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BR-112022003716-B1 - METHOD FOR RECOVERING Cr CONTAINED IN A PICKLING BATH FOR PICKLING METALLIC MATERIALS AND UNIT FOR RECOVERING Cr CONTAINED IN A METAL PICKLING BATH

BR112022003716B1BR 112022003716 B1BR112022003716 B1BR 112022003716B1BR-112022003716-B1

Abstract

METHOD FOR RECOVERING Cr CONTAINED IN A PICKLING BATH FOR PICKLING METALLIC MATERIALS AND UNIT FOR RECOVERING Cr CONTAINED IN A METAL PICKLING BATH. Method for recovering Cr from a pickling bath for metallic materials (1), the bath (1) being an aqueous solution containing at least one sulfate and Cr from the pickled metal, the method comprising the steps of: -forming a two-phase aqueous system from at least a portion of the pickling bath (1) and a polymer comprising an unhindered ether function, the proportion of polymer in the ternary mixture consisting of the pickling bath which is considered as a single chemical component, water and polymer, being such that it varies between the line of the equation % by weight of polymer = 100% ? % by weight of pickling bath and the binodal curve of the pickling bath/polymer mixture, the aqueous two-phase system comprising a polymeric phase, in which most of the Cr is located, and a non-polymeric phase; - separate the polymeric and non-polymeric phases; - allow the formation of precipitates containing Cr in the polymeric phase; - perform the solid/liquid separation of the polymeric phase in order to separate the polymer and the precipitates containing Cr;(...).

Inventors

  • Ismael GUILLOTTE
  • Eris SINOIMERI
  • Isabelle BILLARD
  • Jerôme COGNARD
  • Nadine COMMENGES-BERNOLE
  • Jean-Michel Damasse

Assignees

  • APERAM

Dates

Publication Date
20260310
Application Date
20190906

Claims (19)

