Highly surface activated carbon to remove Cr(VI) from aqueous solution with adsorbent recycling

Area of Science:

• Environmental Chemistry
• Materials Science
• Water Treatment Technologies

Background:

• Commercial activated carbon (AC) exhibits limited efficiency in removing hexavalent chromium (Cr(VI)) from aqueous solutions, particularly under neutral pH conditions.
• Developing cost-effective and efficient adsorbents is crucial for mitigating Cr(VI) contamination in water resources.

Purpose of the Study:

• To enhance the Cr(VI) removal capability of commercial AC using ball milling technology under neutral pH.
• To investigate the surface modifications and adsorption mechanisms responsible for the improved performance.

Main Methods:

• Ball milling was employed to modify commercial AC, creating highly activated carbon (HAC).
• Cr(VI) removal efficiency was evaluated at different pH levels (pH 6 and 7).
• Surface properties were analyzed using Raman spectroscopy and Boehm's titration; adsorption mechanisms were studied via SEM-EDX, surface area, and porosity measurements.

Main Results:

• Ball-milled HAC demonstrated significantly higher Cr(VI) removal efficiencies (99.0% at pH 6, 77.8% at pH 7) compared to pristine AC (68.3% at pH 6, 42.7% at pH 7).
• HAC exhibited an increase in surface acid functional groups, notably carboxyl (COOH) groups, from 0.31 to 0.97 mmol/g.
• Adsorption followed Pseudo-second order kinetics and Freundlich isotherm models, indicating multilayer adsorption and specific interactions with the HAC surface.

Conclusions:

• Ball milling is an effective method for enhancing AC's Cr(VI) adsorption capacity under neutral conditions by increasing surface acidity.
• Proposed mechanisms include Cr(VI) reduction to Cr(III) and subsequent precipitation, alongside direct bonding of Cr(VI) to surface COOH groups.
• The enhanced HAC shows potential for practical application in Cr(VI) removal due to its improved efficiency, reusability, and regeneration capabilities.