Two waste soins. withdrawn from a cation-exchange resin regeneration step, contg. Na 2250,846, Ca 3570, 3410; Mg 1380, 1020; K 834, 310; Fe 14, 10, Mn 10, 7; Cl 56 400, 48 700; and SO4 125,29 ppm (HCl 40 600,37 600 ppm), were membrane-distd. at 358 K through PP membranes, total porosity 73016, pore size 0,2 Am, and ext-/int diam. ratio 2.6/1.8. The feed and the distillate were passed in cocurrent at 0.14 and 0.05 m/s, resp. In a batchwise single-stage membrane distn., the permeate HCl concn. varied much. With the feed added continuously and the concentrate withdrawn partially, the compn. was stable. A 4-stage system gave nearly pure water and a HCl soln. As water was sepd. in ca. 83016, CaO4 could ppt. in the feed. At stage I and It, the distillate contained 0.5 and 1.2 g HCI/I., resp.; at higher stages the flux was richer in HCI.