Mechanism of passivation of Pb(Ca)–Sn alloys in sulfuric acid: role of tin

Intensifying separation of Pb and Sn from waste Pb-Sn alloy by ultrasound-assisted acid leaching: Selective dissolution and sonochemistry mechanism

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.

Lyotropic Liquid Crystalline Mesophase of Sulfuric Acid-Nonionic Surfactant Stabilizes Lead(II) Oxide in Sulfuric Acid Concentrations Relevant to Lead Acid Batteries

Concentrated sulfuric acid (SA) and nonionic surfactant (C₁₂H₂₅(OCH₂CH₂)₁₀OH, C₁₂E₁₀) form lyotropic liquid crystalline (LLC) mesophases in a broad range of SA concentrations; the SA/C₁₂E₁₀ mole ratio may vary from 2 to 11 in the LLC mesophases in the presence of a small amount of water. The mesophase is hexagonal at low SA concentration and cubic at higher concentrations. Three different compositions were prepared (one hexagonal and two cubic) with the SA/C₁₂E₁₀ mole ratio of 2.5, 6, and 9, denoted as 2.5LC, 6LC, and 9LC, respectively. They all display electrochemical SA activity in Pt and Pb systems. Most interestingly, they show the electrochemical formation of stable PbO species in a deeply acidic medium as evidenced by the X-ray diffraction, cyclic voltammetry, and linear sweep voltammetry experiments. The preferable properties of PbO over PbSO₄ for lead acid batteries (LABs) make it uniquely positioned as a superior gel electrolyte for the LABs that would mitigate sulfation.

Study on the properties of Pb–Co3O4–PbO2 composite inert anodes prepared by vacuum hot pressing technique

In this research, the Pb–Co₃O₄–PbO₂ composite inert anodes were prepared by vacuum hot pressing technique, which showed good electrochemical performance.

Electrosynthesis and performance of WC and Co3O4 co-doped α-PbO2 electrodes

α-PbO₂ uniformly co-doped with Co₃O₄ and WC particles was prepared as a functional electrode for oxygen evolution.