The Kinetics Study of Dissolving SnPb Solder by Hydrometallurgy

Abstract

Abstract

A large amount of electrical and electronic equipment is being discarded every year, which produces a large number of waste printed circuit boards (WPCBs). The WPCB is a heterogeneous mixture of various metals and nonmetallic materials, especially heavy metals such as lead. It would result in severe environmental pollution if they were not disposed of properly. However, recovery of valuable materials from WPCBs is quite challenging; one of the obstacles is that electronic components (ECs) are often fixed on the board using solders (usually comprised lead and tin), which rendered certain difficulty for the dismantling. In this article, a hydrometallurgical process was carried out to recycle ECs on WPCBs through a mixture of fluoroboric acid and hydrogen peroxide breaking lead−tin solders at room temperature. Results indicated that SnO passivation film would be formed on the solder surface at the initial stage, as a result of the hydrolysis reaction of dissolving stannous ion. Moreover, this passivation film can be rapidly destructed by field sonication-accelerated dissolution. A simulation was conducted by using the solder wire with identical composition. It was found that the passivation film was eroded into the porous structure film due to ultrasonic cavitation and microfluids, enabled the mixture to penetrate through passivation film more readily to reach the fresh solder wire interior, and subsequently accelerated the dissolving. By comparing dissolving kinetics between in the absence and the presence of the ultrasonic field, it was found that the kinetic data fitted well to the surface chemical control of the shrinking core model. The activation energies for the dissolution of lead and tin in both cases were determined.