Selective separation and recovery of fluoride ion from ammonia-based flue gas desulfurization slurry using electrodialysis

BACKGROUND The ammonia-based wet flue gas desulfurization (FGD) system generates fluoride-rich slurry, the concentration of which reaches several thousand mg L-1. Therefore this slurry has to be treated to avoid damage to industrial equipment, human health and environment safety. This work aims at separating fluoride from high-concentrated ammonia-based wet FGD slurry and purifying the ammonium sulfate byproduct using electrodialysis (ED). RESULTS The effects of experimental conditions such as applied potential, circular flow rate, pH and temperature were investigated for the ED process. The influence of competing ions such as Cl- and SO42- on the removal efficiency was also studied. The use of a homogeneous AMX membrane in the first stage of ED and an ACS monovalent anion selective membrane in the second stage of ED proved to be a feasible and cost-effective strategy for F- removal. The total recovery rate of F- was 81.4%, while the content of NH4F increased from 0.35 to 40.70%. The power consumption and current efficiency were also studied to evaluate the suitability of ED for the defluoridation of FGD slurry. CONCLUSION The separation and recovery of F- using the designed ED is cost-effective and efficient, and the process can be extended to other FGD techniques. (c) 2019 Society of Chemical Industry