(JP4501978-W)      Sepn. is in a cell with at least one bipolar membrane having cation plus anion layers and positioned between anion membranes. Bipolar membrane anion layer and first anion membrane define a feed compartment; a prod. compartment is defined by corresp. cation layer; and second anion membrane. DC potential is applied across the cell via anode and cathode. Aq. feed contg. acid and salt is passed to the feed compartment. Aq. prod. stream e.g. contg. acid and soluble salts is fed to corresp. prod. compartment. H+ ions form at the bipolar membrane cation layer in prod. compartment and feed anions. An- transfer across anion membranes into the prod. compartment to form acid prod. for removal.    USE/ADVANTAGE -   Acid/salt mixts. for sepn. are e.g. HCl/NaCl, HAc/NaOAc, HCl/NH4CL, Na2SO4/H2SO4, HF/HNO3/Ni(NO3)2 etc. Several alternate bipolar and anion membranes are useable. Aq. feeds for treatment are e.g. uranium extraction, stainless steel pickle liquor or battery acid reclamation wastes etc., spent Al anodising bath liq.    (US5162076-A)      Sepn. of a strong acid from an aq. feed stream comprising a strong acid and salt contg. cations and anions includes using an appts. comprising one bi-polar membrane with a cation layer and an anion layer. Each bi-polar membrane is between a first and second anion membrane with a feed compartment between anion layer and anion membrane and a prod. compartment between cation layer and second anion membrane. Method comprises feeding an aq. feed stream, with a pH of less than 3, to one feed compartment; feeding aq. prod. stream to one prod. compartment; applying an electrical potential across the appts. to cause a direct current to introduce H+ from the bi-polar membrane into the prod. compartment and transporting anions across membrane into the prod. compartments; and removing prod. stream for prod. compartment and feed stream from feed compartment.    Appts. pref. comprises at least one feed compartment. Pref. conc. of acid in the feed is 1-3N and pref. salt conc. is 0.1 mol. or more. Pref. operating temp. is 35-50deg.C. and if sulphuric acid is used then a temp. above 45deg.C. is pref. Current densities are pref. 50-150 amps. per sq. ft.    USE/ADVANTAGE -   Increased efficiency. Prodn. is more compact which affords greater space and economy.