Sorption Of Rare Earth Elements Research Articles

Electro-assisted sorption behavior and mechanism of low-concentration rare earth elements on carbon based materials

With increasing demands for rare earth elements (REEs) in high-tech and futuristic applications, developing efficient methods for recovering low-concentration REEs is necessary. Here, electro-assisted sorption of low-concentration REEs, La(III), Gd(III) and Y(III) (as symbol of light, medium, and heavy REEs) on carbon-based materials, activated carbon (AC), graphene, and graphite by a facile method was reported. Recovery of La(III), Gd(III) and Y(III) could reach ∼100 % under low-concentration condition where the maximum adsorption capacity was up to 342.38 mg/(g·dm2). Variants including applied voltage, electrodes-distance, pH, impurities, and concentration were considered to study the effects on REEs recovery. Interestingly, adsorption capacity and recovery under low voltage were respectively almost 20 and 14 folds than that without voltage, because voltage promoted REEs transfer and strengthened electrostatic interaction between electrodes and REEs. The mechanism for enhancing REEs recovery on carbon-based electrodes was resulted from high electric double layer (EDL) capacitance and low charge transfer resistance. Total desorption of REEs from electrodes could be quickly realized using NH4Cl or HCl solution. Overall, the study gave a new insight of low-concentration REEs recovery using carbon-based materials, and provided an efficient route using electric method with porous materials for REEs recovery.

Influence of ionic radius on the degree of extraction of rare earth metals during sorption by the interpolymer system AMBERLITE IR-120 –AВ-17-8

Studies have been carried out on the sorption of rare earth metal ions in solution using the interpolymer system Amberlite IR-120:AB-17-8. The purpose of the work is to search for conditions for maximum sorption of rare earth elements (Dy, Tb, Gd, Eu and Sm) from aqueous solutions using the effect of remote interaction of ion exchange resins. Methodology. The residual concentrations of rare earth ions were determined using an Optima 8300DV Duo inductively coupled plasma spectrometer. Results. The best sorption characteristics were determined by the interpolymer system at a ratio of 3:3. The residual concentration of rare earth elements in the solution was: Dy – 4.64 mg/l, Tb – 4.16 mg/l, Gd – 4.21 mg/l, Eu – 4.16 mg/l, Sm – 4.56 mg/l. The variations in the ionic radius of the ions chosen for the study are Dy3+<Tb3+<Gd3+<Eu3+<Sm3+. The degree of sorption of interpolymer system increased with increasing ionic radius of the metals. For dysprosium with the smallest ionic radius, the degree of sorption was η – 52%, and for terbium, gadolinium and europium it increased to η – 58%. For individual Amberlite IR-120 (6:0), the degree of sorption of terbium ions was 47%. Conclusion. The results of the study showed that the interpolymer system with a ratio of 3:3 has the best sorption activity. It has been established that the degree of sorption of interpolymer pairs increases with increasing order of the ionic radius of metals (Tb3+< Gd3+< Eu3+).

High efficiency simultaneous adsorption of rare earth elements from aqueous solutions using carbon xerogel-chitosan composite

ABSTRACT This study investigated the simultaneous sorption of rare earth elements (REEs) from acidic media using carbon xerogel functionalised with chitosan. The combined carbon xerogel with chitosan that was synthesised has a sphere-like structure and a larger BET surface area (275 m2 g−1) than pure carbon xerogel alone (228 m2 g−1). To determine the optimal conditions, adsorption of REEs was established under different variables, including pH, contact time, initial concentration, adsorbent wt. and temperature, as well as desorption experiments. The adsorption isotherms showed that both the Freundlich and Langmuir models were followed, in addition to a pseudo-second order kinetic model. The adsorption is likely exothermic, which confirms it is favourable at low temperatures, and a dissociative adsorption process is involved, according to analysis of thermodynamic state functions. Langmuir calculations revealed that the maximum amount of REEs that were adsorbed was 164 mg/g. Because of its superior adsorption capacity and simplicity in using a recycled material following several desorption cycles, carbon xerogel-chitosan is being employed as a novel adsorbent material to remove REEs from aqueous solutions.

