Cadmium adsorption characteristics of biochars derived using various pine tree residues and pyrolysis temperatures

Pb/As simultaneous removal from soil leachate of Pb/Zn smelting sites by magnetic biochar

Lead (Pb) and arsenic (As) contaminated soils, caused by Pb and zinc (Zn) smelting activities, pose an urgent environmental issue. Magnetic biochar (MB) has been regarded as an increasingly appealing candidate for the remediation of multi-metals in contaminated soils or their leachate. Finding economically feasible preparation methods for MB and demonstrating its remediation potential is desperately required for the remediation of such complex smelting sites. In this study, a modified MB was prepared using an optimized co-precipitation method, and its application potential for Pb/As simultaneous removal based on the basic properties of a typical Pb/Zn smelting site was evaluated. The surface modifications of MB facilitated the encapsulation of various ultrafine iron oxide particles, predominantly γ-Fe2O3 and Fe3O4, whilst notably enhancing the presence of oxygen-containing surface functional groups. The adsorption of Pb(II) and As(III) by MB was well-described using the pseudo-second-order adsorption and Langmuir models. The existence of SO42- and Ca2+ in the soil leachate competed with the adsorption sites for Pb(II) and As(III). Notably, within the pH range of 5-9, the adsorption efficiency of Pb(II) by MB increased with the rising solution pH, whereas alterations in pH minimally affected the removal rate of As(III), maintaining a consistent removal rate exceeding 95%. Furthermore, dissolved organic matter (DOM) abundant in organic functional groups, particularly CO and CC groups, significantly augmented the adsorption affinity for both Pb(II) and As(III). An application rate of 2 g/L could effectively reduce the concentration of Pb(II) and As(III) in soil leachate to <0.05 mg/L. The findings demonstrated the potential of the prepared MB for simultaneous removal of As(III) and Pb(II) in soil leachate, which should be beneficial to multi-metals polluted soil remediation in Pb/Zn smelting sites.

Machine learning screening of biomass precursors to prepare biomass carbon for organic wastewater purification: A review

In the past decades, the amount of biomass waste has continuously increased in human living environments, and it has attracted more and more attention. Biomass is regarded as the most high-quality and cost-effective precursor material for the preparation carbon of adsorbents and catalysts. The application of biomass carbon has extensively explored. The efficient application of biomass carbon in organic wastewater purification were reviewed. With briefly introducing biomass types, the latest progress of Machine learning in guiding the preparation and application of biomass carbon was emphasized. The key factors in constructing efficient biomass carbon for adsorption and catalytic applications were discussed. Based on the functional groups, rich pore structure and active site of biomass carbon, it exhibits high efficiency in water purification performance in the fields of adsorption and catalysis. In addition, out of a firm belief in the enormous potential of biomass carbon, the remaining challenges and future research directions were discussed.

Enhanced copper removal by magnesium modified biochar derived from Alternanthera philoxeroides

Adsorption processes are being widely used by various researchers for the removal of heavy metals from waste streams and biochar has been frequently used as an adsorbent. In this study, a MgO-loaded biochar derived from Alternanthera philoxeroides (MAPB) was synthesized for the removal of Cu(II). Compared with other biochar absorbents, MAPB showed a relatively slow adsorption kinetics, but an effective removal of Cu(II) with a maximum sorption capacity of 1, 238 mg/g. The adsorption mechanism of Cu(II) by MAPB was mainly controlled by chemical precipitation as Cu2(OH)3NO3, complexation and ion replacement. Fixed bed column with MAPB packed in same dosage (1, 000 mg) and different bed depth (1.3, 2.6 and 3.9 cm) showed that the increased of bed depth by mixing MAPB with quartz sand could increase the removal of Cu(II). The fitted breakthrough (BT) models showed that mixing MAPB with support media could reduce the mass transfer rate, increase the dynamic adsorption capacity and BT time. Therefore, MAPB adsorbent act as a highly efficient long-term adsorbent for Cu(II) contaminated water treatment may have great ecological and environmental significance.

Birnessite-Type MnO2 Modified Sustainable Biomass Fiber toward Adsorption Removal Heavy Metal Ion from Actual River Aquatic Environment

In this work, a novel birnessite-type MnO2 modified corn husk sustainable biomass fiber (MnO2@CHF) adsorbent was fabricated for efficient cadmium (Cd) removal from aquatic environments. MnO2@CHF was designed from KMnO4 hydrothermally treated with corn husk fibers. Various characterization revealed that MnO2@CHF possessed the hierarchical structure nanosheets, large specific surface area, and multiple oxygen-containing functional groups. Batch adsorption experimental results indicated that the highest Cd (II) removal rate could be obtained at the optimal conditions of adsorbent amount of 0.200 g/L, adsorption time of 600 min, pH 6.00, and temperature of 40.0 °C. Adsorption isotherm and kinetics results showed that Cd (II) adsorption behavior on MnO2@CHF was a monolayer adsorption process and dominated by chemisorption and intraparticle diffusion. The optimum adsorption capacity (Langmuir model) of Cd (II) on MnO2@CHF was 23.0 mg/g, which was higher than those of other reported common biomass adsorbent materials. Further investigation indicated that the adsorption of Cd (II) on MnO2@CHF involved mainly ion exchange, surface complexation, redox reaction, and electrostatic attraction. Moreover, the maximum Cd (II) removal rate on MnO2@CHF from natural river samples (Xicheng Canal) could reach 59.2% during the first cycle test. This study showed that MnO2@CHF was an ideal candidate in Cd (II) practical application treatment, providing references for resource utilization of agricultural wastes for heavy metal removal.

New-style electrokinetic-adsorption remediation of cadmium-contaminated soil using double-group electrodes coupled with chitosan-activated carbon composite membranes

Global soil cadmium (Cd(II)) contamination threatens the soil environment, food safety, and human health. Conventional electrokinetic remediation (EKR) and enhancement methods usually operate in strong electric fields, leading to strong side reactions and uneven removal. In this work, to remove Cd(II) from soil effectively in a low-voltage electric field, a new-style electrokinetic-adsorption remediation using double-group electrodes coupled with chitosan-activated carbon composite membranes (DE-EKR-CAC) was developed. Chitosan-activated carbon (CAC) composite membranes were synthesized for easy recovery and reuse of adsorbents. The effects of pH, contact time, initial concentration, and foreign ions on the removal of Cd(II) by the CAC composite membranes were determined. The CAC composite membranes performed well except in a strongly acidic environment (pH = 2.0). The soil pH varied between 3.4 and 5.0 in DE-EKR-CAC, where the CAC composite membranes were applicable. High concentrations of Ca2+ interfered with the adsorption of Cd(II), which means that the selectivity of CAC composite membranes for Cd(II) is not high enough. The Langmuir (R2 = 0.999) and pseudo-second-order kinetic (R2 = 1.0) models revealed the monolayer coverage and chemisorption mechanism, and the maximum adsorption capacity was 40.81 mg/g. Furthermore, SEM, FTIR, and XPS analyses suggest that physical adsorption, complexation of oxygen-containing functional groups, chelation of amino groups, and ion exchange are potential mechanisms for the adsorption of Cd(II) on CAC. DE-EKR-CAC performed better than the group remediated with one set of electrodes, with higher removal efficiencies and more uniform removal. The lowest energy consumption was 3.33 kWh/m3, which is lower than other enhancement methods. Separation of CAC composite membranes from soil is easy, and reuse performance is good. DE-EKR-CAC provides a potential option for Cd(II) removal from soil because of its better performance using low-voltage direct current, low energy consumption, and ease of recycling the adsorbent.

