Enhancing the Adsorption of Cephalexin onto the Pristine and Iron-Impregnated Biochars via Mechanical Ball Milling

In order to improve the adsorption performance of biochars for aqueous antibiotics via low-cost and environmentally friendly methods, the pristine and iron-impregnated biochars derived from corn bract biomass were ball–milled mechanically by using a planetary ball mill and characterized. The adsorption performance and mechanism of cephalexin, a widely used cephalosporin antibiotic, onto the resultant biochars were investigated via batch and column adsorption experiments. Mechanical ball milling significantly improves the BET specific surface area, total pore volume and content of carboxyl or lactone groups and significantly decreased the particle sizes and C contents of the resulting adsorbents. Langmuir maximum adsorption capacities were 14.8 and 13.9 mg·g⁻¹ for ball-milled pristine and iron-impregnated biochars, respectively, significantly higher than those of un-ball-milled biochars. Ball-milled pristine and iron-impregnated biochars had similar stable adsorption capacity between pH 4.0 and 9.0, showing pH adaptability. About 75% of the equilibrium adsorption capacities within about 60 min suggests the fast adsorption of cephalexin. Mass transfer analyses show that membrane diffusion and intraparticle diffusion were the key rate-limiting step in the sorption process. Column adsorption data were fitted well with Thomas model and Yoon-Nelson model. Both batch and column adsorption confirm that mechanical ball milling is a low-cost and highly efficient approach to develop biochar-based adsorbents for treatment of cephalexin-polluted wastewater.