A novel recyclable nano-adsorbent for enhanced oil recovery with efficient removal of Ca2+ and Cr6+ from oilfield wastewater

Oilfield wastewater has a significantly negative influence on the recovery efficiency due to its hypersalinity. Therefore, magnetic graphene oxide (GO) modified with ethylene diamine tetraacetic acid (EDTA) and grafted by polyethylene glycol (PEG) nano-adsorbent was prepared to remove the Ca 2+ and Cr 6+ in Jidong Oilfield wastewater specifically. It was noteworthy that PEG- g -EDTA/Fe 3 O 4 /GO nano-adsorbent had excellent adsorption performance, with removal ratios up to 71.6% for Ca 2+ and 42.7% for Cr 6+ at 30 min. After the fifth recycling run, the nano-adsorbent still remained with high removal ratios (69.3% for Ca 2+ and 30.5% for Cr 6+ ) and high reuse rates (89.4% for Ca 2+ and 95.2% for Cr 6+ ), indicating that the nano-adsorbent had outstanding adsorption-desorption efficacy and high reusability. The adsorption test results demonstrated that the total salinity of the treated oilfield wastewater decreased by about 5,000 ppm, and the displacement efficiency further increased by 12.5% by chemical flooding compared with the untreated wastewater. Therefore, PEG- g -EDTA/Fe 3 O 4 /GO nano-adsorbent is an adsorbent with excellent potential which can effectively remove Ca 2+ and Cr 6+ in oilfield wastewater to enhance oil recovery (EOR).