Separable calcium sulphate modified biochar gel beads for efficient cadmium removal from wastewater

This study outlines the synthesis of a novel, cost-effective composite material comprising calcium sulphate-modified biochar (Ca-BC) cross-linked with polyethyleneimine (PEI) and sodium alginate (SA), which was subsequently transformed into gel beads (Ca-BC@PEI-SA). These beads were engineered to enable effective cadmium ion (Cd(II)) adsorption from wastewater. Batch adsorption experiments were conducted to evaluate the effects of pH, contact time, temperature, and coexisting ions on adsorption performance. The isotherms and kinetics in the adsorption process were investigated. The results indicated that the removal of Cd(II) by Ca-BC@PEI-SA adheres more closely to the Langmuir model, with maximum adsorption capacities of 138.44 mg/g (15 °C), 151.98 mg/g (25 °C), and 165.56 mg/g (35 °C) at different temperatures. The pseudo-secondary model fit well with Cd(II) adsorption kinetics, suggesting that the removal process was a monolayer process controlled by chemisorption. Moreover, the mechanical strength of the Ca-BC@PEI-SA gel beads allowed easy recovery and reduced secondary contamination. In addition, the adsorption capacity remained nearly constant after four cycles. The main Cd(II) adsorption mechanisms involved surface complexation, ion exchange, and cation-π-bonding interactions.

Use of thermally activated Fenton sludge for Cd removal in zinc smelter wastewater: Mechanism and feasibility of Cd removal

Fenton sludge is a byproduct of the Fenton process that contains large amounts of Fe and Ca. Because of the secondary contamination generated during the disposal of this byproduct, ecofriendly treatment methods are needed. In this study, we used Fenton sludge to remove the Cd discharged from a zinc smelter factory, using thermal activation to enhance the Cd adsorption capacity. Among the various temperatures considered (300-900 °C), the Fenton sludge that was thermally activated at 900 °C (TA-FS-900) adsorbed the highest amount of Cd because of its high specific surface area and high Fe content. Cd was adsorbed onto TA-FS-900 via complexation with C-OH, C-COOH, FeO-, and FeOH and cation exchange with Ca2+. The maximum adsorption of TA-FS-900 was 260.2 mg/g, indicating that TA-FS-900 is an efficient adsorbent, comparable to those reported in the literature. The initial Cd concentration in the zinc smelter wastewater discharged was 105.7 mg/L, 98.4% of which was removed by applying TA-FS-900, suggesting the applicability of TA-FS-900 for real wastewater containing high concentrations of various cations and anions. The leaching of heavy metals from TA-FS-900 was within the EPA standard limits. We concluded that the environmental impact of Fenton sludge disposal can be reduced, and the use of Fenton sludge can add value to the treatment of industrial wastewater in terms of the circular economy and environment.

Aromaticity, polarity, and longevity of biochar derived from disposable bamboo chopsticks waste for environmental application

Transforming disposable bamboo chopstick (DBC) wastes into biochar is an effective way to achieve waste-to-resource conversion. This research focused on the elemental and chemical composition of biochar and revealed how these properties affect biochar performance in real-world applications, particularly with respect to climate change mitigation. This research is aimed at examining the effect of pyrolysis temperature on the aromaticity, polarity, and longevity of DBC biochar. The DBC feedstock was pyrolyzed at different temperatures of 400 °C, 450 °C, 500 °C, and 550 °C with a holding time of 20 min at a constant heating rate of 20 °C min-1. The chemical composition, including carbon (C), hydrogen (H), nitrogen (N), oxygen (O), volatile matter (VM), ash, and fixed carbon (FC) contents, were analyzed. The aromaticity, polarity, and longevity of biochar are presented by the atomic ratios of H/C, O/C, (O + N)/C, and C/N, and these ratios are used to determine the potential of biochar for use in climate change mitigation applications. The findings demonstrated that DBC biochar produced at various pyrolysis temperatures contained C contents ranging from 77.54% to 88.06%, ash contents ranging from 2.62% to 2.99%, and a half-life of over 1000 years (O/C < 0.2). Pyrolysis temperature significantly affected biochar properties, as supported by the results for the FC/ash ratio (>10); the ash, FC, C, and N contents increased with increasing temperature; in contrast, the VM, H, and O contents decreased. The results revealed that DBC wastes are the potential feedstock to produce good-quality biochar that could be applied for environmental purposes. Furthermore, the research demonstrated that the best-performing DBC biochar was produced at 500 °C, which had the highest C content, aromaticity, and longevity and the lowest polarity as represented by the values of O/C, H/C, and (O + N)/C, and this biochar could be applied for climate change mitigation purposes.

Remediation of cadmium contaminated soil using K2FeO4 modified vinasse biochar

The remediation of cadmium (Cd) contaminated soil is challenging for agricultural practices. In this study, a novel vinasse biochar modified by potassium ferrate (K₂FeO₄) was synthesized to immobilize Cd in agricultural soil. Three biochars [i.e., vinasse biochar (BC), KMnO₄ modified vinasse biochar (MnBC), and K₂FeO₄ modified vinasse biochar (FeBC)] were applied to compare their efficiencies of Cd immobilization. The results showed that the orders of pH, ash content, and functional groups in different biochar were the same following BC < MnBC < FeBC. Scanning electron microscope images showed that the FeBC has more micropores than MnBC and BC. X-ray diffraction identified manganese oxides and iron oxides within MnBC and FeBC, indicating that Mn and Fe were well loaded on the biochar. In the soil-based pot experiment, both MnBC and FeBC significantly reduced soil available Cd by 23-38% and 36-45% compared with the control, respectively (p < 0.05). In addition, the application of BC, MnBC, and FeBC significantly increased the yield, chlorophyll, and vitamin C of Chinese cabbage (p < 0.05), and decreased its Cd uptake compared with the control. Notably, shoot Cd significantly reduced when 2% FeBC was applied (p < 0.05). Overall, using K₂FeO₄ to modify vinasse biochar enriched the surface functional groups and minerals as well as reduced Cd availability in soil and its uptake by the plant. Our study showed that K₂FeO₄ modified vinasse biochar could be used as an ideal amendment for the remediation of Cd-contaminated soil.

NaHCO3 activated sludge-derived biochar by KMnO4 modification for Cd(II) removal from aqueous solutions

The surface flat pristine biochar provides limited adsorption sites for Cd(II) adsorption. To address this issue, a novel sludge-derived biochar (MNBC) was prepared by NaHCO₃ activation and KMnO₄ modification. The batch adsorption experiments illustrated that the maximum adsorption capacity of MNBC was twice that of pristine biochar and reached equilibrium more quickly. The pseudo-second order and Langmuir model were more suitable for analyzing the Cd(II) adsorption process on MNBC. Na⁺, K⁺, Mg²⁺, Ca²⁺, Cl^- and NO^-₃ had no effect on the Cd(II) removal. Cu²⁺ and Pb²⁺ inhibited the Cd(II) removal, while PO^3-₄ and humic acid (HA) promoted it. After 5 repeated experiments, the Cd(II) removal efficiency on MNBC was 90.24%. The Cd(II) removal efficiency of MNBC in different actual water bodies was over 98%. Furthermore, MNBC owned excellent Cd(II) adsorption performance in fixed bed experiments, and the effective treatment capacity was 450 BV. The co-precipitation, complexation, ion exchange and Cd(II)-π interaction were involved in Cd(II) removal mechanism. XPS analysis showed that NaHCO₃ activation and KMnO₄ modification enhanced the complexation ability of MNBC to Cd(II). The results suggested that MNBC can be used as an effective adsorbent for treating of Cd-contaminated wastewater.

