WO2023148516A1 - Procédé de récupération d'acide fluorhydrique libre et combiné à partir d'un bain de décapage d'acier inoxydable - Google Patents

Procédé de récupération d'acide fluorhydrique libre et combiné à partir d'un bain de décapage d'acier inoxydable Download PDF

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Publication number
WO2023148516A1
WO2023148516A1 PCT/IB2022/050884 IB2022050884W WO2023148516A1 WO 2023148516 A1 WO2023148516 A1 WO 2023148516A1 IB 2022050884 W IB2022050884 W IB 2022050884W WO 2023148516 A1 WO2023148516 A1 WO 2023148516A1
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WO
WIPO (PCT)
Prior art keywords
pickling
process according
metal
hydrofluoric acid
free
Prior art date
Application number
PCT/IB2022/050884
Other languages
English (en)
Inventor
Franco Falcone
Anastasios VERGANI
Original Assignee
C.I.E. - Compagnia Italiana Ecologia Srl
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by C.I.E. - Compagnia Italiana Ecologia Srl filed Critical C.I.E. - Compagnia Italiana Ecologia Srl
Priority to PCT/IB2022/050884 priority Critical patent/WO2023148516A1/fr
Publication of WO2023148516A1 publication Critical patent/WO2023148516A1/fr

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
    • C23G1/36—Regeneration of waste pickling liquors
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
    • C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
    • C23G1/08—Iron or steel
    • C23G1/086—Iron or steel solutions containing HF

