Investigation On The Mechanism Of ZrSiO₄Silicate Decomposed By Alkali Fusion

With the increasing demand of zirconium in modern industry, it is significant to make use of the zirconium resoursful in a high efficiency and low cost way. Alkali fusion is one of the effective methods to treat the zircon. In order to extract the valuable elements such as Zr, Hf in the nature zirconium deposits, further research about the mechanism of silicate decomposed by alkali fusion in different condition is necessary. In this work, the transformation behavior and mechanism of ZrSiO4by alkali fusion using NaOH, Na2CO3and KOH were studied. This work will provide theoretical basis for the treatment of nature zircon.The main research results of this work were reported as follows:(1) The reaction of zircon and alkali was detected by TG-DTA analysis. The results showed that a continuous weight loss appear during the reactions are due to the release of water in NaOH and KOH system and the release of CO2in Na2CO3system.(2) XRD analysis of the products indicated that the structure of reaction products associate with the base strength of alkali. The structure of products with two (Q2) bridging oxygen in the NaOH fusion reaction was broken into non-bridging oxygen with the development of reaction, to generate Na4SiO4as the terminal products, zirconia released from silicate lattice react with alkali to generate zirconate. The final products are K2Si2O5with three bridging oxygen (Q3) and K4ZrO4in the KOH fusion.The final products is Na2ZrSiO5in Na2CO3fusion reaction, which have the isolated structure (Qo). (3) FTIR analysis showed that in NaOH and KOH fusion reaction, some Si-Onb in isolated [SiO4] tetrahedron of ZrSiO4broke down, the Si which lost its connecting O form into bridge oxygen through a pattern of hydroxylation dehydration and condensation reaction. The Zr-O-Si connection cannot be fully broke down after alkali roasting experiment under the same ratio of Na2CO3due to the relatively weak alkaline.(4) XPS analysis of the products show that in NaOH and KOH system, the Onb in [SiO4] tetrahedron changed into Ob after alkali fusion reaction. And all the system, the bonging energy of Zr, O, Si atoms changed after alikali fusion.