Enhanced cadmium removal by biochar and iron oxides composite: Material interactions and pore structure

The combination of biochar (BC) and iron minerals improves their pollutant adsorption capacity. However, little is known about the reactivity of BC-iron mineral composites regarding their interaction and change in the pore structure. In this study, the mechanism of cadmium (Cd) adsorption by BC-iron oxide composites, such as BC combined with ferrihydrite (FH) or goethite (GT), was explored. The synergistic effect of the BC-FH composite significantly improved its Cd adsorption capacity. The adsorption efficiencies of BC-FH and BC-GT increased by 15.0% and 10.8%, respectively, compared with that of uncombined BC, FH, and GT. The strong Cd adsorption by BC-FH was attributed to stable interactions and stereoscopic pore filling between BC and FH. The scanning electron microscopy results showed that FH particles entered the BC pores, whereas GT particles were loaded onto the BC surface. FTIR spectroscopy showed that GT covered a larger area of the BC surface than FH. After loading FH and GT, BC porosities decreased by 9.3% and 4.1%, respectively. Quantum chemical calculations and independent gradient mode analysis showed that van der Waals interactions, H-bonds, and covalent-like interactions maintained stability between iron minerals and BC. Additionally, humic acid increased the agglomeration of iron oxides and formed larger particles, causing additional aggregates to load onto the BC surface instead of entering the BC pores. Our results provide theoretical support to reveal the interfacial behavior of BC-iron mineral composites in soil and provide a reference for field applications of these materials for pollution control and environmental remediation.

Twice-milled magnetic biochar: A recyclable material for efficient removal of methylene blue from wastewater

Although magnetic modification has potential for preparing recyclable biochar, the traditional preparation methods of loading magnetic materials on biochar will probably lead to pore blockage and consequently remarkable adsorption recession. Herein, a preparation method was developed in which ball milled biochar was loaded with ultrafine magnetite and then milled for a second time, thus generating a magnetic, recyclable biochar with minimal pore blockage. The deposits of magnetite did not significantly wrap the biochar, although a decreased sorption performance was still detectable. Benefitting from the extra milling step, surface functional groups and specific surface areas of the adsorbents were largely restored, thus leading to a 93.8 % recovery adsorption of 84.6 ± 2.5 mg/L on methylene blue. Meanwhile, the recyclability of the material was not affected. The adsorption was driven by multiple interactions. These twice-milled magnetic biochar is quite outstanding for sustainable removal of aqueous contaminants with its recyclability and high sorption efficiency.

Effects of biochars derived from four crop straws on a Cd-polluted cinnamon soil

Crop straw biochar is an efficient and low-cost alternative amendment for heavy metal immobilization in acidic soil. However, reports on the effect of these biochars on the amendment of actual Cd-polluted calcareous soil are limited. Therefore, four biochars, derived from peanut, rice, maize, and wheat straws, were applied to determine the changes in the chemical properties of alkaline cinnamon soil and effects on Cd immobilization. The results showed that the cation exchange capacity and the contents of organic C, Mehlich-3 K, and Mehlich-3 P in the biochar-amended soil increased by 4.87-22.02%, 68.78-218.83%, 1.9-10.3 times, and 19.18-74.40%, respectively, indicating the potential high performance of biochar in improving soil fertility and productivity. The Community Bureau of Reference sequential extraction results showed that decrease in acid-extractable Cd resulted in a reduced availability of Cd. Thus, crop straw biochar could be a promising alternative for soil Cd decontamination and fertilization.

Effective Usage of Biochar and Microorganisms for the Removal of Heavy Metal Ions and Pesticides

The bioremediation of heavy metal ions and pesticides is both cost-effective and environmentally friendly. Microbial remediation is considered superior to conventional abiotic remediation processes, due to its cost-effectiveness, decrement of biological and chemical sludge, selectivity toward specific metal ions, and high removal efficiency in dilute effluents. Immobilization technology using biochar as a carrier is one important approach for advancing microbial remediation. This article provides an overview of biochar-based materials, including their design and production strategies, physicochemical properties, and applications as adsorbents and support for microorganisms. Microorganisms that can cope with the various heavy metal ions and/or pesticides that enter the environment are also outlined in this review. Pesticide and heavy metal bioremediation can be influenced by microbial activity, pollutant bioavailability, and environmental factors, such as pH and temperature. Furthermore, by elucidating the interaction mechanisms, this paper summarizes the microbe-mediated remediation of heavy metals and pesticides. In this review, we also compile and discuss those works focusing on the study of various bioremediation strategies utilizing biochar and microorganisms and how the immobilized bacteria on biochar contribute to the improvement of bioremediation strategies. There is also a summary of the sources and harmful effects of pesticides and heavy metals. Finally, based on the research described above, this study outlines the future scope of this field.

Removal of cadmium in aqueous solutions using a ball milling-assisted one-pot pyrolyzed iron-biochar composite derived from cotton husk

A novel iron-biochar composite adsorbent was produced via ball milling-assisted one-pot pyrolyzed BM-nZVI-BC 800. Characterization proved that nano zero valent iron was successfully embedded in the newly produced biochar, and the nZVI payload was higher than that of traditional one-pot pyrolyzed methods. BM-nZVI-BC 800 provided a high adsorption performance of cadmium reaching 96.40 mg·g^-1 during batch testing. Alkaline conditions were beneficial for cadmium removal of BM-nZVI-BC 800. The pseudo-second-order kinetic model and Langmuir isotherm fitted better, demonstrating that the Cd adsorption on the BM-nZVI-BC 800 was a chemical and surface process. The intraparticle diffusion controlled the adsorption of BM-nZVI-BC 800. The physisorption dominated by high specific surface area and mesoporous structure was the primary mechanism in the removal of cadmium, though electrostatic attraction and complexation also played a secondary role in cadmium adsorption. Compared to adsorbents prepared by more traditional methods, the efficiencies of the ball milling-assisted one-pot pyrolyzed method appears superior.

Carbon-based adsorbents as proficient tools for the removal of heavy metals from aqueous solution: A state of art-review emphasizing recent progress and prospects

Carbon-centric adsorbents (CCA) are diverse forms, from simple biochar (BC) to graphene derivatives, carbon nanotubes (CNTs), and activated carbon (AC), which have been vastly explored for their removal of a plethora of pollutants, including heavy metals (HM). The prominent features of CCA are their operational attributes like extensive surface area, the occurrence of flexible surface functional groups, etc. This work offers a comprehensive examination of contemporary research on CCA for their superior metal removal aptitude and performances in simulated solutions and wastewater flows; via portraying the recent research advances as an outlook on the appliances of CACs for heavy metal adsorption for removal via distinct forms like AC, BC, Graphene oxide (GO), and CNTs. The bibliometric analysis tool was employed to highlight the number of documents, country-wise contribution, and co-occurrence mapping based on the Scopus database. The coverage of research works in this review is limited to the last 5 years (2017-2021) to highlight recent progress and prospects in using CCAs such as AC, BC, GO, and CNTs to remove HM from aqueous media, which makes the review unique. Besides an overview of the common mechanisms of CACs, the future scope of CAC, especially towards HM mitigation, is also discussed in this review. This review endorses that further efforts should be commenced to enhance the repertory of CCAs that effectively eliminate multiple targeted metals in both simulated and real wastewater.

