LABORATORY DEVELOPMENT OF A CARRIER-PRECIPITATION PROCESS FOR THE RECOVERY OF STRONTIUM FROM PUREX WASTES

Strontium recovery from Purex 1WW was investigated with simulated feeds and tracer activities. Initial experiments demonstrated recovery of over 70% of the strontium by sulfate precipitation from partially neutralized 1WW by either increasing the sulfate concentration to about 3 M or by adding carriers such as lead. Precipitation of iron was avoided by addition of one or more moles of tartrate per two moles of iron. Precipitation at elevated temperatures and addition of lead after pH adjustment were shown to be beneficial. Strontium recoveries of over 95% were achieved by precipitation at about 80 deg C at pH values of 0.4 to 4.0 with sulfate concentrations of 0.67 to 3 M and over 0.02 M lead carrier added. High sulfate concentrations were required at low pH, but the sulfate concentration is not critical above pH 1. Some separation of strontium from cerium was observed at pH 2 to 4, with the degree of separation being dependent on both tartrate concentration and pH. Recovery of strontium from the sulfate precipitate by leaching with nitric acid, sodium acetate, or oxalic acid was unsatisfactory because of the large volumes required. Metathesis with sodium hydroxide removed most of the lead as plumbite and converted the precipitate to an acid-soluble form, but resulted in excessive strontium losses. Metathesis with carbonate-- hydroxide mixtures retained the benefits of hydroxide metathesis, and resulted in only very low strontium losses. Selective leaching of rare earths from the suIfate or carbonate precipitates using various complexing agents was generally unsuccessful. Recovery of strontium from the carbonate precipitate by washing with mixtures of nitric and oxalic acids, or by dissolution in nitric acid followed by oxalate precipitation was demonstrated. The techniques developed were successfully applied in the Purex plant in meeting Hanford's megacurie commitment of Sr/sup 90/ for the SNAP program prototypes. (auth)