# Neodymium and Yttrium Adsorption on Citrate-Modified Cellulose: Experimental and Computational Insights

## TL;DR

This paper explores using citrate-modified cellulose to adsorb neodymium and yttrium, offering a sustainable alternative to traditional separation methods.

## Contribution

The study introduces cellulose citrate as a novel adsorbent for rare earth elements with pH-dependent selectivity and validated mechanisms.

## Key findings

- Cellulose citrate shows higher adsorption capacity for neodymium at higher concentrations.
- Adsorption equilibrium is reached within 60 minutes and is strongly pH-dependent.
- Computational models confirm the experimental adsorption behavior and binding mechanisms.

## Abstract

Neodymium (Nd) and yttrium (Y), two rare earth elements,
play a
crucial role in a wide range of technologies, and their separation
is a challenging process. Adsorption-based approaches offer a sustainable
and cost-efficient substitute for the most widely used solvent extraction
procedure. Here, we assess the potential of cellulose citrate (CC)
as an adsorbent for the removal of Y and Nd through both experimental
and computational approaches. CC was successfully synthesized by reacting
raw cellulose extracted from Spartium junceum (Spanish broom) with molten citric acid using a green approach that
does not require any solvent. The final goal is to shed light on the
mechanism of adsorption by citrate-functionalized cellulose by interpreting
the adsorption measurements through kinetics and isotherm adsorption
models, as well as Density functional theory (DFT) calculations and
molecular mechanics (MM) simulations. Adsorption properties of the
sorbent are investigated at different contact times, pH values, and
metal concentrations. Cellulose citrate has proven to be a highly
effective material for the adsorption of the two metals, exhibiting
a slight preference for Y at low-to-medium concentrations and for
Nd at higher concentrations, suggesting a different binding stoichiometry
of the two cations. The adsorption process is found to be pH-dependent,
with equilibrium being reached after approximately 60 min. Interestingly,
a certain degree of selectivity toward Nd is observed, which becomes
more pronounced at pH values below 3 and at higher metal concentrations.
DFT and MM modeling confirm the experimental results and allow an
adsorption mechanism to interpret the measured performance of this
material.