Formation and Inhibition Mechanism of Na8SnSi6O18 during the Soda Roasting Process for Preparing Na2SnO3.

To produce Na2SnO3, 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 (Na8SnSi6O18) was easily formed due to the main gangue of quartz in cassiterite concentrates, which was almost insoluble and decreased the quality of Na2SnO3. The formation and transitions of Na8SnSi6O18 in the SnO2-SiO2-Na2CO3 system roasted under a CO-CO2 atmosphere were determined. The results indicated that the formation of Na8SnSi6O18 could be divided into two steps: SnO2 reacted with Na2CO3 to form Na2SnO3, and then Na2SnO3 was rapidly combined with SiO2 and Na2CO3 to form low melting point Na8SnSi6O18. In addition, Na8SnSi6O18 can be decomposed into Na2SiO3 and Na2SnO3 by using excess Na2CO3.

A value-added multistage utilization process for the gradient-recovery tin, iron and preparing composite phase change materials (C-PCMs) from tailings.

Tin-, iron-bearing tailing is a typically hazardous solid waste in China, which contains plenty of valuable tin, iron elements and is not utilized effectively. In this study, a multistage utilization process was put forward to get the utmost out of the valuable elements (tin and iron) from the tailings, and a gradient-recovery method with three procedures was demonstrated: (1) An activated roasting followed by magnetic separation process was conducted under CO-CO2 atmosphere, tin and iron were efficiently separated during magnetic separation process, and 90.8 wt% iron was enriched in magnetic materials while tin entered into non-magnetic materials; (2) The tin-enriched non-magnetic materials were briquetted with CaCl2 and anthracite and roasted, then tin-rich dusts were collected during the chloridizing roasting process; (3) The roasted briquettes were infiltrated in melting NaNO3 to prepare NaNO3/C-PCMs by a infiltration method. Three kinds of products were obtained from the tailings by the novel process: magnetic concentrates containing 64.53 wt.% TFe, tin-rich dusts containg 52.4 wt.% TSn and NaNO3/C-PCMs for high temperature heat storage. Such a comprehensive and clean utilization method for tin-, iron-bearing tailings produced no secondary hazardous solid wastes, and had great potential for practical application.