Nano-chlorapatite modification enhancing cadmium(II) adsorption capacity of crop residue biochars

• Published in: The Science of the total environment Vol. 865; p. 161097
• Main Authors: Yuan, Qiusheng, Wang, Peifang, Wang, Xun, Hu, Bin, Wang, Chao, Xing, Xiaolei
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 20.03.2023
• Subjects: Adsorption; Aquatic environment; Biochar; Cadmium - chemistry; Cadmium adsorption; Charcoal - chemistry; Crop residue; Nano-chlorapatite; Temperature; Aquatic environment; Crop residue; Biochar; Nano-chlorapatite; Cadmium adsorption
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2022.161097

Cadmium (Cd) contamination in rivers or lakes has attracted worldwide concerns. Biochar pyrolyzed form crop residues (CR) could adsorb Cd(II) from aquatic environments, while the removal capacity of single CR biochar is relatively low. Nano-chlorapatite (nClAP) modification can enhance metal scavenging ability, but little is known about the behaviors and mechanisms of Cd(II) adsorption by nClAP-modified CR biochars. In this study, the influences of feedstock type, pyrolysis temperature, nClAP modification and aquatic environments on Cd(II) adsorption of biochars derived from rice (RB) and wheat (WB) husks were investigated comprehensively. Results showed that the pristine RB and WB showed low and similar Cd(II) adsorption capacities, while the rise of pyrolysis temperatures from 300 to 600 °C significantly improved the adsorption capacities. The Cd(II) adsorption of both RB and WB was regarded as monolayer chemical processes controlled by chemical precipitation, surface complexation and cation exchange mechanisms. Moreover, the nClAP modification notably enhanced Cd(II) adsorption capacities from 13.2 to 39.9 mg·g−1 of pristine biochars to 25.2–60.7 mg·g−1 of modified biochars attributed to the improved contribution of Cd(II)-phosphate precipitation. Among all biochars, the nClAP-modified RB and WB pyrolyzed at 500 °C had the highest Cd(II) adsorption capacities with 60.7 and 48.3 mg·g−1, respectively. These biochars could maintain good adsorption performances under the neutral-alkaline (pH 6–8), low ionic strength, high dissolved organic matter and all oxidation-reduction potential conditions. In conclusion, this study reveals the importance of nClAP modification to optimize Cd(II) adsorption of CR biochars, which provides a promising future for its practical application in aquatic Cd(II) scavenging. [Display omitted] •Pristine rice/wheat husk biochars showed low and similar Cd(II) adsorption capacity.•High-temperature pyrolysis notably improved Cd(II) adsorption capacity of biochars.•Modification of nClAP enhanced Cd(II) adsorption capacity by phosphate precipitation.•Aquatic influence analysis determined the optimum environments for Cd(II) adsorption.