International Journal of Biological Macromolecules 81 (2015) 400–409 Contents lists available at ScienceDirect International Journal of Biological Macromolecules j ourna l ho me pa g e: www.elsevier.com/locate/ijbiomac Metal adsorption by agricultural biosorbents: Adsorption isotherm, kinetic and biosorbents chemical structures Sadeek A. Sadeek a , Nabel A. Negm b,∗ , Hassan H.H. Hefni b , Mostafa M. Abdel Wahab b a Faculty of Science, Zagazig University, Zagazig, Egypt b Petrochemicals Department, Egyptian Petroleum Research Institute, Cairo, Egypt a r t i c l e i n f o Article history: Received 28 June 2015 Received in revised form 29 July 2015 Accepted 13 August 2015 Available online 15 August 2015 Keywords: Wastewater treatment Agricultural wastes Heavy metal ions Adsorption isotherm Kinetics a b s t r a c t Biosorption of Cu(II), Co(II) and Fe(III) ions from aqueous solutions by rice husk, palm leaf and water hyacinth was investigated as a function of initial pH, initial heavy metal ions concentration and treat- ment time. The adsorption process was examined by two adsorption isotherms: Langmuir and Freundlich isotherms. The experimental data of biosorption process were analyzed using pseudo-first order, pseudo- second order kinetic models. The equilibrium biosorption isotherms showed that the three studied biosorbents possess high affinity and sorption capacity for Cu(II), Co(II) and Fe(III) ions. Rice husk showed more efficiency than palm leaf and water hyacinth. Adsorption of Cu(II) and Co(II) was more efficient in alkaline medium (pH 9) than neutral medium due to the high solubility of metal ion complexes. The metal removal efficiency of each biosorbent was correlated to its chemical structure. DTA studies showed for- mation of metal complex between the biosorbents and the metal ions. The obtained results showed that the tested biosorbents are efficient and alternate low-cost biosorbent for removal of heavy metal ions from aqueous media. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Industrial processes including: mining [1], electroplating [2], and battery manufacturing [3], release several heavy metals in the ecosystems. Heavy metals are considered as toxic pollutants, due to their accumulation in animals, fished and plants. This accu- mulation causes various diseases, biological and genetic disorders. Accumulated heavy metal ions are non-biodegradable, so that they must be removed from the environment to keep their abundance at the minimum standards for living organisms. Many physico- chemical methods have been developed for the removal of heavy metals from aqueous solutions including: metal extraction [4], ion exchange process [5], chemical precipitation of metals in form of insoluble salts [2] and membrane separation [6]. These methods have several difficulties included in their high operating costs, lack of selectivity, imperfect removing of metal ions, in addition to the production of wastes during their production. Original metal removal methods have limitation at low metal ions contamina- tion lower than 50 ppm. Development of efficient and low-cost separation processes is therefore of most importance. Alternative ∗ Corresponding author at: 1-Ahmed El-Zommer Street, Nasr city, 7 th region, Cairo, Egypt. Tel.: +20 1275704384; fax: +20 242233123. E-mail address: nabelnegm@hotmail.com (N.A. Negm). relevant technique used in heavy metals removal from aqueous media is the adsorption process. The limitations which consid- ered when choosing suitable adsorbents are: the adsorption and regeneration abilities, market availability, and kinetic parameters. Adsorption capacity parameter is very important for estimation of process costs. Regeneration of the sorbent is important in cyclic processes when the used sorbents are expensive. Kinetic param- eters allow determining the rate of the sorption process. Recent studies showed that common agricultural waste products or natu- ral polymers can be used as potential biosorbents for the removal of heavy metals. Several studies showed that various lignocellulose biomaterials, plant biomass [7], tobacco dust [8], coconut shells powder [9], short hemp fibers [10], rice [11], and nut shells [12] have been studied. Chitin rich wastes, such as crab carapaces [13] or shrimp shells [14] have also shown a potential for the removal of toxic metals. In recent years, some industrial and agricultural wastes, such as Neem oil cake [15], sugar-beet pectin [16], and waste activated sludge [17] have been examined in the removal of heavy metals from aqueous solutions. The adsorption process of metal ions from the environment comprised several physico- chemical processes including: electrostatic interactions, metal ion exchange, and ion complexation [18]. Description of the adsorption process makes use of numerous models to determine the sorbent volume. There are many models that allow describing both the equilibrium, and the kinetics of adsorption. Models most commonly http://dx.doi.org/10.1016/j.ijbiomac.2015.08.031 0141-8130/© 2015 Elsevier B.V. All rights reserved.