Redox Reactions of Chromium, Copper, and Iron Mixtures in Contaminated Waters: Integration of Laboratory Experiments, Reactive Transport Modeling, Spectroscopy, and Electrochemical Sensing
Abstract
The goal of the proposed work is to investigate redox chemical reactions in complex fluids containing toxic mixtures of chromium (Cr) and copper (Cu), relevant environmental contaminants in waters and soils. This goal will be accomplished by the scientific objective of integrating state-of-the-art spectroscopy, aqueous chemistry, reactive transport modeling, and electrochemistry to investigate interactions of these contaminants with iron (Fe), the most abundant redox-active transition metal on earth. The significance of the proposed work provides an opportunity for the U.S. Army Research Office (ARO) to invest in high-risk cutting-edge research that is mission relevant and useful for fate and transport and remediation of redox active toxic metal mixtures in earth and environmental systems. The outcomes from this work will result in new geochemical mechanistic insights about electron transfer, chemical speciation, and kinetics in complex environmentally relevant reactions. Our overarching hypothesis is that Fe facilitates electron transfer causing the reduction of Cr and Cu in environmentally relevant conditions. The reduction of Cr and Cu can result in their adsorption onto and inclusion within Fe-minerals. The knowledge gained regarding redox speciation and mechanisms for the transformation of highly soluble Cr(VI) and Cu(II) can be translated to environmental systems containing mixtures of oxyanions (e.g., selenium, molybdenum, vanadate, arsenate, etc.) and Lewis acids (lead, cadmium, uranium, etc.). The organic ligand citrate will be used to enhance cation solubility as a simple analogue to natural organic matter (NOM). We will conduct experiments at pH 2 resembling waters affected by acid mine drainage, and pH 7 resembling well-buffered waters. The proposed experimental methods employed will systematically address redox mechanisms through the following aims: Aim 1: Investigate the kinetics of redox reactions for binary mixtures of Cr, Cu, and Fe in aqueous homogeneous solutions. Electrochemistry measurements will facilitate a better understanding of charge transfer kinetics which remains a gap in the environmental chemistry literature for redox active elements such as Cr, Cu, and Fe. Experiments will be conducted using linear sweep voltammetry, pulsed voltammetry and chronoamperometry to investigate redox speciation of systems containing mixtures of Cr and Cu. These electrochemical measurements will allow us to obtain chemical speciation via redox process potential determination and kinetic information of redox reactions. Aim 2: Investigate adsorption, precipitation, and ion exchange interfacial heterogeneous reactions of Cr and Cu mixtures with Fe solids and clay minerals. Batch experiments will be conducted to investigate the reaction of aqueous Cr and Cu with iron minerals (e.g., ferrihydrite, lepidocrocite, and jarosite) and the clay mineral montmorillonite. We will also conduct flow through experiments to investigate the competition of Cu and Cr ion exchange in montmorillonite. This experiment will integrate microscopy techniques (e.g., scanning and transmission electron microscopy), with spectroscopy (e.g. X-ray photoelectron spectroscopy), X-ray diffraction, aqueous chemistry, and reactive transport modeling. Aim 3: Reactive transport modeling of kinetic and chemical equilibrium data. The modeling of chemical speciation and kinetics with PFLOTRAN will allow us to validate data from Aims 1 and 2 with existing databases and estimated values resulting from this work. These results will facilitate the use of reactive transport modeling for predicting contaminant transport and remediation. This abstract is publicly releasable.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jun 25, 2021
- Source ID
- W911NF2110249
Entities
People
- José M. Cerrato
Organizations
- Army Contracting Command
- United States Army
- University of New Mexico