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.