Method for recovering chromium contained in a bath for pickling metallic materials and facility for implementing same

A method for recovering Cr contained in a pickling bath for pickling metallic materials, the pickling bath being held in a tank, said pickling bath being an aqueous solution containing at least one sulphate and Cr derived from a pickled metal, wherein:

• an aqueous two-phase system is formed from at least one portion of said pickling bath and from a polymer comprising an unhindered ether function, the polymer being selected from the group consisting of PEG-200, PEG-400, PEG-600, tetraethylene-glycol dimethylether, triethylene-glycol dimethylether, and block copolymers of polyethylene glycol and polypropylene glycol,
• a proportion of the polymer in a ternary mixture-formed by the pickling bath considered to be a single chemical component, water and the polymer-being such that said proportion lies between a line of an equation weight % of polymer=100%−weight % of pickling bath and a binodal curve of the pickling bath/polymer mixture at bath temperature, said aqueous two-phase system comprising a polymer phase, in which most of the Cr is found, and a non-polymer phase;
• said polymer and non-polymer phases are separated, the polymer phase containing less than 0.03% S;
• Cr-containing precipitates are formed in the polymer phase;
• solid-liquid separation is performed on said polymer phase to separate the polymer and the Cr-containing precipitates;
• said Cr-containing precipitates are treated to recover the Cr contained in said Cr-containing precipitates;
• and
• said non-polymer phase of said aqueous two-phase mixture is sent to the tank containing the pickling bath,
• wherein, before said non-polymer phase of said aqueous two-phase mixture is sent to the tank containing the pickling bath, a treatment is performed on the non-polymer phase comprising degrading residual polymer via an advanced oxidation process.