Preparation and characterization of a new alkali-activated binder for superfine-tailings mine backfill

Study on mechanical properties and damage characteristics of cemented waste rock-tailing backfill

Tailing and waste rock-cemented filling is an effective way to solve the problem solid waste in mines. In this paper, the effects of waste rock content and cement-sand ratio on the properties of tailing-waste rock-cemented filling materials and cemented backfill were analyzed based on the single-factor multi-level experimental design method. The results show that with the increase of waste rock content, the fluidity of the filling slurry increases first and then decreases, the bleeding rate increased gradually, and the compressive strength of the backfill increases first and then decreases. When the waste rock content is 60% and the cement-sand ratio is 1:4, the cemented backfill has higher compressive strength. With the increase of waste rock content, the interface failure area between waste rock particles and cementitious matrix under loading gradually increases, the crack extension is more complex, and the acoustic emission (AE) ringing count is higher. Microstructural analysis showed that the main hydration products in the cemented backfill were calcium silicate hydrated (C-S-H) gels, ettringite (AFt), and calcium hydroxide (Ca(OH)2). Because there is more content of hydration products, the microstructure of the cemented backfill was denser and the compressive strength was higher. Based on the results of uniaxial compression tests, the damage constitutive model of cemented backfill with different waste rock contents and cement-sand ratios was established, which could provide guidance for the design and safety production of phosphate rock filling engineering.

Production of a new type of cemented paste backfill with solid waste from carbide slag, soda residue, and red mud: mechanism, optimization, and its environmental effects

To solve the disposal problems of carbide slag (CS), soda residue (SR), and red mud (RM) solid wastes, a new type of cemented paste backfill (CPB) was prepared with CS, SR, and RM solid wastes. The mixing proportion for the CPB was optimized by combining the Box‒Behnken design (BBD) response surface method and the satisfaction function method. The strength formation mechanism for the CPB was analyzed with physical and mechanical property tests, X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), etc. The safety of the CPB was evaluated with heavy metal leaching testing. The results showed that the 28-day unconfined compressive strength (UCS) of CPB first increased and then decreased with increasing CS/RM (0.2 ~ 0.6) and SR/RM (0.2 ~ 0.6); the optimum mixing ratios were CS/RM = 0.45 and SR/RM = 0.37, and the solid mass concentration was 64.75%; dense calcium silicate (aluminum) hydrate (C-S-H/C-A-S-H) bound to the solid particles of red mud and filled pores to provide early strength for the CPB, laminar interwoven Friedel's salt (Fs), ettringite and portlandite hydration products provided late strength for the CPB; and the leaching concentrations of five heavy metals (Fe, Mn, Cu, Zn, and Cr) in the solidified CPB were greatly reduced and far below the leaching limits specified in China's Quality Standard for Groundwater (GB/T 14848-2017).

Development of Cemented Paste Backfill with Superfine Tailings: Fluidity, Mechanical Properties, and Microstructure Characteristics

Previous studies have shown that the effectiveness of superfine tailings cemented paste backfill (SCPB) is influenced by multiple factors. To optimize the filling effect of superfine tailings, the effects of different factors on the fluidity, mechanical properties, and microstructure of SCPB were investigated. Before configuring the SCPB, the effect of cyclone operating parameters on the concentration and yield of superfine tailings was first investigated and the optimal cyclone operating parameters were obtained. The settling characteristics of superfine tailings under the optimum cyclone parameters were further analyzed, and the effect of the flocculant on its settling characteristics was shown in the block selection. Then the SCPB was prepared using cement and superfine tailings, and a series of experiments were carried out to investigate its working characteristics. The flow test results showed that the slump and slump flow of SCPB slurry decreased with increasing mass concentration, which was mainly because the higher the mass concentration, the higher the viscosity and yield stress of the slurry, and thus the worse its fluidity. The strength test results showed that the strength of SCPB was mainly affected by the curing temperature, curing time, mass concentration, and cement-sand ratio, among which the curing temperature had the most significant effect on the strength. The microscopic analysis of the block selection showed the mechanism of the effect of the curing temperature on the strength of SCPB, i.e., the curing temperature mainly affected the strength of SCPB by affecting the hydration reaction rate of SCPB. The slow hydration process of SCPB in a low temperature environment leads to fewer hydration products and a loose structure, which is the fundamental reason for the strength reduction of SCPB. The results of the study have some guiding significance for the efficient application of SCPB in alpine mines.