Equilibrium and dynamic study on hexavalent chromium adsorption onto activated carbon

Area of Science:

• Environmental Chemistry
• Adsorption Science
• Water Treatment Technologies

Background:

• Hexavalent chromium (Cr(VI)) is a toxic pollutant requiring effective removal from water.
• Activated carbon is a widely used adsorbent, but its performance with Cr(VI) needs detailed understanding.
• Chromium speciation and redox reactions significantly influence adsorption behavior.

Purpose of the Study:

• To present equilibrium and dynamic adsorption data for Cr(VI) on activated carbon.
• To investigate the impact of pH, temperature, and Cr(VI) speciation on adsorption.
• To model and interpret both equilibrium isotherms and dynamic breakthrough curves.

Main Methods:

• Equilibrium adsorption isotherm tests at varying pH and temperature.
• Dynamic adsorption tests using lab-scale fixed-bed columns.
• Analysis of breakthrough curves under different operational conditions (pH, concentration, flow rate).
• Application of multi-component Langmuir and mass transfer models for data interpretation.

Main Results:

• Adsorption isotherms and breakthrough curves exhibited non-linear and unconventional trends.
• Chromium speciation and Cr(VI)-to-Cr(III) reduction reactions were identified as key factors.
• External mass transfer controlled adsorption at pH 11.
• At pH 6, a transition to an inter-particle adsorption mechanism was observed at higher sorbent coverage.

Conclusions:

• Cr(VI) adsorption on activated carbon is complex, influenced by speciation and redox reactions.
• Accurate modeling requires consideration of multi-component interactions and mass transfer limitations.
• Understanding the shift in adsorption mechanisms is crucial for optimizing water treatment processes.