Prediction of acidity potential with sulfur containing lead-zinc tailings and damage constitutive model of cemented paste backfill

Cemented paste backfill (CPB) has emerged as a leading solution for waste-free mining. However, lead-zinc tailings often contains pyrite minerals, exploring the influence of sulfide on the CPB is an important prerequisite for mining environment and safety. Tailings with four sulfur contents (2 wt%(natural tailings), 5 wt%, 10 wt%, 15 wt%) static acidity potentials were predicted by using acid base accounting(ABA) and net acid generation(NAG) methods. The failure mode and compressive strength of specimens in 28 to 360 days were analyzed. Results indicated that tailings with sulfur contents of 2 wt%, 5 wt% and 10 wt% didn' t produce acid, while 15 wt% sulfur content tailings produced acid. High sulfur tailings should be paid attention to environmental pollution issues. The strength first increased and then decreased, the sulfur content of 5 wt% CPB reached the highest strength of 3.6 MPa at 90 days. X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis revealed that with the increase of time and sulfur content, the content of gypsum and ettringite increased, while hydrated calcium silicate decreased. A damage constitutive model of the CPB after strength degradation was established. The stress-strain fitting curve was in good agreement with experimental curve. The critical damage value of reached 0.57 at 360 days with the sulfur content of 15 wt% CPB. The analysis of variance indicated that both sulfur content and time had a significant impact on the strength, and the influence of sulfur content was greater than that of time. A negative exponential function between sulfur content, time, and strength was proposed. The research results could provide some theoretical basis for resolving pollution problems and management of sulfur containing tailings.