Straw biochar enhanced removal of heavy metal by ferrate

Insight into the enhanced removal of dimethoate by ferrate(Ⅵ)/biochar system: Contributions of adsorption and active oxidants

Dimethoate is a toxic organophosphorus insecticide and its contamination of water poses a threat to the surrounding ecosystem. In order to enhance the removal effect of ferrate (Fe(VI)) on dimethoate, modified graphene-like biochar (SIZBC) with reduction and adsorption properties was prepared in this study. Compared with Fe(VI) alone, the removal of dimethoate by Fe(VI)/SIZBC increased from 26 % to more than 97 %, and the reaction rate was accelerated by 34 times. The oxidizing property of Fe(VI) was enhanced by the reducing groups loaded on SIZBC, and more active species were produced with the contributions ranked as SO4•¯ > ∙OH > Fe(V). And the contributions of adsorption and active oxidants in the reaction process accounted for 25 % and 75 %, respectively. Enlarging the sulfite solution concentration of modified biochar, the transformation from ∙OH/Fe(V) to SO4•¯ was promoted in the system. As the concentration of Fe(Ⅵ) increased, the contributions of ∙OH and SO4•¯ gradually decreased and Fe(V) became the main active oxidant. Fe(VI)-induced core/shell nanoparticles exhibited in situ adsorption of phosphate which was a mineralization product of dimethoate, thus total phosphorus (TP) removal was increased by 27 %. Through the three degradation pathways, dimethoate and its toxic intermediates were further mineralized to inorganic substances. Finally, the Fe(VI)/SIZBC system was proven to be feasible for actual water treatment and was able to reduce water toxicity.

Adsorption of heavy metals by biochar in aqueous solution: A review

Heavy metal pollution (e.g., Cd, Hg, Pb, Cu, Ni, Zn, As and Cr) has become a crucial issue worldwide. Among various remediation strategies, adsorption is widely recognized for its environmental sustainability, cost-effectiveness, and operational simplicity. In this context, biochar has gained significant attention due to its promising adsorption performance. To systematically support adsorption studies, this review compiled essential models for adsorption experiments, including commonly used adsorption kinetics models, isotherm models, and thermodynamic analysis methods. Moreover, we systematically analyzed key factors affecting heavy metal adsorption by biochar, such as its physicochemical properties, environmental pH, temperature, initial concentration, dosage, and the presence of coexisting ions, to identify the conditions that govern adsorption capacity. In addition, the adsorption performance of biochar toward eight significant heavy metals is reviewed in detail, with a focus on elucidating the underlying mechanisms, including complexation, ion exchange, cation-π bonding, electrostatic interactions, and precipitation. Finally, based on identified research gaps and critical challenges, we discuss emerging research tools, including machine learning and advanced surface modifications, to guide the targeted design of biochar materials for enhanced adsorption capacity.

Carbonaceous materials in structural dimensions for advanced oxidation processes

Carbonaceous materials have attracted extensive research and application interests in water treatment owing to their advantageous structural and physicochemical properties. Despite the significant interest and ongoing debates on the mechanisms through which carbonaceous materials facilitate advanced oxidation processes (AOPs), a systematic summary of carbon materials across all dimensions (0D-3D nanocarbon to bulk carbon) in various AOP systems remains absent. Addressing this gap, the current review presents a comprehensive analysis of various carbon/oxidant systems, exploring carbon quantum dots (0D), nanodiamonds (0D), carbon nanotubes (1D), graphene derivatives (2D), nanoporous carbon (3D), and biochar (bulk 3D), across different oxidant systems: persulfates (peroxymonosulfate/peroxydisulfate), ozone, hydrogen peroxide, and high-valent metals (Mn(VII)/Fe(VI)). Our discussion is anchored on the identification of active sites and elucidation of catalytic mechanisms, spanning both radical and nonradical pathways. By dissecting catalysis-related factors such as sp2/sp3 C, defects, and surface functional groups that include heteroatoms and oxygen groups in different carbon configurations, this review aims to provide a holistic understanding of the catalytic nature of different dimensional carbonaceous materials in AOPs. Furthermore, we address current challenges and underscore the potential for optimizing and innovating water treatment methodologies through the strategic application of carbon-based catalysts. Finally, prospects for future investigations and the associated bottlenecks are proposed.

