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Recoveryof vanadium from various sources is important to the environmentand industry. This work investigates vanadium leaching from a spentselective catalytic reduction catalyst by sulfuric acid at atmosphericpressure. It includes the effects of stirring speed, solid to liquidratio, temperature, and sulfuric acid concentration on the vanadiumrecovery yield. The results show that the vanadium recovery yieldincreases with increases in temperature, sulfuric acid concentration,and leaching time and decreases with an increase in solid to liquidratio. The leaching data can not be described well by kinetic modelscommonly adopted for similar processes in the literature. The Avramiequation, originally developed for crystallization, is found to bemost suitable. The leaching is controlled by diffusion in the solidwith an activation energy of 5.90 kJ/mol. [ABSTRACT FROM AUTHOR]

A chemiresistive gas sensor based on a three-dimensional Ag-modified reduced graphene oxide (3D Ag-rGO) aerogel is reported. We improve the graphene-based sensor performance by optimization of operating temperature, chemical modification, and new design of the material geometrical structure. The self-assembly and Ag nanoparticle (NP) decoration of the Ag-rGO aerogel are realized by a facile, one-step hydrothermal method. An integrated low-power microheater fabricated on a micromachined SiO 2 membrane is employed to enhance the performance of the sensor with a fast response to NO 2 and a shortened recovery time. The 3D Ag-rGO-based sensor at a temperature of 133 °C exhibits the highest response. At the same time, the response to other gases is suppressed while the response of the Ag-rGO sensor toward ammonia at 133 °C is reduced to half of the value at room temperature, demonstrating a greatly improved selectivity toward NO 2 . Additionally, the sensor exhibits a remarkably fast response to 50 ppb NO 2 and a low limit of detection of 6.9 ppb.