Abstract
A new environmentally friendly cemented oil shale residue–steel slag–ground granulated blast furnace slag backfill (COSGB) was prepared using oil shale residue (OSR), steel slag (SS) and ground granulated blast furnace slag (GGBS) as constituent materials. Based on univariate analysis and the Box–Behnken design (BBD) response surface method, the three responses of the 28 days unconfined compressive strength (UCS), slump and cost were used to optimize the mix ratio. Using a combination of scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP), the reaction products, microscopic morphology and pore structure of the specimens with the optimal mix ratio at different curing ages were analyzed. The influence of heavy metal ions from the raw materials and the COSGB mixtures on the groundwater environment was studied by leaching tests. The research demonstrates that the optimal mix ratio is GGBS mixing amount 4.85%, mass ratio of SS to OSR 0.82, and solid mass concentration 67.69%. At shorter curing age, the hydration products are mainly calcium alumino silicate hydrate (C-A-S-H) and calcium silicate hydrate (C-S-H) gels. With the increase of curing age, ettringite (AFt) and C-S-H gels become the main source of the UCS. Meanwhile, the porosity of the filler decreases continuously. The leaching concentration of heavy metal ions from the COSGB mixtures is all lower than the leaching concentration of raw materials and meet the requirements of the Chinese groundwater quality standard (GB/T 14848-2017). Therefore, this new COSGB cannot pollute the groundwater environment and meets backfill requirements. The proposed technology is a reliable and environmentally friendly alternative for recycling OSR and SS while simultaneously supporting cemented paste backfill (CPB).
Highlights
A high concentration of cemented paste backfill (CPB) material, a mixture of tailings, coal gangue, ground granulated blast furnace slag (GGBS), construction waste and other solid wastes with cementitious materials, is used to fill goafs
The results indicated that PG and construction and demolition waste (CDW)-based CPB could support an underground stope after failure
The micromorphologies of the three raw materials obtained through scanning electron microscopy (SEM) testing are shown analaysnshiaoslwyasrniesinsahrFoeigwsuhnroeiwn4.nTTaihnbelTema3ab.ilne c3h. emical compositions obtained by X-ray fluorescence
Summary
A high concentration of cemented paste backfill (CPB) material, a mixture of tailings, coal gangue, ground granulated blast furnace slag (GGBS), construction waste and other solid wastes with cementitious materials, is used to fill goafs. Ordinary Portland cement (OPC) is often used as a cementitious material in CPB materials, but the cost is high. It is an inevitable choice to use mine solid waste as a substitute for cement to reduce the cost of filling materials. Or completely replacing OPC with solid wastes can reduce carbon emissions in the climate emergency and the cost of CPB at the same time [4]. The OSR in Fushun, Liaoning Province, China and the SS in Anshan, Liaoning Province, China are piled up like mountains. These solid wastes occupy land and cause serious damage to the ecological environment. It will provide a pathway to achieving a circular economy in mines [6]
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