Open Access

ARTICLE

Adsorption and Desorption Characteristics of Cadmium Ion by Ash-Free Biochars

Li Fu^1,2, Xianying Xu^1,2,*, Guiquan Fu², Renduo Zhang³, Hujun Liu²

1 College of Forestry, Gansu Agricultural University, Lanzhou, 730070, China
2 State Key Laboratory Breeding Base of Desertification and Aeolian Sand Disaster Combating, Gansu Desert Control Research Institute, Lanzhou, 730070, China
3 Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University, Guangzhou, 510006, China

* Corresponding Author: Xianying Xu. Email:

Journal of Renewable Materials 2020, 8(7), 801-818. https://doi.org/10.32604/jrm.2020.09369

Received 07 December 2019; Accepted 27 April 2020; Issue published 01 June 2020

Abstract

The aim of this study was to investigate adsorption and desorption characteristics of cadmium ion (Cd(II)) by ash-free biochars and the adsorption mechanism. Biochars were prepared using peanut shell, bamboo, and Sophora japonica Linn. Ash-free biochars were obtained by treating the biochars with acid elution. Adsorption and desorption data from batch experiments were analyzed using the Langmuir and Freundlich models and three adsorption kinetics models (i.e., the Pseudo second-order, Elovich model, and the Intraparticle diffusion models). Results showed that the acid elution improved the pore structure of biochars, increased C content and aromatic functional group content, enhanced biochars hydrophobicity and adsorption capacity for Cd(II). Ash-free peanut shell biochar showed the best Cd(II) adsorption performance among the biochars. Adsorption of ash-free peanut shell biochar reached the equilibrium within 6 h with adsorption capacity of 34.2 mg/g. The adsorption conditions were optimized by orthogonal experiment. The Cd(II) removal efficiency achieved 91.7% with the optimized condition: initial concentration of Cd(II) of 50 mg/L, pH of 5, adsorption time of 12 h, and temperature of 15°C. Isothermal adsorption of Cd(II) by the six biochars was best described with the Langmuir model, indicating that the adsorption was a physical-chemical composite process. The desorption isotherm showed the hysteresis between adsorption and desorption. The main mechanism of Cd(II) adsorption of the ash-free biochars was a complex interaction of physical and chemical reactions, mainly including electrostatic adsorption, cationic-π, and ligand exchange.

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