Microwave-assisted Caustic Leaching of Bauxite for ICP-OES for Process-simulation of the Bayer Process of Al₂O₃ Production

Multiwave 5000 and Rotor 20SVT50 improve reproducible leaching of bauxite samples to simulate the industrial Bayer process over a wide range of temperatures. A correction of the temperature calibration is given in this report.

Bauxite, a mixture of alumina, iron oxides, silica and a few other minerals, significantly varies from region to region. Small scale bauxite leaching is performed in the refinery laboratory to simulate the caustic leaching of the Bayer process, which is used globally for separation of pure alumina (AlO). The goal of this leaching is to determine the amount of “available alumina” in the bauxite ore. The amount of “reactive silica“ is normally assessed too for cost reasons, as it consumes a considerable amount of NaOH.
Depending on the composition of the ore, the temperature of the process needs to be between 150 and 240 °C. The contents of alumina and silica are traditionally determined in small-scale high-pressure steel bombs, in which it is difficult to control the heating to target temperature and to maintain it. Thus, microwave heating offers an attractive way to efficiently control the process thanks to benefits such as instant on-and-off heating and fast power input. In addition, magnetic stirring of individual reactor vessels is possible.
The parameters for this study cover a wide temperature range used in industry. The target temperature and the temperature calibration (for digestion acids) had to be corrected for sodium hydroxide for the range from 150 °C to 240°C.

For reference material measurements a temperature of 148 °C was selected according to the certificate. This report also addresses the extraction efficiency for alumina and reactive silica from bauxite ores of different origin at different temperatures.

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