Screening of metal-modified biochars for practical phosphorus recovery

The utilization of metal-modified biochars (MBCs) for practical phosphorus recovery has attracted significant research interest recently. However, the optimal choice of metals and modification methods for MBCs remains unclear. This study addresses this gap by comparing the phosphate adsorption capabilities of various MBCs using real municipal wastewater. The results show that zinc-modified biochar exhibits superior phosphate adsorption compared to biochars modified with calcium, magnesium, aluminum, and iron. Specifically, zinc-modified biochar prepared through metal-mediated biomass pyrolysis with alkaline soaking (ZnBC-OH) demonstrates the highest adsorption capacity, achieving 36.6 mg P/g in wastewater with a phosphate concentration of 5 mg P/L. This performance surpasses that of previously reported non-lanthanide modified biochars and is comparable to lanthanide-modified biochars. Mechanistic investigations reveal that the exceptional performance of ZnBC-OH is due to the presence of highly dispersed ZnO sites, which facilitate the formation of Zn3(PO4)2·4H2O precipitation, effectively retaining phosphate. Furthermore, a techno-economic analysis indicates that using ZnBC-OH in a fixed-bed column system can reduce phosphate levels from 6 mg L-1 to below 0.5 mg L-1 at a cost of 1.834 USD per ton of secondary treated wastewater, underscoring its promising application potential.

Photo-induced protonation assisted nano primary battery for highly efficient immobilization of diverse heavy metal ions

Highly-stable heavy metal ions (HMIs) appear long-term damage, while the existing remediation strategies struggle to effectively remove a variety of oppositely charged HMIs without releasing toxic substances. Here we construct an iron-copper primary battery-based nanocomposite, with photo-induced protonation effect, for effectively consolidating broad-spectrum HMIs. In FCPBN, Fe/Cu cell acts as the reaction impetus, and functional graphene oxide modified by carboxyl and UV-induced protonated 2-nitrobenzaldehyde serves as an auxiliary platform. Due to the groups and built-in electric fields under UV stimuli, FCPBN exhibits excellent affinity for ions, with a maximum adsorption rate constant of 974.26 g∙mg-1∙min-1 and facilitated electrons transfer, assisting to reduce 9 HMIs including Cr2O72-, AsO2-, Cd2+ in water from 0.03 to 3.89 ppb. The cost-efficiency, stability and collectability of the FCPBN during remediation, and the beneficial effects on polluted soil and the beings further demonstrate the splendid remediation performance without secondary pollution. This work is expected to remove multi-HMIs thoroughly and sustainably, which tackles an environmental application challenge.

Removal of environmental pollutants using biochar: current status and emerging opportunities

In recent times, biochar has emerged as a novel approach for environmental remediation due to its exceptional adsorption capacity, attributed to its porous structure formed by the pyrolysis of biomass at elevated temperatures in oxygen-restricted conditions. This characteristic has driven its widespread use in environmental remediation to remove pollutants. When biochar is introduced into ecosystems, it usually changes the makeup of microbial communities by offering a favorable habitat. Its porous structure creates a protective environment that shields them from external pressures. Consequently, microorganisms adhering to biochar surfaces exhibit increased resilience to environmental conditions, thereby enhancing their capacity to degrade pollutants. During this process, pollutants are broken down into smaller molecules through the collaborative efforts of biochar surface groups and microorganisms. Biochar is also often used in conjunction with composting techniques to enhance compost quality by improving aeration and serving as a carrier for slow-release fertilizers. The utilization of biochar to support sustainable agricultural practices and combat environmental contamination is a prominent area of current research. This study aims to examine the beneficial impacts of biochar application on the absorption and breakdown of contaminants in environmental and agricultural settings, offering insights into its optimization for enhanced efficacy.

Immature persimmon residue as a novel biosorbent for efficient removal of Pb(II) and Cr(VI) from wastewater: Performance and mechanisms