Definitions

  • the present invention relates to a process for recovering, with high yields, the hydrofluoric acid remaining inside spent the pickling baths used during the metal processing, such as the stainless steel processing, allowing it to be reused with obvious economic and environmental advantages.
  • the pickling is a chemical operation carried out to remove surface layers of a material by means of acid or base solutions.
  • this treatment When performed on metallic materials, this treatment is able to remove the layer of surface oxide or other contaminants, also with the purpose of making the surface suitable for further processing. In fact, after the pickling the exposed surface becomes “porous" and allows for possible bonding with another material. Furthermore, the outer layer of the material is thus cleaned of possible unwanted residues such as, for example, rust formed by hot-rolled steel products, surfactants or other chemicals, and rolling flakes.
  • the pickling is one of the commonly used methods to prepare the steel surfaces on which further cold rolling or mechanical finishing is to be performed.
  • the pickling operation is carried out by immersing the material to be treated in tanks containing acid solutions at high temperature.
  • acid solutions such as hydrochloric, sulfuric, phosphoric, nitric and/or hydrofluoric acids, also in mixture with each other, are used.
  • Corrosion inhibitors can also be introduced into the pickling solutions in order to limit the attack of the acids at the level of the "bare" metal portions, i.e. those areas deprived of the oxide layer more quickly than others.
  • the pickling Since the pickling leaves the metal surface completely clean and exposed, it is usually followed by further treatments adapted to cover it and protect its integrity, which depend on the type of material and the required finish. For example, some operations that can be carried out after the pickling process are the passivation, chrome plating, anodic oxidation and painting.
  • the stainless steels are materials characterized by greater resistance to the oxidation and corrosion, especially in humid air or fresh water, than the so-called "carbon steels". Such capability is mainly due to almost the absence of carbon (less than 0.07%) and the concomitant presence of chromium inside the alloy. The latter, in fact, is able to be "passivated” i.e., to cover itself with a thin and adherent layer of oxides that superficially protects the underlying material from the action of the oxygen and possible other external chemical agents.
  • Austenitic steels Chromium is accompanied by Nickel and the standard alloy is called 18/8 since it contains 18% Chromium and 8% Nickel.
  • Ferritic steels only Chromium is present in amounts from 11% to 30%. In both cases the rolled or forged products have a strong dark layer of oxides that must be chemically removed to obtain the classic light gray color, Such operation is known as pickling.
  • the pickling of a stainless steel provides for the use of strong acid solutions, in order to remove the surface oxides present on its surface, such as slag, dust, iron rust, welding oxides, as well as to remove from the surface the possible layer of steel depleted in chromium due to the alterations suffered by the steel itself during processing. This operation will be followed by a passivation process that will restore in a uniform manner the protective film of oxides.
  • ARU Acid Recovery Units
  • the recoverable free acids are H 2 SO 4 and HF
  • ARU Acid Retard Resin
  • the second phase of the process is started, which involves the introduction of counter-current water in order to free the acids held by the inside of the chromatographic resin (ARR) and return them to the pickling tank.
  • the volumes of spent solution entering the ARU system from the first step and the volumes of counter-current water from the second step are equivalent.
  • Bonded fluorides 58.2 g/L it follows that the maximum recovery achievable by applying only the ARU system will be:
  • an object of the present invention to provide a process for recovering the hydrofluoric acid from the pickling baths that produces high yields in recovering hydrofluoric acid and allows it to be reused, even inside the same pickling system.
  • a further object of the invention is to recover and recycle the hydrofluoric acid present in a pickling solution containing high concentrations of metal fluoride salts.
  • Object of the present invention is a process which allows for recovering the hydrofluoric acid from the pickling bath solutions, particularly for the pickling of metals, preferably stainless steel, including the hydrofluoric acid bound to the Me +3 forms present.
  • pickling bath solutions is meant to denote the liquid phase that fills the tanks in which the materials, that are to undergo the pickling treatment, are immersed. As previously described, said solutions must be periodically replaced due to the accumulation of metal ions that form salts/complexes with the acids present, making the process progressively less efficient.
  • Object of the present invention is a process which allows for reducing the economic and environmental costs of using and disposing of such pickling solutions thanks to an efficient recovery of the hydrofluoric acid dissolved therein and enabling its subsequent possible recycling,
  • the process of the present invention has to be employed upstream of the ARU system and is based on the possibility to free hydrofluoric acid (HF) from its salified/complexed forms with the metal ions, and in particular from the FeF 3 , form.
  • HF hydrofluoric acid
  • hydrofluoric acid occurs thanks to the use of a strongly reducing chemical system.
  • said system may comprise the use of different chemicals and/or modes:
  • organic reducing agents such as oxalic acid, formic acid, ascorbic acid, urea, aldehydes and ketones etc.;
  • hypophosphites and phosphorus derivatives 4. hypophosphites and phosphorus derivatives; 4. catalytic reducing agents (H 2 catalyzed with Palladium, Platinum, Nickel);
  • metal-based or bimetal-based sacrificial anodes such as Fe, Zn, Bi. Ca, Sr, Mg, Ni, in combination or not with carbon.
  • the reducing system is based on the use of NaHSOj (1); a practical example of this aspect is given, for illustrative and non-limiting purposes, in the Experimental Section below (Example 1).
  • the reducing system is constituted by a hydrogen electrolytic cell (3).
  • the reducing system is based on the use of metal-based sacrificial anodes (4), a practical example of this aspect is given, for illustrative and non-limiting purpose, in the Experimental Section below (Example 2).
  • Said metal-based sacrificial anodes may be, according to the present invention, a special mixture of metals (Me 0 ), such as Fe, Zn, Bi, Ca, Mg and Ni, also combined with the carbon, which undergo an oxidation reaction in acid environment, then allowing the reduction of the iron present in the pickling bath from Fe 3+ to Fe 2+ , resulting in the breakdown of the FeFj complex and the formation of FeSO 4 .
  • metals Fe 0
  • metal sacrificial anode an assembly of one or more metals to form an alloy with the carbon, such as the cast iron, iron/ carbon alloy.
  • Said sacrificial anode may be in the form of flakes or powder of the metal itself, its particle size only affecting the process times.
  • the sacrificial anode is constituted by an alloy (Fe/C or FeNi/C, 95% purity) in the powder state, average particle size between 50 and 500 pm.
  • the reaction takes place inside a special reactor made of polypropylene (PP) and equipped with a mixer, thanks to the use of a cell in which the sacrificial anode or the hydrogen electrolytic generator are housed, if present, at a temperature between 20 and 50°C, preferably between 30 and 40°C.
  • PP polypropylene
  • the reaction time required for the conversion of FeF 3 to HF depends on the type of reducing reaction and, in the case of the sacrificial anode, on the particle size of the metal mixture, According to a particular aspect of the present invention, said mixture is in powder form and the reaction time is between 1 and 4 hours.
  • the reaction occurring inside the reactor comprises the following two main steps, sequentially; a. Me 0 + H 2 SO 4 MeSO 4 + H 2 oxidation of the metal from Me 0 to Me 2+ b. 2FeF 3 + H 2 + 2H 2 SO 4 2FeSO 4 + 6HF
  • a stoichiometric amount of H 2 SO 4 must be added from outside, adding to the sulfuric acid already present in the pickling bath solution.
  • Said added amount of H 2 SO 4 is between 5% and 11% by weight to the total volume of the solution introduced into the reactor, depending on the reduction method selected.
  • reaction completion can be verified experimentally by using an instrument capable of reading the redox potential of the solution once all the Fe' 3 has been converted to Fe +2 .
  • a mechanical filtration is performed on a column filter filled with inert material (e.g., polypropylene granules).
  • the solution in which the conversion from Fe +3 to Fe +2 has taken place is sent to the ARU system where, thanks to the presence of the chromatographic resin (ARR), the free acids present can be retained and separated from the metallic salts and finally, thanks to the water introduced in counter-current as previously described, reintroduced into the pickling tanks.
  • ARU chromatographic resin
  • the process of the present invention allows for the conversion of Fe +3 to Fe 4-2 , resulting in the release of HF but at the expense of the simultaneous formation of FeSO 4 , thereby reducing, as a result, the amount of sulfuric acid that can be re-uptaken in the subsequent step through the ARU system and that must be rebalanced.
  • the yields obtained downstream of the ARU system used after the conversion process to free hydrofluoric acid of the present invention are equal to 81,2% with respect to HF, compared to a recovery yield of hydrofluoric acid of, at most, 37.5% according to the known technique, as described above.
  • the process of the present invention therefore allows to achieve significant economic advantages, which reside mainly in the possibility of reusing a greater amount of hydrofluoric acid, thus lowering its living costs as well as those related to the difficulty of its management and storage.
  • the percentage of HF recovered and reusable thanks to the process of the invention increases, as a matter of fact and as already stated above, from about 37,5% achieved with the use of the ARU system alone to 81.22% thanks to the present invention.
  • the economic saving is sufficiently high to absorb, without being significantly affected, the costs, however low, related to the purchase of the mixture of metals to be used for the conversion process from Fe +3 to Fe +2 .
  • the present invention also results in considerable benefits from the environmental point of view, thanks to the consequent reduction of all the problems generated by its management and disposal.
  • Fe +3 (FeFa) 40 g/L (corresponding to F" 40.7 g/L)
  • the reaction bath is kept under mechanical stirring and we proceed to the immersion of a pre- weighed sacrificial anode (Me 0 ) constituted by a iron/carbon alloy, of which 95% iron.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)

