Effect on ceramic grade CaF 2 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 SO 4 2− was found to be the main barrier for high quality CaF 2 production, while CaSO 4 could also contribute to CaF 2 precipitation. The optimum SO 4 2− content was adjusted by the introduction of barium salts, to keep a balance between the CaF 2 quality and the settlement process. The ceramic grade CaF 2 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 SO 4 2− content should be kept in the range of 100–130 mg L −1 , and the formation of CaSO 4 , combined with CaF 2 could accelerate the CaF 2 precipitation by the co-precipitation method, with a larger particle size from 758 nm (without SO 4 2− ) to 898 nm. The gradient settlement of CaF 2 contributes to the recovery of fluoride from etching wastewater, while CaF 2 preparation should be carried out in a dynamic experiment, such as a fluidized bed, for further research.