title: The precipitation of indium at elevated pH in a stream influenced by acid mine drainage.
abstract: Indium is an increasingly important metal in semiconductors and electronics and has uses in important energy technologies such as photovoltaic cells and light-emitting diodes (LEDs). One significant flux of indium to the environment is from lead, zinc, copper, and tin mining and smelting, but little is known about its aqueous behavior after it is mobilized. In this study, we use Mineral Creek, a headwater stream in southwestern Colorado severely affected by heavy metal contamination as a result of acid mine drainage, as a natural laboratory to study the aqueous behavior of indium. At the existing pH of ~3, indium concentrations are 6-29μg/L (10,000× those found in natural rivers), and are completely filterable through a 0.45μm filter. During a pH modification experiment, the pH of the system was raised to >8, and >99% of the indium became associated with the suspended solid phase (i.e. does not pass through a 0.45μm filter). To determine the mechanism of removal of indium from the filterable and likely primarily dissolved phase, we conducted laboratory experiments to determine an upper bound for a sorption constant to iron oxides, and used this, along with other published thermodynamic constants, to model the partitioning of indium in Mineral Creek. Modeling results suggest that the removal of indium from the filterable phase is consistent with precipitation of indium hydroxide from a dissolved phase. This work demonstrates that nonferrous mining processes can be a significant source of indium to the environment, and provides critical information about the aqueous behavior of indium.
authors.affiliation: Dept. of Civil and Environmental Engineering, MIT, Cambridge, MA, United States; Dept. of Environmental Health, Harvard T.H. Chan School of Public Health, Boston, MA, United States; Dept. of Geosciences, Princeton University, Princeton, NJ, United States. Electronic address: sjowhite@princeton.edu.
authors.forename: Sarah Jane O
authors.initials: SJO
authors.lastname: White
authors.affiliation: Dept. of Civil and Environmental Engineering, MIT, Cambridge, MA, United States.
authors.forename: Fatima A
authors.initials: FA
authors.lastname: Hussain
authors.affiliation: Dept. of Civil and Environmental Engineering, MIT, Cambridge, MA, United States.
authors.forename: Harold F
authors.initials: HF
authors.lastname: Hemond
authors.affiliation: Dept. of Chemical and Biological Engineering, Princeton University, Princeton, NJ, United States.
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Sacco
authors.affiliation: Dept. of Environmental Health, Harvard T.H. Chan School of Public Health, Boston, MA, United States.
authors.forename: James P
authors.initials: JP
authors.lastname: Shine
authors.affiliation: US Geological Survey, Boulder, CO, United States.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Runkel
authors.affiliation: US Geological Survey, Denver, CO, United States.
authors.forename: Katherine
authors.initials: K
authors.lastname: Walton-Day
authors.affiliation: US Geological Survey, Salt Lake City, UT, United States.
authors.forename: Briant A
authors.initials: BA
authors.lastname: Kimball
keywords: Aqueous behavior; Emerging metal contaminant; Environmental cycling; Freshwater; River; Sorption