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EP-4740256-A1 - IRON CHROMIUM ELECTROLYTES

EP4740256A1EP 4740256 A1EP4740256 A1EP 4740256A1EP-4740256-A1

Abstract

A process for producing an iron chromium electrolyte, the process includes leaching iron and chromium from a ferrochrome alloy at an elevated leaching temperature, using hydrochloric acid. A raw iron chromium electrolyte comprising dissolved iron and dissolved chromium is produced. The raw electrolyte is purified and adjusted to produce a functional iron chromium electrolyte.

Inventors

  • CHENNELLS, Peter, Maurice
  • ROOPA, Shriya
  • BIJZET, Johannes, Ferdinand
  • BRUINSMA, ODOLPHUS, SIMON, LEO

Assignees

  • Redox One Limited

Dates

Publication Date
20260513
Application Date
20240627

Claims (17)

  1. 1. A process for producing an iron chromium electrolyte, the process including leaching iron and chromium from a ferrochrome alloy at an elevated leaching temperature, using hydrochloric acid, to produce a raw iron chromium electrolyte comprising dissolved iron and dissolved chromium; and purifying the raw electrolyte to produce a purified iron chromium electrolyte.
  2. 2. The process according to claim 1, wherein the ferrochrome alloy has an Fe content of between about 35% by mass and about 45% by mass, preferably between about 37% by mass and about 44% by mass, more preferably between about 39% by mass and about 44% by mass, e.g., about 42% by mass; and a Cr content of between about 45% by mass and about 60% by mass, preferably between about 46% by mass and about 54% by mass, more preferably between about 48% by mass and about 52% by mass, e.g., about 50% by mass.
  3. 3. The process according to claim 1 or claim 2, wherein the ferrochrome is a particulate ferrochrome alloy having a particle size with a D50 of between about 0.5mm and about 1.5mm, preferably between about 0.5mm and about 1.2mm, more preferably between about 0.5mm and about 1mm.
  4. 4. The process according to any one or claims 1 to 3, wherein the hydrochloric acid is at a molar concentration of between about 3M and about 8M, preferably about 6.0M.
  5. 5. The process according to any one of claims 1 to 4, wherein a ratio of ferrochrome alloy to hydrochloric acid is in the range of about lOOg/B to about 200g/B, preferably in the range of about 120g/B to about 180g/B, more preferably in the range of about 140g/B to about 170g/B, e.g., about 155g/B.
  6. 6. The process according to any one or claims 1 to 5, wherein the elevated leaching temperature is between about 80°C and about 100°C, preferably between about 85°C and about 95°C, more preferably between about 95°C and about 100°C, e.g., about 95°C.
  7. 7. The process according to any one of claims 1 to 6, wherein the iron and chromium are leached from the ferrochrome alloy for a period of between about 30 minutes and about 24 hours, preferably between about 8 hours and about 14 hours, more preferably between about 4 hours and about 12 hours, e.g., for a period of about 14 hours.
  8. 8. The process according to any one of claims 1 to 7, wherein the iron and chromium are leached from the ferrochrome alloy in a solid-liquid fluidised bed.
  9. 9. The process according to any one of claims 1 to 8, wherein purifying the raw iron chromium electrolyte comprises removing Ni and Cu, either simultaneously or separately, from the raw electrolyte by subjecting the raw electrolyte to a pH adjustment step and, subsequently, to an ion exchange step, wherein in the pH adjustment step, the pH of the raw iron chromium electrolyte is adjusted to between 0.0 and 2, e.g. about 1.5 by using a base or an acid; and in the ion exchange step, the raw iron chromium electrolyte is contacted with a strong cation ion exchange resin.
  10. 10. The process according to any one of claims 1 to 9, which includes concentrating or diluting the purified iron chromium electrolyte to a Cr and/or Fe concentration of at least about 80g/E, preferably at least about 75g/B, more preferably at least about 72g/B.
  11. 11. The process according to claim 10, wherein the purified iron chromium electrolyte is concentrated by heating the purified iron chromium electrolyte to evaporate water or by using an iron and/or chromium rejecting membraned process
  12. 12. The process according to any one of claims 1 to 11, which includes adjusting the Fe and/or Cr concentration of the purified iron chromium electrolyte upwards to an Fe and/or Cr concentration of at least about 80g/E, preferably at least about 75g/B, more preferably at least about 72g/B, by adding Fe as metal, or Fe as a salt such as iron sulphate or iron chloride; and/or adding Cr as metal, or as a Cr salt such as chromium sulphate or chromium as chromium chloride.
  13. 13. The process according to any one of claims 1 to 12, which includes adjusting the electrical conductivity of the purified iron chromium electrolyte to be in the range of between about 112 mS/cm and about 140 mS/cm, preferably in the range of between about 118 mS/cm and about 135 mS/cm, more preferably in the range of between about 125 mS/cm and about 133 mS/cm, e.g., about 133 mS/cm by cooling the purified iron chromium electrolyte to a temperature which does not exceed about 30°C, preferably to a temperature which does not exceed about 25°C, and by adding hydrochloric acid, ammonium hydroxide, or sulphuric acid to the cooled purified iron chromium electrolyte.
  14. 14. A process for producing a raw iron chromium electrolyte, the process including leaching iron and chromium from a ferrochrome alloy at an elevated leaching temperature, using hydrochloric acid, to produce said raw iron chromium electrolyte comprising dissolved iron and dissolved chromium.
  15. 15. A purified iron chromium electrolyte produced according to the process according to any one of claims 1 to 13, or a raw iron chromium electrolyte produced according to the process according to claim 14.
  16. 16. Use of the purified iron chromium electrolyte produced by a process according to any one of claims 1 to 13 as an electrolyte of an iron chromium redox flow battery.
  17. 17. An iron chromium redox flow battery which includes a purified iron chromium electrolyte produced according to the process according to any one of claims 1 to 13.

