Key Takeaways & Executive Findings
- •• • Continuous manufacturing achieved with disc pelletizer parameters: rotation speed 30–60 r·min−1, disc angle 45°, alkali activator modulus 1.5, alkali activator-to-water mass ratio 3:1, solid-to-liquid ratio 4:1; equipment capacity utilization >80%, granulation rate >90%. • • FMG catalyst retained 87.27% catalytic activity after 15 reuse cycles and maintained TOC removal of 69.44%–75.46% over 60 days of continuous-flow operation, demonstrating exceptional long-term stability. • • Production cost of FMG is 1,351.44 CNY·t−1, with unit TOC removal cost of 0.06 CNY·(g TOC)−1, achieving a cost reduction of 78.69%–86.85% compared to commercial catalysts (0.30–0.48 CNY·(g TOC)−1). • • Radical quenching experiments identified ·OH as the primary reactive species; Fe0 acts as an electron donor, driving the redox cycling of Mn species (Mn3+ to Mn2+), which enhances ozone decomposition and catalytic activity.
Abstract
The high cost of catalysts is a critical barrier to the upgrading and cost reduction of catalytic ozonation technology. This study developed a low-cost, long-life Fe–Mn-based ozone catalyst (FMG) derived from solid wastes (red mud and blast-furnace slag), leveraging iron and manganese components to construct dual active centers. A continuous manufacturing process was achieved by integrating alkali-activated cementitious reactions with disc pelletization via a cascade spray-coating and multi-stage curing technique. Under optimal conditions (ozone dosage 3.5 mg·L−1), the catalyst achieved 81.81% total organic carbon (TOC) removal of phenol solution within 60 min, retaining 87.27% of its initial activity after 15 reuse cycles. Long-term continuous-flow tests over 60 days demonstrated stable TOC removal between 69.44% and 75.46%. The production cost of FMG was 1,351.44 CNY·t−1, and the unit TOC removal cost was only 0.06 CNY·(g TOC)−1, representing a 78.69%–86.85% reduction compared to commercial catalysts (0.30–0.48 CNY·(g TOC)−1). This work provides a theoretical and technical foundation for cost-effective catalytic ozonation and high-value conversion of bulk solid wastes.
1. Introduction
Catalytic ozonation is a promising advanced oxidation process for phenolic wastewater treatment, yet its widespread adoption is hindered by the high cost and insufficient longevity of conventional catalysts. Commercial catalysts often suffer from active component leaching, surface fouling, and structural degradation, leading to rapid deactivation and frequent replacement. For instance, Co-Fe/ZSM-5 catalysts showed a decline in phenol removal from 92.90% to 83.10% after only five cycles, while Mn-Cu-Ce/Al2O3 catalysts experienced a TOC removal drop from 70.2% to 66.3% after six cycles. These performance losses escalate operational costs and compromise process stability, underscoring the urgent need for durable, cost-effective catalyst materials.
This study addresses this bottleneck by valorizing bulk solid wastes—red mud and blast-furnace slag—which are rich in iron oxides and aluminosilicate precursors, respectively. By integrating alkali-activated cementitious reactions with disc pelletization, a novel continuous manufacturing process was developed, overcoming the incompatibility between the rapid setting of alkali-activated slurries and the slower granulation dynamics. The resulting Fe–Mn-based catalyst (FMG) not only exhibits robust catalytic activity and stability but also achieves a dramatic cost reduction, offering a sustainable pathway for both wastewater treatment and solid waste management.
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HUANG Yanli, LI Yanhong, JI Zehua, et al. (2026). Continuous Manufacturing Process Design of Solid-Waste-Based Ozone Catalysts and Their Long-Term Performance Study. Chinese Journal of Environmental Engineering. https://doi.org/10.12030/j.cjee.202511011
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Frequently Asked Questions
What are the specific failure mechanisms that could compromise the long-term stability of the FMG catalyst under continuous operation?
The FMG catalyst retained 87.27% activity after 15 cycles and maintained TOC removal between 69.44% and 75.46% over 60 days of continuous flow. Potential failure mechanisms include leaching of active metal ions (Fe, Mn) and fouling by intermediate products. However, the alkali-activated matrix provides structural integrity, and the presence of Fe0 facilitates redox cycling, mitigating deactivation. The study indicates that small-molecule acids formed during reaction protonate Al-O and Si-O structures, generating Brønsted acid sites that aid degradation, but prolonged exposure may lead to structural changes, as evidenced by 27Al NMR analysis.
How does the production cost of FMG compare to commercial catalysts on a normalized basis, and what are the main cost drivers?
FMG production cost is 1,351.44 CNY·t−1, resulting in a unit TOC removal cost of 0.06 CNY·(g TOC)−1, which is 78.69%–86.85% lower than commercial catalysts (0.30–0.48 CNY·(g TOC)−1). The cost advantage stems from using abundant solid wastes (red mud and slag) as raw materials, which are significantly cheaper than synthetic precursors. The continuous manufacturing process also reduces labor and energy costs compared to batch processes.
What are the critical process parameters for scaling up the continuous disc pelletization method, and how do they affect granule quality?
Optimal parameters include disc rotation speed of 30–60 r·min−1, disc angle of 45°, alkali activator modulus of 1.5, alkali activator-to-water mass ratio of 3:1, and solid-to-liquid ratio of 4:1. These conditions ensure proper mixing, nucleation, and growth of granules, achieving a granulation rate above 90% and equipment capacity utilization above 80%. Deviations from these parameters could lead to poor granule formation or incomplete alkali activation, affecting catalyst mechanical strength and catalytic performance.
What is the role of Fe0 and Mn species in the catalytic mechanism, and how does the catalyst maintain its activity over multiple cycles?
Radical quenching experiments confirmed that ·OH is the primary reactive species. Fe0 acts as an electron donor, being oxidized to Fe2+, which in turn reduces Mn3+ to Mn2+, maintaining the redox cycle essential for ozone decomposition and generation of ·OH. This self-regenerating mechanism prevents rapid deactivation. Additionally, the alkali-activated matrix provides a stable porous structure that resists collapse, and the formation of Brønsted acid sites during reaction may enhance organic adsorption and degradation.
How does the FMG catalyst perform under different pH conditions and ozone dosages, and what are the optimal operating conditions?
The study investigated pH range 3–11 and found optimal performance at a specific pH (likely neutral to slightly alkaline, though exact value not provided in the excerpt). Ozone dosage was optimized at 3.5 mg·L−1, achieving 81.81% TOC removal in 60 min. Catalyst dosage and oxygen flow rate were also optimized (exact values not given in excerpt). These conditions balance removal efficiency and cost, as higher ozone dosages increase operational costs without proportional improvement.
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