Improved Pb(II) removal in aqueous solution by sulfide@biochar and polysaccharose-FeS@ biochar composites: Efficiencies and mechanisms

Biochar-based composites for removing chlorinated organic pollutants: Applications, mechanisms, and perspectives

Chlorinated organic pollutants constitute a significant category of persistent organic pollutants due to their widespread presence in the environment, which is primarily attributed to the expansion of agricultural and industrial activities. These pollutants are characterized by their persistence, potent toxicity, and capability for long-range dispersion, emphasizing the importance of their eradication to mitigate environmental pollution. While conventional methods for removing chlorinated organic pollutants encompass advanced oxidation, catalytic oxidation, and bioremediation, the utilization of biochar has emerged as a prominent green and efficacious method in recent years. Here we review biochar's role in remediating typical chlorinated organics, including polychlorinated biphenyls (PCBs), triclosan (TCS), trichloroethene (TCE), tetrachloroethylene (PCE), organochlorine pesticides (OCPs), and chlorobenzenes (CBs). We focus on the impact of biochar material properties on the adsorption mechanisms of chlorinated organics. This review highlights the use of biochar as a sustainable and eco-friendly method for removing chlorinated organic pollutants, especially when combined with biological or chemical strategies. Biochar facilitates electron transfer efficiency between microorganisms, promoting the growth of dechlorinating bacteria and mitigating the toxicity of chlorinated organics through adsorption. Furthermore, biochar can activate processes such as advanced oxidation or nano zero-valent iron, generating free radicals to decompose chlorinated organic compounds. We observe a broader application of biochar and bioprocesses for treating chlorinated organic pollutants in soil, reducing environmental impacts. Conversely, for water-based pollutants, integrating biochar with chemical methods proved more effective, leading to superior purification results. This review contributes to the theoretical and practical application of biochar for removing environmental chlorinated organic pollutants.

Characterization of phosphate modified red mud-based composite materials and study on heavy metal adsorption

In this paper, Bayer red mud (RM) and lotus leaf powder (LL) were used as the main materials, and KH2PO4 was added to modify the material. Under the condition of high-temperature carbonization, RMLL was prepared and phosphate modified red mud matrix composite (PRMLL) was prepared based on KH2PO4 modification, which can effectively remove Pb2+ from water. The optimum preparation and application conditions were determined through orthogonal experiment: dosage 0.1g, ratio 1:1, and temperature 600 °C. The effects of pH, dosage, and initial concentration on the adsorption of Pb2+ were studied. The pseudo-first-order, pseudo-second-order, and Elovich kinetic models were fitted to the experimental data. It was found that RMLL and PRMLL were more consistent with the pseudo-second-order kinetic model and chemisorption. Langmuir, Freundlich, Timkin, and Dubinin-Radushkevich isothermal adsorption models were used to fit the experimental data. It was found that RMLL and PRMLL were more consistent with Langmuir model. In addition, the maximum adsorption capacity of RMLL and PRMLL was 188.1 mg/g and 213.4 mg/g, respectively. It is larger than the adsorption capacity of their monomers. Therefore, the use of RMLL and PRMLL as the removal of Pb2+ from water is a potential application material.

Study on the adsorption of Zn(II) and Cu(II) in acid mine drainage by fly ash loaded nano-FeS

Aiming at the acid mine drainage (AMD) in zinc, copper and other heavy metals treatment difficulties, severe pollution of soil and water environment and other problems. Through the ultrasonic precipitation method, this study prepared fly ash-loaded nano-FeS composites (nFeS-F). The effects of nFeS-F dosage, pH, stirring rate, reaction time and initial concentration of the solution on the adsorption of Zn(II) and Cu(II) were investigated. The data were fitted by Lagergren first and second-order kinetic equations, Internal diffusion equation, Langmuir and Freundlich isotherm models, and combined with SEM, TEM, FTIR, TGA, and XPS assays to reveal the mechanism of nFeS-F adsorption of Zn(II) and Cu(II). The results demonstrated that: The removal of Zn(II) and Cu(II) by nFeS-F could reach 83.36% and 70.40%, respectively (The dosage was 8 g/L, pH was 4, time was 150 min, and concentration was 100 mg/L). The adsorption process, mainly chemical adsorption, conforms to the Lagergren second-order kinetic equation (R2 = 0.9952 and 0.9932). The adsorption isotherms have a higher fitting degree with the Langmuir model (R2 = 0.9964 and 0.9966), and the adsorption is a monolayer adsorption process. This study can provide a reference for treating heavy metals in acid mine drainage and resource utilization of fly ash.

