Comparison Study of the Adsorption of Copper Ions By Activated Carbon and A Locally Collected Bentonite

In this study, a locally collected bentonite and activated carbon (AC) synthesized from spent lubricant oils by chemical treatment were used as new non conventional and low cost adsorbents for the copper (Cu ions adsorption in a batch mode at various initial concentrations and different temperatures. Systematic studies on Cu ions adsorption equilibrium and kinetics by both adsorbents were carried out. The investigation were performed at different initial concentrations of Cu ions (10, 20, 30, 40, 50, 60 mg/L), contact time (10-90 min), and temperatures (25-55 °C). Depending on the results of temperature effect, thermodynamic parameters (ΔG°, ΔH and ΔS°) were estimated from two sources. First; from the adsorption distribution constant (Kd) which is represented by the ratio between the adsorbed and remained Cu ions in solution at equilibrium and second, from Freundlich isotherm constant (Kf). Comparable results are obtained. Freundlich and Langmuir isotherm models were applied to the adsorption data of the studied systems. The results obtained indicated that, the clay adsorbs Cu ions more intense than AC, with higher maximum adsorption capacity. Langmuir isotherm is better fitted to the adsorption data of the study system than Freundlich isotherm. The effect of contact time data of Cu ions adsorption onto clay, conducted at various initial concentrations were applied to pseudo first and second order kinetic models. The rate of adsorption was found to conform to pseudo second order kinetic with good correlation (R>0.99) and consistent values of the experimental (qe(exp)) and calculated (qe(cal)) adsorption capacities. The initial rate of adsorption was found to increase with initial concentration, where as the over all rate constant exhibited opposite variation. The employed adsorbents might be successfully used for the removal of other heavy metal ions from industrial wastewater. Introduction The presence of heavy metals in the environment has become a major threat to the plants, animals and human life due to their Emad A. S. AL-Hyali & Abraheem A. M. & Alaa A. Azeez 3 bioaccumulation tendency and toxicity. They are therefore must be removed from industrial effluents before discharge. Clay is a natural, earthy, fine grained materials composed largely of a group of minerals .It has been used for thousands of years and they still keep their position, as very important industrial materials. Clays have also been used for chemical studies for various purposes, including the adsorption of various organic, inorganic substances, radioactive specimens and heavy metals [1,2]. Original clay, also termed as natural clay, is the product of weathering rocks and primarily consists of between 75 to 85% of montmorillonite. It has an excess of negative charge on its lattice and is characterized by a three layers structure with two silicate layers enveloping an aluminates layer [3]. In theory, the presence of a negative charge on the clay surface should affect the adsorbent’s capacity to adsorb ions such that natural clay has an affinity for cationic species. Thus, it could be assumed that natural clay would have a greater capacity to adsorb basic substances than acidic. Ramakrishna et al. found that ,the bentonite clay exhibited high removals efficiency of a cationic dye (basic blue 9) reached to about 99.9% at acidic medium ( pH = 2) and exceeded 90% at other pH levels [4]. Clays can satisfy the various conditions of applications. The ion exchanges properties of clays have been intensively studied. The ion exchangers have a varying degree of preference. For instance, each metal ion depending on exchange type operating conditions and the metal being removed [5]. The mechanism by which the adsorption process takes place by clay is concerned mainly with the nature of forces acting between the adsorbed trace element and the adsorbent surface. According to the forces involved three basic kinds of adsorption can be distinguished as; physical, chemical and electrostatic adsorption [6]. The most widely used methods for removing heavy metals are chemical or electrochemical precipitation, both of which pose a significant problem in terms of disposal of the precipitated waste [7,8], and ion exchange treatments, which do not appear to be economical [9]. It has been reported that some aquatic plants [10], wood materials, agricultural by products [11], clay natural zeolite and other adsorbents have the capacity to adsorb and accumulate heavy metals [12, 13]. The need for low cost adsorbent is still vitals and attracting researcher's attention. Adsorption of metal ions onto clay minerals is an interesting Topic and has been studied extensively. Both metal ions and clays are common components in nature and such study would provide useful information on the state of the metal ions and how they distribute in the environment. Comparison Study of the Adsorption of Copper Ions By Activated Carbon and ... 4 In addition, it can also enrich the knowledge of the adsorption process for the environmental remediation of the polluted heavy metal ions in water [14, 15]. The ability of clay minerals to adsorb heavy metal cations is an important property in the context of the increasing contamination of aquatic environments and soils by toxic wastes. Also sorption of metals on clays is becoming important for preparing clay catalysts. Laboratory studies of the adsorption of heavy metals by clay have mostly been carried out using montmorillonite and illit. Several factors influence the adsorption efficiency of metal ions on clays, including salt concentration, pH of the solution, degree of loading on the adsorbent, presence of ligands and complex formation [16]. A wide range of methods is available for determination of the specific surface areas of clays. In general, these methods are of different reliability and accuracy. Vapor phase adsorption methods, using the nitrogen or rare gases at low temperatures, have been widely accepted as the most reliable methods [17, 18]. Experimental 1. Preparation of stock solution of Cu ion An exact weight of copper nitrate Cu(NO3)2 .3H2O was dissolved in de-ionized water in a 250ml volumetric flask in order to prepare a solution of 1000mg/L concentration. The prepared sample was kept in a reagent bottle and used for preparing other solutions. 2. Effect of concentration The experiments were achieved in batch mode. 50ml of Cu ion solution of different concentrations (10, 20, 30, 40, 50 and 60) mg/L was put in six dry and closed flasks in sequence. 0.1g from the adsorbent was added to each flask. The solutions were shacked for 70min with speed of 140rpm at 25°C. The solutions were then filtered, and the amount of adsorbed substance was determined by (Perkins Elmer, Analyst 200) atomic absorption (AA) spectrophotometer. 3. Effect of temperature The same steps those followed in finding the effect of concentration were repeated here with using the same concentration and keeping other conditions constant but under various temperatures (25, 35, 45, and 55) °C.