Key Takeaways & Executive Findings
- •• • Optimal single-stage water leaching achieved 87% Cl removal at liquid-to-solid ratio 5 mL/g, 70 °C, 60 min, and 160 r/min, demonstrating a simple, cost-effective dechlorination route. • • Three-stage countercurrent washing at room temperature (liquid-to-solid ratio 6 mL/g, 45 min) boosted Cl removal to 90.15%, reducing water consumption and energy input for industrial application. • • Water washing increased BET surface area from 2.71 to 10.11 m²/g and total pore volume from 0.0087 to 0.0412 cm³/g, enhancing the sludge's reactivity for downstream metal recovery. • • The process reduced metal leaching toxicity, mitigating environmental risks and enabling safer disposal or resource recovery from the treated sludge.
Abstract
Zinc-containing steel dust sludge, a by-product of steelmaking, contains high levels of chlorine (Cl) along with valuable metals such as Fe, Zn, K, and Na. When recycled into the steel production process, Cl accumulates, causing sintering instability and severe corrosion of blast furnace linings. This study investigated water leaching for Cl removal from zinc-containing steel dust sludge. Under optimal conditions (liquid-to-solid ratio 5 mL/g, temperature 70 °C, time 60 min, rotation speed 160 r/min), the Cl leaching rate reached 87%. Furthermore, a three-stage countercurrent water washing process at a liquid-to-solid ratio of 6 mL/g and room temperature for 45 min achieved a Cl leaching rate exceeding 90%. The water washing also reduced the leaching toxicity of metals in the sludge to a certain extent. Characterization via XRD, SEM, FT-IR, and XPS revealed that water washing primarily dissolved soluble chlorides (NaCl, KCl, etc.), increasing the specific surface area from 2.71 to 10.11 m²/g and average pore size from 12.83 to 16.29 nm. These findings provide theoretical and technical support for efficient Cl removal from zinc-containing steel dust sludge, facilitating its safe resource utilization.
1. Introduction
Zinc-containing steel dust sludge, generated at 8–12% of crude steel output, represents a massive industrial waste stream exceeding 100 million tons annually in China. While rich in Fe, Zn, K, and Na, its high chlorine content (up to 28.51% in this study) poses a critical bottleneck: during recycling, Cl accumulates and causes sintering instability and severe corrosion of blast furnace linings, rendering conventional recycling routes technically and economically unviable. Existing dechlorination methods, such as high-temperature roasting or alkaline washing, are energy-intensive or cause zinc loss, and none have been systematically applied to this specific sludge type.
This study addresses the gap by employing water leaching, a green and low-cost approach, to selectively dissolve soluble chlorides (NaCl, KCl, etc.) without significant loss of valuable metals. By systematically optimizing liquid-to-solid ratio, temperature, time, and agitation, and further implementing a multi-stage countercurrent washing design, the authors achieved high Cl removal efficiency (up to 90.15%) under ambient conditions, while also improving the sludge's physical properties for subsequent resource recovery. This work provides a practical, scalable solution to a pressing industrial challenge.
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LIAO Shushu, ZHAO Hongyuan, WANG Jing, YOU Yanyan, PENG Cheng, LIU Changzheng, XUE Kai, SHU Jiancheng, CHEN Mengjun (2026). Water Leaching Dechlorination of Zinc-Containing Steel Dust Sludge. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202608023
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Frequently Asked Questions
What is the maximum chlorine removal efficiency achievable with single-stage water leaching, and what are the optimal conditions?
Single-stage water leaching achieved 87% Cl removal under optimal conditions: liquid-to-solid ratio 5 mL/g, temperature 70 °C, time 60 min, and rotation speed 160 r/min. This provides a baseline for process design.
How does three-stage countercurrent washing compare to single-stage in terms of efficiency and water usage?
Three-stage countercurrent washing achieved 90.15% Cl removal at a liquid-to-solid ratio of 6 mL/g, room temperature, and 45 min per stage. This design reduces fresh water consumption by reusing wash water, making it more sustainable and cost-effective for industrial scale.
What is the effect of water washing on the physical properties of the sludge, and why does it matter?
Water washing increased BET surface area from 2.71 to 10.11 m²/g and total pore volume from 0.0087 to 0.0412 cm³/g. This enhances the reactivity of the sludge for subsequent metal recovery processes, such as leaching or roasting, by improving mass transfer and accessibility.
Does water washing affect the leaching toxicity of heavy metals in the sludge?
Yes, water washing reduced the leaching toxicity of metals to a certain extent, as stated in the abstract. This is crucial for meeting environmental regulations and enabling safe disposal or further treatment.
What are the limitations of this method regarding zinc loss and applicability to other sludge types?
The study indicates that water washing primarily removes soluble chlorides, with minimal zinc loss (not quantified in the provided text). However, the method's effectiveness may vary with sludge composition, particularly the speciation of chlorine and the presence of insoluble chlorides. Further research is needed to assess its applicability to other industrial dusts.
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