As(III) and As(V) removal by using iron impregnated biosorbents derived from waste biomass of Citrus limmeta (peel and pulp) from the aqueous solution and ground water

Potential in treating arsenic-contaminated water of the biochars produced from hyperaccumulator Pteris vittata and its environmental safety

In this study, biochar derived from pyrolyzed aboveground parts of Pteris vittata (P. vittata) was modified with iron(Fe) and applied to aqueous solutions containing arsenite (As[III]) or arsenate (As[V]) for remediation purposes. The adsorption efficiency, biochar characteristics pre- and post-adsorption, microscopic As distribution, and As morphology were analyzed. Additionally, the potential and leaching safety of P. vittata biochar for As-contaminated water remediation were evaluated. Results indicated that P. vittata biochar contained oxygen-containing functional groups and aromatic structures. Modification with Fe increased specific surface area and total pore volume. Unmodified P. vittata biochar displayed low adsorption of As(III) and As(V), while Fe modification significantly enhanced As adsorption capacity and reduced As leaching by 69%-89%. Maximum adsorption capacities of Fe-modified P. vittata biochar for As(III) and As(V) were 7.64 and 10.2 mg/g, respectively, as determined by Langmuir fitting. The superior adsorption efficiency of As(V) over As(III) by Fe-modified biochar was attributed to better electrostatic interaction with the adsorbent. Analysis revealed similar As species in P. vittata biochar before and after adsorption, with a significant presence of As(III). Remarkably, As in P. vittata remained highly stable during pyrolysis and adsorption, possibly due to strong Fe-As binding. Fe-modified P. vittata biochar shows promise for application, but further pretreatment may be necessary to achieve optimal results.

Remediation of arsenic and fluoride from groundwater: a critical review on bioadsorption, mechanism, future application, and challenges for water purification

In the past few decades, the excessive and inadequate use of technological advances has led to groundwater contamination, mainly caused by organic and inorganic pollutants, which are highly harmful to human health, agriculture, water bodies, and aquaculture. Among all toxic pollutants, As and F- play a significant role in groundwater contamination due to their excellent reactivity with other elements. To mitigate the prevalence of arsenic and fluoride within the water system, the use of biochar gives an attractive strategy for removing them mainly because of the substantial surface area, pore size, pH, aromatic structure, and functional groups inherent in biochar, which are primarily dependent upon its raw material and pyrolysis temperature. Researcher develops different methods like physiochemical and electrochemical for treating arsenic and fluoride contamination. Among all removal methods, bioadsorption using agricultural waste residues shows effective/feasible removal of As and F- due to its low cost, ecofriendly nature, readily available, and efficient reuse compared with several other harmful synthetic materials that demand costly design specifications. This study discusses current developments in bioadsorption methods for As and F- that use agricultural-based biomaterials and describes the prevailing state of arsenic and fluoride removal strategies that use biomaterials precisely.

Enhanced arsenic removal by graphene oxide chitosan composites through FeOx decoration: Influences and mechanism

Iron decoration has been recognized as one of the most important paths to enhance contaminant adsorption by carbon-based composites. In this study, varying amounts of Fe (II) are used for the modification of graphene oxide chitosan (GOCS) materials to assess the impact of iron oxide (FeOx) morphology on the composites and their efficiency in arsenic (As) removal. Results show that incorporating 0.08 mol Fe(II) into GOCS yields better As removal performance, leading to a remarkable enhancement by 5 times for As(V) and 6 times for As(III). The iron minerals in the material consist of goethite (FeO(OH)) and magnetite (Fe3O4), with FeO(OH) playing a predominant role in As removal through the complexation and electrostatic attraction of -OH and Fe - O groups. The adsorption capacity for As (Qe) decreases with the increasing pH and the mass and volume ratio (m/v) but increases with the increasing initial concentration (C0). Besides, the presence of SO42- and HPO42- can significantly reduce As removal by the FeOx-modified GOCS. Under the conditions of pH = 3, m/v = 1.0 g/L, and C0 = 10 mg/L, a maximum Qe value reaches 61.94 mg/g. The adsorption is well-fitted to a pseudo-second-order kinetic model and is an endothermic, spontaneous, and monolayer adsorption process.

