Abstract
Clay minerals are one of the potential good adsorbent alternatives to activated carbon because of their large surface area and high cation exchange capacity. In this work the adsorptive properties of natural bentonite and kaolin clay minerals in the removal of zinc (Zn2+) from aqueous solution have been studied by laboratory batch adsorption kinetic and equi- librium experiments. The result shows that the amount of adsorption of zinc metal ion increases with initial metal ion concentration, contact time, but decreases with the amount of adsorbent and temperature of the system for both the ad- sorbents. Kinetic experiments clearly indicate that adsorption of zinc metal ion (Zn2+) on bentonite and kaolin is a two-step process: a very rapid adsorption of zinc metal ion to the external surface is followed by possible slow decreas- ing intraparticle diffusion in the interior of the adsorbent. This has also been confirmed by an intraparticle diffusion model. The equilibrium adsorption results are fitted better with the Langmuir isotherm compared to the Freundlich model. The value of separation factor, RL from Langmuir equation give an indication of favourable adsorption. Finally from thermodynamic studies, it has been found that the adsorption process is exothermic due to negative ?H0 accompa- nied by decrease in entropy change and Gibbs free energy change (?G0). Overall bentonite is a better adsorbent than kaolin in the the removal of Zn2+ from its aqueous solution.
Highlights
Heavy metal ion pollution is currently of great concern due to the increased awareness of the potentially hazardous effects of elevated levels of these materials in the environment [1,2]
The results obtained in this study demonstrated that kaolin and natural bentonite both can be used as an excellent natural adsorbent to remove Zn (II) from wastewaters with good efficiency and low cost
The amount of metal ion Zn (II) adsorption on both clay minerals was found to increase with increase in initial metal ion concentration and contact time but found to decreases with an increase in amount of adsorbent and temperature
Summary
Heavy metal ion pollution is currently of great concern due to the increased awareness of the potentially hazardous effects of elevated levels of these materials in the environment [1,2]. The main sources of zinc in the environment are the manufacturing of brass and bronze alloys and galvanization [3,4]. Precipitation, ion exchange, filtration, solvent extraction and membrane technology and adsorption on activated carbon are the conventional method for the removal of heavy metal ions from aqueous solutions and all of which may be ineffective or extremely expensive, when the metals are dissolved in large volumes of solution at relatively low concentration [3]
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