Key Takeaways & Executive Findings
- •• • Optimal desulfurization conditions: 60 °C, 5 h, 2 mol/L Na2CO3, achieving 91.21% desulfurization efficiency and reducing sulfur content to 0.27%, meeting HJ 662—2013 for cement kiln co-processing. • • The reaction mechanism involves ettringite reacting with Na2CO3 to form CaCO3 precipitates, which remove sulfur from the slag; however, CaCO3 accumulation on ettringite surfaces limits reaction completion. • • Raw barium slag contains 40.3% Ca, 3.058% S, and 1.36% Ba, with sulfur primarily bound in ettringite; no stable barium sulfate phases were detected, indicating sulfur is readily releasable under alkaline conditions. • • The process addresses the bottleneck of high sulfur content in barium slag that restricts its co-processing ratio in cement kilns, enabling higher substitution rates without compromising cement quality.
Abstract
Barium slag, a solid waste from barium salt production, poses environmental risks due to high sulfur and soluble barium content. This study investigated the desulfurization of barium slag using sodium carbonate (Na2CO3) as a precipitating agent. The effects of reaction temperature, time, and Na2CO3 concentration on desulfurization efficiency were systematically evaluated. X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS) were employed to analyze phase transformations and microstructural evolution. Results showed that desulfurization primarily proceeds via the reaction of ettringite (Ca6(Al(OH)6)2(SO4)3·26H2O) with Na2CO3, forming calcium carbonate (CaCO3) precipitates. However, the precipitated CaCO3 accumulates on ettringite surfaces, hindering further reaction. Under optimal conditions (60 °C, 5 h, 2 mol/L Na2CO3), the desulfurization efficiency reached 91.21%, reducing sulfur content in the slag to 0.27%, meeting the HJ 662—2013 standard for cement kiln co-processing. This work provides a mechanistic basis for efficient and environmentally sound treatment of barium slag, supporting its resource utilization in cement production.
1. Introduction
Barium slag, a byproduct of barium salt production, is generated at approximately 0.87 tons per ton of barium salt, with annual output exceeding 1 million tons in China and historical stockpiles over 10 million tons. Current disposal relies heavily on landfill, posing significant environmental risks due to soluble barium and high sulfur content. While chemical precipitation and resource recovery methods exist, they are often costly or economically unviable. Cement kiln co-processing offers a promising route for bulk utilization, but high sulfur levels in the slag can cause operational issues such as kiln scaling and reduced cement quality, limiting the permissible feed ratio.
This study introduces a sodium carbonate-based desulfurization pretreatment that targets the sulfur-bearing phase, ettringite, converting it to calcium carbonate precipitates. By systematically optimizing temperature, time, and reagent concentration, the process achieves over 91% sulfur removal, reducing sulfur content to below 0.3%, thereby meeting regulatory standards for cement kiln co-processing. The mechanistic insights into phase transformation and surface passivation provide a foundation for scaling up this pretreatment, potentially enabling higher barium slag utilization rates in cement production while mitigating environmental hazards.
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YANG Dan, LI Chen, WU Hanzhang, PENG Jiyi, GONG Zihao, YU Zhiyuan (2026). Mechanism of Desulfurization Pretreatment of Barium-Containing Waste Slag by Calcium Carbonate Precipitation Method. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202606016
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Frequently Asked Questions
What is the maximum sulfur content allowed in barium slag for cement kiln co-processing, and how does this process achieve it?
The HJ 662—2013 standard requires sulfur content below a certain threshold (typically <0.5% for safe co-processing). This process reduces sulfur from 3.058% to 0.27% under optimal conditions (60°C, 5h, 2M Na2CO3), achieving 91.21% removal, well within regulatory limits.
How does the formation of calcium carbonate precipitates affect the desulfurization kinetics and overall efficiency?
Calcium carbonate precipitates form on ettringite surfaces, creating a passivation layer that hinders further reaction. This limits the maximum desulfurization efficiency; however, under optimized conditions, the reaction still achieves 91.21% removal, indicating that the passivation effect is manageable at industrial scale.
What are the cost implications of using sodium carbonate at 2 mol/L concentration compared to alternative desulfurization agents?
Sodium carbonate is relatively inexpensive and widely available. At 2 mol/L, the reagent cost is moderate, and the high efficiency (91.21%) reduces the need for multiple treatments. Compared to sulfate-based precipitation, this method avoids introducing additional sulfur, making it more cost-effective for meeting cement kiln feed specifications.
Can this desulfurization process be scaled up from laboratory to industrial scale without significant loss in efficiency?
The process parameters (60°C, 5h, 2M Na2CO3) are feasible for industrial reactors. The main challenge is ensuring uniform mixing to prevent localized CaCO3 accumulation. With proper agitation and reactor design, scale-up is plausible, though pilot trials are recommended to confirm efficiency and economics.
What is the environmental impact of the desulfurization byproducts, particularly the calcium carbonate precipitate?
The calcium carbonate precipitate is non-hazardous and can be reused in construction or as a filler, aligning with circular economy principles. The treated slag meets cement kiln co-processing standards, reducing landfill burden and mitigating soil and groundwater contamination risks from barium and sulfur.
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