Abstract
SYNOPSIS The properties and deterioration in strength of cemented tailings backfill (CTB )in the underground acidic environment under oxidizing conditions were studied. X-ray diffraction analysis and scanning electron microscopy of the surface of the CTB was carried out, and the sulphuric acid corrosion mechanism elucidated. The properties tested included compressive strength, elastic modulus, cohesion, internal friction angle, variation in the hydrogen ion concentration, and stress-strain relationship in different corrosion periods. The damage model of the CTB was established considering the effects of parameters such as corrosion time and strain on the damage evolution. It was found that the compressive strength, elastic modulus, cohesion (binder effect), and internal friction angle increased at first and then decreased with exposure time. In the long term, the peak stress decreased with corrosion time while the peak strain increased; elastic modulus, and deformation modulus also decreased. The damage caused by corrosion and by load were related by means of a mathematical model, which revealed the relationships between sulphuric attack, load, and damage to backfill in complex underground environments. During corrosion, the expansion of gypsum and ettringite caused microfractures in the CTB. With increasing corrosion time, micro-cracks developed and proliferated. The mechanism of corrosion damage was found to be the dissolution of hydrogen ions and a sulphate ion reaction that produces an expansive substance, resulting in deterioration of the strength of CTB. Keywords: underground environment, sulphuric acid corrosion, porosity, cemented tailings backfill, damage evolution model.
Highlights
Underground mining operations can bring problems such as overburden pressure, surface subsidence, and instability of mined-out areas
This suggests that the dissolution rate of Ca(OH)2 is slowing; the surface of the cemented tailings backfill (CTB) and the pore structure are covered by gypsum crystals and colloids, hindering the reaction from proceeding inside the CTB, the chemical reaction rate is lowered, and the phenomenon becomes more obvious with increasing time
The colloids are observed in this solution, the amount is less than for P1, indicating that the rate of chemical reaction in the acidic environment is slowed down
Summary
Underground mining operations can bring problems such as overburden pressure, surface subsidence, and instability of mined-out areas. Backfilling of underground workings with cemented tailings is one of the effective methods of solving these problems. Much research has focused on the influence of different proportions of ingredients on the strength of backfill (Alireza and Fall, 2016; Djurdjevac, Ignjatovic, and Ljubojev 2016; Yang, Yang, and Gao, 2016; Liang, Dong, and Jiang, 2015; Li, Feng, and Guo, 2016a; Li, Jin, and Tan, 2016b; Chang, Zhou, and Qin, 2009; Li et al, 2005; Cao, Song, and Xue, 2016; Song, Li, and Lei, 2012). Only limited research has been done on the influence of corrosion on the strength of the backfill. Such research as has been done has focused mainly on corrosion by salts, such as NaCl, Na2SO4, Na2CO3, and other solutions
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