Fluoride removal from brine with ion exchange resin

The presence of fluoride has caused a number of complications in various industrial applications. In the sodium sulfate salt splitting technology developed by NORAM Engineering and Constructors, the undesirable fluoride ions in brine solution could cause the breakdown of the protective passivation layer on the titanium anode, resulting in pit corrosion or spalling of the coating on the dimensionally stable anode (DSA). Conventionally, adsorbents such as activated alumina (AA), coagulation including calcium fluoride precipitation method, ion-exchange (IX), solvent extraction (SX), and reverse osmosis (RO) have been used to remove fluoride from solution. Of all the options, CaF2 precipitation method is the most commonly used to remove fluoride from solution. However, along with its slow nucleation, CaF₂ has a theoretical solubility limit of 8 ppm F- at stoichiometric concentration of calcium in wastewater [1]. Therefore, a different approach for a robust fluoride removal system is required. In this work, aluminum or zirconium was pre-loaded onto LANXESS Lewatit Monoplus TP 260 amino phosphonic acid functional group cation chelating resin. These resins were then used to selectively load fluoride from Na₂SO₄ brine solution. Preliminary batch isotherm studies revealed that aluminum can be readily loaded onto this resin type; however, the zirconium loading capacity was poor due to the solubility limit of zirconium where low pH inhibits an effective loading process. Subsequently, fluoride batch isotherm studies revealed that the maximum fluoride loading capacity of Al pre-loaded and Zr pre-loaded resin were 1.30 mol/kg Al-resin and 0.70 mol/kg Zr-resin from 12 wt.% Na2SO4 brine, respectively. However, in the column loading trials, an increase in fluoride loading capacity was recorded with Zr pre-loaded resin as the cycles of loading and regeneration continued. Most notably, Zr pre-loaded resin provided minimal metal leakage (Zr) during the sorption process while reducing the fluoride concentration below 0.5 mg/L throughout all the loading cycles.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat