Waste-to-soil in 10 days: Synergistic driving of rapid red mud soilization by Maotai-flavor liquor brewing wastes and sawdust

Abstract Red mud (RM), a highly alkaline solid waste, remains a global environmental disposal bottleneck, yet its mineralogy offers untapped soil formation potential—if alkalinity and structure can be overcome rapidly. We report a 10-day protocol using acidic distiller's grains (DG), Maotai-flavor liquor wastewater (MFW), and sawdust (SD) to rapidly transform bauxite residue into a plant growth substrate, drastically shortening a process that conventionally takes weeks to months. Single and combined treatments were assessed using pH, electrical conductivity (EC), organic matter (OM), excitation-emission matrix (EEM) fluorescence, X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS), particle-size distribution (PSD), X-ray fluorescence (XRF), and inductively coupled plasma optical emission spectrometry (ICP-OES) of water extracts. At the 10-day endpoint, DG and MFW-containing treatments lowered RM pH from 11.23 to 8.87-9.33, while EC in every amended group decreased below 600 µS·cm-1 by day 15. OM increased from 10.50 to 24.82-49.29 g·kg-1, and six amended groups exceeded 30 g·kg-1. EEM results showed that MFW supplied readily soluble fluorescent organics, whereas DG promoted humification (humification index, HIX, up to 0.987); the adjusted EEM coordinate grid placed the two DG-containing combined-treatment peaks at excitation/emission (Ex/Em) coordinates of 382/470 and 384/472 nm. SEM-EDS, particle-size, and normalized XRF patterns were consistent with mineral-organic association and a shift from fine particles (<20 µm) toward aggregate-sized assemblages (>50 µm). The best-performing SD-containing treatment achieved 65-70% ryegrass survival, whereas DG-containing formulations showed greater EC-related stress. Under HJ 557-2010 water-extraction conditions, maximum total Cr, Mn, Cu, and Ni concentrations were 0.142, 0.187, 0.780, and 0.114 mg·L‑1, respectively, and Zn, Pb, and Cd were below the instrument detection limits used in this analysis. This work establishes a 10-day, waste-treats-waste route for red-mud soilization—shifting rehabilitation from a slow process to a practical timescale while co-valorizing bauxite residue and Maotai-flavor liquor wastewater.