Scale formation induced by less soluble salts in sea-water is a common problem to be solved ina desalination plant. Barium sulphate and strontium sulphate, which have small solubilities in seawater, are thought to be scale components on a membrane in an RO desalination plant or on abrine heater and an evaporator in a multi-stage flash evaporation-type desalination plant. In thisstudy, equilibrium distributions of barium sulphate and strontium sulphate in sea-water wereexamined. The amount of barium from 5 ppb to 3 ppm and that of strontium from 2 ppb to 40 ppmcould be determined by using an inductively coupled plasma emission spectrophotometer (ICP). The relation between a solubility product and an ion strength of synthetic sea-water was obtainedto estimate the degree of saturation. Based on this relationship, a calculated apparent solubilityproduct of barium sulphate in natural sea-water agreed with that obtained from an equilibrium distribution experiment.
A concept of adsorber for the uranium recovery from the seawater was proposed. An adsorberwas placed under the surface of the sea and utilized the energy of the ocean current. The shapeof adsorber was a folding screen to increase the area contacting with the seawater. The replacementof adsorbent was carried out by the slurry transport. The design method of a fixed-bed adsorber was applied to the uranium recovery by taking intoaccount the adsorption isotherm and the intraparticle diffusivity of uranium. The fixed-bed runsusing amidoxime resin particles and the natural seawater were conducted. The observed breakthroughcurve and the uptake amount of uranium almost agreed with the simulated ones. Therefore, this method was provided to design the system of uranium recovery including the proposedadsorber concept. Basis for the cost estimation of the uranium recovery was fixed, and the total recovery cost wasestimated. Production scale of 1,000 ton-uranium per year was supposed. The fixed-bed ofamidoxime resin particles (diameter was 1.0mm) whose thickness was 20cm was operated by theadsorption-desorption cycle of 90days, and the total cost of 190,000 yen/kg-U was obtained. Inthis case, the adsorbent cost, the adsorber cost, and the transportation cost of adsorbent were 35, 38 and 17% of the total cost, respectively. It should be noted that the present cost estimation contains many undefined factors. However, as for a fixed-bed adsorption system utilizing the ocean current, the proposed simulation schemeis basically reasonable. If the detailed and accurate data on the adsorbent performance, the adsorbent cost and the adsorber cost are given, the cost estimation would be improved.