instead of operating in the soluble anode mode the concentration of the treated solution is reconstituted by the addition and dissolution of a salt of the metal whose hydroxide is to be produced for example a carbonate a non soluble anode for example of lead or ruthenised titanium is used it is also possible to produce hydroxides of metals such as chromium nickel cadmium cobalt zinc or uranium or double or triple hydroxides such as nickel cadmium hydroxide or nickel cadmium cobalt hydroxide the applications of this method concern notably the treatment of uranium ore to recover the metal through its hydroxide the starting acid solution containing the uranium salt being an acid feed solution of an uranium ore fig2 shows a similar installation comprising a vat 1 a cathode compartment 2 with a cathode 5 and an anode compartment 3 with an anode 6 in this instance the cathode compartment 2 and the anode compartment 3 are separated by a cation exchange membrane 7 the anode compartment is filled with the solution to be treated or anolyte from which the hydroxide is to be precipitated and which it should be recalled is a solution of a metal in an alkaline medium advantageously a highly concentrated solution of caustic soda or caustic potash is used for example 8n caustic soda or caustic potash the cathode compartment is filled with the catholyte for example a 0 5n solution of caustic potash and the anode and cathode compartments are fitted with respective electrodes of dimensionally stable insoluble metal for instance as mentioned above the alkaline cations for example.