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• The durability and leaching behavior of rm-cpb were studied systematically. • The UCS of RM-CPB was investigated by orthogonal experiment. • The environmental impact of RM-CPB was studied by three different leaching methods. Red mud (RM) is a potential supplementary backfill material. However, little is known about cemented paste backfill (CPB) preparation from reused RM. Here, the feasibility of Bayer RM in CPB technology is discussed to expand the utilization of solid waste. With Bayer RM, Fly ash (FA), and cement as raw materials, the strength performance of Bayer RM in cemented paste backfill (RM-CPB) was evaluated by the orthogonal experiment method, and the optimal ratio of RM-CPB was determined. The effects of slurry concentration, mixing ratio of RM to FA, and the cement dosage on uniaxial compressive strength (UCS) were studied. Its durability, microstructure, permeability, and environmental properties were investigated. The experimental results show that the strength of the optimum proportion reached 1.25 MPa and 2.37 MPa after curing for 3 d and 28 d respectively and meet the mine design standard when the ratio of RM-CPB is: 60% of the slurry concentration, the RM: FA is 3:2, and the dosage of cement is 5%. RM-CPB material has good durability, and the main hydration products are C-S-H gel, ettringite, and gmelinite, which is conducive to the development of UCS of the backfill material. Meanwhile, the permeability k 20 of RM-CPB is only 6.005 × 10-6 cm/s, indicating that the material has few internal pores, which can effectively prevent external water intrusion. The leaching test results showed that both the heavy metal concentration and pH value of the leachate were within the range specified in the Chinese standard (DZ/T 0290–2015), and it was found that the effect of the three ion leaching tests is successive: toxicity leaching test > immersion test > eluviation test. The comprehensive analysis found that the reuse of Bayer RM as a supplementary cemented paste backfill material provides a new idea for the large-scale utilization of industrial solid waste. [ABSTRACT FROM AUTHOR]

• The relationship between flowing properties and sulfur content of cemented sulfur tailings backfill (CSTB) is revealed. • Based on SEM and XRD techniques, the effect of sulfur content variation on mechanical properties of cemented sulfur tailings backfill is investigated. • By adding polypropylene fibers to the CSTB, the prediction models for compressive and tensile strength are proposed considering fiber modification coefficient. • Based on SEM and XRD techniques, the effect of polypropylene fibers on mechanical properties of cemented sulfur tailings backfill is investigated. In this paper, the mechanics, flowing and microstructural properties of the cemented sulfur tailings backfill (CSTB) have been studied by means of flow performance test, uniaxial compression test, scanning electron microscope test and X-ray energy spectrum test. On the basis of previous results, a new way was proposed to improve the mechanical performance of CSTB. The research results show that the fluidity of sulfur tailings slurry increases exponentially with the increase of sulfur content, because the density of sulfide concentrate is greater than that of tailings. The adding of polypropylene fiber will reduce the fluidity of sulfur tailings slurry and the fluidity of the slurry decreases exponentially with the increase of fiber content. The compressive strength and 28d splitting tensile strength of the CSTB both increased first and then decreased with the increase of the sulfur content, and reached the maximum when the sulfur content was 12%. However, the CSTB exhibits obvious strength deterioration characteristics when the curing age exceeds 28 days. The compressive strength and 28d tensile strength of the CSTB both increased first and then decreased with the increase of fiber content, and then, reached the maximum when the fiber content is 0.6%. In addition, the effect of adding polypropylene fiber on improving the tensile strength is better than that of compressive strength. SEM and X-ray energy spectrum analysis results show that a certain amount of secondary gypsum and ettringite crystals can effectively fill the pores in the CSTB, which contributes to the development of strength. However, when the sulfur content exceeds the critical content, there are obvious pore structures and a large number of expansive minerals such as gypsum and ettringite in the CSTB, which leads to the strength deterioration of the CSTB. The special spatial skeleton structure formed by polypropylene fibers in the CSTB matrix can play a significant physical reinforcement effect and the reinforcement effect is mainly controlled by the bonding effect between the fiber and the CSTB matrix interface. In addition, the compressive strength, tensile strength and fluidity prediction models of the fiber reinforced CTSB constructed based on the fiber modification coefficient can accurately predict the compressive strength, tensile strength and fluidity parameters, which can provide certain guidance for engineering applications. [ABSTRACT FROM AUTHOR]