Gallium (Ga), indium (In), and germanium (Ge) play an important role in the modern high-tech material field. Due to their low content and scattered distribution in the crust, and the increasing demand for these metals in recent years, their supply risks have sharply increased. Therefore, the recycling of these metals is of great significance. In this work, a systematic review was performed using the Web of Science, Scopus, MDPI, Elsevier, and Springer Link databases. The combined terms used for the search were Ga/In/Ge, extraction, separation, and recycling. After a careful evaluation of the titles, abstracts, and full texts, a total of 106 articles were included. This paper briefly describes the resource features of Ga, In, and Ge. After that, the chemical principles, technical parameters, and metal recovery in various extraction and separation methods from monometallic and polymetallic resources are systematically reviewed. Leaching followed by solvent extraction or ion exchange is the main process for Ga, In, and Ge recovery. Although many attempts have been made to separate multiple metals from leaching solutions, highly selective solvents and resins are still the research priority. This review can provide theoretical and technical guidance for the separation of Ga, In, and Ge from various resources.

Due to the advancement of industrialization and the development of the metal smelting industry, cadmium (Cd), as a highly toxic heavy metal element, is discharged into the natural environment in the form of dust, slag, and waste solutions during the Cu-Pb-Zn smelting process, causing great harm to the soil, water environment, and human health. Meanwhile, Cd is a key component of Ni-Cd batteries and CdTe semiconductor materials. The removal and recovery of Cd from the Cu-Pb-Zn smelting process faces a dual concern with respect to resource recycling and environmental protection. This paper briefly introduces the Cd-containing secondary resources produced in the Cu-Pb-Zn smelting process, systematically reviews the recovery methods of Cd from dust, slag and waste solutions, and compares the technical principles, process parameters, separation efficiency, advantages and disadvantages, and application requirements. In addition, a new route to treat Cd-containing solutions via the foam extraction method was proposed, which has the advantages of a short reaction time, large handling capacity, high removal efficiency, and simple operation equipment, showing superior application prospects, especially for industrial bulk waste solutions with ultralow concentrations.

Clean and efficient extraction and separation of precious metals from discarded Pb-Sn alloy is critical to the sustainable utilization of solid waste resources. Dense oxide layer and compact alloy texture in the waste Pb-Sn alloy pose challenges to the effective leaching process. Ultrasonic waves are demonstrated to improve separation efficiency via the favorable physical and chemical effects in solution system. In this study, ultrasound-assisted leaching technology is attempted to rapidly and selectively extract Pb from the waste Pb-Sn alloy, and gives emphasis on ultrasonic electrochemical behaviors. The Eh-pH diagrams of Sn-H₂O and Pb-H₂O systems were firstly analyzed to lay the selective dissolution foundation. It's indicated that oxidizing HNO₃ lixiviant is suitable to realize the selective separation of Pb. Both Sn and Pb can be dissolved to ionic Sn²⁺ and Pb²⁺ in the HNO₃ solution. However, Sn²⁺ rapidly oxidizes to Sn⁴⁺ and Sn⁴⁺ further hydrolyzes to insoluble SnO₂, which will agglomerate on unreacted materials to limit internal metal leaching in conventional leaching process. Due to the vibratory stripping of oxide layer by physical effect of ultrasound, the conventional acid leaching time for Pb extraction can be halved with the ultrasound assistance. About 99.12 % Pb and only 0.1 % Sn are dissolved in ultrasound-assisted leaching under the following optimal parameters: 0.5 mol/L HNO₃, leaching temperature of 80 °C, time of 30 min, liquid-to-solid ratio of 20 mL/g, and ultrasound intensity of 0.52 W/cm². Leaching kinetics of Pb, phase transition, microstructure evolution, Pb-Sn galvanic corrosion and dissolution polarization curve were studied to determine the ultrasonic enhanced dissolution mechanism. Notably, Pb and Sn form a microcorrosion galvanic cell in which Sn acts as a cathode and is protected while the Pb undergoes intensifying corrosion as the anode giving rise to the higher Pb dissolution efficiency. Eventually, it's suggested that Pb can be rapidly extracted and separated from the waste Pb-Sn alloy during the ultrasound-assisted HNO₃ leaching process via the ultrasound physical and chemical effects, especially the sonochemistry aspect of intensified spot corrosion and galvanic corrosion. The proposed ultrasonic electrochemical corrosion in this work were applicable to the extraction of valuable metals from various waste alloys through leaching method.