Roles of pH and phosphate in rare earth element biosorption with living acidophilic microalgae

The increasing demand for rare earth elements (REEs) has spurred interest in the development of recovery methods from aqueous waste streams. Acidophilic microalgae have gained attention for REE biosorption as they can withstand high concentrations of transition metals and do not require added organic carbon to grow, potentially allowing simultaneous sorption and self-replication of the sorbent. Here, we assessed the potential of Galdieria sulphuraria for REE biosorption under acidic, nutrient-replete conditions from solutions containing ≤ 15 ppm REEs. Sorption at pH 1.5–2.5 (the growth optimum of G. sulphuraria) was poor but improved up to 24-fold at pH 5.0 in phosphate-free conditions. Metabolic activity had a negative impact on REE sorption, additionally challenging the feasibility of REE biosorption under ideal growth conditions for acidophiles. We further examined the possibility of REE biosorption in the presence of phosphate for biomass growth at elevated pH (pH ≥ 2.5) by assessing aqueous La concentrations in various culture media. Three days after adding La into the media, dissolved La concentrations were up to three orders of magnitude higher than solubility predictions due to supersaturation, though LaPO4 precipitation occurred under all conditions when seed was added. We concluded that biosorption should occur separately from biomass growth to avoid REE phosphate precipitation. Furthermore, we demonstrated the importance of proper control experiments in biosorption studies to assess potential interactions between REEs and matrix ions such as phosphates.Key points• REE biosorption with G. sulphuraria increases significantly when raising pH to 5• Phosphate for biosorbent growth has to be supplied separately from biosorption• Biosorption studies have to assess potential matrix effects on REE behavior

Sorption of Rare Earth Elements by Organic Matter from Aqueous Solutions according to Experimental Data

Sorption of Rare Earth Elements by Organic Matter from Aqueous Solutions according to Experimental Data

A mechanistic surface complexation approach for the prediction of rare earth element reactive transport in quartz porous media

Although rare earth elements (REE) are now considered as emerging contaminants, the mechanisms controlling the mobility of REE in geochemical systems remain elusive. The complexity and multi-element characteristics of REE including potential synergistic and antagonistic interactions with environmental surfaces make the prediction of REE fate in nature a challenging task. In this study, a comprehensive set of batch and column transport experiments were conducted to examine the interactions of REE group, as well as some co-occurring or chemically analogous elements (Sc, Y, Th and U), with 100–300 μm quartz sand particles. Results from batch experiments showed that middle REE (MREE) and heavy REE (HREE) are preferentially adsorbed at low and high REE loadings, which showed the occurrence of two different types of binding sites. A surface complexation model has been developed, which successfully predicted sorption of REE, Sc, Y, Th and U. Experimental data and reactive transport modeling evidenced the importance of the strong sites, and highlighted the competitive binding of MREE with other REE and Y for the quartz surface sites. These results may have strong implications for the development of new prediction tools for accurately assessing the reactive transport of REE in natural systems.

Physicochemical Variation of Clay Minerals and Enrichment of Rare Earth Elements in Regolith-hosted Deposits: Exemplification from The Bankeng Deposit in South China

