Synthesis and adsorption of FeMnLa-impregnated biochar composite as an adsorbent for As(III) removal from aqueous solutions

Potassium permanganate-modified eggshell biosorbent for the removal of diclofenac from liquid environment: adsorption performance, isotherm, kinetic, and thermodynamic analyses

This study assess how well diclofenac (DCF) can be separated from aqueous solution using potassium permanganate-modified eggshell biosorbent (MEB). The MEB produced was characterised using XRD, FTIR, and SEM. Batch experiments were conducted to examine and assess the impact of contact time, adsorbent dosage, initial concentration, and temperature on the adsorption capacity of the MEB in the DCF sequestration. The best parameters to obtained 95.64% DCF removal from liquid environment were 0.05 g MEB weight, 50 mg/L initial concentration, and 60 min contact time at room temperature. The maximum DCF sequestration capacity was found to be 159.57 mg/g with 0.05 g of MEB at 298 K. The adsorption isotherm data were more accurately predicted by the Freundlich model, indicating a process of heterogeneous multilayer adsorption. The results of the kinetic study indicated that the pseudo-second-order kinetic models best matched the experimental data. The findings revealed that the dynamic of DCF entrapment is largely chemisorption and diffusion controlled. Based on the values of thermodynamic parameters, the process is both spontaneous and endothermic. The primary processes of DCF sorption mechanism onto the MEB were chemical surface complexation, hydrogen bonding, π-π stacking, and electrostatic interactions. The produced MEB showed effective DCF separation from the aqueous solution and continued to have maximal adsorption capability even after five regeneration cycles. These findings suggest that MEB could be highly efficient adsorbent for the removal of DCF from pharmaceutical wastewater.

Simultaneous detection and removal of mercury (II) using multifunctional fluorescent materials

Environmental problems caused by mercury ions are increasing due to growing industrialization, poor enforcement, and inefficient pollutant treatment. Therefore, detecting and removing mercury from the ecological chain is of utmost significance. Currently, a wide range of small molecules and nanomaterials have made remarkable progress in the detection, detoxification, adsorption, and removal of mercury. In this review, we summarized the recent advances in the design and construction of multifunctional materials, detailed their sensing and removing mechanisms, and discussed with emphasis the advantages and disadvantages of different types of sensors. Finally, we elucidated the problems and challenges of current multifunctional materials and further pointed out the direction for the future development of related materials. This review is expected to provide a guideline for researchers to establish a robust strategy for the detection and removal of mercury ionsin the environment.

Enhancing arsenic adsorptions by optimizing Fe-loaded biochar and preliminary application in paddy soil under different water management strategies

Arsenic (As) is widely distributed in nature and is a highly toxic element impacting human health through drinking water and rice. In this study, an optimized approach was attempted to improve As adsorption capabilities by combining pre- and post-pyrolysis modification of Fe(oxy)hydroxides to rice husk biochar (FRB), of which the method is rarely addressed in previous studies. Maghemite and goethite were successfully loaded onto biochar, characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoemission spectroscopy (XPS) analyzer. The FRB had maximum As(III) and As(V) adsorption capabilities of 7908 and 11,268 mg/kg, respectively, which was significantly higher than that of Fe-modified biochar in the pre-pyrolysis and/or post-pyrolysis process. Adsorption mechanisms for As explored by Fourier-transform infrared spectroscopy (FTIR), XPS analysis mainly included electronic attraction and ligand exchange with hydroxyl groups on the FRB. It was noteworthy that more than half of the As(II) species loaded on FRB were converted into less toxic As(V) species, which could be mediated by the redox-active groups on the biochar. The preliminary application of FRB in soil indicated that it has an effective remediation potential for As-contaminated soil under flooded conditions, while promoted As release under dry conditions. Finding of this study highlighted that the loading of metal oxides onto biochar by combining pre- and post-pyrolysis modification could potentially increase As adsorption capabilities and further help in strategic water management.