Advances in Fe-modified lignocellulosic biochar: Impact of iron species and characteristics on wastewater treatment

Lignocellulosic biomass is an attractive feedstock for biochar production owing to its high abundance and renewability. Various modified biochars have been extensively studied for wastewater treatment to improve the physical and chemical properties of lignocellulosic biochar (L-BC). Particularly, Fe-modified L-BCs have garnered attention owing to the abundance and eco-friendliness of Fe and the outstanding ability to remove various organic and inorganic contaminants via adsorption, oxidation, reduction, and catalytic reactions. Different iron species (e.g., Fe(0), Fe (hydr)oxide, Fe sulfide, and Fe-Metal) are formed during the preparation of Fe-L-BCs, which can completely differentiate the physical and chemical properties of BCs. This review discusses the advances in the synthesis of different Fe-L-BCs, specific changes in the physical and chemical properties of Fe-L-BCs upon Fe addition, and their impacts on wastewater treatment. The results of this review can demonstrate the unique advantages and drawbacks of Fe-L-BCs for the removal of different types of pollutants.

Synergistic removal performance and mechanism of Cd(II) and As(III) from irrigation water by iron sulfide-based porous biochar

Since Cd(II) and As(III) have extremely opposite chemical characteristics, it is a huge challenging to simultaneously remove these two ions from aqueous solutions. Therefore, a novel iron sulfide-based porous biochar (FSB) was synthesized and used to evaluate its Cd(II) and As(III) removal performance and mechanisms. The characterization and batch experiments results indicated that FeS was successfully loaded on the surface of biochar and increased its adsorption sites. The iron sulfide-based porous biochar was very favorable for the removal of Cd(II) and As(III) in the weakly acidic environment. The maximum adsorption of Cd(II) and As(III) by FSB was 108.8 mg g-1 and 76.3 mg g-1, respectively, according to the Langmuir and Freundlich isothermal adsorption model, and the adsorption equilibrium time was 12 h and 4 h, respectively, according to the pseudo-second-order kinetic model. In the coexisting ion system, Cd(II) adsorption was suppressed by Ca2+, Mg2+, and humic acid, but enhanced by PO43- and As(III). As(III) adsorption was inhibited by PO43- and humic acid. Precipitation and complexation are the predominant adsorption mechanisms of Cd(II) and As(III), which contribute to the formation of Cd-O, Fe-O-Cd, As-O, Fe-O-As, ternary complex Cd-Fe-As, and stable compounds FeAsO4·2H2O and CdS. Therefore, The iron sulfide-based porous biochar can be an efficient and environmentally friendly candidate for the treatment of Cd(II) and As(III) co-polluted irrigation water.

Muscovite clay for methylene blue removal: advanced optimization and Al-guided breakthroughs-an independent application from prior antibiotic removal investigation

This study evaluates the efficacy of muscovite mineral clay as an adsorbent for removing Methylene Blue (MB) from water-based solutions. The research examined the impact of initial MB concentration, adsorbent mass, and time on the MB removal process. Two modeling techniques, namely Box-Behnken design with response surface methodology (BBD-RSM) and Artificial Neural Network (ANN), were employed to accurately predict the MB removal efficiency. The RSM and ANN models yielded satisfactory results in estimating MB removal efficiency. To further enhance the optimization process, conventional and techno-economic methods were implemented. The conventional method aimed to maximize dye removal efficiency (R), while the techno-economic approach incorporated multiple objectives. The comparative analysis demonstrated that the techno-economic optimization method outperformed the conventional method. This study emphasizes the significance of considering multiple objectives and integrating techno-economic factors in optimizing clay adsorption processes. The successful application of the techno-economic optimization approach highlights its potential as a robust optimization method, particularly in the field of wastewater treatment. The findings provide valuable insights for optimizing adsorption and advancing environmental remediation practices.

The modified biochar from wheat straw by the combined composites of MnFe2O4 nanoparticles and chitosan Schiff base for enhanced removal of U(VI) ions from aqueous solutions

In the last few decades, U(VI) is a significant environmental threat. The innovative and environmentally friendly adsorbent materials for U(VI) removal were urgent. Preparation of the modified biochar from wheat straw by combined composites of MnFe2O4 nanoparticles and chitosan Schiff base (MnFe2O4@CsSB/BC) was characterized, and adsorption experiments were carried out to investigate the performance and interfacial mechanism of U(VI) removal. The results showed that MnFe2O4@CsSB/BC exhibited high adsorption capacity of U(VI) compared with BC. The adsorption process of U(VI) removal by MnFe2O4@CsSB/BC could be ascribed as pseudo-second-order model and Langmuir model. The maximum adsorption capacity of U(VI) removal by MnFe2O4@CsSB/BC reached 19.57 mg/g at pH4.0, 30 mg/L of U(VI), and 25 °C. The possible mechanism was a chemical adsorption process, and it mainly contained electrostatic attraction and surface complexation. Additionally, it also was an economic and environmental friendly adsorbent.

