Research Project 9
| EPA Grant Number: | R828771-0-01 |
| Title: | Solubilization of Particulate-Bound Ni(II) and Zn(II) |
| Investigators: | Alan Stone |
| Institution: | Johns Hopkins University |
| Project Period: |
October 1, 2003 to September 30, 2004 |
| Description: |
|
At present, the management of metal-contaminated sites relies heavily upon
equilibrium speciation models. These models 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 become"buried" and hence physically unaccessible; and (3) Soil
organic constituents are difficult to characterize and hence difficult to
account for. The three issues just raised can be resolved using the approaches described below. Our objective is to provide the basis for predicting toxic metal solubilization by soil organic constituents. |
| Approach: |
|
Experiments will examine the dissolution of NiO(s) and the desorption of
NiII and ZnII from FeOOH(goethite) and Fe(OH)3(amorphous) surfaces.
Experiments will begin with individual low molecular weight organic
compounds with well defined adsorbent, complexant, and reductant
properties, then expand to include natural organic matter amendments. The
first of the three issues raised will be addressed through the use of
Capillary Electrophoresis (CE), which allows us to directly monitor metal
ion speciation, regardless of whether speciation is kinetically or
thermodynamically controlled. The second issue will be addressed using
High Resolution Transmission Electron Microscopy (HRTEM) in a small number
of carefully-selected experiments. Godtfredsen and Stone (1) offer a way
of resolving the third issue. By linking extents of toxic metal
solubilization to alterations in the host phase, it is possible to
distinguish among competitive adsorption, complex formation, and redox
reactions of organic constituents. Emphasis will be placed upon distinguishing among the following mechanisms of organic constituent-assisted solubilization: (1) competitive adsorption; (2) ligand-assisted desorption; (3) ligand-assisted dissolution of the host phase; and (3) reductive dissolution of the host phase. |
| Expected Results: |
| Because our approach is applicable to complex systems, synergistic and antagonistic interactions among constituent chemicals should be identifiable, and the effects of soil amendments, changing hydrologic conditions, and other system perturbations should be more easily evaluated. This work should draw attention to molecular-level phenomena that control toxic metal ion partitioning between solid and solution phases. An improved understanding of toxic metal ion partition will help in modeling toxic metal transport and toxicity. |
| Improvements in Risk Management: |
| Supplemental Keywords: |
| toxic metal |