Spectrophotometric determination of iron in process samples from the chemical cleaning of coal

Iron is removed during the desulphurization and demineralization of coal by a chemical cleaning process utilizing a mixture of molten sodium hydroxide and potassium hydroxide. When 1,10-phenanthroline is used for spectrophotometric determination of the iron in the various caustic, aqueous and acidic process streams, organic materials leached from the coal by the molten caustic interfere with the colour-forming reaction. Pre-oxidation of the samples with potassium persulphate has proved to be an effective means of removing the interfering organic material before the iron determination.