Chromium (VI) removal kinetics by magnetite-coated sand: Small-scale flow-through column experiments

Area of Science:

• Environmental Science
• Materials Science
• Chemical Engineering

Background:

• Magnetite nanoparticles offer potential for hexavalent chromium (Cr(VI)) remediation.
• Challenges exist in safely handling and applying nanoparticles due to their small size.
• Developing stable, effective media for Cr(VI) removal is crucial for water treatment.

Purpose of the Study:

• To evaluate the efficiency of magnetite-coated sand in removing Cr(VI) from contaminated water.
• To investigate the impact of Cr(VI) concentration, pH, and oxygen levels on removal.
• To develop and validate a reactive-transport model for predicting Cr(VI) removal.

Main Methods:

• Preparation of flow-through columns with varying percentages (10% and 100% v/v) of magnetite-coated sand.
• Experimental determination of Cr(VI) removal efficiency under different conditions (concentration, pH, oxic/anoxic).
• Formulation and application of a reactive-transport model to simulate Cr(VI) sorption and transport.

Main Results:

• Magnetite-coated sand columns achieved high Cr(VI) removal rates (>99% for 10% v/v, 72% for 100% v/v).
• The material demonstrated both reversible and irreversible (chemi)sorption of Cr(VI).
• Model accurately predicted Cr removal, with higher sorption capacity observed in the 100% column attributed to increased reactive surface area from micro-particle detachment.

Conclusions:

• Magnetite-coated sand is a promising medium for Cr(VI) remediation in water treatment.
• The material exhibits robust performance, including under oxic conditions (47% removal).
• The developed reactive-transport model provides a valuable tool for designing and optimizing fixed-bed reactors and permeable reactive barriers for Cr(VI) removal.