1.2 WASTE SEPARATION AND PRETREATMENT USING TITANATE ION EXCHANGERS

TASK DESCRIPTION

This project is focused on the development and demonstration of advanced, efficient separation technologies to selectively remove Cs-137 and other radionuclides from a wide spectrum of radioactive defense wastes. Crystalline silicotitanates (CST) and amorphous hydrous titanium oxide (HTO) ion-exchange technology will be developed and demonstrated for the removal of the radioactive materials from Hanford-type supernatant solutions and salt cake. The project objectives will be accomplished within four tasks:

• the evaluation of the ion exchange properties, especially the effects of pH and sodium content on the ability of crystalline silicotitanate to remove Cs-137;

• the assessment of the feasibility of regenerating the crystalline silicotitanate ion exchangers;

• the measurement of the radiation stability of the crystalline silicotitanate materials; and

• the delivery of the materials to Pacific Northwest Laboratories (PNL) for testing on actual Hanford wastes.

TECHNOLOGY NEEDS

Within the DOE Complex there are currently more than 200 tanks being used for processing and storing radioactive waste by-products generated by weapons materials production facilities. These tanks contain tens of millions of gallons of highly radioactive supernate and grout feed liquid, salt cake, and sludges. The major radioactive constituents are isotopes of cesium, strontium, iodine, technetium, and transuranics. The technology developed and demonstrated in this work is needed to remediate radioactive wastes currently contained in defense waste storage tanks. Specifically, titanate ion-exchange materials and ion-exchange processes will be used to develop advanced, efficient radioactive waste separation technology.

ACCOMPLISHMENTS

A variety of CSTs have been synthesized to evaluate the effect of structure and composition on ion exchange properties. Transmission electron microscopy micrographs show cuboidal crystals ranging from 20 to 50 nm and preliminary X-ray structural studies indicate a tetragonal structure. Cs adsorption was measured at various pHs and the distribution coefficient (Kd) was calculated. From pH 2 to 10, the Kd exceeds 10,000 ml/g. However, at a pH of approximately 10 the Kd decreases markedly and drops to 100 mL/g at pH 14.

A second generation of CST ion exchangers was prepared and is undergoing testing and evaluation. The main effect of the structural and compositional modification has been to increase the Kd to 1000 ml/g in 2.5 N NaOH to pH 11. Stability tests have been conducted on CST in high pH solutions for 100 days at 40°C and ambient temperature by measuring the Cs concentration. No change in Cs concentration and the Kd for Cs adsorption was measured.

COLLABORATION/TECHNOLOGY TRANSFER

Pacific Northwest Laboratories

Texas A&M University

For further information, please contact:

Norm E.Brown

Principal Investigator

Sandia National Laboratory

(505) 845-8180

Dennis L.Berry

Technical Program Manager

Sandia National Laboratory

(505) 844-0234