Competitive adsorption of heavy metals onto modified biochars: Comparison of biochar properties and modification methods

Cerium added corn-based biochar as particle electrode for electrochemical oxidation industrial wastewater

Three-dimensional (3D) electrochemical oxidation has become a popular advanced oxidation technology for wastewater treatment due to its various benefits. In this study, cerium (Ce) loaded biochar (Ce/BC) was used as a particle electrode to conduct the degradation of industrial wastewater released by the chemical industry. SEM, EDS, XRD, FTIR, XPS, and BET were used to characterize the properties of Ce/BC. The effects of some variables, including Ce loading (0-5%), pH (5-9), Ce/BC dosage (12.5-50.0 g/L), and working voltage (12-20 V), were evaluated with regard to COD elimination. The kinetics of COD oxidation and the energy consumption were carefully investigated. Tert-butanol significantly reduced the removal efficiency of COD, indicating that hydroxyl radicals generated during the process rather than direct electro-oxidation were the main mechanism for COD degradation. The treatment of industrial wastewater might benefit from the use of Ce/BC as particle electrode.

Selective lead capture using amide-containing COFs: A novel strategy for efficient soil remediation

A critical consideration in the application of phytoremediation to remediate sludge soil contaminated with heavy metals is the potential for leaching risks that prevail prior to the efficient uptake of these metals by plants. The most cost-effective method is to use heavy metal stabilizers with selective adsorption. A novel amide-based COF material (COF-TH) has been synthesized as a heavy metal stabilizer for Pb. COF-TH exhibits significant selectivity for Pb in five-metal-mixed solutions, with a distribution coefficient KD as high as 3279 mL·g-1, which was more than 7.3 times that of other heavy metals. The maximum adsorption capacity of COF-TH for Pb was 189 mg·g-1. The adsorption fitted Langmuir model and intra-particle diffusion model, and satisfied pseudo-second-order kinetic model. The excellent selectivity and adsorption performance originate from the complexation between abundant amide groups and Pb ions. Pot experiments and leaching assays confirm that COF-TH decreased Pb leachate concentrations by 77.8 % without significantly decreasing total phytoextracted amounts of other heavy metals, due to the high selectivity of COF-TH to Pb. Additionally, its positive impact on plant growth and microbial diversity makes it a promising soil remediation agent. This investigation offers a novel approach to mitigate the leaching risk of a specific heavy metal Pb during sludge land application by integrating soil phytoremediation with stabilization techniques.

CaAl-Layered Double Hydroxides-Modified Biochar Composites Mitigate the Toxic Effects of Cu and Pb in Soil on Pea Seedlings

Compound contamination of soil with heavy metals copper (Cu) and lead (Pb) triggered by mining development has become a serious problem. To solve this problem, in this paper, corncob kernel, which is widely available and inexpensive, was used as the raw material of biochar and modified by loading CaAl-layered double hydroxides to synthesize biochar-loaded CaAl-layered double hydroxide composites (CaAl-LDH/BC). After soil remediation experiments, either BC or CaAl-LDH/BC can increase soil pH, and the available phosphorus content and available potassium content in soil. Compared with BC, CaAl-LDH/BC significantly reduced the available content of Cu and Pb in the active state (diethylenetriaminepentaacetic acid extractable state) in the soil, and the passivation rate of Cu and Pb by a 2% dosage of CaAl-LDH/BC reached 47.85% and 37.9%, respectively. CaAl-LDH/BC can significantly enhance the relative abundance of beneficial microorganisms such as Actinobacteriota, Gemmatimonadota, and Luteimonas in the soil, which can help to enhance the tolerance and reduce the enrichment ability of plants to heavy metals. In addition, it was demonstrated by pea seedling (Pisum sativum L.) growing experiments that CaAl-LDH/BC increased plant fresh weight, root length, plant height, catalase (CAT) activity, and protein content, which promoted the growth of the plant. Compared with BC, CaAl-LDH/BC significantly reduced the Cu and Pb contents in pea seedlings, in which the Cu and Pb contents in pea seedlings were reduced from 31.97 mg/kg and 74.40 mg/kg to 2.92 mg/kg and 6.67 mg/kg, respectively, after a 2% dosage of CaAl-LDH/BC, which was a reduction of 90.84% and 91.03%, respectively. In conclusion, compared with BC, CaAl-LDH/BC improved soil fertility and thus the plant growth environment, and also more effectively reduced the mobility of heavy metals Cu and Pb in the soil to reduce the enrichment of Cu and Pb by plants.

