Suitability Study of Carbon-Based Sorbents for Critical Mineral Recovery from Oil and Gas Produced Water

Produced water (PW) generated from wells during crude oil production contains various inorganic chemicals some of which are considered critical minerals (CM). Through fluid characterization studies of 33 produced water samples in the Bakken Petroleum System of North Dakota, the Energy & Environmental Research Center (EERC) has quantified several CM, including barium, lithium, zinc, magnesium, manganese, and rubidium, at more than 95% frequency with cesium in 9% of the samples. The aim of this study was to test various carbon materials to ascertain their ability to remove these CM from the PW. Carbon materials such as biochar, leonardite, and coal-based materials such as lignite and activated carbon (AC) were obtained and tested. Batch experiments were performed with PW and sorbents to evaluate sorption conditions such as pH, kinetics, sorbent-to-water ratio, and sorbent properties for their suitability for CM recovery. Among the sorbents, coal-based activated carbon had the highest recovery of CM, especially barium, magnesium, manganese, and zinc, between 60% and near 100% at neutral and acidic pH. Brunauer-Emmett-Teller (BET) studies showed that activated carbon had the best sorption properties such as porosity and surface area, which validated these results. Recovery efficiency of sorbents increased in synthetic water that was spiked with only the previously mentioned CM and no other salts added. With activated carbon as the sorbent in the synthetic water, the recovery of barium, magnesium, manganese, and zinc was near 100% and the recovery of lithium, cesium, and rubidium was above 50%. The near 100% capture from the solution is evidenced by the level of the mineral in the solution after interaction with the AC that was below instrument detection level.