INFLUENCE OF THERMAL HISTORY OF IRON-OXIDES ON THEIR DISSOLUTION BEHAVIOR IN CITRIC-ACID EDTA ASCORBIC-ACID MIXTURE

Earlier investigations have shown that the dissolution of moderately s intered haematite: in a reductive-complexing formulation containing ci tric acid, EDTA and ascorbic acid (CEA) in the initial concentration r atio of 11:44:4 mol m(-3) at pH 2.8 is faster than at other concentrat ion ratios when the amount of haematite initially taken corresponded t o 22 mol m(-3) iron. The dissolution was considered for a system havin g a surface area to volume ratio of 67 m(-1) with oxide thickness of 5 microns, a system volume of similar to 6 m(3) and no regeneration of chelant. In the present work, the dissolution behaviour of iron oxides prepared from ferrous hydroxide heated at different temperatures rang ing from 373-1073 K in CEA 11:44:4 mol m(-3) was investigated. It was observed that the dissolution of samples prepared at lower temperature s was fast, analogous to the behaviour of haematite sols. The results have been interpreted on the basis of 'Grain model'.