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Effective disposal of phosphorus slag (PS) is crucial for ecosystem protection. Herein, this study proposed that Na 2 SO 4 (SS), Na 2 SiO 3 (NS), Na 2 CO 3 (SC) and NaOH (NH) were performed to prepare alkali-activated phosphorus slag cemented paste backfill material (AAPS-PB). The evolution mechanisms of setting time, rheological behavior and mechanical properties at different contents of various activators were systematically investigated. The mineral compositions, bonding structure, micromorphology and pore structure characteristics of AAPS-PB hydration products were further clarified by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy-energy dispersive spectrometer (SEM-EDS) and mercury intrusion porosimeter (MIP). Results indicated that activators were proved to significantly promote the dissolution of PS at appropriate content. NH had stronger alkali activation ability in the early hydration period, whereas NS sufficiently improved the later strength, enhanced the denseness of hydration products and refined the pore structure characteristics. This study expands the avenues for high-value applications of PS. • AAPS samples with 2.5% NS content exhibit the highest 28 days strength. • The activation effects of various activators were compared. • Cemented paste backfill technique provides new thoughts for the large consumption of PS. • The hydration mechanism of AAPS-PB was revealed. [ABSTRACT FROM AUTHOR]

• The effects of sulfur content and polypropylene fiber on the mechanical properties, failure pattern and damage evolution of the CSTB were systematically studied. • The fiber factor γ is introduced to measure the impact of polypropylene fiber on mechanical behavior of CSTB. • The piecewise damage constitutive model taking fiber factor γ into consideration was established. In order to explore the mechanical properties of cemented sulfur tailings backfill (CSTB), uniaxial compression tests of cemented sulfur tailings backfill (CSTB) were carried out in the laboratory, and the effects of sulfur content and polypropylene fiber on the mechanical properties, failure pattern and damage evolution of the CSTB were systematically studied. Moreover, fiber factor γ is introduced to measure the impact of polypropylene fiber on mechanical behavior of CSTB. The peak stress, residual stress and elastic modulus of the CSTB all increase initially and decrease afterwards with the fiber factor γ increasing. When the fiber content is 0%∼0.6%, the three factors show exponential and quadratic function with the fiber factor γ increasing. The total strain energy, elastic strain energy and dissipative strain energy of CSTB at the peak stress point all increase first and then decrease with the fiber factor γ increasing, and all reach the maximum value when the fiber content is 0.6%. Under uniaxial loading, the elastic strain energy of CSTB presents a change characteristic of "gentle - rapid increase - slow increase - rapid decline" with the increasing axial strain, while the dissipative strain energy presents a change characteristic of "gentle - steady increase - rapid increase". In addition, each strain energy (dissipative strain energy, total strain energy and total strain energy) of CSTB at the peak stress point all increase initially and decrease afterwards with the fiber factor γ increasing. Then, the piecewise damage constitutive model taking fiber factor γ into consideration was established. Under uniaxial loading, the damage evolution of backfill can be divided into four stages: no damage stage, slow growth stage, acceleration stage and damage failure stage. It shows that polypropylene fiber can effectively inhibit the damage and failure of CSTB, thus improving the bearing capacity and anti-deformation and failure ability of CSTB. The CSTB without fiber shows obvious shear failure characteristics, and there are obvious large-scale "Y-shaped" and "linear" failure cracks on the sample surface. There is not only one or two major large-scale cracks in the failure of CSTB containing fiber, but also the range of fracture surface is very limited, indicating that adding fiber can effectively inhibit the crack propagation of CSTB during failure and improve the overall anti-crack ability of CSTB. [ABSTRACT FROM AUTHOR]

• 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]

• The energy parameters at characteristic stress point for diffetent curing ages was studied. • The energy damage evolution mechanism of the CTB was revealed. • An energy criterion for strength failure of the CTB was established. This study attempted to explore, at curing age, the characteristics stress and energy evolution of the cemented tailings backfill (CTB) under uniaxial compression. Based on the energy consumption theory, the energy parameters at the characteristic stress varing with the curing age was analyzed. Furthermore, the evolution law of energy distribution and the energy damage mechanism of the CTB were revealed, and the failure criterion of the CTB was established based on the elastic energy consumption ratio. The results showed that the characteristic stress of the CTB follow an exponential function increasing law with the increase of curing age and the characteristic stress of the CTB with larger cement-to-tailings (c/t) ratio increases more rapidly when the curing age is 3d ~ 14d. The total energy, elastic strain energy and consumption energy at the peak stress point of the CTB all follow the exponential function increasing law with the increase of curing age, and the increase of cement-to-tailings (c/t) ratio and curing age can significantly improve the energy storage limit of the CTB. The deformation and failure of the CTB mainly go through five stages: initial crack compaction stage, linear elastic deformation stage, steady development stage of microcrack, accelerated crack expansion stage and post-peak failure stage. According to the damage value D of the CTB and the growth law of dissipated energy, elastic strain energy and axial strain, the loading damage of cemented CTB can be divided as follow: initial damage stage, damage stationary stage, damage stable stage, damage rapid stage and damage failure stage. The slow growth and abrupt change of the elastic energy consumption ratio K in the post-peak stage can be used as the criterion for strength instability of the CTB. [ABSTRACT FROM AUTHOR]