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This study investigated the gaseous products evolution behaviors and the recovery performance of cathode materials from spent LiFePO₄ batteries by vacuum pyrolysis. The thermogravimetric-differential scanning calorimetry analysis coupled with electron ionization mass spectrometry (TG-DSC-EI-MS) results indicated that inorganic gases (H₂O, CO, CO₂), alkane gases (CH₄, C₂H₄, C₂H₆, CH₃OH, C₃H₆, C₃H₄O₃, C₄H₈O₃), and fluoride-containing gases (HF, OPF₃, C₂H₂F₂) were the resulting gaseous products in the vacuum pyrolysis of cathode materials. At the same time, the gaseous product species and relative yield were significantly affected by pyrolysis temperature. Combined with the GC-MS analysis of pyrolysis tar obtained from vacuum pyrolysis simulation experiments, it could be inferred that pyrolysis tar was formed as a result of the cleavage and recombination of chemical bonds in solvents. The simulation experiments also showed that the increase of vacuum pyrolysis temperature and decrease of residual gas pressure enhanced the recovery efficiency of cathode materials. Further, the carbon and fluorine content of the cathode materials were found to decrease slowly during vacuum pyrolysis, while the aluminum content increased. When the vacuum pyrolysis temperature was above 600 °C, Al foils ablated and even melted to strips. The phase composition of cathode materials was still LiFePO₄ after vacuum pyrolysis. The leaching performance tests of cathode materials demonstrated that the increase of vacuum pyrolysis temperature and decrease of residual gas pressure can lead to the decrease of leaching efficiency for Fe. This technology offers an efficient way to recycle organic compounds and valuable materials from spent LiFePO₄ batteries, and it has been demonstrated to be of good economic benefit and energy savings.

The leaching behavior of hemimorphite in neutral solution (NH4 +-Cl--H2O) was investigated at high temperature (T > 100?C) under a range of experimental conditions. Thermodynamic calculations indicate that the tendency of dehydration of silica gel is significantly enhanced with the increasing temperature. It was shown that the temperature, ammonium chloride concentration, or L/S ratio increased resulted in greater leaching efficiency. The following optimized leaching conditions were obtained: stirrer speed 400r/min, NH4Cl concentration 5.5M, L/S ratio 9mL/g at 160?C for 3h. Under these optimized conditions, the average leaching yield of zinc was 97.82%. The silicon was converted to quartz and remained in the residue. This process can be used to dispose willemite and hemimorphite as it solves the problem of silica gel dehydration.

Zinc-electrowinning in Zn(II)-NH4Cl-H2O systems has many advantages, such as a high current efficiency and insensitivity to F−, Cl− and metallic impurities. Additives in electrowinning are important because they influence the growth and structure of the resulting deposits and current efficiency. The effect of gelatin and polyoxyethylene ether (PEO) on the nucleation, growth mechanism, and morphology of samples are investigated through cathodic polarization, chronoamperometry, X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses during the electrowinning of Zn from an ammonium solution. The fraction-temperature diagram shows that the dominant species is ZnNH3Cl3− in the 5 M NH4Cl electrolyte when the temperature is between 298 K and 373 K. The average current efficiency reaches 95.48% in samples containing both gelatin and PEO. The surface morphology of samples with both gelatin and PEO is basically free of dendrites and shows a dense, layer-by-layer, stacked structure. The preferred growth orientation of zinc is enhanced by the presence of PEO and gelatin. The reduction kinetics of zinc are inhibited by the addition of gelatin. In the presence of gelatin and PEO, Zn nucleation and growth can be explained by the 3D growth characteristics of zinc nuclei under diffusion-limited nucleation. The arrangement and size of zinc grains are characterized through front and cross-section SEM.

In this study, the effects of oxidizing roasting process on the liberation of cathode materials from Al foil under different conditions were investigated systematically. The mineralogical characteristics of the cathode materials before and after thermal treatment were extensively characterized using scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) as well as Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The results indicated that the increase in roasting temperature, oxygen concentration, and air flow rate enhanced the liberation of cathode materials. The cathode materials were gradually oxidized to Li3Fe2(PO4)3 and Fe2O3. Further, the carbon and fluorine content in the cathode materials decreased slowly during the thermal treatment, while the Al content increased. When the roasting temperature exceeded the melting point of Al, the Al foils were ablated and the cathode materials adhered to the Al foils again, resulting in difficulty in separation. The cathode materials leaching performance test results demonstrated that the oxidation of cathode materials had a negative effect on the leaching of Fe in sulfuric acid leaching system.

In this research, some experimental steps were investigated to recover zinc contained in crude zinc oxide (C.Z.O.). In the first stage, the C.Z.O. was treated in NH3–NH4Cl–H2O solution to dissolve the metals. The optimized leaching conditions in batch experiments were obtained: agitation speed 250 rpm, concentration of ammonia and ammonium chloride 2.5 mol/L and 5 mol/L, respectively, time 30min, temperature 40 °C, and L/S = 6 mL/g. The extraction percentage of zinc was over 81% under the optimized leaching conditions. The kinetic study indicates that zinc extraction from the C.Z.O particles was very rapid. In the second stage, the solution from the leaching process was purified by adding zinc dust to the solution. The Cu, Cd, Pb, Sb, and As could be reduced to levels of 0.03, 0.09, 0.87, 0.22, and 0.12 mg/L after the purification process. Finally, the electrowinning process was used to recover dissolved Zn from the final solution. The zinc content in the electrowon zinc was more than 99.99%.

In this paper, thermal reaction behaviors and gas evolution characteristics of cathode electrodes separated from spent LiFePO4 batteries were systematically characterized using thermogravimetric-differential scanning calorimetry analysis coupled with mass spectrometry equipped with electron ionization system (TG-DSC-EI-MS). TG-DSC-EI-MS analysis indicated tail gases were mainly released in a low-temperature range of 60−250 °C, which attributed to the hydrolysis and decomposition reactions of lithium salt electrolyte. Additionally, H2O, HF and CO2 were detected at the range of 380−600 °C, which responded to thermal decomposition of the binder. H2O and CO2 were the main gaseous products at around 520 °C, which might be released from the oxidation combustion reactions of the binder. At the same time, phase transformation of the cathode active material during thermal treatment was further investigated by SEM-EDS, FT-IR, XRD and Mossbauer spectrum analysis techniques. The results indicated LiFePO4 was oxidized to Li3Fe2(PO4)3 and Fe2O3 during the heating process.