The activation of fluorgypsum with slag activator and the fluorine solidification mechanics

The mechanism of activator to fluorgypsum and the fluorine solidification were investigated by the performances of composite binding material. Through the setting time testing of fluorgypsum with NaOH, Na₂SO₄ and NaF, the least activator dosage were all 1%. And the cementitious material over 80% of fluorgypsum was processed to improve its quality with slag, fly ash and clinker. The maximum compressive strength of composite binding material was over 12.90 MPa in 28 days, and the concentration of fluroride reduced 64.7% which compared with the pure fluorgypsum binding material. Analysis of X-ray diffraction and scanning electron microscopy images showed that ettringite crystals, dihydrate gypsum crystals and C-S-H gel were filled with each other. The unreacted CaF₂ crystals were embedded by a great deal of network and filamentous C-S-H gel. It was the main reason that the composite binding material strength improved, water resistance increased and leaching toxicity reduced.