Ammonia chloride assisted air-chlorination recovery of tin from pyrometallurgical slag of spent lead-acid battery

Abstract

Tin-containing slag from pyrometallurgical recovery process of spent lead-acid battery is a valuable secondary Sn resource. However, the low content of Sn (~4 wt%) in this slag with complex impurities (Fe, Al, Pb, Zn, and Cu, etc.) makes it challenging for efficient tin separation. In this study, a low-temperature chlorinating process is proposed for tin recovery from the tin-containing slag by using ammonium chloride as the chlorinating reagent. Under the optimized chlorinating conditions, tin volatilization ratios of above 96% under both air and vacuum atmospheres could be achieved. However, the discrepancy between the temperatures of tin chlorinating and impurity metal chlorinating is more dramatic under the air atmosphere than that under vacuum, which facilitates the separation of impurities. Meanwhile, the decomposition rate of NH4Cl in air is much lower than that under vacuum atmosphere, resulting in less consumption of NH4Cl. The obtained chlorinated condensation product in air is subjected to a subsequent water leaching-alkali smelting-leaching-crystallization process to effectively separate Fe impurity and obtain the final sodium stannate product with a total tin recovery ratio of 94%. This study provides a promising strategy for the recovery of tin, and significant environmental benefit could be generated simultaneously with solid waste recycling.