A critical review on the development of lanthanum-engineered biochar for environmental applications

Biochar and lanthanum (La) have been widely used in environment. However, there is a lack of knowledge and perspective on the development of La-engineered biochar (LEB) for environmental applications. This review shows that LEBs with a variety of La species via pre-/post-doping routes are developed for environmental applications. Specifically, precipitation, gelation, and calcination are the common sub-processes involved in the pre-/post-doping of La on the resultant LEB. The dominant La species for LEBs is La(OH)₃, which is formed through precipitation of La ions with various bases. Various La carbonates, e.g., LaOHCO₃, La₂(CO₃)₃, La₂CO₅, and NaLa(CO₃)₂, are also involved in the preparation of LEBs. The LEBs are high-efficient in the adsorption of phosphate, arsenic, antimonate and fluoride ions, attributed to the strong affinity of La to oxyanions and Lewis hard base. Lanthanum is also favorable for co-doping with transition metal species to further enhance the performances in adsorption or catalysis. This review also analyzes the prospects and future challenges for the preparation and application of LEBs in environment. Finally, this review is beneficial to inspire new breakthroughs on the preparation and environmental application of LEBs.

Arsenic removal from aqueous solution: A comprehensive synthesis with meta-data

Removal of arsenic from drinking water is one of the most important global concerns. Among the various techniques, adsorptive removal of arsenic is considered as a viable most effective method. However, limited attention is given to understand the overall relative sorption capacity of different sorbents (e.g., biocomposite, biochar and nano-composite etc.) since various factors influence the sorption capacity. The aim of this study is to assess the effectiveness of various adsorbents with quantitative estimation (Langmuir adsorption maxima, Qmax) as well as to evaluate the influence of experimental conditions on the achievement of maximum adsorption. A number of analyses including meta-analysis, analysis of variance (ANOVA), scientometric and regression were performed. The results revealed that among the sorbents, nanoparticles show the greatest sorption capacity while pre-doped biochar performed the best among different biochars. Average across all sorbents, As (V) removal efficacy was higher than As (III). As expected, a high point of zero charge (PZC) and higher positive surface charge favored adsorption. The relative contribution of different mechanisms was also discussed. Our scientometric analyses revealed that, research should focus on the development of low-cost adsorbents and increase their reusability, safe disposal of adsorbed arsenic. Altogether, our findings provide a molecular understanding of arsenic sorption to different sorbents with implications for tailoring a good sorbent for arsenic removal from drinking water.

The enhanced removal of arsenite from water by double-shell CuOx@MnOy hollow spheres (DCMHS): behavior and mechanisms

To facilitate removing As(III) from water through an "oxidation-adsorption" process, the double-shell CuO_x@MnO_y hollow spheres (DCMHS) have been fabricated via a two-step co-precipitation route combined with the soft-template method. The surface characterization results showed that Mn oxides were formed without segregation and uniformly distributed on the surface of CuO_x hollow spheres. DCMHS could achieve outstanding performance to remove As(III) with an As maximum adsorption capacity of 32.15 mg/g. Meanwhile, the kinetics results illustrated that the oxidative activity of DCMHS was strengthened due to its specific structure, and part of As(III) was converted to As(V) during the adsorption process. Also, air aeration could further enhance As(III) oxidation and thus improving As removal. The As(III) removal performance could be maintained under neutral and weak alkaline conditions. Phosphate, silicate, and carbonate anions could depress the removal performance, while chloride ions and sulfate anions barely influenced As removal. Moreover, DCMHS could be regenerated using NaOH and KMnO₄ solutions without breaking the hollow sphere structure. Based on the spectroscopic analysis results, As(III) molecules were converted to As(V) via two pathways, including the oxidation by Mn oxides or superoxide radicals. The Cu-Mn synergistic effect could not only enhance the oxidative activity of Mn oxides but also produce superoxide radicals via the activation of surface-adsorbed oxygen molecules. Afterwards, the newly formed As(V) could be attached to the hydroxyl groups through surface complexation. Therefore, this work has provided insights into the morphology design of Mn-oxide-containing adsorbents and supplemented the interface reaction mechanisms for enhancing As(III) removal.

