Grantee Research Project Results
2004 Progress Report: Solubilization of Particulate-Bound Ni(II) and Zn(II)
EPA Grant Number: R828771C012Subproject: this is subproject number 012 , established and managed by the Center Director under grant R828771
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: Center for the Study of Childhood Asthma in the Urban Environment
Center Director: Hansel, Nadia
Title: Solubilization of Particulate-Bound Ni(II) and Zn(II)
Investigators: Stone, Alan T.
Institution: The Johns Hopkins University
EPA Project Officer: Aja, Hayley
Project Period: October 1, 2001 through September 30, 2007
Project Period Covered by this Report: October 1, 2003 through September 30, 2004
RFA: Hazardous Substance Research Centers - HSRC (2001) Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management
Objective:
Models currently used to manage metal-contaminated sites currently have three principal shortcomings: (1) toxic metal speciation in many instances is under kinetic control rather than thermodynamic control; (2) host solids are often reworked by precipitation/dissolution reactions such that toxic metal ions are “buried” and hence physically inaccessible; and (3) soil organic constituents are difficult to characterize and hence difficult to account for. The objective of this research project is to perform carefully designed laboratory experiments to gain specific, quantitative information about these three phenomena. Our work will focus on the dissolution of NiO(s) and the desorption of Ni(II) and Zn(II) from FeOOH (goethite) and Fe(OH)3 (amorphous) surfaces. We are aided in this research by capillary electrophoresis (CE), which allows us to monitor processes taking place in aqueous solutions, and by high resolution transmission electron microscopy (HRTEM), which allows us to see surface structural changes.
Progress Summary:
Orthophosphate, which we have previously employed as the electrolyte buffer for the CE analysis of Ni(II) and Fe(III), is a moderate complexant and has the potential of altering speciation while electromigration is taking place. To get the best possible speciation information from our experiments, we have investigated using MOPS as the CE buffer. In an electropherogram obtained using an equilibrated solution of the aminocarboxylate chelating agent HEDTA (N-(2-hydroxyethyl)ethylenediamine-triacetic acid), Ni(II), and Fe(III), peaks corresponding to free HEDTA, Fe(III)-HEDTA, and Ni(II)-HEDTA are readily distinguished. The change in peak area when the detection wavelength is shifted from 214 nm to 244 nm allows the three peaks to be identified. Absorbance by free chelating agent is limited to very low wavelengths; absorbance by Fe(III) complexes exhibits the widest range of wavelengths.
We have conducted kinetic experiments by allowing Ni(II) 24 hours of contact with FeOOH (goethite), and then adding a chelating agent which solubilizes Ni(II) via ligand-assisted desorption and Fe(III) via ligand-assisted dissolution.
Figure 1 shows loss of free HEDTA, production of Ni(II)-HEDTA, and production of Fe(III)-HEDTA as a function of time. It is interesting to note that Ni(II)-HEDTA concentration reaches a maximum, then decreases. The source term, as mentioned, is ligand-assisted desorption. The sink term is interesting. Clearly, “metal ion exchange” is taking place; Fe(III) is displacing Ni(II) within the HEDTA complex. Owing to the low solubility of unchelated Fe(III) species, this displacement reaction likely takes place at the FeOOH (goethite)-water interface.
Results from a preliminary experiment with nitrilotriacetic acid (NTA) are shown in Figure 2. The 1:1 Fe(III)-NTA complex is electrically neutral and, therefore, not readily quantified using our existing CE technique. (We will have to develop an alternative technique for monitoring this complex.) The fact that NTA solubilizes Ni(II) more slowly than HEDTA is reasonable, given the fact that the two ligands adsorb to FeOOH(goethite) to about the same extent, but the equilibrium constants (K values) for Ni(II)-NTA complexes are lower than for Ni(II)-HEDTA complexes.
Future Activities:
The experiments we have performed so far are illustrative of “contaminant mixture” scenarios that will occur at some contaminated sites. It also is important to include chelating agents that occur naturally. We would like to do experiments with deoxymugineic acid, a siderophore released by the growing roots of some grass species. Although deoxymugineic acid possesses the same Lewis Base functional groups as HEDTA, they are arranged within the molecular structure quite differently. Indeed, inclusion of a half-dozen or more chelating agents with the same Lewis Base functional groups yet different molecular structure will be needed to systematically compare factors controlling Ni(II) desorption and those controlling Fe(III) dissolution.
Metal-mobilizing redox processes also are important. After the Ni(II) plus FeOOH(goethite) contact period, we could spike suspensions with Fe(II). Some Ni(II) desorption is expected arising from competitive adsorption with Fe(II) for available surface sites. Any Fe(III)-Fe(II) electron transfer could alter this, however, by burying the reduced iron within particle interiors, or by creating mixed Fe(III)/Fe(II) or “magnetite-like” surface layers. An additional perspective could be gained by adding an organic reductant in the place of Fe(II). By choosing the concentration carefully, an experiment could be performed with the amount of reductant capacity in the organic reductant addition experiment equal to the reductant capacity in the Fe(II) addition experiment. The nature and extent of surface alteration caused by Fe(II) addition and by organic reductant addition, however, could be different.
Journal Articles:
No journal articles submitted with this report: View all 1 publications for this subprojectSupplemental Keywords:
nickel, zinc, metal ions, capillary electrophoresis, toxics, exposure, hazardous substances, assessment, cleanup, risk communication,, RFA, Scientific Discipline, INTERNATIONAL COOPERATION, Waste, POLLUTANTS/TOXICS, Environmental Chemistry, Chemicals, Hazardous Waste, Ecological Risk Assessment, Hazardous, Environmental Engineering, hazardous waste disposal, hazardous waste management, hazardous waste treatment, contaminated waste sites, nickel oxide, Zinc, chemical releases, hazardous waste characterization, capillary electrophoresisRelevant Websites:
Progress and Final Reports:
Original AbstractMain Center Abstract and Reports:
R828771 Center for the Study of Childhood Asthma in the Urban Environment Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R828771C001 Co-Contaminant Effects on Risk Assessment and Remediation Activities Involving Urban Sediments and Soils: Phase II
R828771C002 The Fate and Potential Bioavailability of Airborne Urban
Contaminants
R828771C003 Geochemistry, Biochemistry, and Surface/Groundwater Interactions
for As, Cr, Ni, Zn, and Cd with Applications to Contaminated Waterfronts
R828771C004 Large Eddy Simulation of Dispersion in Urban Areas
R828771C005 Speciation of chromium in environmental media using capillary
electrophoresis with multiple wavlength UV/visible detection
R828771C006 Zero-Valent Metal Treatment of Halogenated Vapor-Phase Contaminants in SVE Offgas
R828771C007 The Center for Hazardous Substances in Urban Environments (CHSUE) Outreach Program
R828771C008 New Jersey Institute of Technology Outreach Program for EPA Region II
R828771C009 Urban Environmental Issues: Hartford Technology Transfer and Outreach
R828771C010 University of Maryland Outreach Component
R828771C011 Environmental Assessment and GIS System Development of Brownfield Sites in Baltimore
R828771C012 Solubilization of Particulate-Bound Ni(II) and Zn(II)
R828771C013 Seasonal Controls of Arsenic Transport Across the Groundwater-Surface Water Interface at a Closed Landfill Site
R828771C014 Research Needs in the EPA Regions Covered by the Center for Hazardous Substances in Urban Environments
R828771C015 Transport of Hazardous Substances Between Brownfields and the Surrounding Urban Atmosphere
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.
Project Research Results
Main Center: R828771
108 publications for this center
20 journal articles for this center