The recycling market of waste electric and electronic equipment (WEEEs) is growing up in the world due to short life cycle. Printed circuit boards(PCBs) are found in most electronic items. Among them, solder integrates circuits and other electronic devices on PCBs.
Typically Sn-Pb solder has been widely used because of low melting point and outstanding solderability and reliability. The European Union Directive on the restriction of the use of hazardous substances in electrical and electronic equipment(RoHS) prohibited the use of lead in most electronics equipments produced in the EU after 2006. and it increased the use of lead-free solder.
Lead-free solders, generally, contain tin, copper, silver, bismuth, and other metals. Among them, Sn-Bi-Cu solder are widely used in TFT-LCD manufacturing due to relatively low melting point. More than 99% of Sn, Bi, Cu has been imported in Korea, so the present study is aimed at investigating recycling technologies for the recovery of each metals Sn, Bi, Cu from the e-waste solder.
Solder paste, used in the study, generally contains resin and metals. The resin was removed by swelling to leach metal components. The swelling process was conducted under the following conditions 0.5M HCl concentration with 5000mg/L Sn4+, 300rpm, 50℃, and 1% pulp density.
Therefore in this study, waste Sn-Bi-Cu solder paste can be separated into resin and metals. Tin and copper could be leached selectively by subsequent hydrochloric acid and ammonia leaching, respectively. reagent MEK(methyl ethyl ketone), pulp density 50g/L, temperature 25℃, agitation speed 200rpm (with magnetic bar) and swelling time 60minute. After swelling, selective leaching was carried out so as not to require further separation processes.
Ammonia was used to form the copper complex ions for the selective Cu leaching. The effects of leaching factors such as pulp density, agitation speed, temperature and ammonia concentration were investigated to establish the optimum leaching conditions. The leaching efficiency of copper increased with decreasing pulp density or increasing agitation speed. The temperature increase to 50℃ enhances the leaching efficiency of Cu and further increase reduces the efficiency. The effects of ammonia concentration was negligible.
Hydrochloric acid with Sn4+ was used in order to selectively leaching of the Sn. The effects of Sn4+ concentration, HCl concentration, pulp density, agitation speed, temperature were examined. The leaching efficiency of Sn increased with increasing the concentration of Sn4+ or HCl and decreasing the pulp density. The leaching efficiency increased to 99% under the leaching conditions