Micro volume changes due to Pb(II) and Cu(II) sorption on amorphous Fe(III) hydroxide

Area of Science:

• Environmental Chemistry
• Geochemistry
• Materials Science

Background:

• Amorphous Fe(III) hydroxide (AFH) is a key sorbent for heavy metals in aquatic environments.
• Understanding metal-ligand interactions at the solid-solution interface is crucial for contaminant remediation.
• Volume changes during sorption provide insights into structural and hydration alterations.

Purpose of the Study:

• To quantify micro volume changes during Pb(II) and Cu(II) sorption onto AFH at pH 4.50.
• To elucidate the mechanism of Pb(II) and Cu(II) sorption, including hydration status and complexation.
• To compare sorption behavior with bulk hydroxide precipitation.

Main Methods:

• Dilatometry was used to precisely measure system volume changes.
• Experiments were conducted at a controlled pH of 4.50.
• Sorption of Pb(II) and Cu(II) on AFH was analyzed.

Main Results:

• System volume increased upon Pb(II) and Cu(II) sorption, indicating release of hydrated water.
• Volume increases were smaller than those expected from bulk hydroxide precipitation.
• Pb(II) and Cu(II) likely formed inner-sphere complexes on AFH, retaining some hydration.

Conclusions:

• Pb(II) and Cu(II) form inner-sphere complexes on AFH at pH 4.50.
• Sorption involves the release of hydrated water molecules from the AFH surface and/or ions.
• Cu(II) retained more hydrated water upon sorption compared to Pb(II).