AbstractThe wide application of rare earth elements (REEs) in the development of a carbon–neutral society has urged resource exploration worldwide in recent years. Regolith-hosted REE deposits are a major source of global REE supply and are hosted mostly in clay minerals. Nonetheless, the ways in which changes in the physicochemical properties of clay minerals during weathering affect the concentrations of REEs in the regolith are not well known. In the current study, a world-class regolith-hosted REE deposit (Bankeng, South China) has been studied to illustrate further the effect of clay minerals on sorption and fractionation of REEs during weathering to form economic deposits. In the weathering profile, halloysite and illite are abundant in the saprolite due to weathering of feldspars and biotite from the bedrock. During weathering, halloysite and illite transform gradually to kaolinite and vermiculite. The large specific surface area, pore volume, and cation exchange capacity of the clay mineral assemblages are favorable to the sorption of REEs, probably because of the formation of vermiculite. The abundance of vermiculite could explain the enrichment of REEs in the upper part of the lower pedolith. For the saprolite-pedolith interface, halloysite is probably the main sorbent for the REEs, as indicated by the distinctive appearance of pore sizes of 2.4–2.8 nm characteristic of halloysite. The progressive transformation of halloysite to kaolinite reduces the pores and desorbs the REEs, causing REE depletion in the shallower soils. As a result, REEs were mobilized downward and re-sorbed in the lower pedolith-upper saprolite causing gradual enrichment and formation of these regolith-hosted deposits.

Insight into the mechanisms involved in the removal of toxic, rare earth, and platinum elements from complex mixtures by Ulva sp.

Hazardous leachate/effluent from fluorescent lamps contains potentially toxic elements such as Hg and Pb, and critical raw materials such as rare earth elements (REEs). This work evaluated the ability of the live macroalgae Ulva sp. to remediate a simulated lamp industry wastewater consisting of a complex mixture of elements (Y, Eu, La, Ce, Tb, Gd, Hg, Pb, Zn, Cu, Co, Cd, and Pt), with particular emphasis on the investigation of the sorption mechanisms. Experiments were performed with 3.0 g/L (fresh weight) of Ulva sp., salinity 25, and an initial concentration of 100 µg/L for each element. Hierarchical cluster analysis highlighted two main groups according to removal: Pt and Cd as the less removed, and all others with removals > 76 %, underlining Hg and Ce with the fastest kinetics (up to 92 %). Apart from Co, Zn and Cd, all mathematical models described sorption kinetics well, with Akaike Information Criteria identifying the Elovich model as the best for describing REEs sorption. FTIR analysis identified the sulphated polysaccharide Ulvan as intervening in binding elements to Ulva biomass. Extraction with EDTA 0.001 mol/L showed that most elements were mainly localized in the outer fraction (surface), except for Hg, which was entirely in the inner part. SEM analysis supported the EDTA analysis and showed a clean surface after washing. The results are an important contribution to the understanding of sorption mechanisms in macroalgae and demonstrate the feasibility of macroalgae-based biotechnologies with reduced costs and high efficiency for water decontamination, in complex saline mixtures.

Mechanisms and influencing factors of yttrium sorption on paddy soil: Experiments and modeling

High-technology rare earth elements (REEs) as emerging contaminants have potentially hazardous risks for human health and the environment. Investigating the sorption of REEs on soils is crucial for understanding their migration and transformation. This study evaluated the sorption mechanisms and influencing factors of the rare earth element yttrium (Y) on paddy soil via integrated batch sorption experiments and theoretical modeling analysis. Site energy distribution theory (SEDT) combined with kinetics, thermodynamics, and isotherm sorption models were applied to illustrate the sorption mechanism. In addition, the effects of phosphorus (P), solution pH, particle size of soil microaggregates, and initial Y content on the sorption processes were evaluated by self-organizing map (SOM) and Boruta algorithm. The sorption kinetic behavior of Y on paddy soil was more consistent with the pseudo-second-order model. Thermodynamic results showed that the Y sorption was a spontaneous endothermic reaction. The generalized Langmuir model well described the isotherm data of Y sorption on heterogeneous paddy soil and soil microaggregates surface. The maximum sorption capacity of Y decreased with increasing soil particle size, which may be related to the number of sorption sites for Y on paddy soil and soil microaggregates, as confirmed by SEDT. The heterogeneity of sorption site energy for Y was the highest in the original paddy soil compared with the separated soil microaggregates. The SOM technique and Boruta algorithm highlighted that the initial concentration of Y and coexisting phosphorus played essential roles in the sorption process of Y, indicating that the addition of phosphate fertilizer may be an effective way to reduce the Y bioavailability in paddy soil in practice. These results can provide a scientific basis for the sustainable management of soil REEs and a theoretical foundation for the remediation of REEs-contaminated soils.

Novel phosphonate-functionalized composite sorbent for the recovery of lanthanum(III) and terbium(III) from synthetic solutions and ore leachate

A new process of phosphorylation of algal/polyethyleneimine composite beads allows to dramatically increase the sorption of rare earth elements (La(III) and Tb(III), as light and heavy REE elements, respectively). Sorption proceeds through interactions with several functional groups (phosphonate, but also amine, and carboxylate groups). The sorption capacity at optimum pH (pH0 : 5, pHeq : 4–4.2) reaches 1.44 mmol La g−1 and 1.02 mmol Tb g−1 (increased by 4.5 to 6.7 compared with raw beads). Sorption isotherms are fitted by the Langmuir equation, while fast uptake kinetics (equilibrium within 20–30 min) is described by the pseudo-first order rate equation. Bound metal ions are quantitatively desorbed using a 0.2 M HCl/0.5 M CaCl2 solution; the recycling of the sorbent for five cycles of sorption and desorption shows high stability of sorption (loss of sorption capacity < 9%) and desorption (efficiency > 99%). The sorbent exhibits a remarkable preference for REEs against Si(IV), Ca(II), and Mg(II). The sorbent is used efficiently for the recovery of REEs from acidic leachates of a sedimentary ore. A global process is designed including acidic leaching, pre-treatment of leachates by U(VI) sorption on quaternary ammonium (QA) resin (about 94% of U content). The outlet solution of QA resin is treated at different pH values: the best results are obtained at pH0 5 (pHeq : ~4.5). The REEs are selectively recovered from the eluates by precipitation with oxalic acid: the REE-oxalate precipitate retains 70–76% of its content in the acidic leachates. After precipitation of Al(III) and Fe(III) at pH 5, residual uranium is recovered by precipitation at pH 9 (4.3% of metal leached from the ore).

Сорбционное извлечение редкоземельных элементов на сульфокатионите КУ-2-8 из азотнокислых растворов вскрытия лопаритового концентрата

The experimental-industrial study results of the process of sorption of rare-earth elements on sulfonic cation-exchange resin KU-2-8 from nitrate solutions of loparite concentrate development are presented. Values of different obtained elements are discussed. Different changes in processes are described. Reprocessing loparine raw materials in the close cycle without hydrochloric and sulfuric acid, and excess of normative sodium content in productional concentrate is possible. Keywords: ionite, sorption, loparite concentrate, rare-earth element, thorium.

Simultaneous sorption of rare earth elements (including scandium and yttrium) from aqueous solutions using zeolite clinoptilolite: A column and speciation study

Rare earth elements including scandium and yttrium (REY) are valuable elements that are used in different economically valuable applications. Moreover, these elements are in demand especially in electronic products and energy gadgets such as solar panels and wind turbines. Thus, their recovery from industrial wastewaters will be very beneficial to the economy of the world. The current study reports on the simultaneous recovery of REY (Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu) from aqueous solutions using column studies. The role of pH (2 – 8), concentration (2 – 10 mg L−1), bed height (3 – 9 cm) and flow rate (2.0 – 5 mL min−1) on the uptake of REY was investigated. The effect of the presence of SO42−, Cl− and PO43− at different conditions was also assessed. Column models were used to describe the column sorption data. The speciation of the elements was determined using PHREEQC geochemical modelling. The highest adsorption capacity was reached with 3 cm bed height and 2 mL min−1 flow rate at pH 5.5, with>98% removal efficiency of all the elements. The REY removal process was ineffective in highly acidic pH. There was no significant difference on the removal of REY in the absence or presence of Cl−. >75 and 90% removal percentage of REY was observed in the presence of SO42− and Cl−, respectively, but the adsorption was low in the presence of PO43−. Natural zeolite proved to be a suitable adsorbent for simultaneous removal of REY from wastewaters.

