Ion-Exchange Adsorption of Cerium (III) Using AmberChrom 50WX2 Resin: Investigation of Mechanisms and Process Optimization.
LawrenceBrandonHermalin1
HameedMuhamad1✉Emailhmuhamad@torontomu.ca
HuuDoan1
1
A
Department of Chemical EngineeringToronto metropolitan University350 Victoria StreetM5B 2K3TorontoOntarioCanadaLawrence Brandon Hermalin, Hameed Muhamad*, Huu Doan
Department of Chemical Engineering, Toronto metropolitan University, 350 Victoria Street, Toronto, Ontario, Canada M5B 2K3.
*Corresponding author
Email: hmuhamad@torontomu.ca
Abstract
Rare earth elements (REEs) are essential to modern technologies, yet their recovery from secondary sources remains a major challenge. This study investigated the adsorption of cerium (III), selected as a model REE, onto AmberChrom 50WX2, a commercial cation-exchange resin. Batch experiments evaluated the effects of resin dosage, solution pH, and initial concentration on adsorption performance, supported by kinetic, isotherm, and thermodynamic modeling. The Elovich model best fit the adsorption kinetics, consistent with reversible ion-exchange (specific ionic bonding) between Ce³⁺ and the resin sites, rather than irreversible chemisorption, while equilibrium data were consistent with the Langmuir isotherm, confirming monolayer adsorption on a homogeneous surface. Adsorption capacity increased with initial concentration but decreased per unit mass at higher resin dosages, as expected. Thermodynamic analysis revealed the process to be endothermic and increasingly spontaneous with temperature. AmberChrom 50WX2 exhibited stable performance over four adsorption–desorption cycles, demonstrating reusability, though it showed limited selectivity among trivalent REEs of similar ionic radii. These findings highlight the potential of AmberChrom 50WX2 for bulk REE recovery under acidic conditions typical of waste streams, providing a foundation for process development at larger scales.
Key words:
Adsorption
Rare earth metal
Isotherm model
Resin
Ion-Exchange
1. Introduction
Rare earth elements (REEs) that are comprised of lanthanides, scandium, and yttrium are indispensable to advanced technologies including renewable energy systems, electronics, catalysts, and permanent magnets [1, 2]. Rapidly growing demand, coupled with supply risks tied to geopolitical concentration and environmentally damaging extraction practices, underscores the urgency of developing alternative recovery strategies.
Acid mine drainage (AMD) and industrial waste streams (IWS) represent underutilized waste-to-resource (WTR) opportunities. Both contain appreciable REE concentrations that, if recovered, could simultaneously expand supply and reduce environmental liabilities [3, 4]. However, the heterogeneous composition of these streams, often containing other metals such as Fe, Al, and Zn, poses significant challenges for selective recovery [2].
Numerous separation methods have been investigated, yet most face fundamental drawbacks. Chemical precipitation is low-cost but yields voluminous sludge, limited selectivity, and poor recovery of Ce(III) [5–9]. Solvent extraction (SX) is widely adopted at industrial scale but requires hundreds of stages, high chemical input, and suffers from inefficiency in dilute waste streams [7–9]. Cloud point extraction (CPE) and ionic liquids (ILs) are innovative, but their scalability and lifecycle sustainability remain unproven [10, 11]. Ion flotation and molecular recognition technology (MRT) demonstrate selectivity under controlled conditions, but their effectiveness diminishes in complex matrices containing high levels of interfering ions [12–18]. Membrane filtration can achieve separation but suffers from stability and fouling issues in acidic environments typical of AMD [19–21].
Against this backdrop, adsorption, particularly ion-exchange (IX), has emerged as a promising approach. IX resins offer broad pH tolerance, high adsorption capacity, ease of regeneration, and minimal sludge generation compared to precipitation or biosorption methods [22–26]. Their reusability further enhances economic and environmental feasibility. Additionally, adsorption can effectively target soluble cerium species under conditions relevant to waste streams, which will be the focus in this study [5–9].