Owing to the powerful affinity of tannin toward heavy metal ions, it is frequently immobilized on adsorbents to enhance their adsorption properties. However, natural adsorbents containing tannin have been overlooked owing to its water solubility. Herein, a novel natural adsorbent based on the immature persimmon residue (IPR) with soluble tannin removed was fabricated to eliminate Pb(II) and Cr(VI) in aquatic environments. The insoluble tannin in IPR endowed it with prosperous properties for eliminating Pb(II) and Cr(VI), and the IPR achieved maximum Pb(II) and Cr(VI) adsorption quantities of 68.79 mg/g and 139.40 mg/g, respectively. Kinetics and isothermal adsorption analysis demonstrated that the removal behavior was controlled by monolayer chemical adsorption. Moreover, the IPR exhibited satisfactory Pb(II) and Cr(VI) removal efficiencies even in the presence of multiple coexisting ions and showed promising regeneration potential after undergoing five consecutive cycles. Additionally, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) analysis unveiled that the elimination mechanisms were primarily electrostatic attraction, chelation and reduction. Overall, the IPR, as a tannin-containing biosorbent, was verified to possess substantial potential for heavy metal removal, which can provide new insights into the development of novel natural adsorbents from the perspective of waste resource utilization.

Effect of different production methods on physicochemical properties and adsorption capacities of biochar from sewage sludge and kitchen waste: Mechanism and correlation analysis

Different pyrolysis methods, parameters and feedstocks result in biochars with different properties, structures and removal capacities for heavy metals. However, the role of each property on adsorption capacity and corresponding causal relationships remain unclear. Here, we investigated various physicochemical properties of biochar produced via three different methods and two different feedstocks to clarify influences of biomass sources and pyrolysis processes on biochar properties and its heavy metal adsorption performance. Experimental results showed biochars were more aromatic and contained more functional groups after hydrothermal carbonization, while they had developed pores and higher surface areas produced by anaerobic pyrolysis. The inclusion of oxygen resulted in more complete carbonization and higher CEC biochar. Different biochar properties resulted in different adsorption capacities. Biochar produced by aerobic calcination showed higher adsorption efficiency for Cu and Pb. Correlation analysis proved that pH, cation exchange capacity and degree of carbonization positively affected adsorption, while organic matter content and aromaticity were unfavorable for adsorption. Microstructure and components determined biochar macroscopic properties and ultimate adsorption efficiency for metal ions. This study identifies the degree of correlation and pathways of each property on adsorption, which provides guidance for targeted modification of biochar to enhance its performance in heavy metal removal.

Study on improvement of copper sulfide acid soil properties and mechanism of metal ion fixation based on Fe-biochar composite

In this study, Fe modification of bamboo biochar (BC) with ferrate was used to construct a composite soil amendment based on K2FeO4-biochar (Fe-BC) system. Based on soil culture experiments, Fe-BC combined with organic-inorganic materials at the application levels of 3%, 5% and 10% to copper sulfide contaminated acid soil was studied. Adsorption kinetics experiment was used to investigate the adsorption capacity of Fe-modified biochar to heavy metal Cu. The results showed that the pH value of bamboo biochar could be increased by 1.12 units after K2FeO4 modification. Compared with the BC, the adsorption capacity of Cu2+ increased from 190.48 to 276.12 mg/g, which was mainly reflected in single-layer surface adsorption and chemisorption. Pore diffusion, electrostatic interaction and surface interaction are the possible mechanisms of Fe-BC interaction with Cu2+ ions. And the contents of Pb, Cu and Zn in soil leaching state decreased by 59.20%, 65.88% and 57.88%, respectively, at the 10% application level of Fe-BC. In general, the composite modifier based on ferrate and biochar has a positive effect on improving the characteristics of acidic soil in copper mining area.

Insight into the impacts of pyrolysis time on adsorption behavior of Pb2+ and Cd2+ by Mg modified biochar: Performance and modification mechanism

Co-pyrolysis biomass and alkaline metals can effectively improve the adsorption performance of heavy metals (HM). Nevertheless, the researchers have ignored the relationship between the change of alkaline metal morphology and adsorption during pyrolysis. In this article, according to control the pyrolysis time (30, 60, and 180 min) synthesized Magnesium (Mg) modified biochar (MBCX) by using MgCl2·6H2O and soybean straw under 400 °C. The sorption capacities of MBC60 and MBC180 for Pb2+/Cd2+ increased by 38.65%/213.29%, 44.57%/230.36%, and the selectivity coefficient of Pb2+/Cd2+ increased by 113.28%/209.49%, 213.58%/253.62%, respectively, compared with MBC30. Additionally, the characterization results demonstrated that MgO dominated the surface phases of MBC60 and MBC180, whereas MgCl2 dominated the surface phases of MBC30. Moreover, according to the results of DFT calculation, the adsorption energy (Eads) of MgO for Pb2+ (-0.537 eV) and Cd2+ (-0.347 eV) was lower than that of MgCl2 (Pb2+: 0.37 eV, Cd2+: -0.185 eV), so that, MBC60 and MBC180 had higher sorption capacities for Pb2+ and Cd2+ than MBC30. Therefore, this work provides a new sight to clear the mechanism for modified biochar by alkali metal oxide and practical and theoretical guidance for adsorbent preparation with high adsorption ability for HMs.

