The liquid waste processing is carried out by processes of purification and concentration. The solvent extraction and the processes of separation per membrane are particularly gravitational for economic reasons. Their use for the treatment of the solutions which is compatible from the technological and kinetic point of view. We were interested in the extraction of trivalent Chromium in phase liquid-liquid because of its presence with the state of traces in many industrial effluents. We have examined the systems of extraction comprising Chromium (III) in sulphuric acid medium by differents solvants: exchangers of cations like di(2,4,4-trimethyl-pentyl) the phosphonic acid (Cyanex), exchangers of anions such as Primene JMT and the Tri-n-octylamine (T.O.A) M in various diluents (chloroform, kerosene). We applied to these synthetic systems the conventional variables. Interesting outputs were obtained for diluted solutions (0.05 M). The study of the chemical variables made it possible to determine chemical parameters giving of the outputs of optimum extraction. A chemical modelling made it possible to identify the mechanisms of extraction. The process purification by membrane permitted to obtain the interesting performances. The association with the concentration would be particularly judicious in the case of the treatments of the industrial wastes containing heavy metals, it is very sparing out of water and raw materials (recycling of the reagents and extractants).