There are critical knowledge gaps with regards to adsorption literature. Much of the literature is descriptive rather than analytical, emphasizing batch capacities or equilibrium models while neglecting mechanistic understanding, thermodynamic drivers, and long-term regeneration performance [27, 28]. Moreover, selectivity against competing ions, which is essential for real-world AMD and IWS applications, is insufficiently explored, limiting translation to industrial practice.
This study aims to advance adsorption-based ion-exchange from descriptive demonstration to practical application by systematically evaluating cerium recovery through kinetic modeling, isotherm analysis, thermodynamic profiling, and regeneration testing. This study aims to provide critical data to support adsorption via ion-exchange as a viable technology for REE recovery from waste streams
2.
Methods
3. 2.1 Materials and Reagents
Cerium(III) sulfate (Millipore Sigma, USA) was used to prepare stock solutions by dissolving in dilute H2SO4 (10–25 mL) before dilution with deionized water to minimize hydrolysis [29]. Calibration standards (0.0–75.0 ppm) were prepared from a certified ICP cerium standard (Millipore Sigma, Canada). Solution pH was adjusted with NaOH (2 M) or dilution, measured using a portable pH meter (Oakton pH100, Environmental Express, USA). Zeta potential was determined with a Zetasizer Nano analyzer (Malvern Instruments Ltd., UK).
Four ion-exchange resins were tested: Dowex 50W-X8 (H + form), AmberChrom 50WX2 (200–400 mesh, H + form), AmberChrom 50WX4 (50–100 mesh, H + form), and Amberlyst 15 (H + form) (Millipore Sigma, USA). AmberChrom 50WX2 was selected for detailed study.
2.2 Batch Adsorption Experiments
Experiments were performed in 250 mL Erlenmeyer flasks containing 150 mL of cerium solution and the desired resin mass. Flasks were agitated in a temperature-controlled shaker bath (ORS 200, Boekel/Grant, USA) at 100 rpm. Samples (3 mL) were withdrawn hourly, diluted to 20 mL with 2% HNO3, and analyzed by inductively coupled plasma–optical emission spectrometry (ICP-OES; Agilent 5100/5110 VDV, Agilent Technologies, USA). Resin morphology and cerium uptake were characterized using SEM (JEOL JSM-6380 LV, Japan) coupled with EDS (Oxford INCA X-sight).
2.3 Data Analysis
The concentration at time t (Ct, mg/L) was used to determine the mass of cerium remaining in the solution, mt:
2.1
where V is the solution volume (L). The adsorption capacity at time t was then calculated as:
2.2
where M is the resin mass (g).
Kinetic models (pseudo-first order, PFO; pseudo-second order, PSO) were applied to experimental data. Equilibrium behavior was described using the Langmuir and Freundlich isotherms, and thermodynamic parameters were determined from the Van’t Hoff and Arrhenius analyses. Statistical fit was evaluated using sum of squared error (SSE), mean squared error (MSE), and percent deviation.
The pseudo-first order (PFO) kinetic model for adsorption is expressed as [30]
2.3a
2.3b
The pseudo-second order (PSO) kinetic model for adsorption is expressed as [31]
2.4a
2.4b
The Van’t Hoff equation describes the temperature dependence of a chemical reaction's equilibrium constant is expressed as [32]
The Langmuir model for monolayer adsorption can be expressed as [33]:
2.6
Where Ce (mg/L) and qe (mg/g) are the La(III) concentration remaining in the solution and the La(III) adsorbed amount at equilibrium, respectively. KL (L/mg) is the Langmuir isotherm constant and qL (mg/g) is the adsorption capacity of the resin.
The Freundlich model for multiple layers adsorption can be written as below [34]:
2.7a
2.7b
Where KF ([mg1 − n. Ln]/g) represents the Freundlich adsorption capacity and n is the heterogeneity factor indicating the multilayer adsorption.
