Formation and Inhibition Mechanism of Na(8)SnSi(6)O(18) during the Soda Roasting Process for Preparing Na(2)SnO(3)

To produce Na(2)SnO(3,) which is widely used in the ceramics and electroplating industries, a novel process for the preparation of sodium stannate from cassiterite concentrates was developed successfully by the authors’ group. It was found that sodium stannosilicate (Na(8)SnSi(6)O(18)) was easily formed due to the main gangue of quartz in cassiterite concentrates, which was almost insoluble and decreased the quality of Na(2)SnO(3). The formation and transitions of Na(8)SnSi(6)O(18) in the SnO(2)–SiO(2)–Na(2)CO(3) system roasted under a CO–CO(2) atmosphere were determined. The results indicated that the formation of Na(8)SnSi(6)O(18) could be divided into two steps: SnO(2) reacted with Na(2)CO(3) to form Na(2)SnO(3), and then Na(2)SnO(3) was rapidly combined with SiO(2) and Na(2)CO(3) to form low melting point Na(8)SnSi(6)O(18). In addition, Na(8)SnSi(6)O(18) can be decomposed into Na(2)SiO(3) and Na(2)SnO(3) by using excess Na(2)CO(3).