Simultaneous and efficient removal of multiple heavy metal(loid)s from aqueous solutions using Fe/Mn (hydr)oxide and phosphate mineral composites synthesized by regulating the proportion of Fe(II), Fe(III), Mn(II) and PO43

In this work, a novel adsorbent FMPs consisting of Fe/Mn (hydr)oxides and phosphate minerals was synthesized by regulating the proportion of Fe(II), Fe(III), Mn(II) and PO₄^3-, and its removal behaviors and possible mechanisms for Cd(II), Pb(II), Cu(II), Zn(II), As(III), Sb(III), As(V) and Sb(V) were systematically investigated. Batch adsorption experiments revealed that the adsorption process of FMPs to these metal(loid) ions conformed to pseudo-second-order (R² > 0.99) and Redlich-Peterson (R² > 0.94) models in the mono-component system, demonstrating a hybrid chemical reaction-adsorption process. In addition, the solution pH and ionic strength could affect the adsorption capacity of FMPs to heavy metal(loid)s with varying degrees. Besides, FMPs presented feasible stability and reusability even after four cycles. Combining the macroscopic and microscopic characteristics, the adsorption mechanisms of FMPs mainly included surface complexation, electrostatic adsorption, inner-sphere complexation, hydrogen bonding, redox and pore-filling. In a multi-component system, FMPs exhibited an excellent affinity for capturing Pb(II) and Sb(III/V). This work provides an alternative method for designing and developing a series of novel adsorbent in removing multiple heavy metal(loid)s from wastewater, and demonstrated its application prospect in the remediation of multi-metal(loid) composite polluted water.

Recent advances in application of iron-manganese oxide nanomaterials for removal of heavy metals in the aquatic environment

Heavy metal pollution has a serious negative impact on the ecological environment and human health due to its toxicity, persistence, and non-biodegradable properties. Among the technologies applied in heavy metals removal, adsorption has been widely used as the most promising method because of its simple operation, high removal efficiency, strong applicability, and low cost. Iron-manganese oxide nanomaterials, as an effective absorbent, have attracted wide attention due to their simple preparation, wide material sources, and lower ecological impact. So far, no quantitative investigation has been conducted on the preparation and application of iron-manganese oxide nanomaterials in heavy metals removal. This review discussed the preparation methods and characteristics of iron‑manganese oxide nanomaterials over the past decade and provided some basic information for the improvement of preparation methods. The physicochemical properties of iron‑manganese oxide nanomaterials and environmental conditions are regarded as important factors that affect the removal efficiency of heavy metals. In addition, the removal mechanisms of heavy metals in aqueous solution with iron‑manganese oxide nanomaterials were mainly included redox, complex precipitation, electrostatic attraction, and ion exchange. The reusability and practicability in actual wastewater treatment of 3nganese oxide nanomaterials were further discussed. Several key problems still need to be solved in the existing progress, such as improving the ability and stability of the iron‑manganese oxide nanomaterials to remove heavy metals from actual wastewater. In conclusion, this review provides a future direction for the application of iron‑manganese oxide nanomaterials for heavy metals removal and even in the large-scale treatment of actual wastewater.

Manganese-doped ferrihydrite/cellulose/polyvinyl alcohol composite membrane: Easily recyclable adsorbent for simultaneous removal of arsenic and cadmium from soil

Simultaneous removal of arsenic (As) and cadmium (Cd) from soil has been a matter of great concern. In this study, manganese-doped ferrihydrite/cellulose/polyvinyl alcohol composite membranes were prepared via loading manganese-doped ferrihydrite on cellulose mesh and then wrapping with polyvinyl alcohol. The obtained composite membranes exhibited excellent mechanical properties and could be easily separated from soil. The adsorption capacities of Cd(II) and As(III) on the composite membrane were 11.11 mg/g and 72.08 mg/g respectively. After mixing the composite membrane with polluted soil at dosage of 0.3% (w/w), the removal efficiency of the toxicity characteristic leaching procedure leachable As and Cd reached 65% and 69% respectively with one cycle. The stability and reusability of composite membrane were demonstrated by no decrease in tensile strength and the retention of 94% and 96% of As(III) and Cd(II) removal efficiency respectively after four adsorption cycles. The prepared composite membrane had application prospect in the remediation of As and Cd co-polluted soil.

