Cashew nut shell (CNS) is an agricultural waste was investigated as a new adsorbent for the removal of zinc(II) from aqueous environment. Effects of solution pH, CNS dose, contact time, initial zinc(II) concentration and temperature on removal efficiency were tested and optimum conditions were evaluated. The equilibrium data were fitted well with Langmuir isotherm model and pseudo‐second‐order kinetic model. Langmuir monolayer adsorption capacity of CNS was examined as 24.98 mg/g. Changes in standard Gibbs free energy (▵G°), standard enthalpy (▵H°) and standard entropy (▵S°) showed that the sorption of zinc(II) ions onto CNS are spontaneous and exothermic at 303–333 K. Sorption process was found to be controlled by both surface and pore diffusion. A batch adsorber was designed for different CNS dose to effluent volume ratios using Langmuir equation. Effective diffusivity values were found to be 1.927 × 10−11 (10 mg/L), 2.135 × 10−11 (20 mg/L), 2.267 × 10−11 (30 mg/L), 2.305 × 10−11 (40 mg/L) and 2.362 × 10−11 (50 mg/L) m2/s. © 2011 Canadian Society for Chemical Engineering

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This paper discusses about the adsorption of metal ions such as Cu(II), Cd(II), Zn(II), and Ni(II) from aqueous solution by sulfuric acid treated cashew nut shell (STCNS). The adsorption process depends on the solution pH, adsorbent dose, contact time, initial metal ions concentration, and temperature. The adsorption kinetics was relatively fast and equilibrium was reached at 30 min. The adsorption equilibrium follows Langmuir adsorption isotherm model. The maximum adsorption capacity values of the modified cashew nut shell (CNS) for metal ions were 406.6 mg/g for Cu(II), 436.7 mg/g for Cd(II), 455.7 mg/g for Zn(II), and 456.3 mg/g for Ni(II). The thermodynamic study shows the adsorption of metal ions onto the STCNS was spontaneous and exothermic in nature. The kinetics of metal ions adsorption onto the STCNS followed a pseudo-second-order kinetic model. The external mass transfer controlled metal ions removal at the earlier stages and intraparticle diffusion at the later stages of adsorption. A Boyd kinetic plot confirms that the external mass transfer was the slowest step involved in the adsorption of metal ions onto the STCNS. A single-stage batch adsorber was designed using the Langmuir adsorption isotherm equation. IntroductionThe presence of heavy metals in wastewater is always a serious environmental problem because the heavy metals are not biodegradable and it can be accumulated in living tissues. The presence of these heavy metals in water even at a very low level concentration, it would be harmful to human health and also aquatic organisms in terms of toxicity and carcinogenicity. The heavy metals such as copper, cadmium, zinc, and nickel are among the most common pollutants available in industrial wastewater because it finds many industrial applications. But its removal and recovery from the wastewater is important for the living environment [1]. Different methods were investigated and applied to remove excessive heavy metals from wastewater includes chemical precipitation, electrolysis, evaporation, ion exchange, and membrane processes. However, these methods are either expensive or inefficient when heavy metals exist in low concentrations [2]. So it is important to find new treatment methods for removing heavy metals from wastewater. In the present days, adsorption is proved to be one of the simplest and most effective treatment methods for the treatment of heavy metals containing wastewater. Now-a-days activated carbon is widely used as an adsorbent in water and wastewater treatments because of its high porosity, large internal surface area, and relatively high mechanical strength.Despite its widespread application in industries, activated carbon remains an expensive material [3]. Therefore, it is important to investigate and develop a new low-cost effective adsorbent from the low-cost materials that can be applied to the wastewater treatment. Some of the effective adsorbent from low-cost materials that have been exploited to remove the metal ions from the aqueous solutions such as vegetable biomas...

In the present study, batch adsorption experiments were performed for the removal of methylene blue (MB) dye from its aqueous solution using newly prepared surface modified cashew nut shell (SMCNS) by varying the operating parameters like solution pH, adsorbent dose, initial dye concentration, contact time and temperature. The SMCNS has been prepared by treating the cashew nut shell with the sulphuric acid. Adsorption equilibrium data were analyzed by the model equations such as Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherms and it was found that the Freundlich isotherm model best fitted the equilibrium data. The maximum monolayer adsorption capacity of the SMCNS was found to be 71.33 mg of MB dye molecules / g of SMCNS. A single stage batch adsorber was designed using Freundlich adsorption isotherm model. Kinetic models such as pseudo-first-order, pseudo-second-order, Elovich, intra particle diffusion, and Boyd kinetic model were applied to describe the adsorption mechanism and the results shows that pseudo-second-order equation fits the kinetic data very well. Thermodynamic studies reveal that the adsorption of MB dye onto the SMCNS is spontaneous and exothermic in nature. This study shows that surface modified cashew nut shell is a potential low cost adsorbent and can be an alternative to the commercially available adsorbents.