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Pressure acid leaching of zinc refinery residues containing 0.266 wt.% Ga and 0.363 wt.% Ge was performed. The effects of the experimental parameters on the leaching of gallium and germanium and the filtration performance of the leach slurry were systematically investigated. The results show that the losses of Ge and Ga rapidly decreased because of the aggregation of amorphous silica under the pressure leaching conditions. Furthermore, the Ge leaching and filtration performance of the leach slurry were improved by adding calcium nitrate, which can be attributed to the oxidation of metallic Ge and its sulfides and the formation of calcium sulfate. The optimal leaching conditions are as follows: temperature of 150℃, sulfuric acid concentration of 156 g•L -1 , liquid-to-solid ratio (mL•g -1 ) of 8, total pressure of 0.40 MPa, calcium nitrate addition of 20 g•L -1 , stirring rate of 300 r•min -1 , and leaching time of 3 h. Under the optimal conditions, more than 98% of the Ga and 94% of the Ge were leached. Moreover, the filtration rate of the studied leach slurry was 20 times faster than that of the leach slurry that was obtained under atmospheric pressure acid leaching conditions.

Cooperative performance of mixed-valent Eu(2+) /Eu(3+) in single-compound phosphors offers significant advantages in color rendering and luminescence efficiency, but their synthesis is challenging because of Eu(2+) oxidation. Using the tunable nature of the metal-ion nodes in metal-organic frameworks (MOFs), we present an in situ reduction and crystallization route for preparing MOFs and doping Eu(2+) /Eu(3+) with a controlled ratio. These materials exhibit rich photoluminescence, including intrinsic- and sensitized-emissions of Eu(2+) and Eu(3+) , and long-lived luminescence from charge transfer. Color rendering can be easily achieved by fine-tuning the valence states of Eu. A linear relation between temperature and the intensity ratio of Eu(2+) /Eu(3+) emissions provides outstanding properties for applications as self-calibrated luminescent thermometers with a wide working temperature range. Further incorporation of Tb(3+) into the MOFs results in white light, utilizing all Eu(2+) ,Tb(3+) , and Eu(3+) emissions in a single crystalline lattice.

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