Conditioning Fixed-Bed Filters with Fine Fractions of Granulated Iron Hydroxide (µGFH)

Abstract

The fine fraction of granular ferric hydroxide (µGFH, <0.3 mm) is a promising adsorbent for the removal of heavy metals and phosphate, but properties of µGFH were hitherto not known. The present study aimed at characterizing µGFH regarding its physical and chemical properties and at evaluating methods for the conditioning of fixed-bed filters in order to develop a process that combines filtration and adsorption. Conditioning was done at different pH levels and for different particle sizes. Anthracite, coke, pumice and sand were studied as potential carrier materials. A method for the evaluation of the homogeneity of the iron hydroxide particle distribution on pumice filter grains using picture analysis was developed. Pre-washed pumice (pH 8.5) proved to lead to high embedment and a homogeneous distribution of µGFH. Filter runs with phosphate (2 mg/L P) showed similar breakthrough curves for the embedded fine fraction adsorbent and for conventional GFH.