Remediation of heavy metal polluted waters using activated carbon from lignocellulosic biomass: An update of recent trends

The use of a cheap and effective adsorption approach based on biomass-activated carbon (AC) to remediate heavy metal contamination is clearly desirable for developing countries that are economically disadvantaged yet have abundant biomass. Therefore, this review provides an update of recent works utilizing biomass waste-AC to adsorb commonly-encountered adsorbates like Cr, Pb, Cu, Cd, Hg, and As. Various biomass wastes were employed in synthesizing AC via two-steps processing; oxygen-free carbonization followed by activation. In recent works related to the activation step, the microwave technique is growing in popularity compared to the more conventional physical/chemical activation method because the microwave technique can ensure a more uniform energy distribution in the solid adsorbent, resulting in enhanced surface area. Nonetheless, chemical activation is still generally preferred for its ease of operation, lower cost, and shorter preparation time. Several mechanisms related to heavy metal adsorption on biomass wastes-AC were also discussed in detail, such as (i) - physical adsorption/deposition of metals, (ii) - ion-exchange between protonated oxygen-containing functional groups (-OH, -COOH) and divalent metal cations (M²⁺), (iii) - electrostatic interaction between oppositely-charged ions, (iv) - surface complexation between functional groups (-OH, O^2-, -CO-NH-, and -COOH) and heavy metal ions/complexes, and (v) - precipitation/co-precipitation technique. Additionally, key parameters affecting the adsorption performance were scrutinized. In general, this review offers a comprehensive insight into the production of AC from lignocellulosic biomass and its application in treating heavy metals-polluted water, showing that biomass-originated AC could bring great benefits to the environment, economy, and sustainability.

Application of Orange Peel Waste as Adsorbent for Methylene Blue and Cd2+ Simultaneous Remediation

Pollution by dyes and heavy metals is one of the main concerns at the environmental level due to their toxicity and inefficient elimination by traditional water treatment. Orange peel (OP) without any treatment was applied to effectively eliminate methylene blue (MB) and cadmium ions (Cd²⁺) in mono- and multicomponent systems. Although the single adsorption processes for MB and Cd²⁺ have been investigated, the effects and mechanisms of interactions among multicomponent systems are still unclear. Batch experiments showed that in monocomponent systems, the maximum adsorption capacities were 0.7824 mmol g⁻¹ for MB and 0.2884 mmol g⁻¹ for Cd²⁺, while in multicomponent systems (Cd²⁺ and MB), both contaminants competed for the adsorption sites on OP. Particularly, a synergic effect was observed since the adsorption capacity of Cd²⁺ increased compared to the monocomponent system. Results of desorption and adsorbent reuse confirmed that the adsorbent presents good regeneration performance. The low cost of this material and its capacity for the individual or simultaneous removal of Cd²⁺ and MB in aqueous solutions makes it a potential adsorbent for polluted water treatment processes.

Copper removal from aqueous solution using chemical precipitation and adsorption by Himalayan Pine Forest Residue as Biochar

This research deals with the use of pine residue biochar as an adsorbent for the removal of copper from aqueous solution which is a major component of printed circuit boards from E-waste. Biochar was produced from pine residue such as bark, cone and needle through pyrolysis, and the effect of temperature on biochar properties was assessed. The biochar yield of about 33% and maximum surface area of 368 m²/g was obtained at pyrolysis temperature of 650°C. FTIR analysis revealed the existence of C-O, O-H and C = C functional groups on the surface of biochars. The point of zero charge of pine biochars were in the range 5.55 to 5.75. Batch adsorption studies revealed maximum copper adsorption capacity of 60-81 mg/g at near neutral pH. The batch adsorption data fitted well with Langmuir isotherm and followed the pseudo-second order kinetics. Adsorption of copper onto the biochar surface mainly followed physisorption which was reversible in nature. Desorption study revealed that pine biochar could be reused up to three cycles. Column adsorption data fitted well with Thomas model. These investigations revealed that the pine residue, which otherwise results in adverse environmental impacts, can be converted into useful resource like biochar as a heavy metal adsorbent.

Potential exploration of Fe3O4/biochar from sludge as the media of bioretention system and its comparison with conventional media

The selection and configuration of soil media are a core issue of the bioretention system. A porous carbon material of Fe₃O₄/biochar (BSF) was prepared by adding pickling wastewater to modified sludge biochar, which could serve as a good adsorption performance and cheap media for bioretention system. Through the analytic hierarchy process (AHP), different media were evaluated according to their characteristics. By comparing the characteristics of BSF to bio-ceramic (BC), zeolite (ZE), and activated carbon (AC), it was found that BSF has a larger specific surface area and pore volume. The hydrological characteristics of the medium were also tested. The results show that BSF has better water-absorbing quality and hydraulic conductivity than the other three media, but the water-retention property of the medium seems to be inferior. BSF has stable adsorption performance for ammonia nitrogen (NH₄⁺-N) and total phosphorus (TP) in rainwater. Its high adsorption capacity is maintained at 5-35°C, but it is very susceptible to pH factors. The adsorption process by BSF and other media conforms to pseudo-second-order kinetics and the Langmuir model in rainwater. In general, the performance of BSF is shown to be superior to BC, ZE, and AC, making it a potential medium for bioretention system.

Optimization of the raw materials of biochars for the adsorption of heavy metal ions from aqueous solution

In this paper, the material types were preferentially selected for different kinds of heavy metals, the effect of calcination temperatures on metal adsorption was investigated, and the adsorption mechanism was explored and summarized. The results show that the pseudo-first-order kinetic was better to fit the adsorption of heavy metals. The biomass type and pyrolysis temperature had an effect on the rate at which heavy metals were absorbed. Based on their adsorbed capacity, 350 °C pyrolyzed corn stalk char, 550 °C pyrolyzed peanut shell char, 450 °C pyrolyzed peanut shell char, 450 °C pyrolyzed peanut shell char, and 500 °C pyrolyzed wheat stalk char were shown to be the best adsorbents for Cr₂O₇^2-, Cd²⁺, Cu²⁺, Zn²⁺ and Pb²⁺, respectively. The largest adsorption rate were in the order of Cr⁶⁺ (Cr₂O₇^2-, 0.5380 /min) > Pb²⁺ (0.2276 /min) > Cd²⁺ (0.1354 /min) > Cu²⁺ (0.1273 /min) > Zn²⁺ (0.1000 /min), which might be positively related to the ion radius. Meanwhile, the yield of biomass decreased from 43.9% to 29.0% with the increase of pyrolysis temperature from 350 °C to 550 °C. In addition, the specific surface area and functional groups of the biochar, as well as the ionic radius and initial concentration of heavy metals affect the adsorption rate.