Synergistic mechanism of iron manganese supported biochar for arsenic remediation and enzyme activity in contaminated soil

This study prepared and characterized bamboo-derived biochar loaded with different ratios of iron and manganese; evaluated its remediation performance in arsenic-contaminated soil by studying the changes in various environmental factors, arsenic speciation, and arsenic leaching amount in the soil after adding different materials; proposed the optimal ratio and mechanism of iron-manganese removal of arsenic; and explained the multivariate relationship between enzyme activity and soil environmental factors based on biological information. Treatment with Fe-Mn-modified biochar increased the organic matter, cation exchange capacity, and N, P, K, and other nutrient contents. During the remediation process, O-containing functional groups such as Mn-O/As and Fe-O/As were formed on the surface of the biochar, promoting the transformation of As from the mobile fraction to the residual fraction and reducing the phytotoxicity of As, and the remediation ability for As was superior to that of Fe-modified biochar. Mn is indispensable in the FeMn-BC synergistic remediation of As, as it can increase the adsorption sites and the number of functional groups for trace metals on the surface of biochar. In addition to electrostatic attraction, the synergistic mechanism of ferromanganese-modified biochar for arsenic mainly involves redox and complexation. Mn oxidizes As(Ⅲ) to more inert As(V). In this reaction process, Mn(Ⅳ) is reduced to Mn(Ⅲ) and Mn(II), promoting the formation of Fe(Ⅲ) and the conversion of As into Fe-As complexes, while As is fixed due to the formation of ternary surface complexes. Moreover, the effect of adding Fe-Mn-modified biochar on soil enzyme activity was correlated with changes in soil environmental factors; catalase was correlated with soil pH; neutral phosphatase was correlated with soil organic matter; urease was correlated with ammonia nitrogen, and sucrase activity was not significant. This study highlights the potential value of FM1:3-BC as a remediation agent in arsenic-contaminated neutral soils.

Kinetics and modeling of Pb (II) adsorption in pellet biochar based on micro-computed tomography characterization

Biochar, a cost-effective adsorbent for the removal of heavy metals from aqueous solutions, has gained increasing attention. In this study, an advanced micro-computed tomography (micro-CT) system was used to investigate the adsorption kinetics by direct localization and visualization of Pb (II) on wheat straw pellet biochar. The normalized digital images indicating the dynamic changes of Pb (II) adsorption on biochar samples at different initial Pb (II) concentrations of 100, 200, 300, and 400 mg/L and adsorption times were obtained. It was found that image grayscale (GS) changes over adsorption time (t) followed the power function, GSe/GSt=2.45∗t-0.27. Based on this finding, modified pseudo-first-order (PFO) and pseudo-second-order (PSO) models incorporated with time-dependent kinetic constants kPFOt=KPFO∗GSe/GSt and kPSOt=KPSO∗GSe/GSt were proposed, resulting in a better interpretation of the adsorption mechanism. The micro-CT-guided novel approach demonstrated visual evidence-based superiority and should prove valuable to the existing body of research in related fields.

Promoting Effect of Silver Oxide Nanoparticles on the Oxidation of Bisphenol B by Ferrate(VI)

Bisphenol B (BPB, 2,2-bis(4-hydroxyphenyl) butane), as a substitute for bisphenol A, has been widely detected in the environment and become a potential threat to environmental health. This work found that silver oxide nanoparticles (Ag2O) could greatly promote the removal of BPB by ferrate (Fe(VI)). With the presence of 463 mg/L Ag2O, the amount of Fe(VI) required for the complete removal of 10 μM BPB will be reduced by 70%. Meanwhile, the recyclability and stability of Ag2O have been verified by recycling experiments. The characterization results and in situ electrochemical analyses showed that Ag(II) was produced from Ag(I) in the Fe(VI)-Ag2O system, which has a higher electrode potential to oxidize BPB to enhance its removal. A total of 13 intermediates were identified by high-resolution mass spectrometry, and three main reaction pathways were proposed, including oxygen transfer, bond breaking, and polymerization. Based on the toxicity assessment through the ECOSAR program, it is considered that the presence of Ag2O reduced the toxicity of BPB oxidation intermediates to aquatic organisms. These results would deepen our understanding of the interaction between Fe(VI) and Ag2O, which may provide an efficient and environmentally friendly method for water and wastewater treatment.

