Experimental study on the production of carbon-absorbing backfill material from freshly mixed modified magnesium slag slurry

Abstract

AbstractWet carbonisation of alkaline industrial solid waste is considered to be an effective method for CO2 capture/processing of solid waste resources. Aiming at the high-value utilisation of modified magnesium slag in Shaanxi Province, a new method for producing carbon absorption backfill materials (CABM) is proposed by introducing CO2 into freshly mixed modified magnesium slag slurry. Through rheological, mini-slump, isothermal microcalorimeter test, uniaxial compressive strength, X-ray diffraction (XRD), thermogravimetry (TG-DTG) and scanning electron microscopy (SEM) experiments, the effects of CO2 on the fluidity, hydration, mechanical and microstructural properties of freshly modified magnesium slag slurry are investigated. The results show that: (1) while the introduction of CO2 significantly reduces the fluidity of a CABM, it can still meet the requirements of pipeline transportation in backfill mines; (2) the tiny calcium carbonate grains produced during the carbonation reaction can provide additional nucleation sites for the growth and diffusion of hydration products in CABM, and accelerate the hydration heat release rate; (3) the introduction of CO2 into the freshly mixed modified magnesium slag slurry not only helps to improve the compressive strength of the CABM samples at 28 days, but also has a good carbon absorption effect (5.2–7.6%); (4) through XRD, TG-DTG and SEM experiments, it is concluded that the carbonation reaction in the slurry does not prevent the further hydration of the modified magnesium slag, but is helpful for promoting a rapid hydration reaction in a later stage. Therefore, to maintain good fluidity and carbon absorption of the CABM, the backfill slurry should have a water/modified magnesium slag mass ratio of 0.5, a ventilation rate to of 1 L/min, and a ventilation stirring time of 5 min.