State-of-the-art adsorption and adsorptive filtration based technologies for the removal of trace elements: A critical review

Water and wastewater are contaminated with various types of trace elements that are released from industrial activities. Their presence, at concentrations above the permissible limit, will cause severe negative impacts on human health and the environment. Due to their cost-effectiveness, simple design, high efficiency, and selectivity, adsorption, and adsorptive filtration are techniques that have received lots of attention as compared to other water treatment techniques. Adsorption isotherms and kinetic studies help to understand the mechanisms of adsorption and adsorption rates, which can be used to develop and optimize different adsorbents. This state-of-the-art review provides and combines the advancements in different conventional and advanced adsorbents, biosorbents, and adsorptive membranes for the removal of trace elements from water streams. Herein, this review discusses the sources of different trace elements and their impact on human health. The review also covers the adsorption technique with a focus on various advanced adsorbents, their adsorption capacities, and adsorption isotherm modeling in detail. In addition, biosorption is critically discussed together with its mechanisms and biosorption isotherms. In the end, the application of various advanced adsorptive membranes is discussed and their comparison with adsorbents and biosorbents is systematically presented.

Preparation of pyrolysis products by catalytic pyrolysis of poplar: Application of biochar in antibiotic wastewater treatment

Poplar waste is acted as feedstock to produce renewable biofuel and green chemical by catalytic pyrolysis using ferric nitrate and zinc chloride as additive. The additive contributes to the generation of furfural in bio-oil. Additive promotes the generation of H2 and inhibits the generation of CO with bio-gas heating value of 12.16 MJ (Nm3)-1. Biochar exists ZnO and Fe3O4 with large surface area, which could be used as absorbent and photocatalyst for tetracycline and ciprofloxacin removal. The tetracycline and ciprofloxacin adsorption amount of biochar are 316.41 and 255.23 mg g-1 respectively. While the photocatalytic degradation removal of the tetracycline and ciprofloxacin is close to 100%. The adsorption and photocatalytic degradation mechanism are investigate and analyzed using the density functional theory and electron paramagnetic resonance analysis. Biochar can be quickly recycled and regenerated after use. Besides, biochar can be used in lithium ion battery industry for energy storage, which specific capacity is 535 mAh g-1.

Utilizing biochar to decorate nanoscale FeS for the highly effective decontamination of Se(IV) from simulated wastewater

Selenium (Se) as an essential nutrient for human beings at trace concentrations, the allowable concentration for the human is only 40 μg/L. Iron sulfide (FeS) nanoparticles have been applied for excessive of selenium (Se) remediation in surface water and groundwater. In this study, FeS nanoparticles were anchored onto biochar (BC) to reduce agglomeration of FeS and prepared into the composite of FeS-BC by pyrolysis to economically and efficiently remove Se(IV) from simulated wastewater based on the excellent performance of FeS and the low cost of BC. Characterizations presented the uniform anchorage of FeS on the BC surface to prevent agglomeration. The results of batch experiments revealed that the removal of Se(IV) by FeS-BC nanomaterials significantly depended on the pH value, with the maximum removal of ∼174.96 mg/g at pH 3.0. A pseudo-second-order kinetic model well reflected the kinetic removal of Se(IV) in pure Se(IV) solution with different concentration, as well as the coexistence of K+, Ca2+, Cl-, and SO42- ions. The presence of K+ ions significantly inhibited the removal of Se(IV) with the increase of K+ ion concentration compared with the effect of the other three ions. SEM-EDS and XPS analyses indicated that the removal process was achieved through adsorption by surface complexation, and reductive precipitation of Se(IV) into Se0 with the electron donor of Fe(II) and S(-II) ions. The FeS-BC nanomaterial exhibited an excellent application prospect in the remediation of Se(IV).

Effective elimination of hexavalent chromium and lead from solution by the modified biochar with MgMn2O4 nanoparticles: adsorption performance and mechanism

