# Rare Earth Elements Uptake by Synthetic Polymeric and Cellulose-Based Materials: A Review
## 7 Synthetic Polymeric Materials for REE Uptake
### Novel Synthetic Polymeric Materials  
Other synthetic resins different from the commercial ones have also been studied for REE uptake from aqueous media. Using polystyrene (PS), which is one of the most used polymers in commercial ion exchange resins, together with poly (hydroxamic acid) to form an interpenetrating polymer network (IPN), the capture capacity for REEs increases up to 200 mg/g for Ce (III), 150 mg/g for La (III), and 120 mg/g for Y [31]. This drastic increase in the capture capacity, compared with other commercial ion exchange resins, could be explained by the chelating effect of hydroxamic acid, which has been used as a flotation agent in REE mining [44]. The nature of IPN, where two crosslinked polymers are entangled [45], gives the resulting material a better availability of the functional polar groups found in hydroxamic acid possibly due to repulsion with the polystyrene network. PS-DVB resin with diglycolamic acid groups shows a similar capture capacity for REEs to commercial ion exchange resins for Dy (III) at low pH values [32]. Interestingly, diglycolamic acid captures  
\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 (°C, pH)** & **Ref.** \\ \hline Poly(acrylamide-acrylic acid-sodium 4-styrenesulfonate)@SiO\({}_{2}\) & & & & & \\  & & & & & \\ \hline Poly(taconic acid)@sepiolite & & & & & \\  & & & & & \\  
REEs only by a chelating effect and not through ion exchange because, at the low pH values evaluated, carboxylic acid moieties are protonated. Rescorincl-terephthalaldehyde resin is abundant in carbonyl groups due to the presence of terephthalaldehyde and deprotonated hydroxyl groups due to treatment with NaOH during synthesis. It shows a capture capacity of 70 mg/g for Eu (III) at pH 4.0. According to researchers, it is a nontoxic resin due to its nonhazardous starting materials [33]. However, the aldehyde moiety present in this resin could be oxidized to a carboxylic acid, and protonation of hydroxyl groups under the conditions found in mining wastewaters and AMD should be considered because it could change the REE uptake properties. It has also been reported that using a lanthanide ion imprinted polymer (IPP) of poly(4-vinylpyridine), which is also a chelating resin, captures approximately 130 mg/g of REEs [34]. It seems that the capture capacity in this type of material increases for heavier REEs, probably because of the lanthanide contraction, which makes imprinted ion cavities found in the material more available for the size of the ions evaluated. It should be noted that poly (4-vinylpyridine) was evaluated at pH 6.0, which keeps nitrogen groups present in the pyridine ring deprotonated. Based on REE recovery from mining wastewaters or AMD, nitrogen-chelating resins are not suitable for this type of application, and carboxylic-acid-based chelating resins should be preferred because they work under acidic conditions near the pH of mining wastewaters and AMD.