Study On The Morphology And Separation Law Of Silicon And Zirconium In Zirconium Oxychloride Octahydrate Production By NaOH Alkali Melt Method

Zirconium oxychloride octahydrate?ZrOCl₂·BH₂O?,an important basic chemical products of zirconium salt,is the main raw material for zirconium chemicals.These chemicals have extensive applications in ceramics,textile,electronics,communications,jewelry,metallurgy,fiber optic cable,industrial catalyst,nuclear power plant and nuclear industry.The general "an acid-an alkali fusion" technology concludes the procedure of alkali fusion,water leaching,transition,the decomposition with hydrochloric acid,water filtration,concentration and crystallization,acid leaching iron removal,centrifugal drying.With the analysis of the mechanism of zirconium oxychloride octahydrate production and the separation pattern of zirconium and silica,The new alkali fusion technology concluding "alkali fusion,water leaching,transiton,acid leaching and flocculation,crystallization" was put forward.The new technology can not only increases the removal of sodium and silicon,while achieving once crystalline zirconium oxychloride,but also reduce the waste production,greatly improve the alkali fusion process,production efficiency,automation level,working environment and shorten the process,save energy and reduce consumption.The main research contents in the current paper are as follows:1.Water leaching separates sodium zirconate?Na₂ZrO₃?,sodium metasilicate?Na₂SiO₃?,and sodium orthosilicate?Na₄SiO₄?formed during the alkaline melting,which is critical for silicon removal in the whole line.Washing technique conditions were determined:washing ratio,4:1;washing time,30 min;countercurrent washing times,3 and washing temperature,50?.Operation optimization of washing process can decrease SiO2%from 9.71%to 6.77%and Na₂O%from 9.22%to 7.05%.The water leaching and transition process in manufacturing zirconium oxychloride octahydrate was examined.Results from X-ray diffraction?XRD?and Fourier-transform infrared?FT-IR?spectra showed that most of the soluble sodium silicate was dissolved and the residue hydrolyzed into H₂SiO₃ during the water leaching process.In addition,Na+ from sodium zirconate?NaZrO₃?in the interlayer was removed during the first and second water leaching and the in-host layer was distinguished in the third water leaching.This process,resulted in the hydrolysis of NaZrO₃ into ZrO?OH?₂.2.Transition is performed not only to remove Na+ from the material,but also influence the acid solution and flocculation process.Transition technique conditions were determined:pH was adjusted to 3.0 on the washing ratio 2:1 at 65?,stirring for 40min,and the washing ratio was 9:1 in the end.Na+ was eliminated in the transition material.Results from the scanning electron microscopy?SEM?,FT-IR spectra,nuclear magnetic resonance?NMR?and XRD of the transition process showed the main reaction and properties of the products at different pH values.Na₂ZrSiO₅ reacted with HCl at pH=7,producing ZrO?OH?₂·SiO₂ and NaCl.ZrO?OH?₂·SiO₂ partially reacted with HCl,forming ZrOCl₂ and H₂SiO₃ with a decrease in pH.3.The remaining SiO₂ is removed by acid leaching and flocculation,which is critical for high-purity ZrOCl₂·8H₂O production.The general method is time consuming and involves crystallization and filtration twice.The new technology should shorten the precipitation time and decrease the SiO₂ content of ZrOCl₂ solution.The optimum conditions of acid leaching were found to be as follows:transiton material,300 g;HCl?6 mol/L?,600 mL;leaching time,4 h;and leaching temperature,100?.The nonionic polyoxyethylene lauryl ether?AE09?was adopted as the flocculant.The optimum flocculation conditions were found to be as follows:temperature,40?;flocculant amount,10 ml?concentration 1%?;time,1 h.The zirconium oxychloride solution after purification contained 36 ppm SiO₂ and 160 g/1 ZrOCl₂.The polymerization and flocculation mechanisms of silicic acid were analyzed.Results showed the main transformation and properties of the products in the acid leaching and flocculation processes.