Heavy metal pollution is one of the environmental problems that need to be solved urgently. The adsorption method is thought as the most effective and economical treatment technology. Nature biochar usually showed unsatisfactory adsorption capacity due to its relatively small adsorption capacity and slow adsorption rate. The metal of Mn has been widely applied in the modification of biochar, which could effectively improve the adsorption capacity of biochar. However, leaching of Mn2+ on the adsorbent materials would appear during the adsorption process. And it would increase the risk of secondary pollution. The multifunctional binary modified biochar could improve the adsorption capacity of environmental pollutant removal. In addition, it could also act as a metal support carrier, reducing the risk of secondary pollution. A novel effective biochar loaded by Mg-Mn binary oxide nanoparticles (MgMn2O4@Biochar) was prepared and applied for the Cr(VI) and Pb(II) removal in aqueous solution. The characteristic of MgMn2O4@Biochar was analyzed by SEM, TEM, FTIR, and XRD. The irregular and somewhat flaky shaped particles of different shape and sizes clustered on the surface of MgMn2O4@Biochar appeared. Abundant functional groups of O-H, -C-OH, C-O, and C-OOH could be observed on the surface of MgMn2O4@Biochar. The elements of Mg and Mn elements besides of C, O, and Si elements were presented on the surface of MgMn2O4@Biochar. The wt% of C, O, Mg, Mn, and Si were 42.82%, 48.99%, 2.83%, 4.44%, and 0.93%, respectively. The operational parameters had an important influence on adsorption capacity of Cr(VI) and Pb(II) removal. The results showed that the adsorption capacity of MgMn2O4@Biochar for Cr(VI) and Pb(II) would reach 33.5 mg/g and 536 mg/g, respectively, within 360 min. Additionally, the adsorption processes of Cr(VI) and Pb(II) in solution could be described with pseudo-second-order. For Cr(VI), the Langmuir model was suitable to the adsorption process. However, the adsorption process of Pb(II) in solution could be described with Freundlich model. Furthermore, it could be concluded that the possible mechanism of Cr(VI) and Pb(II) removal by MgMn2O4@Biochar was physical adsorption, surface complexation reaction, and electrostatic adsorption.

Selective removal of total Cr from a complex water matrix by chitosan and biochar modified-FeS: Kinetics and underlying mechanisms

Cr(VI) is difficult to remove from wastewater via a one-step method because it is a type of oxyanion. Developing ARPs to selectively remove total Cr is critical for Cr(VI) remediation, including Cr(VI) adsorption-reduction and Cr(III) complexation. Hereon, chitosan and biochar modified-FeS (CTS-FeS@BC) was prepared to apply in the selective removal of total Cr from wastewaters. The results showed that the activity of amorphous FeS on CTS-FeS@BC for Cr(VI) removal (110.0 mg/g FeS) was significantly enhanced by CTS and BC, and efficiency was inhibited slightly by many anions and humic acid (HA). Meanwhile, the removal of total Cr by CTS-FeS@BC (99.1 mg/g FeS) via ARPs was improved by 1.2 and 40.3 times when compared with CTS-FeS and raw FeS, respectively. Besides, CTS-FeS@BC exhibited an outstanding selectivity for total Cr removal in metal cations-Cr binary solutions and in a complex water matrix. The mechanism of ARPs on CTS-FeS@BC demonstrated by the results of the 1,10-phenanthroline experiment and the distribution of Cr species was that Cr(VI) was first adsorbed by outer-sphere complexation for reduction, and then adsorbed Cr(III) combined with Fe(III) species to generate Fe(III)-Cr(III) complex for total Cr removal. Overall, this study provides an ARP to effectively solve Cr pollution in wastewaters.

Application of zeolite synthesized from coal fly ash via wet milling as a sustainable resource on lead(II) removal

In this work, zeolite based on coal fly ash was firstly synthesized via wet milling for the adsorption of lead (Pb(II)). The effects of contact time, solid-to-liquid ratio and initial pH of solution on Pb(II) removal were investigated in detail. The experimental data showed that synthesized zeolite has high adsorption capacity of 99.082 mg of Pb(II) per gram of adsorbent. Coal fly ash zeolite synthesized by wet milling has good Pb(II) adsorption performance when the initial pH of the solution is above 5. The adsorption kinetic results demonstrated that removal of Pb(II) via the synthesized zeolite followed pseudo-second-order kinetic model. X-ray photoelectron spectroscopy results directly demonstrated the adsorption between Pb(II) and synthesized zeolite, and a possible reaction pathway was proposed. Specifically, the removing mechanism of Pb(II) from aqueous solution via the synthesized zeolite involves two stages: one is that Pb(II) in aqueous solution is absorbed on the interior of the synthesized zeolite, and the other is chemical precipitation.

