Recycling phosphogypsum (PG) for cemented paste backfill (CPB) has been widely used at phosphate mines in China. However, the impurities in PG prolong the setting time and reduce the uniaxial compressive strength (UCS), limiting the engineering application of PG. This paper aims to investigate the feasibility of treated PG (TPG) washed repeatedly using deionised water (DW) for CPB. A water-washing pre-experiment was first conducted to find the proportion with the least DW demand and the effects of water-washing on ordinary PG (OPG). Then, based on the PG:DW ratio obtained from the pre-experiment, the properties of the OPG-based CPB (OCPB) and TPG-based CPB (TCPB) were tested using slump tests, UCS tests, and microstructural analysis. The results show that (1) after 11 water-washings at the PG:DW ratio of 1:1.75, the pH of the supernatant (pH = 6.328) meets the requirements of Chinese standard GB 8978-1996. (2) Water-washing improves the particle gradation quality of PG and removes the soluble impurities adsorbed at the surface of PG crystals. (3) The initial slump values of TCPB are 0.19–1.15 cm higher than that of OCPB, furthermore, the diffusivity values of TCPB are better than the performance of OCPB, with 0.61–1.68 cm of superiority. (4) The UCS values of TCPB are up to 0.838 MPa, 1.953 MPa, and 2.531 MPa, after curing for 7, 14, and 28 days. These are 0.283 MPa, 0.823 MPa, and 0.881 MPa higher than that of OCPB, respectively. It can be concluded that water-washing pre-treatment greatly improves the workability and mechanical property of PG-based CPB. These results are of great value for creating a reliable and environmentally superior alternative for the recycling of PG and for safer mining production.

This study demonstrates the feasibility of recycling lead–zinc tailing (LZT) as a cemented paste backfill (CPB) by considering the mechanical properties and environmental effects, thus providing an approach for safe and environmentally friendly treatment of LZT. First, the mechanical properties of CPB samples were tested. When the cement/tailing ratio was 1:6 and the slurry concentration was 70%, the maximum unconfined compressive strength (UCS) of the CPB cured for 28 days reaching 2.05 MPa, which could ensure safe mining. Then, the metals with pollution potential in the backfill slurry were investigated through static leaching. Finally, after adding immobilisation materials to stabilise excessive metals, the environmental stability of the CPB was demonstrated through dynamic leaching and a toxicity characteristic leaching procedure. The results show that the lead leached from the backfill slurry still exceeds the Chinese standard for groundwater quality (GB/T14848-2017 Class III). The addition of 2 mg/L polyaluminium sulfate (PAS) can further improve the strength of the CPB and maintain the environmental friendliness of the CPB. Therefore, the technology of recovering LZT as a CPB proposed in this study is an effective alternative to deal with LZT, which can help lead–zinc mines meet the requirements of cleaner production.

Cemented paste backfill (CPB), a technology placing the solid waste into mined-out stopes in the mine through pipeline transportation, has been widespread all over the world. The resistance loss is an important parameter for pipeline transport, which is significantly affected by the slurry characteristics. However, the coupling effect of inlet velocity (IV), particle mass concentration (PMC), and particle size (PS) has not been well evaluated and diagnosed. Hence, the CFD-based three-dimensional network simulation of CPB slurry flow in an L-shaped pipe at different combinations of the three parameters was developed using COMSOL Multiphysics software, and the findings were validated through a loop experiment. The results show that increasing IV and reducing PS will contribute to the homogeneity of the slurry in the pipeline, while the PMC presents little effect. The pipe resistance loss is positively correlated with IV and PMC and negatively correlated with PS. The sensitivity to the three parameters is IV > PS > PMC. In particular, the resistance loss is minimal at IV of 1.5 m/s, PMC of 72%, and PS of 1000 um. The calculation model of resistance loss regressed from simulation presented a high accuracy with an error of 8.1% compared with the test results. The findings would be important for the design of the CPB pipeline transportation and provide guidance in the selection of transfer slurry pumps, prepreparation of backfill slurry, and pipe blockage, which will improve the safety and economic level of a mine.

Cemented paste backfill (CPB) is the primary solution to improving the safety of continuous mining. The interaction between rock mass and backfill is an important indicator of backfill stability. The creep behavior of weak rock mass is an essential factor, which causes the evolution of stresses and displacements in the backfill stope. In this paper, numerical models were constructed to analyze the interactions between rock mass and backfill by considering the creep behavior of the rock mass, filling interval, and backfill strength. The numerical simulation results showed the effects of different parameters, including the number of backfilling layers, filling interval time (FIT), and backfill strength under creep behavior on stress, displacements, and plastic deformation. The horizontal displacement near the mid-height and vertical displacement at the top of the backfilled stope is the largest compared to layered backfilling. The stress within the backfilled stope is smallest when the stope is filled in a single layer. With increasing FIT, stress in the backfilled stope decreases. FIT mainly affected the horizontal displacement of the stope. The stresses on the stope bottom decrease when the strength of the middle-backfilled stope decreases. Overall, this study provides important insights for understanding the creep behavior of rock mass in underground backfilling practices.

Red mud is a by-product of alumina production, and its disposal can have severe environmental consequences. This study experimentally investigates the feasibility of using red mud from the Bayer process for cemented paste backfill (CPB). Different binders and activators were used to improve the mechanical properties, water resistance, and environmental behaviors of red mud-based CPB. In addition, water immersion tests were introduced, for the first time, to evaluate the water resistance of CPB. Furthermore, the environmental behaviors of red mud-based CPB were investigated by conducting leaching experiments. The results showed that the red-mud specimens had an unconfined compressive strength (UCS) of less than 0.2 MPa and disintegrated after being immersed in water. Different binders significantly improved the mechanical properties of red mud-based CPB. In addition, the specimens with different binders showed excellent water resistance, and the softening coefficient of CPB with different binders could exceed 0.7 after being cured for 28 days. The binders exhibited a substantial inhibitory effect on the leaching of hazardous substances in red mud under the solidification and stabilization effects. The leaching concentration of hexavalent chromium, selenium, fluoride, arsenic, lead, and vanadium was reduced by more than 70%. Therefore, this study provides an effective method for the environmental-friendly and large-scale utilization of red mud from the Bayer process.

This study aimed to investigate the environmental impact of modified granulated copper slag (MGCS) utilization in blended cement production at a representative cement plant in China. Sensitivity analysis was performed on the substance inputs, and the life cycle impact assessment (LCIA) model was applied. A detailed comparative analysis was conducted of the environmental impact of cement production in other studies, and ordinary Portland cement production at the same cement plant. Results showed that calcination has the largest contribution impact of all the impact categories, especially in causing global warming (93.67%), which was the most prominent impact category. The life cycle assessment (LCA) result of blended cement was sensitive to the chosen LCIA model and the depletion of limestone and energy. In this study, producing blended cement with MGCS effectively mitigated the environmental impact for all the selected impact categories. Results also show a reduction in abiotic depletion (46.50%) and a slight growth (6.52%) in human toxicity. The adoption of MGCS in blended cement would therefore generally decrease the comprehensive environmental impact of cement, which contributes to the development of sustainable building materials.