A robust approach for sustainable removal and recovery of fluoride via cryolite crystallization in an enhanced electrocoagulation process

Owing to the decrease in fluorite reserves and ineffective fluorine resource recovery, cryolite is considered for its potential in fluorine recovery. In this study, we explored the optimal conditions for an electrocoagulation (EC) system using aluminum electrodes for fluoride removal and recovery from simulated semiconductor wastewater through cryolite crystal formation. The investigated conditions include the pH, NaCl concentrations in the electrolyte, initial fluoride concentrations, and effects of co-existing anions. The results indicate that fluoride was effectively removed in the initial acidic conditions at pH = 3 after 20 min of reaction. F removal in EC in the presence of anions is influenced by their affinity for Al³⁺ as the order SO₄²⁻ > NO₃⁻ > Cl⁻. In addition, the cryolite obtained from the experiment with 7 g L⁻¹ NaCl concentration in the electrolyte solution exhibited substantial aluminum (32.61 wt%), fluorine (35.9 wt%), and sodium (11.11 wt%) content. Together, it emphasizes that the energy consumption and the average electrode consumption were determined to be 0.22 kWh m⁻³ and 0.105 kg m⁻³, respectively.