Fe(II)-Catalyzed\nRecrystallization Drives Phosphorus\nand Aluminum Release from Goethite

Goethite often harbors impurities,\nsuch as phosphorus (P) and aluminum\n(Al), which are incorporated into its structure through direct substitution\nor coprecipitation with nanocrystalline phases. Understanding the\nprocesses that drive the release of P and Al from goethite is of paramount\nimportance for the iron ore industry and for managing nutrient and\npollutant behavior in the environment. This study investigates the\nimpact of Fe(II)-catalyzed recrystallization on the release of P and\nAl from goethite. We evaluated the solubility and extractability of\nP and Al in suspensions of Al- and P-coprecipitated goethite, treated\nwith <sup>57</sup>Fe-enriched Fe(II)<sub>aq</sub> under oxygen-free\nconditions for 30 days at neutral pH and room temperatures. The addition\nof Fe(II)<sub>aq</sub> induced the recrystallization of goethite dominant\ninitial synthetic phases (i.e., low P- and Al-containing phases) and\nthe transformation of higher P- and/or Al-bearing starting material\nthat was actually a mixture of goethite and minor amounts of lepidocrocite\nand feroxyhyte. Our results reveal that Fe(II)-catalyzed mineral and\nstructural evolution led to the repartitioning of P and, to a lesser\nextent, Al throughout the crystal structure, mineral surface, and\naqueous solution. Following a 30 day reaction with Fe(II)<sub>aq</sub>, we extracted approximately 80, 68.8, 73.9, and 83.2% of P from\nP-only, low, medium, and high P + Al goethite, respectively. Additionally,\nwe observed total Al removals of approximately 17, 27, and 25% from\nlow, medium, and high P + Al goethite, respectively. The results demonstrate\nthat treating both P-only and P + Al goethite with Fe(II) at room\ntemperature, followed by a 24 h extraction using 1 M NaOH, significantly\nenhances the overall extractability of P and Al, including both aqueous\nand surface-adsorbed fractions, compared to Fe(II)-free controls.\nThese findings advance our understanding of the recrystallization\nprocess and impurity substitution in goethite, offering promising\navenues for developing new environmentally friendly methods to extract\nP and other impurities from goethitic iron ores at lower temperatures.