Lithium recovery from hydraulic fracturing flowback and produced water using a selective ion exchange sorbent

Abstract

Increased demand for lithium products for use in lithium-ion batteries has led to a search for new lithium resources in recent years to meet projected future consumption. One potential lithium resource is low lithium bearing brines that are discharged from hydraulically fractured oil and gas wells as flowback and produced water (FPW). In this way, hydraulic fracturing presents an opportunity to turn what is normally considered wastewater into a lithium resource. In this research, two manganese-based lithium-selective adsorbents were prepared using a co-precipitation method and were employed for lithium recovery from FPW. At optimized conditions, lithium uptake reached 18 mg g−1, with a > 80% lithium recovery within 30 min. The recovered lithium was isolated and concentrated to 15 mM in an acidic final product. The degree of sorbent loss during acid desorption of lithium was significantly higher for sorbents used in the FPW as compared to recovery from a synthetic lithium-bearing brine (4.5% versus 0.8%). Thus, we propose that organic molecules present in the FPW reduce manganese in the sorbent structure during lithium sorption, leading to increased sorbent loss through reductive dissolution. Systematic characterization including wet chemical manganese valence measurements, along with EXAFS, XPS, and TEM-EELS show that exposure to FPW causes tetravalent manganese in the bulk sorbent structure to be reduced during lithium sorption, which subsequently dissolves during acid desorption. Partial removal of these organic molecules by nanofiltration leads to decreased sorbent dissolution in acid. In this way, we show that dissolved organic molecules represent a critical control on the reductive dissolution of manganese-based lithium ion exchange sorbents. This research provides promising results on the use of manganese-based lithium sorbents in FPW.