Sorption of rare-earth elements onto a ligand-associated media for pH-dependent extraction and recovery of critical materials

Toward recovering rare-earth elements, we prepared a solid-phase media that binds and elutes metals for extraction and enrichment. We report the synthesis and methodology for a solid-phase media that exhibits pH-dependent binding of aqueous rare-earth elements. The media shows pH-dependent binding of NdIII and retains efficiency over at least six cycles of binding and elution. Mixed solutions of rare-earth elements demonstrated a preference for mid and heavy rare-earth elements based on thermodynamic binding preferences of the ligand, and selectivity for rare-earth elements over iron and aluminum were observed with coal fly ash leachate. We expect this new recovery method to be a significant step towards aqueous-based extraction and enrichment of critically important rare-earth elements.

Synthesis of polyamide 6/nano-hydroxyapatite hybrid (PA6/n-HAp) for the sorption of rare earth elements and uranium

Polyamide (PA6) and hydroxyapatite (n-HAp) have intrinsic sorption properties for metal ions. Their association by melt compounding allows manufacturing a composite material (PA6/n-HAp) efficient for the binding of uranyl and rare earth metal ions (REEs) in acidic solution (in the pH range 2–2.5). The composite shows enhanced sorption capacities (5–7 times) compared with single PA6 material. The structuration of the material slightly improves textural properties but contributes to improve the accessibility and availability of reactive groups (including by size distribution). Metal sorption proceeds mainly through complexation of amide reactive groups as shown by FTIR characterization (modification of the environment of CO and NH groups) rather than ion-exchange/electrostatic attraction. Maximum sorption capacities approach 0.34 mmol U g−1, 0.49 mmol Er g−1 and 0.70 mmol Nd g−1: the preference may be correlated to the covalent rather than ionic character of these metal ions. Uptake kinetics are relatively slow (requiring up to 6−8 h, under selected experimental conditions): the textural properties of the composite (pore size: 2.6 nm) limit the mass transfer properties (though slightly enhanced compared with PA6 precursor). The resistance to intraparticle diffusion constitutes the major controlling step for uptake kinetics. Nitric acid is the most efficient eluent for the desorption of loaded metals (efficiency exceeds 94 %); noticeably U(VI) elution is optimal at 1 M HNO3 concentration, contrary to REEs that require lower concentration (i.e., 0.1 M). Preliminary tests on sulfuric acid leachates of Egyptian ores demonstrate that the sorbent maintains good sorption properties for REEs and U despite the complexity of the solution. The sorbent has a marked preference for REEs, U and Th against base and alkali metals.

Competition among rare earth elements on sorption onto six seaweeds

Sorption has been proposed as a promising approach towards a sustainable water decontamination and recently to the recycling of rare earth elements (REE). Although living seaweed have been shown to be capable of removing REE from contaminated solutions, no studies have yet compared the effects of REE competition on sorption onto different groups of seaweed. These effects were analysed in the present study by exposing six living seaweeds (Ulva lactuca, Ulva intestinalis, Fucus spiralis, Fucus vesiculosus, Gracilaria sp. and Osmundea pinnatifida) (3 g/L, fresh weight) to mono-element and multi-element solutions of Y, La, Ce, Pr, Nd, Eu, Gd, Tb and Dy (1 μmol/L). Results show a preference towards light REE in mono-element solutions, which is reduced when in competition with other REE. The competitive effect is less pronounced in heavy REE indicating that these are still able to bind to the macroalgae despite the presence of competing ions. Contrary to water content (%), seaweed specific surface area (cm2/g) shows to be an important factor in the sorption of REE, since larger surface area is associated with higher removal and larger competitive effect.

