A rapid and mercury pollution-free redoximetry determination of total iron in copper ore

A rapid and mercury pollution-free method for the determination of total iron in the presence of copper is described. The sample was decomposed either by an acid attack of hydrochloric acid-nitric acid (1 + 2) or by fusion with sodium peroxide. The ferric ion in the sample solution was amenable to direct reduction to ferrous ion with potassium borohydride in sulphuric acid medium under the catalysis of cupric ion, followed by titration with potassium dichromate using sodium diphenylaminesulfonate as an indicator. After reduction, the iron (II) in the solution was stable for 300 min. The proposed method is free of interference from copper and has been successfully used for the large-scale routine determination of total iron in copper ores showing the same or better degree of precision and accuracy as those obtained by the classic standard stannous chloride-mercuric chloride method with the separation of iron from copper.