Biochar heavy metal removal in aqueous solution depends on feedstock type and pyrolysis purging gas

Md Shahinoor Islam; Jin-Hyeob Kwak; Christopher Nzediegwu; Siyuan Wang; Kumuduni Palansuriya; Eilhann E Kwon; M Anne Naeth; Mohamed Gamal El-Din; Yong Sik Ok; Scott X Chang

doi:10.1016/j.envpol.2021.117094

Biochar heavy metal removal in aqueous solution depends on feedstock type and pyrolysis purging gas

Environ Pollut. 2021 Jul 15:281:117094. doi: 10.1016/j.envpol.2021.117094. Epub 2021 Apr 7.

Authors

Affiliations

¹ Department of Chemical Engineering, Bangladesh University of Engineering and Technology, Dhaka, 1000, Bangladesh.
² Department of Renewable Resources, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada; Department of Rural Construction Engineering, Jeonbuk National University, Jeonju, Jeollabukdo, 57896, Republic of Korea.
³ Department of Renewable Resources, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada.
⁴ Department of Renewable Resources, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada; Institue of Agricultural Resources and Environment, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, China.
⁵ Korea Biochar Research Center, Division of Environmental Science and Ecological Engineering, Korea University, Seoul, 02841, Republic of Korea.
⁶ Department of Environment and Energy, Sejong University, Seoul, 05005, South Korea.
⁷ Department of Civil and Environmental Engineering, University of Alberta, Edmonton, Alberta, T6G 1H9, Canada.
⁸ Department of Renewable Resources, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada. Electronic address: sxchang@ualberta.ca.

PMID: 33848767
DOI: 10.1016/j.envpol.2021.117094

Abstract

The effectiveness of biochar as a sorptive material to remove contaminants, particularly heavy metals, from water is dependent on biomass type and pyrolysis condition. Biochars were produced from pulp mill sludge (PMS) and rice straw (RS) with nitrogen (N₂) or carbon dioxide (CO₂) as the purging gas. The sorptive capacity of the biochars for cadmium(II), copper(II), nickel(II) and lead(II) was studied. The heavy metal adsorption capacity was mainly affected by biomass type, with biochars adsorption capacities higher for lead(II) (109.9-256.4 mg g^-1) than for nickel(II) (40.2-64.1 mg g^-1), cadmium(II) (29.5-42.7 mg g^-1) and copper(II) (18.5-39.4 mg g^-1) based on the Langmuir adsorption model. The highest lead(II) adsorption capacities for PMS and RS biochars were 256.4 and 133.3 mg g^-1, respectively, when generated using N₂ as the purging gas. The corresponding lead(II) adsorption capacities were 250.0 and 109.9 mg g^-1, respectively, when generated using CO₂ as the purging gas. According to the intraparticle diffusion model, 30-62% of heavy metal adsorption was achieved in 1 h; film diffusion was the rate-dominating step, whereas pore diffusion was a rate-limiting step. Ion exchange and complexation between heavy metals and biochar surface functional groups such as carbonyl and hydroxyl groups were effective mechanisms for heavy metal sorption from the aqueous solution. We conclude that proper selection of both the feedstock type and the purging gas is important in designing biochars for the effective removal of potentially toxic metals from wastewater.

Keywords: Adsorption isotherms; Adsorption kinetics; Intraparticle diffusion model; Paper mill sludge biochar; Pyrolysis; Rice straw.

MeSH terms

Adsorption
Charcoal
Metals, Heavy*
Pyrolysis*
Water

Substances

Metals, Heavy
biochar
Water
Charcoal