Geochemical behavior of rare earth elements in acid drainages: Modeling achievements and limitations

Rare earth elements (REE) concentrations in acid mine drainage (AMD) are several orders of magnitude higher than those in other surface waters and could be a future supplementary source of highly valuable REE. Therefore, knowing the mobility constraints of REE in natural waters, particularly in AMD, is of interest.Precipitation of schwertmannite and basaluminite occurs due to mixing of REE-enriched AMD and neutral streams. The REE fractionation between AMD and solid phases has been investigated in several localities in the Odiel-Tinto (SW Spain) and Arroyo del Val (N Spain) basins. The mobility of REE is related to the precipitation of Fe and Al phases that occurs at different pH values. The behavior of REE during the mixing is conservative under low pH conditions (pH <4 approximately), at which schwertmannite precipitates, whereas REE are scavenged under near-neutral pH conditions, at which basaluminite precipitates and what suggest that this phase could be responsible for REE retention. Indeed, when Fe and Al phases can be sampled separately, schwertmannite does not contain REE, which are entirely retained in basaluminite, confirming the REE removal by this later phase.The strengths and limitations of a recently proposed thermodynamic model of REE sorption on basaluminite have been assessed by comparing the model predictions with observations of samples recovered in the field. The model is able to predict the REE distribution pattern and confirms the preferential sorption of heavy REEs (HREEs) and Y over light REEs (LREEs) in all the samples. However, the lack of synchronicity between basaluminite precipitation and REE sorption during mixing in an open flow setting precludes an accurate prediction of the REE concentration in the solid phase.

Sorption of rare earth elements on schwertmannite and their mobility in acid mine drainage treatments

Rare Earth Elements (REE) are nowadays considered critical raw materials due to their increasing use in modern industry and their shortage of supply. Acid mine drainage (AMD) contains REE concentrations several orders of magnitude higher than the rest of continental and marine waters, and the sludge from its treatment may become a supplementary source of REE. Schwertmannite, a Fe(III)-sulfate-hydroxide is the most common mineral precipitated from AMD and a main constituent of the neutralization sludge. The objective of this work is to study the mechanism of REE retention in synthetic schwertmannite and to predict the REE behavior in a column experiment mimicking an AMD passive remediation system.Suspensions of synthetic schwertmannite in sulfate solutions show that Y and the lanthanides are effectively sorbed at pH values higher than 4.5, and sorption is complete at pH values higher than 6.5. The experimental partition coefficients clearly show a preferential enrichment of heavy REE in the solid phase. Unlike the rest of the REE, Sc sorption occurred at a lower pH, from 3 to 5. The experimental results have been described with a non-electrostatic surface complexation model in which the aqueous complex MSO4+ exchanges with two H+ from the surface of schwertmannite, forming a bidentate surface complex, (XO)2MSO4-. Scandium sorption was also accurately predicted with the addition of a second bidentate surface complex, (XO)2MOH.The equilibrium constants for REE sorption on schwertmannite calculated in the present work, together with those for REE sorption on basaluminite (Lozano et al., 2019, GCA, 258, 50–62) were used to model the behavior of different REE observed in the pore water and solid of a column experiment. Schwertmannite and basaluminite were the main solid phases formed due to the progression of the neutralization. First schwertmannite precipitated at pH below 4 and then basaluminite precipitated at pH above 4. Both minerals can sorb REE in a similar pH range. However, since Y and the lanthanides sorbed at pH values higher than 5, their sorption only occurred on basaluminite. In contrast, the Sc sorption edge extended from pH 3 to 5 and Sc partially sorbed on schwertmannite. As a practical consequence, REE preferentially accumulated in the basaluminite residue of AMD neutralization systems, but a minor fraction of Sc can be retained in the schwertmannite waste.

Recovery of Rare Earth Elements by Carbon-Based Nanomaterials-A Review.