Adsorption of Pb(II) from wastewater using a red mud modified rice-straw biochar: Influencing factors and reusability

Efficient environmental remediation of toxic chemicals using effective sorbents has received considerable attention recently. For the present study, the synthesis of a red mud/biochar (RM/BC) composite was performed from rice straw with the aim of achieving Pb(II) removal from wastewater. Characterization was performed by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS), Zeta potential analysis, elemental mapping, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Results showed that RM/BC had higher specific surface area (S_BET = 75.37 m² g^-1) than raw biochar (S_BET = 35.38 m² g^-1). The Pb(II) removal capacity (q_e) of RM/BC was 426.84 mg g^-1 at pH 5.0, and the adsorption data well fitted pseudo second order kinetics (R² = 0.93 and R² = 0.98), as well as the Langmuir isotherm model (R² = 0.97 and R² = 0.98) for both BC and RM/BC. Pb(II) removal was slightly hindered with the increasing strength of co-existing cations (Na⁺, Cu²⁺, Fe³⁺, Ni²⁺, Cd²⁺). The increase in temperatures (298 K, 308 K, 318 K) favored Pb(II) removal by RM/BC. Thermodynamic study indicated that Pb(II) adsorption onto BC and RM/BC was spontaneous and primarily governed by chemisorption and surface complexation. A regeneration study revealed the high reusability (>90%) and acceptable stability of RM/BC even after five successive cycles. These findings indicate that RM/BC evidenced special combined characteristics of red mud and biochar, hence its use for Pb removal from wastewater offers a green and environmentally sustainable approach fitting the "waste treating waste" concept.

Highly efficient removal of aqueous Hg(II) by FeS micro-flakes

FeS (mackinawite) is known to be effective in the sorption of aqueous Hg(II). However, FeS nanoparticles are apt to aggregate and easy to be oxidized, which limits their wide applications. Here, we have synthesized FeS micro-flakes which can be uniformly dispersed in water without aggregation. Owing to the good stability and dispersibility, FeS micro-flakes exhibit high efficiency in the removal of Hg(II) from water. The sorption of Hg(II) on the FeS micro-flakes is more consistent with the pseudo-second-order kinetic model and Langmuir model, indicating that the sorption of Hg(II) is mainly monolayer sorption dominated by chemical sorption. The maximum sorption capacity is 2680 mg/g at pH 5.6 and 30 °C, significantly higher than those of FeS nanoparticles and other Hg(II) scavengers. The pH studies indicate that FeS (0.31 g/L) can effectively remove >97.6 % of 200 mg/L Hg(II) in the pH range of 2-12 at 30 °C. Powder X-ray diffraction, elemental and sorption analyses suggest that Hg(II) is removed via chemical precipitation and surface adsorption. This study demonstrates the potential and viability of FeS micro-flakes for efficient removal of aqueous Hg(II).

Super-stable mineralization of Cu, Cd, Zn and Pb by CaAl-layered double hydroxide: Performance, mechanism, and large-scale application in agriculture soil remediation

The synthesized CaAl-layered double hydroxide (CaAl-LDH) shows excellent performance in potentially toxic metals (PTMs) removal, and the removal capacity of CaAl-LDH toward Cu²⁺, Zn²⁺ and Pb²⁺ in aqueous solution is 502.4, 315.2 and 600.0 mg/g respectively. Cu²⁺ and Zn²⁺ are removed through isomorphic substitution of laminate Ca and dissolution-reprecipitation, leading to the formation of CuAl-LDH and ZnAl-LDH mineralization products. Pb²⁺ is removed by the complexation and precipitation to form Pb₃(CO₃)₂(OH)₂. The application of CaAl-LDH in laboratory-scale soil remediation shows that target PTMs are gradually mineralized into relatively stable oxidizable and residual state, and the immobilization efficiency of available Cu, Zn, Cd and Pb reaches 84.62 %, 98.66 %, 96.81 % and 70.27 % respectively. In addition, practical application in farmland results in the significant reduction of available Cu, Zn, Cd and Pb with the immobilization efficiency of 30.15 %, 67.30 % and 57.80 % and 38.71 % respectively. Owing to the super-stable mineralization effect of CaAl-LDH, the content of PTMs in the roots, stems and grains of cultivated buckwheat also decreases obviously, and the growth and yield of buckwheat are not adversely affected but improved. The above prove that the super-stable mineralization based on CaAl-LDH is a promising scheme for the remediation of PTMs contaminated agriculture soil.

Immobilization of tannin onto dialdehyde chitosan as a strategy for highly efficient and selective Au(III) adsorption

Recycling of Au(III) from wastewater can not only increase resource utilization but also reduce environmental pollution. Herein, a chitosan-based bio-adsorbent (DCTS-TA) was successfully synthesized via crosslinking reaction between tannin (TA) and dialdehyde chitosan (DCTS) for the recovery of Au(III) from the solution. The maximum adsorption capacity for Au(III) was 1146.59 mg/g at pH 3.0, which fitted well with the Langmuir model. The XRD, XPS, and SEM-EDS analyses demonstrated that Au(III) adsorption on DCTS-TA was a collaborative process involving electrostatic interaction, chelation, and redox reaction. Existence of multiple coexisting metal ions did not significantly affect the Au(III) adsorption efficiency, with >90 % recovery of DCTS-TA obtained after five cycles. DCTS-TA is a promising candidate for Au(III) recovery from aqueous solutions due to its easy preparation, environmental-friendliness, and high efficiency.

