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Highly selective solvent extraction of Zn( II ) and Cr( III ) with trioctylmethylammonium chloride ionic liquid

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  • Décio F. Alves‐Lima
  • Carmina F. Rodrigues
  • Carolina T. Pinheiro
  • Licínio M. Gando‐Ferreira
  • Margarida J. Quina
  • Abel G. Ferreira
<mark>Journal publication date</mark>31/01/2022
<mark>Journal</mark>The Canadian Journal of Chemical Engineering (Wiley InterScience Publishers)
Issue number1
Number of pages12
Pages (from-to)131-142
Publication StatusPublished
Early online date22/03/21
<mark>Original language</mark>English


This study investigates the recovery of Zn(II) and Cr(III) from aqueous solutions based on solvent extraction with trioctylmethylammonium chloride [TOMA+][Cl-], commercialy named Aliquat 336. Single metal solutions and binary mixtures of both metals were considered. The effect of relevant operating conditions such as pH, contact time, initial concentration, O/A phase volumetric ratio, and temperature were evaluated. Additionally, loading capacity and stripping studies were performed. Results showed that [TOMA+][Cl−] is an effective extracting agent for Zn(II), reaching maximum removal capacity at pH 1.8 and demonstrating fast extraction kinetics. Extraction efficiencies above 99% were achieved at 0.5, 0.75, and 1.00 O/A volumetric phase ratios for 0.1 g/L initial Zn(II) concentration. At 1 g/L and 10 g/L concentration, for the same O/A ratios, approximately 88% of the initial Zn(II) was extracted. In contrast, it was found that negligible amounts of Cr(III) were transferred to the [TOMA+][Cl−] phase at the 1-5 pH range. Selectivity studies showed that Zn(II) removal is boosted in the presence of Cr(III), although no Cr(III) is extracted. [TOMA+][Cl−] exhibited a high Zn(II) storage capacity, since after 25 loading cycles with 1 g/L, the loading capacity reached approximately 13.5 g/L, and after five loading cycles with 5 g/L, the capacity reached 19.4 g/L. Stripping tests revealed that NaOH is an efficient agent for the removal of Zn(II) from the ionic liquids, reaching 98.5% removal after two cycles, whereas HNO3 is not a suitable agent, reaching less than 40% removal after three cycles. [TOMA+][Cl−] revealed high potential for separating Zn(II) from Cr(III).