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Inderjit Nirdosh

Malcolm H Baird

Sirugamani V Muthuswami

Sanjoy Banerjee

The removal of radium from acid-leached uranium mill tailings has been difficult due to its strong retention as mixed sulfates and in adsorbed forms. With this invention the leaching action of a complexing agent (reducing the free radium cation concentration in solution) is combined with that of a reducing agent. Thus, high valency metal hydroxides and basic salts (notably Fe.sup.3+) which tend to retain radium are converted to the lower valency form which is much more soluble in the complexing agent. The reducing agent employed is sodium hydrosulfite, in combination with various organic complexing agents; the preferred complexing agent is EDTA. Over 90% of the radium in uranium leach tailings from Elliot Lake can be removed in 1 hour contact at room temperature with a solution comprising 0.04M of both sodium hydrosulfite and EDTA, with 1.0M potassium chloride added as a surface charge depressant. The gradual addition of the solids to liquid permits the use of low liquid/solid ratios.

Processes for extracting radium from uranium mill tailings

Ferric nitrate leaching at 75.degree. C. is found to remove up to 97% of the uranium and 93% of the radium from ores occurring in the Elliot Lake area of Canada, after an initial flotation-separation of the sulfide minerals from the ore. In processes of the invention an aqueous acidic ferric nitrate solution of relatively low concentration, e.g. 0.01M to 0.1M is used, giving tailings which are effectively sulfide-free (less than 0.45 wt %) and with radium levels approaching a desired maximum value of 24 pCi/g. Radium may be removed from the leachate by adsorption and uranium by solvent extraction. 80-87% of the ferric nitrate may be recirculated for further leaching. Because of the low reagent concentrations and the recycle of the ferric nitrate, it is possible to keep nitrate ion levels in the effluent below the prescribed level of 10 ppm.

Processes for extraction of uranium and radium from uranium-containing

Ferric chloride leaching at temperatures in the range 47.degree.-74.degree. C. is found to remove up to 97% of the uranium from ores occurring in the Elliot Lake area of Canada, but radium removal was found to be poor due to the formation of sulphates from the sulphides present in the ore. In processes of the invention the sulphides are initially removed by flotation, when aqueous acidic ferric chloride of relatively low concentration, e.g. 0.1 M can extract as much as 92% of the radium, giving tailings which are effectively sulphide-free and with radium levels approaching a desired maximum of 24 pCi/g. Radium may be removed by adsorption on manganese dioxide and uranium may be removed by liquid extraction with D2EHPA (DAPEX process). The ferric chloride may be recirculated for further leaching, with reduction before the uranium extraction and reoxidation afterwards. Because of the recycle, it is possible to keep chloride ion levels in the effluent below the prescribed level in Ontario, Canada of 750 ppm.

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Thunder Bay, Canada

Inderjit Nirdosh