Effect on ceramic grade CaF2 recovery quality from the etching wastewater under the optimum sulfate content

The improvement of fluorite quality is an attractive measure to recover fluoride from high F- content wastewater and thus reduces the fluorite sludge generation rate, and the removal of contaminant pollutants could be helpful for the production of ceramic grade fluorite (>85%). In this work, typical etching wastewater was collected and characterized, and SO42- was found to be the main barrier for high quality CaF2 production, while CaSO4 could also contribute to CaF2 precipitation. The optimum SO42- content was adjusted by the introduction of barium salts, to keep a balance between the CaF2 quality and the settlement process. The ceramic grade CaF2 of 88% was obtained under the conditions: [Ca]/[F] of 1.29, pH 8.14 and C-sulfate of 117.4 mg L-1. The residual SO42- content should be kept in the range of 100-130 mg L-1, and the formation of CaSO4, combined with CaF2 could accelerate the CaF2 precipitation by the co-precipitation method, with a larger particle size from 758 nm (without SO42-) to 898 nm. The gradient settlement of CaF2 contributes to the recovery of fluoride from etching wastewater, while CaF2 preparation should be carried out in a dynamic experiment, such as a fluidized bed, for further research.