Separation and determination of metallic iron in the presence of iron hydroxide, iron oxyhydroxide and iron oxide

Abstract

Mercuric chloride method and bromine-methanol method had been generally used to determine metallic iron and gave a good results for determination of metallic iron in the presence of iron oxide. However, these were not suitable for the determination of metallic iron in iron oxide which included iron hydroxide and iron oxyhydroxide.The authors devised a new method in which iron hydroxide was removed by cold 3N hydrochloric acid and then metallic iron in the residue was determined by conventional mercuric chloride method.The procedure is as follow:Sample is treated with 100 ml of 3N cold hydrochloric acid for 5 to 10 minutes in water bath (about 15°C).In this condition, iron hydroxide is dissolved and metallic iron stays undissolved. The solution is rapidly filtered off by apparatus of Fig. 1 to avoid the dis solution of metallic iron, and then metallic iron in residue is determined by conventional mercuric chloride method.The recovery of metallic iron, standard deviation and coefficient of variation were >97%, 0.48 mg and 0.49 respectively in levels of 100 mg iron.The time required for analysis was about 40 minutes per sample.