FEASIBILITY OF CRITICAL METALS RECOVERY FROM PETROLEUM PRODUCED WATER BY DOLOMITE

Produced water (PW) from oil and gas reservoirs poses environmental and technical challenges due to its elevated concentrations of dissolved salts (mostly NaCl) and toxic metals. However, PW from some oil and gas reservoirs also contain minable quantities of critical metals. This study stems from the growing demand for critical metals such as Li, and previous results we obtained showing that dolomite has superior capacity to remove toxic metals commonly present in PW than other rock materials. In previous studies we explored dolomite's efficiency to remove divalent toxic metals (e.g., Ba, Sr, Cd, and Pb) from PW, but the influence and removal of monovalent cations such as Li by dolomite remains understudied. To bridge this knowledge gap, we conducted column-flow (filtration) experiments using synthetic PW of various compositions and filters made of dolomite grains. Samples were taken at the completion of each filtration cycle to monitor aqueous phase changes. Dolomite grain samples were taken from the top, middle, and bottom of the dolomite filter at the completion of each experiment to analyze changes in the mineral phase. ICP-EOS was used to examine the aqueous phase, and X-ray diffraction and SEM-EDS were used to investigate the mineral phase. As the pH increased, the aqueous phase results demonstrated that toxic and critical elements such as Ba, Sr, Cd, Li, and Co were decreasing at every filtration cycle. Furthermore, the mineral phase analysis using SEM-EDS detected precipitates on the dolomite grain surface, while the XRD spectra revealed presence of carbonate mineral phases like Strontianite (Ca-bearing), Lithium Barium Rutherium Oxide, Calcite (Mg-bearing), and Spodumene (Li-bearing). Thus far, this study has demonstrated that dolomite filtration is an effective and inexpensive alternative of removing not only divalent toxic metals but also monovalent critical metals. The findings help to address environmental issues as well as possible prospects for critical metals recovery from PW.