Modern societies depend strongly on electronic and electric equipment (EEE) which has a side effect result on the large production of electronic wastes (e-waste). This has been regarded as a worldwide issue, because of its environmental impact—namely due to non-adequate treatment and storage limitations. In particular, EEE is dependent on the availability of rare earth elements (REEs), considered as the “vitamins” of modern industry, due to their crucial role in the development of new cutting-edge technologies. High demand and limited resources of REEs in Europe, combined with potential environmental problems, enforce the development of innovative low-cost techniques and materials to recover these elements from e-waste and wastewaters. In this context, sorption methods have shown advantages to pre-concentrate REEs from wastewaters and several studies have reported the use of diverse nanomaterials for these purposes, although mostly describing the sorption of REEs from synthetic and mono-elemental solutions at unrealistic metal concentrations. This review is a one-stop-reference by bringing together recent research works in the scope of the application of carbon nanomaterials for the recovery of REEs from water.

Sorption of rare earth elements onto basaluminite: The role of sulfate and pH

Abstract Scandium, yttrium and lanthanides (REE) are critical raw materials in increasing demand for modern technology, so identifying and developing new sources of REE has become a pressing need. REE concentrations in acid mine drainage (AMD) are several orders of magnitude higher than those in natural water, and their recovery is of economic interest. Passive remediation systems designed to minimize AMD impact on the ecosystem retain REE in solid waste, where basaluminite, Al4SO4(OH)10·5H2O, is the mineral responsible for the scavenge. However, no information about the retention mechanisms of REE is currently available in the literature. The objective of the present work is to study the adsorption of lanthanides, yttrium and scandium onto synthetic basaluminite over a pH range of 4–7 at room conditions. Since sulfate is ubiquitous in AMD, the adsorption has been investigated with variable sulfate concentrations. Experimental results show that sorption onto basaluminite is strongly dependent on pH, starting at pH 5 for lanthanides and yttrium and at pH 4 for scandium. At any given pH values, sorption increases with sulfate concentration. Distribution coefficients, defined as KD = [REEsorbed]/[REEsolution], are higher for Sc, and across the lanthanide series, the distribution coefficients increase from La to Lu according to decreasing ionic radius, where yttrium is considered close to Ho. Experimental results were modeled using a sorption model that considers mass law equations where the strong sulfate aqueous complex, MSO4+, is adsorbed by exchanging a proton with the mineral surface. The dependence of the experimental results on pH suggests the formation of monodentate binding for Y and lanthanides. The bidentate complex for Sc is deduced by the two proton exchange per mol of Sc extracted from the experiments. The thermodynamic constants for the surface complexation reactions were obtained from experiments with high sulfate concentration and were successfully applied to the experiment with low sulfate content and different solid-liquid ratios. Therefore, the model can be applied to interpret the REE geochemistry in natural systems with variable pH and sulfate concentrations.

A new carbamoylmethylphosphonic acid-based polymer for the selective sorption of rare earth elements

Sorption properties of a new hydrosoluble polymer containing carbamoylmethylphosphonic diacid (hcmp) moieties were investigated. This polymer was obtained by hydrolysis of the poly(diethyl-6-(acrylamido)hexylcarbamoylmethylphosphonate) (P(CPAAm6C)). The study allowed the determination of an experimental maximum capacity Qmax equal to 1.5 mmol⋅g−1 which is three times higher than the one obtained for P(CPAAm6C), as previously described (i.e. 0.6 mmol⋅g−1). Experimental data were fitted with the Langmuir equation and parameters QmaxL and KL, were found to be 1.72 ± 0.067 mmol⋅g−1 and 0.302 ± 0.063 L⋅mmol−1, respectively. Additionally, this capacity depends on different parameters (concentration of metals and sorbent, pH, and ionic strength). The study proved that the hP(CPAAm6C) was selective of gadolinium in Gd/Ni mixtures. Additionally, the precipitation of the polymer was observed simultaneously to the Gd complexation. The results described in this paper proved that the hP(CPAAm6C) is a very promising hydrosoluble material for the purification of lanthanide elements or in the field of nuclear fuel reprocessing by using new solvent free and low energy consuming processes.