Charles A. Cravotta Stephen C. Peters Jill E. Burrows 2017 <p id="abspara0010">Net-alkaline, anoxic coal-mine drainage containing ∼20&nbsp;mg/L Fe^II and ∼0.05&nbsp;mg/L Al and Zn was subjected to parallel batch experiments: control, aeration (Aer 1 12.6&nbsp;mL/s; Aer 2 16.8&nbsp;mL/s; Aer 3 25.0&nbsp;mL/s), and hydrogen peroxide (H₂O₂) to test the hypothesis that aeration increases pH, Fe^II oxidation, hydrous Fe^III oxide (HFO) formation, and trace-metal removal through adsorption and coprecipitation with HFO. During 5.5-hr field experiments, pH increased from 6.4 to 6.7, 7.1, 7.6, and 8.1 for the control, Aer 1, Aer 2, and Aer 3, respectively, but decreased to 6.3 for the H₂O₂ treatment. Aeration accelerated removal of dissolved CO₂, Fe, Al, and Zn. In Aer 3, dissolved Al was completely removed within 1&nbsp;h, but increased to ∼20% of the initial concentration after 2.5&nbsp;h when pH exceeded 7.5. H₂O₂ promoted rapid removal of all dissolved Fe and Al, and 13% of dissolved Zn.</p><p id="abspara0015">Kinetic modeling with PHREEQC simulated effects of aeration on pH, CO₂, Fe, Zn, and Al. Aeration enhanced Zn adsorption by increasing pH and HFO formation while decreasing aqueous CO₂ available to form ZnCO₃⁰ and Zn(CO₃)₂²⁻ at high pH. Al concentrations were inconsistent with solubility control by Al minerals or Al-containing HFO, but could be simulated by adsorption on HFO at pH&nbsp;&lt;&nbsp;7.5 and desorption at higher pH where Al(OH)₄⁻ was predominant. Thus, aeration or chemical oxidation with pH adjustment to ∼7.5 could be effective for treating high-Fe and moderate-Zn concentrations, whereas chemical oxidation without pH adjustment may be effective for treating high-Fe and moderate-Al concentrations.</p> application/pdf 10.1016/j.apgeochem.2016.12.019 en International Association of Geochemistry and Cosmochemistry Enhanced Al and Zn removal from coal-mine drainage during rapid oxidation and precipitation of Fe oxides at near-neutral pH article