# Rare Earth Elements Uptake by Synthetic Polymeric and Cellulose-Based Materials: A Review
## 7 Synthetic Polymeric Materials for REE Uptake
### Commercial Ion Exchange Resins  
Commercial cation exchange resins, such as Dowex 50 WX8, Lewatit MDS 200H, and Purolite C160, have low capture capacity for REEs in batch studies, although researchers have found selectivity toward light REEs [16]. Interestingly, those resins were evaluated at low pH values, up to 3.4, which is a characteristic pH value for mining wastewaters and AMD [16]. In another study, Dowex SCX HCR-S/S resin showed high capture capacity for Eu (III) coming from radioactive waste of nuclear-related processes [30]. It should be noted that evaluated resins are based on polystyrene-divinylbenzene (PS-DVB), which has a sulfonic group in their structure, and possibly due to differences in manufacturing processes, which impact resin grain size and the degree of crosslinking, they have different capture capacities for the same REE cations. Furthermore, commercial cationic exchange resins by themselves have low capture capacity for REEs, and they require modifications to improve their REE uptake. According to the information given in those selected works, it  
Figure 3: Interactions between REE cations and common functional groups included in polymeric materials for REE uptake.  
is unknown whether the presence of other metal cations could interfere with REE capture in those resins, although ion exchange theory suggests high selectivity toward REE cations due to their high charge (3+) [27; 43]. Moreover, selectivity toward light REEs in those resins could be explained by the polarizability of the ions evaluated. Light REE cations are larger ions than heavy REE cations due to lanthanide contraction of ionic radii, giving light REEs greater polarizability and, thus, more affinity in commercial ion exchange resins [27; 43].  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Polymeric Material** & **Functional Groups** & **Ion** & **Capacity q** & **Conditions** & **Ref.** \\  & **Involved** & **Captured** & **(mg/g)** & **Temperature (\({}^{\circ}\)C, pH)** & **Ref.** \\ \hline  & & Y (III) & 11.2 & & \\  & & La (III) & 25.4 & & \\  & & Ce (III) & 23.3 & & \\  & & Nd (III) & 21.1 & 25, 3.4 & [16] \\  & & Dy (III) & 16.9 & & \\  & & Gd (III) & 17.7 & & \\ \hline  & & Y (III) & 10.6 & & \\  & & La (III) & 26.8 & & \\  & & Ce (III) & 24.9 & 25, 3.4 & [16] \\  & & Nd (III) & 20.9 & & \\  & & Dy (III) & 16.2 & & \\  &  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Polymeric Material** & **Functional Groups** & **Ion** & **Capacity q** & **Conditions** & **Ref.** \\  & **Involved** & **Captured** & **(mg/g)** & **Temperature (\({}^{\circ}\)C, pH)** & **Ref.** \\ \hline Resorcinol- & & & Eu (III) & 70.0 & 25, 4.0 & [33] \\erephthalalaldehyde resin & & & & & \\ \hline Poly(4-vinylpyridine)–Schiff base lanthanide ion–imprinted polymer (Ln-IIP) & & & Pr (III) & 125.3 & & \\  & & & Nd (III) & 126.5 & & \\  & & & Sm (III) & 127.6 & 25, 6.0 & [34] \\  & & & Eu (III) & 128.2 & & \\  & & & Gd (III) & 129.1 & & \\ \hline  & & & La (III) & 29.0 & & \\  & & & Ce (III) & 32.0 & & \\  & & & Pr (III) & 33.0 & & \\  & & & Nd (III) & 35.0 & & \\  & & & Sm (III) & 39.0 & & \\  & & & Eu (III) & 42.0 & & \\  & & & Gd (III) & 51.0 & & \\  & & & Tb (III) & 48.0 & 25, 2.0–3.0 & [35] \\  & & & Dy (III) & 51.0 & & \\  & & Ho (III) & 52.0 & & \\  & & & Er (III) & 51.0 & & \\  & & & Tm (III) & 50.0 & & \\  & & & Yb (III) & 48.0 & & \\  & & & Lu (III) & 49.0 & & \\ \hline  & & & & & \\ \hline Polyacrylamide–sodium 4-styrenesulfonate)@SiO2 & & & Tb (III) & 24.2 & 25, 6.0 & [36] \\  & & & & 29.4 & 25, 6.0 & [36] \\  & & & La (III) & 136.0 & & \\  & & & Ce (III) & 132.0 & & \\  & & & Nd (III) & 124.0 & & \\  & & & Eu (III) & 108.0 & & \\ \hline \hline \end{tabular}
\end{table}
Table 2: _Cont._