Abstract

La présente invention concerne un procédé de récupération, avec des rendements élevés, de l'acide fluorhydrique restant à l'intérieur des bains de décapage utilisés pendant le traitement de métal, tel que le traitement de l'acier inoxydable, ce qui permet de réutiliser l'acide fluorhydrique avec des avantages économiques et environnementaux évidents.
PCT/IB2022/050884 2022-02-02 2022-02-02 Procédé de récupération d'acide fluorhydrique libre et combiné à partir d'un bain de décapage d'acier inoxydable WO2023148516A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/IB2022/050884 WO2023148516A1 (fr) 2022-02-02 2022-02-02 Procédé de récupération d'acide fluorhydrique libre et combiné à partir d'un bain de décapage d'acier inoxydable

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/IB2022/050884 WO2023148516A1 (fr) 2022-02-02 2022-02-02 Procédé de récupération d'acide fluorhydrique libre et combiné à partir d'un bain de décapage d'acier inoxydable

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1993002227A1 (fr) * 1991-07-15 1993-02-04 Eco-Tec Limited Procede et dispositif de traitement de solutions acides contenant du fluorure
IT1290947B1 (it) * 1997-02-25 1998-12-14 Sviluppo Materiali Spa Metodo e dispositivo per il decapaggio di prodotti in lega metallica in assenza di acido nitrico e per il recupero di soluzioni esauste

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1993002227A1 (fr) * 1991-07-15 1993-02-04 Eco-Tec Limited Procede et dispositif de traitement de solutions acides contenant du fluorure
IT1290947B1 (it) * 1997-02-25 1998-12-14 Sviluppo Materiali Spa Metodo e dispositivo per il decapaggio di prodotti in lega metallica in assenza di acido nitrico e per il recupero di soluzioni esauste

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
REGEL-ROSOCKA ET AL: "A review on methods of regeneration of spent pickling solutions from steel processing", JOURNAL OF HAZARDOUS MATERIALS, ELSEVIER, AMSTERDAM, NL, vol. 177, no. 1-3, 15 May 2010 (2010-05-15), pages 57 - 69, XP026928925, ISSN: 0304-3894, [retrieved on 20091216], DOI: 10.1016/J.JHAZMAT.2009.12.043 *

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