Adsorption of cobalt (Co2+) from aqueous solution using nano-scale graphite carbon alginate bead (NGCAB) : equilibrium, kinetic and thermodynamics studies

Abstract

In many industrial activities such as paints, pigment, electronics and mining, the increasing of toxic metal such as Co2+ which are discharged into the environment as industrial wastes, represent a serious threat to human health, living resources, and ecological systems. Cobalt expose to through breathing air, drinking water and eating cobalt-containing food that’s why cobalt may be easily. In these days, lots of techniques have been appeared for the purification from metal ions such as cobalt in wastewater including adsorption, precipitation, oxidation, ion-exchange and membrane electrolysis, etc. Adsorption, among the above method, is very promising because adsorption is high efficiency, inexpensiveness and simple to handling. To Co2+ removal from aqueous solution, a novel adsorbent was developed by impregnating graphite nano-carbon (GNC) onto alginate bead (AB). Nano-scale Graphite Carbon Alginate Bead (NGCAB) which had physicochemical and spectroscopic properties of the novel adsorbent was characterized and compared with AB. The Co2+ adsorption onto NGCAB was quantitatively assessed by determining the kinetics and thermodynamics parameters. The Co2+ adsorption capacity was highest at neutral pH condition and the adsorption equilibrium time reached in 10 days using NGCAB. Increasing the temperature from 288 to 318 K resulted in a 2.5-fold higher Co2+ adsorption onto AB, while the thermal dependence of Co2+ adsorption on NGCAB was not found. Kinetics studies showed an applicability of pseudo-second-order kinetic model for AB and NGCAB. Monolayer adsorption was the dominant mechanism of Co2+ adsorption on AB and NGCAB, which was demonstrated by a better overall fit of Langmuir model to the experimental data. Separation factor (RL) and Freundlich constant (n) were well in the range of values for favorable adsorption. Thermodynamics studies revealed that Co2+ adsorption onto AB and NGCAB was endothermic and spontaneous processes. Positive values of entropy indicate randomness in the solid/aqueous phases and the activation energy (Ea) fits in the range of chemisorption.