Machine learning-based exploration of biochar for environmental management and remediation

Biochar has a wide range of applications, including environmental management, such as preventing soil and water pollution, removing heavy metals from water sources, and reducing air pollution. However, there are several challenges associated with the usage of biochar for these purposes, resulting in an abundance of experimental data in the literature. Accordingly, the purpose of this study is to examine the use of machine learning in biochar processes with an eye toward the potential of biochar in environmental remediation. First, recent developments in biochar utilization for the environment are summarized. Then, a bibliometric analysis is carried out to illustrate the major trends (demonstrating that the top three keywords are heavy metal, wastewater, and adsorption) and construct a comprehensive perspective for future studies. This is followed by a detailed review of machine learning applications, which reveals that adsorption efficiency and capacity are the primary utilization targets in biochar utilization. Finally, a comprehensive perspective is provided for the future. It is then concluded that machine learning can help to detect hidden patterns and make accurate predictions for determining the combination of variables that results in the desired properties which can be later used for decision-making, resource allocation, and environmental management.

Heavy metals immobilization and bioavailability in multi-metal contaminated soil under ryegrass cultivation as affected by ZnO and MnO2 nanoparticle-modified biochar

Pollution by heavy metals (HMs) has become a global problem for agriculture and the environment. In this study, the effects of pristine biochar and biochar modified with manganese dioxide (BC@MnO2) and zinc oxide (BC@ZnO) nanoparticles on the immobilization and bioavailability of Pb, Cd, Zn, and Ni in soil under ryegrass (Lolium perenne L.) cultivation were investigated. The results of SEM-EDX, FTIR, and XRD showed that ZnO and MnO2 nanoparticles were successfully loaded onto biochar. The results showed that BC, BC@MnO2 and BC@ZnO treatments significantly increased shoots and roots dry weight of ryegrass compared to the control. The maximum dry weight of root and shoot (1.365 g pot-1 and 4.163 g pot-1, respectively) was reached at 1% BC@MnO2. The HMs uptake by ryegrass roots and shoots decreased significantly after addition of amendments. The lowest Pb, Cd, Zn and Ni uptake in the plant shoot (13.176, 24.92, 32.407, and 53.88 µg pot-1, respectively) was obtained in the 1% BC@MnO2 treatment. Modified biochar was more successful in reducing HMs uptake by ryegrass and improving plant growth than pristine biochar and can therefore be used as an efficient and cost effective amendment for the remediation of HMs contaminated soils. The lowest HMs translocation (TF) and bioconcentration factors were related to the 1% BC@MnO2 treatment. Therefore, BC@MnO2 was the most successful treatment for HMs immobilization in soil. Also, a comparison of the TF values of plant showed that ryegrass had a good ability to accumulate all studied HMs in its roots, and it is a suitable plant for HMs phytostabilization.

Unlocking the potential of biochar: an iron-phosphorus-based composite modified adsorbent for adsorption of Pb(II) and Cd(II) in aqueous environments and response surface optimization of adsorption conditions

In this work, iron-phosphorus based composite biochar (FPBC) was prepared by modification with potassium phosphate and iron oxides for the removal of heavy metal ions from single and mixed heavy metal (Pb and Cd) solutions. FTIR and XPS characterization experiments showed that the novel modified biochar had a greater number of surface functional groups compared to the pristine biochar. The maximum adsorption capacities of FPBC for Pb(II) and Cd(II) were 211.66 mg·g-1 and 94.08 mg·g-1 at 293 K. The adsorption of Pb(II) and Cd(II) by FPBC followed the proposed two-step adsorption kinetic model and the Freundlich isothermal adsorption model, suggesting that the mechanism of adsorption of Pb(II) and Cd(II) by FPBC involved chemical adsorption of multiple layers. Mechanistic studies showed that the introduction of -PO4 and -PO3 chemisorbed with Pb(II) and Cd(II), and the introduction of -Fe-O increased the ion exchange with Pb(II) and Cd(II) during the adsorption process and produced precipitates such as Pb3Fe(PO4)3 and Cd5Fe2(P2O7)4. Additionally, the abundant -OH and -COOH groups also participated in the removal of Pb(II) and Cd(II). In addition, FPBC demonstrated strong selective adsorption of Pb(II) in mixed heavy metal solutions. The Response Surface Methodology(RSM) analysis determined the optimal adsorption conditions for FPBC as pH 5.31, temperature 26.01 °C, and Pb(II) concentration 306.30 mg·L-1 for Pb(II). Similarly, the optimal adsorption conditions for Cd(II) were found to be pH 5.66, temperature 39.34 °C, and Cd(II) concentration 267.68 mg·L-1. Therefore, FPBC has the potential for application as a composite-modified adsorbent for the adsorption of multiple heavy metal ions.

