EP-4735652-A1 - METHOD FOR REUSING A CYANIDE REFRACTORY PRODUCT

Abstract

The invention relates to a method for reusing a spent refractory product initially arranged, in a service position, within a thermal installation and contaminated with an alkaline cyanide compound, the method comprising the following successive steps: a) - extracting the spent refractory product from the service position, - reducing the particle size of the spent refractory product so as to obtain a particulate mixture; b) before the extraction and/or during the extraction, and/or between the extraction and the particle size reduction and/or during the particle size reduction of step a) and/or after step a), placing the particulate mixture in contact with a solution comprising a thiosulphate compound, or a "thiosulphate solution", so as to obtain a two-phase mixture; and e) separating the liquid phase from the two-phase mixture and using the particulate mixture to produce a new refractory product.

Inventors

• AVHAD, Mangesh Ramesh
• CHAMPION, THIBAULT
• PAUL, Nathalie

Assignees

• SAINT-GOBAIN CENTRE DE RECHERCHES ET D'ETUDES EUROPEEN

Dates

Publication Date

20260506

Application Date

20240628

Claims (20)

1. 1. Method for reusing a used refractory product initially placed, in a service position, within a thermal installation and contaminated by an alkaline cyanide compound, said method comprising the following successive steps: a) - extraction of the used refractory product out of the service position, - particle size reduction of the used refractory product so as to obtain a particulate mixture; b) before said extraction and/or during said extraction, and/or between said extraction and said particle size reduction and/or during said particle size reduction of step a) and/or after step a), contacting the particulate mixture with a solution comprising a thiosulfate compound, or “thiosulfate solution”, so as to obtain a two-phase mixture; e) separation of the liquid phase of the two-phase mixture and use of the particulate mixture to manufacture a new refractory product.
2. 2. Method according to the preceding claim, in which step b) is simultaneous with the particle size reduction of step a).
3. 3. Method according to any one of the preceding claims, comprising the following step: c) after step a), subsequently, simultaneously or before step b), and before step e), bringing the particulate mixture into contact with a solution with a pH greater than 8, or “basic solution”.
4. 4. Method according to the immediately preceding claim, in which steps b) and c) follow one another without an intermediate cleaning operation.
5. 5. Method according to claim 3, in which steps b) and c) are carried out simultaneously.
6. 6. Method according to any one of the three immediately preceding claims, in which the basic solution comprises an alkali and/or alkaline-earth oxide and/or a halide of at least one alkali or alkaline-earth element.
7. 7. A method according to any preceding claim, wherein the thiosulfate compound is an alkali metal thiosulfate or an alkaline earth metal thiosulfate.
8. 8. Method according to any one of the preceding claims, comprising the following step: d) after steps b) and optionally c), carried out in any order, and before step e), treatment of the particulate mixture with an acid solution, of pH less than 5 or “acid attack”.
9. 9. Method according to the immediately preceding claim, in which step d) follows step b) or c), carried out successively or simultaneously, without an intermediate cleaning operation.
10. 10. Method according to any one of the two immediately preceding claims, in which the basic solution comprises an alkali and/or alkaline earth hydroxide.
11. 11. Method according to any one of the preceding claims, in which, in step a), a deposit of a slag or a solidified fusion bath adheres to the used refractory product extracted from the thermal installation, and in which, in step a), said deposit is separated, so as to purify the used refractory product extracted.
12. 12. A method according to any preceding claim, wherein the thiosulfate solution comprises more than 5 grams of thiosulfate compound per kilogram of used refractory product.
13. 13. A method according to any preceding claim, wherein the thiosulfate solution provides more than one mole of thiosulfate ions per mole of free cyanide present in said used refractory product.
14. 14. Method according to any one of the preceding claims, in which, before step b), the thiosulfate solution is prepared by diluting in a solvent a salt of said thiosulfate compound in which the thiosulfate function is linked to at least one atom of a chemical element chosen from alkali metals and alkaline earth metals.
15. 15. A method according to any preceding claim, wherein, in step b), - the particulate mixture is soaked in said thiosulfate solution, or - said thiosulfate solution is sprayed onto the particulate mixture.
16. 16. A method according to any preceding claim, wherein, in step e), the new refractory product has the same composition as the used product before use.
17. 17. Method according to any one of the preceding claims, in which the thermal installation is a metallurgical furnace or an electrolysis cell in a bath of molten salt(s).
18. 18. Particulate mixture obtained at the end of a step c) or d) of a process according to any one of claims 3 to 17.
19. 19. A method of treating a refractory product contaminated with an alkaline cyanide compound, said method comprising contacting the used refractory product with a solution comprising a thiosulfate compound.
20. 20. A method according to the immediately preceding claim, wherein said solution comprises a catalyst containing a metal, preferably copper, the molar content of catalyst is preferably greater than 5% and less than 50%, as a percentage based on the number of moles of thiosulfate compound.

