Introducing the new model of chemical adsorption for heavy metals by Jacobi activated carbon adsorbents, Iranian activated carbon and blowy sand

Abstract

In the adsorption process, the adsorbed elements are established in different layers on the adsorbent surface. The first layer is placed on the adsorbent surface due to the direct contact and covalent bonding (chemical adsorption) and the other layers are placed on top of the adsorbent surface due to the covalent force (physical adsorption). In this research, for the first time, the law of mass conservation is used to calculate the chemical capacity of adsorbents in “aqueous solution”. In this study, first, the theory of the new model is presented. Then, the results of kinetic adsorption and adsorption experiments of heavy metals and metalloid (Fe2+, Pb2+, Cr6+, Ni2+, Cd2+ and As2+) by Jacobi activated carbon adsorbents, Iranian activated carbon and blowy sand are described. Next, the capability of the new model is compared to the Langmuir and Freundlich isotherm models (in the equilibrium absorption range). Ultimately, the chemical adsorption capacity for different adsorbents is determined. The results of kinetic adsorption of heavy metals study by Jacobi carbon adsorbent demonstrated that with decreasing the initial concentration of the solution, the adsorption efficiency increases. Therefore, when the initial concentration decreases to 20 mg/L, all elements are adsorbed with 100% efficiency. It means at low concentrations, the chemical adsorption (one-way reaction) has occurred and equilibrium concentration was not seen. Moreover, the results of isotherm adsorption studies illustrate that all three models describe the adsorption isotherm data well in the equilibrium concentrations (physical absorption). But, Shamohammadi model has presented a better determination coefficient (0.964>R2<0.999) than the Langmuir (0.890 <R2 <0.990) and the Freundlich (0.927 <R2 <0.931) models. The comparison of adsorption capacity gives the idea that the adsorbent capacity by Shamohammadi model has a much greater range of variation (11.05 mg/g to 142.2 mg/g) than the Langmuir model (12.12 mg/g to 31.4 mg/g). The chemical adsorption model's graph is linear for all adsorbents and the maximum chemical adsorption capacity for Fe2+ was figured out 4.890 mg/g by Jacobi activated carbon and the minimum chemical adsorption was obtained 0.379 mg/g for As2+ by wind sand.