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The decomposition process for zircon sand concentrate using mixed base of sodium hydroxide partly replaced by calcium oxide was inrestigated.It is found that the decomposition rate of zircon gradually increased with the increase of the reaction temperature and time.The decomposition rate is over 97％ with the conditions that CaO/zircon molar ratio is 0.25 ～ 0.75 at 800 ℃ for l h.Whereas the decomposition rate decreased when the molar ratio was more than 0.75.Also,thermogravimetry-differential thermal analysis(TG-DTA)and X-ray diffraction(XRD)were used to study the reaction mechanism of zircon decomposition process with CaO-NaOH.The results showed that Na2O,which was generated by the reaction of CaO and Na4SiO4,increased the decomposition rate of zircon owing to its spread to the surface of zircon and played a role in decomposition process.