Catalytic oxidation of sodium sulphide in the presence of carboxylic ion exchangers: B.N. Laskorin, N.G. Zhukova, O.P. Polyakova, V.V. Krylova, A.N. Astanina, V.I. Volkov, A.A. Proboi and N.P. Stupin, All-Union Scientific Research Institute of Chemical Technology, Moscow, U.S.S.R.