Novel Selective Magnetic Metal Organic Framework (MOF) for Barium Removal from Oilfield Waters

Abstract Highly efficient capture of barium from produced water is a meaningful task in oilfield water management, such as for water disposal, irrigation or barium recycling. Here, we invented a barium trap made of magnetite Fe3O4 and a metal-organic framework (MOF) structure with sulfuric group modification. This magnetite Fe3O4@MOF material can remove over 90% barium selectively in high salinity produced water, regardless of other ion interferences. The magnetite Fe3O4 particles with COOH exposed surface were first prepared by FeCl2, FeCl3 and citric acid. The Fe3O4@Zr-BDC-NH2-SO4 material was prepared by mixing Fe3O4 particles with the ligand 2-aminoterephthalic acid and the ion Zr(SO4)2·4H2O. The materials assembly at 98 °C under stirring for 16 hours. After washing with water and ethanol, the material was dried at 60 °C overnight, and then characterized by XRD and SEM. In the adsorption experiment at room temperature, 0.6 g Fe3O4@Zr-BDC-NH2-SO4 MOF material was immersed in series of concentrations of barium in deionized water or high salinity water (TDS > 60,000 ppm) for 2 hour-incubation. The barium concentration was from 20 to 7,500 ppm. Barium concentration after the MOF treatment was measured by ICP-MS. In the structure of the Fe3O4@MOF material, the COOH is coordinated with Zr, then the MOF grows from Zr cluster. The sulfate anions modify the material by coordinating to the Zr cluster node with a monodentate O atom. SEM images show the Fe3O4 is around 100 nm and the final product is ~ 1 μm. The adsorption results in deionized water and produced water both shown that the adsorption amount of barium increase with initial barium concentration. At 7,500 ppm of barium concentration, the adsorption amount can be reached to 500 mg/g. And the adsorption curve presented that the highest value was not reached yet. It also indicates that the adsorption of barium is not affected by other ions in produced water because of the high selectivity of the sulfate functioned material. More importantly, the magnetic property makes the material easily to be attracted by a magnet and thus separated from water. This work provides a novel magnetic Fe3O4@MOF with very high barium uptake capacity, which surpasses most of reported adsorbents. It can selectively capture barium from high salinity oilfield waters.