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

verfasst von

Rahul Ramesh Nair, Andreas Schaate, Lars Frederik Klepzig, Ariel E. Turcios, Jacek Lecinski, Madina Shamsuyeva, Hans Josef Endres, Jutta Papenbrock, Peter Behrens, Dirk Weichgrebe

Abstract

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 kg_CO2/kg_biomass 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.]

Organisationseinheit(en)

Laboratorium für Nano- und Quantenengineering
Institut für Anorganische Chemie
PhoenixD: Simulation, Fabrikation und Anwendung optischer Systeme
Institut für Physikalische Chemie und Elektrochemie
Institut für Botanik
Institut für Kunststoff- und Kreislauftechnik
Institut für Siedlungswasserwirtschaft und Abfalltechnik

Typ

Artikel

Journal

Clean Technologies and Environmental Policy

Band

25

Seiten

2727-2746

Anzahl der Seiten

20

ISSN

1618-954X

Publikationsdatum

10.2023

Publikationsstatus

Veröffentlicht

Peer-reviewed

Ja

ASJC Scopus Sachgebiete

Environmental engineering, Umweltchemie, Betriebswirtschaft, Management und Rechnungswesen (insg.), Volkswirtschaftslehre und Ökonometrie, Management, Monitoring, Politik und Recht

Elektronische Version(en)

https://doi.org/10.1007/s10098-023-02525-z (Zugang: Offen)