Reverse osmosis applied to the recovery of water from aqueous salt solutions

A cellulose acetate membrane was applied to the study of reverse osmosis on aqueous solutions of LiCl, NaCl, KCl, CaCl₂, SrCl₂ and BaCl₂. This membrane, 71 microns thick and having an effective diameter of 1 1/2 in. was mounted within a specially constructed cell, made of stainless steel and designed to withstand pressures up to 1500 psi. The cell consisted of two chambers, which were separated by the membrane, and a porous plate supporting it. Solutions of 0·05 N, for all of these salts, were used to establish the osmotic pressure of each solution, the water fluxes through the membrane, and the extent of salt rejection. These variables were also determined for NaCl normalities of 0·2 and 0·6. On a single pass basis, the salt rejections ranged from 76% for KCl up to 95% for CaCl₂. The results are discussed in terms of the size of the hydrated cation. The water fluxes for all these solutions were found to be essentially the same and were independent of the type of salt. For solutions of 0·05 N, the water fluxes ranged from zero at the osmotic pressure up to about 44 × 10^?5 g sec^?1cm^?2 (8·8 gal day^?1ft^?2) at 800 psi and 77°F. Also, for the 0·05 N-NaCl solution, the temperature was varied from 77°F to 120°F. The results of this temperature study show that the extent of salt rejection remains essentially fixed, while the water flux at any given pressure at 120°F becomes nearly double that of 77°F.