Comparison of Two Methods for the Determination of Stability Constants for Metal-NOM Interactions

Çetin KANTAR

Article Details

Comparison of Two Methods for the Determination of Stability Constants for Metal-NOM Interactions

Authors:

Çetin KANTAR

Publisher:

TUBITAK

Journal:

Turkish Journal of Engineering and Environmental Sciences 2005 Vol.29 Issue 5, pp.297-308

Document Type:

Article

Publication Date:

4/2005

Document Language:

Turkish

Document ID (Org No.):

2000745046

Frequency:

Tri-annual

eISSN:

1303-6157

pISSN:

1300-0160

Abstract:

 

The inherent polyfunctional and heterogeneous nature of  natural organic matter (NOM) has made the modeling of metal  complexation reactions difficult.  Historically, a number of modeling  approaches have been developed to describe metal complexation by NOM.  These models can be grouped into two: chemical and non-chemical.  In  the present study, we compare a non-chemical model (Schubert's method)  to a chemical model (discrete ligand, non-electrostatic approach) to  determine the stability constants of metal/NOM complexes.  Our  analyses of Co/fulvic acid complexation data using Schubert's equation  result in an apparent nonintegral number of ligands binding the  Co2+ ion.  The model fit was improved assuming a mixture of 1:1/1:2  Co(II)-ligand complexes.  Schubert's method can be used as an  effective tool to provide information on reaction stoichiometries and  average stability constants over the whole NOM. However, the binding  of metals by NOM occurs on specific sites, mostly associated with  carboxylic groups.  In the discrete ligand approach, NOM is  conceptualized as being composed of a suite of monoprotic acids,  HLi, of arbitrarily assigned pKa (i) values (e.g., 4, 6, 8 and  10).  Although the discrete ligand approach is more complex and  requires more fitting parameters (i.e. usually more than 5) compared  to Schubert's approach, it provides a means of capturing the  complexation behavior of metals with specific sites in a framework  suitable for use in equilibrium speciation models under variable  chemical conditions.  In addition, all of the potential mononuclear  and polynuclear metal and organic species can be considered within the  framework of the chemical model.

 

The inherent polyfunctional and heterogeneous nature of  natural organic matter (NOM) has made the modeling of metal  complexation reactions difficult.  Historically, a number of modeling  approaches have been developed to describe metal complexation by NOM.  These models can be grouped into two: chemical and non-chemical.  In  the present study, we compare a non-chemical model (Schubert's method)  to a chemical model (discrete ligand, non-electrostatic approach) to  determine the stability constants of metal/NOM complexes.  Our  analyses of Co/fulvic acid complexation data using Schubert's equation  result in an apparent nonintegral number of ligands binding the  Co2+ ion.  The model fit was improved assuming a mixture of 1:1/1:2  Co(II)-ligand complexes.  Schubert's method can be used as an  effective tool to provide information on reaction stoichiometries and  average stability constants over the whole NOM. However, the binding  of metals by NOM occurs on specific sites, mostly associated with  carboxylic groups.  In the discrete ligand approach, NOM is  conceptualized as being composed of a suite of monoprotic acids,  HLi, of arbitrarily assigned pKa (i) values (e.g., 4, 6, 8 and  10).  Although the discrete ligand approach is more complex and  requires more fitting parameters (i.e. usually more than 5) compared  to Schubert's approach, it provides a means of capturing the  complexation behavior of metals with specific sites in a framework  suitable for use in equilibrium speciation models under variable  chemical conditions.  In addition, all of the potential mononuclear  and polynuclear metal and organic species can be considered within the  framework of the chemical model.

Article Details

Comparison of Two Methods for the Determination of Stability Constants for Metal-NOM Interactions

Authors: Çetin KANTAR

Publisher: TUBITAK

Journal: Turkish Journal of Engineering and Environmental Sciences 2005 Vol.29 Issue 5, pp.297-308

Document Type: Article

Publication Date: 4/2005

Document Language: Turkish

Document ID (Org No.): 2000745046

Frequency: Tri-annual

eISSN: 1303-6157

pISSN: 1300-0160

Issues

Authors:

Çetin KANTAR

Publisher:

TUBITAK

Journal:

Turkish Journal of Engineering and Environmental Sciences 2005 Vol.29 Issue 5, pp.297-308

Document Type:

Article

Publication Date:

4/2005

Document Language:

Turkish

Document ID (Org No.):

2000745046

Frequency:

Tri-annual

eISSN:

1303-6157

pISSN:

1300-0160