Extraction of boric acid from tincal mineral by supercritical ethanol

• Boric acid was extracted from tincal mineral by supercritical ethanol.
• Boric acid in the solution can be separated by esterification reaction.
• The maximum boric acid extraction efficiency was determined as 32.6% by wt.
• Supercritical conditions of ethanol enhanced the extraction of boric acid from tincal mineral by reducing by-product formation.

In this study, extraction of boric acid from tincal mineral and borax by ethanol was investigated at supercritical and subcritical ethanol conditions. Experiments were carried out in a high pressure stainless steel reactor having volume of 0.1 dm3 under a mixing rate of 800 rpm. Solid/liquid ratio of 0.05 and 0.075; three different particle sizes were used between 20–63 microns. Tincal mineral decomposed at high temperature and the liberated boric acid reacted with ethanol to form volatile tri-ethylborate. Characterization of the powder crystallized from the ethanol phase and the remaining powder in the reactor was carried out by FTIR, XRD and TGA and have revealed that boric acid was extracted from tincal mineral by an esterification reaction. The maximum boric acid extraction efficiency was determined as 32.6 wt% at 250 °C and particle size of −20 μm for the solid/liquid ratio of 0.05 g/cm3 from tincal mineral.

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