Effect of humic acid-loaded biochar on the adsorption performance of Mn2+ in soil leachate from mining area

Abstract

Humic acid modified biochar (CSB-HA) was prepared using corn stover-based biochar (CSB) loaded with humic acid for the adsorption of Mn2+ from the soil leachate in the mining area and its adsorption characteristics were analyzed. With the help of SEM, BET, XRD, XPS and FT-IR, the prepared samples were characterized and analyzed. The results show that the specific surface area of CSB-HA is 7.911 m2/g, which is 1.98 times that of CSB, and the pores are mostly mesoporous. The excellent pore structure provides a large number of adsorption sites and promotes the contact with pollutants, so that the adsorption performance is enhanced. The surface of CSB-HA is enriched with the oxygen-containing functional groups such as C=O, O=C—O and —COOH, and the oxygen atoms in the functional groups can be complexed and coordinated with heavy metal ions to form a stable ligand bond, thus removing Mn2+. The maximum adsorption of Mn2+ by CSB-HA is 21.493 mg/g, and the quasi-primary kinetic model, quasi-secondary kinetic model, Langmuir isotherm and Temkin isotherm can fit the adsorption process well, and the Temkin constant bkid2=0.287), and the fitted lines do not pass through the origin, so that the intra-particle diffusion stage is the key stage of the adsorption process for controlling the rate. In the thermodynamic simulations, the separation coefficients RL are in the range of 0.4−0.6, ΔH=15.41 kJ/mol>0, and ΔG is negative and decreases with increasing temperature, indicating that the adsorption process is reversible and spontaneous heat absorption, and the adsorption reaction can be facilitated by warming up. ΔS=49.90 J/(mol·K)>0, which proves that the solid-liquid interface stoichiometry increases during the adsorption process. The simulated adsorption experiments on leaching solution show that CSB-HA has a good adsorption effect on Mn2+ and a regulating effect on the pH of leaching solution.

Keywords

• carbon material
• humic acid
• tailings soil
• adsorption modelling
• diffusion modelling