Adsorption Capacity Of Cd Research Articles

KMnO4-activated spinach waste biochar: An efficient adsorbent for adsorption of heavy metal ions in aqueous solution

Developing advanced carbon materials by utilizing biomass waste has attracted much attention. Herein, a novel carbon adsorbent derived from Spinach waste was prepared by using pyrolysis procedure with KMnO4 as the activator. The preparation condition such as activator mass ratio (0–0.16) and activation temperature (200–800 °C) were comprehensively studied. The optimal sample (SBC-0.08–500) showed a 7.38-fold increase in specific surface area compared to the original biochar (SBC-500). Adsorption experiments revealed that SBC-0.08–500 had efficient removal capabilities for Cd(II), Pb(II), Cu(II), and Zn(II) ions. The maximum adsorption capacities for Cd(II), Pb(II), Cu(II), and Zn(II) ions at 298.15 K were 1.66, 2.88, 1.31, and 2.09 mmol∙g−1, respectively. Thermodynamic results indicated that the adsorption of Cd(II), Pb(II), and Zn(II) ions on SBC-0.08–500 was a spontaneous endothermic process. Additionally, SBC-0.08–500 had a high affinity for Pb(II) ions, making it a potential selective adsorbent for the removal of mixed heavy metal ions. The mechanism underlying the adsorption process was attributed to multiple interactions, including ion exchange, electrostatic interaction, and surface complexation. The as-prepared biochar by oxidative activation pyrolysis effectively solves the issues of subsequent chemical recycling and secondary pollution, thus providing greater potential for large-scale use.

Exploring adsorption capacity and mechanisms involved in cadmium removal from aqueous solutions by biochar derived from euhalophyte

Biochar has shown potential as a sorbent for reducing Cd levels in water. Euhalophytes, which thrive in saline-alkali soils containing high concentrations of metal ions and anions, present an intriguing opportunity for producing biochar with inherent metal adsorption properties. This study focused on biochar derived from the euhalophyte Salicornia europaea and aimed to investigate its Cd adsorption capacity through adsorption kinetics and isotherm experiments. The results demonstrated that S. europaea biochar exhibited a high specific surface area, substantial base cation content, and a low negative surface charge, making it a highly effective adsorbent for Cd. The adsorption data fit well with the Langmuir isotherm model, revealing a maximum adsorption capacity of 108.54 mg g−1 at 25 °C. The adsorption process involved both surface adsorption and intraparticle diffusion. The Cd adsorption mechanism on the biochar encompassed precipitation, ion exchange, functional group complexation, and cation-π interactions. Notably, the precipitation of Cd2+ with CO32− in the biochar played a dominant role, accounting for 73.7% of the overall removal mechanism. These findings underscore the potential of euhalophytes such as S. europaea as a promising solution for remediating Cd contamination in aquatic environments.

Biomass chitosan/sodium alginate colorimetric imprinting hydrogels with integrated capture and visualization detection for cadmium(II)

Due to Cd(II) with highly toxic, persistent and bioaccumulative, the discharge of it into the environment brings serious pollution. Developing strategies that are efficient, low-cost, pollution-free and specific to removing Cd(II) from wastewater is therefore of great urgency and prime importance. A novel chitosan/sodium alginate ionic imprinting(IICA) hydrogels with specific adsorption capacity for Cd(II) was prepared through freeze-thaw and ion imprinting, and finally the colorimetric sensor (IICAS) was prepared via introducing Rhodamine B(RhB) and Victoria blue(VBB) by immersion to achieve visual detection of Cd(II). The IICA hydrogels with imprinted hole structure had higher adsorption capacity and better specific selectivity for Cd(II). As well as internal diffusion, coordination, ion exchange, and hydrogen bonding influenced the adsorption rate. Moreover, the IICAS exhibited good selective detection ability and linearity for Cd(II) with the fitted correlation coefficient (R2) = 0.98, limit of detection (LOD) = 35 nmol/L. Combined with the smartphone platform, portable and quantitative detection of Cd(II) can be achieved, Within the 0–100 mg/L range, R2 remained 0.94, and LOD was 75 nmol/L. This strategy of preparing a novel whole biomass IICAS integrating capture and visual detection provides a new insight into the construction of a promising candidate sensor for the removal and detection of Cd(II).

