Process for the stabilization of mercury metal by reaction of the mercury metal with sulphur in the solid state, in which the mercury and the sulphur are brought into contact, at an Hg/S molar ratio of 1/1 to 1/3, in a reactor integral with a hollow pipe in fluid communication with the interior space of the said reactor, the said hollow pipe comprising a first end connected to the wall of the said reactor and a second end distant from the said reactor; the said hollow pipe and the said reactor being hermetically sealed, the said hollow pipe being provided with rotating means external to the said pipe and to the said reactor for rotating the said reactor and the said pipe around the axis of the said pipe, and the said hollow pipe being provided, at its end distant from the reactor, with means for introducing the sulphur and the mercury inside the reactor and discharging the reaction products.