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: Hiscock, Michael
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 , Engineering and Environmental Chemistry


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.


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: Exit EPA icon

Progress and Final Reports:

  • 1998 Progress Report
  • 1999 Progress Report
  • Final Report