Equilibrium isotherm studies for the uptake of cadmium and lead ions onto sugar beet pulp
Introduction
The pollution of the environment with heavy metals is a result of human activities, and the effects of these toxic metals on the ecosystems are of public health significance. Toxic metals can be distinguished from other pollutants, since they are not biodegradable and can be accumulated in living tissues, causing various diseases and disorders (Gode and Pehlivan, 2003, Gode and Pehlivan, 2005, Gode and Pehlivan, 2006). Cadmium and lead ion is one of the heavy metals considered toxic to humans and aquatic life. There has been a sharp rise in the global use of cadmium and lead for batteries and other applications, such as pigments, polyvinyl chloride stabilizers, and plating (Gaballah and Kibertus, 1998, Romero-Gonzalez et al., 2001). The wastewaters of metal cleaning and plating baths, pulp, paperboard mills, wood pulp production and fertilizer industry, etc. contain high level of toxic metal ion and in order to avoid, water pollution treatment is needed before disposal.
Conventional methods for removing metals from industrial effluents include chemical precipitation, coagulation, solvent extraction, electrolytic processes, membrane separation, ion-exchange (Gode and Pehlivan, 2003, Gode and Pehlivan, 2005, Pehlivan et al., 2006, Pehlivan and Arslan, 2006), activated carbon (Lin and Chang, 2001, Lopez et al., 1995), reverse osmosis, ultra filtration, biological systems (Zhang et al., 1999, Leinonen and Lehto, 2000), and adsorption (Gupta et al., 2003). Conventional methods used to remove of heavy metal concentrations in industrial effluents have showed limited applicability and are often extremely expensive. Recently, adsorption has become one of the alternative treatments (Leung et al., 2000, Kurniawan et al., 2006). Adsorption is a mass transfer process by which a substance is transferred from the liquid phase to the surface of a solid, and becomes bound by physical and/or chemical interactions.
The search for low-cost adsorbents that have metal-binding capacities has intensified and materials locally available in large quantities such as natural materials, agricultural waste or industrial by products can be utilized as low-cost adsorbents. Adsorption involves complexation, coordination, chelation, ion exchange, and adsorption (Volesky, 1990). Biosorption is assumed metabolism-independent due to the use of dead biomass. The sorption of metals by these kinds of materials might be attributed to their proteins, carbohydrates, and phenolic compounds that have carboxyl, hydroxyl, sulfate, phosphate, and amino groups that can bind metal ions. Metal-ion binding to living cells occurs either through surface adsorption or through intracellular accumulation. Significant practical limitations to living biomass-employing methods to treat wastewaters arise from the inhibition of the biomass growth when the metal cation concentrations are too high. However, methods for water treatment that employ non-living biomass are not complicated by such considerations. Many efforts have been made recently to find cheaper pollution control methods and materials (Ali and Bishtawi, 1997, Acemioglu and Alma, 2001). Processes for metal removal like adsorption have been suggested as being cheaper and more effective than the other technologies (Lopez et al., 1995, Allen and Brown, 1995). Previous investigations were mainly focused on the use of low-cost sorbents as a replacement for costly methods of removing heavy metals from solution. Numerous by-products of agro-industrial production have been studied for potential use as inexpensive biosorbents (Laszlo and Dintzis, 1994, Reddad et al., 2002). The biosorption phenomenon (Volesky, 1990) has provided an alternative treatment of industrial effluents from that of the traditional physico-chemical methods. It involves the use of natural substrates that are provided, for example chitosan (Guibal et al., 1995, Piron et al., 1997, Gerente et al., 1999), biomass (Gadd and White, 1993, Kapoor and Viraraghavan, 1995, Tobin and Roux, 1998), algal biomass (Matheickal et al., 1999, Davis et al., 2003), bark (Al-Asheh et al., 2000). Agricultural by-products such as onion skins (Omgbu and Iweanya, 1990), palm kernel husk, modified cellulosic materials (Ho, 2003, Ho, 2005), sunflower stalks (Sun and Shi, 1998) and pine bark (Al-Asheh and Duvnjak, 1998) etc., have received attention in these type of applications.