Sequestration of Ni (II), Pb (II), and Zn (II) utilizing biogenic synthesized Fe3O4/CLPC NCs and modified Fe3O4/CLPC@CS NCs: Process optimization, simulation modeling, and feasibility study

The present study reports low-cost novel biogenic magnetite Citrus limetta peels carbon (Fe3O4/CLPC) nanocomposites and modified Fe3O4/CLPC@CS nanocomposites cross-linked with glutaraldehyde and subsequently employed in batch mode sequestration of heavy metals ions. Diverse techniques fully characterized them, and the influence of operating variables on adsorption reactions from aqueous solutions was investigated. The Brunauer, Emmett, and Teller (BET) surface areas of synthesized Fe3O4/CLPC and Fe3O4/CLPC@CS NCs were 53.91 and 32.16 m2/g, while the mesoporous diameters were 7.69 and 7.57 nm, respectively. The Langmuir isotherm and Pseudo second order kinetic were well-fitting and capable of explaining the adsorption reaction. The Langmuir-based monolayer adsorption (qmax) for Fe3O4/CLPC@CS NCs was 82.65, 95.24, and 64.10 mg/g, higher than Fe3O4/CLPC NCs, which were 70.92, 84.75, and 59.17 mg/g for Ni (II), Pb (II), and Zn (II), respectively. Each metal's pseudo second order correlation coefficient (R2 ≥ 0.99) reveals that nanocomposites surface binding functional groups controlled the adsorption rate via chemisorption. Further, thermodynamic results confirm that each studied metal ions' adsorption was spontaneous, endothermic, and characterized by an increase in randomness. In addition to magnetic separability, three ad-desorption cycles yielded exceptional adsorption efficacy and > 93% regenerability. The present study also reveals the effective utilization of Fe3O4/CLPC and Fe3O4/CLPC@CS NCs as cost-effective magnetic separable green adsorbents for heavy metals sequestration from electroplating wastewater.

Effective biosorption of As(V) from polluted water using Fe(III)-modified Pomelo (Citrus maxima) peel: A batch, column, and thermodynamic study

Pomelo, Citrus maxima, peel was chemically modified with lime water and then loaded with Fe(III) to develop anion exchange sites for effective sequestration of As(V) from water. Biosorbent characterizations were done by using FTIR, SEM, XRD, EDX, and Boehm's titration. The batch biosorption studies were carried out at various pHs using modified and non-modified biosorbents and optimum biosorption of As(V) occurred at acidic pH (3.0-5.0) for both the biosorbents. A kinetic study showed a fast biosorption rate and obtained results fitted well with the pseudo-second-order (PSO) model. When isotherm data were modeled using the Langmuir and Freundlich isotherm models, the Langmuir isotherm model fit the data better and produced maximal As(V) biosorption capacities of 0.72 ± 03, 0.86 ± 06, and 0.95 ± 05 mmol/g at temperatures 293± 1K, 298± 1K and 303± 1K, respectively. Desorptionof As(V) was effective using 0.1 M NaOH in batch mode. Negative values of ΔG° for all temperatures with positive ΔH° confirmed the spontaneous and endothermic nature of As(V) biosorption. The existence of co-existing chloride (Cl^-), nitrate (NO₃ ^-), sodium (Na⁺), and calcium (Ca²⁺) showed insignificant interference whereas a high concentration of sulphate (SO₄ ^2-) and phosphate (PO₄ ^3-) significantly lowered As(V) biosorption percentage. Arsenic concentrations in actual arsenic polluted groundwater could be reduced to the WHO drinking water standard (10 μg/L) by using only 1 g/L of investigated Fe(III)-SPP. The dynamic biosorption of As(V) in a fixed bed system showed that Fe(III)-SPP was effective also in continuous mode and different design parameters for fixed bed system were determined using Thomas, Adams-Bohart, BDST, and Yoon-Nelson models. Therefore, from all of these results it is suggested that Fe(III)-SPP investigated in this study can be a potential, low cost and environmentally benign biosorbent material for an effective removal of trace amounts of arsenic from polluted water.