CTAB-functionalized δ-FeOOH for the simultaneous removal of arsenate and phenylarsonic acid in phenylarsenic chemical warfare

This study prepared a cetyltrimethylammonium bromide (CTAB) functionalized δ-FeOOH using the coprecipitation method to remove arsenate and phenylarsonic acid in water polluted by phenylarsonic chemical warfare agents. Under neutral conditions, the adsorption capacity for arsenate and phenylarsonic acid was 45.7 and 85.3 mg g^-1, respectively. The adsorption process conformed to the pseudo-second-order kinetics and Freundlich isothermal adsorption model, and the adsorption was spontaneous and endothermic. The CTAB-functionalized δ-FeOOH could effectively resist the interference of coexisting anions except for CO₃^2-, SiO₃^2- and PO₄^3-. Furthermore, the adsorption mechanism was proposed by combining the adsorption experimental results, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and density functional theory analyses. The results showed that the adsorption of arsenate by the CTAB-functionalized δ-FeOOH was mainly through the formation of bidentate-dinuclear inner-sphere complexes and electrostatic interactions. While for phenylarsonic acid, the formation of monodentate-mononuclear inner-sphere complexes on (100) and (110) crystal facets, and the formation of bidentate-dinuclear inner-sphere complexes on the (002) crystal facet, as well as hydrogen bonding, electrostatic interaction, and π-hydrophobic interaction between organic compounds were the primary mechanism. Moreover, the CTAB-functionalized δ-FeOOH could maintain about 60% of the adsorption capacity for the two pollutants after five cycles. Overall, CTAB-functionalized δ-FeOOH has good potential for the remediation of inorganic and organic arsenic-contaminated water bodies.

Self-enhanced and efficient removal of As(III) from water using Fe-Cu-Mn composite oxide under visible-light irradiation: Synergistic oxidation and mechanisms

Here, we prepared a novel nanostructured Fe-Cu-Mn composite oxide (FCMO_x) adsorbent using an ultrasonic coprecipitation method. The maximum adsorption capacity of As(III) and As(V) reached 158.5 and 115.2 mg/g under neutral conditions, respectively. The effects of several environmental factors (coexisting ions, solution pH, etc.) on the removal of inorganic arsenic using FCMO_x were studied through batch experiments. The results showed that except for PO₄^3- and high initial pH, it was not significantly affected by ionic strength and other existing anions, implying a higher selectivity and adaptability. Combined with EPR, FTIR, and XPS analysis, we concluded that the Cu component and the reactive oxygen species (ROS) it generates played a decisive role in maintaining the stability of the redox cycle between Mn(IV)/Mn(III)/Mn(II) and enhancing the oxidation efficiency of As(III). Meanwhile, the adsorption mechanism of As(V) was mainly through the replacement of the FCMO_x surface -OH to form stable inner-sphere arsenic complexes, while the removal mechanism of As(III) may involve the process of synergistic oxidation and chemisorption coupling. Additionally, the effective removal of As from the simulated As-contaminated water and its satisfactory reuse performance make FCMO_x adsorbents favorable candidates for the removal of As-contaminated water in the future.

Arsenic(iii) removal from aqueous solution using TiO2-loaded biochar prepared by waste Chinese traditional medicine dregs