Two recyclable and complementary adsorbents of coal-based and bio-based humic acids: High efficient adsorption and immobilization remediation for Pb(II) contaminated water and soil

Humic acid can effectively bind heavy metals and is a promising remediation agent for heavy metals-contaminated water and soil. Many successful applications of humic acid have been reported, but rarely studied the specific process and mechanism of heavy metal removal by humic acids from water and soil, especially the simultaneous application of coal-based and bio-based humic acids. In this work, two kinds of coal-based and bio-based humic acid materials (CHA and BHA) from weathered coal and rice husk were industrially produced and studied their Pb(II) adsorption and immobilization characteristics and mechanisms in water and soil. The batch adsorption experiments obtained the Pb(II) adsorption by CHA and BHA both were spontaneous and endothermic monolayer chemisorption and controlled by three rate-limiting steps (bulk, film, and pore) in the adsorption process. CHA and BHA had highly efficient Pb(II) adsorption capacities, obtained their maximum adsorption capacity was 201 and 188 mg g^-1, respectively. In addition to the two main adsorption mechanisms of ion exchange and surface complexation, electrostatic interaction, precipitation reaction, and π-π interaction were also involved. Soil culture experiments showed that CHA and BHA both exhibited a highly efficient immobilization effect on Pb(II)-contaminated soil, and CHA and BHA had a better synergistic promotion effect. Compared with the CK soil, the content of DTPA-Pb(II) decreased by 10.2-13.2% and the content of RES-Pb(II) increased by 14-22% in soils treated with different humic acids. Ion exchange, complexation, precipitation, and electrostatic attraction promote the transformation of unstable Pb(II) to stable Pb(II), which was of great significance for the immobilization of Pb(II) in soil. Overall, CHA and BHA have the potential to be used as green, efficient, and promising adsorbents to remove and immobilize Pb(II) from wastewater and soil.

Simultaneous adsorption of As(III) and Pb(II) by the iron-sulfur codoped biochar composite: Competitive and synergistic effects

Simultaneous elimination of As(III) and Pb(II) from wastewater is still a great challenge. In this work, an iron-sulfur codoped biochar (Fe/S-BC) was successfully fabricated in a simplified way and was applied to the remediate the co-pollution of As(III) and Pb(II). The positive enthalpy indicated that the adsorption in As-Pb co-pollution was an endothermic reaction. The mechanism of As(III) removal could be illustrated by surface complexation, oxidation and precipitation. In addition to precipitation and complexation, the elimination mechanism of Pb(II) also contained ion exchange and electrostatic interactions. Competitive and synergistic effects existed simultaneously in the co-contamination system. The suppression of As(III) was ascribed to competitive complexation of the two metals on Fe/S-BC, while the synergy of Pb(II) was attributed to the formation of the PbFe₂(AsO₄)₂(OH)₂. Batch experiments revealed that Fe/S-BC had outstanding ability to remove As(III) and Pb(II), regardless of pH dependency and interference by various coexisting ions. The maximum adsorption capacities of the Fe/S-BC for As(III) and Pb(II) were 91.2 mg/g and 631.7 mg/g, respectively. Fe/S-BC could be treated as a novel candidate for the elimination of As(III)-Pb(II) combined pollution.

Chitosan Nanoparticles as Potential Nano-Sorbent for Removal of Toxic Environmental Pollutants

Adsorption is the most widely used technique for advanced wastewater treatment. The preparation and application of natural renewable and environmentally friendly materials makes this process easier and more profitable. Chitosan is often used as an effective biomaterial in the adsorption world because of its numerous functional applications. Chitosan is one of the most suitable and functionally flexible adsorbents because it contains hydroxyl (-OH) and amine (-NH₂) groups. The adsorption capacity and selectivity of chitosan can be further improved by introducing additional functions into its basic structure. Owing to its unique surface properties and adsorption ability of chitosan, the development and application of chitosan nanomaterials has gained significant attention. Here, recent research on chitosan nanoparticles is critically reviewed by comparing various methods for their synthesis with particular emphasis on the role of experimental conditions, limitations, and applications in water and wastewater treatment. The recovery of pollutants using magnetic nanoparticles is an important treatment process that has contributed to additional development and sustainable growth. The application of such nanoparticles in the recovery metals, which demonstrates a "close loop technology" in the current scenarios, is also presented in this review.