Efficient removal of total arsenic (As3+/5+) from contaminated water by novel strategies mediated iron and plant extract activated waste flowers of marigold

In this investigation, marigold flower-waste was activated with iron salts (MG-Fe), subsequently marigold plant extract (MG-Fe-Ex) for the adsorptive elimination of As³⁺ and As⁵⁺ from contaminated water. The governing factor such as medium pH, temperature, pollutant concentration, reaction time, adsorbent dose were considered for the study. The complete elimination of As^3+/5+ was recorded with MG-Fe-Ex at pH 8.0, 90 min, 30 °C, dose 4 g/L, 20 mg/L of As^3+/5+ and shaking rate 120 rpm, while under the identical experimental condition, MG-Fe exhibited 98.4% and 73.3% removal for As⁵⁺ and As³⁺, respectively. The MG-Fe-Ex contains iron oxides (Fe₂O₃ and Fe₃O₄) as a result of iron ions reaction with plant bioactive molecules as evident from x-ray diffraction analysis (XRD), energy dispersive x-ray spectroscopic (EDS) and Fourier transform infrared (FTIR) spectroscopic study. The adsorption data of As^3+/5+ on MG-Fe and MG-Fe-Ex was best fitted by pseudo-first order kinetic and freundlich isotherm except As⁵⁺ adsorption on MG-Fe-Ex that can be described by langmuir isotherm model. The prevailing mechanism in adsorption of As^3+/5+ on both adsorbent might be hydrogen bonding, electrostatic attraction and complexation. From the above, it is confirmed that MG-Fe-Ex adsorbent has high potential and can be used for the adsorptive elimination of As^3+/5+ from contaminated water in sustainable and environmentally friendly way.

Removal of arsenic from semiarid area groundwater using a biosorbent from watermelon peel waste

Groundwater is one of the most important reservoirs in semi-arid and arid zones of the world, particularly in Mexico. The aims of this work were to produce a biosorbent from watermelon peel waste and a biosorbent with citric acid treatment and to evaluate both biosorbents with different concentrations of arsenic in groundwater. The biosorbents were produced with watermelon peel residues, which were observed by SEM microscopy to evaluate their physical morphology. Its removal potential was tested at concentrations of 0, 1, 13, 22, and 65 μg/L of arsenic, and both adsorption capacity and removal percentage were analyzed by final measurement obtained by atomic absorption spectrometry. The pH was measured throughout the experimentation maintaining ranges between 5.5 and 7.5. The biosorbent without treatment presented clearer and more compact flakes. At the microscopic level, the biosorbent without treatment presented pores with a more circular shape, and the biosorbent with treatment was more polygonal, similar to a honeycomb. The highest removal percentage was 99.99%, for both treatments at 4 h. The biosorbent without treatment at 4 h with arsenic concentrations of 65 μg/L presented the highest adsorption capacity (2.42 μg/g). It is concluded that watermelon peel biosorbent is a material that has the potential to remove arsenic from groundwater. This type of biosorbent is effective to remove arsenic and could be used in the field, however, it still needs to be optimized to convert it into a material completely suitable for large-scale use.

Elevated Adsorption of Lead and Arsenic over Silver Nanoparticles Deposited on Poly(amidoamine) Grafted Carbon Nanotubes

