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 dm(3) 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 degrees C and particle size of -20 mu m for the solid/liquid ratio of 0.05 g/cm(3) from tincal mineral. (C) 2015 Elsevier B.V. All rights reserved.