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We assessed the effect of redox conditions on the mobility of lead (Pb), copper (Cu), and iron (Fe) from sediments affected by acid mine drainage (AMD). This was accomplished by integrating laboratory microcosm experiments, aqueous chemistry, diffraction, and electron microscopy. Microcosm experiments underwent 3 consecutive 5 day redox phases: oxic-anoxicoxic. The sediments contained Fe (51,000 mg/kg), Pb (307 mg/kg), and Cu (30 mg/kg), and minerals such as Illite, albite, and goethite. Microscopy analyses revealed that Pb and Cu are associated with Al-silicates and jarosite. Iron release peaked under anoxic conditions (∼250 mg/L), then decreased in the second oxic phase (<70 mg/L). Extraction experiments confirmed that Pb and Cu are water-labile at pH 3.4 (Pb: 27 μg/L exceeding the United States Environmental Protection Agency drinking water action level of 15 μg/L, Cu: 75 μg/L), but less labile at pH 6.4 (Pb: 7 μg/L, Cu: 3 μg/L). DNA sequencing detected metal-tolerant fungal genera (Trichoderma, Fusarium, Penicillium, and Aspergillus) in the sediments. This study provides insights into the biogeochemical processes influencing the lability of metals in AMD-affected sites, which have relevant implications for risk assessment, remediation strategies, and recovery of critical minerals. 

The co-occurrence of uranyl and arsenate in contaminated water caused by natural processes and mining is a concern for impacted communities, including in Native American lands in the U.S. Southwest. We investigated the simultaneous removal of aqueous uranyl and arsenate after the reaction with limestone and precipitated hydroxyapatite (HAp, Ca10(PO4)6(OH)2). In benchtop experiments with an initial pH of 3.0 and initial concentrations of 1 mM U and As, uranyl and arsenate coprecipitated in the presence of 1 g L−1 limestone. However, related experiments initiated under circumneutral pH conditions showed that uranyl and arsenate remained soluble. Upon addition of 1 mM PO43− and 3 mM Ca2+ in solution (initial concentration of 0.05 mM U and As) resulted in the rapid removal of over 97% of U via Ca−U−P precipitation. In experiments with 2 mM PO4 3− and 10 mM Ca2+ at pH rising from 7.0 to 11.0, aqueous concentrations of As decreased (between 30 and 98%) circa pH 9. HAp precipitation in solids was confirmed by powder X-ray diffraction and scanning electron microscopy/energy dispersive X-ray. Electron microprobe analysis indicated U was coprecipitated with Ca and P, while As was mainly immobilized through HAp adsorption. The results indicate that natural materials, such as HAp and limestone, can effectively remove uranyl and arsenate mixtures. 

The objective of this study was to investigate the application of manganese oxide [MnO x(s) ] and granular activated carbon (GAC) media for the removal of caffeine and acetaminophen from water. Organic contaminants of emerging concern represent a developing issue due to their effects on human health and the environment. Manganese oxides are effective for water treatment because of their ability to mediate adsorption and oxidation–reduction reactions for many organic and inorganic constituents. Laboratory scale column experiments were performed using different combinations of commercial MnO x(s) and GAC for assessing the removal of caffeine and acetaminophen, and the subsequent release of soluble Mn due to the reductive dissolution of MnO x(s) . The removal of acetaminophen was detected for all media combinations investigated. However, the removal of caffeine by adsorption only occurred in columns containing GAC media. There was no removal of caffeine in columns containing only MnO x(s) media. Manganese release occurred in columns containing MnO x(s) media, but concentrations were below the secondary drinking water standard of 50 μg L −1 set by the US Environmental Protection Agency. Soluble Mn released from a first process by MnO x(s) media column was removed through adsorption into the GAC media used in a second process. The results of this investigation are relevant for implementation of MnO x(s) and GAC media combinations as an effective treatment process to remove organic contaminants from water.