ABSTRACT This study develops supervised machine learning models based on least squares support vector machine (LSSVM) and its hybrid variants integrated with particle swarm optimization (PSO), ant colony optimization (ACO) and grey wolf optimization (GWO) to predict CS of red-mud-based concrete. A comprehensive database of 198 experimental datasets including eight input variables and one output variable employed for model development and validation of models. Model performance was evaluated using statistical and error indices. The results indicate that hybrid optimization significantly enhances prediction accuracy, with the PSO-LSSVM model achieving the best performance (R2 = 0.944, RMSE = 0.047, MAE = 0.034), outperforming the standalone LSSVM model (R2 = 0.909, RMSE = 0.058, MAE = 0.045). Sobol sensitivity analysis reveals that fly ash content is the most influential parameter (0.583), followed by water (0.352), superplasticizer (0.277) and red mud (0.259). The findings demonstrate that hybrid LSSVM models provide a reliable and efficient approach for accurate CS prediction and mix optimization in sustainable red-mud-based concrete. The developed models were further integrated into a user-friendly web-based application to facilitate rapid and practical compressive strength prediction for engineers and researchers.

To promote ultra-high performance concrete (UHPC) as an advanced material with greater economic and environmental benefits, this study combined recycled coarse aggregates (RCA) and red mud (RM) to further reduce the proportions of mineral material. Compared to natural coarse aggregates (NCA), the introduction of RCA can lead to the formation of numerous weaker interfacial transition zones (ITZs) between RCA and the new cement matrix due to the presence of old adhered mortar, resulting in insufficient mechanical properties of RCA-UHPC. Herein, the addition of 10 wt% RM did not improve the mechanical properties of NCA-UHPC, but significantly narrowed the strength gap between RCA-UHPC and NCA-UHPC, reducing the difference in compressive and splitting tensile strength at 28 d from 32.6 MPa and 4.7 MPa to 2.9 MPa and 1.1 MPa, respectively. Microscopic results indicate that ultrafine RM particles can fill the ITZs between RCA and new cement mortar, reducing their width to an almost invisible level. In detail, RM particles can serve as fillers and nucleation sites to promote the formation of high-crystallinity CaCO 3 crystals that can fill micropores and improve the microstructure between the old adhered mortar and the RM layer. Additionally, the bonds between the RM layer and the new cement mortar can be slightly enhanced by the hydration reactions induced by RM’s pozzolanic activity. The increase in hydration products from the continuous pozzolanic reaction of RM contributes to improved bonding strength, as reflected in the higher mechanical properties observed at 56 days compared to the reference group without RM. In this study, the combination of 20 wt% RCA and 10 wt% RM in the UHPC matrix under standard curing achieves a trade-off, offering a promising strategy for the combined reuse of construction and solid waste in the construction industry.

Dual regulatory role of Penicillium oxalicum and Lolium perenne in bauxite residue soilization: Labile organic carbon dynamics and community assembly.

Synergistic effect of CaO and red mud on the water resistance of phosphogypsum-based cementitious materials

Valorization of agricultural and industrial wastes in geopolymer foam concrete, a ternary binder approach using corncob ash, red mud, and fly ash

Chemical speciation and release characteristics in different environments of heavy metals in thermally activated red mud.

Sustained-thermal-regulation composite PCMs using porous waste-derived support and epoxy encapsulation for enhanced thermal resilience of asphalt pavements

A study on cemented paste backfill using red mud and coal gasification slag based on extreme vertices mixture design

High-strength self-compacting concrete incorporating red mud: Development and comprehensive performance evaluation

Magnetic waste-derived Fe₃O₄/activated carbon–red mud composite for enhanced adsorption and photocatalytic removal of methyl orange

Degradation mechanism of red mud solidified/stabilized by solid waste-based binder: Role of freeze-thaw, dry-wet, and immersion

In this study, red mud was adopted as a partial replacement for the precursor, and recycled waste glass aggregate (RWGA) was employed as a substitute for natural river sand in slag-fly ash based alkali-activated mortar. Five mix proportions were designed (with red mud replacement ratios of 10% and 20%, and RWGA replacement ratios of 50% and 100%) to explore the effects of these replacements on the workability, mechanical strength, interfacial transition zone (ITZ), and reaction products of the mortar. Tests conducted included flowability measurement, setting time determination, compressive and flexural strength tests, along with microstructural characterisation using Scanning Electron Microscope (SEM) equipped with Energy Dispersive Spectrometer (EDS), X-ray diffraction (XRD), and Fourier Transform Infra-red spectroscopy (FTIR). The results indicated that although increasing the replacement ratios of red mud and RWGA led to a reduction in workability and mechanical properties, the developed alkali-activated mortar still exhibited satisfactory workability (minimum flow diameter of 212.5 mm) and mechanical strength (28-day compressive strength up to 62 MPa). The reduction in strength was primarily attributed to the dilution effect and inert filler role of red mud, and the formation of the loose gel structure.

