Enhanced Al and Zn removal from coal-mine drainage during rapid oxidation and precipitation of Fe oxides at near-neutral pH. (March 2017)

• Record Type: Journal Article
• Authors: Burrows, Jill E.; Cravotta, Charles A.; Peters, Stephen C.
• Is Part Of: Applied geochemistry. Volume 78(2017:Mar.)
• Page Start: 194
• Page End: 210
• Publication Date: 2017-03
• Subjects: PHREEQC modeling -- Fe oxidation kinetics -- CO2 outgassing -- Metals adsorption -- Coprecipitation -- Carbonate complexing; Environmental geochemistry -- Periodicals; Water chemistry -- Periodicals; Geochemistry -- Social aspects -- Periodicals; Geochemistry -- Periodicals; 551.9
• DOI: 10.1016/j.apgeochem.2016.12.019
• Languages: English
• ISSNs: 0883-2927

Abstract

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 (H2 O2 ) 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 H2 O2 treatment. Aeration accelerated removal of dissolved CO2, 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. H2 O2 promoted rapid removal of all dissolved Fe and Al, and 13% of dissolved Zn. 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 ZnCO3 0 and Zn(CO3 )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. Highlights: PHREEQC kinetics model simulates changes in pH, dissolved O2, CO2, Fe, Al, and Zn. Fe oxidation, HFO formation, and Al and Zn attenuation vary with pH. Adsorption by HFO was the main removal mechanism for Al and Zn, not coprecipitation. CO2 outgassing increased pH, with Al(OH)4 − formation and Al desorption at pH > 7.5.