AN INVESTIGATION OF URANIUM MILL
WASTEWATER TREATABILITY
Paul H. Werthman, Project Engineer
Malcolm Pirnie, Inc.
Buffalo, NY 14219
Kent L. Bainbridge, Senior Water Chemist
Calspan Corporation
Advanced Technology Center
Buffalo, NY 14225
INTRODUCTION
There are 20 domestic uranium mills currently in operation in the United States. All are
located in arid regions of the country and, with a single exception, attain zero point discharge of wastewater by evaporation and seepage from tailing impoundments. However,
state and federal regulations are being considered which would require the elimination of
seepage from uranium mill tailing impoundments to protect groundwater resources. This
could result in point discharges of wastewater from some existing uranium mills. In the
future, uranium mills might also be constructed near undeveloped uranium ore deposits in
areas of net precipitation (e.g., Wisconsin, Tennessee and New York). In such areas, the
discharge of wastewater would almost certainly be required.
The objectives of this study were twofold: (1) to investigate the technical feasibility of
uranium mill wastewater treatment; and (2) to develop some of the information required to
provide a basis for the evaluation of alternatives relevant to the handling and disposal of
uranium mill wastewater.
Two basic methods are employed to extract uranium from ore: acid leaching with sulfuric
acid or alkaline leaching with a hot solution of sodium carbonate and sodium bicarbonate.
Wastewater produced from an acid-leach circuit is uniquely different from wastewater produced from an alkaline-leach circuit. For this reason, uranium mills representative of both
processes were selected for study.
URANIUM ORE BENEFICIATION PROCESSES
Crushing, Blending, Roasting
Uranium ore is blended, crushed and ground as the physical preparatory steps prior to the
physicochemical beneficiation processes of extraction, concentration, and product precipitation. Ore high in vanadium is sometimes roasted with sodium chloride or soda ash prior to
grinding in order to convert insoluble heavy metal vanadates (complex vanadium) into more
soluble vanadate, which is then extracted with water.
Acid Leach
Ores with a calcium carbonate content of less than 12% are preferentially leached in
sulfuric acid. The addition of an oxidizing agent, typically sodium chlorate or manganese
dioxide, facilitates the oxidation of U(IV) to U(VI) in conjunction with the reduction of
Fe(III) to Fe (II) at a redox potential of -450 mV. Free-acid concentration is held between
1 and 100 g/1.
Alkaline Leach
A solution of sodium carbonate (40 to 50 g/1) in an oxidizing environment selectively
leaches uranium and vanadium values from the ore. A controlled amount of sodium bicar-
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