Influence of salinity on heavy metal and oil removal from hypersaline oilfield-produced water by electrocoagulation: mechanistic insights

The focus of the present study was to explore how and to what extent ultrahigh salinity affects the adsorption of cadmium and hydrocarbon pollutants onto aluminum hydroxide adsorbents formed in an electrocoagulation process. The changes in the nature and structure of the electro-generated aluminum particles and the possible removal mechanisms due to high salt content were investigated by using FE-SEM/EDS, FTIR, BET, and XRD analyses. The pseudo-second order and Freundlich models proved to fit the data for cadmium adsorption onto the aluminum hydroxides best. It was demonstrated that the adsorption capacities were significantly affected by the high salinity. With the rise of the salinity from 2 to 170 g/L, the cadmium and COD removal yields dropped from 81 to 60% and from 90 to 72%. The increase of the oil content led to the enhanced cadmium adsorption capacity due to surface complexation and ion exchange mechanisms. It was proved that Lagergren pseudo-first-order kinetic model could justify COD abatement trends. FTIR spectra depicted that the negative impact of high salinities on the adsorption was due to causing the formation of less stable adsorbents. According to BET analysis, the occurrence of much wider pore size distribution and smaller specific surface area in high salinity case was the main reason for the decreased adsorption capacity. Based on XRD analysis, the higher crystallinity of the produced aluminum hydroxide particles and their consequential smaller surface areas resulted in the lower adsorption capacity in the hypersaline environment. It was concluded that adsorption via inner-sphere and outer-sphere complexation and sweep flocculation were the possible removal mechanisms. Total treatment cost of 8.75 and 3.49 €/m3 were estimated for low and ultrahigh salinity conditions.

Effects of biochar pyrolysis temperature on thermal properties of polyethylene glycol/biochar composites as shape-stable biocomposite phase change materials

The characteristics of biochar are of great significance to its application in the field of phase change energy storage. The objective of this research was to explore the effects of pyrolysis temperature on the characteristics of a biochar matrix and further on the heat energy storage properties of the promising green biochar-supported shape-stable biocomposite PCMs (ss-BCPCMs). Corn straw biochars (CSBCs) obtained under different pyrolysis conditions were loaded with polyethylene glycol (PEG) by an ultrasound-assisted vacuum impregnation method. The micro-morphology, specific surface area, pore structure and surface properties of biochar have been characterized and analyzed by scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) method and Fourier transform infrared spectroscopy (FTIR). The thermal properties (chemical stability, latent heat storage, thermal conductivity, thermal stability, and thermal insulation) of PEG/CSBC composites have been characterized by FTIR, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and laser flash analysis (LFA). The study revealed that both pore structure and surface activity of biochar are key factors affecting the energy storage performance of biochar-based ss-BCPCMs. The obtained PEG/CSBC composite showed a high latent heat storage up to 100.2 J g⁻¹, good shape stability and leakage resistance, suggesting its high thermal storage stability that is beneficial for thermal energy storage applications. In addition, its excellent photothermal conversion efficiency (68.95%) provides application potential in photothermal energy storage.

The micropore and mesopore of biochar and the interaction between PEG and biochar surface effectively prevented the leakage of PEG and affected the crystallization and adsorption properties of PEG and the heat storage of composite PCMs.

Novel Zn-Fe engineered kiwi branch biochar for the removal of Pb(II) from aqueous solution

In this study, a novel adsorbent made from kiwi branch biochar modified with Zn-Fe (KB/Zn-Fe) was compared with original biochar to the Pb(II)'s adsorptivity from waste water. The adsorbent was synthetized by liquid-phase deposition. Batches of sorption tests were performed, and the biochars' representative properties were tested. Characterizations revealed the physicochemical properties of biochars and showed that the KB/Zn-Fe composites were successfully synthesized. The Langmuir model and pseudo-second-order kinetic model were proven to satisfactorily fit the original biochar and KB/Zn-Fe. The KB/Zn-Fe showed Langmuir maximum adsorption ability to Pb (II) in aqueous solution of 161.29 mg g^-1, compared with 36.76 mg g^-1 for original biochar. The adsorption ability of Pb(II) decreased and the Pb(II) removal efficiency increased with increasing biochar dose. The effect of co-existence of NO₃^- to the absorptive capacity of KB/Zn-Fe on Pb(II) was unremarkable, but Cl^- could increase the absorptive capacity. Multiple Pb(II) adsorption mechanisms by KB/Zn-Fe include surface precipitation of metal hydroxides, complexation with active functional groups and ion-exchange. This work provides guidance for future production of biochar with efficient adsorption ability, which could be used to remove Pb(II) ions from wastewater.

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.

A critical review of biochar-based materials for the remediation of heavy metal contaminated environment: Applications and practical evaluations

The contamination of heavy metals (HMs) in the environment has aroused a global concern. The valid remediation of HM contaminated environment is a highly significant issue. As alternative to carbon materials, biochar has been vastly documented for the remediation of HM contaminated environment. However, there are some possible imperfections to meet the actual remediation tasks as the finite properties of raw biochar, and the remediation process is complex and unexpectedly. This review focuses on the progress made on environmental HM remediation by biochar-based materials within the past six years. The property analysis and key modifications of biochar are summarized inspired by their applicability or necessity for HM decontamination, and the environmental remediation as well as the implicated mechanisms are thoroughly elaborated from multiple pivotal sides. The evaluations of practical application associated with biochar amendment are also presented. Finally, some pertinent improvements and research directions are proposed. To our knowledge, this article is the first time to make a systematic summary on the reliability and practicability of biochar-based materials for environmental HM remediation, and critically pointed out the existing issues to facilitate the judicious design of biochar-based materials and understanding the research trends. It is also aims to provide reference for subsequent research and propel the practical applications.

A review on adsorptive separation of toxic metals from aquatic system using biochar produced from agro-waste

Water is a basic and significant asset for living beings. Water assets are progressively diminishing due to huge populace development, industrial activities, urbanization and rural exercises. Few heavy metals include zinc, copper, lead, nickel, cadmium and so forth can easily transfer into the water system either direct or indirect activities of electroplating, mining, tannery, painting, fertilizer industries and so forth. The different treatment techniques have been utilized to eliminate the heavy metals from aquatic system, which includes coagulation/flocculation, precipitation, membrane filtration, oxidation, flotation, ion exchange, photo catalysis and adsorption. The adsorption technique is a better option than other techniques because it can eliminate heavy metals even at lower metal ions concentration, simplicity and better regeneration behavior. Agricultural wastes are low-cost biosorbent and typically containing cellulose have the ability to absorb a variety of contaminants. It is important to note that almost all agro wastes are no longer used in their original form but are instead processed in a variety of techniques to improve the adsorption capacity of the substance. The wide range of adsorption capacities for agro waste materials were observed and almost more than 99% removal of toxic pollutants from aquatic systems were achieved using modified agro-waste materials. The present review aims at the water pollution due to heavy metals, as well as various heavy metal removal treatment procedures. The primary objectives of this research is to include an overview of adsorption and various agriculture based adsorbents and its comparison in heavy metal removal.