  1. 1. METHOD FOR RECOVERING Cr CONTAINED IN A PICKLING BATH FOR PICKLING METALLIC MATERIALS (1), the pickling bath being maintained in a tank (2), the pickling bath (1) being an aqueous solution containing at least one sulfate and Cr derived from a pickled metal, characterized by: - a two-phase aqueous system is formed from at least a portion of the pickling bath (1) and a polymer comprising an unhindered ether function, the polymer being selected from PEG-200, PEG-400, PEG-600, tetraethylene glycol dimethyl ether and triethylene glycol dimethyl ether, a proportion of polymer in the ternary mixture formed by the pickling bath considered as a single chemical component, water and the polymer, such that the proportion lies between the line of the equation “% by weight of polymer = 100% - % by weight of bath of "pickling (equation 1)" and the binodal curve of the pickling bath/polymer mixture at bath temperature, the aqueous two-phase system comprising a polymeric phase, in which most of the Cr is found, and a non-polymeric phase; - the polymeric and non-polymeric phases are separated; - Cr-containing precipitates are allowed to form in the polymeric phase; - solid-liquid separation is performed in the polymeric phase to separate the polymer and the Cr-containing precipitates; - the Cr-containing precipitates are treated to recover the Cr contained in the Cr-containing precipitates; - and the non-polymeric phase of the aqueous two-phase mixture is sent to tank (2) containing the pickling bath (1); wherein, before the non-polymeric phase of the aqueous two-phase mixture is sent to tank (2) containing the pickling bath (1), a treatment is performed on the non-polymeric phase comprising the degradation of the residual polymer by means of an oxidation process advanced.
  2. 2. METHOD, according to claim 1, characterized by, in order to accelerate the kinetics of formation of the Cr-containing precipitates and the polymer, the polymeric phase is irradiated before solid-liquid separation by exposing the polymeric phase to at least one light source with a wavelength between 340 and 860 nm.
  3. 3. METHOD, according to claim 2, characterized by, before exposing the polymeric phase to the light source, the polymeric phase being placed in the form of a liquid film.
  4. 4. METHOD, according to any one of claims 1 to 3, characterized in that, after solid-liquid separation in the polymeric phase, a liquid fraction resulting from the separation is dehydrated to recover the polymer contained in the liquid fraction and the polymer is reused to form the aqueous two-phase mixture.
  5. 5. METHOD, according to claim 4, characterized in that the dehydration is carried out by distillation.
  6. 6. METHOD, according to any one of claims 4 to 5, characterized in that the water resulting from dehydration is sent to the tank (2) containing the pickling bath (1).
  7. 7. METHOD, according to any one of claims 1 to 6, characterized in that the recovery of Cr from Cr-containing precipitates is carried out by a pyrometallurgical process.
  8. 8. METHOD, according to claim 7, characterized in that the pyrometallurgical process is a pyrometallurgical reduction process of oxides using carbon.
  9. 9. METHOD, according to any one of claims 1 to 8, characterized by: - the part of the pickling bath (1) is extracted from the tank (2) containing the pickling bath (1); - the aqueous two-phase system is formed from the part of the pickling bath (1) and the polymer comprising an unhindered ether function, the polymer being selected from PEG-200, PEG-400, PEG-600, tetraethylene glycol dimethyl ether and triethylene glycol dimethyl ether, the proportion of polymer in the ternary mixture formed by the pickling bath considered as a single chemical component, water and the polymer, being such that the proportion lies between the line of the equation “% by weight of polymer = 100% - % by weight of pickling bath (equation 1)” and the binodal curve of the pickling bath/polymer mixture at the bath temperature, the aqueous system two-phase comprising the polymeric phase in which most of the Cr is found, and the non-polymeric phase; - and the non-polymeric phase of the two-phase aqueous mixture is sent to tank (2) containing the pickling bath (1).
  10. 10. METHOD, according to claim 9, characterized in that the tank (2) containing the pickling bath (1) is continuously fed with pickling bath (1).
  11. 11. METHOD, according to any one of claims 1 to 10, characterized in that the pickled metal is a stainless steel.
  12. 12. UNIT FOR RECOVERING Cr CONTAINED IN A METAL PICKLING BATH (1) according to the method as defined in claim 1, the pickling bath (1) being an aqueous solution containing at least one sulfate and Cr(VI) derived from a pickled metal, characterized by comprising: - a tank (2) containing the pickling bath (1); - a mixing reactor (3) connected to the tank (2); - a receptacle (4) containing a polymer intended to be placed in the mixing reactor (3) to form a two-phase aqueous system with the pickling bath (1), the polymer being selected from PEG-200, PEG-400, PEG-600, tetraethylene glycol dimethyl ether and diethylene glycol dimethyl ether; - a device (5) for separating the phases of the two-phase aqueous system into a polymeric phase and a non-polymeric phase; - and an installation solid-liquid (7) acting on the polymer phase to separate, from the polymer, the Cr(VI) containing precipitates present in the polymer phase, wherein the unit comprises means, by means of an advanced oxidation process, to treat the non-polymer phase, comprising the degradation of the residual polymer.
  13. 13. UNIT, according to claim 12, characterized in that the unit comprises an installation (6) for irradiating the polymeric phase with radiation from at least one light source with a wavelength in the wavelength range of 340-860 nm, to accelerate the formation of Cr-containing precipitates.
  14. 14. UNIT, according to claim 13, characterized in that the unit comprises means for placing the polymeric phase in film form and exposing the film to at least one light source in the wavelength range of 340-860 nm.
  15. 15. UNIT, according to any one of claims 12 to 14, characterized in that the unit comprises an installation (10) for recovering Cr from Cr-containing precipitates.
  16. 16. UNIT, according to claim 15, characterized by the installation (10) for recovering Cr using a pyrometallurgical process, such as pyrometallurgical reduction of oxides using carbon.
  17. 17. UNIT, according to any one of claims 12 to 16, characterized in that the unit comprises an installation (9) for dehydrating the polymer after separating the polymer from the Cr-containing precipitates.
  18. 18. UNIT, according to any one of claims 12 to 17, characterized in that the mixing reactor (3) and the device (5) for separating the phases of the two-phase aqueous system are constituted by the same item of equipment.
  19. 19. UNIT, according to any one of claims 12 to 18, characterized by comprising at least one of the following means: - means for recycling the non-polymer phase in the pickling bath (1); - means for returning the spent polymer, after dehydration of the polymer, back to the receptacle (4) containing the polymer; - and means for returning the water, resulting from the dehydration of the polymer, back to the pickling tank (2).

