Abstract

This is the novel measurement of the apparent formation constants of trivalent lanthanide with humic substances by potentiometric titration using an ion selective electrode (ISE) consisting of bis(diphenylphosphoryl)methane as an ionophore. The ISE prepared exhibited a Nernstian response to the Eu3+ concentration in the test solutions in the presence of humic acid and fulvic acid. The effect of the solution conditions, including the pH, initial metal and humic substance concentrations, and ionic strength, on the formation constants was examined. The present formation constants were compared with the reported data using solvent extraction method.

Highlights

  • Occurring humic substances exist in colloidal, suspended, and dissolved forms in groundwater

  • This is the novel measurement of the apparent formation constants of trivalent lanthanide with humic substances by potentiometric titration using an ion selective electrode (ISE) consisting of bis(diphenylphosphoryl)methane as an ionophore

  • The ISE prepared exhibited a Nernstian response to the Eu3+ concentration in the test solutions in the presence of humic acid and fulvic acid

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Summary

Introduction

Occurring humic substances (fulvic and humic acids) exist in colloidal, suspended, and dissolved forms in groundwater. Understanding the impact of humic substances on the migration behavior of trivalent radionuclides has been essential for safety assessments related to the disposal of such radioactive waste. Titration method using a pH- and/or ion selective electrodes (ISE) [10,11,12]. A few ion-selective electrodes have been developed for the potentiometric determination of trivalent lanthanide and actinide ions [13,14,15,16], no application to determine the formation constant has been reported. We developed a novel technique to determine the formation constants of trivalent metal ions with carboxylic acid electrochemically, using a liquid membrane electrode [17,18]. A titration technique using an ISE was utilized for the systematic measurement of the formation constants of europium with three humic substances. The constants were determined using the traditional batch solvent extraction method for comparison

Reagents
Titration with ISE
Solvent Extraction
Determination of Apparent Formation Constants by Titration with ISE
Determination of βapp by Solvent Extraction
Electrochemical Response of ISE
Titration Plot
Apparent Formation Constants
Conclusion

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