Investigation on cadmium ions removal from water by different raw materials-derived biochars

Removal of heavy metals from water by biochar is necessary and benefit for human life and environmental protection. In this study, biochar from sludge (SB), cow dung (DB), corn stalk (CB) and willow branches (WB) were synthesized and activated by potassium hydroxide (KOH), and these biochars were used as adsorbent to remove divalent cadmium ion (Cd(II)) from water. The materials were further characterized by using N-2-sorption, scanning electron microscopy (SEM), elemental analysis, thermal gravity and differential thermal gravity (TG/DTG) and fourier transform infrared spectroscopy (FTIR). It found that external surface area of biochar had significant effect on the adsorption of Cd(II). Batch adsorption experiments were performed to investigate the effects of various parameters, including initial pH value, adsorbent dosage, concentration of Cd(II) and adsorption time. The results showed that CB had a better adsorption ability to remove Cd(II) from water than the other biochars. The pseudo-second-order and pseudo-first-order kinetics models were introduced to study the adsorption kinetics of Cd(II) by CB. The Freundlich model and Langmuir model were both fit for the experimental isotherm data. The maximum adsorption capacity of 40 mg/g was obtained by CB according to the experimental isotherm data by Langmuir model.