GB1312681A - Electrolytic recovery of metals from solution - Google Patents

Abstract

1312681 Electrolytic recovery of metals from solution PPG INDUSTRIES Inc 11 March 1970 [11 March 1969 2 June 1969] 11559/70 Heading C7B A method of recovering metal from a first solution containing trace amounts of the metal as ions comprises (a) subjecting the first solution to electrolysis in an electrolytic cell while passing the solution through a porous cathode of the cell to deposit out metal in the cathode, (b) reversing the potential and having a second solution in the cell resulting in resolution of the metal, the metal being in a more concentrated form in the second solution than in the first, and (c) recovering the metal in metallic form from the second solution by electrolytic deposition on to a cathode. The first and second solutions may be aqueous alkaline, acid or salt solutions (e.g. of NaOH, HCl or Na Cl). Specified metals to be recovered are Hg, Cu, Fe, Ni, Pb, V, Mn, Ru, Rh, Pd, Os, Ir, Pt, Au and Ag. Where different metals are to be selectively removed from the first solution this may be done by passing the solution through a series of cells each having a cathode at a different potential. Where more than one metal has been deposited in the porous cathode the electrode potential during removal of the metal can be controlled to selectively remove particular metals. The porous cathode may be of carbon, e.g. graphite, or sintered or sponge metal, such as sponge Ti or Zr having Pt group metal in the interstices thereof. The anode may be carbon, e.g. graphite, Ni, Pt group metal or Ti coated either with Pt group metal or with an oxide or oxides thereof. The electrolytic cell may comprise a cylindrical body 11 with an anode 13 and porous cathode 12. Solutions may be passed through the cell in either direction between openings 21, 22. Vents 25, 26 are for removal of product gases. Fig. 3 (not shown) illustrates a cell comprising an anode (113) within a blind-end tubular porous cathode (112) within a cylindrical container with solution flow through the wall of the porous tubular cathode between openings (121, 122). The second solution may be passed through the cell one or more times to dissolve the metal deposited in the cathode. The second solution may be different from the first. As illustrated in Fig.1, the method is employed in removing Hg and other metallic impurities from brine which has passed through a Hg cathode electrolytic cell. The metallic impurities are removed in a porous cathode cell and the brine is then electrolyzed in a diaphragm cell. The metallic deposits which build up in the porous cathode can be redissolved by (i) reversing the current and passing therethrough brine containing substantial amounts of free Cl 2 which removes the Hg but not all the Fe and (ii) thereafter removing the remaining Fe by circulating acid, e.g. HCl, through the cell under either normal or reversed potential. Reference is made to what is claimed in Specification 1312682. Reference has been directed by the Comptroller to Specification 1169206.