PURPOSE: To lower a residual mercury concn. to an environmentally permissible value and to reduce an operation cost by executing the stages of the formation of an aqueous solution ionic mercury, the removal of dissolved and unreacted chlorine and the removal of the ion type mercury compd. by bringing the soln. into contact with materials pendent with thiol groups.

CONSTITUTION: A waste thimerosal soln. is mixed with a sodium bisulfide soln. to obtain an aq. soln. mixture of a desired pH condition. The mixture is then sent by a pump 10 into parallel reaction vessels 16, 18 where the aq. soln. of the resulted reaction product is aerated by diffusing air or oxygen with sprayers 34, 36. After the end of the aeration, the aq. metasodium bisulfite of a stoichiometric quantity corresponding to the residual chlorine is added to the soln. to sufficiently effect reaction. The soln. is then sent to liquid feed columns 52, 54 where the sodium hypochlorite bonded to the sodium bisulfite is adsorbed. The soln. is sent to ion exchange resin columns 58, 60, 62 and 64 connected in series where the ion type mercury is removed from the aq. soln. by ion exchange in resin bead beds having the pendent thiol groups.