An efficient adsorbent, CNTs-PAMAM-Ag, was prepared by grafting fourth-generation aromatic poly(amidoamine) (PAMAM) to carbon nanotubes (CNTs) and successive deposition of Ag nanoparticles. The FT-IR, XRD, TEM and XPS results confirmed the successful grafting of PAMAM onto CNTs and deposition of Ag nanoparticles. The absorption efficiency of CNTs-PAMAM-Ag was evaluated by estimating the adsorption of two toxic contaminants in water, viz., Pb(II) and As(III). Using CNTs-PAMAM-Ag, about 99 and 76% of Pb(II) and As(III) adsorption, respectively, were attained within 15 min. The controlling mechanisms for Pb(II) and As(III) adsorption dynamics were revealed by applying pseudo-first and second-order kinetic models. The pseudo-second-order kinetic model followed the adsorption of Pb(II) and As(III). Therefore, the incidence of chemisorption through sharing or exchanging electrons between Pb(II) or As(III) ions and CNTs-PAMAM-Ag could be the rate-controlling step in the adsorption process. Further, the Weber-Morris intraparticle pore diffusion model was employed to find the reaction pathways and the rate-controlling step in the adsorption. It revealed that intraparticle diffusion was not a rate-controlling step in the adsorption of Pb(II) and As(III); instead, it was controlled by both intraparticle diffusion and the boundary layer effect. The adsorption equilibrium was evaluated using the Langmuir, Freundlich, and Temkin isotherm models. The kinetic data of Pb(II) and As(III) adsorption was adequately fitted to the Langmuir isotherm model compared to the Freundlich and Temkin models.

ANN-GA based biosorption of As(III) from water through chemo-tailored and iron impregnated fungal biofilter system

The iron impregnated fungal bio-filter (IIFB) discs of luffa sponge containing Phanerochaete chrysosporium mycelia have been used for the removal of As(III) from water. Two different forms of same biomass viz. free fungal biomass (FFB) and modified free fungal biomass (chemically modified and iron impregnated; CFB and IIFB) have been simultaneously investigated to compare the performance of immobilization, chemo-tailoring and iron impregnation for remediation of As(III). IIFB showed highest uptake capacity and percentage removal of As(III), 1.32 mg/g and 92.4% respectively among FFB, CFB and IIFB. Further, the application of RSM and ANN-GA based mathematical model showed a substantial increase in removal i.e. 99.2% of As(III) was filtered out from water at optimised conditions i.e. biomass dose 0.72 g/L, pH 7.31, temperature 42 °C, and initial As(III) concentration 1.1 mg/L. Isotherm, kinetic and thermodynamic studies proved that the process followed monolayer sorption pattern in spontaneous and endothermic way through pseudo-second order kinetic pathway. Continuous mode of As(III) removal in IIFB packed bed bioreactor, revealed increased removal of As(III) from 76.40 to 88.23% with increased column height from 5 to 25 cm whereas the removal decreased from 88.23 to 69.45% while increasing flow rate from 1.66 to 8.30 mL/min. Moreover, the IIFB discs was regenerated by using 10% NaOH as eluting agent and evaluated for As(III) removal for four sorption–desorption cycles, showing slight decrease of their efficiency by 1–2%. SEM–EDX, pHzpc, and FTIR analysis, revealed the involvement of hydroxyl and amino surface groups following a non-electrostatic legend exchange sorption mechanism during removal of As(III).

Adsorption of As(III) and As(V) from aqueous solution by magnetic biosorbents derived from chemical carbonization of pea peel waste biomass: Isotherm, kinetic, thermodynamic and breakthrough curve modeling studies

The purpose of this research was to investigate the adsorption of arsenic (As) from aqueous solutions using MPAC-500 and MPAC-600 (magnetic-activated carbons synthesized from the peel of Pisum sativum (pea) pyrolyzed at 500 °C and 600 °C temperatures, respectively). The potential of both biosorbents for As adsorption was determined in batch and column mode. The characterization of both biosorbents was performed by energy dispersive spectroscopy, scanning electron microscope, pHZPC, particle size distribution, X-ray diffraction, zeta potential and Fourier-transform infrared spectroscopy. It was found that the efficiency of MPAC-600 was better than MPAC-500 for the adsorption of As(III) and As(V) ions. The adsorption capacities of MPAC-500 and MPAC-600 in removing As(III) were 0.7297 mg/g and 1.3335 mg/g, respectively, while the values of Qmax for As(V) on MPAC-500 and MPAC-600 were 0.4930 mg/g and 0.9451 mg/g, respectively. The Langmuir isotherm model was found to be the best fit for adsorption of As(III) by MPAC-500 and MPAC-600, as well as adsorption of As(V) by MPAC-500. The Freundlich isotherm model, on the other hand, was optimal for As(V) removal with MPAC-600. With R2 values close to unity, the pseudo-second-order kinetics were best fitted to the adsorption process of both As species. The Thomas model was used to estimate the breakthrough curves. The effects of coexisting oxyanions and regeneration studies were also carried out to examine the influence of oxyanions on As adsorption and reusability of biosorbents.

