Technology to harvest uranium from sea - development of radiation grafting reactor systems

Researchers worldwide have renewed interest on the recovery of uranium from seawater to complement uranium deposits from terrestrial ore. With its lean but clean resource, ocean can serve as a potential source of uranium and other valuable heavy metals in the long run. The total volume of the oceans is estimated to be 2x109 km3 and uranium content of oceans is of the order 4.5x109 tonnes. Thus oceans are limitless reservoir of dissolved uranium in a well defined chemical environment. Seawater is an electrolyte with pH of 8-8.5 and uranium exists principally as uranyl tricarbonate complex. Various organic adsorbents have so far been synthesized and evaluated at laboratory level using synthetic seawater solutions. Some of the major requirements of sorbents are - incorporation of selectivity and efficiency into the sorbent materials and suitable recovery system design. With the development of electron beam accelerator technology, novel sorbent materials such as Metal Chelate Embedded Polymers (MCEP) can be synthesized by radiation grafting. Amidoxime groups are embedded into backbone polymers in the form of leaflets, and provide efficient contact patterns with water body of the sea. The recovery system design depends on the shape of adsorbent; mode of operation of adsorbent and contact mode of adsorbent. MCEP facilitates efficient recovery system design also. Systematic optimization for preparation of radiation grafted polymeric sorbents was carried out with respect to radiation dose, dose rate, duration and temperature to enhance grafting levels on different backbone polymers. Out of various backbone polymers, polypropylene has given good grafting yields compare to polystyrene, polyethylene and PTFE. Lab scale; bench scale and pilot scale radiation grafting reactor systems are being developed for engineering scale studies for production of MCEP. Data has been collected w.r.t. time and temperature on pilot scale preparation of metal chelate embedded polymers of size 1Mx1M and grafting levels of up to 150% are observed. The process flow details are reported. The paper also highlights design and development features of radiation grafting reactor systems required for preparation of MCEP for use in aquaculture of uranium and other valuables from seawater and as well as desalination plants effluents. (author)