Charged Membrane Ultrafiltration of Toxic Metal Oxyanions and Cations from Single- and Multisalt Aqueous Solutions

With application to the treatment of nonferrous metals production streams, the toxic metals As(V), Se(IV), As(III), and Cd(II) are separated from single-and multisalt aqueous solutions by continuous-flow, membrane ultrafiltration with charged, noncellulosic membranes. The single-salt aqueous solutions of As(V), Se(IV), As(III), or Cd(II) are investigated over pH 5 to 10, metal concentrations in the range 0.5 to 20.0 mM, and transmembrane pressure differences from 2.8 x 10⁵ to 5.6 x 10⁵ N/m², with the effects of these three independent variables established on the metal rejections. The rejections of the monovalent oxyanions H₂As0₄“, HSe0₃“, and H₂As0₃~ (with sodium as the counterion) are of the order 0.85, and those of the divalent HAs0₄ ²Se0₃ ²~ (and S0₄ ^2-), and of Cd²⁺ are of the order 0.95 for 6.0 mM feed streams. Comparisons are made with the halides, N0₃“, andC10₄.The rejection behavior of multisalt solutions of H₂As0₄ “and HSe0₃” is not influenced by the presence of sulfate, but Cd²⁺ produces a decrease in the rejection of Se(IV). For feed streams 2.0 mM each in H₂As0₄“, HSe0₃, Cd^{2 +}, and Zn²⁺ at pH 5, the presence of a high sulfate concentration does not affect the metal rejections, except at greater than 14.0 mM where the Se(IV) rejection begins to decline sharply.