EXTRACTION OF NA AND WATER-UPTAKE FROM NACL SOLUTION USING D-2-EHPA N-HEPTANE SYSTEM

Sodium extraction and water uptake from a sodium chloride aqueous solu tion by a di (2-ethylhexyl) phosphoric acid (D 2 EHPA)/n-heptane syste m was experimentally studied. The behavior of water uptake was classif ied into three regions based on the pH dependence of the water content , W-0. In the region of pH 1-4 (Region 1), the molar ratio of sodium i n the organic phase to total D 2 EHPA, E-Na, increased when pH was hig her. However, W-0 was low and did not depend on pH. In the pH region o ver 6 (Region 3), W-0 was high and showed no pH dependence. D 2 EHPA e xisted as sodium di(2-ethylhexyl) phosphate (SD 2 EHP) and formed reve rsed micelles in this region. In the region of pH 4-6, both E-Na and W -0 increased with the rise in pH. This region is thought to be a trans ition state from D 2 EHPA-Na complex to the formation of the reversed micelles. The behavior of the water uptake into the organic phase at t he Region 1 and 2 was analyzed by the extraction equilibrium theory. I t was found that the pH dependence of the water content under the low loading ratio could be explained using the model that water molecules coordinated into D 2 EHPA-Na complexes.