This invention is directed to apparatus and methods for separating weakly ionizable substances from mixtures of the same such as carbon dioxide from an enclosed atmosphere. One method employs a four compartment electrolytic cell comprised of end electrodes, a planar anion exchange membrane therebetween, a corrugated cation exchange membrane between and in contact with the anode electrode and the planar membrane and a corrugated anion exchange membrane between and in contact with the cathode electrode and the planar membrane. The projections of each corrugated membrane make point contact with the adjacently placed electrode and planar membrane to form an anode, stripper, scrubber and cathode compartment. In operation the CO2 contaminated air is passed into the scrubber compartment; water is passed through the remaining compartments and a D.C. current is passed between the electrodes to result in the recovery of partially purified air from the scrubber compartment.