TY - JOUR

T1 - Physico-chemical characterization of walnut shell biochar from uncontrolled pyrolysis in a garden oven and surface modification by ex-situ chemical magnetization

AU - Nair, Rahul Ramesh

AU - Schaate, Andreas

AU - Klepzig, Lars Frederik

AU - Turcios, Ariel E.

AU - Lecinski, Jacek

AU - Shamsuyeva, Madina

AU - Endres, Hans Josef

AU - Papenbrock, Jutta

AU - Behrens, Peter

AU - Weichgrebe, Dirk

N1 - Funding Information: Open Access funding enabled and organized by Projekt DEAL. PhD Fellowship German Academic Exchange Service (DAAD) Program number 57381412. P.B. acknowledges funding from the German Research Foundation (Deutsche Forschungsgemeinschaft—DFG) under project number 280642759.

PY - 2023/10

Y1 - 2023/10

N2 - The shells of walnuts (WS) are major refuse in the global fruits and nuts trade. This, otherwise discarded, lignin-rich material can be carbonized to biochar—a value-added product with environmental applications such as carbon sequestration, soil amelioration, and pollutant adsorption. These applications are dictated by structural and chemical characteristics of the biochar carbon. Conventional controlled pyrolysis (CPy) of biomass is cost-intensive and technically too complex for widespread adoption, especially in emerging economies. Here, walnut shell biochar (BWS0) is derived through uncontrolled pyrolysis (UCPy) in a pyrolysis oven and further hybridized as magnetic biochar through ex-situ chemical co-precipitation. The physico-chemical characteristics of biochar and its water-extractable fractions are comprehensively investigated to understand their carbon structure and environmental applicability. The sp2 amorphous carbon sequestered in BWS0 is 0.84 kgCO2/kgbiomass with a BET (N2) surface area of 292 m2/g and is comparable to biochar from CPy in terms of carbon structure. The polyaromatic hydrocarbons present are only trace amounts of naphthalene, biphenyl, and phenanthrene. The magnetization decreases porosity of BWS0 while greatly facilitating its separation from aqueous media. BWS0 is suitable for adsorption of cations (between pH 2.8 and 9.45) and hydrophobic pollutants with only 19 mg L−1 fouling from their intrinsic dissolved organic carbon. In combination with fast-release N, P fertilizers, BWS0 (C/N of 24.8) is suitable for application in hydrophilic soils at higher loading rates. The results suggest an avenue where WS biochar can also be prepared via UCPy for direct environmental applications. Future investigations into soil incubation and adsorption tests are recommended. Graphical abstract: [Figure not available: see fulltext.]

AB - The shells of walnuts (WS) are major refuse in the global fruits and nuts trade. This, otherwise discarded, lignin-rich material can be carbonized to biochar—a value-added product with environmental applications such as carbon sequestration, soil amelioration, and pollutant adsorption. These applications are dictated by structural and chemical characteristics of the biochar carbon. Conventional controlled pyrolysis (CPy) of biomass is cost-intensive and technically too complex for widespread adoption, especially in emerging economies. Here, walnut shell biochar (BWS0) is derived through uncontrolled pyrolysis (UCPy) in a pyrolysis oven and further hybridized as magnetic biochar through ex-situ chemical co-precipitation. The physico-chemical characteristics of biochar and its water-extractable fractions are comprehensively investigated to understand their carbon structure and environmental applicability. The sp2 amorphous carbon sequestered in BWS0 is 0.84 kgCO2/kgbiomass with a BET (N2) surface area of 292 m2/g and is comparable to biochar from CPy in terms of carbon structure. The polyaromatic hydrocarbons present are only trace amounts of naphthalene, biphenyl, and phenanthrene. The magnetization decreases porosity of BWS0 while greatly facilitating its separation from aqueous media. BWS0 is suitable for adsorption of cations (between pH 2.8 and 9.45) and hydrophobic pollutants with only 19 mg L−1 fouling from their intrinsic dissolved organic carbon. In combination with fast-release N, P fertilizers, BWS0 (C/N of 24.8) is suitable for application in hydrophilic soils at higher loading rates. The results suggest an avenue where WS biochar can also be prepared via UCPy for direct environmental applications. Future investigations into soil incubation and adsorption tests are recommended. Graphical abstract: [Figure not available: see fulltext.]

KW - Carbon sequestration

KW - Chemical co-precipitation

KW - Magnetic biochar

KW - Uncontrolled pyrolysis

KW - Walnut shell biochar

UR - http://www.scopus.com/inward/record.url?scp=85153117693&partnerID=8YFLogxK

U2 - 10.1007/s10098-023-02525-z

DO - 10.1007/s10098-023-02525-z

M3 - Article

AN - SCOPUS:85153117693

VL - 25

SP - 2727

EP - 2746

JO - Clean Technologies and Environmental Policy

JF - Clean Technologies and Environmental Policy

SN - 1618-954X

IS - 8

ER -