Adsorption behavior of lead, cadmium, and arsenic on manganese-modified biochar: competition and promotion

Biochar adsorption of heavy metals has been a research hotspot, yet there has been limited reports on the effect of heavy metal interactions on adsorption efficiency in complex systems. In this study, the adsorbent was prepared by pyrolysis of rice straw loaded with manganese (BC-Mn). The interactions of Pb, Cd and As adsorption on BC-Mn were systematically studied. The results of the adsorption isotherms for the binary metal system revealed a competitive adsorption between Pb and Cd, resulting in decreased Pb (from 214.38 mg/g to 148.20 mg/g) and Cd (from 165.73 mg/g to 92.11 mg/g). A notable promotion occurred between As and Cd, showing an increase from 234.93 mg/g to 305.00 mg/g for As and 165.73 mg/g to 313.94 mg/g for Cd. In the ternary metal system, Pb inhibition did not counteract the promotion of Cd and As. Furthermore, the Langmuir isotherm effectively described BC-Mn's adsorption process in monometallic, binary, and ternary metal systems (R2 > 0.9294). Zeta and FTIR analyses revealed simultaneous competition between Pb and Cd for adsorption on BC-Mn's -OH sites. XPS analysis revealed that As adsorption by BC-Mn facilitated the conversion of MnO2 and MnO to MnOOH, resulting in increased hydroxyl radical production on BC-Mn's surface. Simultaneously, Cd combined with the adsorbed As to form ternary Cd-As-Mn complexes, which expedited the removal of Cd. These results help to provide theoretical support as well as technical support for the treatment of Pb-Cd-As contaminated wastewater.

Preparation of Lanthanum-Modified Tea Waste Biochar and Its Adsorption Performance on Fluoride in Water

In this study, tea waste was used as a raw material, and TBC (tea waste biochar) was prepared by pyrolysis at 700 °C. La(NO3)3·6H2O was used as the modifier to optimize one-way modification; the orthogonal experiment was undertaken to determine the optimal preparation conditions; and La-TBC (lanthanum-modified biochar) was obtained. The key factors for the adsorption of fluoride by La-TBC were investigated by means of batch adsorption experiments, and kinetics and isothermal adsorption experiments were carried out on the adsorption of fluoride in geothermal hot spring water. The adsorption mechanism of fluoride by La-TBC was analyzed via characterization methods such as SEM-EDS (Scanning Electron Microscope and Energy Dispersive Spectrometer), BET (Brunauer-Emmett-Teller), FTIR (Fourier transform infrared), XRD (X-ray diffraction), and so on. The results show that La-TBC had the best adsorption effect on fluoride at pH 7. The process of adsorption of fluoride follows the pseudo-second-order kinetics and Langmuir isothermal model, and the maximum theoretical adsorption quantity was 47.47 mg/g at 80 °C, while the removal rate of fluoride from the actual geothermal hot spring water reached more than 95%. The adsorption process was dominated by the monolayer adsorption of chemicals, and the mechanisms mainly include pore filling, ion exchange, and electrostatic interaction.

Novel pretreatment with hydrogen peroxide enhanced microwave biochar for heavy metals adsorption: Characterization and adsorption performance

Hydrogen peroxide (HP) was used to pretreat wheat straw (WS) for microwave biochar production at 100-600 W, the physicochemical properties of pretreated WS and biochar products as well as heavy metals adsorption performance were investigated. Results showed that HP enhanced specific surface area (SSA) and pore volume (PV) of WS, and the largest SSA (190.35 m2 g-1) and PV (0.1493 cm3 g-1) of biochar were obtained at microwave powers of 600 W (HPWS600) and 500 W (HPWS500), respectively. HPWS500 showed maximum adsorption capacities, which were 57.56, 190.21, and 65.16 mg g-1 for Cd2+, Pb2+, and Cu2+, respectively. Solution pH values and cation concentrations exhibited significant effects on adsorption capacities of biochar. The pseudo-second-order kinetic and Langmuir isotherm models fitted better for metal adsorption process. The FTIR results suggested that chemisorption mechanisms including precipitation with carbonate and complexation with oxygen-containing functional groups might be predominant adsorption mechanisms. These results suggest that HP pretreatment has excellent potential for biochar production.