Biosorption is an alternative technology to remove organic pollutants from dilute aqueous solutions using inactive and dead biomasses, such as agricultural and fermentation wastes, various kinds of microorganisms, to bind and accumulate these pollutants by different mechanisms such as physical adsorption, complexation, ion exchange and surface micro precipitation. One of these low-cost sorbents particularly suited to biosorption is (SBP), which exhibits a large capacity to bind metals (Aksu, 2005, Aksu and Isoglu, 2006). The use of (SBP) as natural sorbent for the decontamination of industrial effluents contaminated with toxic metals may be a way to enhance its value. The (SBP) used in this work is a by-product of the sugar industry and is mainly used as animal feed. (SBP) is rich in pectic and cellulosic substances, >40% and ∼20% of the dry matter respectively. The pectic substances, which account for more than 40% of dry matter, are complex heteropoly-saccharides containing galacturonic acid, arabinose, galactose and rhamnose as the major sugar constituents. Due to the carboxyl functions of galacturonic acid, pectic substances are known to strongly bind metal cations in solution (Kartel et al., 1999). Up to now, its main use has been incorporation in animal feeds. This material is very cheap (100 US$ per metric tone) and its production reaches 14 × 106 tones of dry matter each year in Konya city (Pehlivan et al., 2006).
Another application may be the use of (SBP) as a natural sorbent to entrap heavy metals from aqueous solutions. These types of application appear to be promising and could make biosorption a new alternative method for adding value to (SBP). From the standpoint of environmental pollution control, heavy metal uptake of (SBP) has also been studied (Dronnet et al., 1997, Dronnet et al., 1998, Altundogan, 2005). (SBP) consists of rhamnose, fructose, arabinose, xylose, mannose, galactose, glucose, galacturonic acid, methanol, acetic acid and ash. Glucose (mostly from cellulose), arabinose and galacturonic acid were the main components of (SBP) (Micard et al., 1994). The pectic substances are complex heteropoly-saccharides containing galacturonic acid, arabinose, galactose and rhamnose as the major sugar constituents (Dronnet et al., 1996). Chemically, pectins appear as polyuronides, i.e. straight chains of a few hundred molecules of a-d-galacturonic acid linked by 1–4-glycosidic bounds. Pectins are not pure polyuronides, however; the polysaccharide also contains 1–2 linked a-l-rhamnose molecules (1–4%). Pectic substances contain polygalacturonic acids that carry carboxyl functions and they are known to strongly bind metal cations in aqueous solution and consequently exhibit good capacities to retain metal ions. Rhamnose residues are covalently bound to l-arabinose and o-galactose molecules (10–15%). In most pectin, some of the galacturonic acids are methyl esterified (Garnier et al., 1994, Kartel et al., 1999). In the present work, an attempt has been made to develop an inexpensive adsorbent system for the removal of Cd2+ and Pb2+ ions from wastewater using (SBP) which is the basic wastes from the sugar factory in Konya city.
Section snippets
Chemicals
All chemicals and reagents used were of analytical grade and were obtained from Merck, Germany. Stock solutions of lead and cadmium were prepared from cadmium nitrate and lead nitrate in deionised water, respectively. The pH measurements were performed with Jenway 3010 Model pH meter. A thermo-stated shaker (Gallenkamp Incubator) of Orbital model was used for adsorption experiments. The concentrations of metal ions were determined by atomic absorption spectrometer (ScnSAA model). Solutions of
Effect of contact time
The effect of time on the adsorption of metal ions by the (SBP) was studied by taking 0.4 g sorbent with 20.0 ml of 0.001 M metal salt solution in different flasks. The flasks were shaken for different time intervals in a temperature-controlled shaker. Fig. 1 shows the effect of contact time on adsorption of metal ions using (SBF). The results show that the percentage of metal ion adsorption by (SBF) increased with increasing time of equilibration and it reached the plateau value at about 70 min
Conclusion
The sorption of divalent metal cations by (SBP) seemed to involve adsorption phenomenon in addition to ion exchange and electrostatic interactions may be completed by chelation for the binding of Cd2+ and Pb2+ ions. (SBP) is a very cheap industrial by-product, readily obtainable in large quantities and exhibiting excellent binding capacities. (SBP) is cheap raw material or waste product from Konya Sugar Factory.
Metal sorption is pH-dependent and maximum sorption for both metals was found to lie
Acknowledgement
We express our thanks to the Selcuk University Scientific Research Foundation, which has financed, a part of which is presented in this study.
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