Description

IRON CHROMIUM ELECTROLYTES THIS INVENTION relates to iron chromium electrolytes. In particular, the invention relates to a process for producing an iron chromium electrolyte or a raw iron chromium electrolyte, to a raw iron chromium electrolyte and a purified iron chromium electrolyte produced by a process in accordance with the invention, to use of a purified iron chromium electrolyte produced by a process in accordance with the invention in an iron chromium redox flow battery, and to an iron chromium redox flow battery which includes a purified iron chromium electrolyte produced by a process in accordance with the invention. Iron chromium redox flow batteries (ICRFB's) are known, having been studied extensively during the 1970's and 1980's. Energy is stored and released by using the Fe2+-Fe3+ and Cr2+-Cr3+ redox couples, with the iron and chromium species being fully dissolved in an aqueous iron chromium electrolyte at all times. It stands to reason that, at least for use in ICRFB's, there is a need for an efficient, safe, low cost process to produce iron chromium electrolytes, and for iron chromium electrolytes produced by such a process. According to one aspect of the invention, there is provided a process for producing an iron chromium electrolyte, the process including leaching iron and chromium from a ferrochrome alloy at an elevated leaching temperature, using hydrochloric acid, to produce a raw iron chromium electrolyte comprising dissolved iron and dissolved chromium; and purifying the raw electrolyte to produce a purified iron chromium electrolyte. The term "purified iron chromium electrolyte" in this specification is not limited to but includes within its meaning a "functional iron chromium electrolyte", meaning an electrolyte that is functionally suitable as an iron chromium electrolyte of an iron chromium redox flow battery. The purified iron chromium electrolyte herein described is such a functional iron chromium electrolyte. In this regard, purification may include adjustment of Fe content, Cr content, and/or of electrical conductivity, as herein described, to produce such a functional iron chromium electrolyte. According to another aspect of the invention, there is provided a process for producing a raw iron chromium electrolyte, the process including leaching iron and chromium from a ferrochrome alloy at an elevated leaching temperature, using hydrochloric acid, to produce said raw iron chromium electrolyte comprising dissolved iron and dissolved chromium. The ferrochrome alloy may have an Fe content of between about 35% by mass and about 45% by mass, preferably between about 37% by mass and about 44% by mass, more preferably between about 39% by mass and about 44% by mass, e.g., about 42% by mass. The ferrochrome alloy may have a Cr content of between about 45% by mass and about 60% by mass, preferably between about 46% by mass and about 54% by mass, more preferably between about 48% by mass and about 52% by mass, e.g., about 50% by mass. The ferrochrome alloy may be particulate ferrochrome alloy, e.g. milled or atomised ferrochrome alloy. The particulate ferrochrome alloy may have a particle size with a D50 of between about 0.5mm and about 1.5mm, preferably between about 0.5mm and about 1.2mm, more preferably between about 0.5mm and about 1mm. The hydrochloric acid may be at a molar concentration of between about 3M and about 8M, preferably about 6.0M. A ratio of ferrochrome alloy to hydrochloric acid (weight per volume) may be in the range of about lOOg/B to about 200g/B, preferably in the range of about 120g/B to about 180g/B, more preferably in the range of about 140g/B to about 170g/B, e.g., about 155g/B. The elevated leaching temperature may be between about 80°C and about 100°C, preferably between about 85°C and about 95°C, more preferably between about 95°C and about 100°C, e.g., about 95°C. The iron and chromium may be leached from the ferrochrome alloy for a period of between about 30 minutes and about 24 hours, preferably between about 8 hours and about 14 hours, more preferably between about 4 hours and about 12 hours, e.g., for a period of about 14 hours. This period may be the actual leach time used in a process in accordance with the invention employing a batch leaching step, or the average total leach residence time of solids material in a leaching stage of a process in accordance with the invention which employs a continuous leaching stage. The iron and chromium may be leached from the ferrochrome alloy in a solidliquid fluidised bed. Preferably, maximum chromium and iron are leached from the ferrochrome alloy and dissolved in the hydrochloric acid. During the leaching of the ferrochrome alloy, hydrogen would typically be produced. The process thus typically includes removing hydrogen from a leaching vessel, e.g., a solid liquid fluidised bed leaching vessel used in a leaching step during which the leaching is effected. The hydrogen removed from the leaching vessel