Prospects for the recovery of uranium from seawater

Abstract

A computer program entitled URPE (Uranium Recovery Performance and Economics) has been developed to simulate the engineering performance and provide an economic analysis O of a plant recovering uranium from seawater. The conceptual system design used as the focal point for the more general AM analysis consists ofa floating oil-rig type platform, Asinlge-point moored in an open ocean current, using either high volume, low head, propeller pumps or the velocity head 4M of the ambient ocean current to force seawater through a mass transfer medium (hydrous titanium oxide (HTO) coated onto particle beds or stacked tubes), as in most process designs previously suggested for this service. Uranium is recovered Sfrom the seawater by an adsorption process, and later eluted . from the adsorber by an ammonium carbonate solution. A multi-product co-generating plant on board the platform burns coal to raise steam for electricity generation, desalination, and process heat requirements. Scrubbed stack gas from the plant is processed to recover carbon dioxide for chemical make-up needs.

The equilibrium isotherm and the diffusion constant for the uranyl-HTO system, which are needed for bed performance calculations, have been calculated based on the rather sparse data reported in the literature. In addition, a technique for calculating the rate constant of a fixed bed adsorbing system has been developed for use with Thomas' solution for predicting fixed bed performance.

The URPE program has been benchmarked against the results of previous studies by ORNL and Exxon, and found to make comparable performance and economic estimates when applied under the same set of ground rules. The URPE code was then used in an extensive series of parametric and sensitivity studies to identify optimum bed operating conditions and important areas for future research and development. The program showed that thin beds of small, thinly-coated particles were the preferred bed configuration, and that actively pumped systems out-perform current driven units.

Based on the URPE analysis, the minimum expected costs nof uranium recovered from seawater would be no lower than ~316 (1979$)/lb U308 for state-of-the-art adsorber material (capacity equal to 210 mg U/kg Ti), but might be reduced to the level of breakeven attractiveness of ~150 (1979$)/lb U30 8 if at least a four-fold increase in adsorption capacity could be achieved. Specific research and development objectives other than increasing particle capacity are also indentified. Prospects are considered to be sufficiently good to warrant recommending further work.