The effects of temperature and agitation speed on the leaching behaviors of tin and bismuth from spent lead free solder in nitric acid leach solution

Abstract

Nitric acid leaching was performed to separate tin and bismuth in spent Pb-free solder. The effects of agitation speed and leaching temperatures on the leaching behaviors of tin and bismuth were investigated to recover tin and bismuth from the spent solder, respectively. The leaching efficiency of bismuth increased rapidly with increasing agitation speeds and temperatures, and the efficiency is found to be 97.8% under the following leaching conditions: nitric acid concentration of 1 k mol m<sup>- 3</sup>, agitation speed of 400 rpm, 1% pulp density, leaching temperature of 90°C, leaching time of 1 hour. In the case of tin, the leaching efficiency increased and then decreased during leaching tests, and a white precipitate was observed in the reactor. XRD results indicate that tin precipitated as stannic acid (SnO<inf>2</inf> H<inf>2</inf>O). Consequently, bismuth and tin could be separated successfully by nitric acid leaching process.