Method of isolating mercury from a solution, where a solution containing dissolved metal salts and mercury salts is fed into the cathode chamber of an electrodialysis unit, and an electrolyte is placed in its anode chamber separated from the cathode chamber by an anion-permeable membrane, the solution is subjected to electrolysis during which the transition of anions into the anode chamber, the pH of the solution in the cathode chamber is raised to ≥ 8.5, and hydrated oxides and / or hydroxides of dissolved metals to which mercury salts, in particular complex mercury salts, and such prepared suspension is removed from the cathode chamber and filtered to obtain a filtrate and a solid phase containing isolated mercury salts, after which at least a portion of the filtrate is discharged into the anode chamber as an electrolyte. The invention also relates to a device for carrying out the method. The process and apparatus allow wastewater and other mercury-containing solutions to be decontaminated without adding sorbents or other reagents.