This study investigates the utilisation of coal gangue (CG) as a primary raw material for road base construction. An optimised cementitious binder was developed with a mass ratio of CG : RM (Red mud) : KZ (Slag) : cement = 40% : 38.5% : 16.5% : 5%, utilising a 0.3 water–binder ratio and a 2.5% dosage of water-reducing agent. This binder achieved a 28-day compressive strength of 17.5 MPa. The optimal aggregate gradation for the road base was determined to be 17.3 (20–30 mm): 34.7 (10–20 mm) : 24.5 (5–10 mm, CG) : 23.5 (0–5 mm), with a 12% binder content and 7.30% water consumption. The resulting base specimens yielded unconfined compressive strengths (UCS) of 2.1 MPa at 7 days and 4.3 MPa at 28 days, satisfying the requirements of the ‘Highway Pavement Base Construction Technical Rules’ (JTG/T F20, Chinese transportation industry standard). While the 28-day water stability coefficient was recorded at 39.96%, the material exhibited excellent frost resistance; after five freeze–thaw cycles, the mass loss rate was only 1.472%, with a residual UCS of 3.2 MPa (despite a strength loss of 75.58% relative to the binder phase). Furthermore, various risk assessment methods were employed to analyse characteristic heavy metals (HMs) within base specimens crushed to different particle sizes. By applying a leaching kinetics model to evaluate HM migration, an environmental safety control system for CG-based road bases was established to ensure sustainable engineering application.

To explore the resource utilization of electrolytic manganese residue (EMR), this study prepared ecological soils using EMR, red mud, and phosphogypsum as main raw materials, and conducted a pot experiment with Cenchrus fungigraminus to investigate the effects of substrate formulations on plant growth and root morphology. Results showed that pure EMR substrate failed to support bud establishment and seedling growth, while optimized formulations significantly improved establishment rate, plant height and biomass accumulation. Establishment rate of ERP1 reached 91.67%, and plant height of ERP2 was 127.50 cm. Root morphology showed high plasticity; ERP7 and ERP8 had greater total root length and surface area, with values of 1258.01, 1200.54 mm, 1285.51 and 1131.53 cm2, respectively; ERP8 exhibited the highest specific root length and specific root area, at 187.40 and 430.71 cm2/g, respectively. Correlation analysis indicated a significantly negative relationship between EMR content and growth indexes, and red mud and phosphogypsum played complementary roles in substrate improvement. Comprehensive evaluation suggested that ERP1, ERP2 and ERP6 were optimal formulations for Cenchrus fungigraminus growth. This study provides a scientific basis for resource utilization of EMR and development of industrial solid waste-based ecological soils.

Industrial red mud establishes redox-active interfaces to steer metabolic pathways toward chain elongation in sludge anaerobic fermentation.

Red mud, a hazardous industrial waste generated during alumina production, faces great challenges in safe stacking and utilization due to its complex chemical composition and poor engineering properties. Long-term stacking of red mud is accompanied by repeated natural drying-wetting cycles, which significantly alter its strength characteristics and further threaten the stability of red mud stockpiles. In this study, Bayer red mud (BRM) and mixed red mud (MRM) from the No.5 stockpile of Guizhou Aluminum Plant were tested under 0, 1, 3, 7, 12 drying-wetting cycles. Their physical, microscopic, and mechanical properties were investigated. Stockpile stability under extreme rainfall was evaluated using Geo-Studio software (SEEP/W and SLOPE/W modules). The results showed that unconfined compressive strength (qu) and cohesion (c) of BRM decrease with cycles, while those of MRM increased significantly. Specially, the (qu) of MRM rise from 115.78kPa to 150.38kPa and the cohesion (c) doubles from 61.67kPa to 121.91kPa. The internal friction angle (φ) of BRM increases slightly, while that of MRM decreases slightly. Under extreme rainfall conditions, safety factors of red mud are 1.205, 1.219, 1.240, 1.263 and 1.288, respectively, all greater than the critical value of 1.0 and increasing with cycles. This study demonstrates that stacking MRM on BRM is feasible and effective for improving the long term stockpile stability, which provide theoretical support and engineering guidance for the safe stacking and resource utilization of red mud.

Co-hydrothermal treatment of industrial solid wastes and organic material: Red mud weakens carbon stabilization.

ABSTRACT The development of phosphorus adsorbents for capturing phosphorus as a fertilizer source is crucial, as it facilitates phosphorus recovery from waste streams through a “waste-treating-waste” approach, simultaneously addressing the shortage of phosphate fertilizers and pollution from phosphorus-rich wastes. This study concentrated on creating a cost-effective, waste-derived phosphorus adsorbent (RM-La) and assessing its potential as a phosphate fertilizer post-phosphorus adsorption. RM-La was synthesized by modifying red mud (RM) with carboxymethyl cellulose (CMC) and lanthanum nitrate (La(NO3)3) for phosphorus removal. The study examined the adsorbent’s characterization, adsorption isotherms, kinetics, and the effects of preparation/adsorption conditions (e.g. modifiers doping amounts, pH, and coexisting ions). Additionally, the impact of phosphorus-adsorbed RM-La on crop seed growth was evaluated. The results indicated that phosphorus adsorption was most effective when the doping amounts of CMC and (La(NO3)3) were 30 mg/g. RM-La achieved optimal adsorption efficiency at an adsorbent dosage of 120 mg/L, with a pH range of 3 to 10 suitable for phosphorus adsorption. RM-La demonstrated a maximum adsorption capacity of 115.69 mg/g and exhibited superior selectivity against interfering ions. Furthermore, phosphorus-loaded RM-La enhanced Brassica napus rapeseeds growth. This study presented an innovative “waste-to-resource” approach, integrating efficient phosphorus removal with circular economy principles by transforming industrial waste into a sustainable adsorbent-fertilizer, thereby balancing environmental protection and resource conservation.

Valorization of red mud as an alternative filler for asphalt mastic: modification treatment, pavement performance and environmental impact.

Metallurgical solid waste-derived skeleton enables shape-stabilized phase change materials with robust properties for high-temperature (≥600 °C) thermal energy storage