Bioseparation of Pb(II) and Cd(II) from aqueous solution using cork waste biomass. Modeling and optimization of the parameters of the biosorption step

https://doi.org/10.1016/j.cej.2011.07.026Get rights and content

Abstract

In this work the ability of cork wastes to remove Cd(II) and Pb(II) from aqueous solutions has been studied. The kinetics of the biosorption system, the influence of the aqueous pH and the initial metal concentration on the metal uptake were investigated, showing a pH dependent profile. The maximum sorption for both metals was found at pH 5, independently that if the metals were in individual solutions or mixed. When a solution of the mixed metals were studied, a reduction in the Cd(II) uptake was observed showing a clear competition between the metals which was corroborated by the P-factor approach, behavior probably due to a lower attraction of this metal towards the corresponding active groups of the cork. Finally, the cork has been evaluated by FTIR and SEM in order to determine if the biosorption process modifies its chemical structure and morphology, respectively. Cork has been proved to be an efficient biomaterial useful for heavy metal separation purposes that is not altered by the process.

Highlights

► First work using cork waste as biosorbent for Cd and Pb, no morphology changes. ► Complete kinetic study considering the interaction between metals. ► Reduction in the uptake of Cd when Pb is present showing a clear competition. ► The process mechanism occurs by both film and intraparticle diffusion. ► Best correlation for the metal cork system for the P-factor approach based on Langmuir.

Introduction

It is well known that the increase in industrial activities has intensified the environmental pollution and the deterioration of some ecosystems due to the accumulation of pollutants such as heavy metals, synthetic compounds, nuclear waste liquids, etc. Among them, the exposure to heavy metals presents a high risk to the human health, so, increasing attention is focusing on their concentration and elimination from the environment [1]. Heavy metals are dangerous and not biodegradable contaminants that tend to be accumulated in living organisms, causing various diseases and disorders. Nowadays, still there are no widely accepted methods to remove them from the contaminated sites [2], [3]. Some methods like precipitation, ion exchange, electrochemical processes and/or membrane processes are commonly applied to the treatment of industrial effluents. However the application of such processes is sometimes restricted due to technical or economic constraints [4], [5], [2]. The search for new technologies, preferably clean technologies and cheap ones, has directed the attention to biosorption systems, which are based on metal binding capacities of various biological materials through biosorption process [6].

Biosorption can be defined as the ability of biological materials to accumulate compounds as metals and/or heavy metals from waste water through metabolically mediated or psycho-chemical pathways of uptake [7]. Biosorption take place by more than one mechanism. It consists of several quantitative and qualitatively processes according to the type of biomass, origin and processing [8]. Recent biosorption experiments have been performed by the use of by-products or the waste materials from large-scale industrial operations such as the waste from the production of wool, rice, straw, coconuts shaving, peat, waste of tea leaves, mush-rooms, nutshells and waste from sugar production [3], [9], [10], [11], [12], [13], [14]. These biomaterials have different types of functional groups, such as carboxylic, sulfates, phosphates and amino groups, which are the binding sites for ion exchange and complex reactions related to the sorption processes. The choice of the biomass should be based on its origin, chemical composition and type in addition to the composition of the sample solution to be purified [3]. The major advantages of biosorption processes over conventional treatment methods include their low cost, high efficiency, minimization of generation of chemical and/or biological sludge, no additional nutrient requirement, regeneration of biosorbents, the possibility of metal and/or heavy metal recovery and valorization of a waste when it is the origin of the biomass.

In this sense, cork (Quecur suber L.) has been chosen in the present work as biosorbent for the elimination of the heavy metals Cd(II) and Pb(II) from aqueous solution. Cork is the outer bark of the oak tree and it is industrially used for several purposes, principally the manufacturing of wine stoppers [15], [16]. The physical characteristics of the cork (elasticity, impermeability, low density…), and its chemical composition (a complex mixture of fatty acids and heavy organic alcohols ≈45% w/w, tannins ≈6% w/w, polysaccharides ≈12% w/w, lignin ≈27% w/w, alkanes, mineral content ≈5% and the most abundant element Ca 0.038–0.625% w/w), make this waste to be though as an ideal material for the biosorption of heavy metals [3], [17], [18], [19], [20].

Section snippets

Materials and methods

The cork was kindly provided by the wine stopper manufacturer Surochem S.L. (Girona, Spain). Cork samples of three different sizes were selected and labelled as S1, S8 and S9 (nominal diameter of 2–4 mm, 1–2 mm and 0.5–1 mm, respectively). All chemicals used were of analytical grade. A 1000 ppm stock solution of lead and 500 ppm stock solution of cadmium were prepared by diluting the required amounts of Pb(NO3)2 99% and Cd(NO3)2·4H2O 99%, in 1 M of HNO3 (all from Panreac, Spain). Others reactives

Kinetic studies

In order to determine the maximum uptake of the heavy metals on the cork, kinetic studies were run for the three different cork samples (S1, S8 and S9). To do so, individual heavy metal solutions and cork of different particle sizes were contacted during 5, 10, 15, 30 and 45 and 1, 2, 4, 6, 12, 24 and 48 h. Fig. 1 shows that in less than 6 h the maximum metal uptake is reached for all cases. As it can be expected, the highest metal biosorption percentages are found for the cork with the smallest

Conclusions

From the reported results, it can be said that the biomass of cork can be used as biomaterial sorbent for the removal and recovery of heavy metals, specially Pb(II) and Cd(II) from aqueous solutions without modification of its chemical structure and morphology. Biosorption is pH-dependent showing a maximum value at pH 5 and is highly influenced by the metal ion content in the initial solution. The adsorptive sites on the cork biomass showed a higher uptake for Pb(II) ions compared to Cd(II)

Acknowledgements

This work was financial supported by the CICYT projects CTQ2008-06633 and CTQ2009-07432. The authors are grateful to Laia Estivill, Jordi Grau and Alba Valls for their contribution to the preliminary work.

References (34)

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