Preparation and reactivation of magnetic biochar by molten salt method: Relevant performance for chlorine-containing pesticides abatement

Abstract

Molten salt has been regarded as a versatile and environmental-friendly method for the material preparation and waste destruction. In this work, molten FeCl3 was utilized for the generation of magnetic biochar (MBC) derived from simultaneous activation and magnetization of biomass. The sample characterization indicated that MBC had a rough surface with BET surface area of 404 m2/g and total pore volume of 0.35cm3/g. Highly dispersed Fe3O4 and nitrogen could be deposited on the surface, leading to an excellent magnetization property. The MBC exhibited a great 2,4-Dichlorophenol (2.4-DCP) and atrazine removal performance in solution with the maximum adsorption capacity achieved 298.12 mg/g and 102.17 mg/g. Kinetics results demonstrated that MBC adsorption met the Pseudo-first-order model better. Molten NaOH-Na2CO3 was provided for the re-activation of exhausted MBC. 2,4-DCP was firstly desorbed from the MBC and subsequently destructed by the active species in the melt medium. Chlorine can be captured in the molten alkaline medium from the XRD pattern of residues.The MBC could be easily recovered with a yield of 98.2% and fixed carbon content of 61.0% after the molten salt regeneration process. With no 2,4-DCP detected, 65.5% and 31.69% of initial Cl was found in washing water and residues with the molten NaOH-Na2CO3, respectively. After 4 cycles of regeneration and adsorption, 60.55%-72.22% of initial adsorption capacity can be kept. This preparation and regeneration method can be an effective way to reduce the risk of secondary pollution of chlorinated organic compounds during adsorbent regeneration. Implications: Molten salt (MS) is a salt or multiple salts with a low melting point, and has been applied in many sectors and is regarded as a crucial role in terms of energy, environmental, and resource sustainability. In our paper, magnetic biochar was prepared by one-step activation and magnetization of fir dust using molten FeCl∙6HO. Meanwhile, a regeneration method using molten alkaline salt was provided. Magnetic biochar generated in our study performed well in the 2,4-dichlorophenol and atrazine adsorption. After four cycles of regeneration and adsorption, 72.2% of initial 2,4-DCP adsorption capacity can be kept.

Engineered Biochar Production and Its Potential Benefits in a Closed-Loop Water-Reuse Agriculture System

“…In addition to the rapid pore filling process, the diffusion and partitioning of these contaminants into the porous structure simultaneously occur, along with the influences of hydrophobic interaction, aromatic-π interaction, cation-π interaction, electrostatic interaction, and hydrogen bonding, each to different degrees [104]. The adsorption-desorption processes are reversible, indicating that biochar could be reactivated for renewable use after its saturation [105]. Compared with existing technologies for water/wastewater treatment (e.g., chlorination, sand filtration, solar disinfection, etc.…”

Preparation and Application in Water Treatment of Magnetic Biochar

“…For example, Shang et al (Shang et al, 2019) found that the adsorption capacities of magnetic biochar synthesized by ball-milling of biochar and iron oxide for the pharma-ceuticals carbamazepine (CBZ) and tetracycline were 62.7 mg/g and 94.2 mg/g, respectively. In addition, Dai et al ( Dai S.-j. et al, 2019 ) demonstrated that the herbicides dichlorophenol and atrazine were very efficiently removed by magnetic biochar synthesized by the molten salt method.…”

A Humins-Derived Magnetic Biochar for Water Purification by Adsorption and Magnetic Separation

“…In contrast, traditional heating methods require heavy mechanical systems and inert gas to create an inert atmosphere for magnetic biochar production [19]. Other methods such as ball-milling [20], molten salt [21], cross-linking of biochar and iron oxides [22], and microwave-assisted pyrolysis methods [23] have been proposed. Depending on the selected synthetic method used to obtain a magnetic biochar, the physico-chemical properties of magnetic biochar vary and the choice of the synthetic method should be decided by considering the nature of the raw biomass, the physicochemical properties of the pollutants and the method operability [14].…”