Magnetic Adsorbents for Wastewater Treatment: Advancements in Their Synthesis Methods

The remediation of water streams, polluted by various substances, is important for realizing a sustainable future. Magnetic adsorbents are promising materials for wastewater treatment. Although numerous techniques have been developed for the preparation of magnetic adsorbents, with effective adsorption performance, reviews that focus on the synthesis methods of magnetic adsorbents for wastewater treatment and their material structures have not been reported. In this review, advancements in the synthesis methods of magnetic adsorbents for the removal of substances from water streams has been comprehensively summarized and discussed. Generally, the synthesis methods are categorized into five groups, as follows: direct use of magnetic particles as adsorbents, attachment of pre-prepared adsorbents and pre-prepared magnetic particles, synthesis of magnetic particles on pre-prepared adsorbents, synthesis of adsorbents on preprepared magnetic particles, and co-synthesis of adsorbents and magnetic particles. The main improvements in the advanced methods involved making the conventional synthesis a less energy intensive, more efficient, and simpler process, while maintaining or increasing the adsorption performance. The key challenges, such as the enhancement of the adsorption performance of materials and the design of sophisticated material structures, are discussed as well.

Preparation and characterization of carrageenan-embedded lanthanum iron oxide nanocomposite for efficient removal of arsenite ions from water

Arsenic (As) contamination in drinking water has grown into a global concern in recent years, which demands the development of various As remediation approaches. In this study, a new magnetic nanocomposite, carrageenan-embedded LaFeO₃ nanoparticles (abbreviated as CA-LaFeNPs) was synthesized by a sol-gel process and used to remove arsenite [As(III)] from water. The synthesized magnetic adsorbent was characterized by powder XRD, SEM, FTIR, VSM, and TGA. The adsorbent gel, CA-LaFeNP was mainly with LaFeO₃ in nanoscale particles with a saturation magnetization of 13.33 emu g^-1 and could be easily separated from water with a simple hand-held magnet in 2 minutes. The adsorption outcomes of the CA-LaFeNPs could be finely interpreted by Langmuir, Freundlich, and Tempkin isotherm models. The Langmuir isotherm model appears to have good regression coefficients, and maximum adsorption capacity was estimated to be 91 mg g^-1 for CA-LaFeNPs at 27 °C and pH 7. The removal efficiency observed for CA-FeNPs was 91% up to the As(III) concentration of 700 mg L^-1, while it decreased to 85% when the As(III) concentration was above 1200 mg L^-1. This low-cost and environmentally-friendly magnetic nanocomposite, CA-LaFeNPs could be more appropriate for real-world applications and also a substitute for the traditional magnetic nanoparticles.

Modification of naturally abundant resources for remediation of potentially toxic elements: A review

Water and soil contamination due to potentially toxic elements (PTEs) represents a critical threat to the global ecosystem and human health. Naturally abundant resources have significant advantages as adsorbent materials for environmental remediation over manufactured materials such as nanostructured materials and activated carbons. These advantages include cost-effectiveness, eco-friendliness, sustainability, and nontoxicity. In this review, we firstly compare the characteristics of representative adsorbent materials including bentonite, zeolite, biochar, biomass, and effective modification methods that are frequently used to enhance their adsorption capacity and kinetics. Following this, the adsorption pathways and sites are outlined at an atomic level, and an in-depth understanding of the structure-property relationships are provided based on surface functional groups. Finally, the challenges and perspectives of some emerging naturally abundant resources such as lignite are examined. Although both unamended and modified naturally abundant resources face challenges associated with their adsorption performance, cost performance, energy consumption, and secondary pollution, these can be tackled by using advanced techniques such as tailored modification, formulated mixing and reorganization of these materials. Recent studies on adsorbent materials provide a strong foundation for the remediation of PTEs in soil and water. We speculate that the pursuit of effective modification strategies will generate remediation processes of PTEs better suited to a wider variety of practical application conditions.

