Sodium stannate preparation from stannic oxide by a novel soda roasting–leaching process

•Sodium stannate preparation from stannic oxide by soda roasting–leaching was proposed.•Effect of roasting and leaching parameters on the Sn leaching efficiency was tested.•Na2SnO3 was easily formed when SnO2 and Na2CO3 were roasted in a CO/CO2 atmosphere.•Na2SnO3 · 3H2O with 95.8% purity was obtained from the cassiterite concentrate.•Final Na2SnO3 · 3H2O meets the demand of industrial first-grade product.

Sodium stannate is widely used in the electroplating and tin alloy industries. The traditional sodium stannate production processes suffer a variety of disadvantages including long flowsheet, high production cost and strict requirements for the equipment. In this study, a novel process for preparing sodium stannate is developed by roasting tin dioxide and sodium carbonate in CO/CO2 mixed gas followed by leaching the intermediate products in a diluted sodium hydroxide solution. The effects of roasting and leaching parameters on the leaching efficiency of Sn were investigated. The Sn leaching efficiency reaches 85.6% under the optimal experimental conditions: roasting temperature of 875 °C, CO content of 15%, roasting time of 15 min, Na2CO3/SnO2 mole ratio of 1.5, liquid-to-solid ratio of 4 cm3/g, leaching temperature of 40 °C, leaching time of 60 min, and stirring speed of 300 rpm. Sodium stannate trihydrate (Na2SnO3 · 3H2O) having a purity of 95.8% is successfully produced from cassiterite concentrates with a SnO2 content of 76.4% through the new process, which is superior to the traditional approach for producing the industrial first-grade stannate.