The paper describes a simple and systematic state analysis of iron in pseudo-rust including various iron compounds-ferrous hydroxide, green rust-I, metallic iron, goethite, and magnetite-by utilizing the difference of solubilities of these compounds.
The outline of procedure is as follows:
Sample is treated with 100 ml of 3N cold hydrohlocric acid in water bath (about 15°C) for 5 to 10 minutes by passing nitrogen gas. In this condition, ferrous hydroxide and green rust-1 are dissolved and metallic iron, goethite and magnetite stay undissolved. The solution is rapidly filtered off by the apparatus of Fig. 1 to avoid the dissolution of metallic iron, goethite and magnetite. Ferrous hydroxide and green rust-1 in filtrate are determined by potassium bichromate titration method.
Residue including metallic iron, goethite and magnetite is treated with conventional brome-ethanol method, and then metallic iron is dissolved and other iron compounds are remained as insoluble residue.
Metallic iron in filtrate is determined by EDTA titration method. Residue is dissolved with hydrochloric acid (1: 1) in water bath at a constant temperature (about 70°C) while passing nitrogen gas and goethite and magnetite are determined by potassium bichromate titration method.