Sorption–Desorption Behavior of Doxycycline in Soil–Manure Systems Amended with Mesquite Wood Waste Biochar

Elevated levels of doxycycline (DC) have been detected in the environment due to its extensive utilization as a veterinary antibiotic. Sorption–desorption behavior of DC in soil affects its transport, transformation, and availability in the environment. Thus, sorption–desorption behavior of DC was explored in three soils (S1, S2, and S3) after manure application with and without mesquite wood-waste-derived biochar (BC) pyrolyzed at 600 °C. Sorption batch trials demonstrated the highest DC sorption in soil S1 as compared to S2 and S3, either alone or in combination with manure or manure + BC. Chemical sorption and pore diffusion were involved in DC sorption, as indicated by the kinetic models. Soil S1 with manure + BC exhibited the highest Langmuir model predicted sorption capacity (18.930 mg g−1) compared with the other two soils. DC sorption capacity of soils was increased by 5.0–6.5-fold with the addition of manure, and 10–13-fold with BC application in a soil–manure system. In desorption trials, manure application resulted in 67%, 40%, and 41% increment in DC desorption in soil S1, S2, and S3, respectively, compared to the respective soils without manure application. In contrast, BC application reduced DC desorption by 73%, 66%, and 65%, in S1, S2, and S3, respectively, compared to the soils without any amendment. The highest DC sorption after BC application could be due to H bonding, π–π EDA interactions, and diffusion into the pores of BC. Hence, mesquite wood-waste-derived BC can effectively be used to enhance DC retention in contaminated soil to ensure a sustainable ecosystem.

Application of co-pyrolysis biochar for the adsorption and immobilization of heavy metals in contaminated environmental substrates

Heavy metal pollution has been considered as a serious threat to the environment and human in the past decades due to its toxic and unbiodegradable properties. Recently, extensive studies have been carried out on the removal of heavy metals, and various adsorption materials have been successfully developed. Among, biochar is a promising option because of its advantages of various biomass sources, abundant microporous channels and surface functional groups, as well as its attractive economic feasibility. However, the application of pristine biochar is limited by its low adsorption capacity and nonregenerative property. Co-pyrolysis biochar, produced from the pyrolysis of biomass with the addition of another biomass or non-biomass precursor, is potential in overcoming the limitation of pristine biochar and achieving superior performance for heavy metal adsorption and immobilization. Therefore, this article summarizes the recent advances in development and applications of co-pyrolysis biochar for adsorption and immobilization of various heavy metals in contaminated environmental substrates. In details, the production, characteristics and advantages of co-pyrolysis biochar are initially presented. Subsequently, the adsorption behaviors and mechanisms of different heavy metals (including Hg, Zn, Pb, Cu, Cd, Cr, As, etc.) in flue gas and wastewater by co-pyrolysis biochar are reviewed, as well as factors influencing their adsorption capacities. Meanwhile, the immobilization of heavy metals in both biochar itself and contaminated soils by co-pyrolysis biochar is discussed. Finally, the limitations of current studies and future prospects are proposed. It aims at providing a guideline for the exploitation and application of cost-effective and environmental-friendly co-pyrolysis biochar in the decontamination of environmental substrates.

Effect of biochar-immobilized Sphingomonas sp. PJ2 on bioremediation of PAHs and bacterial community composition in saline soil

This study aimed to investigate the bioremediation efficiency and bacterial regulation mechanism of biochar-immobilized bacterium (BM) in polycyclic aromatic hydrocarbon (PAH)-contaminated saline soil by conducting pot experiments. In BM treatment, PAH-degrading strain Sphingomonas sp. PJ2 was inoculated into biochar produced at 400 °C and 600 °C using the pine needles (BM400 and BM600). The removal rates of PAHs, soil physicochemical properties, abundance of PAH-ring hydroxylating dioxygenase (PAH-RHD), and bacterial community composition were determined. After 60 days of bioremediation, BM treatment significantly (P < 0.05) increased the removal rate of PAHs compared with biochar and PJ2 alone (15.94% and 37.3%, respectively). BM treatment clearly improved the physicochemical properties of saline soil. Moreover, the amount of Gram-positive PAH degraders increased in BM-treated soils compared with other treatments, and their gene abundance had a strong positive correlation with the removal rates of PAHs in soils (r = 0.896; P < 0.01). Furthermore, BM treatment increased the abundance of Sphingomonas genus, indicating that the strain PJ2 could survive and colonize in PAH-contaminated saline soil under the protection of biochar. This study provided an effective and green approach for the remediation and improvement of the PAH-contaminated saline soil.

Application of pinewood waste-derived biochar for the removal of nitrate and phosphate from single and binary solutions

We developed biochar by pyrolysis of pinewood wastes at different temperatures and investigated its potential to nitrate and phosphate from single and binary solutions. An in-depth characterization of biochar was carried out to study its physical, surface morphological and chemical characteristics using X-ray diffraction, Fourier transform infrared and scanning electron microscopy analyses. The impact of pyrolysis temperatures (300-600 °C) on the biochar yield, the biochar's elemental composition, and its adsorption characteristics was examined. Biochar produced at 600 °C showed a maximum uptake for both nitrate and phosphate due to its high C content (63.8%), pore volume (0.201 cm³/g), surface area (204.2 m²/g) and reduced acidic binding groups. The influence of pH, initial solute concentrations, contact time on the removal of a single solute at a time by biochar was examined. Results revealed that pinewood-derived biochar had its maximum performance at pH 2, with predicted equilibrium uptakes of 20.5 and 4.20 mg/g for phosphate and nitrate, respectively at initial solute concentrations of 60 mg/L within 360 min. The single solute isotherm was studied using the Freundlich, Langmuir and Toth models, and kinetics was described using the pseudo-first and -second order models. While using dual-solutes, biochar showed preference towards phosphate as confirmed by high affinity factor. The dual-solute kinetic experiments showed that around 95% of phosphate was removed within 45 min, whereas it took 240 min to achieve 95% total nitrate removal from the mixture. Thus, the biochar removes phosphate preferentially with high selectivity as compared to nitrate.

Characterization of pruned tea branch biochar and the mechanisms underlying its adsorption for cadmium in aqueous solution

In the present study, discarded pruned tea branch was used to prepare a new biochar, and the physicochemical properties and adsorption characteristics were investigated by characterization and batch experiments. With increasing pyrolysis temperature from 400 to 800 °C, the yield, specific surface area, and acidic functional groups had significant differences. The optimum adsorption conditions were determined as pH = 6 and dosage of 2 g L^-1. The pseudo-second-order kinetic and Langmuir isothermal model could fit well to the adsorption data, which showed that the adsorption process was dominated by monolayer chemical adsorption. The highest adsorption property (74.04 mg g^-1) was obtained by the pyrolysis of tea branch biochar (TBB) at 700 °C owing to the adsorption mechanisms, including surface complexation, precipitation, metal ion exchange, and Cd²⁺-π interaction. After five cycles of desorption, biochar still showed superior adsorption (80%). Hence, the TBB acted as a regenerable adsorbent for treating Cd²⁺-containing wastewater.

