Effect of biochar artificial ageing on Cd and Cu sorption characteristics

• An optimization of oxidation method for study of biochar artificial ageing is presented
• Artificial ageing has positive effect on Cd sorption and negative effect on Cu sorption of wood-based biochar
• Concentration of oxidation agent represents the most significant factor in optimization process of ageing
• RSM represents a valuable tool in optimization and simulation biological processes such as ageing of biochars

The present investigation was carried out to optimize the artificial ageing process of biochar by the hydrogen peroxide method. For the optimization of three oxidation parameters (concentration of oxidizing agent, reaction time, temperature) the Box–Behnken Design under Response Surface Methodology was effectively applied. As a response, the sorption capacity of aged biochar for Cd and Cu was studied. The results demonstrate the crucial effect of hydrogen peroxide concentration on sorption capacity for both studied metals. For Cd sorption capacity a positive effect was detected whereas the sorption efficiency of aged biochar for Cu decreased with increasing concentration of the oxidizing agent. The effects of reaction time and temperature had lower statistical significances. Differences in sorption mechanism of Cd and Cu by biochar-based sorbent were detected. ANOVA analysis as well as 3D surface plots revealed that maximum sorption capacity of aged biochar-based sorbents for Cd was obtained at CH2O2 = 14.9997%, t = 5.99998 h, T = 20.0 °C and for Cu at CH2O2 = 5.05%, t = 2.00 h, T = 59.5 °C. The results confirm that RSM represents an excellent tool for predicting optimal parameters of chemical engineering processes like the hydrogen peroxide oxidation of biochar to optimize its sorbent behaviour. The application of BBD under RSM could reduce the number of required experiments from 39 to 17.