Description

Description Title: PROCESS FOR REUSING A CYANIDED REFRACTORY PRODUCT Technical field The invention relates to a method for reusing a refractory product contaminated by an alkaline cyanide compound. State of the art The reuse of used refractory products present in a thermal installation, for example in a furnace, generally consists of grinding them in the form of a granular mixture, then reusing this granular mixture in other applications (metallurgy, cement works in particular) but also to manufacture new refractory products, preferably for the same application. Used refractory products, in particular refractory products containing carbon, in particular containing SiC, or containing nitrogen, in particular a nitrogen matrix, for example SiAlON, may however be contaminated by alkaline cyanide compounds. This contamination changes the chemical composition and does not allow, by simple grinding, to obtain a secondary material suitable for manufacturing new refractory products. Furthermore, a reduction in the content of alkali cyanide compounds may require thermal or chemical treatment leading to a modification of the chemical composition or crystallographic structure of the refractory products. Such a reduction in the content of alkali cyanide compounds may thus lead to products unsuitable for the manufacture of new refractory products. Furthermore, treatment to reduce the content of alkaline cyanide compounds must not lead to the generation of new compounds that may be harmful, particularly if the particulate mixture obtained is intended to be reused at high temperatures. In particular, the generation of hydrocyanic acid vapours must be avoided. Finally, used refractory products contaminated with alkaline cyanide compounds are often also contaminated with other compounds that also need to be extracted and/or neutralised, such as fluorides, silica or heavy metals. The succession of treatments requires special precautions so that a first treatment is not detrimental to the following treatment. This makes the process complex. Processes for destroying cyanide compounds by heat treatment are known. US5470559 describes such a treatment which requires grinding, contact with a soda solution, then heating between 160 and 220°C under pressure. This process presents health risks (release of toxic gas) and is difficult to implement industrially on large volumes. Cyanide compounds can also be destroyed by chemical treatment using calcium or sodium hypochlorite, as described in US6696617B1 or hydrogen peroxide followed by washing with soda as described in EP3868907A1. These reagents are highly oxidizing and potentially dangerous. GB2056425 describes a treatment with lime and soda resulting in a dilute liquor comprising fluorides, soda and cyanides. WO94/02263 describes pre-calcination of used refractory product, which can produce harmful fluorinated vapours. Despite these numerous solutions, there is still a need for a reuse process that is simpler, risk-free and suitable for different refractory products contaminated with an alkaline cyanide compound. The present invention aims to at least partially satisfy this need. Summary of the invention According to a first main aspect, the invention relates to a method for treating a refractory product contaminated by an alkaline cyanide compound, said method comprising bringing the used refractory product into contact with a solution comprising a thiosulfate compound. The inventors have in fact discovered that simply bringing a refractory product into contact, for example by painting, dipping or spraying, with a solution containing a thiosulfate compound considerably reduces the risk of cyanide gas emission, in particular when handling the refractory product, in particular with a view to its subsequent treatment. The neutralization of cyanide compounds present in the blood of patients, therefore in a liquid medium, at a substantially neutral pH and at approximately 37°C, by the injection of a thiosulfate compound is known to doctors. The inventors were however surprised to note that a thiosulfate compound had an effect when the alkaline cyanide compound is in the solid phase, and that this effect was present at higher pHs than in the blood, preferably at pHs above 8, and even 9, in particular in the presence of the basic solution. They were also surprised by the intensity of this effect, sufficient for an industrial application of the process. Furthermore, the inventors have discovered that the neutralization of cyanide compounds of a refractory product with a thiosulfate solution can be catalyzed by the addition of a metal such as copper, preferably in organometallic form, for example in the form of copper sulfate. The molar content of catalyst is preferably greater than 5%, preferably greater than 10%, preferably greater than 20% and/or less than 50%, or even less than 40%, as a percentage based on the number of moles of thiosulfate compound. The invention relates in particula