(102a) Synthesizing Lithium Sorbents Using Coal Mine Drainage Solids

Lithium (Li) is a critical mineral essential in many of emerging clean energy technologies. Direct extraction of Li from geothermal brines and oil/gas produced water is a distinctively more sustainable approach than hardrock leaching and evaporation pond extraction with respect to land, water, and energy uses. Inorganic molecular sieve sorbent, such as lithium manganese oxide (LMO) and lithium aluminum layered double hydroxide chloride (Li/Al LDH), is currently the most technologically advanced method for direct lithium extraction. Hydrogen manganese oxide (HMO), an ion sieve derived from LMO, has shown superior capacity and selectivity towards lithium. In this study, we prepared HMO from coal mine drainage (CMD) solids and examined the practicability of recovering Li from oil and gas produced waters and geothermal brines. We aim to innovate high-value added products from the existing extract REEs and CMs processing chain of legacy byproducts associated with coal production. CMD solids, which are precipitates collected from exhausted limestone gravels of passive CMD treatment beds, are enriched in rare earth elements (REEs) and other critical minerals (CMs), and therefore, considered as a viable alternative source for REEs/CMs to supply the Nation’s demands. A patented extraction process developed by NETL (TREE^®) has been demonstrated as a cost-effective and efficient approach to recover REEs/CMs from CMD solids. Here, we selected residuals of CMD solids from the TREE® process that are enriched in manganese (Mn) (>20% w/w) and successfully prepared LMO using a solid-state method modified from Yoshizuka et al. (2002). HMO sorbent was then obtained from the LMO precursor after replacing Li⁺ with H⁺ in a 0.1M hydrochloric acid (HCl) solution. Formation of spinel manganese oxide in the CMD-derived HMO sorbents was identified by X-ray diffraction analysis and Raman spectroscopy. By characterizing the adsorption of Li at three pH levels, i.e., 2.8±0.3, 7.0±0.7, and 9.7±0.5, we demonstrated the maximum adsorption capacity of a selected CMD-derived HMO sorbent, determined by fitting the Langmuir isotherm model, is similar to that of an HMO sorbent prepared from pure chemical reagents across a wide range of pH conditions. We demonstrate it is technically feasible to beneficially use the high-volume/low-value mineral residuals from REE/CM extraction to produce highly selective HMO sorbent for direct Li extraction. We continue to modify LMO synthesis conditions, e.g., Li-to-Mn ratio, calcination temperature and duration, and CMD solid feedstocks, to maximize the adsorption capacity of the CMD-derived HMO sorbent, whose adsorption selectivity in a solution with more complex constituent matrix, i.e., synthetic and actual geothermal brine and produced water, will be further characterized.