2.4 Regeneration Experiments
Resin reusability was evaluated by sequential adsorption–desorption cycles: in each cycle the resin was contacted with the test solution for 7 h with hourly sampling, then filtered and transferred to 150 mL of 0.5 N HCl for desorption (3.5 h, sampled every 30 min); the resin was then filtered again, placed in fresh 0.5 N HCl for a further 1.5 h, filtered, and returned to a fresh feed solution to begin the next adsorption cycle.
4. Results
5.
3.1 Ion-Exchange Resin Selection
Preliminary screening compared four resins (Dowex 50W-X8, AmberChrom 50WX2, AmberChrom 50WX4, and Amberlyst 15) for Ce(IV) adsorption under identical conditions (30.0 ppm solution, pH = 4.0, 25°C, 100 rpm, 7 h). AmberChrom 50WX4 and Amberlyst 15 exhibited negligible adsorption, while Dowex 50W-X8 and AmberChrom 50WX2 showed measurable uptake (Fig. 1).
Fig. 1
Adsorption of Ce(IV) by various adsorbents after 7 h (T = 25.0 ℃, 100 RPM, pH = 4.0): (a) percentage removal; (b) amount adsorbed vs time.
A
A follow-up comparison using 50.0 ppm Ce(IV) solution at pH of 2.0 demonstrated higher efficiency for AmberChrom 50WX2, which adsorbed ~ 3–6% more cerium than Dowex 50W-X8 under the tested conditions (Fig. 2; Table 1). Based on these results, AmberChrom 50WX2 was selected for all subsequent experiments.(a) (b)
Figure 2. Adsorption of Ce(IV) by Dowex 50W-X8 and AmberChrom 50WX2 after 7 h (T = 25.0 ℃, 100 RPM, pH = 2.0): (a) percentage removal; (b) amount adsorbed vs time.
Adsorbent Type | Dowex 50W-X8 | AmberChrom 50WX2 | AmberChrom 50WX4 | Amberlyst 15 |
|---|---|---|---|---|
Removal after 7 h (%) [Ce]o = 30.0 PPM | 45.8 | 51.2 | -11.4 | 6.9 |
Removal after 7 h (%) [Ce]o = 50.0 PPM | 53.8 | 56.9 | NA | NA |
3.2 Effect of Resin Load
Varying resin dosage (0.5, 1.0, 1.5, and 2.0 g) was examined using 100.0 ppm Ce(III) solution at pH of 2.0, 25°C. Higher resin loads removed a greater total amount of cerium from solution (Fig. 3a), while the adsorption capacity per unit mass decreased at higher dosages (Fig. 3b; Table 2).
Fig. 3
The effect of sorbent load (a) The percentage of cerium adsorbed after 7 hours with different resin loads; (b) The capacity of cerium adsorbed per unit mass of resin after 7 hours (T = 25.0 ℃, 100 RPM, pH = 2.0)
Mass of Resin (g) | 0.5 | 1.0 | 1.5 | 2.0 |
|---|---|---|---|---|
Capacity at Equilibrium qe (mg/g) | 16.3 | 9.4 | 8.0 | 6.0 |
Amount of available Ce(III) adsorbed (%) | 56.8 | 66.0 | 83.5 | 95.7 |
A
Kinetic modeling was applied to the adsorption data using the pseudo-first order (PFO), pseudo-second order (PSO), and the Elovich models. The corresponding plots are shown in Fig. 4, and kinetic rate constants derived from linear fits are summarized in Fig. 5. Among the models, the Elovich equation provided the closest agreement with experimental data, with an average deviation of 2.5% compared to 4.0% for PFO and 25.5% for PSO (Fig. 6; Table 3).(a) (b)
(e) (f)
Fig. 4
Kinetic plots of adsorption for various models and IX resin loads (a) PFO kinetics for 0.5 grams of resin; (b) PFO kinetics for 1.0 grams of resin; (c) PFO kinetics for 1.5 grams of resin; (d) PFO kinetics for 2.0 grams of resin; (e) PSO kinetics for 0.5 grams of resin; (f) PSO kinetics for 1.0 grams of resin; (g) PSO kinetics for 1.5 grams of resin; (h) PSO kinetics for 2.0 grams of resin; (i) Elovich kinetics for 0.5 grams of resin; (j) Elovich kinetics for 1.0 grams of resin; (k) Elovich kinetics for 1.5 grams of resin; (l) Elovich kinetics for 2.0 grams of resin
(a) (b)
(c)
Figure 5. The trends of kinetic rates with various IX resin loads: (a) the PFO kinetic rate, KI ; (b) the PSO kinetic rate, KII ; (c) the Elovich kinetic rate,
Fig. 6
The differences in average deviation between experimental values and model predictions of each tested kinetic model.
