This study investigates the use of ball milling technology to enhance the adsorption capacity of biochar for methylene blue, a model pollutant. Comparative adsorption studies were conducted on ball-milled biochar and biochar modified chemically through oxidation and alkaline treatment. [1]

Biochar, derived from the pyrolysis of biomass wastes such as wood, crop residues, and municipal waste under limited oxygen conditions at various temperatures, is a low-cost, renewable, and environmentally friendly material. Biochar is increasingly recognized for its high carbon content, cation exchange capacity, large specific surface area, and stability, making it suitable for pollutant removal, for example in wastewater treatment, biochar offers economic and ecological advantages as an adsorbent for dyes, antibiotics, and phenols. [2]

Although chemical and physical modifications (acid/alkali modifications, steam, and plasma) are effective in enhancing the surface area of biochar and adding oxygen-containing functional groups for adsorption of specific pollutants, these methods are not environmentally sustainable because they have high production costs, harsh working conditions, and generate considerable waste. [3]

Alternatively, ball milling presents a green and efficient method to enhance biochar's surface area and adsorption activity. Mechanochemical approach can reduces the grain size of solids to nanoscale particles, transferring kinetic energy to the sample powder through the impact and shear forces of colliding milling balls as well as providing new ionic and covalent functionalizations for different carbon materials. [4-5].Recent studies have shown that ball milling can even increase the oxygen content of carbon materials through exfoliation and fragmentation, though it primarily exposes existing functional groups on biochar surfaces by increasing surface area.

This study compares the adsorption ability of methylene blue on biochar chemically modified by oxidation and alkalization against that of ball-milled biochar. Experiments demonstrated that milling significantly improves biochar’s adsorption capacity without the need for chemical modification and enhances performance by increasing the number of active sites available for adsorption. The reduction in particle size and consequent increase in surface area are hypothesized to be the primary reasons for the enhanced removal efficiency. Adsorption tests were conducted on biochar samples for methylene blue removal at various pH levels (3, 7, 11) and initial concentrations (50-250 mg/L). The mechanically milled biochar consistently exhibited superior performance, achieving an adsorption capacity of 185.18 mg/g and maintaining high efficiency over six reuse cycles.

In summary, the ball milling method significantly enhances biochar's adsorption capacity for methylene blue, without extra chemical modification steps and provides a green and sustainable approach to improving biochar's effectiveness as an adsorbent for water pollutant removal. This mechanically treated biochar shows promise for practical applications in environmental remediation, offering a cost-effective and environmentally friendly alternative to chemically modified biochar and commercial activated carbon.