Godbout, J, Bussière, B, Benzaazoua, M & Aubertin, M 2010, 'Influence of pyrrhotite content on the mechanical and chemical behaviour of cemented paste backfill', in R Jewell & AB Fourie (eds), Paste 2010: Proceedings of the Thirteenth International Seminar on Paste and Thickened Tailings, Australian Centre for Geomechanics, Perth, pp. 163-173, https://doi.org/10.36487/ACG_rep/1063_14_Godbout
(https://papers.acg.uwa.edu.au/p/1063_14_Godbout/)
Abstract: The chemical weathering related to sulphide minerals oxidation within mine backfill in underground stopes 
can cause serious problems, such as the loss of mechanical strength due to sulphate attack. This can also 
lead, under specific (extreme) conditions, to excessive self-heating of the backfill and to oxygen depleted 
atmosphere. Previous studies indicate that sulphide minerals contained in cemented paste backfill (CPB) are 
less reactive (i.e. less prone to oxidation) than those contained in hydraulic backfill (HB) because the 
favourable hydraulic properties of CPB can help maintain a high degree of water saturation (often more 
than 85%) in the fill material. This paper presents results from an investigation of the influence of pyrrhotite 
content on the physico-chemical behaviour of cemented paste and hydraulic backfills. Oxygen-consumption 
(OC) tests, uniaxial compressive strength (UCS) tests, and a post-testing characterisation were performed on 
different mixtures of cemented backfills made of tailings with 5% wt of binder and various percentages of 
pyrrhotite (2 to 15%). Tailings without binder were also assessed with the OC test (as control samples). All 
samples were cured under controlled temperature and moisture conditions (30°C and 100% respectively) to 
simulate curing under warm mine site conditions, for periods of 3, 7, 28, 56, 182, and 365 days. The OC tests 
results show that pyrrhotite-rich tailings without binder can be very reactive; the consumed oxygen flux 
measured can exceed 35 mol/m2/day when these are exposed to atmospheric concentration. OC tests also 
show that the addition of binder (Portland cement) in the backfill mixtures reduces their reactivity; a more 
significant reduction was observed for paste backfill samples compared with hydraulic backfill specimens. 
The OC tests results furthermore indicate a decrease of the control samples (tailings without binder) 
reactivity over time, suggesting that other factors, such as passivation of the pyrrhotite grains surface during 
weathering, could also influence the evolution of backfill reactivity. The UCS tests results show that paste 
backfill samples reached higher strength than hydraulic backfill. However, a progressive loss of strength 
was also observed for all backfill mixtures after a few months, probably due to sulphate attack.