Influence of wet grinded slag on the hydration of phosphogypsum-slag based cement and its application in backfill tailings

Phosphogypsum-slag based cement (PSBC) has a great potential in tailings backfill because of low cost and CO2 emission in comparison with Portland cement. However, slow early hydration was often observed, and this problem was generally solved by adding cement clinker, which could provide alkalinity to hasten the hydration of ground granulated blast furnace slag (GGBS). In this study, GGBS by wet grinding (i.e., WGGBS) was used to partially replace raw GGBS in PSBC, with intent to promote the early hydration and cementitious performance in backfill tailings. Results showed that 60 % replacement ratio of GGBS by WGGBS enhanced the 3 d compressive strength by 507 %, and that for a 28 d was 45 MPa, which meet the strength requirement of 42.5 grade cement; besides, its carbon emission was only 5 % of that of cement. Due to the high reactivity of WGGBS at the early age, pH of PSBC system was promoted, and this hastened dissolution of GGBS and formation of hydrates. This was the reason for the significant increase in early compressive strength. Moreover, with the continuous hydration of PSBC, the hydrates were produced, and the microstructure was densified over time, leading to the increase in later compressive strength. It seemed that the PSBC with WGGBS showed an excellent cementitious performance in iron tailings filling. Under the condition of 1:10 wt ratio of cementitious material to iron tailings, 28 d compressive strength of PSBC with WGGBS was up to 3.1 MPa, while that for cement was only 0.8 MPa.