Analysis of Thermodynamics, Kinetics and Equilibrium Isotherm on Fe3+/Fe2+ Adsorption onto Palm Kernel Shell Activated Carbon (PKSAC): A Low-cost Adsorbent

Abstract

Adsorption of Fe3+/Fe2+ from a polluted shallow well water onto a palm kernel shell activated carbon (PKSAC) has been studied.  Batch experiment was adopted to study the Removal efficiency of Fe3+/Fe2+ on varying contact time, temperature, adsorbent loading and concentrations. Equilibrium isotherm and kinetic were also studied. Removal efficiency progressed with contact time till the peak adsorption time of 100 minutes when the efficiency remained at equilibrium. Also, removal efficiency got to equilibrium at the peak values of 80ºC, 4.8g and 12.5mg/l for temperature, adsorbent loading and concentration variations respectively. The adsorption isotherm models fitted the isotherm data got at 25ºC, 40ºC and 80ºC in this order; Langmuir > Temkin>Freunlich.  The dimensionless separation factor of 0.012, 0.017 and 0.015 for 25ºC, 40ºC and 80ºC respectively confirmed favorable adsorption of Fe3+/Fe2+ on the PKSAC adsorbent. Langmuir  adsorption capacity  increased from 203.9mg Fe3+/Fe2+/g to 389.3 mg Fe3+/Fe2+/g when the temperature increased from 25ºC to 40ºC but decreased to 308.1 mg Fe3+/Fe2+/g  at temperature of 80ºC. The kinetic models described the kinetic study data got at 25ºC, 40ºC and 80ºC as follows; power-function>second-order>Elovick>intra-diffusion>first-order kinetics. Mass transfer through liquid film diffusion controlled the adsorption of Fe3+/Fe2+ onto PKSAC. Negative values of the Thermodynamic parameters ( ,  and ) got at various temperature values showed   favorability of adsorption of Fe3+/Fe2+ onto PKSAC. It is therefore concluded that PKSAC removed Fe3+/Fe2+ from aqueous solution.