Evaluating the Effective Parameters in the Zircon Alkali Decomposition Process and Determining the Optimal Operating Conditions for Zirconium Extraction

Alkali decomposition with NaOH is the most commonly used method for extraction of zirconium from zircon mineral. This process includes alkali fusion, water leaching and acid leaching steps. In this study, Taguchi method was utilized to find the optimum operational conditions of alkali decomposition process. The results showed that under the optimal conditions of NaOH/ZrSiO4 mole ratio of 6:1, NaOH concentration of 30% and fusion temperature of 650 °C, 98.6% of the initial zircon was decomposed, as no pick of ZrSiO4 was observed in the XRD pattern of the alkali fusion product. The conditions of water leaching step were investigated as well, and under the optimal conditions of, liquid–solid ratio of 5:1, leaching temperature of 30 °C and leaching three times, 96.2% of sodium and 77.9% of silica content in the alkali fusion product were removed. The crystal phase structures of ZrO2 and SiO2 were observed in the residual solid after heat treatment. In the acid leaching step, leaching with 4 mol/L sulfuric acid with liquid/solid ratio of 20 at temperature of 60 °C, resulted in 92.73% recovery of zirconium and the silica content in the acid leaching solution was obtained 31 ppm. Results of this research suggest the optimal operational conditions of the facile, low price and proper industrial method for recovery of zirconium from zircon mineral.