Oxidation of As(iii) to As(v) is an effective way to improve the performance of most arsenic removal technologies. In this study, a new alternative biosorbent, TiO₂-loaded biochar prepared by waste Chinese traditional medicine dregs (TBC) was applied in remediation for As(iii) from aqueous solution. Compared with unmodified biochar, the specific surface areas and total pore volumes of TBC increased while the average aperture decreased due to the loading of nano-TiO₂. The X-ray diffraction (XRD) of TBC confirmed that the precipitated titanium oxide was primarily anatase. pH did not have a significant effect on the adsorption capacity at 10 mg L⁻¹ As(iii) in suspension with a pH ranging from 2 to 10. Adsorption kinetics data were best fitted by the pseudo-second-order model (R² > 0.999). The Sips maximum adsorption capacity was 58.456 mg g⁻¹ at 25 °C, which is comparable with other adsorbents reported in previous literature. The Gibbs free energy (ΔG) of As(iii) adsorption was negative, indicating the spontaneous nature of adsorption. The results of free radical scavenging and N₂ purging experiments indicated that O₂ acted as an electron accepter and O₂˙⁻ dominated the oxidation of As(iii). The oxidation of As(iii) obviously affected the adsorption capacity for As(iii) by TBC. X-ray photoelectron spectroscopy (XPS) studies showed that As(iii) and As(v) existed on the surface of TBC, suggesting that the oxidation of As(iii) occurred. TBC played multiple roles for As(iii), including direct adsorption and photocatalytic oxidation adsorption. Regeneration and stability experiments showed that TBC was an environment-friendly and efficient adsorbent for As(iii) removal.

TiO₂-loaded biochar prepared by waste Chinese traditional medicine dregs (TBC) was applied in remediation for As(iii) from aqueous solution.

Anchoring Al- and/or Mg-oxides to magnetic biochars for Co-uptake of arsenate and fluoride from water

The co-occurrence of arsenic and fluoride in the water environment has led to many health concerns for living beings. Simultaneous removal of such ions is crucial to the safety of water resources, and biochar has been extensively engaged to address this issue. Here four magnetic biochars (mBCs) including pristine magnetic biochar and three aluminum (Al) and/or magnesium (Mg) oxides-anchored magnetic biochar (i.e., Al-mBC, Mg-mBC, and MgAl-mBC) were prepared via a facile pyrolysis method and then comprehensively evaluated as adsorbents for enhanced co-uptake of arsenate (As^V) and fluoride (F^-) from synthetic water. The mBC shows a high specific surface area of 205 m² g^-1, which dropped to 116, 80, and 114 m² g^-1 upon the anchoring of Al, Mg, and Mg + Al, respectively. Our results suggest that the adsorption of either As^V or F^- is highly pH-dependent, and pH 4-6 is the optimal range for maximum adsorption. The adsorption isotherm data indicate that the MgAl-mBC adsorbent outranks all other mBCs for co-uptake of both As^V and F^-. The adsorption capacity maxima of MgAl-mBC are 34.45, and 21.59 mg g^-1 for As^V and F^-, respectively (pH = 5, T = 10 °C), also highly outstripping other biochars reported in the literature. The magnetic feature of these mBCs enables us to fast reclaim and regenerate the exhausted adsorbents by an external magnet and dilute NaOH. The Al- and Mg-anchored mBCs are expected to be used as highly efficient adsorbents for environmental remediation of waters contaminated by both As^V and F^-.

As(III) adsorption onto Fe-impregnated food waste biochar: experimental investigation, modeling, and optimization using response surface methodology

Biochar derived from food waste was modified with Fe to enhance its adsorption capacity for As(III), which is the most toxic form of As. The synthesis of Fe-impregnated food waste biochar (Fe-FWB) was optimized using response surface methodology (RSM), and the pyrolysis time (1.0, 2.5, and 4.0 h), temperature (300, 450, and 600 °C), and Fe concentration (0.1, 0.3, and 0.5 M) were set as independent variables. The pyrolysis temperature and Fe concentration significantly influenced the As(III) removal, but the effect of pyrolysis time was insignificant. The optimum conditions for the synthesis of Fe-FWB were 1 h and 300 °C with a 0.42-M Fe concentration. Both physical and chemical properties of the optimized Fe-FWB were studied. They were also used for kinetic, equilibrium, thermodynamic, pH, and competing anion studies. Kinetic adsorption experiments demonstrated that the pseudo-second-order model had a superior fit for As(III) adsorption than the pseudo-first-order model. The maximum adsorption capacity derived from the Langmuir model was 119.5 mg/g, which surpassed that of other adsorbents published in the literature. Maximum As(III) adsorption occurred at an elevated pH in the range from 3 to 11 owing to the presence of As(III) as H₂AsO₃^- above a pH of 9.2. A slight reduction in As(III) adsorption was observed in the existence of bicarbonate, hydrogen phosphate, nitrate, and sulfate even at a high concentration of 10 mM. This study demonstrates that aqueous solutions can be treated using Fe-FWB, which is an affordable and readily available resource for As(III) removal.

