Removal of fluoride from zinc sulfate solution by in situ Fe(III) in a cleaner desulfuration process

Abstract

The desulfuration of fume gas using ZnO slurry is a cleaner process because the SO2 from exhaust is transformed to a valuable ZnSO4 solution, and the ZnSO4 solution can then be reused in industrial processes. However, the existence of fluoride (F) in the cleaner process severely hinders the reuse of the ZnSO4 solution. In this study, an innovative, targeted and simple technique using in situ Fe(III) in the actual ZnSO4 waste liquid for the removal of F was proposed. The results indicated that in situ Fe(III) exhibited a good performance in the removal of F and an increase of Fe concentration is beneficial to the removal of F. The active component in the removal of F was identified as a type of hydroxylation ferric sulfate, schwertmannite, which formed under the strong acidic condition. The removal mechanism of F was recognized as an ionic-exchange with the OH− groups from coordinated FeOH−1/2 and Fe2OH0 and SO42− groups in schwertmannite as well as electrostatic adsorption interactions. Based on above principle, the concentration of F in the actual ZnSO4 solution was successfully reduced to below 50 mg/L, bringing the ZnSO4 solution up to the recycling standard. This research can be used to guide the effective removal of F from the waste liquid with high acidity, salinity and heavy metals, in the practice.