Gamma-Grafted Polymer Separates Zirconium and Yttrium With Impressive Selectivity

A new radiation-grafted polymer that can pull zirconium and yttrium ions out of acidic solutions and then cleanly separate the two metals has been reported by a team of chemists working at the Egyptian Atomic Energy Authority. Writing in Polymer Bulletin, A. El-Tantawy, H. M. M. Abo Eldahab and Reham S. Hassan describe how gamma radiation-induced graft polymerization was used to build a novel sorbent they call polyacrylic acid (vinyl sulfonic acid-co-acrylonitrile), abbreviated PAA(VSA-AN). The material achieved maximum adsorption capacities of 142.2 milligrams of zirconium per gram of sorbent and 198.4 milligrams of yttrium per gram, and it survived seven consecutive adsorption-desorption cycles with the help of a simple citric acid eluent. For a field in which selective metal separation is both scientifically stubborn and industrially expensive, those numbers represent a meaningful step forward.

The chemistry behind the material is what gives it its power. Gamma radiation is used as an energy source to initiate graft polymerization, in which acrylic acid, vinyl sulfonic acid and acrylonitrile are co-polymerized onto a supporting backbone to create a dense network of functional groups. Acrylic acid contributes carboxylate sites that can bind metal cations, vinyl sulfonic acid introduces strongly acidic sulfonate groups that remain ionized across a wide pH range, and acrylonitrile adds mechanical and chemical robustness through its nitrile functionality. The combination produces a sorbent that is simultaneously hydrophilic enough to interact with aqueous metal ions and tough enough to withstand repeated chemical stripping, a balance that many single-function resins struggle to strike.

Before testing the material against metal ions, the team characterized it thoroughly using a battery of analytical techniques. Fourier transform infrared spectroscopy confirmed the presence of the carboxylic, sulfonic and nitrile groups introduced by the three monomers. X-ray diffraction revealed the degree of crystallinity in the grafted structure, while thermogravimetric and differential thermal analysis mapped out its thermal stability, an important consideration for materials destined for hot, acidic processing streams. Scanning electron microscopy exposed the surface morphology that governs how easily ions can penetrate the polymer matrix, and energy-dispersive X-ray spectroscopy provided elemental confirmation of the composition. Together these methods established that the grafting had produced the intended terpolymer architecture rather than a heterogeneous mixture of separate homopolymers.

With the material in hand, the researchers systematically optimized the conditions under which it captures zirconium(IV) and yttrium(III). Contact time, solution pH, sorbent mass, initial metal concentration and temperature were each varied to find the sweet spot for performance. Perhaps the most striking finding is that optimal adsorption and the highest separation factor for the two metals occur at pH 2.0, an intensely acidic environment that would destroy many conventional sorbents and that closely mirrors the conditions of real hydrometallurgical and nuclear waste streams. Operating efficiently at such low pH means the polymer could be inserted into existing process chemistry without extensive neutralization, which would otherwise add cost and generate secondary waste.

Kinetic analysis showed that the uptake of both metals follows a pseudo-second-order model, a signature of chemisorption in which actual chemical bonds form between the metal ions and the functional groups on the polymer rather than weak physical adsorption. This matters for practical use because chemisorption generally produces stronger binding, better selectivity between chemically similar ions, and reduced leaching of captured metals back into solution. Equilibrium isotherm data, meanwhile, fit the Langmuir model closely, indicating that adsorption proceeds as a monolayer on a uniform surface with a finite number of equivalent binding sites. That behavior makes the material predictable: engineers can calculate precisely how much metal a given mass of sorbent will remove under specified conditions.

The thermodynamic story is equally coherent. The study yielded a positive enthalpy change, showing that adsorption is endothermic and therefore improves at elevated temperature, and a positive entropy change, reflecting an increase in disorder at the solid-liquid interface as coordinated water molecules are displaced during binding. Negative Gibbs free energy values across the studied temperature range confirmed that the process is spontaneous and becomes even more favorable as temperature rises. Taken together, these parameters describe a driving force for metal capture that grows stronger with heat, which is convenient because warming a process column is often easier than cooling one.

