Adsorption characteristics of Fe(III) and Fe(III)-NTA complex on granular activated carbon

The adsorption of Fe³⁺ ion on granular activated carbon has been studied in kinetic and equilibrium conditions taking into account the adsorbate concentration, temperature and solution pH as major influential factors. In addition, the effect of nitrilotriacetic acid on adsorption reaction as a complexing agent has been examined. Kinetic studies showed that the adsorption rate was increased as the initial Fe³⁺ concentration was raised. The adsorption reaction was estimated to be first-order at room temperature. The adsorption rate and equilibrium adsorption of Fe³⁺ increased as the temperature rose. The activation energy for adsorption was approximately 2.23kJmol^-1, which implied that Fe³⁺ mainly physically adsorbed on activated carbon. Coexistence of nitrilotriacetic acid with Fe³⁺ resulted in a decrease of equilibrium adsorption and the extent of decrease was proportional to the concentration of nitrilotriacetic acid. In the presence of nitrilotriacetic acid, the adsorbability of Fe ³⁺ decreased with pH. However, the trend was reversed in the absence of nitrilotriacetic acid. When activated carbon was swelled by acetic acid, the specific surface area was increased and maximum swelling was achieved at approximately 48h of swelling time. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° for adsorption reaction were estimated based on equilibrium data and in connection with these results the thermodynamic aspects of adsorption reaction were discussed.