In this study, the Taguchi design method was employed to determine the optimum experimental parameters in extraction of vanadium by NaOH leaching of oil-fired fly. Prior to designed experiments, the raw precipitates were mechanicallly milled using a high-energy planetary ball mill. Experimental parameters were investigated as follows: mechanical milling (MM) times (2 and 5 hours), NaOH (1 and 2 molar concentration) as reaction solution (RS), powder to solution (P/S) ratios (100/400 and 100/600 mg/mL), temperature (T) of reaction system (303 K and 333 K [30 C and 60 C]), stirring times (ST) of reaction media (4 and 12 hours), stirring speed (SS) being adjusted to 400 and 600 rpm, and rinsing times (RT) of remained filtrates (1 and 3 hours). Statistical analysis of signal-to-noise ratio followed by analysis of variance was performed in order to estimate the optimum levels and their relative contributions. Data analysis is carried out using L8 orthogonal array consisting of seven parameters each with two levels. The optimum conditions were MM1 (3 hours), RS2 (2 molar NaOH), P/S2 (100/ 600 mg/mL), T2 (333 K [60 C]), ST2 (12 hours), SS1 (400 rpm), and RT1 (1 hour). Finally, from environmental and economical points of view, the process is faster and better organized by employing this analytical design method.

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