Alkali-circulation-mediated valorization of fluorine-rich silica residue and carbide slag: Coproduction of hydrated silica and calcium fluoride.
- 2026-06
- Journal of hazardous materials 510
- PubMed: 42001751
- DOI: 10.1016/j.jhazmat.2026.142104
Study Design
Fluorine-rich silica residue (FSR), an acidic byproduct from anhydrous hydrogen fluoride production, poses significant environmental threats due to its high fluoride content and instability, leading to toxic fluoride release. This study developed an integrated "alkali circulation" process for the synergistic valorization of FSR and carbide slag. The technology comprises alkali leaching of FSR, carbonation precipitation to recover hydrated silica, and concurrent recovery of calcium fluoride (CaF2) during alkali regeneration. Under optimal conditions, the leaching efficiencies of silicon and fluorine reached 99.64% and 99.89%, respectively. Mechanistic analysis indicated that "free fluorine" was rapidly leached, whereas "structurally incorporated fluorine" was released only after dissolution of the amorphous SiO2 framework. The leaching kinetics followed the shrinking core model, with silicon extraction controlled by chemical reaction and subsequent fluorine release governed by internal diffusion. The hydrated silica recovered at 70-90 °C is suitable for application as a reinforcement in rubber. The carbonation step resulted in minimal fluorine loss (0.02%) due to interfacial charge effects. Treatment with carbide slag slurry achieved simultaneous alkali regeneration (90.11% efficiency) and fluoride precipitation as a primary CaF2 product. Leveraging the lower solubility product of CaF2, secondary fluoride recovery and acid washing increased the CaF2 content to 93.16 wt%, meeting quality standards for construction, metallurgy, and chemical industries. The process exhibited low alkali consumption (70.15 kg NaOH per 1000 kg FSR per cycle) and excellent cyclic stability. This work demonstrates a feasible "waste-treats-waste" strategy, offering a practical circular economy pathway for the high-value utilization of FSR and carbide slag.
Research Insights
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