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Radionuclides in Drinking Water

Module 3: Principles of Radiochemical Separations


This module, "Principles of Radiochemical Separations" goes into specific detail about the traditional and current means of separation techniques used in radiochemical analyses. Five separate sub-sections of module 3 discuss the chemistry of precipitation, redox, complexation, ion exchange and solvent extraction chemistry. Each subsection has specific examples for the student to work out as well as applications for required drinking water analyses.

Although the emphasis in this module is for the chemistry aspect of analytical separations the radiological component of these analyses in terms of contamination, and timing as regards to decay/ingrowth of radionuclides under examination are emphasized so that there is a direct connection between the separation chemistry and the radionuclide determination. Each section of this module should take 30-45 minutes to complete.

Instructional Resources

This module is divided into 5 tutorials. Each tutorial is presented as a self-paced Adobe Flash video with audio narration. The learning aids that are provided for you to use in this module, which you may access via the links in the "Instructional Resources" panel on the right, include the "Multi-Agency Radiological Laboratory Analytical Protocols Manual" (MARLAP) sections covering each of the separation techniques discussed in the tutorials. You may wish to print out the PDF transcript of the audio narration, also available from a link in the "Instructional Resources" panel. The "Links to Additional Information" provide more in-depth discussions of these topic areas.


Tutorial 3.1 - Solubility and Precipitation

At the end of this tutorial you will be able to:

  • Write the mathematical expression for Ksp given the formula of a salt.
  • Calculate the concentrations of ions in solution based on the Ksp and concentrations of other ions present.
  • Describe the phenomenon of precipitation using following terms:
    • Electrical double layer.
    • Inclusion-Isomorphic and Non-isomorphic.
    • Occlusion.
    • Co-precipitation.
  • Explain how each of the above terms is used in different types of precipitates in radiochemical analysis.

Tutorial 3.2 - Oxidation and Reduction ("Redox")

At the end of this tutorial you will be able to:

  • Describe the difference between oxidation and reduction reactions.
  • Define the terms "redox", "valence," and "oxo-ion" and how they are related.
  • Give examples of 3 ways in which redox reactions are used in radiochemical analyses.

Tutorial 3.3 - Complexation

At the end of this tutorial you will be able to:

  • Define the terms "ligand," "complex," "dentate," and "crown ether" as they apply to radiochemistry.
  • Calculate a combined equilibrium constant (called Keq) based on 2 or more individual equilibrium constants.
  • Describe the effect of pH and ionic diameter on complex formation.
  • Give 3 examples of how complexation chemistry is used in radiochemical separations.

Tutorial 3.4 - Ion Exchange

At the end of this tutorial you will be able to:

  • Discuss the chemical and physical properties of ion exchange resins used in radiochemical analyses.
  • Describe how chemical equilibrium processes control analyte retention and elution.
  • Describe the basic technique of ion exchange chromatography.
  • Calculate the capacity of an ion exchange resin.

Tutorial 3.5 - Solvent Extraction

At the end of this tutorial you will be able to:

  • List the 5 steps involved in a typical solvent extraction protocol
  • Define the term "hydration layer."
  • Explain how complexation ligands promote the migration of ions into non-polar solvents.
  • Calculate the volumes and number of re-extractions required to extract a given fraction of a radionuclide based on its distribution ratio.
  • Discuss the similarities and differences between traditional solvent extraction and solid-phase solvent extraction.

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