The Quantitative Assay of Minerals for Fe ²⁺ and Fe ³⁺ Using 1,10‐Phenanthroline: II. A Photochemical Method

Abstract

Abstract A photochemical method for measuring Fe 3+ and total Fe in minerals is described. The method determines Fe 2+ concentration by measuring the Fe(phen) 3 2+ (phen = 1,10‐phenanthroline) complex formed during HF‐H 2 SO 4 digestion of the mineral. To measure Fe 2+ accurately in the presence of Fe 3+ from the mineral, the sample digestion and analysis are performed under red light to prevent photochemical reduction of the ferric‐phen species. Total iron is measured by converting any Fe 3+ in the digestate to Fe(phen) 3 2+ by photochemical reduction using a fluorescent lamp. This procedure avoids the problems associated with adding chemical reducing agents to iron‐phen solutions. The calibration curves were linear up to 8‐µg Fe/ml with a lower detection limit of 0.011 µg/ml. The absorptivities of the calibration curves were 0.1852 ± 0.0017 and 0.1960 ± 0.0018 ml/cm‐µg for Fe 2+ and total Fe, respectively. Ferric iron in the mineral samples was calculated by difference.