The surface treatment industry produces a large volume of aqueous effluents highly polluant due to an important concentration in heavy metals. In most of the time, in order to clear off their waste water, the companies use coprecipitation processes which give a lot of hydroxide sludges. These sludges are very pollutant and are up to now directly stored in class I or 2 dumps, without any treatment, thereby causing severe pollution problems. So, current European environmental legislation on dump storage will be introduced to collect only stabilized wastes in class I dumps from 1999. Anticipating the legislation, this project aims at converting 100% hydroxide sludges into an inert solid waste meeting at least the European criteria of storage in dumps, and able to be valorised a l raw material in building and motorways construction for instance. In a first step, the sludges will be solubilized by means of selective solvants in order to extract heavy metals. Then the solution containing the pollutant elements will be concentrated and vitrified to confine the toxic wastes in inert glasses able to preserve environment from pollution (resistance to leaching) and thus allowing valorisation. The project aim at achieving an inert solid waste at effective cost, reducing the bulk of this solid waste (5 factor or more) and reducing the water consumption (whole or partial recycling).