Pristine and Magnetic Kenaf Fiber Biochar for Cd2+ Adsorption from Aqueous Solution

Development of strategies for removing heavy metals from aquatic environments is in high demand. Cadmium is one of the most dangerous metals in the environment, even under extremely low quantities. In this study, kenaf and magnetic biochar composite were prepared for the adsorption of Cd2+. The synthesized biochar was characterized using (a vibrating-sample magnetometer VSM), Scanning electron microscopy (SEM), X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The adsorption batch study was carried out to investigate the influence of pH, kinetics, isotherm, and thermodynamics on Cd2+ adsorption. The characterization results demonstrated that the biochar contained iron particles that help in improving the textural properties (i.e., surface area and pore volume), increasing the number of oxygen-containing groups, and forming inner-sphere complexes with oxygen-containing groups. The adsorption study results show that optimum adsorption was achieved under pH 5-6. An increase in initial ion concentration and solution temperature resulted in increased adsorption capacity. Surface modification of biochar using iron oxide for imposing magnetic property allowed for easy separation by external magnet and regeneration. The magnetic biochar composite also showed a higher affinity to Cd2+ than the pristine biochar. The adsorption data fit well with the pseudo-second-order and the Langmuir isotherm, with the maximum adsorption capacity of 47.90 mg/g.

Preparation and Characterization of Physicochemical Properties of Spruce Cone Biochars Activated by CO2

In this study the pyrolysis of Norway spruce cones, a lignocellulosic biomass was made. The biochar product was obtained by means of the physical activation method. CO₂ was used as the activating gas. The surface properties of biochars were characterized by the nitrogen adsorption/desorption isotherms, scanning electron microscopy (SEM/EDS), X-ray fluorescence energy dispersion spectroscopy (ED-XRF), thermal analysis (TGA/DTA), infrared spectroscopy (ATR FT-IR), Raman spectroscopy and the Boehm’s titration method as well as the point of zero charge (pH_pzc). The adsorption capacity and the possibility of ammonia desorption (TPD) were also examined. It has been shown that spruce cones can be successfully used as a cheap precursor of well-developed surface biochars, characterized by a large pore volume and good sorption properties. All obtained activated biochars exhibit a largely microporous structure and an acidic character surface. The investigated activated materials have the specific surface areas from 112 to 1181 m² g⁻¹. The maximum NH₃ adsorption capacity of the activated biochar was determined to be 5.18 mg g⁻¹ (88.22 mmol g⁻¹) at 0 °C. These results indicate the applicability of spruce cones as a cheap precursor for the sustainable production of the cost-effective and environmentally friendly biochar adsorbent.

Mechanism of novel MoS2-modified biochar composites for removal of cadmium (II) from aqueous solutions

The purpose of this study was to develop a MoS₂-impregnated biochar (MoS₂@BC) via hydrothermal reaction for adsorption of cadmium (Cd) from an aqueous solution. The prepared adsorbents were characterized, and their abilities to remove Cd(II) were evaluated. The Langmuir and pseudo-second-order models better described the removal of Cd(II) by MoS₂@BC. The prepared MoS₂@BC exhibited excellent monolayer adsorption capacity. The S-containing functional groups on MoS₂@BC enhanced the adsorption of Cd(II). Multiple Cd(II) sorption mechanisms were identified; including Cd(II)-π interactions, ion exchange, electrostatic interaction, and complexation. The dominant mechanism involved Cd-O (38.3%) bonds and Cd-S complexation (61.7%) on MoS₂@BC. The as-prepared MoS₂@BC is both economical and efficient, making it an excellent material for environmental Cd(II) remediation.

The combined use of arbuscular mycorrhizal fungi, biochar and nitrogen fertilizer is most beneficial to cultivate Cichorium intybus L. in Cd-contaminated soil

We assessed Cichorium intybus L. (chicory) growth, nutrients and Cd uptake in the presence of arbuscular mycorrhizal fungi (AMF), biochar (BC) and nitrogen (N) fertilizer applications in experimental pot studies. Mycorrhizal colonization was improved by BC addition but not N addition. However, in the presence of AMF, BC and N had positive effects on shoot biomass and plants grown in the presence of all 3 components yielded the highest levels of shoot biomass compared to pair-wise combinations or individual components singly added. AMF inoculation also increased root biomass and this effect was apparent in the combinations that included AMF without BC. Fungal inoculation also led to increased contents of phosphorus (P), magnesium (Mg) and copper (Cu) in both chicory shoots and roots and potassium (K) and manganese (Mn) in roots. Moreover, in the presence of BC, AMF inoculation evidently enhanced the shoot Ca content. In contrast, the presence of AMF inhibited plant Cd absorption and BC addition further inhibited root Cd concentration following the AMF inoculation. Applying N fertilizer alone increased Cd transfering from soil to plants. However, when combined with use of AMF and BC, Cd toxicity to plants was reduced. This study demonstrated that AMF inoculation combined with BC and N fertilizer could improve chicory growth, nutrient absorption and reduction of Cd uptake in Cd-contaminated soil.

Removal of potentially toxic metal by biochar derived from rendered solid residue with high content of protein and bone tissue

The purpose of this study was to produce rendering animal carcass residue char (RACR-C) by pyrolyzing the solid residues of low-recyclable rendered pig carcasses and to evaluate their cadmium (Cd) adsorption characteristics and mechanisms. As the pyrolysis temperature increased, the inorganic content of RACR-C increased, while the carbon content decreased. In particular, the surface structure and chemistry of RACR-Cs prepared at different pyrolysis temperatures were well described by SEM-EDS, XRD, XRF, TGA, and FTIR. The Cd adsorption characteristics of RACR-C were in good agreement with the Langmuir isotherm and pseudo-second-order models, and the Cd adsorption capacities of RACR-Cs prepared at various pyrolysis temperatures were in the order of RACR-C500 (73.5 mg/g)> RACR-C600 (53.8 mg/g)> RACR-C400 (41.5 mg/g) " RACR-C250 (15.9 mg/g). The intraparticle diffusion model suggested that the adsorption of Cd by RACR-C is greatly influenced by internal diffusion as well as external boundary. Since the Cd adsorption capacity of RACR-C is greatly influenced by the initial dosage, pH, and co-existing metals, it is necessary to manage these influencing factors when treating wastewater containing heavy metals. Our results suggest that Cd adsorption by RACR-C is a complex adsorption phenomenon by various mechanisms such as adsorption by functional group (C˭C and C-O), precipitation of Cd-P and ion exchange reaction by exchangeable cation occurring rather than by a single specific mechanism.

Carbon tubes from biomass with prominent adsorption performance for paraquat

Paraquat (PQ) pollution has become an increasing seriously threat to the ecological environment. Thus, it is vital to study novel adsorption materials capable of removing PQ. Modified carbon tubes (MCT-600) were prepared by carbonizing the seed hair fibers of Metaplexis japonica at 600 °C and further modifying with nitric acid. The MCT-600 was found to possess a regular morphology, a good graphitization degree and an abundance of carboxyl functional groups. Moreover, this materil exhibits excellent adsorption performance for paraquat (PQ), such as a fast adsorption rate (adsorption equilibrium within 20 min), large adsorption capacity (218.61 mg g^-1) and good regeneration ability (reused more than 5 times). The adsorption process for PQ onto MCT-600 was found to be well matched to a Langmuir isotherm and pseudo-second-order kinetics model. Owing to its unique surface properties, green raw material source and simple preparation process, MCT-600 shows potential as an outstanding candidate for PQ removal from water.

