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EP-4735654-A1 - PROCESS FOR SELECTIVELY EXTRACTING COBALT FROM AN AQUEOUS NICKEL-COBALT SOLUTION

EP4735654A1EP 4735654 A1EP4735654 A1EP 4735654A1EP-4735654-A1

Abstract

The present invention provides a multi-stage solvent extraction process for selectively extracting cobalt from an aqueous mixed metal solution comprising nickel and cobalt, whereby each solvent extraction stage is characterized by maintaining a magnesium concentration in an aqueous phase above a predetermined magnesium concentration.

Inventors

  • ROOSEN, Joris
  • LUYTEN, JAN
  • VAN DAEL, Carl
  • SCHURMANS, MAARTEN

Assignees

  • Umicore

Dates

Publication Date
20260506
Application Date
20240701

Claims (16)

  1. 1. A multi-stage solvent extraction process for selectively extracting cobalt from an aqueous mixed metal feed comprising nickel, cobalt and sodium, whereby each solvent extraction stage comprises the steps of: i. maintaining a magnesium content in an aqueous phase in an amount of at least 25 mol% of the amount of nickel in the aqueous phase during the solvent extraction; ii. contacting the aqueous phase of step i. with an organic phase comprising a dialkylphosphinic acid extractant and an organic diluent; and iii. separating the organic phase obtained in step ii. from the aqueous phase, thereby obtaining a cobalt rich organic phase and an aqueous nickel sulphate raffinate solution.
  2. 2. Process according to claim 1, whereby said magnesium content corresponds to at least 50 mol% of the amount of nickel in said aqueous phase, preferably to more than 80 mol%.
  3. 3. Process according to claim 1 or 2, whereby said predetermined magnesium concentration is sufficiently high to ensure that at least 75 mol% of nickel, relative to the total amount of nickel, remains in the aqueous phase.
  4. 4. Process according to any of claims 1 to 3, whereby said aqueous mixed metal feed comprising 0.1 to 30 g/L sodium.
  5. 5. Process according to any of claims 1 to 4, wherein the dialkylphosphinic acid extractant is bis-(2,4,4-trimethylpentyl)phosphinic acid.
  6. 6. Process according to any of claims 1 to 5, whereby said multi-stage solvent extraction process is operated in counter-current mode.
  7. 7. Process according to any of claims 1 to 6, whereby magnesium is added to an aqueous phase in one or more stages of the multi-stage solvent extraction process.
  8. 8. Process according to claim 7, whereby magnesium is added to said aqueous phase an amount of at least 2 mol%, relative to the amount of nickel in said aqueous phase.
  9. 9. Process according to any of claims 1 to 8, whereby said aqueous mixed metal feed and/or said aqueous phase comprises nickel in an amount of 5 to 120 g/L.
  10. 10. Process according to any of claims 1 to 9, whereby said aqueous mixed metal feed and/or said aqueous phase further comprises sodium in an amount of less than 60 g/L.
  11. 11. Process according to any of claims 1 to 10, whereby said aqueous mixed metal feed and/or said aqueous phase comprises cobalt in an amount of 10 g/L to 60 g/L.
  12. 12. Process according to any of claims 1 to 11, whereby the concentration of said dialkylphosphinic acid extractant in the organic phase can range from 1 to 45 vol%.
  13. 13. Process according to any of claims 1 to 12, whereby said solvent extraction is performed at a temperature of 20 °C to 80 °C.
  14. 14. Process according to any of claims 1 to 13, whereby cobalt is back-extracted from the organic phase obtained in step iii ., whereby the organic phase is regenerated and cobalt is recovered in an aqueous medium.
  15. 15. Process according to any of claims 1 to 14, whereby the pH of the aqueous phase containing nickel and cobalt is between 1.0 and 4.0 prior to step ii.
  16. 16. Process according to any of claims 1 to 15, whereby said multi-stage solvent extraction process is operated in continuous, counter-current mode.