Investigating the different transformations of tetracycline using birnessite under different reaction conditions and various humic acids

Prior studies have successfully used manganese oxides to facilitate the transformation of tetracycline in aqueous solution. To further understand the kinetic and the transformation pathway of tetracycline via birnessite (δ-MnO2) under different conditions, experiments were conducted at pH levels of 3, 6, and 9 in the presence or absence of Aldrich humic acid (ADHA). Tetracycline removal followed the pseudo-second-order reaction model in all investigated cases, and the removal efficiency (g mg-1 h -1) followed the following trend: pH 3 (0.45/0.27) > pH 6 (0.036/0.087) > pH 9 (0.036/0.103) in the absence/presence of ADHA. Liquid chromatography-mass spectrometry/mass spectrometry results identified five main transformation products at m/z 495, 477, 493, 459, and 415, produced by the transformation reactions, including hydration, oxidation, desaturation, and oxy reduction. Notably, in the presence of ADHA at pH 3, products with higher toxicity secondary (m/z 477 and 495) were reduced, while less toxicity products (m/z 459 and 415) were enhanced. The experiments utilizing tetracycline and δ-MnO2 with varied humic acids (HA) revealed that HA with high polar organic carbon groups, such as O-alkyl, exhibited higher removal efficiency at pH 6. This research offers the first comprehensive insights into the pathway transformations of tetracycline via δ-MnO2 under different pH conditions and HA types. For further understanding, future work should investigate the binding of HA, TTC, and/or Mn2+ and the oxidation capacity of MnO2 after the reaction to clarify Mn2+ elution mechanisms.

Screening the optimal modified biochar for nitrogen retention in black soil

Reducing the environmental problems caused by nitrogen loss and nitrogen pollution is of great significance. The addition of biochar to soil is a new method for increasing nitrogen interception due to the special structural and physicochemical properties of biochar. The optimal modified biochar was screened out after acid-base modification and batch adsorption test in this paper. And then the effects of different soil and biochar mixing methods on soil physicochemical properties and nitrogen adsorption and retention were explored through soil column leaching test. The results showed that the biochar with a pyrolysis temperature of 700 °C had the best adsorption effect on nitrogen after being modified by 0.1 mol/L HCI, and the adsorption capacity of nitrate nitrogen reached 121.46 mg/g. The adsorption process of ammonia nitrogen and nitrate nitrogen conformed to the Langmuir model and was mainly homogeneous monolayer. After mixing the selected modified biochar with black soil, the pH increased by 4.77%, the content of ammonia nitrogen increased by 4.89%, and the nitrate content increased by 16.62%. In this study, the adsorption effect of biochar on nitrogen in black soil was discussed, so as to explore the optimal use of biochar in soil, which provided some reference basis for the relevant research.

Biochar preparation and evaluation of its effect in composting mechanism: A review

This article provides an overview of biochar application for organic waste co-composting and its biochemical transformation mechanism. As a composting amendment, biochar work in the adsorption of nutrients, the retention of oxygen and water, and the promotion of electron transfer. These functions serve the micro-organisms (physical support of niche) and determine changes in community structure beyond the succession of composing primary microorganisms. Biochar mediates resistance genes, mobile gene elements, and biochemical metabolic activities of organic matter degrading. The participation of biochar enriched the α-diversity of microbial communities at all stages of composting, and ultimately reflects the high γ-diversity. Finally, easy and convincing biochar preparation methods and characteristic need to be explored, in turn, the mechanism of biochar on composting microbes at the microscopic level can be studied in depth.

Synthesizing sulfhydryl-functionalized biochar for effectively removing mercury ions from contaminated water

Biochar is regarded as an effective adsorbent for heavy metal pollution treatment, and functional optimization is still needed to improve its performance. We created raw biochar (BC and BP) from corn straw and pine sawdust, which were modified to produce sulfhydryl-modified biochar (MBC and MBP). Isothermal adsorption experiments and adsorption kinetics experiments as well as the related model fitting were performed to evaluate the adsorption performance of biochar on Hg(II). According to the results of the Langmuir model fitting, the maximum adsorption capacities of sulfhydryl-modified biochar were 193.05 mg/g (MBC) and 178.04 mg/g (MBP), respectively, which were approximately 1.6 times higher than the raw biochar. The results showed that adding sulfhydryl groups to biochar can improve its adsorption performance. The prompt effect resulted from the sulfhydryl modification providing additional functional groups and enhanced chemisorption and physical adsorption properties.

Fe-modified fly ash/cotton stalk biochar composites for efficient removal of phosphate in water: mechanisms and green-reuse potential

