Comparison of cadmium adsorption by hydrochar and pyrochar derived from Napier grass. (December 2022)

• Record Type: Journal Article
• Authors: Wang, Jiangtao; Wang, Yuting; Wang, Junxia; Du, Guiyue; Khan, Kiran Yasmin; Song, Yanxing; Cui, Xiaoqiang; Cheng, Zhanjun; Yan, Beibei; Chen, Guanyi
• Is Part Of: Chemosphere. Volume 308:Part 3(2022)
• Publication Date: 2022-12
• Subjects: Hydrochar -- Pyrochar -- Cadmium -- Sorption mechanisms; Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2022.136389
• Languages: English
• ISSNs: 0045-6535

Abstract

Abstract: Biochar (e.g. pyrochar and hydrochar) is considered a promising adsorbent for Cd removal from aqueous solution. Considering the vastly different physicochemical properties between pyrochar and hydrochar, the Cd 2+ sorption capacity and mechanisms of pyrochars and hydrochars should be comparatively determined to guide the production and application of biochar. In this study, the hydrochars and pyrochars were prepared from Napier grass by hydrothermal carbonization (200 and 240 °C) and pyrolysis (300 and 500 °C), respectively, and the physicochemical properties and Cd 2+ sorption performances of biochars were systematically determined. The pyrochars had higher pH and ash content as well as better stability, while the hydrochars showed more oxygen-containing functional groups (OFGs) and greater energy density. The pseudo second order kinetic model best fitted the Cd 2+ sorption kinetics data of biochars, and the isotherm data of pyrochar and hydrochar were well described by Langmuir and Freundlich models, respectively. In comparison with hydrochar, the pyrochar exhibited better Cd 2+ sorption capacity (up to 71.47 mg/g). With increasing production temperature, the Cd 2+ sorption capacity of pyrochar elevated, while the reduction was found for hydrochar. The mineral interaction, complexation with surface OFGs, and coordination with π electron were considered the main mechanisms of Cd 2+ removal by biochars. The minerals interaction and the complexation with OFGs was the dominant mechanism of Cd 2+ removal by pyrochars and hydrochars, respectively. Therefore, the preparation technique and temperature have significant impacts on the sorption capacity and mechanisms of biochar, and pyrochar has better potential for Cd 2+ removal than the congenetic hydrochar. Graphical abstract: Image 1 Highlights: Cd 2+ sorption capacity of biochar was affected by production technique and temperature. Pyrochar exhibited greater Cd 2+ adsorption capacity than hydrochar. The interaction with minerals dominated the Cd 2+ adsorption on pyrochars. Complexation with OFGs was the main mechanism of Cd 2+ adsorption on hydrochars.