Influence of ageing on the catalytic activity of ferric sludge for oxidation of fe(II)

Abstract

The catalytic effect of freshly formed or added ferric iron on the Fe(II) oxidation has been demonstrated by previous studies. High Fe(III) concentrations significantly accelerate the oxygenation rate. High Fe(III) concentrations can be maintained only by sludge recycle which eventually leads to sludge ages as high as 10 days. Therefore, the aim of this study was to determine whether ageing of ferric hydroxide sludge affects its catalytic effect on the oxidation of ferrous iron by aeration. In order to reach this aim four different groups of experiments were carried out using ferric hydroxide sludge aged for a period of 0 to 10 days. Initial Fe(III) concentrations were varied within the range of 50 mg/l to 200 mg/l. It has been demonstrated that the catalytic effect of ferric hydroxide sludge on the oxidation of ferrous iron by aeration increases with increasing sludge age contrary to what is commonly expected. It has been concluded that, catalytic oxidation rate constant kcat obtained from the batch systems can safely be used in design of continuous flow iron oxidation reactors with sludge recycle.