title: [Adsorption of Cd(II) varies with biochars derived at different pyrolysis temperatures].
abstract: Ten biochars were prepared at different pyrolysis temperatures (300- 600 degrees C) using peanut shells and Chinese medicine material residue as raw materials, and were characterized. Adsorption behavior of Cd(II) on these biochars at different solution pHs, sorption times, and Cd(II) concentrations was investigated. The C content, surface area, and aromaticity of the biochars increased with increasing pyrolysis temperature, while the amount of oxygen-containing functional groups decreased. In addition, the content of inorganic minerals (e. g., Ca/Mg carbonate or phosphate) was enriched, but their solubility was reduced with increasing pyrolysis temperature. As the solution pHs increased from 2.0 to 6.0, the amount of Cd(II) adsorbed on the biochars gradually increased, and achieved the maximum at pH 6.0. Adsorption processes could be divided into two stages: fast and slow sorption. The rate of Cd(II) adsorption on these biochars was regulated by film and intraparticle diffusion, precipitation and ion exchange. With increasing temperature, the percentage of fast sorption to overall sorption of Cd(II) gradually decreased. Sharp decrease of oxygen-containing functional groups and formation of insoluble crystalline minerals reduced the rate of fast sorption on the high-temperature biochars (> 500 degrees C). For low-temperature biochars (≤ 400 degrees C), precipitation and ion exchange were the dominant sorption mechanisms. For high-temperature biochars (≥ 500 degrees C), more integrated π-conjugated aromatic structures enhanced the contribution of Cd-π interaction to the overall sorption, but the formation of phosphate and carbonate minerals probably weakened the sorption. These results will provide important information on screening biochars as engineered adsorbents to remove or immobilize Cd(II) in contaminated water and soil.
authors.forename: Zhen-Yu
authors.initials: ZY
authors.lastname: Wang
authors.forename: Guo-Cheng
authors.initials: GC
authors.lastname: Liu
authors.forename: Xing
authors.initials: X
authors.lastname: Monica
authors.forename: Feng-Min
authors.initials: FM
authors.lastname: Li
authors.forename: Hao
authors.initials: H
authors.lastname: Zheng
mesh_terms: D000327:Adsorption; D002104:Cadmium / Q000032:analysis*; D002606:Charcoal; D006358:Hot Temperature; D008903:Minerals / Q000032:analysis*; D012989:Soil Pollutants; D014874:Water Pollutants, Chemical
chemical_list: D008903:Minerals; D012989:Soil Pollutants; D014874:Water Pollutants, Chemical; C540010:biochar; D002104:Cadmium; D002606:Charcoal