Applied Basic Research On The Decomposition Of The Zircon Sand By Sodium Hydroxide Sub-molten Salt

As an important strategic metal element,zirconium is widely used in ceramics,electronics,aerospace,nuclear industry,optical fiber and other fields according to the excellent properties of its compounds.Zirconium oxychloride(ZrOCl2·8H2O)is an important intermediate chemical product used to prepare zirconium salt chemicals such as zirconium,zirconium oxide,zirconium carbonate,zirconium sulfate and zirconium acetate.According to the statistics of the Titanium,Zirconium and Hafnium Branch of the.China Nonferrous Metals Industry Association,more than 90%of the world’s zirconia.production capacity is concentrated in China,and China has become the largest producer and exporter of zirconium oxychloride.The preparation process of zirconium oxychloride used now mainly includes a chlorination method and an alkali fusion sintering method.At present,the main process applied domestically is alkali fusion sintering method,that is,an "one acid-base method".The raw material used in this method is zircon sand(ZrSi04),and sodium hydroxide is used as a decomposing agent.After the alkali fusion reaction in the sintering pot,the zircon sand is decomposed into soluble salts.The product is subjected to water washing,crystallization.and the like to realize zirconium/silicon separation to obtain a zirconium oxychloride product.In the process of alkali melting zircon sand,the disadvantages include:high reaction temperature,open operation process,alkali mist pollution in the environment,and safety to the operator;intermittent alkali fusion,low degree of automation,high labor intensity;Solid alkali,after the water washing process,will form a large amount of waste solution,which is difficult to recycle,has poor utilization rate,and has potential pollution threats.In this paper,in view of these problems in the alkali fusion sintering method,combined with the successful application of the sub-molten salt cleaning production process in the extraction of elements such as chromium and titanium,the sub-molten salt medium is applied to the decomposition of zircon sand to weaken or eliminate the shortcoming of alkali fusion sintering method.The basic research on the macroscopic kinetics and microscopic mechanism of zircon sand in sodium hydroxide sub-molten medium is mainly carried out.The main research contents are as follows:1.The reaction kinetics of decomposition of ilmenite by sodium hydroxide sub-molten salt was studied.Increasing the concentration of sodium hydroxide,the reaction temperature and prolonging the reaction time would significantly increase the conversion rate.The effect of increasing alkali-base ratio and stirring rate on conversion rate was not obvious.It is found that the decomposition process of zircon sand in sodium hydroxide sub-molten salt can be described by the "unreacted nuclear shrinkage" model,controlled by the surface chemical reaction,and the apparent activation energy is 77.98 KJ/mol.2.The phase change law of the reaction product of zircon sand in sodium hydroxide sub-molten salt was explored.It was found that the reaction product was extremely sensitive to the sodium hydroxide concentration,and it was necessary to coordinate the temperature,alkali-mine ratio and reaction time.Relationship can effectively inhibit the formation of sodium zirconate.Two optimal combinations of process conditions were obtained:alkali concentration 80%,temperature 245 ℃,alkali-mine ratio 4:1,reaction time 10 h,stirring rate 400 r/min,alkali concentration 80%,temperature.275 ℃,alkali ore The ratio is 4.2:1,the reaction time is 4 h,and the stirring rate is 400 r/min.Through the analysis of infrared spectrum,Raman spectroscopy and XPS of the product,the structural changes during the decomposition of zircon sand by NaOH sub-molten salt were obtained.The structure of silicate from zircon sand to reaction product passed the change of Q0→Q2→Q0.It is speculated that the reaction process of zircon sand decomposition under the sub-molten salt system is obtained.3.The principle flow chart of the process route was designed.The circulation of lye under different product conditions was studied,and the alkali consumption under the two route conditions was calculated.The effects of washing times,washing temperature,liquid-solid ratio and washing time on the removal rate of sodium and silicon during the washing process were studied.The optimum washing conditions were obtained:liquid-solid ratio 2:1,washing temperature 50 ℃,washing time 30 min,washed 3 times.It is verified that the transformation and acidification process in the alkali fusion sintering process is also applicable to the sub-molten salt decomposition process.