Mass of Resin (g) | 0.5 | 1.0 | 1.5 | 2.0 | Average Deviation between experimental and modeled values (%) |
|---|---|---|---|---|---|
PFO Ki (1/h) | 0.365 | 0.352 | 0.443 | 0.521 | 4.0 |
PSO Kii (g/mg.h) | 0.286 | 0.430 | 0.479 | 0.664 | 25.5 |
Elovich α (mg/g.h) | 10.85 | 8.50 | 7.84 | 8.03 | 2.5 |
3.3 Effect of Solution pH
(a) (b)
Fig. 7
The Effect of pH on (T = 25.0 ℃, 100 RPM): (a) the percentage of cerium adsorbed at various times at different solution pH; (b) the Elovich kinetic rate constant, α, at various pH; (c) the zeta potential of the adsorbent exposed to 100 ppm Ce(III) solution
3.4 Effect of Initial Cerium Concentration
Initial Ce(III) concentrations of 40.0–120.0 ppm were tested (pH = 2.0, 25°C, 1.0 g resin, 10 h). Adsorption capacity at equilibrium increased with concentration (Fig. 8c), and kinetic rates also rose with increasing Ce(III) load, indicating mass transfer effects (Fig. 8b). Time-course adsorption curves are shown in Fig. 8d, and model fit comparisons in Fig. 8a.
Fig. 8
The effect of adsorbate load; (a) verification of the Elovich model by comparing the average deviation between modeled and experimental qe using each kinetic model; (b) the Elovich kinetic rate constant, α, at various initial concentrations of cerium; (c) the adsorption capacity at equilibrium for various initial concentrations of cerium (d) Variation of amount of Ce(III) adsorbed with adsorption time at different initial concentrations (100 RPM, 1.0 g resin, pH = 2.0, T = 25.0 ℃).
3.5 Adsorption Isotherms
Equilibrium data were fitted to the Freundlich and Langmuir isotherm models. The Freundlich constants were n = 2.57 and KF = 7.34, while the Langmuir constants were QL = 18.8 mg/g and KL = 0.654 L/mg. The Langmuir model provided a stronger fit (R² = 0.998, deviation 1.54%) compared to the Freundlich model (R² = 0.877, deviation 6.23%) (Fig. 9; Table 6). SEM and EDS analyses showed the resin morphology and confirmed the Ce(III) uptake (Figs. 10–11).
Fig. 9
Isotherm plots: (a) Linearized Freundlich isotherm; (b) Linearized Langmuir isotherm; (c) Non-linear comparison of model prediction
Fig. 10
High resolution SEM images of AmberChrom 50WX2; (a) unused with 100 times magnification; (b) unused with 550 times magnification; (c) used for a 7-hour experiment for the adsorption of cerium, with 500 times magnification; (d) used and marked with the surface areas of study.
