Synergistic Sorption of Gallium(III) and Scandium(III) Ions by the Interpolymer System of Poly(Acrylic Acid)/Poly(4-vinylpyr-idine) Hydrogels: Kinetics, Selectivity, and Mechanism

Bakytgul Totkhuskyzy, Talkybek Jumadilov, Kh. Khimersen, Arailym Akhmetova, Józef Tadeusz Haponiuk, Juozas Gražulevicius

Molecules, 2026

Full text Open access: Gold Metadata (CSL-JSON)
DOI 10.3390/molecules31183324
Data confidence 70 medium
How this score is calculated

It is built from checkable properties of the record itself: whether the article has a DOI, how many independent sources confirmed its data, whether the required fields are filled in, and how recent the latest confirmation is. Disagreement between sources and a missing identifier lower it. A value of 80 or above means the record was published without further checking; 60 to 79 means it is published at reduced confidence, with a manual check advisable. A record verified by an editor by hand is never pushed below 90 by a recalculation. This scores our data about the article, not the article itself.

Abstract

Selective recovery of critical metals such as gallium and scandium from dilute, multicomponent process streams remains challenging due to their low concentrations and complex matrices. Here we investigate a remotely interacting intergel system based on crosslinked poly(acrylic acid) (hPAA) and poly(4-vinylpyridine) (hP4VP) hydrogels across seven mass ratios (6:0–0:6) for sorption of Ga(III) and Sc(III) from binary sulfate solutions. Inductively coupled plasma optical emission spectroscopy shows that mutual activation of the weak polyacid/polybase pair markedly enhances metal uptake, with maximum sorption degrees of 73.17% for Ga(III) at hPAA:hP4VP = 3:3 and 56.00% for Sc(III) at 2:4, corresponding to distribution coefficients up to 2726.7 mL g−1 and Ga/Sc selectivity factors β up to 6.41. Sorption is well described by Langmuir-type isotherms, and desorption with 2 wt.% HNO3 reveals an inverse sorption–release relationship, indicating stronger binding at compositions of maximal mutual activation. FTIR spectroscopy evidences inner-sphere complexation through bidentate carboxylate coordination in hPAA and M←N dative bonding in hP4VP, while TGA/DSC shows that metal-loaded hydrogels retain their structural integrity up to approximately 320–340 °C, with the onset of significant decomposition occurring at ~350 °C for hP4VP-containing samples. The composition-dependent magnitude of Ga(III)-over-Sc(III) preferential uptake—with selectivity coefficients β = Kd(Ga)/Kd(Sc) remaining greater than 1 across all seven compositions studied—is rationalized using Hard–Soft Acid–Base considerations and demonstrates that hPAA:hP4VP intergels constitute a composition-tunable platform for enhancing Ga(III) recovery and partial Ga/Sc separation from simplified sulfate media, motivating future validation in real hydrometallurgical liquors and in the presence of competing multivalent cations.