The invention relates to a column for carrying out gas/liquid mass-transfer processes, wherein, in the column (27), at least one lock (15) bordered by an upper separating tray (17) and a lower separating tray (19) is received, which lock is designed in such a manner that, during the mass-transfer process, gas (23) flows through the lock (15) and a liquid (25) situated on the upper separating tray (17), when the gas supply is interrupted the liquid (25) flows into the lock (15) onto the lower separating tray (19) and when the gas supply is renewed, the liquid (25) drains downward out of the lock (15). The lower separating tray (19) has a tray (1) that can be mounted so as to be fixed and has at least one opening (3), and a rotatable tray (13) which is connected to a rotatable axle (21) that is conducted through the tray (1) that can be mounted so as to be fixed, in such a manner that the rotatable tray (13) can be turned in relation to the tray (1) that can be mounted so as to be fixed, wherein the rotatable tray (13) of the lower separating tray (19) is designed in such a manner that the at least one opening (3) in the tray (1) that can be mounted so as to be fixed is closed in a first position of the rotatable tray (13) and can be opened by turning the rotatable tray (13).