Relative distribution of Cd2+ adsorption mechanisms on biochars derived from rice straw and sewage sludge

• Published in: Bioresource technology Vol. 272; no. C; pp. 114 - 122
• Main Authors: Gao, Li-Yang, Deng, Jin-Huan, Huang, Guo-Fu, Li, Kai, Cai, Kun-Zheng, Liu, Yan, Huang, Fei
• Format: Journal Article
• Language: English
• Published: United Kingdom Elsevier Ltd 01.01.2019; Elsevier
• Subjects: adsorption; Adsorption characteristics; Adsorption mechanisms; aqueous solutions; Biochar; cadmium; cation exchange; electrons; energy-dispersive X-ray analysis; Fourier transform infrared spectroscopy; Heavy metal; rice straw; scanning electron microscopy; sewage sludge; temperature; titration; X-ray diffraction; Biochar; Adsorption characteristics; Adsorption mechanisms; Heavy metal
• ISSN: 0960-8524; 1873-2976; 1873-2976
• DOI: 10.1016/j.biortech.2018.09.138

[Display omitted] •The adsorption on RSBs out-performed SSBs.•The contribution of each mechanism to total adsorption varied with feedstock.•Precipitation and cation exchange mechanism dominated Cd2+ adsorption on RSBs.•Coordination with π electrons was always predominant mechanism in SSBs. Qualitative and quantitative characterization of Cd2+ adsorption mechanisms was performed with rice-straw and sewage-sludge biochars produced at different temperature (300–700 °C), respectively. The pH effect, adsorption kinetics and isotherms were investigated, and chemical analyses of Cd2+-loaded biochars were conducted by SEM-EDS, XRD, FTIR and Boehm titration. This demonstrated that rice-straw biochars (RSBs) have greater adsorption capacities for Cd2+ than sewage-sludge biochars (SSBs), which was mainly due to precipitation and cation exchange mechanisms, with their contribution proportion to total adsorption from 76.1% to 80.8%. While in SSBs, both mechanisms were overshadowed by coordination with π electrons mechanism accounting for 59.2%–62.9% of total adsorption, even the role of cation exchange was negligible in the adsorption mechanisms accounting for 2.3%–6.7%. The relationship of each mechanism with biochar’s properties were discussed, which further deepen our understanding of adsorption on biochars. These results suggest RSBs have great potential for removing Cd2+ from aqueous solutions.