A simple model to predict chromate partitioning in selected soils from China

Area of Science:

• Environmental Science
• Soil Science
• Geochemistry

Background:

• Chromate (Cr(VI)) mobility and toxicity in soils, particularly the vadose zone, pose significant environmental risks.
• Understanding Cr(VI) soil partitioning is crucial for environmental risk assessment and remediation strategies.

Purpose of the Study:

• To develop and validate a mechanism-based multi-surface complexation model for predicting Cr(VI) partitioning in Chinese soils.
• To assess the role of different soil reactive surfaces, specifically goethite and hydrous ferric oxide (HFO), in Cr(VI) retention.

Main Methods:

• Utilized published parameters to construct a multi-surface complexation model.
• Applied the CD-MUSIC model to describe Cr(VI) adsorption onto goethite, using a standard reactive surface area of 45.8 m²/g.
• Evaluated model performance across 12 organic matter-depleted Chinese soils with varying properties.

Main Results:

• The model incorporating goethite alone provided the best prediction of Cr(VI) soil partitioning.
• Inclusion of HFO led to an overestimation of Cr(VI) adsorption in certain soils.
• Available soil phosphate was identified as a significant competitor for Cr(VI) adsorption, particularly when the Fe/P ratio was low (<1).

Conclusions:

• A simplified, mechanism-based model using goethite effectively predicts Cr(VI) soil partitioning across diverse soil types and conditions.
• Phosphate competition must be considered in Cr(VI) retention assessments, especially in soils with low iron to phosphorus ratios.
• The developed model offers a practical tool for predicting Cr(VI) behavior in soils, applicable to various environmental scenarios.