Fast and effective arsenic removal from aqueous solutions by a novel low-cost eggshell byproduct

Developing alternative green solutions for local and correct recycling of eggshells waste (ES) are needed by the egg-processing industries. In this study, we proposed transforming ES into a novel low-cost chemical compound named hydroxyl-eggshell (ES-OH) and investigated its capacity for arsenic (As) removal from aqueous solutions. Laboratory experiments were conducted to investigate the effects of ES-OH doses, pH, kinetics, and isotherms on As removal efficiency. The kinetics study showed that ES-OH removed nearly all As from solution in less than 15 min. The pseudo-second-order model described the process, and the maximum As removal capacity predicted by the Langmuir isotherm model was 529 mg g^-1. Using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy with energy dispersive X-ray detector (SEM-EDS), and X-ray diffraction (XRD), we found that the As removal mechanism by ES-OH was due to vladimirite precipitation, followed by weak electrostatic interactions between the precipitate and arsenate ions. Finally, after an economic analysis, we conclude that besides being a novel and economical income source, egg-producing companies might implement the ES-OH production process as a local environmentally-friendly way of recycling eggshells and reducing water As contamination.

Ecofriendly remediation technologies for wastewater contaminated with heavy metals with special focus on using water hyacinth and black tea wastes: a review

Treatment of water contaminated with heavy metals is challenging. Heavy metals are non-degradable, persistent in the environment, have a high dispersion capacity by water, can bioaccumulate, and represent risks to human and environmental health. Conventional treatment methods have disadvantages; however, adsorption in biomass is a highly promising method with high efficiency and low cost that avoids many of the disadvantages of conventional methods. Black tea (BT) wastes and water hyacinth (WH) have attracted attention for their ability to remove heavy metals from wastewater. Utilizing these approaches can remove contaminants and effectively manage problematic invasive species and wastes. The conventional uses of BT and WH were efficient for removing heavy metals from wastewater. Due to the unique and distinct properties and advantages of biochar and nano-forms of biosorbents, the use of BT and WH in these forms is promising to achieve sustainable heavy metals removal from wastewater. However, more study is needed to confirm preliminary results.

Performance and mechanisms for remediation of Cd(II) and As(III) co-contamination by magnetic biochar-microbe biochemical composite: Competition and synergy effects

Contaminations by heavy metals in the environment always exist as a mixture of both metal and metalloid. Thus, it is a challenge to simultaneously remove both components due to their adverse chemical behaviors. Herein, effective cadmium (Cd) and arsenic (As) removal in aqueous solution was achieved by use of a novel composite, which was synthesized by Bacillus sp. K1 loaded onto Fe₃O₄ biochar (MBB). The combination with Bacillus sp. K1 provided new biosorption sites such as amine and hydroxyl groups in the composite surface, which significantly increasing the removal capability of Cd(II) by 230% when compared with the raw magnetic biochar. Both competition and synergy effects were found in binary system. Adsorption of As(III) extended active sites for capturing Cd(II), which appeared on the surface of the MBB as type B ternary surface complexes. The maximum adsorption capacity of Cd(II) and As(III) reached 25.04 and 4.58 mg g^-1 in a binary system, respectively. In summary, this environmentally friendly composite is promising for simultaneous Cd(II) and As(III) remediation.

