Lead Trace Removal from Waste Electronic Scraps by Organic Acids

The removal of Pb traces from Pb-free solder is an important process in the recycling of solder. Pb must be removed before the more valuable metals are extracted, otherwise the recycling becomes less efficient and the end product impure. Pb removal by three organic acids is investigated here. Acetic acid was shown to dissolve Pb selectively from waste solder better than citric acid or oxalic acid could. Leaching for 72 h in 0.01 M acetic acid removed approximately 137 mg/L Pb from the solder at 30°C, 220 rpm; in addition, no Sn was leached. Higher concentrations of acetic acid (0.05 and 0.1 M) led to increased Sn leaching and decreased Pb leaching, similar to the results observed in citric acid. A total of 0.01 M citric acid leached 7 mg/L Pb and 1831 mg/L Sn; 0.01 M oxalic acid leached 8 mg/L Pb and 1318 mg/L Sn. A comparison using pure Pb and Sn powders showed that the leaching of both metals increased with increasing concentrations of acetic acid and citric acid, contrary to the results observed using solder.