The global demand for lithium has increased due to the recent boom in the electric vehicle industry, and new resources are necessary to meet the growing demand. The lithium concentration in flowback and produced water (FPW) from the oil and gas industry often range from 50-100 ppm and is an untapped lithium resource that would otherwise be considered wastewater. Manganese-based sorbents have the potential for selective separation of lithium from FPW, with lithium uptake in the range 20-40 mg Li per g of sorbent. Previous work from our research group indicates that organic materials and H2S present in FPW reduce manganese during the lithium extraction process, leading to manganese loss from the sorbent through reductive dissolution. The reduced Mn dissolves into acid during the desorption process. In this study, we synthesized nanoparticles of Li1.6Mn1.6O4 through a co-precipitation method; sorbents were coated with zirconium(IV) dioxide to inhibit manganese reduction and increase the sorbent recyclability. The sorbent was coated using different amounts of Zr-butoxide solution using a solvent casting method. The final product was obtained by calcinating the Zr-coated Li1.6Mn1.6O4 to form ZrO2. The extent of lithium extraction and manganese loss were studied for both bare and coated sorbents with both field-collected FPW and synthetic brine (100ppm LiOH solution). The results show that the manganese loss in synthetic brine is less than 1%, whereas it is more than 5% in FPW for bare sorbents. This shows that organic compounds, likely containing phenolic groups, and other compounds such as H2S found in FPW reduce manganese, leading to a reduction in the chemical stability of the sorbent and ultimately manganese loss. The zirconium coating acts as a physical barrier, decreasing the reductive dissolution of Mn, which is supported by experimental observation of 50% less Mn loss from coated sorbents while the Li+ uptake remained the same. To have a more uniform sorbent size distribution, we also ground the sorbents prior to coating into bins of size &lt;75, 75-250, 250-500, and &gt;500µm, and compared them to unsorted powder with a broad range of particle sizes. The &lt;75µm coated sorbent had ~20% higher uptake while the manganese loss remained similar to unsorted coated sorbents. The results from this study indicate that coating of Mn-based sorbents with ZrO2 reduces sorbent loss and is a promising technique to increase the durability of lithium ion-exchange materials.

Lithium extraction from flowback and produced water using ion-exchange sorbents

ACS Spring 2022

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