Optimization of Ratio and Hydration Mechanism of Titanium-Extracted Residual Slag-Based Filling Cementitious Materials

Using metallurgical solid waste Titanium-extracted Residual Slag (TRS) as mine-filling cementitious material is crucial to reduce the filling cost and promote the utilization of solid waste resources. In this paper, taking the strength of the backfill at different curing ages as the response target, the Design-expert mixing design was used to optimize the proportioning experiment of titanium-extracted residual slag, titanium gypsum, silicate cement, and total tailings, to analyze the interactions and influences of the materials on the strength of the backfill, and to analyze the hydration mechanism of the titanium-extracted residual slag-based filling cementitious materials under the optimal proportioning. The results show that: (1) the order of the sensitivity of each component to the strength of backfill is: composite activator > cement > titanium gypsum > titanium-extracted residual slag, and there are different degrees of interaction between them; (2) the optimal ratio of titanium-extracted residual slag-based filling cementitious materials is TRS:titanium gypsum:cement:composite activator = 55:25:17:3; (3) early strength formation of backfill is mainly related to its hydration products ettringite and C-S-H, the rapid nucleation and cross-growth of ettringite in the early stage forms an effective physical filling effect, which is the main reason for the formation of high early strength, and the later strength of backfill benefited from the continuous accumulation of C-S-H encapsulation and bonding, which further densified its internal structure; (4) the use of titanium-extracted residual slag-based filling cementitious materials contributes to safe, green, and economic mining.