Research Investigates and Simulation Behavior of the Failure Characteristics of Red Mud–Loess Type Permeable Reactive Barriers PRB in Fixed‐Bed Column Experiments

Controlling and remediating water and soil pollution while efficiently utilizing solid waste is essential for comprehensive environmental protection and sustainable development, particularly in establishing green, low‐carbon economic systems in China. We evaluate the impact of initial concentration, flow rate, and bed height on breakthrough performance and adsorption capacity using the Tessier method under dynamic water flow conditions. Additionally, we analyze micromorphological changes in the red mud–loess mixture before and after breakthrough by acid mine drainage containing Pb and Cd in mining areas, employing soil column experiments and numerical simulations with COMSOL Multiphysics. Our findings suggest that reducing initial concentration and flow rate while increasing bed height leads to higher breakthrough time, saturation time, and adsorption capacity for Pb and Cd in the red mud–loess mixture (7 : 3). Furthermore, the red mud–loess blend (7 : 3) demonstrates sustained and efficient acid‐buffering capability in the presence of acid mine drainage containing Pb and Cd. Notably, under specific conditions (initial Pb content at 100 mg/L, a height of 7 cm, and flow rate set at 1 mL/min), the adsorption capacity of red mud–loess (7 : 3) reaches 17.30 mg/g. The prescribed minimum length for PRBs is 11.40 cm. Under specified conditions (Cd concentrations at 100 mg/L, a height of 5 cm, and a flow rate of 1 mL/min), the material exhibits a notable adsorption capacity of 29.91 mg/g, with a theoretical minimum length for PRBs at 8.95 cm. Increasing bed heights successfully remove Pb and Cd ions through chemical precipitation. The BDST model accurately describes the breakthrough curves of Pb and Cd and develops a correlation formula for the breakthrough time of red mud–loess PRB medium. As the saturation of Pb increases from 0.05 to 0.85, the maximum volume adsorption capacity of Pb increases from 1.78 to 2.98 mg/L, while for Cd, it increases from 4.15 to 7.87 mg/L. Elevating the bed height first triggers chemical precipitation, hence improving Pb and Cd removal. Consequently, the longevity of red mud–loess PRB in acidic mine effluent containing Pb and Cd surpasses predicted theoretical outcomes. These observations reveal correlations between the breakthrough length for red mud–loess permeable reactive barriers and the bed height. Furthermore, the distribution of Pb speciation within the red mud–loess mixture (7 : 3) is primarily governed by the presence of iron–manganese oxide, while the composition of Cd speciation is chiefly influenced by the carbonate form and iron–manganese oxide. After treating acidic mine wastewater with Pb and Cd, the red mud–loess mixed material (7 : 3) undergoes surface changes, shifting from smooth to rough due to H+ corrosion. Pores between particles enlarge, yet heavy metal ions, adsorbates, and precipitates reoccupy and cover the surface, transforming the particle morphology from dense lamellar to clustered spherical. Our innovative approach to combining waste materials for environmental remediation presents a cost‐effective and impactful solution for heavy metal pollution.

Remediation of Cd(II) contamination in aqueous solution by modified sludge biochar with molten salt-assisted pyrolysis

In this work, modified sludge biochar was prepared using molten salt-assisted pyrolysis method to remove Cd(II) from aqueous solution. The biochar was characterized using XRD, FTIR, Raman, XPS and pore structure analysis techniques, and the effects of initial pH, adsorption temperature, adsorption time and initial Cd(II) concentration on the Cd(II) removal were investigated. Compared with the virgin sludge biochar (VSBC), the modified sludge biochar (MSBC) by molten salt-assisted pyrolysis method was rougher surface, more developed pore structure and higher graphitization. The initial pH had a greater effect on the Cd(II) removal, and the high adsorption temperature promoted the Cd(II) removal. The Cd(II) removal behavior was in accordance with the pseudo-second-order kinetic model and Langmuir model, which indicated that the adsorption reaction was a single and uniform chemisorption. Thermodynamics indicated that the Cd(II) removal by VSBC and MSBC was spontaneous and heat-absorbing reaction. Additionally, the maximum adsorption capacities of Cd(II) by VSBC and MSBC were 39.02 and 101.26 mg/g at pH 5.0 and 25 °C, respectively. The mechanisms of Cd(II) removal included complexation of O-containing groups, ion exchange, precipitation, and electrostatic interaction. After three adsorption-desorption experiments, the Cd(II) removal efficiency by VSBC was maintained at 33.26%, while the Cd(II) removal efficiency on MSBC was maintained at 90.18%. This finding suggested that the modified sludge biochar using molten salt-assisted pyrolysis could be effective in remediating Cd(II)-contaminated water body.

