Removal of Ferrous Ion in Synthetic Waters by Catalytic Air Oxidation

Abstract

Catalytic air oxidation of ferrous ion in synthetic waters (Fe(NH₄)₂ (SO₄)₂·6H₂O solution) was studied at neutral medium in batch reactors. Sepiolite, ZnO, NiO, MgO, Co₃O₄, MoO₃., MnO₂ and Al(OH)₃ were separately used as catalyst. Iron(II) ion in water samples was analyzed by the bipyridine spectrophotometric method. Firstly, non-catalytic oxidation of Fe(II) in aqueous solution was investigated. However, low values of conversion percentage were obtained even if air was bubbled through the solution. An oxidation yield of 97 % was minimally obtained by resting only the solution at open air when an effective catalyst such as NiO was used. The activation energies were determined as 14.8 and 43.2 kJ/mol and the corresponding rate equations were obtained as -r_A = 9.72 e^-1779/T C_A and -r_A = 1672 e^-5197/T C_A for catalytic (NiO) and non-catalytic oxidation, respectively. The reaction order was found to be one with respect to Fe(II) concentration. Experiments were also conducted in a continuous system as a fixed bed reactor; however the obtained yields were very low.