Use of Saline Water in Cemented Fine Tailings Backfill with One-Part Alkali-Activated Slag

Abstract

To evaluate the feasibility of mixing saline underground water (SUW) in the preparation of cemented fine tailings backfill (CFTB), the compressive strength, pore fluid pH, slag hydration degree, hydration phase composition/structure, and pore morphology of CFTB have been tested. The binder used was a one-part alkali-activated slag composed of ground-granulated blast furnace slag (67.8% by weight) as precursor and desulfurized gypsum (25.9% by weight) and hydrated lime (6.3% by weight) as composite activator. The results showed that using SUW instead of deionized water as mixing medium had both negative and positive effects on the strength development of CFTB, depending on the curing time. At the very early ages (1–3 days), mixing SUW resulted in a decrease of the pore solution pH, which is due to the reaction of positive ions in SUW with OH− ions and the decrease of slag hydration rate, leading to a lower strength of CFTB. The positive effects were observed at the later ages (7–28 days). The higher later-age strength of SUW-mixed CFTB is attributed to two factors: (1) a smaller amount of ettringite (AFt) was generated at the very early ages, which reduced the encapsulation-hindering effect on the slag decomposition; and (2) SUW increased the slag hydration rate, promoting the condensation of calcium silicate hydrates, which results in increased formation of a calcium silicate aluminate hydrate [C-(A)-S-H] phase with rigid three-dimensional structure. These findings can provide important information for the use of SUW in CFTB in coastal and arid regions.