Enhanced ferrate(VI) oxidation of organic pollutants through direct electron transfer

Fe(VI) is a versatile agent for water purification, and various strategies have been developed to improve its pollutant removal efficiency. Herein, it was found that in addition to intermediate iron species [Fe(IV)/Fe(V)], direct electron transfer (DET) played a significant role in the abatement of organic pollutants in Fe(VI)/carbon quantum dots (CQDs) system. Around 86, 83, 73, 64, 52, 45 and 17% of BPA, DCF, SMX, 4-CP, phenol, p-HBA, and IBP (6 μM) could be oxidized by 30 μM of Fe(VI), whereas with the addition of CQDs (4 mg/L), the oxidation ratio of these pollutants increased to 98, 99, 80, 88, 87, 66 and 57%, respectively. The negative impact induced by solution pH and background constituents on Fe(VI) abatement of pollutants could be alleviated by CQDs, and CQDs acted as catalysts for mediating DET from organic pollutants to Fe(VI). Theoretical calculation revealed that iron species [Fe(VI)/Fe(V)/Fe(IV)] was responsible for the oxidation of 36% of phenol, while DET contributed to the oxidation of 64% of phenol in the Fe(VI)/CQDs system. Compared with iron species oxidation, the CQDs mediated DET from pollutants to Fe(VI) was more efficient for utilizing the oxidation capacity of Fe(VI). The DET mechanism presented in the study provides a prospective strategy for improving the pollution control potential of Fe(VI).

Magnetic hydrochar derived from waste lignin for thallium removal from wastewater: Performance and mechanisms

Waste lignin, such as black liquor (BL) from paper and pulping industries, is an agro-industrial biowaste while its reuse raised global concerns. In this work, a hydrothermal carbonization procedure was employed to convert BL into magnetic lignin-based hydrochar (MLHC) for thallium elimination from wastewater. The results exhibited water purification potential due to a wider working pH window (2-9) with the magnetization intensity of 11.12 emu/g. The maximum adsorption capacity for Tl(III) was 278.9 mg/g, while the contribution of various mechanisms was elucidated with the order: surface precipitation (31.3 %), complexation (20.6 %), physical adsorption (18.2 %), chemical reduction (15.0 %), and ion exchange (14.9 %). This study revealed that hydrothermal treatment could be a potential and promising method to convert waste lignin into magnetic bio-adsorbent to recycle pulping black liquor and apply it for thallium pollution control.

Improvement of Fe(VI) oxidation by NaClO on degrading phenolic substances and reducing DBPs formation potential

Ferrate(VI) is a green oxidant and can effectively oxidize micropollutants. However, the instability of Fe(VI), i.e., self-decomposition, in the aqueous solution limited its application. Herein, it was found that the degradation of phenolic substances had been substantially improved through the combination of Fe(VI) with NaClO. At the condition of pH 8.0, 50 μM of Fe(VI) degraded 18.66 % of BPA (bisphenol A) at 0.5 min or 21.67 % of phenol at 2 min. By contrast, Fe(VI)/NaClO (50/10 μM) oxidized 38.21 % of BPA at 0.5 min or 38.08 % of phenol at 2 min with a synergistic effect. At the end of the reaction, the concentration of Fe(VI) in Fe(VI)/NaClO (50/10 μM) was 28.97 μM for BPA degradation, higher than the 25.62 μM of Fe(VI) group. By active species analysis, intermediate iron species [i.e., Fe(V) and Fe(IV)] played a vital role in the synergistic effect in Fe(VI)/NaClO system, which would react with the applied NaClO to regenerate Fe(VI). In natural water, the Fe(VI)/NaClO could also degrade phenolic substances of natural organic matter (NOM). Although the NaClO reagent was applied, disinfection by-products (DBPs) formation potential decreased by 22.75 % of the raw sample after Fe(VI)/NaClO treatment. Significantly, THMs, mainly caused by phenolic substances of NOM, even declined by 29.18 % of raw sample. Based on that, this study explored a novel ferrate(VI) oxidation system using the cheap NaClO reagent, which would present a new insight on ferrate(VI) application.

