Speciation and the structure of lead(II) in hyper-alkaline aqueous solution

Area of Science:

• Inorganic Chemistry
• Aqueous Geochemistry
• Spectroscopy

Background:

• Understanding lead speciation is crucial for environmental and industrial processes.
• Lead(II) behavior in hyper-alkaline solutions is complex and not fully understood.
• Previous studies suggested various lead species, but definitive identification was lacking.

Purpose of the Study:

• To identify the predominant lead(II) species in hyper-alkaline aqueous solutions.
• To determine the structure of the identified lead(II) complex.
• To elucidate the bonding characteristics of lead(II) in alkaline media.

Main Methods:

• Raman spectroscopy was used to analyze lead(II) solutions.
• Ab initio quantum chemical calculations predicted complex stability and spectra.
• Extended X-ray Absorption Fine Structure (EXAFS) determined the complex's structure.

Main Results:

• Raman spectra matched calculations for the [Pb(OH)3](-) complex, excluding other possibilities.
• EXAFS analysis revealed a short Pb-O bond distance (2.216 Å) and low symmetry.
• The [Pb(OH)3](-) complex likely possesses trigonal pyramidal geometry.

Conclusions:

• The [Pb(OH)3](-) complex is the dominant lead(II) species in hyper-alkaline solutions.
• Hydroxide ions form short bonds with d(10)s(2) metal ions like lead(II).
• Findings provide insights into lead and tin speciation analogies in alkaline environments.