Long-term reverse osmosis tests were conducted with electroplating wastes on a new membrane referred to as NS-100. This membrane consists of a polyurea layer, formed by the reaction of tolylene diisocyanate with polyethylenimine, deposited on a porous polysulfone support film. The membranes were tested as liners within 1/2-inch diameter fiber glass tubes. A total of 2360 hours of continuous reverse osmosis operation was achieved, 1220 hours on pH 1.2 acid copper rinse water and 1140 hours on pH 12.8 alkaline zinc cyanide rinse water. The membranes exhibited remarkable chemical stability during exposure to these two pH extremes. Copper and zinc rejections were generally greater than 99 percent, while cyanide rejections were typically 96 percent or greater. Membrane fluxes were in the range of 18 to 24 liters per sq. m. per hr. (11 to 14 gfd) for acid copper, but only 8 to 15 1/sq m-hr (5 to 9 gfd) for zinc cyanide at 41.4 bars (600 psig) and 25C. Rejection of organics (including brighteners) was 60 to 78 percent for acid copper and greater than 95 percent for zinc cyanide. NS-100 membranes did not reject sulfuric acid. A modified membrane NS-101, demonstrated twice the permeate flux of NS-100 toward zinc cyanide baths, but cyanide rejections were low at 90 percent. Difficulties of producing reproducible, high-flux tubular membranes were not fully resolved in this study.

Performed by Midwest Research Institute under EPA grant no. R-803264-01-0. "October 1976." "EPA-600/2-76-197." Project officer: Donald L. Wilson. Includes bibliographical references (p. 38-39).