Ion-pair-assisted recovery of nickel(ii) tris(2,2'-bipyridine) complexes from spent catalysts by extraction and precipitation.
- 1Department of Resources and Environmental Engineering, Faculty of Science and Engineering, Waseda University 169-8555 Tokyo Japan [email protected].
- 2Department of System Innovation, Faculty of Engineering, The University of Tokyo 113-8656 Tokyo Japan.
- 3Next-Generation Technology Design and Creation, Takahata Precision Co., Ltd 160-0023 Tokyo Japan.
Abstract
Recovery of metals from spent homogeneous catalysts is challenging because strong metal-ligand complexation often prevents conventional inorganic precipitation. In this study, ion-pair-based separation processes were developed for the direct recovery of Ni-2,2'-bipyridine (bpy) complexes from spent catalyst solutions. Perchlorate (ClO₄ ⁻) was introduced as a counterion to form the poorly water-soluble ion pair Ni(bpy)₃(ClO₄)₂ (NIP), and ion-pair extraction (IPE) using 1,2-dichloroethane and ion-pair precipitation (IPP) were systematically compared. Alkaline pretreatment was required to adjust the dissolved bpy/Ni ratio to approximately 3, thereby favoring the formation of Ni(bpy)₃ ²⁺. Repeated IPE subsequently achieved >99% Ni recovery from both model and actual spent catalyst solutions. In contrast, IPP strongly depended on the initial Ni concentration and solution composition, requiring increasingly large ClO₄ ⁻/Ni ratios at lower Ni concentrations. PHREEQC modeling showed that the experimentally determined apparent solubility product governed the onset of NIP precipitation, whereas formation of a dissolved Ni(bpy)₃(ClO₄)₂ ion pair limited the Ni recovery by IPP. ATR-FTIR spectroscopy supported the recovery of the Ni-bpy complex containing ClO₄ ⁻ as the counterion. Furthermore, more than 95% of the ClO₄ ⁻ counterions were successively exchanged with Cl⁻ using an anion-exchange resin. These results demonstrate that ion-pair separation enables direct recovery of a functional Ni-bpy complex and provides a strategy for closed-loop recycling of homogeneous catalysts.
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BibTeX
@article{iwai2026ionpairassisted,
title = {{Ion-pair-assisted recovery of nickel(ii) tris(2,2'-bipyridine) complexes from spent catalysts by extraction and precipitation.}},
author = {Hisanori Iwai and Yutaro Takaya and Naoki Yokota and Yuko Takahashi and Chiharu Tokoro},
journal = {RSC advances},
year = {2026},
month = oct,
doi = {10.1039/d6ra08431a},
url = {https://europepmc.org/article/MED/42923176},
note = {CC BY},
}
RIS
TY - JOUR
TI - Ion-pair-assisted recovery of nickel(ii) tris(2,2'-bipyridine) complexes from spent catalysts by extraction and precipitation.
AU - Hisanori Iwai
AU - Yutaro Takaya
AU - Naoki Yokota
AU - Yuko Takahashi
AU - Chiharu Tokoro
PY - 2026
DA - 2026/10/22
JO - RSC advances
DO - 10.1039/d6ra08431a
UR - https://europepmc.org/article/MED/42923176
AB - Recovery of metals from spent homogeneous catalysts is challenging because strong metal-ligand complexation often prevents conventional inorganic precipitation. In this study, ion-pair-based separation processes were developed for the direct recovery of Ni-2,2'-bipyridine (bpy) complexes from spent catalyst solutions. Perchlorate (ClO₄ ⁻) was introduced as a counterion to form the poorly water-soluble ion pair Ni(bpy)₃(ClO₄)₂ (NIP), and ion-pair extraction (IPE) using 1,2-dichloroethane and ion-pair precipitation (IPP) were systematically compared. Alkaline pretreatment was required to adjust the dissolved bpy/Ni ratio to approximately 3, thereby favoring the formation of Ni(bpy)₃ ²⁺. Repeated IPE subsequently achieved >99% Ni recovery from both model and actual spent catalyst solutions. In contrast, IPP strongly depended on the initial Ni concentration and solution composition, requiring increasingly large ClO₄ ⁻/Ni ratios at lower Ni concentrations. PHREEQC modeling showed that the experimentally determined apparent solubility product governed the onset of NIP precipitation, whereas formation of a dissolved Ni(bpy)₃(ClO₄)₂ ion pair limited the Ni recovery by IPP. ATR-FTIR spectroscopy supported the recovery of the Ni-bpy complex containing ClO₄ ⁻ as the counterion. Furthermore, more than 95% of the ClO₄ ⁻ counterions were successively exchanged with Cl⁻ using an anion-exchange resin. These results demonstrate that ion-pair separation enables direct recovery of a functional Ni-bpy complex and provides a strategy for closed-loop recycling of homogeneous catalysts.
SN - 2046-2069
ER -