| Title | Mechanism of Dissolving Tin Solders from Waste Printed Circuit Board Assemblies by Cyclic Fluoboric Acid Composite System |
|---|---|
| ID_Doc | 15506 |
| Authors | Ping, Z; Liu, XK; Tao, Q; Ma, Y; Wang, YJ; Li, ZL; Wang, JP; Cao, ZB; Hao, Y; Qian, GR |
| Title | Mechanism of Dissolving Tin Solders from Waste Printed Circuit Board Assemblies by Cyclic Fluoboric Acid Composite System |
| Year | 2019 |
| Published | Environmental Engineering Science, 36, 8 |
| Abstract | There are many electronic components (ECs) in waste printed circuit boards (WPCBs), which can be reused if they can be dismantled without damage. At present, the popular thermal treatment would cause serious ECs damage and toxic gas leakage. In the chemical method, ECs can be dismantled by dissolving the tin solders without toxic gas leakage. But there is difficulty in choosing right chemical reagent to avoid discharge of wastewater, which obstructs its industrial application in recycling waste printed circuit board assemblies (PCBAs). In this article, ECs were dismantled by a mixture solution of hydrogen peroxide (H2O2) and fluoboric acid (HBF4), dissolving the tin solders on waste PCBAs. It was found that the tin solders were mildly dissolved at room temperature, and most of the ECs were preserved completely. Moreover, the mixture solution can be recycled to dissolve the tin solders repeatedly by supplementing H2O2, which avoided second pollution of fluoride wastewater discharge. So it is necessary to investigate the cyclic reaction mechanism of dissolving tin solders on waste PCBAs by a solder wire simulation system. It was observed that oxidation-reduction potential (ORP) of the solution changed regularly, and precipitate of copper corresponded to dissolution of tin with addition of H2O2. This is because copper, tin, and lead formed a microcorrosion cell, which promoted dissolution of solder wire effectively. And the ORP value can be used as an indication point for addition of H2O2 to recycle the mixture solution. The dissolution process was analyzed by mass distributions of tin, lead, and Cu in the solder wires, precipitate and solution, the E-pH diagram of Sn-H2O system, and the X-ray diffraction of precipitate. It was found that excessive amounts of H2O2 caused Sn2+ to form SnO passivation film at the beginning of the reaction. With decrease of pH value and oxidation degree, most of the tin formed SnO2 precipitate and lead formed Pb(BF4)(2) in solution. SnO2 and PbO can be calcined to regenerate into SnO2 and PbO metallic oxide raw materials. The process provides an environmentally friendly method for industrial applications of recovering ECs, realizes reduction and reuse of WPCBs, and can further recycle Sn and Pb. It reflects the concept of circular economy and sustainable development. |
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