Adsorption of Mn(II) and Co(II) ions from aqueous solution using Maize cob activated carbon: Kinetics and Thermodynamics Studies

Abstract

The adsorption of Mn(II) and Co(II) ions from aqueous solution was investigated using batch adsorption experiment at room temperature. The effect of pH, contact time, metal ion concentration and temperature were evaluated. The residual concentrations of the metal ions were determined by atomic absorption spectrophotometer. The results showed that maximum removal of Mn(II) and Co(II) ions occurred at pH 9. Some physico-chemical and spectroscopic characterization of the adsorbents were done such as moisture content, ash content, bulk density, volatile matter, iodine number, point of zero charge (PZC), XRF, and FTIR. The moisture and ash content of MCAC adsorbent were found to be 9.85±0.06 and 5.5±0.1% respectively. The bulk density was found to be 0.37±0.01g/m 3 , iodine number of 367.66±30 mg/g and PZC of 6.8. The SEM micrograph shows particle grains and jelly like rough surfaces, FTIR analysis results show different functional group in the MCAB adsorbent such as O-H, C=O, and C=C stretching. Kinetic study shows that the pseudo-second order kinetic model best described the adsorption of metal ions. The equilibrium data fitted Langmuir, Freundlich and Temkin adsorption isotherms, in each case, the Langmuir model appears to have better regression coefficients than the Freundlich and Temkin. Thermodynamics investigation showed that Gibb's free energy change () was negative indicating that the adsorption of Mn(II) and Co(II) ions by maize cob activated carbon were feasible and spontaneous. The positive value of enthalpy change () implies that the reaction was endothermic while positive value of entropy change () implies an irregular increase in the randomness at the solid/solution interface of the adsorbent during the adsorption process. © JASEM Introduction The increase in use of potentially toxic elements over the past few decades has unavoidably resulted in the flux of metallic substances in the aquatic and terrestrial environment (Jimoh et al., 2012). These metals once released through anthropogenic activities cannot be destroyed or degraded and thus persist indefinitely in the environment, accumulate in living tissues throughout the food chain and pose a serious menace to human and public health (Renuga et al., 2010). Numerous concerted efforts have been made to remedy this occurrence, which includes the use of conventional methods such as ion exchange, membrane processing, electrolytic methods, chemical oxidation or chemical reduction, filtration, chemical precipitation and electrochemical treatment (Selvaraj et al., 2003). However, most of these methods are not economically feasible for small and medium size industries; they also suffered from high operational and maintenance costs, generation of toxic sludge and elaborated procedure involved in the wastewater treatment. Commercial activated carbon is