorption onto immobilized Scenedesmus quadricauda: equilibrium and kinetic modeling studies,” Desalination, vol. 249, no. 3, pp. 1308–1314, 2009.
[30]
N. K. Hamadi, X. D. Chen, M. M. Farid, and M. G. Q. Lu, “Adsorption kinetics for the removal of chromium(VI) from aqueous solution by adsorbents derived from used tyres and sawdust,” Chemical Engineering Journal, vol. 84, no. 2, pp. 95–105, 2001.
[31]
S. Lagergren, “Zur theorie der sogenannten adsorption gel?ster stoffe,” Kungliga Svenska Vetenskapsakademiens Handlingar, vol. 24, no. 4, pp. 1–39, 1898.
[32]
C. K. Ko, C. W. Cheung, K. K. Choy, J. F. Porter, and G. McKay, “Sorption equilibria of metal ions on bone char,” Chemosphere, vol. 54, no. 3, pp. 273–281, 2004.
[33]
Y. S. Ho and G. McKay, “Pseudo-second order model for sorption processes,” Process Biochemistry, vol. 34, no. 5, pp. 451–465, 1999.
[34]
W. J. Weber and J. C. Morris, “Intraparticle diffusion during the sorption of surfactants onto activated carbon,” Journal of Sanitary Engineering Division American Society for Civil Engineers, vol. 89, pp. 53–61, 1963.
[35]
S. Arivoli, M. Hema, M. Karuppaiah, and S. Saravanan, “Adsorption of chromium ion by acid activated low cost carbon-kinetic, mechanistic, thermodynamic and equilibrium studies,” E-Journal of Chemistry, vol. 5, no. 4, pp. 820–831, 2008.