Grantee Research Project Results
1998 Progress Report: Formation of Metal-Phosphonate Complexes and Their Subsequent Chemical Reactions with Mineral Surfaces
EPA Grant Number: R826376Title: Formation of Metal-Phosphonate Complexes and Their Subsequent Chemical Reactions with Mineral Surfaces
Investigators: Stone, Alan T.
Institution: The Johns Hopkins University
EPA Project Officer: Chung, Serena
Project Period: February 1, 1998 through January 31, 2001
Project Period Covered by this Report: February 1, 1998 through January 31, 1999
Project Amount: $276,944
RFA: Exploratory Research - Environmental Chemistry (1997) RFA Text | Recipients Lists
Research Category: Water , Land and Waste Management , Air , Safer Chemicals
Objective:
Synthetic phosphonate chelating agents are brought into contact with toxic +II and +III metal ions during their use in scale/corrosion inhibition, metal finishing, ore recovery, oil drilling, industrial cleansing, pulp, paper, and textile dyeing, and agricultural production. The objectives of this project are to (i) explore processes that generate toxic metal ion-phosphonate complexes; (ii) study their speciation and sorption behavior in aqueous environmental media; and (iii) explore pathways and rates of complex dissociation and ligand breakdown.
Progress Summary:
Free HEDP, NTMP, EDTMP, and DTPMP concentrations have been determined using the method of Nowack (J. Chromatogr. A 1997, 773: 139-146). Additional ion chromatography and capillary electrophoresis methods have been developed for mono- and di-phosphonates, phosphonate breakdown products, and metal ion-phosphonate complexes. Using these analytical methods, studies have been conducted in the following areas: (1) the adsorption of representative phosphonates at the FeOOH(goethite)/water interface; (2) the influence of CaII, CuII, ZnII, and FeIII on adsorption; (3) the degradation of NTMP in the presence of Mn2++ and O2; (4) the degradation of NTMP in the presence of MnOOH(manganite); and (5) the formation of substitution-inert CrIII-phosphonate complexes.
Accomplishments and Research Results:
- When the FeOOH surface site loading (in moles per liter of suspension) is high, NTMP is completely adsorbed at pH o7. The extent of adsorption decreases to negligible levels as the pH is increased to 12. Surprisingly, increasing the background electrolyte (NaNO3) concentration from 1.0 mM to 1.0 M had no effect on the extent of NTMP adsorption. Seven other phosphonates ranging from methylphosphonic acid to DTPMP adsorb in a similar manner when the FeOOH surface site loading is high. At low surface site loadings, differences in surface area occupied per molecule become evident.
- The effects of metal ions on phosphonate adsorption (and phosphonates on metal ion adsorption) were examined using 10 mM concentrations of FeIII, and CuII, and varying concentrations of CaII and ZnII (up to 1.0 mM). Metal ions exerted an effect on phosphonate adsorption only when concentrations were in the mM range; ternary surface complex formation and adsorption onto precipitated (hydr)oxides of Zn are believed to be responsible. Polyphosphonates increase the adsorption of 10 mM CuII at pHs below its= adsorption edge, but decrease adsorption at higher pHs, owing to formation of CuII-polyphosphonate complexes in solution.
- Following the lead of Steber and Wierich (Chemosphere 1987, 16: 163-178), non-photochemical degradation of NTMP in surface water samples has been confirmed. A survey of common water constituents has identified manganese as the causative agent. Mn2+ forms a complex with NTMP. MnII within this complex reacts with O2 far more rapidly than Mn2++(aq); oxidation of NTMP-complexed MnII has been observed at pHs as low as 3.5. The MnIII-NTMP complex then undergoes intramolecular electron transfer, generating NTMP breakdown products and Mn2++.
- Oxidation of NTMP by MnIIIOOH(manganite) generates the same breakdown products as the MnII + NTMP + O2 reaction. The heterogeneous reaction consumes NTMP at lower rates, however, and changes product yields. A lag period is observed, which can be shortened or eliminated by adding Mn2++ to the reaction medium. The presence or absence of O2 also affects reaction rates and product yields. Reaction with MnIIIOOH and other MnIII,IV-containing minerals may represent an important sink for phosphonates in soils and sediments.
- CrIII(IDA)2- was synthesized following the procedure of Weyh and Hamm (Inorganic Chemistry 1968, 7: 2431-2435) and brought into contact with the carboxylate ligands NTA and EDTA, the mixed phosphonate-carboxylate ligands BPMG and PMIDA, and the phosphonate ligand EDTMP. All five added ligands form complexes which are thermodynamically more stable than the parent complex. Ligands possessing at lease one phosphonate group capture CrIII more rapidly than ligands possessing only carboxylate functional groups. In contaminated waters where CrIII speciation is under kinetic control, complexation by phosphonates may therefore be especially important.
Future Activities:
Additional work in all five areas is anticipated. Mixed phosphonate-carboxylate ligands used in commerce and possessing pronounced biological activity (e.g. phosphonoformic acid, phosphonoacetic acid, glyphosate) will be included in our adsorption experiments and manganese-catalyzed oxidation experiments. Formation of CrIII-phosphonate complexes via ligand exchange will be examined under different medium conditions (e.g. vary the pH and dissolved CaII concentration) and with different parent and product ligands. Experiments will examine the phosphonate ligand-assisted dissolution of adsorbed and precipitated CrIII.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 19 publications | 4 publications in selected types | All 4 journal articles |
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Type | Citation | ||
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Nowack B, Stone AT. Adsorption of phosphonates onto the goethite-water interface. Journal of Colloid and Interface Science 1999;214(1):20-30. |
R826376 (1998) R826376 (1999) R826376 (Final) |
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Supplemental Keywords:
redox reactions, coordination chemistry, iron, chromium, iminodiacetic acid, nitrilotriacetic acid, ethylenediaminetetraacetic acid, hydroxymethylphosphonic acid, nitrilotris(methylphosphonic acid), ethylenedinitrilotetrakis(methylenephosphonic acid), diethylenetrinitrilopentakis(methylenephosphonic acid), N-(phosphonomethyl)glycine, N-(phosphonomethyl)iminodiacetic acid, N,N-bis(phosphonomethyl)glycine, 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 kineticsRelevant Websites:
http://www.jhu.edu:80/~dogee/stone.html
Progress and Final Reports:
Original AbstractThe 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.