Hydroxypicolinic acid tethered on magnetite core-silica shell (HPCA@SiO2@Fe3O4) as an effective and reusable adsorbent for practical Co(II) recovery

John Edward L Sio; Erwin C Escobar; Hern Kim; Wook-Jin Chung; Grace M Nisola

doi:10.1016/j.chemosphere.2022.134301

Hydroxypicolinic acid tethered on magnetite core-silica shell (HPCA@SiO₂@Fe₃O₄) as an effective and reusable adsorbent for practical Co(II) recovery

Chemosphere. 2022 Jul:298:134301. doi: 10.1016/j.chemosphere.2022.134301. Epub 2022 Mar 11.

Authors

John Edward L Sio¹, Erwin C Escobar², Hern Kim¹, Wook-Jin Chung³, Grace M Nisola⁴

Affiliations

¹ Environmental Waste Recycle Institute (EWRI), Department of Energy Science and Technology (DEST), Myongji University, Myongji-ro 116, Cheoin-gu, Yongin-si, Gyeonggi-do, 17058, South Korea.
² Environmental Waste Recycle Institute (EWRI), Department of Energy Science and Technology (DEST), Myongji University, Myongji-ro 116, Cheoin-gu, Yongin-si, Gyeonggi-do, 17058, South Korea; Department of Engineering Science, College of Engineering and Agro-Industrial Technology, University of the Philippines Los Baños, College Laguna, 4031, Philippines.
³ Environmental Waste Recycle Institute (EWRI), Department of Energy Science and Technology (DEST), Myongji University, Myongji-ro 116, Cheoin-gu, Yongin-si, Gyeonggi-do, 17058, South Korea. Electronic address: wjc0828@gmail.com.
⁴ Environmental Waste Recycle Institute (EWRI), Department of Energy Science and Technology (DEST), Myongji University, Myongji-ro 116, Cheoin-gu, Yongin-si, Gyeonggi-do, 17058, South Korea. Electronic address: grace.nisola@gmail.com.

PMID: 35288181
DOI: 10.1016/j.chemosphere.2022.134301

Abstract

The soaring demand and future supply risk for cobalt (Co) necessitate more efficient adsorbents for its recycling from electronic wastes, as a cheaper and less hazardous option for its production. Herein, a magnetic adsorbent covalently tethered with 5-hydroxypicolinic acid (HPCA) as Co(II) ligand was developed. The magnetic component (Fe₃O₄) was protected with silica (SiO₂), then silanized with chloroalkyl linker and subsequently functionalized with HPCA via S_N2 nucleophilic substitution (HPCA@SiO₂@Fe₃O₄). Results from FTIR, TGA, EA, and XPS confirm the successful adsorbent preparation with high HPCA loading of 2.62 mmol g^-1. TEM-EDS reveal its imperfect spherical morphology with ligands well-distributed on its surface. HPCA@SiO₂@Fe₃O₄ is hydrophilic, water-dispersible and magnetically retrievable, which is highly convenient for its recovery. The Co(II) capture on HPCA@SiO₂@Fe₃O₄ involves monodentate coordination with carboxylate (COO^-) and lone pair acceptance from pyridine (aromatic -N = ) moiety of HPCA, with minor interaction from acidic silanols (Si-O^-). The binding occurs at 2 HPCA: 1 Co(II) ratio, that follows the Sips isotherm model with competitive Q_max = 92.35 mg g^-1 and pseudo-second order kinetics (k₂ = 0.0042 g mg^-1 min^-1). In a simulated LIB liquid waste, HPCA@SiO₂@Fe₃O₄ preferentially captures Co(II) over Li(I) with α_Li(I)^Co(II)=166 and Mn(II) with α_Mn(II)^Co(II)=55, which highlights the importance of HPCA for Co(II) recovery. Silica protection of Fe₃O₄ rendered the adsorbent chemically stable in acidic thiourea solution for its regeneration by preventing the deterioration of the magnetic component. Covalent functionalization averted ligand loss, which allowed HPCA@SiO₂@Fe₃O₄ to deliver consistent and reversible adsorption/desorption performance. Overall results demonstrate the potential of HPCA@SiO₂@Fe₃O₄ as a competitive and practical adsorbent for Co(II) recovery in liquid waste sources.

Keywords: Adsorption; Cobalt; Covalent functionalization; Magnetic adsorbent; Picolinic acid; Waste recycling.

MeSH terms

Adsorption
Cobalt
Ferrosoferric Oxide*
Ligands
Silicon Dioxide*

Substances

Ligands
Cobalt
Silicon Dioxide
Ferrosoferric Oxide