Hydration process and fluoride solidification mechanism of multi-source solid waste-based phosphogypsum cemented paste backfill under CaO modification

IF 10.8 1区工程技术 Q1 CONSTRUCTION & BUILDING TECHNOLOGY

Cement & concrete composites Pub Date : 2024-10-18 DOI:10.1016/j.cemconcomp.2024.105804

Daolin Wang , Qing Na , Yikai Liu , Yan Feng , Qinli Zhang , Qiusong Chen

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引用次数: 0

Abstract

The large-scale, environmentally friendly utilization of phosphogypsum (PG) remains a global challenge. PG cemented paste backfill (PCPB) is a promising method to manage PG, but using ordinary Portland cement as the binder has drawbacks such as high cost, low mechanical strength, and high fluoride leaching risk. This paper presents a multi-source solid waste-based PCPB (MPCPB) material that enhances mechanical properties and reduces fluoride leaching risks. In MPCPB, industrial waste residues like steel slag (SS) and ground granulated blast furnace slag (GBFS) are used as precursors (SS: GBFS = 1:2). Additionally, 4–8 wt% CaO (relative to the dry weight of PG) is used as a neutralizing modifier and alkaline activator. The results indicate that an optimal amount of CaO can neutralize the residual acidity of PG, provide sufficient Ca(OH)₂ for MPCPB hydration, and react with PG to produce significant amounts of AFt. Furthermore, CaO promotes the geopolymerization reaction between SS and GBFS, generating more calcium silicate hydrate (C-S-H) and calcium aluminate silicate hydrate (C-A-S-H) gels. Fluoride stabilization in MPCPB results from synergistic effects involving hydration reactions, complexation, ionic mobility, rearrangement, and physical adsorption. Notably, CaO enhances the conversion of free fluoride ions into stable compounds like fluorapatite, fluorite (CaF₂), [AlF₆]^3-, and [FeF₆]^3- complexes. This approach offers a cost-effective, environmentally friendly, and efficient solution to the PG stockpiling challenge.

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CaO 改性条件下多源固废基磷石膏胶结浆料回填的水化过程和氟化物固化机理

大规模、环保地利用磷石膏（PG）仍然是一项全球性挑战。磷石膏水泥浆回填（PCPB）是一种很有前景的磷石膏管理方法，但使用普通硅酸盐水泥作为粘结剂存在成本高、机械强度低、氟化物浸出风险高等缺点。本文介绍了一种基于多源固体废物的 PCPB（MPCPB）材料，它能提高机械性能并降低氟化物沥滤风险。在 MPCPB 中，钢渣（SS）和磨细高炉矿渣（GBFS）等工业废渣被用作前体（SS: GBFS=1:2）。此外，4-8 wt%的氧化钙（相对于 PG 干重）被用作中和改性剂和碱性活化剂。结果表明，最佳量的 CaO 可以中和 PG 的残余酸性，为 MPCPB 水合提供足够的 Ca(OH)2，并与 PG 反应生成大量的 AFt。此外，CaO 还能促进 SS 和 GBFS 之间的土工聚合反应，生成更多的水合硅酸钙（C-S-H）和水合硅酸铝钙（C-A-S-H）凝胶。水合反应、络合、离子迁移率、重排和物理吸附等协同效应使 MPCPB 中的氟化物趋于稳定。值得注意的是，CaO 能增强游离氟离子向氟磷灰石、萤石 (CaF2)、[AlF6]3- 和 [FeF6]3- 复合物等稳定化合物的转化。这种方法为解决 PG 储存难题提供了一种具有成本效益、环保且高效的解决方案。

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来源期刊

Cement & concrete composites 工程技术-材料科学：复合

CiteScore

18.70

自引率

11.40%

发文量

459

审稿时长

65 days

期刊介绍： Cement & concrete composites focuses on advancements in cement-concrete composite technology and the production, use, and performance of cement-based construction materials. It covers a wide range of materials, including fiber-reinforced composites, polymer composites, ferrocement, and those incorporating special aggregates or waste materials. Major themes include microstructure, material properties, testing, durability, mechanics, modeling, design, fabrication, and practical applications. The journal welcomes papers on structural behavior, field studies, repair and maintenance, serviceability, and sustainability. It aims to enhance understanding, provide a platform for unconventional materials, promote low-cost energy-saving materials, and bridge the gap between materials science, engineering, and construction. Special issues on emerging topics are also published to encourage collaboration between materials scientists, engineers, designers, and fabricators.