(142e) Selective Removal of Selenium from High-Salinity Wastewater Using Metal-Organic Frameworks

Selenium shows the tendency of bioaccumulation in the food chain and shortens the life span of aquatic and wild animals. The concentration of selenium greater than 0.05 ppm is hazardous to human health; hence, removing it from drinking water is crucial. In addition, selenium is one of the components of the produced water (the waste stream in the oil extraction process with high salinity (ranging from 5000 ppm to 300 ppt)), which limits the reuse of the treated stream. Metal-organic frameworks (MOFs) are gaining significant attention recently as adsorbents due to their high porosity, tunability, and selectivity. In this study, the nickel-based ionic MOF (Ni-iMOF), zirconium-based MOF (MOF-808), iron MOF(Fe-MOF), copper MOF (Cu-MOF), and graphene oxide immobilized MOFs (GO-Fe-MOF and GO-Cu-MOF) were synthesized via different methods (such as solvothermal and acid-free-nonthermal process) using several metal salts and ligands and examined for the removal of selenium from water and saline water. The isotherm adsorption tests were conducted for all the MOFs (500 ppm) with 60 ppm selenium. The Ni-iMOF showed 15.48% selenite and 26.36% selenate removal, MOF-808 showed 62.44% selenite and 37.54% selenate removal, Fe-MOF showed 44.14% selenite and 1.53% selenate removal, GO-Fe-MOF showed 40.76% selenite and 1.64% selenate removal, Cu-MOF showed 1.18% selenite and 1.02% selenate removal and lastly, GO-Cu-MOF showed 0.82% selenite and 0.78% selenate removal. Among all the MOFs, the MOF-808 and Fe-MOF showed better adsorption of selenite and selenate in water. The better performance of MOF-808 is attributed to the coordination bonding between the charged metal in the MOF nodes and selenite and selenate molecules. To envisage the selectivity of MOFs toward selenium and selenate, isotherm adsorption tests were conducted in the presence of different salts (Na₂SO₄ (2000 ppm) and NaHSO₃ (2000 ppm)) for MOF-808 and Fe-MOF. The data shows that MOF-808 could remove 53.55% of selenite and 2.15% of selenate in the presence of Na₂SO₄ (2000 ppm), whereas it could remove 5.2% of selenite and 1.26% of selenate in the presence of NaHSO₃ (2000 ppm) salt in water. Similarly, Fe-MOF could remove 41.33% of selenite and 1.41% of selenate in the presence of Na₂SO₄ (2000 ppm) and it could remove 22.52% of selenite and 16.09% of selenate in the presence of NaHSO₃ (2000 ppm) from water. The effect of different experimental parameters such as pH (2-10), temperature (25-65°C), and initial adsorbate concentration ( 0.1-61 ppm) on the adsorption capacity of MOFs are currently under investigation.