Selective Scandium Adsorption by Mechanochemically Synthesized α-Magnesium and α-Disodium Zirconium Phosphates

Area of Science:

• Materials Science
• Inorganic Chemistry
• Environmental Science

Background:

• Zirconium phosphates exhibit excellent thermal and acidic stability.
• They are effective ion exchangers for recovering valuable elements.
• Bauxite residue is a source of rare earth elements, including scandium.

Purpose of the Study:

• To evaluate the selective uptake of scandium (Sc3+) by two mechanochemically synthesized zirconium phosphates: α-disodium zirconium phosphate (α-Na2ZrP) and α-magnesium zirconium phosphate (α-MgZrP).
• To assess the performance of these materials in the presence of other rare earth elements and iron, common contaminants in bauxite residues.

Main Methods:

• Minimalistic mechanochemical synthesis using only reactant water for homogenization.
• Stoichiometric or near-stoichiometric reactant ratios.
• Evaluation of selective Sc3+ uptake and ion exchange capacity.
• Stripping of loaded Sc3+ using phosphoric acid.

Main Results:

• Both α-Na2ZrP and α-MgZrP demonstrated high selectivity for Sc3+ over other rare earth ions and iron.
• α-MgZrP showed higher uptake efficiency at low Sc3+ concentrations.
• α-Na2ZrP exhibited a greater overall ion exchange capacity (1.2 mmol/g) compared to α-MgZrP (0.56 mmol/g).
• Stripping with phosphoric acid yielded pure α-zirconium phosphate (α-ZrP), confirming complete Sc3+ removal.

Conclusions:

• Mechanochemically synthesized zirconium phosphates are highly selective ion exchangers for scandium recovery.
• α-Na2ZrP is a promising material for scandium recovery from complex matrices due to its high capacity.
• The ion exchangers can be regenerated efficiently using phosphoric acid, allowing for potential recycling.