Excessive phosphate content input into natural water can lead to the waste of resource and eutrophication. Biochar is a kind of low-cost adsorbent. However, its adsorption capacity for phosphate is low. In order to solve this problem, Fe compound-modified fly ash/cotton stalk biochar composites (Fe-FBC) were prepared through co-pyrolyzed fly ash and cotton stalk at 800℃, followed by infiltration of FeSO₄ solution. The samples were characterized by scanning electron microscopy, Brunauer-Emmett-Teller, X-ray diffraction, Fourier transform infrared spectroscopy, and zeta potential. After modification, the hydrophilicity and polarity of Fe-FBC increased. In addition, the pore volume, specific surface area, and surface functional groups were significantly improved. The adsorption behavior of Fe-FBC for the removal of phosphate from water can be well fitted by the pseudo-second-order kinetic and Sips isotherm adsorption model, with a maximum adsorption capacity of 47.91 mg/g. Fe-FBC maintained a high adsorption capacity in the pH range of 3-10. The coexisting anions (NO₃^-, SO₄^2-, and Cl^-) had negligible effects on phosphate adsorption. The adsorption mechanisms of Fe-FBC include electrostatic attraction, ligand exchange, surface complexation, ion exchange, chemical precipitation, and hydrogen bonding. Moreover, the desorption process of phosphate was investigated, indicating that the phosphate-saturated Fe-FBC could use as slow-release phosphate fertilizer. This study proposed a potentially environmental protection and recycling economy approach, which consists of recycling resources and treating wastes with wastes.

MgFe-LDH@biochars for removing ammonia nitrogen and phosphorus from biogas slurry: Synthesis routes, composite performance, and adsorption mechanisms

Layered double hydroxide-biochar composites (LDH@BCs) have been developed for ammonia nitrogen (AN) and phosphorus (P) removal from wastewater. Improvement of LDH@BCs was limited due to the lack of comparative evaluation based on LDH@BCs characteristics and synthetic methods and information on the adsorption properties of LDH@BCs for N and P from natural wastewater. In this study, MgFe-LDH@BCs were synthesized by three different co-precipitation procedures. The differences in physicochemical and morphological properties were compared. They were then employed to remove AN and P from biogas slurry. The adsorption performance of the three MgFe-LDH@BCs was compared and evaluated. Different synthesis procedures can significantly affect the physicochemical and morphological characteristics of MgFe-LDH@BCs. The LDH@BC composite fabricated through a novel method (labeled 'MgFe-LDH@BC1') has the largest specific surface area, Mg and Fe content, and excellent magnetic response performance. Moreover, the composite has the best adsorption property of AN and P from biogas slurry (30.0% and 81.8%, respectively). The main reaction mechanisms include memory effect, ion exchange, and co-precipitation. Applying 2% MgFe-LDH@BC1 saturated with AN and P adsorption from biogas slurry as a fertilizer substitute can substantially improve soil fertility and increase plant production by 139.3%. These results indicate that the facile LDH@BC synthesis method is an effective method to overcome the shortcomings of LDH@BC in practical application, and provide a basis for further exploration of the potential application of biochar based fertilizers in agriculture.

Characterization and Co-Adsorption Mechanism of Magnetic Clay-Biochar Composite for De-Risking Cd(II) and Methyl Orange Contaminated Water

The application of the adsorption method in sewage treatment has recently become a hot spot. A novel magnetic clay-biochar composite (BNT-MBC) was fabricated by co-pyrolysis of bentonite and biomass after being impregnated with Fe (NO3)3·9H2O. Its adsorption capacity for Cd(II) and methyl orange was approximately doubled, reaching a maximum of 26.22 and 63.34 mg/g, and could be easily separated from the solution by using external magnets with its saturation magnetization of 9.71 emu/g. A series of characterizations including surface morphology and pore structure, elemental analysis, functional group analysis and graphitization were carried out, showing that the specific surface area was increased 50 times by loading 20 wt.% bentonite, while its graphitization and oxygen-containing functional groups were also enhanced. The isotherm fitting indicated that Cd(II) was adsorbed in multiple layers, while methyl orange was in both monolayer and multilayer adsorptions. The kinetic fitting indicated that chemisorption was the rate-limiting step of both, and it was also a complex process controlled by two steps with the fitting of intra-particle diffusion. In the binary system of Cd(II) and methyl orange, the co-existing pollutants facilitated the adsorption of the original one, and there was no competition between adsorption sites of Cd(II) and methyl orange. BNT-MBC also exhibited good reusability and can be magnetically recovered for recycling. Thus, the magnetic clay-biochar composite BNT-MBC is a cost-effective and promising adsorbent for simultaneous removing Cd(II) and methyl orange from wastewater.

