An Effective Metal Organic Framework (MOF) for Selective Barium Removal from Oil Field Waters

Highly efficient capture of barium from oil field produced water is a meaningful task in water treatment, such as for water disposal, irrigation or barium recycling. Here, we propose a barium trap with metal-organic framework (MOF) modified by strong barium combining group (sulfate and sulfonic acid group). This MOF material can remove > 90% barium selectively in high salinity produced water, regardless of the ion interferences. The Zr-BDC-NH2-SO4 material was prepared by 2-aminoterephthalic acid and Zr(SO4)2·4H2O assembly at 98 ºC under stirring for 16h. After washing with water and ethanol, the material was dried at 60 ºC overnight, and then characterized by XRD and SEM. In the adsorption experiment at room temperature, 0.2 g 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’s incubation. The barium concentration was from 20 to 5,000 ppm. Barium concentration after Zr-BDC-NH2-SO4 removed was measured by ICP-MS. In the theoretical structure of the MOF material, the sulfate anions located around the Zr6-cluster in Zr-BDC-NH2-SO4, and the sulfate anions are coordinated to the Zr6 inorganic node by a monodentate O atom. The sulfate anions in Zr-BDC-NH2-SO4 is fully exposed, indicating that Zr-BDC-NH2-SO4 will be easier to bind with Ba2+ ions. The adsorption results in deionized water shown that the adsorption amount of barium increase with initial barium concentration. At 5,000 ppm, the amount can be as large as 200 mg/g. And the adsorption curve was linear and did not reach the highest value yet. More importantly, the adsorption amount in produced water is almost the same comparing to deionized water, indicating that the adsorption of barium is not affected by salts in produced water because of the high selectivity of the sulfate functioned material. This work provides a remarkable, sulfate group functionalized MOF with very high barium uptake capacity which surpasses most of reported adsorbents. It can selectively capture barium from high salinity oil field waters.