Very severe troubles of scale formation might be expected to occur when recovery of water from sea water increases. The main constituents of the scale are CaCO₃, Mg(OH)₂, CaSO₄ and so on, all of which are salts of alkaline earth metals. Therefore, if a key technology is developed by which the main constituents of the scale, alkaline earth metal ions mentioned above, can be removed and/or separated from sea water, the recovery of desalted water from raw sea water by high-pressure reverse osmosis (HPRO) can be increased up to 75-80%, the solubility limit of the remaining scale components. Then it will be possible to make use of all valuable materials existing in sea water, by an integrated system which combines conventional recovery technologies with a set of the proposed technologies such as HPRO, alkaline earth metal ions removal process, inorganic ion-exchangers for recovery of trace elements and so on. Furthermore, almost complete usage of sea water may be accomplished by irrigation of the brackish water by-product for salt-resistant plants such as mangrove, salt bush and, if possible, gene-recombinated plants.

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The behavior of a saturated solute in a system, in which the saturated solute is salted out by unsaturated solutes, is discussed and is almost completely explained by the three phenomena of solubility of saturated solute, solubility product and restriction of solvent in the system. It was confirmed in the whole range of brine concentration that the square of the quantity of solvent is expressed with good accuracy as a linear function of quadratic homogeneous products of (the quantities of saturated solute and of all the unsaturated solutes) and (the quantities of solvent and of all the unsaturated solutes). Among the behaviors of the saturated solutes discussed in this paper, the behaviors of sodium chloride and potassium chloride on the saturated region of calcium sulfate and the behaviors of sodium chloride and potassium chloride in systems which also contain calcium chloride, magnesium chloride and water are of special importance for the salt manufacturing industry using ion-exchange membranes.

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A process for Li separation from eluate was studied using a model solution containing LiCl (C_Li=1,500mg·dm^-3), NaCl, KCl, MgCl₂, CaCl₂, and MnCl₂ in 0.35mol·dm^-3 HCl solution. A promising process was proposed which consists of 4 steps such as addition of alkali, concentration by heating, precipitation as Li₂CO₃, and washing with hot water. Most (99.8%) of Mg and Mn, and 92% of Ca were precipitated as hydroxides by adding NaOH solution up to pH>12. The supematant solution was concentrated by heating; most of the remaining Ca was precipitated in this step and the Li concentration reached above 8,500mg·dm^-3. The Li in the concentrate was precipitated as Li₂CO₃ by adding Na₂CO₃(1.2 equivalents to dissolved Li) at 95°C. The precipitate was washed by a small amount of hot water. The Li₂CO₃ obtained has a purity of reagent grade. The total yield was 75%.

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A fluidized-bed type adsorption bench was constructed for bench scale studies of Li recovery from sea water. Granulated adsorbent (2.5 kg) of manganese oxide was set on a cone-shaped column and sea water was passed at a flow rate of 15dm³·min^-1 for 28 days. The desorption of Li was carried out batchwise using 0.5mol·dm^-3 HCl solution. The adsorption-desorption cycle was repeated 7 times; the total amount of sea water passed was 4,200m³. The eluate obtained was concentrated by heating, and finally the Li was precipitated as Li₂CO₃. The Li₂CO₃ product (750g) showed a purity of 99.1%. Recovery of Li was 27% based on the total amount of sea water passed and the total Li₂CO₃ yield was 20%. Several R/D themes were found for future industrial application of the recovery system, such as improvement of chemical stability of adsorbent, development of efficient desorption process, and design of recovery system with sea-water waste of power plant.

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