| Zirconium is a kind of important strategic metal,the excellent nuclear performance it has makes it the indispensable material for the developments of aerospace and nuke industry.Zirconium oxychloride octahydrate(ZrOCl2·8H2O),as a sort of fundamental zirconium chemicals,is the important raw material of producing zirconium,zirconium oxide,stable zirconium and other zirconium chemicals such as zirconium carbonate,zirconium sulfate and zirconium acetate,and it is widely applied to the industries of ceramics,electronics,cottonocracy,metallurgy,communication,optical fiber,jewelry,and nuclear power station.In foreign countries,the production of ZrOCl2·8H2O has been cancelled in succession because of the environment protection and China has been the most important country of ZrOCl2·8H2O production and export.The principal raw material for producing ZrOCl2·8H2O is zircon sand(ZrSiO4),and the first step of producing zirconium chemicals from zircon sand is decomposing zircon sand."An acid an alkali fusion" technology is mostly used in China to produce ZrOCl2·8H2O which also known as intermittent alkali fusion method.The disintegrant is NaOH and the decomposition reaction takes place in sintering pots.Through the reaction,zircon sand turns to soluble salt and then Zr/Si separation is achieved by subsequent processing to obtain ZrOCl2·8H2O.During the technology,the decomposition of zircon sand is the most important step.However,there are several disadvantages in the traditional process as follows:(1)The intermittent alkali fusion has a low degree of automation and needs a high labor intensity.What's more,it lead to alkali fog pollution because of a open operation.(2)A mass of waste alkali liquid formed after water washing sintering products is difficult to use effectively,which results a high alkali consumption.(3)How to control the amount of Na2ZrSiO5 is also one of the crutial problems during the alkali fusion process.The traditional technology uses high temperature intermittent alkali fusion mode,which makes it very easy to generate water-insoluble Na2ZrSiO5.The silicon in Na2ZrSiO5 can only be removed by the flocculation in the following steps.The high content of Na2ZrSiO5 will result in a high amount of silicon slags which will entrain a mass of zirconium,thus the recovery rate of zirconium is decreased.This paper will study the process of decomposition of zircon sand aimed at the above problems.The main contents are as follows:1.We studied the process of decomposition of zircon sand with NaOH solution in the hydrothermal system and ascertained the optimal technological condition as follows:the average size of zircon sand of 2.53 ?m,the NaOH solution concentrate of 35%,the liquid/solid ratio of 5:1,the stirring rate of 100 r/min,the temperature of 290?,and the reaction time of 8 h.We also performed the kinetics study of the process and found that the process could be described with the shrinking core model of chemical reaction kinetics which controlled by the product internal diffusion.2.We studied the novel two-step alkali fusion technology which can achieve continuously decompose zircon sand through the control of alkali mass in the reaction.Through the research,we ascertained the optimal technological condition as follows:the fusion temperature of 750?;the NaOH/zircon mass ratio of 0.6+0.7;the fusion time of 0.5 h +0.5 h.The decomposition rate could reach about 98%under these conditions.And we also investigated the mechanism aim at the novel two-step alkali fusion technology with XRD and SEM.3.We studied the parameters and regulation rules of the formation of Na2ZrSiO5 during the alkali fusion process as follows:the fusion temperature of 750?;the NaOH/zircon mole ratio of 6:1;the zircon sand particle size of ?95.2 ?m.And the content of Na2O in washing products was 2.21%,lower than before. |
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