Immobilization effect of heavy metals in biochar via the copyrolysis of sewage sludge and apple branches

The excess sludge produced by sewage treatment plants can be recycled into energy through pyrolysis, and the byproduct biochar can be used for soil remediation. However, the heavy metals in sludge are retained in biochar after pyrolysis and may cause secondary pollution during its soil application. Herein, a fast copyrolysis method of activated sludge (AS) and apple branches (AT) was proposed to immobilize heavy metals while improving bio-oil yield. The results showed that the heavy metal release from the copyrolyzed biochar was markedly reduced compared with that from the biochar produced through the pyrolysis of AS alone (78% for Cr and 28% for Pb). The kinetic behavior of ion release from different biochars could be described by a first-order kinetic model. The excellent fixation of heavy metals was attributed to complexation by abundant oxygen-containing surface functional groups (-O-, =O, and -CHO) that were mainly donated by AT. Furthermore, high-temperature pyrolysis was conducive to the fixation of metals, and the release of Pb²⁺ and Cr³⁺ from the biochar pyrolyzed at 600 °C was approximately 2/3 and 1/10 of that from the biochar pyrolyzed at 400 °C, respectively. A growth experiment on Staphylococcus aureus and Escherichia coli revealed that the toxicity of the copyrolyzed biochar was greatly reduced. This work can provide a method for heavy metal fixation and simultaneous resource recovery from organic wastes.

Regeneration mechanism of a novel high-performance biochar mercury adsorbent directionally modified by multimetal multilayer loading

Biochar that is directly obtained by pyrolysis exhibits a low adsorption efficiency; furthermore, the process of recycling adsorbents is ineffective. To solve these problems, conventional chemical coprecipitation, sol-gel, multimetal multilayer loading and biomass pyrolysis coking processes have been integrated. After selecting specific components for structural design, a novel high-performance biochar adsorbent was obtained. The effects of the O₂ concentration and temperature on the regeneration characteristics were explored. An isothermal regeneration method to repair the deactivated adsorbent in a specific atmosphere was proposed, and the optimal regeneration mode and conditions were determined. The microscopic characteristics of the regenerated samples were revealed along with the mechanism of Hg⁰ removal and regeneration by using temperature-programmed desorption technology and adsorption kinetics. The results show that doping multiple metals can reduce the pyrolysis reaction barrier of the modified biomass. On the modified surface of the sample, the doped metals formed aggregated oxides, and the resulting synergistic effect enhanced the oxidative activity of the biochar carriers and the threshold effect of Ce oxide. The optimal regeneration conditions (5% O₂ and 600 °C) effectively coordinated the competitive relationship between the deep carbonization process and the adsorption/oxidation site repair process; in addition, these conditions provided outstanding structure-effect connections between the physico-chemical properties and Hg⁰ removal efficiency of the regenerated samples. Hg⁰ adsorption by the regenerated samples is a multilayer mass transfer process that involves the coupling of physical and chemical effects, and the surface adsorption sites play a leading role.

Microwave biochar produced with activated carbon catalyst: Characterization and adsorption of heavy metals

Novel microwave biochar derived from wheat straw (WS) using a range of power levels, with activated carbon catalyst as microwave absorber, was produced, characterized and tested as adsorbent of three heavy metals (Pb²⁺, Cd²⁺, and Cu²⁺). The microwave biochar with the greatest specific surface area (156.09 m² g^-1) and total pore volume (0.0790 cm³ g^-1) were produced at 600 W (WS600) and 500 W (WS500) power level, respectively. Maximum adsorption capacities of WS500 to Pb²⁺, Cd²⁺ and Cu²⁺ were 139.44 mg g^-1, 52.92 mg g^-1, and 31.25 mg g^-1, respectively. Optimal pH value for heavy metal removal was at range of 5-6, and Pb²⁺ showed the strongest affinity in competitive adsorption experiments. The adsorption data were fitted better by pseudo-second-order model and Langmuir isotherm, indicating that adsorption process was mainly explained by monolayer adsorption, and chemical adsorption occupied important role. The predominant adsorption mechanisms of heavy metals on microwave pyrolysis biochar included complexation with oxygen-containing functional groups (i.e., carboxylic acid CO and -OH) and precipitation with carbonate. In addition, reused WS600 maintained 76.17% and 96.07% of their initial adsorption capacity for Cu²⁺ and Cd²⁺, respectively. These results suggest that microwave biochar produced with activated carbon catalyst has excellent potential for efficient use in the removal of heavy metals from waste water.

Review on treatment and utilization of barium slag in China

Barium slag (BS) is generated as a by-product waste during the production of barium salts from barite. A large amount of BS is discharged annually threating the ecological environment and restricting the development of the barium salts industry. In China, BS is classified as hazardous waste due to its corrosivity, and more importantly because of its extraction toxicity of barium. Soluble barium is toxic and can result in barium poisoning for environment and human beings. The current review presents a detailed summary on general characteristics, discharge and disposal status, harmless treatment pathways and comprehensive utilization of BS in China. BaO, SiO₂, CaO, and SO₃ occur as main chemical compositions in BS, especially BaO accounting approximately for 35-40%. The mineral compositions include unreacted barite, quartz, clay minerals, newly-formed phases from the side reactions such as BaCO₃, BaSiO₃ and BaSO₃, and residual carbon. A special attention is given to the assessment of the harmless treatment methods for BS from hazardous waste to general waste, which will decrease its management costs. Precipitation and solidification of soluble barium is the common pathway for harmless treatment of BS, and the using of other industrial waste can realize cost-saving. Methods for comprehensive utilization of BS include recovery of barium and carbon, application in building materials, and using as adsorbents for wastewater treatment. In particular, we analyzed and discussed the advantages and disadvantages of these existing process routes, intending to promote potentials for comprehensive utilization of BS in the future.

