Determination of the optimum conditions for the dissolution of stibnite in HCl solutions

The Taguchi method has been used to determine optimum conditions for the dissolution of stibnite in HCl solutions. Chosen experimental parameters and their ranges were (i) reaction temperature, 25-70 degrees C; (ii) solid-to-liquid ratio (in weight), 0.1-0.25; (iii) acid concentration (in weight), 23.71-37%; (vi) mean particle size; 0.1061-0.8426 mm; (v) stirring speed, 200-800 rpm; (vi) reaction time, 5-60 min. The optimum conditions were found to be reaction temperature, 70 degrees C; solid-to-liquid ratio, 0.125; acid concentration, 37%; mean particle size, 0.1061 mm; stirling speed, 700 rpm; reaction time, 60 min. Under these optimum conditions the dissolution of stibnite was approximately 99%. Next, for the experimental conditions of a time value 15 min less than its optimum value, a value of solid-to-liquid ratio twice its optimum value, and the remaining parameters at their optimum values, it was found that a benefit of 0.023 $/g SbCl3 could be gained from the cost of acid and electricity against a loss of 7.5 x 10(-4) $/g SbCl3 as a result of the 1.5% decrease in the Sb recovery due to the changes in optimum conditions.