Description

PROCESS FOR SELECTIVELY EXTRACTING COBALT FROM AN AQUEOUS NICKEL-COBALT SOLUTION TECHNICAL FIELD The present invention relates to a novel method for selectively extracting cobalt from an aqueous feed solution containing also nickel using a dialkyl phosphinic acid extractant in an organic solvent. INTRODUCTION The development of lithium-ion batteries, and specifically the use of nickel-manga- nese-cobalt and nickel-cobalt-aluminium cathode materials, has increased the demand for high-purity cobalt sulphate, either as a solid or in solution. Impurities in the cathode materials strongly affect the performance of the batteries. As such, much effort has been devoted to producing high-purity cobalt sulphate in an industrially viable process. Cobalt is typically separated from nickel by solvent extraction, whereby nickel and cobalt compete for the capacity of the extractant, especially at higher nickel content in the feed solution. Process solutions composed of a high nickel matrix certainly originate from leaching battery materials with NMC battery chemistries with Ni :Mn:Co ratios of 6: 1 : 1, 8: 1 : 1 or even higher. Moreover, recycling towards battery-grade nickel sulphate requires an efficient extraction process yielding a nickel sulphate raffinate solution with low presence of residual cobalt. In addition to providing a sufficient number of extraction stages, deep removal of cobalt from the feed solution requires a sufficient excess of solvent capacity, thus increasing co-extraction of nickel even more. CA 1,170,839 discloses an improved method of separating cobalt and nickel using an organic phosphoric acid within a pH range of 4 to 7. The extractants used are di-(2- ethylhexyl)phosphoric acid 20 vol% and tri-n-butyl phosphate 5 vol%, 2-ethylhex- ylphosphonic acid mono-2-ethylhexyl ester 20 vol% and tri-n-butyl phosphate 5 vol% CN 112 375 910 describes a method for recycling waste battery powder and involves leaching nickel, cobalt, and manganese from the battery powder. The extractant used is Cyanex 272, i.e. bis(2,4,4-trimethylpentyl)phosphinic acid. Yet, there is a need for improved separation of cobalt and nickel from an aqueous solution, until deep removal of cobalt from the raffinate, in presence of a high nickel content in the feed solution, all this under stable process conditions. SUMMARY The inventors found that maintaining a sufficiently high magnesium concentration in an aqueous phase containing cobalt and nickel increases the efficiency of a solvent extraction process with a dialkylphosphinic acid extractant for the extraction of cobalt. The improved efficiency originates from the fact that magnesium is extracted in favour of nickel. By reducing competition from nickel, a higher solvent capacity can be exploited without entering the risk zone where the organic phase becomes instable. Indeed, it was observed that solvent solidification occurs with phosphinic acid based extractants at higher nickel loadings, with the processing window depending mainly on extractant concentration in the solvent and temperature. Two significant benefits result from a more efficient exploitation of the solvent capacity: i. feed solutions comprising a comparatively higher nickel content can be processed; and ii. deep removal of cobalt from the feed solution, resulting in nickel sulphate raffinate solutions with low residual traces of cobalt. The inventors found that the magnesium concentration in the aqueous phase should be maintained at a sufficiently high level to avoid a content of nickel in the organic phase higher than the threshold value for solvent solidification. This threshold value depends on the temperature, the extractant concentration in the organic phase, and the sodium concentration in the aqueous phase. In the absence or in the presence of only low levels of magnesium, nickel is the only candidate for co-extraction. If magnesium is also sufficiently present in the aqueous feed solution, magnesium will be co-extracted instead of nickel. In that case, a higher nickel content in the aqueous feed solution can be processed or a higher solvent capacity can be used, e.g. by increasing the extractant concentration or the organic-to-aqueous flow ratio. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a graphical representation of the stability zone as a function of nickel and cobalt concentrations in the organic phase composed of 45 vol% Cyanex 272 in Escaid 110 (Example 1). The content of sodium in the aqueous phase varies from 21 g/L to 26 g/L. Figure 2 shows a mass balance for cobalt, nickel and magnesium in an extraction section consisting of four stages in a counter-current configuration for a feed solution low in magnesium (Example 2). Example 2 shows solidification of the organic phase through the low levels of magnesium. Figure 3 shows a mass balance for cobalt, nickel and magnesium in an extraction section consisting of four stages in a counter-current configuration for a feed solution similar to