Comparative removal of As(V) and Sb(V) from aqueous solution by sulfide-modified α-FeOOH

Efficient elimination of As(V) and Sb(V) from wastewater streams has long been a major challenge. Herein, sulfide-modified α-FeOOH adsorbent was fabricated via a simple sulfidation reaction for removing As(V) and Sb(V) from aqueous media. Compared with the pristine α-FeOOH, sulfide-modified α-FeOOH increased the adsorption of As(V) from 153.8 to 384.6 mg/g, and Sb(V) adsorption from 277.8 to 1111.1 mg/g. The enhanced adsorption of both As(V) and Sb(V) was maintained at the pH range from 2 to 11, and was not interfered by various coexisting anions such as Cl^-, SO₄^2-, NO₃^-, SiO₃^2- and PO₄^3-. The adsorption affinity increased from 0.0047 to 0.0915 and 0.0053 to 0.4091 for As(V) and Sb(V), respectively. X-ray photoelectron spectroscopic investigation demonstrated a reductive conversion of As(V) to As(III) during the adsorption process with sulfide-modified α-FeOOH, but with no obvious variation of Sb(V) speciation. While the removal mechanism for As(V) was reduction followed by adsorption via hydroxyl groups, mainly surface complexation was involved in the removal of Sb(V). This study presented a simple strategy to enhance the adsorption capacity and adsorption affinity of α-FeOOH toward As(V)/Sb(V) via sulfide-modification.

Mitigating arsenic accumulation in rice (Oryza sativa L.) using Fe-Mn-La-impregnated biochar composites in arsenic-contaminated paddy soil

Arsenic (As) is a prominent metal contaminant of the soil in China. Pot experiments were conducted to examine the effects of corn stem powder biochar (BC) and Fe-Mn-La-impregnated biochar composites (FMLBC₁, FMLBC₂, and FMLBC₃; BC:Fe:Mn:La at different weight ratios) on As accumulation in an indica cultivar of rice (Oryza sativa L.). The application of FMLBCs and BC improved the dry weight of the grains, leaves, stems, and roots of rice. The As uptake in different rice organs was significantly reduced in the FMLBC-amended soils (FMLBC₃ > FMLBC₂ > FMLBC₁) compared with the BC treatment. Compared to the concentration of As in the control, the concentration of As in rice grains decreased by 56.0-89.4% with the addition of 2% FMLBC₃. The application of FMLBCs significantly increased the ratio of essential amino acids in grains and the contents of Fe and Mn plaques on root surfaces. The reduction in As accumulation can be ascribed to the Fe, Mn, and La oxides that enhance the adsorption and retention of As, as well as the FMLBCs that provide nutrients and create a rhizosphere environment, promoting rice growth. This study demonstrated that applications of 2% FMLBC₂ and FMLBC₃ have the potential to remediate As-contaminated soils, reduce As accumulation in rice plants, and improve rice grain quality.

Treatment of aqueous arsenic - A review of biochar modification methods

Arsenic (As) is an ever-present worldwide environmental contamination issue. The process of As sorption for treatment of contaminated waters is regarded as a promising treatment technology approach due to its simplicity and potential for high efficiency. Biochars are carbon-rich porous solids produced by heating of biomasses under low oxygen conditions. Biochars are considered to be environmentally friendly sorbents that can be used to treat various As-containing waters. However, unmodified biochar is generally a poor sorbent for As species due to static repulsion between the As oxyanions and the negatively charged biochar surface. The As sorption capacity of biochars can be substantially improved by treatments using various physical and chemical activation and modification methods. Thus, this review includes 63 research studies using physical and chemical approaches to enhance biochar physicochemical structures and As sorption efficiencies. The effectiveness of each method for altering the characteristics and sorption capacity of biochars is described. This review can help to focus the scope of future As biochar sorption studies and aid researchers in optimization of biochar-based sorbents for As treatment.

