Spectroscopic Analysis of Metal Sorption Mechanisms on Mineral Surfaces

The interaction of metal ions with mineral surfaces governs contaminant mobility, nutrient cycling and the efficacy of remediation technologies in soils and aquifers. Spectroscopic techniques have matured to resolve the molecular-scale processes by which metals attach, transform and immobilise on clays, oxides and mixed mineral phases. Inner-sphere adsorption involves direct covalent or coordinate bonding between metal ions and surface functional groups, whereas outer-sphere adsorption is driven by electrostatic attraction within the electrical double layer. Under varying pH, redox and ionic strength conditions, surface precipitation and the formation of layered double hydroxide (LDH) phases may further stabilise metal species. Modern synchrotron-based X-ray absorption methods, complemented by surface-sensitive analyses, have enabled direct characterisation of metal coordination environments, bond distances and local structure. These insights underpin predictive models for metal fate in natural and engineered settings, inform design of sorbents and guide risk assessment for heavy-metal contamination on a global scale.

Research from Nature Portfolio

Recent investigations of nickel sorption at the illite–water interface have combined batch sorption experiments, surface complexation modelling and extended X-ray absorption fine structure (EXAFS) to delineate pH- and concentration-dependent mechanisms. At low Ni(II) loadings, ion-exchange species coexist with inner-sphere surface complexes, while surface-induced precipitation of amorphous nickel hydroxides and gradual transformation to Ni–Al LDH occur under neutral to alkaline conditions. Temperature elevation accelerates this conversion and favours the thermodynamically stable LDH phase.

Studies employing EXAFS and sequential extraction have also probed Ni(II) sorption on calcareous aridisol soils. Under acidic conditions, rapid ion exchange and surface complexation dominate, whereas prolonged contact and higher temperatures promote nucleation and growth of Ni–Al LDH on the soil matrix. Coordination numbers and interatomic distances derived from spectroscopy confirm the evolution from surface-bound Ni to layered hydroxide structures, highlighting the role of soil mineralogy in metal fixation.

Spectroscopic Analysis of Metal Sorption Mechanisms on Mineral Surfaces publication trend

The graph below shows the total number of articles in spectroscopic analysis of metal sorption mechanisms on mineral surfaces across all publications each year (not limited to Nature Index journals).

Technical terms

EXAFS: Extended X-ray absorption fine structure, a synchrotron technique that yields bond distances and coordination numbers around a target element.

XPS: X-ray photoelectron spectroscopy, a surface-sensitive method measuring photoelectron binding energies to identify elemental composition and oxidation states.

Inner-sphere adsorption: Adsorption mode in which metal ions form direct chemical bonds with surface functional groups.

Outer-sphere adsorption: Adsorption driven by electrostatic attraction without direct ligand exchange between metal and surface.

Layered double hydroxide (LDH): Mixed metal hydroxide minerals with brucite-like layers and interlayer anions, often formed by surface precipitation.

Cation exchange capacity (CEC): A measure of the total number of exchangeable cations a sorbent can hold per unit mass.

References

1. Sorption Mechanisms of Chemicals in Soils. Soil Systems (2021).
2. Exploring the Sorption Mechanism of Ni(II) on Illite: Batch Sorption, Modelling, EXAFS and Extraction Investigations. Scientific Reports (2017).
3. Sorption of Nickel(II) on a Calcareous Aridisol Soil, China: Batch, XPS, and EXAFS Spectroscopic Investigations. Scientific Reports (2017).
4. Sorption of Cu2+ Ions by Bentonite Modified with Al Keggin Cations and Humic Acid in Solutions with pH 4.5. Minerals (2020).
5. Removal of Cu(II) Contamination from Aqueous Solution by Ethylenediamine@β-Zeolite Composite. Molecules (2021).