Sustainable removal of arsenic from simulated wastewater using solid waste seed pods biosorbents of Cassia fistula L

The present investigation is focused to develop a new type of solid waste based biosorbent, derived from the Cassia fistula pod biomass. The prepared biosorbent has been characterized through different techniques including field emission scanning electron microscopy, fourier transform infrared spectroscope and X-ray diffraction to investigate the physiochemical properties which are potential for the bioadsorbent application. The experiments have been performed considering four parameters namely; pH, biosorbent dose, initial concentration of As⁺³ and duration in the batch reactor. The experimental results have been analyzed using the design-expert software for the optimization of different parameters. The maximum removal of arsenic could be achieved ∼91% whereas monolayer adsorption capacity is found to be 1.13 mg g^-1 in 80 min at pH 6.0 and 30 °C by using 60 mg dose of bioadsorbent. The arsenic adsorption behavior of the bio-adsorbent has been well interpreted in terms of pseudo-first order and Freundlich model.

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.

Performance of a novel iron infused biochar developed from Raphanus sativus and Artocarpus heterophyllus refuse for trivalent and pentavalent arsenic adsorption from an aqueous solution: mechanism, isotherm and kinetics study

Fabrication of magnetic biochar was done by pyrolysis of waste leaves of Raphanus sativus (MRB) and Artocarpus heterophyllus (MJB) peel pretreated with FeCl₃ was examined for As(III and V) adsorption from an aqueous solution. The synthesized bioadsorbents were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), particle size analysis (PSA), scanning electron microscope (SEM), energy dispersive x-ray (EDX), zeta potential, Vibrating sample magnetometer (VSM) and point of zero charge (pH_ZPC). MRB-800 exhibits greater efficiency toward the removal of both As species with q_max value 2.08 mg/g for As(III) and 2.03 mg/g for As(V). Whereas, the q_max value was 1.13 mg/g for As (III) and 1.26 mg g^-1 for As (V) adsorption using MJB-800. Temkin and Freundlich isotherm were best fitted to the adsorption of As(III) and As(V) by MRB-800, respectively. Langmuir isotherm was best followed to the adsorption of As (III and V) by MJB-800. Pseudo-second-order kinetics was well simulated by the experimental data of As adsorption using both the bioadsorbents. Surface complexation and electrostatic attraction was dominant mechanism for As (III) and As (V) adsorption. Thermodynamic study shows that removal of As (III) was exothermic while the As (V) adsorption was endothermic for MRB-800 and MJB-800.

Arsenic removal via a novel hydrochar from livestock waste co-activated with thiourea and γ-Fe2O3 nanoparticles

Arsenic (As) contaminants post tremendous threats to environment safety. Pristine hydrochar (PHC), thiourea-activated hydrochar (THC), and thiourea-Fe(NO₃)₃-activated hydrochar (Fe₂O₃@THC) were fabricated from dairy cattle manure via one-pot hydrothermal carbonization at 250 ℃ and applied for aqueous As(V) removal. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were conducted to characterize hydrochars and As(V) adsorption. Thiourea increased N and S functional groups (-NH₂, C-N, C=S and S=O). Fe(NO₃)₃ introduced γ-Fe₂O₃ nanoparticles and provided Fe₂O₃@THC with Fe-O. The combination of thiourea and Fe(NO₃)₃ granted Fe₂O₃@THC with the largest surface area (33.45 m²/g), and the highest total pore volume (0.095 cm³/g) among three hydrochars. As(V) adsorption was a physicochemical process involving electrostatic attraction, complexation, ion exchange and H-bond interaction. The maximum As(V) adsorption capacities and partition coefficients decreased as follows: Fe₂O₃@THC (44.80 mg/g; 38.44 L/g) > THC (38.77 mg/g; 5.94 L/g) > PHC (19.05 mg/g; 1.17 L/g). Three hydrochars exhibited preferable reusability in NaOH solution with only 24.2%, 11.8% and 14.1% decrease in adsorption rates after four cycles for PHC, THC and Fe₂O₃@THC, respectively. Fe₂O₃@THC is a promising adsorbent for efficient As(V) removal. This study explored the efficient As(V) removal by activated hydrochars with future research potential.