Highly efficient removal of hexavalent chromium by magnetic Fe-C composite from reed straw and electric furnace dust waste

Reed straw and electric furnace dust (EFD) waste were used to prepare magnetic Fe-C composite (EFD&C) by co-precipitation and high-temperature activation method to remove Cr(VI) from water. The magnetic EFD&C owned a large specific surface (536.61 m²/g) and a porous structure (micropores and mesopores), and had an efficient removal capacity for Cr(VI). Under conditions of pH (2), the addition amount of EFD&C (1 g/L), the adsorption time (760 min), and the temperature (45 °C), the maximum adsorption capacity reached 111.94 mg/g. The adsorption mechanism mainly attributed to chemical adsorption (redox), Cr(VI) reduced to Cr(III) by Fe(II) and Fe(0) (from Fe₃O₄ and Fe components in EFD) and surface functional groups of -OH, C = C, C-C and O-C = O (from biochar), and secondary attributed to physical adsorption, Cr(VI) and Cr(III) (from reduced Cr(VI)) adsorbed into the porous structure of EFD&C. This study provided a feasible solution for the preparation of adsorbents for adsorbing heavy metals from iron-containing metallurgical solid waste and biomass waste, which contributed to reducing the environmental pollution and lowering the cost of adsorbent preparation.

Indirect spectrophotometric determination of aqueous ferrate(VI) based on its reaction with iodide in acidic media

Ferrate(VI) (Fe(VI)) is utilized as an efficient and environmentally friendly water treatment agent that can be widely used for degradation of (in)organic pollutants in practical applications. However, only a few spectrophotometric methods for Fe(VI) determination were reported. In this study, a novel method for determining trace levels of aqueous Fe(VI) was developed based on the fact that Fe(VI) reacts with iodide at acidic pH to form iodine, which subsequently is treated with starch to yield the blue starch-iodine complex measured spectrophotometrically at 590 nm. The key measurement parameters, including acidic medium, starch dosages, temperature, time, and addition order were optimized to improve the sensitivity of detection. The increase in absorbance at 590 nm was linear with respect to Fe(VI) added (0.022-50 µM). Its sensitivity was determined as (4.61 ± 0.05) × 10⁴ M^-1 cm^-1, which was higher than that of existing spectrophotometric methods. The principle for Fe(VI) determination was studied by investigating stoichiometry, kinetics, and mechanism of Fe(VI) reaction with iodide. The molar stoichiometry of Fe(VI) with I₃^- species was determined to be 1:2. The reaction of Fe(VI) with iodide followed a second-order rate law with first order in each reactant and displayed apparent anti-Arrhenius kinetics, then its reaction pathway was proposed as well. Furthermore, the established method was successfully applied to measure Fe(VI) in various environmental water samples. The results show that the proposed approach is simple, convenient, highly reproducible and extremely sensitive, and is also expected to be of use for kinetic studies of Fe(VI) reaction with (in)organic compounds under acidic conditions.

Synthesis and application of starch-stablized Fe-Mn/biochar composites for the removal of lead from water and soil

Starch-stablized and Fe/Mn bimetals modified biochar derived from corn straw (SFM@CBC and SFM@CBC-350) were firstly prepared, characterized (FTIR, XRD, SEM, EDS, BET and XPS), and applied in Pb removal from water and soil. SFM@CBC and SFM@CBC-350 displayed highly effective adsorption performance of Pb²⁺ from wastewater with the maximum adsorption capacity of 170.91 mg g^-1 and 190.17 mg g^-1, respectively, which were much greater than that of FM@CBC (149.25 mg g^-1) and CBC (101.10 mg g^-1). Studies of adsorption kinetics, isotherms and thermodynamics indicated that the absorption of Pb²⁺ by SFM@CBC and SFM@CBC-350 was spontaneous and endothermic reaction, and it was controlled by monolayer chemisorption. The mechanism studies indicated that Pb²⁺ removal involved with multiple mechanism, including complexation (dominant process confirmed by XPS analysis), physical adsorption, electrostatic attraction, and cation exchange. The reusability test demonstrated that SFM@CBC and SFM@CBC-350 had very good stability and reusability. In addition, in order to further explore Pb removal performance of the modified biochar, SFM@CBC-350 was used in soil-ryegrass pot systems. Compared with the controls, the addition of SFM@CBC-350 reduced Pb content in soil and ryegrass, increased the biomass and total chlorophyll content, reduced the activity of antioxidant enzymes (CAT, SOD, MDA and POD) and ROS fluorescence intensity of ryegrass, thus alleviating Pb stress of ryegrass. Besides, the addition of SFM@CBC-350 could increase the richness and diversity of soil microorganisms, which was beneficial to the growth of ryegrass. Hence, SFM@CBC-350 has the potential of being used as a green, efficient and promising adsorbent in Pb removal from wastewater and soil.

