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THE RELATIONSHIP BETWEEN SOIL ORGANIC MATTER AND THE ACTINIDE ELEMENTS

Objective

THIS PROJECT IS INTENDED TO INVESTIGATE IN DETAIL THE ASSOCIATION BETWEEN ARTIFICIAL ACTINIDE ELEMENTS AND SOIL ORGANIC MATTER. PRELIMINARY INVESTIGATIONS HAVE SHOWN THAT IT IS POSSIBLE TO ISOLATE ORGANIC MATTER FRACTIONS WITH SPECIFIC ACTIVITIES IN EXCESS OF 15000 BQ KG-1 PU-239,240 FROM SOILS IN AREAS OF WEST CUMBRIA AND TO FRACTIONATE THESE ON THE BASIS OF MOLECULAR SIZE.

THE OBJECTIVES OF THE PROJECT ARE THUS THREEFOLD:
1. TO ISOLATE ON A LARGE SCALE (5-10 G) ORGANIC MATTER FRACTIONS OF HIGH SPECIFIC ACTIVITY AND DETERMINE THEIR CHEMICAL COMPOSITION AND SPECTROSCOPIC CHARACTERISTICS.
2. TO OPTIMISE MOLECULAR SIZE FRACTIONATION TECHNIQUES, PARTICULARLY GEL FILTRATION AND ULTRAFILTRATION, AND APPLY THEM TO THE ORGANIC FRACTIONS.
3. TO DETERMINE THE CHARGE CHARACTERISTICS OF THE ACTINIDE ENRICHED ORGANIC FRACTIONS BY ION EXHANGE AND ELECTROPHORESIS.
Experiments have shown that it is possible to isolate, from a contaminated soil, humic and fulvic fractions with specific activities much greater than those in the soil from which they were derived. In particular, the humic acid fraction has activities 4 or 5 times higher than whole soil. Humic and fulvic acids can each be separated into 2 fractions of differing nominal molecular weights (MW) using gel filtration chromatography. Plutonium and americium are not distributed uniformly throughout the fractions isolated with the plutonium-239 to plutonium-240 ratio decreasing in the order: high MW humic > high MW fulvic > low MW humic > low MW fulvic.
THE PRELIMINARY EXPERIMENTS HAVE SHOWN THAT THE ISOLATION OF SUITABLE ORGANIC FRACTIONS, EVEN ON THIS LARGE SCALE, IS RELATIVELY STRAIGHTFORWARD. ISOLATION WILL BE ACHIEVED BY ALKALI EXTRACTION, FRACTIONAL PRECIPITATION AND DIALYSIS, FOLLOWED BY FREEZE-DRYING. THE ISOLATES WILL BE CHARACTERISED BY CONVENTIONAL CHEMICAL AND SPECTROSCOPIC TECHNIQUES.

MUCH OF THE EFFORT IN THE MOLECULAR SIZE FRACTIONATION EXPERIMENTS WILL BE DIRECTED TOWARDS IMPROVING THE RESOLUTION ACHIEVED IN THE PRELIMINARY EXPERIMENTS BY USING DIFFERENT GRADES AND TYPES OF GEL.

THE POTENTIAL OF ULTRAFILTRATION AS AN ALTERNATIVE TO GEL CHROMATOGRAPHY WILL BE ASSESSED. HAVING IDENTIFIED THE MOST SUITABLE TECHNIQUE, THE ORGANIC FRACTIONS WILL BE SEPARATED AND THE RELATIONSHIP OF PLUTONIUM, AMERICIUM, IRON AND MANGANESE CONTENT TO MOLECULAR SIZE WILL BE DETERMINED USING RADIOCHEMICAL SEPARATION AND ALPHA SPECTROMETRY FOR THE ACTINIDES, ATOMIC SPECTROSCOPY FOR TRACE METALS, AND UV SPECTROMETRY.

THE CHARGE CHARACTERISTICS OF THE ACTINIDE-CONTAINING COLLOIDS WILL BE INVESTIGATED, INITIALLY USING ION EXCHANGE MEDIA. IF THE RESULTS FROM THESE EXPERIMENTS JUSTIFY, THE ORGANIC ISOLATES WILL BE FRACTIONATED ON THE BASIS OF POLARITY USING ELECTROMIGRATION METHODS. PREPARATIVE-SCALE THIN LAYER CHROMATOGRAPHY USING SOLVENTS OF DIFFERING POLARITIES IS ANOTHER TECHNIQUE WHICH MAY BE WORTH EXPLORING TO OBTAIN MORE INFORMATION ON MOLECULAR CHARGE CHARACTERISTICS.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

NATURAL ENVIRONMENT RESEARCH COUNCIL
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