Key Takeaways & Executive Findings
- •• • At pH 0.1, Bi-PM achieved 53.6% chloride removal in dark and 69.3% under light, demonstrating a 15.7 percentage-point enhancement from photoactivation, critical for acidic industrial effluents. • • At pH 0.5, dark removal was 31.0% rising to 38.1% under light; this pH was selected as optimal for balancing efficiency and shape retention, preventing Bi layer detachment. • • Over five cycles at pH 0.5, average removal efficiency was 25% (dark) versus 41.2% (light), with the fifth cycle maintaining ~40% under light, indicating superior operational stability and reduced Bi loss. • • Radical trapping experiments ranked active species as h+ > Cl· > O2·− > ·OH, with holes being the dominant contributor, guiding mechanistic understanding for process optimization.
Abstract
High-concentration chloride ions (Cl−) in industrial wastewater cause severe corrosion and environmental hazards. Conventional removal methods suffer from low efficiency, high cost, and difficulty in product recovery. This study fabricated porous metallic bismuth-based blocks (Bi-PM) via 3D printing, combining chemical precipitation with additive manufacturing. Systematic evaluation of Cl− removal under varying pH and light irradiation revealed that at pH 0.1 and 0.5, dark-condition efficiencies were 53.6% and 31.0%, respectively, increasing to 69.3% and 38.1% under light. Radical trapping identified photogenerated holes as the primary active species, oxidizing metallic Bi to release Bi3+ and enhance precipitation. At pH 0.5, Bi-PM exhibited balanced efficiency and structural stability; over five cycles, average removal efficiency was 25% in darkness versus 41.2% under light, with superior stability under illumination. XRD and SEM confirmed abundant BiOCl formation on the surface under light, mitigating Bi loss. This approach ensures high chloride removal while minimizing material degradation, offering a novel pathway for industrial wastewater treatment.
1. Introduction
Industrial wastewater laden with high chloride ion concentrations poses a persistent challenge, accelerating corrosion of steel infrastructure and limiting water reuse. Conventional treatment methods—membrane separation, capacitive deionization, and chemical precipitation—each present critical bottlenecks: membrane fouling and high operational costs, electrode stability issues, or inefficient product recovery. Chemical precipitation using bismuth (Bi) offers rapid kinetics and environmental compatibility, yet conventional powder forms suffer from material loss and difficult separation.
This study addresses these limitations by integrating 3D printing to fabricate porous metallic bismuth-based monoliths (Bi-PM). The approach leverages the design freedom of additive manufacturing to create a structured block that retains Bi while maximizing surface area. By systematically evaluating pH effects and light irradiation, the work demonstrates enhanced chloride removal efficiency and material stability, providing a scalable solution for deep chloride removal in industrial effluents.
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LV Hongying, ZHOU Xiaoyu, LIU Qijia, LI Xin, GE Dongdong, HUANG Shouqiang (2026). Fabrication of Porous Metallic Bismuth-Based Blocks via 3D Printing and Their Performance in Chloride Removal. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2025111302
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Frequently Asked Questions
What is the maximum chloride removal efficiency achieved by Bi-PM under optimal conditions, and how does light irradiation influence performance?
At pH 0.1, Bi-PM achieved 69.3% removal under light versus 53.6% in dark, a 15.7 percentage-point increase. At pH 0.5, removal was 38.1% under light versus 31.0% in dark. Light generates holes that oxidize Bi to Bi3+, enhancing precipitation.
How does the Bi-PM block maintain structural integrity over multiple cycles, and what is the trade-off between efficiency and stability at different pH levels?
At pH 0.5, Bi-PM retained shape over five cycles, with average removal of 41.2% under light versus 25% in dark. Lower pH (0.1) gave higher initial efficiency but caused Bi layer detachment, compromising stability. Thus pH 0.5 balances efficiency and durability.
What are the dominant reactive species in the light-enhanced chloride removal mechanism, and how was this determined?
Radical trapping experiments identified holes (h+) as the primary active species, followed by Cl·, O2·−, and ·OH. Holes oxidize metallic Bi to release Bi3+, which precipitates Cl− as BiOCl.
How does the 3D-printed block design mitigate bismuth loss compared to conventional powder methods?
The porous block structure retains Bi on the substrate, and under light, BiOCl forms on the surface, reducing Bi dissolution. Over five cycles, efficiency remained ~40% under light, indicating minimal material loss, whereas powder systems often suffer from recovery difficulties.
What are the potential scalability and cost implications of using 3D printing for Bi-PM fabrication in industrial wastewater treatment?
3D printing enables precise control over porosity and shape, potentially reducing material waste. However, scalability depends on printing speed and resin costs. The study demonstrates technical feasibility, but economic viability requires further assessment against conventional precipitation methods.
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