Marked Changes in Biochar’s Ability to Directly Immobilize Cd in Soil: Implication for Biochar Remediation of Cd Contaminated Soil

Abstract To investigate the change in biochar’s ability to directly immobilize Cd in soil ，a successive wheat cultivation with experiment was conducted. Three biochar with different Cd adsorption mechanisms were added into soils and a mesh bag was used to separate the soil particles (> 1 μm) from biochar. The results showed that the ash contents and anionic contents (CO 3 2- and PO 4 3- ) of the biochar decreased with the cultivation time, while the oxygen-containing functional groups content and CEC of the biochar increased. Resultly, the Cd concentration on biochar decreased, highly decreased by 68.9% for WBC300, while unstable Cd species (acid soluble and reducible fraction of Cd) on biochar increased with successive cultivation, increasing from 3% to 17% for WBC300 in FS. Correspondingly, the ability of biochar to inhibit Cd accumulation in wheat decreased. The results of this study illustrated that the ability of biochar to directly immobilize Cd in soil is not permanent, it gradually decreases with aging in soil. The adsorption mechanism of Cd on biochar changed from precipitation to complexation and ion exchange processes could be the main reason.

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Adsorption Mechanisms and Characteristics of Hg2+ Removal by Different Fractions of Biochar

Water ◽

10.3390/w12082105 ◽

2020 ◽

Vol 12 (8) ◽

pp. 2105

Author(s):

Xiaoli Guo ◽

Menghong Li ◽

Aijv Liu ◽

Man Jiang ◽

Xiaoyin Niu ◽

...

Keyword(s):

Ion Exchange ◽

Adsorption Capacity ◽

Adsorption Mechanism ◽

Raw Material ◽

Mercury Contamination ◽

Main Reaction ◽

Hydroxyl Groups ◽

Complexation Reaction ◽

X Ray ◽

Adsorption Mechanisms

The adsorption mechanisms of mercury ion (Hg2+) by different fractions of biochar were studied, providing a theoretical basis and practical value for the use of biochar to remediate mercury contamination in water. Biochar (RC) was prepared using corn straw as the raw material. It was then fractionated, resulting in inorganic carbon (IC), organic carbon (OC), hydroxyl-blocked carbon (BHC), and carboxyl-blocked carbon (BCC). Before and after Hg2+ adsorption, the biochar fractions were characterized by several techniques, such as energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Obtained results indicate that the reaction mechanisms of RC for Hg2+ removal mainly include electrostatic adsorption, ion exchange, reduction, precipitation, and complexation. The equilibrium adsorption capacity of RC for Hg2+ is 75.56 mg/g, and the adsorption contribution rates of IC and OC are approximately 22.4% and 77.6%, respectively. Despite the lower rate, IC shows the largest adsorption capacity, of 92.63 mg/g. This is attributed to all the mechanisms involved in Hg2+ adsorption by IC, with ion exchange being the main reaction mechanism (accounting for 39.8%). The main adsorption mechanism of OC is the complexation of carboxyl and hydroxyl groups with Hg2+, accounting for 71.6% of the total OC contribution. BHC and BCC adsorb mercury mainly via the reduction–adsorption mechanism, accounting for 54.6% and 54.5%, respectively. Among all the adsorption mechanisms, the complexation reaction of carboxyl and hydroxyl groups with Hg2+ is the dominant effect.

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Adsorption mechanism of NH3, NO, and O2 molecules over FexOy/AC catalyst surface: a DFT-D3 study

New Journal of Chemistry ◽

10.1039/d0nj05628f ◽

2021 ◽

Author(s):

Chaoyue Xie ◽

Yunlan Sun ◽

Baozhong Zhu ◽

Weiyi Song ◽

Minggao Xu

Keyword(s):

Activated Carbon ◽

Adsorption Mechanism ◽

Catalyst Surface ◽

Specific Adsorption ◽

Adsorption Mechanisms ◽

Iron Based ◽

Iron Based Catalysts ◽

Supported Iron ◽

Denox Efficiency

Activated carbon-supported iron-based catalysts (FexOy/AC) show excellent deNOx efficiency. However, the specific adsorption mechanisms of NH3, NO, and O2 molecules on their surfaces are still unknown. In this study, the...

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Theoretical Modelling of Ion Exchange Processes in Glass: Advances and Challenges

Applied Sciences ◽

10.3390/app11115070 ◽

2021 ◽

Vol 11 (11) ◽

pp. 5070

Author(s):

Xesús Prieto-Blanco ◽

Carlos Montero-Orille

Keyword(s):

Ion Exchange ◽

Diffusion Coefficients ◽

Molten Salts ◽

Theoretical Modelling ◽

Copper Films ◽

Theoretical Frameworks ◽

Self Diffusion ◽

Exchange Processes ◽

The One ◽

Made In

In the last few years, some advances have been made in the theoretical modelling of ion exchange processes in glass. On the one hand, the equations that describe the evolution of the cation concentration were rewritten in a more rigorous manner. This was made into two theoretical frameworks. In the first one, the self-diffusion coefficients were assumed to be constant, whereas, in the second one, a more realistic cation behaviour was considered by taking into account the so-called mixed ion effect. Along with these equations, the boundary conditions for the usual ion exchange processes from molten salts, silver and copper films and metallic cathodes were accordingly established. On the other hand, the modelling of some ion exchange processes that have attracted a great deal of attention in recent years, including glass poling, electro-diffusion of multivalent metals and the formation/dissolution of silver nanoparticles, has been addressed. In such processes, the usual approximations that are made in ion exchange modelling are not always valid. An overview of the progress made and the remaining challenges in the modelling of these unique processes is provided at the end of this review.

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