Abstract: A method for treating heavy metal contaminated soils, particularly those containing hexavalent chromium, which includes a first soil washing at pH 9-12 with an anionic synthetic organic flocculant followed by a liquid-solid phase separation such as by gravity separation including sedimentation, an optional second soil sludge washing at pH 2.5-3.0 with addition of a metal valency reducing agent which when done is followed by a second liquid-solid phase separation using a cationic synthetic organic flocculant, combining the first and second stage liquids and optional treating the liquid phase with a metal valency reduction agent such as sodium metabisulfite under acidic conditions followed by treatment with an alkaline agent to form insoluble metal hydroxide which is separated in a phase separation process and is combined with the final sludge, recycling the liquid from washing stage or stages for use in soil processing, dewatering the separated sludge or sludges using a separation method (e.g.