Abstract: In environmental geotechnical engineering, the use of red mud-based binders for the remediation of lead-contaminated soil offers significant economic and environmental benefits. Three types of red mud-based binders are prepared by incorporating 30% red mud and 40% slag, fly ash, or steel slag, while adjusting the proportions of carbide slag and phosphogypsum. Their mechanical properties and micro-mechanisms are investigated. The developed binders are then applied to stabilize lead-contaminated soils, and the mechanical performance and leaching behavior of the stabilized soil were evaluated. The results show that the mortar prepared with 30% red mud, 40% slag, 20% carbide slag, and 10% phosphogypsum exhibited the highest strength, achieving an unconfined compressive strength (UCS) of 23.8 MPa after 28 days of curing. Excessive phosphogypsum is found to induce overproduction of ettringite, leading to significant expansive cracking and subsequent deterioration of mechanical strength. Under the high lead contamination level, the UCS of the stabilized soil increases markedly from 0.27 MPa (untreated) to 4.75 MPa, while the Pb²⁺ leaching concentration dropped from 3.83 mg/L to 0.34 mg/L.