Production Technology Of Zirconium Oxychloride By Decomposition Of Zircon Sand With Ca（OH）₂-NaOH

Zirconium oxychloride has be potentially recognized as the most important fundamental products of zirconium salt. Besides, it is the main raw material for the production of zirconium chemicals such as zirconium carbonate, zirconium sulfate, zirconium and other chemical products, which is now being widely used in areas such as ceramics, machinery, electronics, energy and so on. China is the world’s largest producer of zirconium oxychloride, and the production capacity and production accounts for over90%of the estimated total world production. Generally, a classical acid-alkali production process was employed in the industrial production of zirconium oxychloride. In order to enhance the recovery ratio of zirconium element, enterprises have proposed a new process that the excessive caustic soda was added in zircon alkali fusion decomposition process. However, the application of this process is extremely limited due principally to the consumption of caustic soda and energy, increasing of waste water. In this paper, the additives-caustic soda complex decomposition of zircon concentrate new technology is carried out, aiming to reducing the amount of caustic soda decomposition and decomposition of zircon sand temperature of Alkali fusion process.In this paper, calcium hydroxide is regarded as an candidate additive to systematically research the Ca(OH)2-NaOH complex decomposition of zircon ore sintering, washed and acid leaching process conditions through the establishing of the thermodynamic Ca(OH)2-NaOH-ZrSiO4ternary system reaction model. Analyzing the products of decomposition and the decomposition reaction of zircon sand by XRD, DSC-TG and other analytical testing methods. Preliminary study the mechanism of action of additives on zircon alkali fusion decomposition. The main results as follows:The Ca(OH)2-NaOH-ZrSiO4ternary reaction system which the thermodynamic calculations of the chemical reaction showed the Ca(OH)2can be involved in the decomposition of zircon sand during600℃～800℃.The decomposition of Ca(OH)2was occurred firstly decomposed to CaO and H2O, the CaO was reacted with ZrSiO4, CaZrO3, ZrO2and Ca2SiO4further during the reaction. The ΔGRθ of chemical reaction was less than0, the ΔGRθ was more negative as the temperature rising during600℃-800℃.The Ca(OH)2-NaOH complex decomposition of zircon concentrate sintering process showed the decomposition rate of zircon sand with calcium hydroxide and the molar ratio of zircon sand trends increasing first and then decreasing. When calcium hydroxide and the molar ratio of zircon sand was0.5:1, zircon decomposition rate reached the maximum98.4%; The decomposition rate of zircon sand was increasing with increasing decomposition temperature. And the suitable decomposition temperature was700℃. Extending the reaction time helps to increase the rate of decomposition of zircon sand. The decomposition rate of zircon sand has improved significantly with the reaction time no longer after the reaction time more than30min. The optimum sintering conditions of calcium hydroxide and caustic soda complex decomposition of zircon sand was calcium hydroxide and the molar ratio of zircon sand was0.5:1, the suitable decomposition temperature was700℃, the reaction time was30min.The Ca(OH)2-NaOH compound decomposition of zircon sand impurities separation process research shows the efficiency of sodium silicon impurity removal increasing with the increasing of liquid-solid ratio, washing temperature and washing time. The removal rate of sodium and silicon can reach48.4%and53.2%respectively, When the liquid-solid ratio was1:6, washing temperature was20℃and washing time was20min. The pH value of leaching liquid and the leaching temperature on leaching rate was more significant. The leaching time of Na+and Ca2+has little effect on the leaching rate. The leaching rate of Na+and Ca2+was79.6%and70.2%respectively, when the pH value of leach solution was4, leaching temperature was70℃and leaching time was30min.The decomposition products were mainly Na2ZrO3and Na2CaSiO4, after high-temperature sintering during Ca(OH)2-NaOH complex decomposition of zircon concentrate. The molar ratio of calcium hydroxide and zircon sand was0.5, the decomposition products were more loose particles. The particle diameter was range from0.1nm to0.3nm, dissolved in water easily. The DTA-TGA of reaction system Ca(OH)2-NaOH-ZrSiO4showed the decomposition reaction of zircon sand was reacted above590℃.The Water vapor was generated and escaped during the reaction. The reaction system resulting system constantly escaping weightlessness which causing weight loss system. The added Ca(OH)2helped to increase the rate of decomposition reaction of Zircon sand.The industrialized assessment tests of Ca(OH)2-NaOH complex decomposition of zircon sand ore concentrates preparation of zirconium oxychloride show the new technology can reduce the amount of NaOH, enhancing the decomposition rate of zircon sand. The Na+, Si4+, Ca2+ions and other impurities can be removed by washing with water and acid leaching step efficiently. The obtained product ZrOCl2meets HG/T2772-2007the requirements. The new technology was connected with the traditional process well. The new technology was workable, stable and controllable impurity elements, suitable for industrial production.