Development and optimization of high–performance nano–biochar for efficient removal Cd in aqueous: Absorption performance and interaction mechanisms

Cadmium (Cd) pollution has aroused wide public attention due its high mobility, bioaccumulation and carcinogenic properties, and biochar has been proven as an efficient adsorbent for removal of Cd due to its environmentally friendly and economic approach. In this study, three variables (grinding time, rotational speed, and mass ratio of ball–to–powder) were established through response surface methodology and Box–Behnken design, and the preparation process of ball–milled biochar (BMBC) was successfully optimized. The results indicated that the impact factors on Cd removal by BMBC were in the order of milling speed > grinding time > ball to powder mass ratio, and the optimum parameters for Cd removal were found to be: milling time = 16 h, speed = 448 rpm, and ball to powder mass ratio = 1.5:100. BMBC (300 nm) has a dramatically larger specific surface area and pore volume by 22 and 15 times, respectively, and was companied with richer oxygen–containing functional groups. The adsorption of Cd2+ on BMBC conformed to the pseudo–second–order kinetic model and the Langmuir model. The maximum adsorption capacity of Cd2+ was 3 times that of BC. Precipitation and complexation were the main mechanisms for the adsorption of Cd. Therefore, BMBC was a promising and effective adsorbent for the removal of Cd, which has potential application value.