Selective nitric acid leaching for recycling of lead-bearing solder dross

Lead pollution is one of the most serious threats of our natural environment. Lead emissions come from various human activities such as the use of leaded gasoline for motor vehicles, lead smelter and accumulator recycling as well as the manufacturing and utilisation of lead-bearing solder. In the present study, a selective nitric acid leaching method to separate lead and tin from a lead-bearing solder dross, wherein about half of the tin content was already oxidised as stannic oxide (SnO2), was proposed. The mechanisms that enable the lead and tin separation in the nitric acid solutions as well as the behaviour of iron, which was found as a minor impurity in the dross, were discussed. The optimum separation conditions were determined by studying the effect of acid concentration, slurry density and temperature. The results showed that the optimum separation of lead from tin can be achieved using 4.0 mol/L nitric acid at a slurry density of 100 g/L and temperature of 55 degrees C, wherein 99.78% of lead were dissolved, while 99.96% and 93.25% of tin and iron were separated in the residue after 24 h. The residue obtained under this optimum condition contained only 370 ppm of lead allowing the residue to be regarded as nonhazardous waste. The present study demonstrated that the proposed method presents the potential to maximise the economic value of lead in the dross as well as to recycle tin from lead-bearing solder dross. (C) 2020 Elsevier Ltd. All rights reserved.