Biochar derived carbonaceous material for various environmental applications: Systematic review

Biochar is the solid material produced from the carbonization of organic feedstock biomass. This material has several unique characteristics such as greater carbon content, good electrical conductivity, high stability and large surface area, which can be applied in several research areas such as generation of power and wastewater treatment. In connection with this, recently, the investigations on biochar significantly focus on the removal of toxic heavy metals since the biochar material is easily available and environmentally friendly. According to an environmental analytical device, biochar-derived carbonaceous material has been additionally applied to the synthesis of an effective, sensitive, and low-cost electrochemical sensor. Biochar with an assessment of electrochemical properties has engaged with different redox reactions in water. In this survey, electrochemical ways of behaving of biochar in light of the electrochemical structures were analytically compiled as well as the impact from biomass sources and manufacturing process including carbonization strategies, pre-treatment/changed techniques. This review emphasizes the various synthesis methods of biochar form organic feedstock, properties and different modulations of biochar for the bioremediation of heavy metals. This review study emphasizes the utilization of biochar as sensing platform and supercapacitor for electrode fabrication in electrochemical biosensor to enhance the remediation of toxic contaminants from water streams and by switching the less ecological traditional materials. Brief information on the techniques employed for packaging biochar as carbon electrode is summarized. Scope in the aspect of environmental concern of biochar, future challenges and prospects are proposed in detail.

Cadmium ion removal from aqueous media using banana peel biochar/Fe3O4/ZIF-67

In the present study, banana peel waste was used as a suitable source for biochar production. The banana peel biochar (BPB) was modified using Fe₃O₄ magnetic and ZIF-67 nanoparticles. The modification of the BPB surface (4.70 m²/g) with Fe₃O₄ and Fe₃O₄/ZIF-67 significantly increased the specific surface of the nanocomposites (BPB/Fe₃O₄: 78.83 m²/g, and BPB/Fe₃O₄/ZIF-67: 1212.40 m²/g). The effect of pH, temperature, contact time, adsorbent dose, and concentration of Cd²⁺ on the efficiency of the Cd²⁺ adsorption was explored. Maximum adsorption efficiencies for BPB (97.76%), BPB/Fe₃O₄ (97.52%), and BPB/Fe₃O₄/ZIF-67 (99.14%) were obtained at pH 6, Cd²⁺ concentration of 10 mg/L, times of 80 min, 50 min, and 40 min, and adsorbent doses of 2 g/L, 1.5 g/L, and 1 g/L, respectively. Thermodynamic measurements indicated that the process is spontaneous and exothermic. The maximum capacity of Cd²⁺ adsorption using BPB, BPB/Fe₃O₄, and BPB/Fe₃O₄/ZIF-67 were obtained 20.63 mg/g, 30.33 mg/g, and 50.78 mg/g, respectively. The Cd²⁺ adsorption using magnetic nanocomposites followed the pseudo-first-order kinetic model. The results showed that studied adsorbents especially BPB/Fe₃O₄/ZIF-67 have a good ability to adsorb-desorb Cd²⁺ and clean an effluent containing pollutants.

Adsorption of vanadium (V) ions from the aqueous solutions on different biomass-derived biochars

The paper presents the results of the studies on the vanadium (V) ions removal from the aqueous solutions in the adsorption process on biochars from different biomass types (cow manure BC1, wet distiller grains BC2, spent mushroom substrates BC3). The adsorbents were characterized by means of the SEM-EDS, FTIR, XRD and XPS techniques. The influence of adsorbent type and basic process parameters, such as pH and metal ion concentration in aqueous phase, adsorbent dose and time of contact of phases on the efficiency of V(V) was determined. Based on the obtained results, the mechanism and kinetics of the adsorption processes occurring on the biochar originating from the wet distiller grains as adsorbents with the greatest affinity for the V(V) ions were characterized, using isotherm models of Langmuir, Freundlich, Temkin and Dubinin-Radushkevich and pseudo-first-order, pseudo-second-order as well as intraparticle diffusion kinetic models. Under the constant process conditions (pH = 3.0; m = 0.5 g; c₀ = 50 mg/L) the order of V(V) ions removal from aqueous solutions was as follows: BC2 > BC1 = BC3. The biochar BC2 exhibited the maximum sorption capacity of 1.61 mg V(V)/g. The experimental kinetic data show the adsorption course according to the pseudo-second order model.