Fig. 11
EDS reports of (a) Fresh sample of AmberChrom 50WX2, and (b) sample of AmberChrom 50WX2 used in an experiment for 7 hours of cerium adsorption
Sorbate Load (ppm) | 36.21 | 66.77 | 83.22 | 100.70 | 120.63 | NA |
|---|---|---|---|---|---|---|
qe,experimental (mg/g) | 5.34 | 9.80 | 12.35 | 14.48 | 16.60 | Average Deviation (%) |
qe,Langmuir (mg/g) | 5.98 | 9.61 | 11.61 | 14.23 | 16.69 | 1.54 |
qe,Freundlich (mg/g) | 6.43 | 8.80 | 10.42 | 13.44 | 19.25 | 6.23 |
3.6 Effect of Temperature
Temperature effect (20–40°C) was evaluated. Equilibrium constants were derived and used to construct the Van’t Hoff and Arrhenius plots (Fig. 12). The adsorption process was endothermic, with increasing temperature enhancing spontaneity as reflected in the Gibbs free energy trend (Table 7).
Fig. 12
Thermodynamic figures; (a) Van’t Hoff plot generated from experimental data; (b) Gibbs free energy change; (c) the Arrhenius plot used to determine the activation energy
Temperature (°C) | 20 | 25 | 30 | 35 | 40 |
|---|---|---|---|---|---|
Amount of Ce(III) adsorbed (%) | 79.2 | 85.2 | 87.4 | 90.9 | 92.6 |
qe (mg/g) | 11.30 | 12.83 | 13.24 | 13.79 | 14.06 |
Ce (mg/L) | 19.71 | 14.85 | 12.75 | 9.17 | 7.49 |
Kd (L/g) | 0.57 | 0.86 | 1.04 | 1.50 | 1.88 |
ΔG (kJ/mol) | 1.27 | 0.53 | -0.21 | -0.95 | -1.70 |
3.7 Adsorption in Mixed Rare Earth Systems
Binary mixtures of Ce(III)–La(III) and Ce(III)–Y(III) at 2:1, 1:1, and 1:2 (total REE = 60 ppm) showed comparable percent removals with no strong selectivity (Figs. 13–14), and the ternary mixture (20 ppm each of Ce, La, and Y) behaved similarly (Fig. 15; Table 8). The slightly lower % removal at 2:1 (Ce:La) is plausibly due to competitive site blocking by the majority ion (Ce3+) and a slower approach to equilibrium at the fixed 7-h contact time (T = 25 oC, 100 rpm, pH = 2). By contrast, the Elovich initial rate constant (α) peaks at 1:1, where equal activities minimize single-ion crowding and near-surface resistance, giving a faster early uptake; nevertheless, endpoint removals converge across ratios (and in the ternary case) because capacity is mainly site-limited and the REEs have similar affinities under these conditions (Table 8).
Fig. 13
Mixtures of Ce(III) and La(III) (T = 25.0 ℃, 100 RPM, pH 2, t = 7h): (a) the percentage of rare earths adsorbed; (b) comparing the Elovich rate constant
Fig. 14
Mixtures of Ce(III) and Y(III) (T = 25.0 ℃, 100 RPM, pH 1.2, t = 7h): (a) the percentage of rare earths adsorbed; (b) comparing the Elovich rate constant
Fig. 15
Mixture of Ce(III), La(III) and Y(III) (T = 25.0 ℃, 100 RPM, pH 1.36, t = 7h): (a) the percentage of rare earths adsorbed (b) comparing the Elovich rate constant
Ratio (Ce:La) | 2:1 | 1:1 | 1:2 |
|---|---|---|---|
Amount of Ce(III) adsorbed (%) | 62.9 | 73.2 | 70.5 |
Amount of La(III) adsorbed (%) | 63.3 | 74.3 | 72.6 |
qe,Ce (mg/g) | 3.94 | 3.21 | 2.56 |
qe,La (mg/g) | 1.89 | 2.84 | 4.07 |
α,Ce (mg/g h) | 2.632 | 4.742 | 1.393 |
α,La (mg/g h) | 1.232 | 3.998 | 2.287 |
5.8 Resin Regeneration and Reuse
AmberChrom 50WX2 was cycled four times using a fixed protocol of 7 h adsorption followed by two-stage desorption in 0.5 N HCl (3.5 h, then 1.5 h). Recovery (%) for each cycle was the total Ce released in both desorption steps divided by the Ce adsorbed in that cycle, and cumulative recovery (%) was computed from cumulative desorbed over cumulative adsorbed. Under these conditions, the endpoint percent recovery remained high (Fig. 16a), and the equilibrium capacity was essentially retained (Fig. 16b;
), with small increases in cycles 2–3 attributable to incomplete removal in the prior cycle. The Elovich rate constant (
) declined modestly with reuse (Fig. 16c), suggesting minor kinetic slowing (e.g., partial site fouling or diffusional resistance), but overall performance was preserved. Cerium was subsequently recovered from the desorbate by pH-induced precipitation, with onset near pH
7.8, consistent with speciation trends (Fig. 17).