Performance, life cycle assessment, and economic comparison between date palm waste biochar and activated carbon derived from woody biomass

Currently, comparisons between biochar and activated carbon in terms of performance, environmental impacts as well as financial implications are limited. In this study, biochar sourced from date palm waste were analysed using gate-to-grave life cycle assessment approach and results were compared to activated carbon derived from woody biomass. Simapro 8.5 software was used to quantitatively simulate the environmental impacts of both adsorbents. Date palm waste biochar and activated carbon global warming potentials (GWPs) were found to be 1.53 and 8.96 kg CO_2eq/kg respectively. The cumulative energy demand (CED) for producing date palm waste biochar was found to be 20.3 MJ/kg, whereas, activated carbon resulted in 119.5 MJ/kg. Both adsorbents' performance in terms of adsorption capacity were compared, and it was found that biochar is comparable with activated carbon. The economic performance demonstrated that the average cost of production of date palm waste biochar and activated carbon were $1.06/kg and $1.34/kg, respectively. Sensitivity analysis showed that when the source of energy was changed to renewable energy, a CED dropped to 105.2 MJ/kg and 7.68 MJ/kg, a GWP dropped to 7.29 kg CO₂ eq. and 0.665 kg CO₂ eq. and production costs dropped to $1.30 and to $1.04 for producing activated carbon and biochar respectively. Based on the results of the study, date palm waste biochar is more cost-effective, shows less environmental impact, and has comparable adsorption efficiency as compared to activated carbon.

Biochar for the removal of contaminants from soil and water: a review

Biochar shows significant potential to serve as a globally applicable material to remediate water and soil owing to the extensive availability of feedstocks and conducive physio-chemical surface characteristics. This review aims to highlight biochar production technologies, characteristics of biochar, and the latest advancements in immobilizing and eliminating heavy metal ions and organic pollutants in soil and water. Pyrolysis temperature, heat transfer rate, residence time, and type of feedstock are critical influential parameters. Biochar’s efficacy in managing contaminants relies on the pore size distribution, surface groups, and ion-exchange capacity. The molecular composition and physical architecture of biochar may be crucial when practically applied to water and soil. In general, biochar produced at relatively high pyrolysis temperatures can effectively manage organic pollutants via increasing surface area, hydrophobicity and microporosity. Biochar generated at lower temperatures is deemed to be more suitable for removing polar organic and inorganic pollutants through oxygen-containing functional groups, precipitation and electrostatic attraction. This review also presents the existing obstacles and future research direction related to biochar-based materials in immobilizing organic contaminants and heavy metal ions in effluents and soil.

Graphical Abstract

Modified biochar: synthesis and mechanism for removal of environmental heavy metals

With social progress and industrial development, heavy metal pollution in water and soils environment is becoming more serious. Although biochar is a low-cost and environmentally friendly adsorbent for heavy metal ions, its adsorption and immobilization efficiency still need to be improved. As an upgraded version of biochar, modified biochar has attracted extensive attention in the scientific community. This review summarized the recent research progress on the treatment methods on heavy metal pollutants in water and soils using biochar. The features and advantages of biochar modification techniques such as physical modification, chemical modification, biological modification and other categories of biochar were discussed. The mechanism of removing heavy metals from soil and water by modified biochar was summarized. It was found that biochar had better performance after modification, which provided higher surface areas and more functional groups, and had enough binding sites to combine heavy metal ions. Biochar is a very promising candidate for removing heavy metals in environment. Furthermore, some high valent metal ions could be reduced to low valent metals, such as Cr(VI) reduction to Cr(III), and form precipitates on biochar by in-situ sorption-reduction-precipitation strategy. However, it is still the direction of efforts to develop high-efficiency modified biochar with low-cost, high sorption capacity, high photocatalytic performance, environmentally friendly and no secondary pollution in future.

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

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

Thermochemical study of Cr(VI) sequestration onto chemically modified Areca catechu and its recovery by desorptive precipitation method

A new biosorbent for Cr(VI) sequestration was investigated from betel nut waste (BNW), Areca catechu, by H₂SO₄ charring. Aqueous insolubility and Cr(VI) uptake capacity of native BNW were potentially improved after H₂SO₄ modification due to cross-linking reaction of betel nut cellulose, thereby creating suitable complexation sites for Cr(VI) ion removal. Langmuir isotherm and pseudo second order (PSO) kinetic models described well with the experimental data. A trace amount of Cr(VI) was effectively removed below the safe drinking water standard (WHO, 0.05 mg/L) using charred BNW (CBNW). The negative value of ΔG° evaluated for all the temperatures suggested the spontaneous nature of Cr(VI) sequestration and positive value of ΔH° (42.43±0.13 kJ/mol) confirmed an endothermic reaction. Co-existing NO3−, Cl⁻, Na⁺ and Zn²⁺ ions showed negligible interferences, whereas SO42− and PO43− notably reduced Cr(VI) uptake capacity of CBNW. More than 98% of adsorbed Cr(VI) was desorbed using 1M NaOH solution. A light yellow precipitate of BaCrO₄ was recovered from the desorbed solution after precipitation with BaCl₂ solution. Therefore, the CBNW biosorbent investigated in this work is expected to be a promising material for Cr(VI) sequestration and its recovery from polluted water.