Adsorption of As(V) by the Novel and Efficient Adsorbent Cerium-Manganese Modified Biochar

Arsenic has become a global concern in water environment, and it is essential to develop efficient remediation methods. In this study, a novel adsorbent by loading cerium and manganese oxide onto wheat straw-modified biochar (MBC) was manufactured successfully aiming to remove arsenic from polluted water. Through scanning electron microscopy and energy-dispersive spectroscopy (SEM-EDS), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrometer (FT-IR), and other techniques, it was found the loading of cerium and manganese oxide on MBC played a significant role in As(V) adsorption. The results of the batch test showed that the adsorption of MBC followed the pseudo-second order kinetics and Langmuir equation. The adsorption capacity of MBC was 108.88 mg As(V)/g at pH = 5.0 (C0 = 100 mg/L, dosage = 0.5 g/L, T = 298 K) with considerable improvement compared to the original biochar. Moreover, MBC exhibited excellent performance over a wide pH range (2.0~11.0). Thermodynamics of the sorption reaction showed that the entropy (ΔS), changes of enthalpy (ΔH) and Gibbs free energy (ΔG), respectively, were 85.88 J/(moL·K), 22.54 kJ/mol and −1.33 to −5.20 kJ/mol at T = 278~323 K. During the adsorption, the formation of multiple complexes under the influence of its abundant surface M-OH (M represents the Ce/Mn) groups involving multiple mechanisms that included electrostatic interaction forces, surface adsorption, redox reaction, and surface complexation. This study indicated that MBC is a promising adsorbent to remove As(V) from polluted water and has great potential in remediating of arsenic contaminated environment.

Influence of the application of Fe-Mn-La ternary oxide-biochar composites on the properties of arsenic-polluted paddy soil

Arsenic exists ubiquitously in the soil and has been proved to be of significant hazard to human health upon transmission through food chain. Herein, we determined the effects of Fe-Mn-La ternary oxide-biochar composites (FMLBCs) on arsenic (As) fractionation, soil enzyme activities, and microbial communities in arsenic-polluted soils. The results demonstrated that the proportion of non-swappable As fractions reduced and that of the exchangeable As fractions increased with the addition of FMLBCs. Furthermore, the addition of FMLBCs significantly increased the catalase (CAT) activity (P < 0.05), and an increase of 69.2-268% was observed when 2 wt% FMLBCs were added. Supplementation with biochar or FMLBCs increased the relative abundance of Proteobacteria and Acidobacteria and decreased the relative abundance of Firmicutes; moreover, the effect was more obvious as the addition amount of biochar or FMLBCs increased. In addition, the FMLBCs, except for FMLBC3, increased the content of available phosphorus. Moreover, amendments of FMLBCs led to an increase in the available potassium content by an average of 212%, 113%, and 62.1% in highly polluted soil. Therefore, the FMLBCs affected the physical and chemical properties of soil in different manners. The results suggested that the addition of FMLBCs changed the distribution and increased the immobilization of As in the soil; this could indirectly reduce the risk of the transport of As to rice. The amendment mechanism of FMLBCs may include changes to the physicochemical soil properties and consequently, the soil enzyme activities are affected, which can influence the microbial communities in soils.

Nanoscale Zero-Valent Iron and Chitosan Functionalized Eichhornia crassipes Biochar for Efficient Hexavalent Chromium Removal

Sorption is widely used for the removal of toxic heavy metals such as hexavalent chromium (Cr(VI)) from aqueous solutions. Green sorbents prepared from biomass are attractive, because they leverage the value of waste biomass and reduce the overall cost of water treatment. In this study, we fabricated biochar (BC) adsorbent from the biomass of water hyacinth (Eichhornia crassipes), an invasive species in many river channels. Pristine BC was further modified with nanoscale zero-valent iron (nZVI) and stabilized with chitosan (C) to form C–nZVI–BC. C–nZVI–BC adsorbent showed high hexavalent chromium sorption capacity (82.2 mg/g) at pH 2 and removed 97.34% of 50 mg/L Cr(VI) from aqueous solutions. The sorption capacity of chitosan–nZVI-modified biochar decreased while increasing the solution pH value and ionic strength. The results of a sorption test indicated that multiple mechanisms accounted for Cr(VI) removal by C–nZVI–BC, including complexation, precipitation, electrostatic interactions, and reduction. Our study suggests a way of adding value to biomass waste by considering environmental treatment purposes.