The effect of fluorogypsum on the properties of high-water filling materials

Filling mining is an important way to realize the green development of mines. High-water filling materials have been widely used because of their short setting time. In this material, 40% of the raw material is natural anhydrite, and the main component is anhydrous calcium sulfate (CaSO₄). Fluorogypsum is an industrial solid waste produced in the production of hydrofluoric acid. Its main composition is type II CaSO₄. In order to explore the influence of fluorogypsum (F1, lime content of 3%; F2, lime content of 5%) on the performance of high water filling materials, the influence of fluorogypsum content on the setting time and 1, 7 and 28 d compressive strength of high-water filling materials at different experimental water temperatures and water binder ratio of 3∶1 was studied. At the same time, the hydration mechanism was studied by XRD, SEM, and TG-DTA. The results show that the setting time of high-water filling material increases gradually with the increase of fluorogypsum content at different experimental water temperatures. With the increase of F1 content, the low content has little effect on the compressive strength of high-water filling materials at different ages. When its content is higher than 20%, the compressive strength of high-water filling materials at 1, 7, and 28 days decrease gradually; with the increase of F2 content, the compressive strength of the high water filling material increases gradually at 1, 7, and 28 d. At different ages, compared with the blank group, the F2 content is 80%, and the maximum growth rate of its compressive strength is 29.7%. Microscopic analysis shows that the hydration products of high-water filling materials mainly include AFt, Al (OH) ₃ (gel), and CaSO₄ · 2H₂O. After hydration for 1 d, the hydration rate of the F2 group (80% of F2) is fast and the amount of AFt is the largest, while the hydration rate of the blank group is the smallest and the amount of AFt is the smallest; After 28 d of hydration, the amount of aft produced in the three groups was the same. At the same time, based on the hydration kinetics of high-water filling material, the influence of fluorogypsum on the hydration process of high-water filling material is analyzed. It is concluded that fluorogypsum can replace natural anhydrite in high-water filling material systems and be applied to high-water filling material systems.