Removal of arsenic from aqueous solution by novel iron and iron-zirconium modified activated carbon derived from chemical carbonization of Tectona grandis sawdust: Isotherm, kinetic, thermodynamic and breakthrough curve modelling

The aim of the present study was: development of activated carbon modified with iron (Fe@AC) and modified with iron and zirconium (Fe-Zr@AC) from the Tectona grandis sawdust (TGS) waste biomass and its potential applicability for the removal of As (III) from contaminated water by batch and column mode. The biomass waste was pre-treated with ferric chloride (FeCl₃) and the mixture of FeCl₃ and zirconium oxide (ZrO₂) and then pyrolyzed at 500 °C for 2 h. The properties of both bioadsorbents were comprehensively characterized by using Scanning electron microscopy (SEM), Energy dispersive X-ray (EDX), Fourier transform infra-red spectroscopy (FTIR), X-ray diffraction (XRD), Particle Size analysis (PSA), point of zero charge (pH_ZPC), Brunauer-Emmett-Teller (BET) to prove successful impregnation of the Fe and Zr on the surface of AC of TGS. FTIR analysis clearly indicates the Fe and Fe-Zr complexation on biosorbents surface and biosorption of As (III). The results revealed that maximum As (III) removal was achieved 86.35% by Fe-Zr@AC (3 g/L dose, pH-7.0, temperature-25 °C and concentration 0.5 mg/L). However, maximum removal of As (III) was attained ~75% by Fe@AC (with dose-4g/L, pH-7.0, temperature-25 °C and concentration 0.5 mg/L) at the initial concentration of 0.5 mg/L of As (III). Fe-Zr@AC exhibits higher efficiency with q_max value 1.206 mg/g than Fe@AC with the q_max value 0.679 mg/g for the removal of As(III). While in the column study, Fe-Zr@AC exhibited 98.8% removal at flow rate of 5 mL/min and bed height of 5 cm. Biosorption Isotherm and Kinetics were fitted good with Langmuir isotherm (R² ≥ 0.99) and followed pseudo-second-order (R² ≥ 0.99). The regeneration study indicates that the prepared biosorbents efficiently recycled up to five cycles. Therefore, Fe@AC and Fe-Zr@AC derived from TGS has been showed to be novel, effective, and economical biosorbent. The collective benefits of easy development, good affinity towards As (III), good separability, reusability, and inexpensive of magnetized Fe@AC and Fe-Zr@AC make it a novel biosorbent. The application of Fe-Zr@AC for the removal of As (III) from the water was very efficient its concentration in the solution after treatment was found below the 10 μg/L as per the guideline WHO.

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.

Calcium oxide modification of activated sludge as a low-cost adsorbent: Preparation and application in Cd(II) removal

In this study, a simple to produce, low-cost and environment-friendly sludge based adsorbent, prepared from municipal dewatered sludge and modified by calcium oxide (CaO), is described. The enhancement effect of CaO modification on the adsorption capacity and mechanical strength of sludge based adsorbents (CaO-SA), and the modification mechanism of CaO on activated sludge are discussed. Also, the Cd(II) adsorption conditions are optimized using surface optimization experiment. The results indicated that CaO had a good effect on improving the adsorption capacity and mechanical strength of the sludge-based adsorbent. The CaO-SA adsorbent showed best performance with respect to the mechanical strength and Cd(II) adsorption capacity when prepared under 5% CaO dosage and 60 °C drying temperature. CaO modification can increase the specific surface area and calcium ion content of the sludge-based adsorbent and remove the proton of the carboxylic acid in the sludge. The Box-Behnken experimental design results revealed that the importance of operating conditions for CaO-SA adsorption of Cd(II) can be arranged in the order of adsorption time > dosage> pH> temperature. The results also indicated that the interactions between adsorption time and CaO-SA dosage, adsorption time and pH, adsorption time and temperature are all important factors affecting the Cd(II) adsorption. The optimal conditions (adsorption time of 90 min, CaO-SA dosage of 1 g/L, pH of 5 and adsorption temperature of 40 °C) for CaO-SA to adsorb Cd(II) were obtained by surface optimization, at which the Cd(II) adsorption rate could reach a value of 99.74%.

