The invention relates to a process and plant for converting hazardous waste containing the contaminant chromium VI into non-hazardous waste which can be stored without special precautions and which is broken down in the environment without time constraints. The inventive process essentially comprises: a grinding step; the extraction of the chromium VI in liquid phase under controlled agitation, time and temperature conditions; the conversion of the chromium VI into chromium III by means of reduction; and, subsequently, the precipitation thereof as chromium trioxide by means of gasification. The solid resulting from the conversion process can be used as a raw material for the construction of fire bricks or optionally for the production of partitions used in construction using a process that is not included in the description.