Aluminium oxide digestion

[yenstep]

I would like to carry out ICP-AES analysis for a compound containing bismuth oxide and alumium oxide. I need to prepare a standard solution for aluminium oxide as well as my sample.
I already tried using nitric acid and hydrofluoric acid to digest the oxide. However, the oxides can not be dissolved eventhough applying heat treatment for more than one week.

Question: May i know there is any method to prepare a aluminium oxide solution for ICP-AES analysis?

or what acid should i used to dissolve aluminium oxide?

[pollux]

Hi,

do you have tried HF+HNO3+HCl by micro waves?

NF EN 13656 method

[rajan84]

The alumina must be purified before it can be refined to aluminium metal. In the Bayer process, bauxite is washed with a hot solution of sodium hydroxide, NaOH, at 175°C (called digestion). This converts the alumina to aluminium hydroxide, Al(OH)3, which dissolves in the hydroxide solution according to the chemical equation

Al2O3 + 2 OH- + 3 H2O → 2 [Al(OH)4]-
The other components of bauxite do not dissolve and are filtered from the solution as solid impurities (clarification). The mixture of solid impurities is called red mud, and presents a disposal problem. Next, the hydroxide solution is cooled, and the dissolved aluminium hydroxide precipitates out as a white, fluffy solid (precipitation). When then heated to 1050°C, the aluminium hydroxide decomposes to alumina (calcination), giving off water vapor in the process:

2 Al(OH)3 → Al2O3 + 3 H2O
A large amount of the alumina so produced is then subsequently smelted in the Hall-Héroult process in order to produce aluminium.

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