Continuous determination of Fe³⁺ and Al³⁺ in Cr-brick and Cr-ore using oxine, EDTA, and CyDTA

Abstract

The quantitative determination of Al³⁺ and Fe³⁺ in Cr-brick and Cr-ore containing large amounts of Cr³⁺ by the use of oxine (8-hydroxy-quinoline), EDTA (disodium ethylenediaminetetraacetate) and CyDTA (cyclohexanediaminetetraacetic acid) has been investigated.
The sample after fusion with potassium acid sulfate is oxidized with HNO₃, an amount of EDTA excess of that required for the equivalent weight of Fe³⁺, Al³⁺, Cr³⁺, Ca²⁺, and Mg²⁺ is added, and the solution at pH 46 is boiled for the formation of complex salts of Fe³⁺, Al³⁺, and Cr³⁺, and EDTA. It is then treated with oxine, made alkaline with ammonia, heated at about 80°C for precipitation of Fe³⁺ and Al³⁺, and allowed to stand for 10 min. for aging. The precipitate of oxinate is filtered off, taken up in. HCl; and the Fe³⁺ at pH 22.2 is titrated with EDTA using the liberated oxine as an indicator. The solution is then heated to boiling and Al³⁺ is titrated at pH 22.2 with CyDTA using Cu²⁺-PAN (Cu²⁺-α-pyridyl-β-azonaphthol) as an indicator. The results indicated that the masking of Cr³⁺ by EDTA is complete, and that oxine is sensitive as the indicator in the chelate titration of Fe³⁺, and that the presence of oxine is without influence in the determination of Al³⁺. The accuracy and rapidity for practical operation_ were proved to be entirely satisfactory.