Fig. 16
Effects of multiple cycles of resin adsorption-desorption on (T = 25.0 ℃, 100 rpm, pHads. =1.75, adsorption 7h; desorption in 0.5 N HCl: 3.5 h then 1.5 h) ; (a) Adsorption (%), Recovery (%) (sum of both desorption steps per cycle), and cumulative recovery (%) (cumulative desorbed/cumulative adsorbed); (b) capacity retention shown as
, ( cycle capacity normalized to cycle-1 capacity); (c) Elovich initial rate constant (
) per cycle.
Fig. 17
Predominance diagrams of mononuclear Ce(III) species (0.1 mol/L) in aqueous solution as a function of pH [35].
6. Discussion
4.1 Resin Selection
AmberChrom 50WX2 demonstrated superior adsorption performance compared to Dowex 50W-X8, AmberChrom 50WX4, and Amberlyst 15, particularly at lower concentrations resembling waste stream conditions. The superior performance of AmberChrom 50WX2 suggests that resin porosity and active site availability are critical parameters for cerium removal, especially under dilute conditions relevant to industrial waste streams. This aligns with prior findings that the adsorbent’s structure and surface chemistry strongly influence REE uptake efficiency [16].
4.2 Effect of Resin Load and Kinetics
The increase in adsorption with higher resin loads was expected due to the larger number of available ion-exchange sites. However, the decrease in adsorption capacity per unit mass at higher dosages reflects site underutilization, a trend reported in similar lanthanide adsorption studies [36]. Kinetic analysis showed that the Elovich model provided the best description of adsorption dynamics, consistent with a chemisorption mechanism. This is further supported by SEM and EDS analyses, which indicated limited physical binding sites and suggested strong chemical interactions between Ce(III) ions and resin active sites.
4.3 Effect of Solution pH
While final adsorption capacities were similar across the pH range tested, adsorption kinetics increased with pH. The zeta potential data confirmed that surface charge plays an important role in determining ion-exchange rates, with reduced rates near the pHpzc (~ 3.0) where the surface charge is neutral. These results support earlier studies highlighting the role of electrostatic attraction in enhancing REE adsorption [37, 38]. For practical applications, operation at lower pH values may be preferable due to compatibility with acid mine drainage (AMD) conditions, even if kinetics are somewhat slower.
4.4 Effect of Initial Concentration and Isotherm Behavior
The positive correlation between initial concentration and adsorption capacity reflects the influence of driving force and mass transfer in sorption processes [39]. At low concentrations, limited driving force reduces the uptake efficiency, suggesting that pre-concentration may be necessary for diluting waste streams. The Langmuir isotherm provided an excellent fit to equilibrium data, over the Freundlich model, confirming monolayer adsorption on a homogeneous surface with finite binding sites [33, 34]. This behavior, together with the Elovich kinetic model, supports chemisorption as the dominant mechanism, consistent with other studies of metal sorption onto functionalized resins [40].
