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This study aimed to evaluate the potential of replacing fly ash (FA) with bauxite tailing (BT) slurry for geopolymer synthesis and investigate the long-term leaching behaviour of BT slurry/FA geopolymers (BFGs) for heavy metal immobilisation. The mechanical properties and heavy metal immobilisation efficiency of BFGs were tested, and numerical simulations were conducted to assess their environmental impact as a backfill material. The results showed that the incorporation of 5 Wt.% BT increased the early compressive strength of the geopolymer without any additional treatment. A small quantity of Cu2+ improved the mechanical strength, while excess heavy metals harmed the geopolymer. Heavy metal immobilisation efficiency decreased with increased heavy metal addition and exceeded 99.9% for Pb2+ and Cu2+ when simulating acid rain leachate. The modified Elovich equation described the leaching kinetics of Cu2+ well, and the leaching rate decreased with time. Numerical analysis indicated that Cu2+ leaching from landfill leachate occurred in three phases, with an initial increase followed by a gradual decrease, stabilisation, and diffusion into the surrounding soil layer. This study provides insight into the material's long-term stability and environmental performance, offering a scientific basis for relevant engineering applications. Highlights: Direct utilisation of unprocessed tailing slurry to synthesise geopolymer. The leaching pattern of Pb2+ and Cu2+ under acidic conditions was explored. The modified Elovich equation effectively describes the leaching kinetics of Cu2+. The environmental impact of bauxite tailings slurry-based geopolymers was evaluated. [ABSTRACT FROM AUTHOR]

A substantial amount of bauxite tailings (BTs) at abandoned mine sites have been stored in waste reservoirs for long periods, leading to significant land occupation and environmental degradation. Although many studies of the resource utilization of BTs were conducted to address this challenge, there is still a lack of efforts to systematically review the state of the art in BTs. In the present paper, a systematic literature review was carried out to summarize and analyze the properties, treatment, and resource utilization of BTs. Physical characteristics and the mineral and chemical composition of BTs are introduced. The efficacy of physical, chemical, and microbial treatment methods for BTs in terms of dehydration are outlined, and their respective benefits and limitations are discussed. Moreover, the extraction process of valuable elements (e.g., Si, Al, Fe, Li, Na, Nd, etc.) from BTs is examined, and the diverse applications of BTs in adsorption materials, ceramic materials, cementitious materials, lightweight aggregates, foamed mixture lightweight soil, among others, are studied. Finally, an efficient and smart treatment strategy for BTs was proposed. The findings of the present review provide a scientific basis and reference for future research focusing on the treatment and resource utilization of BTs. [ABSTRACT FROM AUTHOR]

This research uses Bayer red mud, metakaolin and cement as raw materials. In order to analyze the influence of Bayer red mud and metakaolin admixture on the mechanical properties of cement mortar, cement mortar is prepared by Bayer process red mud and metakaolin in different mixing ratios. The composite cement mortar were characterized the phase composition and micro morphology by means of X-ray diffraction (XRD), Fourier Transform Infrared Spectrometer (FTIR) and scanning electron microscopy (SEM). The results show that the 28 d compressive strength of cement mortar reaches 47.38 MPa when the content of red mud is 10% and metakaolin is 10%. As the active SiO2 and Al2O3 in the red mud and metakaolin are mixed into the excess Ca(OH)2, the secondary hydration reaction will generate C-S-H and gismondine (CaAl2Si2O8·4H2O) to fill the internal voids, increasing the structural compactness, which improves the compactness of the structure and is beneficial to the mechanics of the composite cement mortar. [ABSTRACT FROM AUTHOR]

Based on the existing research results, this research team developed roadbed stabilized soil materials using nano-SiO2 synergistically modified red mud in order to study whether the strength of the stabilized soil materials meets the strength requirements of the roadbed materials, and at the same time, analyze its strength characteristics to make the feasibility of it being used as a roadbed material clear. Through different combination schemes, the effects of different nano-SiO2 and cement contents on the strength of the stabilized materials were explored. The test results show the following: In the synergistic modification of nano-SiO2 and cement, nano-SiO2 can significantly improve the early unconfined compressive strength of red mud-based stabilized soil. In the synergistic modification of nano-SiO2, gypsum, and cement, the 7 d unconfined compressive strength of red mud-based stabilized soil is greater than 2 MPa, which meets the strength requirements of road base materials and shows the superiority of synergism. The nominal stress–strain curves are divided into five stages: compressed and compacted stage, elastic deformation stage, plastic deformation stage, damage deformation stage, and residual deformation stage. The macroscopic compressive damage pattern of the specimens shows that the modified red mud-based stabilized soil mostly exhibits brittle damage. Tests have shown that the strength of modified terracotta-based stabilized soil meets the requirements of roadbed strength. [ABSTRACT FROM AUTHOR]

In order to effectively utilize red mud and reduce its occupation of land resources, as well as its impact on the environment, experiments were conducted to develop stabilized soil materials using nano-SiO2 synergistically modified red mud and to investigate the curing mechanism of stabilized soil. The unconfined compressive strength, microscopic morphology, and curing mechanism of the red mud-based stabilized soil materials with different amounts of modified materials were investigated. The test results show that after 7 days of curing, the unconfined compressive strength of red mud-based stabilized soil meets the compressive strength requirement of road base material when nano-SiO2, gypsum, and cement are synergistically modified. In such cases, the soil structure has the lowest fracture rate and the best structural compactness when the amount of nano-SiO2 is 1%. It is found that the needle-like and columnar calcium alumina in the modified red mud-based stabilized soil increases, and the binding energy of hydration product ions in the modified material is improved. The chemical curing mechanism of modified red mud-based stabilized soil includes hydration reaction, pozzolanic reaction, promotion effect of nano-SiO2, and enhancement effect of gypsum. On this base, a model of the early start hydration process of red mud-based stabilized soil promoted by nano-SiO2 is established. [ABSTRACT FROM AUTHOR]

An analytical conversion method of self-balanced test of foundation pile bearing capacity is proposed. First, the load transfer matrices for the elastic-plastic state of the upper and lower segment piles in a multi-layer foundation were derived under the assumption of the load transfer function of the pile side associated with the ideal elastic-plastic model. Then the internal forces and vertical displacements at each micro-element of the upper and lower segment of the pile were calculated by programming, and the results of the self-balanced test pile were converted into the load-displacement curve of the conventional static load test by substituting the accurate conversion formula, and the ultimate bearing capacity was obtained. Finally, by combining with an engineering test pile example, two groups of loading results of anchor pile method and self-balanced method were used to verify the theoretical analysis of conversion method in this work. It can be concluded that the load-displacement curves obtained by this conversion method are more consistent with the results of the conventional static pressure tests compared with the simplified conversion method. Moreover, the proposed model can be widely used in the self-balanced test engineering of pile bearing strength with sufficient accuracy. [ABSTRACT FROM AUTHOR]