DEVELOPMENT OF A NEW RADIUM REMOVAL
PROCESS FOR URANIUM MINING EFFLUENTS
Peler M. Huck, Associate Professor
William B. Anderson, Research Technologist
Robert C. Andrews, Graduate Student
Department of Civil Engineering
University of Alberta
Edmonton, Alberta
Canada T6G 2G7
INTRODUCTION
The mining and milling of uranium ores results in large quantities of waste solids (tailings) after
processing. Included in these wastes are all the radioactive isotopes from the uranium, actinium, and
thorium decay series. The tailings are discharged in slurry form to impoundment areas where the
solids settle out of the slurry. In regions having a net excess of precipitation over evaporation, the
liquid used to transport the tailings is discharged from the tailings impoundment areas to surface
waters. These effluents or decants contain little suspended material but appreciable quantities of
dissolved materials; of particular concern for environmental protection is the amount of radium-226
being discharged to the aquatic environment. This isotope has an extremely high radiotoxicity.
Canadian uranium mine/mill tailings decants are treated with barium chloride to remove
radium-226. Historically, this has been accomplished in large ponds which provide an opportunity for
a (Ba,Ra)S04 precipitate to form and subsequently settle. As environmental requirements have
become more strict, two deficiencies have become apparent with this type of treatment system:
acceptable total radium-226 levels are difficult if not impossible to achieve and the radium-bearing
sludge which accumulates in the ponds presents a disposal problem on mine closure. Preliminary
studies [1] have suggested that it may be acceptable to return the sludge produced by barium chloride
treatment systems to tailings areas for final disposal. If this proves feasible, treatment systems which
produce an easily-handled residue on an ongoing basis would be beneficial in avoiding a final disposal
problem.
Within the last few years, effort has been expended in Canada on improving treatment systems.
This work was partly in response to a suggested Atomic Energy Control Board target level for tailings
decants of 10 pCi/1 total radium-226 [2J. A mechanically based system has been developed consisting
of barium chloride addition to stirred tank reactors for precipitation and granular media filtration for
solids separation [3]. This process offers improved effluent quality, reduces treatment time from days
to hours, and produces sludge on a continuous basis for on-going disposal rather than at the end of a
mine's life. However, the filtration step is critical and must be carefully designed and operated. To
date, only one full scale system has been placed into service.
OBJECTIVE AND PROCESS CONCEPT
The objective of the research reported herein was to develop a radium-226 removal process for
tailings pond effluents which would be superior to pond systems but simpler than a mechanically
based stirred tank/filtration system. Previous work by two of the authors [4] had demonstrated that,
under certain conditions, significant quantities of radium-226 could deposit on surfaces during
barium chloride treatment. Pilot scale studies of the mechanical treatment system mentioned
previously had recognized the role which surface effects could play f3]. Seeley [5] had also postulated
adsorption of RaS04 on particle surfaces in a study on the leaching of uranium tailings.
The concept of the new treatment system was to induce the radium to deposit on existing surfaces
of granular material in a reactor rather than in/on a precipitate created in the bulk of solution. The
granular material, being free draining, could subsequently be separated from solution readily, eliminating the need for a separate liquid-solid separation step in the process. This granular material, once
215