Effect of Natural Zeolite on Pore Structure of Cemented Uranium Tailings Backfill

The use of some environmental functional minerals as backfill-modified materials may improve the leaching resistance of cemented uranium tailings backfill created from alkali-activated slag (CUTB), but these materials may participate in the hydration reaction of the cementitious materials, which could have a certain impact on the pore structure of the CUTB, thus affecting its mechanical properties and leaching resistance. In this paper, natural zeolite is selected as the backfill-modified material, and it is added to alkali-activated slag paste (AASP) and CUTB in cementitious material proportions of 4%, 8%, 12%, and 16% to prepare AASP mixtures and CUTB mixtures containing environmental functional minerals. After the addition of natural zeolite, the porosity of the CUTB generally increases, but when the content is 4%, the porosity decreases to 22.30%. The uniaxial compressive strength (UCS) of the CUTB generally decreases, but the decrease is the smallest when the content is 4%, and the UCS is 12.37 MPa. The addition of natural zeolite mainly reduces the number of fine pores in the CUTB, but the pores with relaxation times T2 of greater than 10 ms account for about 10% of the total pores, and there are a certain number of large pores in the CUTB. The main product of alkali-activated slag is calcium (alumino)silicate hydrate (C-(A)-S-H gel). When natural zeolite is added, the hydration products develop towards denser products with a high degree of polymerization and the formation of low polymerization products is reduced. This affects the internal fracture pores of the hydration products and the interface pores of the CUTB, has an irregular effect on the pore characteristics of the CUTB, and influences the UCS.