Grantee Research Project Results

Formation of Metal-Phosphonate Complexes and Their Subsequent Chemical Reactions with Mineral Surfaces

EPA Grant Number: R826376
Title: Formation of Metal-Phosphonate Complexes and Their Subsequent Chemical Reactions with Mineral Surfaces
Investigators: Stone, Alan T. , Nowack, Bernd
Current Investigators: Stone, Alan T.
Institution: The Johns Hopkins University
EPA Project Officer: Chung, Serena
Project Period: February 1, 1998 through January 31, 2001
Project Amount: $276,944
RFA: Exploratory Research - Environmental Chemistry (1997) RFA Text | Recipients Lists
Research Category: Water , Land and Waste Management , Air , Safer Chemicals

Description:

Phosphonates are extensively used in scale/corrosion inhibition, metal finishing, ore recovery, oil drilling, industrial cleansing, pulp, paper, and textile dyeing, and crop production. U.S. use of the industrial scale control and cleansing agent NTMP4- and the herbicide glyphosate, for example, both exceed 4x106 kg/yr.

Solubilization and facilitated transport of toxic metal ions by carboxylate-based chelating agents is well documented. CoIIIEDTA-, for example, has been observed to migrate more than a kilometer in one contaminated aquifer, owing to its low affinity for aquifer mineral surfaces and low rate of ligand exchange. Comparable reactions of phosphonate-based chelating agents have not, however been investigated.

Phosphonates are brought into contact with +II and +III toxic metal ions during their use. Upon disposal, metal-phosphonate complexes persist long enough to significantly alter toxic metal adsorption/desorption behavior. Ultimately, +II toxic metal ions are displaced from their phosphonate complexes by the dissolution of FeIII- and AlIII-containing minerals. This project investigates the potential for toxic metal solubilization by synthetic phosphonates.

Approach:

Three phosphonates (IDMP4-, NTMP6-, and EDTMP8-), two toxic +II metal ions (NiII and CdII) and three naturally-occurring metal ions (CaII, AlIII, FeIII, along with the minerals goethite and diaspore) serve as the focus of this study. Potentiometry, ion-pair HPLC, CE, and ion chromatography will be used to determine the stoichiometry and equilibrium constants for metal ion-phosphonate complexes in solution and on the surfaces of representative minerals. The same methods will also be used to monitor the kinetics of ligand exchange and mineral dissolution reactions as a function of mineral surface properties and aqueous medium composition.

Expected Results:

logKs, reaction pathways, and rate constants will be obtained for metal- phosphonate complexes in homogeneous solution and on mineral surfaces. This information serves as input into computer programs that will be used to predict metal solubilization under a wide range of scenarios and to identify problematic chelating agent/toxic metal combinations.

Publications and Presentations:

Publications have been submitted on this project: View all 19 publications for this project

Journal Articles:

Journal Articles have been submitted on this project: View all 4 journal articles for this project

Supplemental Keywords:

environmental chemistry, water, adsorption, metals, organics, alternatives, environmentally conscious manufacturing, interfaces, equilibrium, kinetics, speciation, complexation, chelating agents, ligands, metal-ligand complexes, ligand exchange, dissolution, desorption, corrosion inhibitors, scale inhibitors, phosphonates., Scientific Discipline, Air, Environmental Chemistry, Chemistry, Engineering, Chemistry, & Physics, Biology, environmentally conscious manufacturing, ligand exchange, chemical composition, pollutant transport, toxic metals, phosphonates, environmental engineering, chemical kinetics

Relevant Websites:

http://www.jhu.edu:80/~dogee/stone.html Exit EPA icon

Progress and Final Reports:

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.