Regeneration is where many promising sorbents falter, so the desorption results are arguably the most consequential part of the work. The team found that a dilute 0.05 molar citric acid solution efficiently strips the bound metals from the polymer, enabling recycling over seven consecutive adsorption-desorption cycles without loss of the reported performance. Citric acid is cheap, biodegradable and far gentler than the concentrated mineral acids often used to regenerate ion-exchange resins, so the finding points toward a lower-cost, lower-waste operating cycle. A sorbent that works brilliantly on its first use but degrades by its third has little industrial value; one that survives seven cycles with a benign eluent is a different proposition entirely.

The separation demonstration ties the whole study together. In a binary solution containing both zirconium(IV) and yttrium(III), the polymer preferentially retained one metal while the other passed through, and selective separation of yttrium from the mixture was successfully achieved using the same 0.05 molar citric acid as eluent. This is significant because zirconium and yttrium are chemical companions in many source materials. Zirconium is a staple of the nuclear industry, where it clads fuel rods thanks to its low neutron absorption, and the isotope zirconium-89 produced in medical cyclotrons is an increasingly important radiolabel for positron emission tomography. Yttrium-90, the daughter of strontium-90 and itself a workhorse of radionuclide therapy, must be produced in high radionuclidic purity, which demands rigorous separation from its precursor chemistry.

Context within the broader literature makes the contribution clearer. Previous approaches to these separations have relied on solvent extraction with reagents such as LIX 84-IC, chelating ion-exchange resins like Diphonix for zirconium-hafnium splitting, macroporous silica-based adsorbents bearing extractants such as bis(2-ethylhexyl) hydrogen phosphate, and more exotic materials including graphene oxide composites and crown ether functionalized silica gels. Each has limitations in cost, stability, selectivity or waste generation. The new PAA(VSA-AN) copolymer distinguishes itself by combining radiation-induced synthesis, tolerance of strongly acidic feed solutions, competitive capacity for both target metals, a benign citric acid regeneration route and demonstrated multimetal selectivity in a single material.

The work also speaks to a larger trend in separation science: the move toward tailored polymeric sorbents whose functionality is engineered at the molecular level rather than borrowed wholesale from extraction chemistry. By grafting three complementary monomers simultaneously, the researchers effectively built a binding landscape in which carboxylate, sulfonate and nitrile sites cooperate to capture hard cations like Zr(IV) and Y(III) at different strengths, creating the selectivity window that makes separation possible. Given the growing demand for reliable supplies of zirconium for nuclear and medical imaging applications and of yttrium for radiopharmaceuticals and phosphors, a recyclable, acid-tolerant polymer capable of sorting these metals from mixed acidic streams could find real traction. The authors suggest the material holds potential for application in metal recovery and separation processes more broadly, and the systematic kinetic, isotherm and thermodynamic groundwork laid out in the study gives future developers a solid quantitative baseline from which to scale the chemistry beyond the laboratory bench.

Subject of Research: Sorption and selective separation of zirconium and yttrium ions using a gamma radiation-grafted polyacrylic acid (vinyl sulfonic acid-co-acrylonitrile) copolymer in a column system.

Article Title: Sorption and Separation of zirconium and yttrium by poly acrylic acid (vinyl sulfonic acid -co- acrylonitrile) backed column

Article References: El-Tantawy, A., Eldahab, H. M. M. A., & Hassan, R. S. (2026). Sorption and Separation of zirconium and yttrium by poly acrylic acid (vinyl sulfonic acid -co- acrylonitrile) backed column. Polymer Bulletin, 83(11), Article 639. https://doi.org/10.1007/s00289-026-06689-8

Image Credits: AI Generated

DOI: 10.1007/s00289-026-06689-8

Keywords: zirconium, yttrium, gamma radiation grafting, polyacrylic acid, acrylonitrile, vinyl sulfonic acid, chemisorption, Langmuir isotherm, pseudo-second-order kinetics, citric acid elution, metal separation, nuclear medicine