4.5 Effect of Temperature and Thermodynamics
Thermodynamic analysis showed the adsorption process to be endothermic, with increased spontaneity at higher temperatures. The positive enthalpy suggests an activated process requiring energy input, while the negative Gibbs free energy at higher temperatures confirms favorable adsorption. The low activation energy determined from the Arrhenius plot supports the feasibility of ion-exchange under moderate thermal conditions. These findings are in line with Allahkarami and Rezai [28], who reported similar thermodynamic trends in REE sorption systems.
4.6 Competitive Adsorption in Mixed Rare Earth Systems
The lack of selectivity between Ce(III), La(III), and Y(III) indicates that AmberChrom 50WX2 cannot discriminate between REEs of similar ionic radii and identical charge. This equal competitiveness has been noted in prior work, where REE separation required either sequential ion-exchange stages or coupling with selective pretreatments such as solvent extraction [35]. For real-world waste streams containing multiple REEs, AmberChrom 50WX2 may therefore be most effective in bulk REE recovery, with downstream processes applied for separation of individual elements.
4.7 Resin Regeneration and Reuse
AmberChrom 50WX2 maintained adsorption capacity across four regeneration cycles, with only minor decreases in kinetic rate. This resilience underscores its suitability for repeated use, reducing overall process costs and waste generation. The observation of > 100% recovery in some cycles reflects residual desorption from previous runs, a phenomenon also reported in repeated ion-exchange studies [41].
4.8 Implications and Limitations
This study provides systematic evidence supporting AmberChrom 50WX2 as a viable resin for REE recovery from acidic waste streams, demonstrating strong adsorption efficiency, reproducible regeneration, and compatibility with real-world conditions. However, its lack of selectivity among REEs highlights a limitation for applications requiring separation of individual elements. Furthermore, while batch-scale results are promising, continuous flow systems and column studies will be necessary to confirm scalability.
4.9 Overall Contribution
By combining kinetic, isotherm, thermodynamic, and regeneration analyses, this study advances adsorption-based ion-exchange from descriptive demonstration toward practical application. The findings emphasize the strengths of IX resins in recovering REEs under acidic, variable waste stream conditions, while identifying challenges in selectivity and scale-up that require further work.
7. Conclusion
This study demonstrated that AmberChrom 50WX2 is an effective cation-exchange resin for cerium recovery from aqueous solutions under a range of operational conditions. Systematic evaluation showed that adsorption followed the Elovich kinetic model and the Langmuir isotherm, supporting a chemisorption mechanism with monolayer coverage. Adsorption capacity and kinetics were influenced by resin load, solution pH, and initial concentration, while thermodynamic analysis confirmed the process to be endothermic and increasingly spontaneous at higher temperatures. The resin maintained stable adsorption performance across four regeneration cycles, highlighting its potential for reuse.
Despite these strengths, AmberChrom 50WX2 exhibited limited selectivity among REEs of similar ionic radius and oxidation state, suggesting that it is best suited for bulk REE recovery rather than selective separation. Future work should focus on coupling ion-exchange with complementary pretreatment steps, or on developing modified resins with improved selectivity for trivalent REEs. Such strategies could enhance the applicability of IX-based adsorption for sustainable rare earth recovery from industrial waste streams.
Declarations
A
Funding:
This research received no external funding.
Ethics approval:
Not applicable.
Consent to participate:
Not applicable.
Consent to publish:
Not applicable.
Competing interests:
The authors declare no competing financial or non-financial interests.
A
Author Contribution
Conceptualization: H.M. and H.D.; Methodology: L.B.H. and H.D.; Investigation: L.B.H.; Formal analysis: L.B.H. and H.D.; Data curation & Visualization: L.B.H.; Writing—original draft: L.B.H.; Writing—review & editing: H.D. and H.M.; Supervision: H.D. and H.M.
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