Application of activated carbon in the removal of heavy metals in water

Heavy metal pollution in water bodies is one of the important environmental issues facing the world today. Heavy metals such as lead (Pb), mercury (Hg), cadmium (Cd), chromium (Cr) and arsenic (As) are not only difficult to degrade, but also accumulate in ecosystems, posing a serious threat to biological and human health. Activated carbon has become an ideal material for removing heavy metals due to its high specific surface area, developed pore structure and adjustable surface chemical properties. This article discusses in detail the application of activated carbon in the removal of heavy metals in water from the aspects of mechanism of action, preparation method, surface modification, practical application and challenges faced.

1. Mechanism of activated carbon for heavy metal removal

The removal effect of activated carbon on heavy metals mainly depends on the following mechanisms:

Adsorption:

Physical adsorption: Heavy metal ions are trapped in the micropores and mesopores of activated carbon through van der Waals forces.

Chemical adsorption: Functional groups on the surface of activated carbon (such as hydroxyl, carboxyl, carbonyl, etc.) react chemically with metal ions to form stable complexes.

Ion exchange:

Exchangeable cations (such as H⁺ or Na⁺) on the surface of activated carbon exchange with heavy metal ions in water, thereby removing heavy metals.

Electrostatic attraction:

The surface of activated carbon usually carries a negative charge, which can adsorb positively charged heavy metal ions in water through electrostatic action.

Precipitation and co-precipitation:

Some heavy metals form insoluble compounds on the surface of activated carbon due to pH changes, and other ions may assist in the co-precipitation of heavy metals.

2. Preparation and performance optimization of activated carbon

The performance of activated carbon depends largely on its raw materials and preparation methods.

Raw material selection:

Activated carbon can be derived from a variety of carbonaceous materials, such as coconut shells, wood, agricultural waste (such as rice husks, corn cobs), coal and synthetic polymers. These raw materials are inexpensive and widely available, and have good sustainability.

Preparation process:

The preparation of activated carbon is usually divided into two stages:

Carbonization: The raw materials are heated in an inert gas environment to remove volatile substances and form a carbon-based skeleton.

Activation:

Physical activation: Use water vapor or CO₂ to activate the carbonization product at high temperature to generate a developed pore structure.

Chemical activation: Further improve the porosity and functional group content by reacting with chemical reagents (such as KOH, H₃PO₄ or ZnCl₂).

Pore structure and surface chemistry optimization:

By controlling the activation conditions (temperature, time and dosage) during the preparation process, the specific surface area, pore size distribution and surface functional group type of activated carbon can be regulated to improve its adsorption performance for heavy metals.

3. Surface modification technology of activated carbon

In order to further improve the removal ability of activated carbon for specific heavy metals, surface modification technology is often used:

Chemical functionalization:

Introducing specific functional groups (such as thiol and amine) to enhance the coordination effect with heavy metal ions.

Metal oxide loading:

Loading metal oxides such as Fe₂O₃, MnO₂, TiO₂ on the surface of activated carbon can significantly improve the selective adsorption capacity for specific heavy metals.

Polymer modification: Introduce polymer coatings such as chitosan and polyacrylamide on the surface of activated carbon to enhance adsorption performance and improve anti-pollution ability.

Nanocomposite materials: By combining with nanomaterials (such as graphene and carbon nanotubes), activated carbon is given a higher adsorption rate and mechanical strength.

IV. Practical application of activated carbon in heavy metal removal in water

Industrial wastewater treatment: Activated carbon is widely used in heavy metal wastewater treatment in industries such as electroplating, mining, electronic manufacturing and battery production, and can efficiently remove metals such as lead, cadmium and chromium.

Drinking water purification: Activated carbon is used in household and municipal drinking water systems to remove low concentrations of toxic metals such as mercury and arsenic to ensure drinking water safety.

Environmental remediation: Activated carbon can be used to repair polluted rivers, lakes and groundwater, reduce heavy metal concentrations to restore the ecological health of water bodies.

Composite treatment technology: Activated carbon is often used in combination with other technologies (such as membrane separation, chemical precipitation, biological treatment, etc.) to achieve efficient removal and comprehensive management of heavy metals.

5. Challenges and development directions of activated carbon technology

Although activated carbon has a wide range of applications in the field of heavy metal removal, it still faces the following challenges:

Regeneration and recycling:

Used activated carbon needs to be regenerated by thermal treatment or chemical methods, but the regeneration process may lose its adsorption capacity and produce secondary pollution.

Selective adsorption problem:

In complex water bodies, different ions may compete with each other, resulting in a decrease in the efficiency of heavy metal removal.

Economic and environmental sustainability:

The preparation cost of high-performance activated carbon is high, and some chemical reagents may burden the environment.

Response to new pollutants:

In actual water treatment processes, activated carbon needs to be combined with other methods to simultaneously deal with the combined pollution problems of emerging pollutants (such as drugs and microplastics) and heavy metals.

Future development direction

To overcome the above challenges, future research can focus on the following areas:

Develop low-cost, high-performance activated carbon materials, such as agricultural waste-based activated carbon.

Improve surface modification technology, and achieve highly selective adsorption of specific metals through the introduction of nanomaterials and functional groups.

Develop green regeneration processes to reduce the cost and environmental impact of activated carbon.

Combined with emerging materials (such as metal organic framework materials and graphene) to construct composite adsorbents.

VI. Conclusion

Activated carbon has excellent performance in the field of heavy metal removal in water due to its excellent adsorption performance and versatility. Through continuous optimization of preparation process and surface modification technology, activated carbon is expected to play a greater role in industrial wastewater treatment, drinking water purification and environmental remediation, providing reliable support for sustainable management of water resources.