Enhanced Al and Zn removal from coal-mine drainage during rapid oxidation and precipitation of Fe oxides at near-neutral pH

Jill E. Burrows; Charles A. Cravotta; Stephen C. Peters

doi:10.1016/j.apgeochem.2016.12.019

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Enhanced Al and Zn removal from coal-mine drainage during rapid oxidation and precipitation of Fe oxides at near-neutral pH

Jill E. Burrows·Charles A. Cravotta·Stephen C. Peters

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Abstract

Net-alkaline, anoxic coal-mine drainage containing ∼20 mg/L Fe II and ∼0.05 mg/L Al and Zn was subjected to parallel batch experiments: control, aeration (Aer 1 12.6 mL/s; Aer 2 16.8 mL/s; Aer 3 25.0 mL/s), and hydrogen peroxide (H 2 O 2 ) 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 H 2 O 2 treatment. Aeration accelerated removal of dissolved CO 2 , Fe, Al, and Zn. In Aer 3, dissolved Al was completely removed within 1 h, but increased to ∼20% of the initial concentration after 2.5 h when pH exceeded 7.5. H 2 O 2 promoted rapid removal of all dissolved Fe and Al, and 13% of dissolved Zn. Kinetic modeling with PHREEQC simulated effects of aeration on pH, CO 2 , Fe, Zn, and Al. Aeration enhanced Zn adsorption by increasing pH and HFO formation while decreasing aqueous CO 2 available to form ZnCO 3 0 and Zn(CO 3 ) 2 2− 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 < 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.

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Applied Geochemistry Article

Source-reported bounding extent: 40.677904184859585° to 40.72631561468468° latitude; -76.38570785522461° to -76.30159378051758° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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Jill E. Burrows, Charles A. Cravotta, Stephen C. Peters. 2017. Enhanced Al and Zn removal from coal-mine drainage during rapid oxidation and precipitation of Fe oxides at near-neutral pH. https://doi.org/10.1016/j.apgeochem.2016.12.019

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