Description

FIELD OF THE INVENTION [001] The present invention relates to the pickling of metallic materials containing Cr, in particular high-Cr content steels, such as stainless steels. More specifically, it relates to the recovery of metals found in the dissolved state in pickling baths containing sulfates, with the purpose of regenerating these baths and thus allowing their reuse or inclusion in a continuous processing method without rapid degradation of the performance of said method, thereby improving the recovered metals as much as possible. BACKGROUND OF THE INVENTION [002] Chemical pickling is an essential operation in the steelmaking process. It consists of removing the oxidized layer on the surface of the part and immersing the part in an aqueous solution, most often highly acidic (in particular a solution containing one or more acids typically selected from HCl, HNO3, H2SO4, HF), but also possibly containing neutral salts, for example, sulfates such as Na2SO4, K2SO4, (NH4)2SO4. [003] Baths rich in sulfates are particularly used in electrolytic pickling processes. [004] The oxidized layers to be pickled are formed during heat treatments carried out in oxidizing atmospheres (air in particular). This pickling is often performed on strips transported in motion. It allows the strips to be rolled without the risk of oxides becoming embedded in the strip surface, thus deteriorating the appearance and quality, or allows the surface to be treated in good condition. [005] Throughout this pickling operation, the baths become enriched with metallic salts derived from the dissolution of the oxide layers and/or the base metal. [006] This loading of baths with metallic salts is detrimental from two points of view. The first is that the presence of metallic cations in the bath in large quantities alters the existing chemical and electrochemical equilibria in new baths, thus reducing the effectiveness of pickling. The second is that when these dissolved metals reach their solubility limit concentration, they precipitate and form sludge within the baths. This sludge can cause surface quality problems if it is deposited on the treated product or on the rollers that guide the product's displacement path. It can also be deposited in the vats, tanks, and pipes of the pickling plant and, therefore, impair the proper functioning of this plant. [007] Given this change in the metal content of pickling baths and the associated loss of effectiveness, the only simple means for industrialists is to regenerate the spent bath, either fully or partially, by adding fresh bath. Before regeneration, all or part of the spent bath is sent to a neutralization station where it is mixed with other spent baths and then treated to reduce the Cr(VI) ions contained therein (by reduction with Fe(II) or sodium NaHSO3, for example), followed by precipitation of the metallic cations through the addition of NaOH or Ca(OH)2. The solid elements are then separated from the liquid by flocculation/decantation and filtered in a filter press. The resulting metal hydroxide sludge cakes are discarded as waste, since there is no economically viable treatment for improving this sludge. [008] This sludge is composed of a mixture of metals dissolved in different surface treatment baths and anions from at least some of these baths. For example, the high S and F content of this sludge derived from acid baths, when using H2SO4 and HF, prevents the reuse of this residue through pyrometallurgical processes. Faced with this drawback, one solution is to separate the neutralization streams to obtain, on one side, the spent baths containing F and S, and on the other side, the baths with byproducts that are less difficult to recycle. [009] Treatment solutions for a given type of bath already exist and are in use. These solutions, such as roast spraying for hydrochloride baths, generally allow for acid regeneration on one hand and metal recovery on the other. These methods are often expensive and do not always allow for the regeneration of an acid at a concentration suitable for use in an industrial process. In addition, these methods generally consume a lot of energy and/or consume large quantities of water and/or use resins or ion exchange membranes that require cleaning cycles during which the plant cannot be used. DESCRIPTION OF THE INVENTION [010] The object of the invention is to propose a method that is efficient and economically viable for regenerating spent electrolytic pickling baths and for recovering the Cr contained in these spent electrolytic pickling baths containing relatively high amounts of one or more sulfur-containing compounds, such as sulfates. [011] To this end, the object of the invention is a method for recovering Cr from a pickling bath of metallic materials contained in a receptacle, such as a pickling tank, said pickling bath being an aqueous solution containing at least one sulfate and Cr derived from the pickled metal, wherein: - a biphasic aqueous s