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Acid mine drainage (AMD) has been identified as a viable secondary resource of Co, and Mn. However, recovery of these elements while treating AMD is challenging due to the unfavorable pH and Eh conditions for Co-Mn precipitation. This study investigated the effects of various ligands (hydroxide, carbonate, ammonium, sulfate, and phosphate) and oxidizers (sodium persulfate, potassium permanganate, and ozone) on the precipitation of Co-Mn from AMD through experimental and solution chemistry studies. Ozone was found to be the most effective agent for the recovery of these elements. Based on the results, an AMD treatment process was formulated for selective recoverymore » of multiple critical elements, including Al, REEs, Co, and Mn. More than 95 % of Co and Mn were recovered through the proposed process utilizing chemical-less ozone oxidative precipitation. In conclusion, a precipitate containing 0.9 % Co and 54.6 % Mn was obtained from an AMD source containing 0.9 ppm Co and 41.8 ppm Mn.« less

The majority of rare earth elements (REEs) in coal fly ash (CFA) are associated with the aluminosilicate glassy phase, hindering their solubility in the acid leaching process. In this study, a sequential chemical roasting, water leaching, and acid leaching process was developed for the recovery of REEs from CFA. The effect of several roasting additives on the transformation of CFA phases into water or acid soluble phases was first studied. The reaction conditions for chemical roasting were selected based on a thermodynamic analysis. The selected reaction conditions were then validated experimentally. NaOH and Na₂CO₃ were the most effective additives tomore » break the glassy phases to sodium silicate and sodium aluminosilicate, which can then be readily dissolved in water or acid. The reactions with NaOH was found to be spontaneous at ambient temperatures, while the reactions with Na₂CO₃ were spontaneous at elevated temperatures. Water leaching was very effective for the dissolution of the sodium silicate product, removal of the majority of silica, and for turning the glassy phases into a porous structure. As a result, mass transfer limitations were reduced, and acid could easily diffuse into the particles, dissolve the majority of remaining, and extract REEs along with other elements such as Al. In closing, this process significantly enhanced the REE recovery to 79% and 89% using NaOH and Na₂CO₃ roasting, respectively, compared to 20% REE recovery in baseline acid leaching.« less