Removal of heavy metal(loid)s from aqueous solution by biogenic FeS-kaolin composite: Behaviors and mechanisms

In this work, a green adsorbent, biogenic FeS-kaolin composite (KL-FeS) was synthesized by sulfate-reducing bacteria (SRB) mediation, and its potential for Cd(II), Pb(II), Cu(II), Zn(II), As(III) and Sb(III) removal was evaluated. Among prepared composites, the KL-FeS synthesized at a concentration of 2 g/L kaolin performed a better removal efficiency on heavy metal(loid)s and the adsorption results followed the pseudo-second-order and Redlich-Peterson models, indicating that the adsorption was a hybrid chemical reaction-adsorption process. Additionally, the maximum adsorption capacities of Cd(II), Pb(II), Cu(II), Zn(II), As(III) and Sb(III) on KL-FeS in monocomponent system were 71.71, 133.54, 51.90, 54.41, 38.71 and 96.38 mg/g, respectively (pH = 5.0 ± 0.1, T = 25 °C). In addition, the increase of pH and ionic strength promoted the adsorption capacities of KL-FeS for metal-(loid)s. Moreover, FTIR, XPS and XRD analyses supported that surface complexation, hydrogen bonding, ion exchange, electrostatic interaction and chemical precipitation were predominately mechanisms involved in the adsorption process. Furthermore, KL-FeS displayed higher affinity for Pb(II), Sb(III) and Cu(II) in the multi-component system. This work highlighted the potential of biogenic FeS-kaolin composite for simultaneous removal of multiple heavy metal(loid)s under aerobic conditions.

Oyster (Crassostrea gigas) ferritin can efficiently reduce the damage of Pb2+in vivo by electrostatic attraction

Heavy metal ions pollution can cause damage to human body through food, so the development of a new kind of macromolecular that can remove heavy metal ions damage has a good application prospect. The possibilities of removing heavy metal ions from food system with ferritin were studied in this paper. In this study, oyster ferritin (GF1) can resistant to denaturation induced by Pb²⁺, Cd²⁺, Cr³⁺ and still maintains its basic structure. GF1 can bind more Pb²⁺, Cd²⁺, Cr³⁺ than recombinant human H-chain ferritin (rHuHF), especially Pb²⁺, and the findings suggest that each GF1 can capture about 51.42 Pb²⁺ in solution. The hard and soft acids and base also verifies that Pb²⁺ have stronger binding ability to the key amino acids at the outer end of the three-fold symmetry channel. Cells preprotected by ferritin could resistant to heavy metal ions. And GF1 can reduce the high blood lead in mice and may play a role in alleviating lead poisoning in vivo. All findings demonstrated that GF1 can be used as a novel macromolecule to bind heavy metal ions, and the study can broaden the research scope of ferritin in contaminated food systems.

Biochar-supported starch/chitosan-stabilized nano-iron sulfide composites for the removal of lead ions and nitrogen from aqueous solutions

Novel materials that nano-FeS and starch (or chitosan) loaded on peanut shells biochar(Starch-FeS@PSB and Chitosan-FeS@PSB) were prepared and applied for removal of Pb(II) and nitrogen(NO₃-N and NH₄-N) in wastewater. It showed that Starch-FeS@PSB and Chitosan-FeS@PSB had excellent absorptive effects compared with PSB. The maximum adsorption capacity of Pb(II) by Starch-FeS@PSB and Chitosan-FeS@PSB reached 91.74 mg/g, 98.04 mg/g, respectively. Absorption of Pb(II) by Starch-FeS@PSB and Chitosan-FeS@PSB were controlled by monolayer chemisorption. Mechanism studies showed that complexation, electrostatic attraction, REDOX and physical absorption happened on the adsorbent surface. In addition, the maximum adsorption capacity of NO₃-N and NH₄-N by Starch-FeS@PSB and Chitosan-FeS@PSB reached 16.89 mg/g, 15.65 mg/g, and 18.45 mg/g, 18.28 mg/g, respectively. Absorption of N by Starch-FeS@PSB and Chitosan-FeS@PSB were controlled by multilayer chemisorption. Mechanism studies showed that complexation, electrostatic attraction and physical absorption happened on the adsorbent surface. Starch-FeS@PSB and Chitosan-FeS@PSB can be utilized in Pb(II) and N wastewater treatment.