| Summary: | Acid mine drainage (AMD) is characterized by low pH, high soluble Fe, and heavy metal concentrations. Conventional lime neutralization produces large amounts of Fe(OH)<sub>2</sub> and Fe(OH)<sub>3</sub>, which complicate subsequent disposal. Secondary iron minerals synthesized by biomineralization can reduce the concentration of soluble Fe in addition to adsorbing and removing heavy metals in AMD. Therefore, an appropriate method for improving the precipitation efficiency of Fe is urgently needed for AMD treatment. Using simulated AMD, this work analyzes the influence of quartz sand (40 g/L) on the Fe<sup>2+</sup> oxidation and total Fe deposition efficiencies, as well as the phases of secondary iron minerals in an <i>Acidithiobacillus ferrooxidans</i> system including K<sup>+</sup>, Na<sup>+</sup>, or NH<sub>4</sub><sup>+</sup> (53.3 mmol/L). Quartz sand had no significant effect on Fe<sup>2+</sup> oxidation and 160 mmol/L Fe<sup>2+</sup> was completely oxidized by <i>A. ferrooxidans</i> in 168 h, but contributed to the oxidized product (Fe<sup>3+</sup>) mineralization, improving the total Fe removal efficiency in simulated AMD. Compared with treatments involving K<sup>+</sup> or Na<sup>+</sup> alone, quartz sand improved the total Fe precipitation efficiency by 26.6% or 30.2%, respectively. X-ray diffraction showed that quartz sand can promote the transformation of the biomineralization pathway from schwertmannite to jarosite with higher yields, which is important for improving the removal efficiency of heavy metals in AMD.
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