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<p>Uranium tailings (UTs), constituting radioactive solid waste generated during uranium ore processing, facilitate radon-222 (Rn-222) emanation into the ambient environment via their intrinsic porous networks, particularly under dynamic soil–water–air coupling conditions, thereby posing substantial radiological hazards. Radon exhalation mitigation may be achieved through cementation treatments that attenuate pore connectivity in uranium tailings. Lithium slag (LS), a solid waste in lithium battery industries possessing latent pozzolanic properties, was selected to explore a high-value utilization strategy as supplementary cementitious material (SCM). In this study, chemical modification via mixing, melting, and water-quenching with CaO reagent was employed to enhance the reactivity of LS. Characterization results demonstrate that CaO incorporation, functioning as a network modifier, promotes the depolymerization of fully polymerized Q<sup>4</sup> silicate units through the cleavage of Si–O–Si bonds. This process facilitates the formation of Q<sup>3</sup> and Q<sup>2</sup> species, which are characterized by an increased population of non-bridging oxygens (NBOs). This structural transformation yields reduced binding energy in silicate glass, thereby conferring enhanced pozzolanic activity to the CaO-activated LS (CLS). Cemented UTs samples (CLSU) were prepared from CLS with CaO additions of 0,10, and 20%, ordinary Portland cement (OPC), UTs, and distilled water at a mass ratio of 1:1:4 (CLS:OPC:UTs) and a water to cement ratio of 0.5. Radon exhalation rates (RER) of CLSU samples were quantified throughout a 28-day curing period. Elevated CaO content correlated with significant RER attenuation, and the sample of CLSU20 exhibited an RER of 0.235 Bq·m<sup>−2</sup>·s<sup>−1</sup> at 28 days, corresponding to a 34% reduction relative to untreated UTs. Enhanced release of amorphous Si and Al from CLSU samples with higher CaO additions promoted pozzolanic reaction with Ca(OH)<sub>2</sub> (CH), generating supplementary calcium aluminosilicate hydrate (C–A–S–H) gel that densified the microstructure via pore channel filling, as revealed by SEM and MIP analyses. These findings demonstrate an effective strategy for utilizing CLS as a high-performance SCMs to mitigate radon exhalation from UTs, contributing to substantial energy saving for the uranium and lithium industries.</p>

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Radon-222 exhalation mitigation from uranium tailings using CaO-activated lithium slag-based cementitious materials

  • 期刊论文

  • 发表日期：

    2026年3月23日

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  • Yan He,
  • Ruixiang Xu,
  • Qianlin Li,
  • Xia Liu,
  • Xilong Xue,
  • Qian Kang

摘要

Uranium tailings (UTs), constituting radioactive solid waste generated during uranium ore processing, facilitate radon-222 (Rn-222) emanation into the ambient environment via their intrinsic porous networks, particularly under dynamic soil–water–air coupling conditions, thereby posing substantial radiological hazards. Radon exhalation mitigation may be achieved through cementation treatments that attenuate pore connectivity in uranium tailings. Lithium slag (LS), a solid waste in lithium battery industries possessing latent pozzolanic properties, was selected to explore a high-value utilization strategy as supplementary cementitious material (SCM). In this study, chemical modification via mixing, melting, and water-quenching with CaO reagent was employed to enhance the reactivity of LS. Characterization results demonstrate that CaO incorporation, functioning as a network modifier, promotes the depolymerization of fully polymerized Q4 silicate units through the cleavage of Si–O–Si bonds. This process facilitates the formation of Q3 and Q2 species, which are characterized by an increased population of non-bridging oxygens (NBOs). This structural transformation yields reduced binding energy in silicate glass, thereby conferring enhanced pozzolanic activity to the CaO-activated LS (CLS). Cemented UTs samples (CLSU) were prepared from CLS with CaO additions of 0,10, and 20%, ordinary Portland cement (OPC), UTs, and distilled water at a mass ratio of 1:1:4 (CLS:OPC:UTs) and a water to cement ratio of 0.5. Radon exhalation rates (RER) of CLSU samples were quantified throughout a 28-day curing period. Elevated CaO content correlated with significant RER attenuation, and the sample of CLSU20 exhibited an RER of 0.235 Bq·m−2·s−1 at 28 days, corresponding to a 34% reduction relative to untreated UTs. Enhanced release of amorphous Si and Al from CLSU samples with higher CaO additions promoted pozzolanic reaction with Ca(OH)2 (CH), generating supplementary calcium aluminosilicate hydrate (C–A–S–H) gel that densified the microstructure via pore channel filling, as revealed by SEM and MIP analyses. These findings demonstrate an effective strategy for utilizing CLS as a high-performance SCMs to mitigate radon exhalation from UTs, contributing to substantial energy saving for the uranium and lithium industries.