Fluid-related performances and compressive strength of clinker-free cementitious backfill material based on phosphate tailings

Abstract

Phosphate tailings are usually used as backfill material in order to recycle tailings resources. This study considers the effect of the mix proportions of clinker-free binders on the fluidity, compressive strength and other key performances of cementitious backfill materials based on phosphate tailings. In particular, three solid wastes, phosphogypsum (PG), semi-aqueous phosphogypsum (HPG) and calcium carbide slag (CS), were selected to activate wet ground granulated blast furnace slag (WGGBS) and three different phosphate tailings backfill materials were prepared. Fluidity, rheology, settling ratio, compressive strength, water resistance and ion leaching behavior of backfill materials were determined. According to the results, when either PG or HPG is used as the sole activator, the fluidity properties of the materials are enhanced. Phosphate tailings backfill material activated with PG present the largest fluidity and the lowest yield stress. Furthermore, the backfill material's compressive strength is considerably increased to 2.9 MPa at 28 days after WGGBS activation using a mix of HPG and CS, all with a settling ratio of only 1.15 percent. Additionally, all the three ratios of binder have obvious solidification effects on heavy metal ions Cu and Zn, and P in phosphate tailings.