Biochars and activated carbons as adsorbents of inorganic and organic compounds from multicomponent systems - A review

Biochars are obtained by biomass pyrolysis, whereas activated carbon is a biochar that has undergone chemical or physical activation. Owing to the large surface area and easy surface modification both solids are widely applied as adsorbents. They are low-costs materials, they could be regenerated and their disposal is not troublesome. Adsorption of heavy metals, dyes, pharmaceuticals on the surface of biochars and activated carbons, from simple systems of adsorbate containing only one compound, are described extensively in the literature. The present paper provides an overview of reports on adsorption of inorganic and organic compounds onto these two types of adsorbents from the mixed adsorbate systems. The described adsorbate systems have been divided into those consisting of: two or more inorganic ions, two or more organic compounds and both of them (inorganic and organic ones). The research of this type is carried out much less frequently due to the more complicated description of interactions in the mixed adsorbate systems.

Steel slag as a potential adsorbent for efficient removal of Fe(II) from simulated acid mine drainage: adsorption performance and mechanism

Acid mine drainage is an extraordinarily acidic and highly heavy metal ion-contaminated leachate, seriously threatening the environment. In this work, an industrial solid waste of steel slag is the adsorbent to remediate the simulated acid mine drainage containing a large amount of Fe(II) ions. Due to the excellent physicochemical properties and structures, steel slag exhibited remarkable Fe(II) removal performance. Its maximum removal efficiency was up to 100%. The initial pH, the dosage and particle size of steel slag, and initial concentration of heavy metal ions on Fe(II) removal efficiency were determined. The pseudo-second-order model and Freundlich isotherm model well described the adsorption behavior of steel slag, implying that the adsorption of Fe(II) by steel slag was mainly multilayer chemisorption. The thermodynamic study demonstrated that the adsorption process was endothermic and spontaneous; the enthalpy change was calculated to equal 91.21 kJ/mol. Mechanism study showed that the entire removal process of Fe(II) by steel slag was completed by electrostatic adsorption, chemical precipitation, and surface complexation in cooperation, and the chemical precipitation was the dominant mechanism. Meaningfully, this study provides a valuable strategy and path for engineering applications of AMD remediation by steel slag, which is prospective as an ideal candidate for Fe(II) ions elimination, inspiring the future development of "Treating the wastes with wastes."

Efficient removal of Cd (II) from aqueous solution by chitosan modified kiwi branch biochar

Production of cost-efficient composite materials from low-cost modified biochar for the removal of Cd (II) from wastewater is much needed to meet the growing needs of industrial wastewater treatments. A novel chitosan-modified kiwi branch biochar (CHKB) was fabricated as low-cost modified biochar for the removal of Cd (II) from aqueous solution. Batch adsorption and characterization experiments indicated that the modification of kiwi biochar (KB) by chitosan remarkably improved its adsorption performance. The results revealed that the adsorption isotherms can be best described by a Langmuir model and that a pseudo-second-order model fits the Cd (II) adsorption kinetics well, which indicates that it is a monolayer process controlled by chemisorption. CHKB exhibited a Langmuir maximum adsorption capacity of Cd (II) (126.58 mg g^-1), whereas that of KB was only 4.26 mg g^-1. The adsorption ability of CHKB was improved by increasing the surface area and an abundance of surface functional groups (-OH, -NH, CO, etc.). The cation exchange, electrostatic interaction, surface complexation, and precipitation were the main mechanisms in the sorption of Cd (II) on CHKB. Excellent adsorption performance, low cost, and environmental-friendliness made CHKB a fantastic adsorbent for the removal of Cd (II) in wastewater.

Manganese oxide-modified biochar: production, characterization and applications for the removal of pollutants from aqueous environments - a review

The development of manganese (Mn) oxides (MnOx) modified biochar (MnOBC) for the removal of pollutants from water has received significant attention. However, a comprehensive review focusing on the use of MnOBC for the removal of organic and inorganic pollutants from water is missing. Therefore, the preparation and characterization of MnOBC, and its capacity for the removal of inorganic (e.g., toxic elements) and organic (e.g., antibiotics and dyes) from water have been discussed in relation to feedstock properties, pyrolysis temperature, modification ratio, and environmental conditions here. The removal mechanisms of pollutants by MnOBC and the fate of the sorbed pollutants onto MnOBC have been reviewed. The impregnation of biochar with MnOx improved its surface morphology, functional group modification, and elemental composition, and thus increased its sorption capacity. This review establishes a comprehensive understanding of synthesizing and using MnOBC as an effective biosorbent for remediation of contaminated aqueous environments.