中国有色金属学报(英文版)
Transactions of Nonferrous Metals Society of China
| Vol. 33 No. 11 November 2023 |
（1. Faculty of Materials Metallurgy and Chemistry, Jiangxi University of Science and Technology, Ganzhou 341000, China;
2. Key Laboratory of Ionic Rare Earth Resources and Environment, Ministry of Natural Resources, Ganzhou 341000, China;
3. Ganzhou Engineering Technology Research Center of Green Metallurgy and Process Intensification, Ganzhou 341000, China;
4. Institute of Resources Utilization and Rare Earth Development, Guangdong Academy of Sciences, Guangzhou 510650, China）
Abstract:Batch experiments were conducted to remove fluoride from simulated flue-gas scrubbing wastewater using La(NO3)3·6H2O. The effects of SO42- concentration and addition sequence on residual fluoride concentration and precipitates properties (mass, morphology, phase structure and composition) were investigated using fluorine ion-selective electrode, SEM, EDS and XRD. The results show that precipitates obtained in the presence of SO42- mainly consisted of LaF3 in irregular bulk shape with high crystallinity. However, amorphous particles were observed in the precipitates, which were speculated to be La[SO4]F. Due to the smaller stoichiometric coefficient of F/La in La[SO4]F compared to that in LaF3, the residual fluoride concentration increased as the SO42- concentration ascended. Subsequent addition of SO42- after lanthanum salt could inhibit the formation of amorphous particles, and further reduce the residual fluoride concentration. At a La/F molar ratio of 1:3.0, the subsequent addition of SO42- (0.02 mol/L) after La(NO3)3？6H2O could obtain a residual fluoride concentration of 6.9 mg/L, lower than the required fluoride emission level. Further increasing the La/F molar ratio could reduce residual fluoride concentration to below 2 mg/L, while the risk of retaining La3+ would emerge.
Key words: fluoride removal; lanthanum salts; amorphous particles; atomic efficiency; addition sequence
