In this work, coal fly ash (CFA) − a byproduct of coal combustion, has been successfully converted into a value-added product zeolite. This study focuses on the production of the Na-A zeolite phase via the fusion method. The effects of fusion reaction temperature, hydrothermal reaction temperature, reaction time, and the concentration of alkaline were investigated. The synthesized products were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) and studied for their purity and yield. A fusion temperature of 550 °C, fusion duration of 1.5 h, and a subsequent hydrothermal temperature of 100 °C for a reaction of 12 h were found to be the optimal conditions. Based on the synthesis conditions found, an up-scale production process was designed and simulated with aid from the Aspen Plus program. It was found that zeolite production via the fusion method obtained high profitability. For a 5000 kg/h coal fly ash feed, a payback period of 7.1 years is feasible over a 20-year operation period. A cost-benefit analysis was studied to compare the improved environmental performance and economics of zeolite production from CFA with current CFA disposal practices.
Carbon black waste, an oil refinery waste, contains a high concentration of vanadium(V) leftover from the processing of crude oil. For the sake of environmental sustainability, it is therefore of interest to recover the vanadium as useful products instead of disposing of it. In this work, V was recovered in the form of vanadium-based metal-organic frameworks (V-MOFs) via a novel pathway by using the leaching solution of carbon black waste instead of commercially available vanadium chemicals. Two different types of V-MOFs with high levels of crystallinity and phase purity were fabricated in very high yields (>98%) based on a coordination modulation method. The V-MOFs exhibited well-defined and controlled shapes such as nanofibers (length: > 10 μm) and nanorods (length: ∼270 nm). Furthermore, the V-MOFs showed high catalytic activities for the oxidation of benzyl alcohol to benzaldehyde, indicating the strong potential of the waste-derived V-MOFs in catalysis applications. Overall, our work offers a green synthesis pathway for the preparation of V-MOFs by using heavy metals of industrial waste as the metal source.
Gasification waste,
also known as carbon soot, is solid industrial
waste from the bottom residual of an oil refinery and contains a substantial
amount of toxic vanadium. In this work, we report an environmentally
responsible pathway to harvest toxic vanadium from gasification waste,
and the extracted vanadium can be utilized to synthesize high-purity
V2O5 nanosheets for the fabrication of flexible,
bendable, efficient supercapacitors. The carbonaceous waste was first
rinsed with alkaline solution to leach out toxic vanadium. The vanadium-rich
leachate was next utilized to synthesize high-quality V2O5 crystals with comparable purity (>98%) and crystallinity
to commercial products. Two-dimensional V2O5 nanosheets were further crystallized by hydrothermal treatment for
the fabrication of high-performance electrochemical electrodes. The
V2O5 electrodes derived from gasification waste
demonstrated similar specific capacitance (172 F g–1) to those from commercial V2O5 (173 F g–1). The waste-derived V2O5 nanosheets
were further mixed with leached carbon nanoparticles for the fabrication
of a symmetric, bendable, and flexible supercapacitor. The waste-derived
V2O5 supercapacitor was able to be bent up to
160° and retained its specific capacitance. An environmental
impact assessment was finally conducted to evaluate the environmental
impacts of producing V2O5 crystals from gasification
waste (in terms of the damage to human health, ecosystem diversity,
and resource availability). The waste-derived approach was compared
with traditional mining processes and showed a large improvement in
all three endpoint damage categories.
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