To protect natural resources and avoid environmental pollution, an effective method is proposed to recover tin (Sn) from waste printed circuit boards (WPCBs). In order to realize the efficient recovery of Sn, it is necessary to study the effects of experimental parameters on Sn leaching and understand the leaching kinetics of leaching processes. The statistical and mathematical technique (response surface methodology (RSM)) was used to study the effects of interactions of experimental parameters on the leaching rate and optimize experimental parameters. Moreover, a comprehensive understanding of the leaching kinetics of Sn in hydrochloric acid solution was obtained. The results show that the maximum Sn leaching rate was 97.6% which was obtained under the following optimal condition: 74.1 °C, 4.94 mol/L HCl, 495.5 rpm, and a solid–liquid ratio of 0.08 g/mL. The leaching mechanism of Sn was controlled by mixed control reaction with an activation energy of 20.3 kJ/mol. A macroscopic kinetic equation was also established, which summarizes the relationships between the experimental parameters and the leaching rates and can predict leaching results. The Sn in pregnant leach solution was recovered as stannic oxide (SnO₂) by precipitation-high temperature calcining technique. In this paper, a complete flowsheet for Sn recovery from WPCBs was developed.

A novel configuration of a four-nozzle flapper servovalve driven by a giant magnetostrictive actuator is described, and giant magnetostrictive actuator displacement model and four-nozzle flapper valve pressure–flow equation are built, which can quantificationally describe the physical process from input current to control pressure in the giant magnetostrictive material–based four-nozzle flapper servovalve. Then, by a computational fluid dynamics method, control pressure under different zero-clearance configurations is determined by the numerical method and compared with the control pressure determined by a theoretical calculation method, which verifies the availability of the above-mentioned numerical method and the accuracy of the implemented numerical model. Subsequently, to elucidate the interaction rule between the control pressure and the orifice flow with the main structural parameters of a four-nozzle flapper servovalve, the parameters and the configurations of a single nozzle, four nozzles and a fixed orifice are investigated, which provides a theoretical basis for the design and optimisation of a giant magnetostrictive material–based four-nozzle flapper servovalve. A test system of a giant magnetostrictive material–based four-nozzle flapper servovalve is established, and the test results of static control pressure and hysteretic control pressure are obtained, which enables the determination of the maximum output control pressure.