Abstract: The present invention relates to a method for treating effluents, especially the effluents from leather tanneries, containing chrome salts, i.e. the salts of chromium having a (III) oxidation degree, characterized in that the supplied effluents or those having a pH that is lower than 6 undergo an electrochemical reaction in a reactor comprising an anode and a cathode in such a way that the chromium having a (III) oxidation degree is transformed into chrome having a (VI) oxidation degree, and in that the treated effluents are recovered. The treatment method is followed in an advantageous manner by a method for recovering the hexavalent chromium by means of selective extraction in an appropriate solvent medium followed by reduction of the hexavalent chromium into trivalent chromium.

Abstract: Both a process and plant are provided for electrolytically coating with a metal layer the casting surface of a roll for twin-roll or single-roll continuous casting of thin metal strip. The casting surface is at least partially immersed in an electrolyte solution containing a salt of the metal to be deposited, so as to face at least one anode. The surface is placed at a cathode and a relative movement is created between the casting surface and the electrolyte solution. Insulating masks are interposed between the anode or anodes and the arrises of the casting surface, the insulating masks preventing a concentration of the lines of current on the arrises and in their vicinity.

Abstract: The subject of the invention is a process for conditioning the copper or copper-alloy external surface of an element of a mold for the continuous casting of metals, of the type including a step of nickel plating of said surface and a step of nickel removal therefrom, wherein:a preparation of said surface, comprising in succession an operation of cleaning said bare surface, an operation of pickling said bare surface in an oxidizing acid medium and an operation of brightening said bare surface, is carried out;then, an operation of nickel plating of said bare surface is carried out by electroplating, by placing said element as the cathode in an electrolyte consisting of an aqueous nickel sulfamate solution containing from 60 to 100 g/l of nickel;then, after said element has been used, an operation of partially or completely removing the nickel from said surface electrolytically is carried out, by placing said element as the anode in an electrolyte consisting of an aqueous nickel sulfamate solution containing fro

Abstract: A process for producing amino alcohols by electrosynthesis of nitro alcohols.Reduction of the nitro group is performed in three stages on a cathode made of a material having a strong hydrogen overpotential. During the second stage of reduction, the electronegative potential is higher, and in the last stage the sulfuric solution of amino alcohol obtained is subjected to a purification operation by electro-electrodialysis (EED), followed by an elimination of water.The process is particularly useful for the production of 2-nitro-2-methyl-1-propanol, 2-nitro-2-methyl-1, 3-propanediol, 2-nitro-2-ethyl-1, 3-propanediol, 2-nitro-1-butanol, tris(hydroxymethyl) nitromethane.

Abstract: In a process for recovering zinc from residues containing it, particularly rom ashes and hard-spelters coming from galvanizing baths, and which comprises the extraction by electrolysis of the zinc contained in the alkaline or acid solutions obtained. The solutions deriving from the ashes are obtained by dissolving their relatively low metallic zinc content granulometric fraction, the high metallic zinc content granulometric fraction of these ashes being re-introduced directly into the galvanizing bath advantageously after a leaching treatment and the solutions deriving from the hard-spelters are obtained by dissolving them either by having recourse to a corrosion cell or by forming by means of these hard-spelters the anodes of an electrolysis circuit.

Abstract: Regeneration of spent hydrochloric acid after use for pickling iron, which herefore contains iron chlorides, by electrolysis in the cathodic and intermediate compartments of an electrodialysis cell. The installation includes electric circuitry for connecting up the anode as well as input conduits for the spent acid but otherwise consists essentially of an electrodialysis cell with an uneven number of compartments wherein each cathodic compartment is separated from the adjacent intermediate compartment by an anion-selective membrane while a cation-selective membrane separates each intermediate compartment from the anodic compartment, the latter being filled with an anolyte whose total Faraday yield for water oxidation is close to 1. Electrolysis is conducted with current densities at the cathode of 0.1 - 20 A/dm.sup.2, at the anode corresponding to the water oxidation reaction and at the membranes such that their perm-selectivity is close to 1.