A Modified Ion‐Exchange Technique for the Determination of Stability Constants of Metal‐Soil Organic Matter Complexes

Abstract

Calculation methods based on Schubert's ion‐exchange equilibrium method were developed for determining stability constants of metal‐soil organic matter complexes. The methods, which were free of certain assumptions and errors inherent in the ion‐exchange technique as applied previously to soil organic matter, were verified using Mn(II)‐citrate and Mn(II)‐oxalate systems. Apparent stability constants (log K) of Zn (II)‐humic acid complexes ranged from 3.13 to 5.13 at pH 6.5.

Soil organic matter interactions with trace elements

“…of bound metal ion _ Mb _ v o -total number of reactive sites -nL t -n [7] By combining equations [5] and [7] , the following is obtained:…”

Aspects of the biogeochemistry of carbohydrates in aquatic environments

“…complexes are described by Clark and Turner (1969), Ardakani andZunino et al (1972). The results obtained by these modifica---tions, however, are not significantly different from those obtained by the simplified method of Schubert (1948).…”

Use of the Ion Exchange Method for Determination of Stability Constants of Uranyl Ions with Three Soil Humic Acids

“…According to Eqs. (10) and (11), the concentration of M,L, obtained is also \lj(MJX -M R / λ 0 ) and M c can also be obtained. The purpose of this paper is to determine the stability constants of uranyl ion complexes with three soil humic acids by using the modified Ardakani-Stevenson's ion exchange method mentioned before.…”

“…In addition, it is also a shortcoming in this method that the concentration of ligand must be extrapolated far away from experimental data to [L] = 1, because in the general case the concentration of ligand is far less than 1. In 1972, Ardakani and Stevenson [10] proposed an ion exchange equilibrium method without assumptions (1) (1) and (3) but still with the assumption (2) mentioned before. In addition, considering the possibility that i or j obtained deviate from an integer, the meaning of Igß calculated is ambiguous and the distance extrapolated to obtain the intercept I a or I b is too far from experimental data.…”