Proton buffering and metal leaching in sandy soils

Area of Science:

• Environmental Science
• Soil Science
• Geochemistry

Background:

• Soil acidification is a growing concern, impacting metal leaching from contaminated sites.
• Understanding metal release mechanisms is crucial for environmental remediation and risk assessment.

Purpose of the Study:

• To investigate the buffering capacity of sandy soils during acidification.
• To model the release of major (Al, Ca, Mg) and trace metals (Cu, Cd, Ni, Zn) from soil surfaces.
• To evaluate the predictive accuracy of a multisurface model for pH changes and metal desorption.

Main Methods:

• Utilized a mechanistic multisurface model to describe metal sorption onto soil components (organic matter, clay, Fe (hydr)oxides).
• Conducted step-wise acidification experiments using a flow-through reactor with contaminated sandy soil samples.
• Measured pH and metal concentrations (major and trace) after successive proton additions.

Main Results:

• The multisurface model provided satisfying predictions of soil pH changes between pH 6 and 4.
• Model predictions for pH were slightly underestimated below pH 4, potentially due to unmodeled Al-buffering minerals.
• Desorption of major and trace metals was generally predicted well, within a factor of 1-5 on a linear scale.

Conclusions:

• The multisurface model effectively predicts proton buffering and metal desorption in sandy soils across a wide pH range and varying metal content.
• The model serves as a valuable tool for assessing the environmental impact of acidification on metal mobility in contaminated soils.
• Further refinement of the model to include Al-buffering minerals could improve accuracy at lower pH levels.