Biochar raw material selection and application in the food chain: A review

As one of the largest carbon emitters, China promises to achieve carbon emissions neutrality by 2060. Various industries are developing businesses to reduce carbon emissions. As an important greenhouse gas emissions scenario, the reduction of carbon emissions in the food chain can be achieved by preparing the wastes into biochar. The food chain, as one of the sources of biochar, consists of production, processing and consumption, in which many wastes can be transferred into biochar. However, few studies use the food chain as the system to sort out the raw materials of biochar. A systematic review of the food chain application in serving as raw materials for biochar is helpful for further application of such technique, providing supportive information for the development of biochar preparation and wastes treating. In addition, there are many pollution sources in the food production process, such as agricultural contaminated soil and wastewater from livestock and aquatic, that can be treated on-site to achieve the goal of treating wastes with wastes within the food chain. This study focuses on waste resource utilization and pollution remediation in the food chain, summarizing the sources of biochar in the food chain and analyzing the feasibility of using waste in food chain to treat contaminated sites in the food chain and discussing the impacts of the greenhouse gas emissions. This review provides a reference for the resource utilization of waste and pollution reduction in the food chain.

Removal of Phosphate from Aqueous Solution by Zeolite-Biochar Composite: Adsorption Performance and Regulation Mechanism

Recently, rampant eutrophication induced by phosphorus enrichment in water has been attracting attention worldwide. However, the mechanisms by which phosphate can be eliminated from the aqueous environment remain unclear. This study was aimed at investigating the adsorption performance and regulation mechanisms of the zeolite-biochar composite for removing phosphate from an aqueous environment. To do this, physicochemical properties of the zeolite-biochar composite were assessed by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) specific surface area (SSA) analyzer, and transmission electron microscopy (TEM). Adsorption tests were performed to evaluate the adsorption ability of the composite material for mitigating excess phosphorus in the aqueous environment. The findings evinced that the phosphorus removed by PZC 7:3 (pyrolyzed zeolite and corn straw at a mass ratio of 7:3) can reach 90% of that removed by biochar. The maximum adsorption capacities of zeolite, biochar, and PZC 7:3 were 0.69, 3.60, and 2.41 mg/g, respectively. The main mechanism of phosphate removal by PZC 7:3 was the formation of thin-film amorphous calcium-magnesium phosphate compounds through ligand exchange. This study suggests that PZC 7:3 is a viable adsorbent for the removal of phosphate from aquatic systems.

Oxidative Degradation of Hazardous Benzene Derivatives by Ferrate(VI): Effect of Initial pH, Molar Ratio and Temperature

Two of the most hazardous benzene derivatives (HBD) that have polluted the aquatic environment are bromobenzene and chlorobenzene. Ferrate can degrade various pollutants quickly and efficiently without producing harmful byproducts. This study aims to determine the ability of ferrate to degrade harmful contaminants such as bromobenzene and chlorobenzene. A series of batch experiments were carried out, including for the molar ratio, initial pH solution, and temperature. The study was conducted at an initial pH of 3.6 to 9.6, a molar ratio of 2 to 8 and a temperature of 15 to 55 °C. The study will also examine the differences in functional groups in these pollutants. As a result of the experiments, the optimum conditions to oxidize HBD in a batch reactor was found to have an initial pH of 7.0, a molar ratio of 8, and a temperature of 45 °C, with a 10 min reaction time. Ferrate has a degradation ability against chlorobenzene greater than bromobenzene. The functional cluster in pollutants also significantly affects the degradation ability of ferrate. The results of the degradation experiment showed that ferrate(VI) could effectively oxidize hazardous benzene derivatives in a solution.