An easily fabricated palladium nanocatalyst on magnetic biochar for Suzuki–Miyaura and aryl halide cyanation reactions

A sustainable biochar material for the synthesis of a novel heterogeneous catalyst for organic reactions is reported.

Efficient Removal of Cu(II), Zn(II), and Cd(II) from Aqueous Solutions by a Mineral-Rich Biochar Derived from a Spent Mushroom (Agaricus bisporus) Substrate

This study evaluated the novel application of a mineral-rich biochar derived from a spent Agaricus bisporus substrate (SAS). Biochars with various pyrolysis temperatures (350–750 °C) were used to remove Cu(II), Zn(II), and Cd(II) from aqueous solutions. The adsorption characteristics and removal mechanisms of the biochars were investigated. The adsorption kinetics and isotherm data were fitted well by pseudo-second-order and Freundlich models. The Langmuir maximum removal capacity (Q_max) values of Cu(II), Zn(II), and Cd(II) were ordered as SAS750 > SAS350 > SAS550, and the Q_max values of SAS750 were 68.1, 55.2, and 64.8 mg·g⁻¹, respectively. Overall, the removal mechanisms of biochar at a low production temperature (350 °C) to Cu(II), Zn(II), and Cd(II) were mainly via ion exchange (54.0, 56.0, and 43.0%), and at a moderate production temperature (550 °C), removal mechanisms were mainly via coordination with π electrons (38.3, 45.9, and 55.0%), while mineral precipitation (65.2, 44.4, and 76.3%, respectively) was the dominant mechanism at a high produced temperature (750 °C). The variation of the mutual effect of minerals and heavy metals was the predominant factor in the sorption mechanism of mineral precipitation and ion exchange. The results demonstrated that spent Agaricus bisporus substrate biochar is a potential candidate for the efficient removal of heavy metals, which provides a utilization route for spent mushroom substrates.

Utilization of biochar produced from invasive plant species to efficiently adsorb Cd (II) and Pb (II)

Global expansion of invasive plant species has caused serious ecological and economic problems. Two such invasive species, ragweed and horseweed, were pyrolyzed at temperatures of 350, 450 and 550 ℃ for biochar production (RB350, RB450, RB550 and HB350, HB450, HB550). The biochars produced were used for Cd(Ⅱ) and Pb(Ⅱ) removal in aqueous solutions. The results indicated that the properties of the biochars varied with pyrolysis temperature, which further affected their adsorption performance. The maximum adsorption capacity of RB450 for Cd(Ⅱ) (139 mg·g^-1) and Pb(Ⅱ) (358.7 mg·g^-1) was much higher than that shown in previous studies. The immobilized Cd(Ⅱ) and Pb(Ⅱ) fraction on RB450, RB550, HB450 and HB550 was mainly attributable to the acid soluble and non-available fractions. These findings suggested that pyrolysis of invasive plants at 450 ℃ could not only be an option to control invasive plants but also could be of benefit in using biochar as excellent adsorbent.

Exploration of the potential capacity of fly ash and bottom ash derived from wood pellet-based thermal power plant for heavy metal removal

This study was conducted to explore the potential capacity for the removal of heavy metals from the fly ash (FA) and bottom ash (BA) emitted by wood pellet thermal power plants. Fly ash consists of inorganic compounds such as CaSiO₃, P₂O₅, and K₂O, whereas BA shows properties very similar to the biochar derived from organic biomass. The adsorption properties of both FA and BA for Cd were described well by the Langmuir and pseudo-second-order models, and the maximum adsorption capacity of FA for Cd was 4.2 times higher than that of BA. The results indicate that FA can be applied to the treatment of wastewater that contains heavy metals over pH range from 2-6; however, BA is considered to be most effective for application with wastewater that contains heavy metals at a pH of 5-6. Study of the mechanism concluded that the adsorption of Cd by FA is dominated by the formation of Cd₂SiO₄ complexes by chemical reactions between CaSiO₃ and Cd ions as well as via the precipitation of Cd(OH)₂ in the neutral and alkaline solutions that is caused by the dissolution of K. It was found that the adsorption of Cd by BA was influenced by the binding of functional groups (CC and COH), coupled CaCO₃ dissolution-CdCO₃ precipitation reaction and ion exchange between some minerals with Si and Cd ions in weakly acidic conditions. Results indicate that the FA and BA emitted from wood pellet thermal power plants have high potential for heavy metal removal, and their practical use in the purification and restoration of heavy metals could be an effective way to reduce the waste produced by power plants and clean the environment.

The Use of Biochar and Pyrolysed Materials to Improve Water Quality through Microcystin Sorption Separation

Harmful algal blooms have increased globally with warming of aquatic environments and increased eutrophication. Proliferation of cyanobacteria (blue-green algae) and the subsequent flux of toxic extracellular microcystins present threats to public and ecosystem health and challenges for remediation and management. Although methods exist, there is currently a need for more environmentally friendly and economically and technologically feasible sorbents. Biochar has been proposed in this regard because of its high porosity, chemical stability, and notable sorption efficiency for removing of cyanotoxins. In light of worsening cyanobacterial blooms and recent research advances, this review provides a timely assessment of microcystin removal strategies focusing on the most pertinent chemical and physical sorbent properties responsible for effective removal of various pollutants from wastewater, liquid wastes, and aqueous solutions. The pyrolysis process is then evaluated for the first time as a method for sorbent production for microcystin removal, considering the suitability and sorption efficiencies of pyrolysed materials and biochar. Inefficiencies and high costs of conventional methods can be avoided through the use of pyrolysis. The significant potential of biochar for microcystin removal is determined by feedstock type, pyrolysis conditions, and the physiochemical properties produced. This review informs future research and development of pyrolysed materials for the treatment of microcystin contaminated aquatic environments.

Superefficient Removal of Heavy Metals from Wastewater by Mg-Loaded Biochars: Adsorption Characteristics and Removal Mechanisms

Six types of biochar (BSB, CSB, FSB, CFSB, MSB, and TSB) were prepared from different raw materials by loading magnesium ions (Mg²⁺) via an impregnation process. The adsorption kinetics and thermodynamics of heavy metals at high concentrations were analyzed. The adsorption mechanisms were investigated by zeta potential, scanning electron microscopy-energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and inductively coupled plasma-atomic absorption spectroscopy analyses. The adsorption of heavy metals by BSB, CSB, FSB, CFSB, MSB, and TSB conformed to the Langmuir model and PS-order. The maximum theoretical saturation adsorption capacities for Cd(II), Cu(II), and Pb(II) were 333.33, 238.10, 75.19, 96.15, 66.23, and 185.19 mg·g^-1; 370.37, 294.12, 111.11, 169.49, 84.75, and 217.39 mg·g^-1; and 302.58, 200.00, 61.73, 90.91, 54.47, and 166.67 mg·g^-1, respectively. According to the analysis of the contribution of adsorption, the adsorption process was mainly controlled by cation-π interactions, ion exchange, mineral precipitation, and functional group interactions. Biochars contain ash, functional groups and load a large number of Mg²⁺, which can form complexes with metal ions and perform strong ion exchange; therefore, mineral precipitation and cation exchange played dominant roles in the adsorption process. The prepared Mg-loaded biochars presented in this research showed excellent adsorption properties for heavy metals and have great potential for practical application; in particular, BSB had the strongest adsorption capacity for the three heavy metal ions.