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The Taguchi method was used to determine optimum conditions for the boric acid extraction from colemanite ore containing As in aqueous media saturated by CO2 gas. After the parameters were determined to be efficient on the extraction efficiency, the experimental series with two steps were carried out. The chosen experimental parameters for the first series of experiments and their ranges were as follows:  (i) reaction temperature, 25−70 °C; (ii) solid-to-liquid ratio (by weight), 0.091 to 0.333; (iii) gas flow rate (in mL/min), 66.70−711; (iv) mean particle size, −100 to −10 mesh; (v) stirring speed, 200−600 rpm; (vi) reaction time, 10−90 min. The optimum conditions were found to be as follows:  reaction temperature, 70 °C; solid-to-liquid ratio, 0.091; gas flow rate, 711(in mL/min); particle size, −100 mesh; stirring speed, 500 rpm; reaction time, 90 min. Under these optimum conditions, the boric acid extraction efficiency from the colemanite containing As was approximately 54%. Chosen experimental parameters for the second series of experiments and their ranges were as follows:  (i) reaction temperature, 60−80 °C; (ii) solid-to-liquid ratio (by weight), 0.1000 to 0.167; (iii) gas pressure (in atm), 1.5; 2.7; (iv) reaction time, 45−120 min. The optimum conditions were found to be as follows:  reaction temperature, 70 °C; solid-to-liquid ratio, 0.1; gas pressure, 2.7 atm; reaction time, 120 min. Under these optimum conditions the boric acid extraction efficiency from the colemanite ore was approximately 75%. Under these optimum conditions, the boric acid extraction efficiency from calcined colemanite ore was approximately 99.55%.

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