Synthesis of nano-zirconium-iron oxide supported by activated carbon composite for the removal of Sb(v) in aqueous solution

In this study, nano zirconium iron oxide based on activated carbon (ZIC) was successfully prepared by using the coprecipitation method. Compared with unmodified activated carbon, ZIC increases the number of active sites by adding metal oxides and hydroxyl groups and greatly improves the adsorption capacity of Sb(v). The synthesized nanocomposites were characterized and analysed by XRD, SEM, FT-IR, VSM and other techniques. The results showed that the zirconium iron oxide particles were successfully loaded and uniformly distributed on the surface of the activated carbon, and the agglomeration phenomenon was reduced. The saturation magnetization of ZIC was 1.89 emu g⁻¹, which easily achieved solid–liquid separation under the action of an external magnetic field. In batch experiments, when the initial concentration was 1 mg L⁻¹, the dosage of ZIC was 600 mg L⁻¹, the pH value was 5.0, the contact time was 180 min, and the removal rate of Sb(v) reached 97.82%. The maximum adsorption capacity of ZIC for Sb(v) was 11.80 mg g⁻¹. Under the interference of various inorganic ions and dissolved organics, the excellent adsorption capacity was still due to ZIC. The adsorption form was multimolecular-layer adsorption, the adsorption process was an endothermic reaction, and chemical adsorption was dominant as the adsorption mechanism. ZIC has good removal efficiency and is reusable, which indicates that ZIC has prospects for practical wastewater treatment.

The adsorbent was highly effective in the removal of Sb(v). The adsorbent easily achieved solid–liquid separation under the action of an external magnetic field.

Efficient removal of As(V) from aqueous media by magnetic nanoparticles prepared with Iron-containing water treatment residuals

Two types of magnetic nanoparticles prepared with chemical agents (cMNP) and iron-containing sludge (iMNP), respectively, were synthesized by co-precipitation process and used to remove arsenate [As(V)] from water. The synthesized magnetic adsorbents were characterized by XRD, XPS, TEM, BET, VSM and FTIR. The adsorbents iMNP and cMNP were both mainly γ-Fe₂O₃ in nanoscale particles with the saturation magnetization of 35.5 and 69.0 emu/g respectively and could be easily separated from water with a simple hand-held magnet in 2 minutes. At pH 6.6, over 90% of As(V), about 400 μg/L, could be removed by both adsorbents (0.2 g/L) within 60 min. The adsorption isotherm of both fabricated materials could be better described by the Langmuir adsorption isotherm model than the Freundlich’s, In addition, the adsorption kinetics of both adsorbents described well by the pseudo-second order model revealed that the intraparticle diffusion was not just the only rate controlling step in adsorption process. With the larger maximum As(V) adsorption capacity of iMNP (12.74 mg/g), compared with that of cMNP (11.76 mg/g), the iMNP could be regarded as an environmentally friendly substitute for the traditional magnetic nanoparticles prepared with chemical agents.

Bio-sorbents, industrially important chemicals and novel materials from citrus processing waste as a sustainable and renewable bioresource: A review

Citrus waste includes peels, pulp and membrane residue and seeds, constituting approximately 40-60% of the whole fruit. This amount exceeds ~110-120 million tons annually worldwide. Recent investigations have been focused on developing newer techniques to explore various applications of the chemicals obtained from the citrus wastes. The organic acids obtained from citrus waste can be utilized in developing biodegradable polymers and functional materials for food processing, chemical and pharmaceutical industries. The peel microstructures have been investigated to create bio-inspired materials. The peel residue can be processed to produce fibers and fabrics, 3D printed materials, carbon nanodots for bio-imaging, energy storage materials and nanostructured materials for various applications so as to leave no waste at all. The article reviews recent advances in scientific investigations to produce valuable products from citrus wastes and possibilities of innovating future materials and promote zero remaining waste for a cleaner environment for future generation.