A mobile or stationary process and assembly decontaminates soil and sludge which contains mercury by exploiting its easy evaporation and high specific weight. The contaminated soil or sludge is introduced into an enclosed system in which it is heated, converting the mercury to a gaseous vapor. The cleaned soil or sludge may then be discharged. The mercury vapor is condensed from air by washing with cold water. The air is repeatedly recirculated , being heated and passed through a revolving kiln. The mercury's high specific weight drives it to the base of the washer from which it is tapped for re-use. The installation is preferably mobile, and installed on a ship or barge.