Capabilities of Novel Carbon Nano Adsorbents in Evaluating the Extraction of 2-Nitrophenol and Heavy Metal from Aqueous Solutions

This study primarily focused on evaluating the efficacy of Metal Oxide-infused Carbon Nano Adsorbents (CNAs), which included both Carbon Nanotubes and Carbon Nanofibers, in removing Cd+2, Cr+3, and 2-NP from water solutions. We synthesized and analyzed four distinct types of CNAs, each impregnated with either Al2O3, TiO2, Fe2O3, or Cu2O3. The metal content in these CNAs was determined by comparing their dry and calcined weights. To investigate their properties, we utilized various techniques such as Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area analysis, Energy-Dispersive X-ray Spectroscopy (EDX), and Thermal Gravimetric Analysis (TGA). These methods helped us understand their morphological traits, surface areas, pore structures, metal oxide distributions, and thermal stabilities, thereby confirming their adsorption effectiveness for pollutants. The findings indicated that CNAs altered with metal oxides showed higher surface areas and adsorption abilities than their unmodified counterparts. Specifically, CNAs/TiO2 exhibited the most significant increase in surface area (140 m2/g) and pore volume (0.460 cm3/g), which resulted in an enhanced adsorption capacity for Cd+3 at 11.4 (mg/g), surpassing the 9.5 (mg/g) capacity of pure CNAs with surface area (90 m2/g) and Pore volume (0.331 cm3/g). Similarly, CNAs/Al2O3 demonstrated an increased surface area of 100 (m2/g), surpassing that of pure CNAs. This enhancement led to a significant improvement in adsorption capacities, elevating the uptake for Cr+3 from 32.2 to 52 (mg/g) and for 2-NP from 24.8 to 49.6 (mg/g). This enhancement in adsorption efficiency is attributed to the increased surface area and improved surface chemistry due to the incorporation of Titania and Alumina, which proved more effective than modifications with copper oxide and Ferric oxide. These insights emphasize the significance of selecting appropriate metal oxides for modifying CNAs, as this can greatly impact their ability to target various contaminants, thus contributing to the development of more advanced water purification methods using CNAs/MO.

Ultra-sensitive electrochemical sensors through self-assembled MOF composites for the simultaneous detection of multiple heavy metal ions in food samples

Using an assemble-able MOF material, we successfully constructed an ultra-sensitive electrochemical sensor based on Bi2CuO4@Al-MOF@UiO-67 nanocomposite material, in order to investigate the adsorption properties of the Bi2CuO4@Al-MOF@UiO-67 functional material on the heavy metal ion. The Cd2+, Cu2+, Pb2+ and Hg2+ can be detected at the same time. Selective recognition and enrichment of various metal ions on different substrates can be achieved through the assembly of a large number of Al-MOF and UiO-67-MOF nanomaterial composites with small particle sizes on the Bi2CuO4 surface. Based on this, a new type of sensor is researched and prepared, which has been shown to have good stability and reproducibility. Due to its unique assembly structure, large active surface area, excellent adsorption capacity, and high electrical conductivity, Bi2CuO4@Al-MOF@UiO-67 presents outstanding performance. In addition, the sensor also exhibits excellent electrocatalytic redox capacity and high selectivity. The adsorption capacity of Cd2+, Cu2+, Pb2+ and Hg2+ is also significantly improved under the action of the sensor electrode, however, this is not the case. The limits of detection for Cd2+, Cu2+, Pb2+ and Hg2+ were found to be 0.02 pM, 0.032 pM, 0.018 pM and 0.041 pM, respectively. In order to investigate the detection mechanism of Cd2+, Cu2+, Pb2+ and Hg2+ was adsorption properties as well as electrochemical accumulation of Bi2CuO4@Al-MOF@UiO-67 on the metal atoms were investigated. This method has been successfully applied to samples of rice, sorghum, maize, milk, honey, and tea, and has enabled the simultaneous detection of Cd2+, Cu2+, Pb2+ and Hg2+, which is of significant practical value.

Effects of high-pressure processing on the physicochemical and adsorption properties, structural characteristics, and dietary fiber content of kelp (Laminaria japonica)

To investigate the effects of high-pressure processing (HPP) on the physicochemical and adsorption properties and structural characteristics of kelp, kelp slice (KS) and kelp powder (KP) were treated under different pressures (300, 450, and 600 MPa) for 5 and 10 min. Compared to untreated KP, HPP-treated KP yielded a 1.31-fold increase in water holding capacity (600 MPa/5 min), a 0.12-fold increase in swelling capacity (450 MPa/10 min), a 1.33-fold increase in oil holding capacity (600 MPa/10 min), a 10-fold increase in glucose adsorption capacity (450 MPa/10 min), and a 0.22-fold increase in cholesterol adsorption capacity (163.1 mg/g DW at 450 MPa/10 min), and exhibited good Cd (Ⅱ) adsorption capacity when its concentration was 10 mmol/L in the small intestine. The physicochemical properties of HPP-treated KS were not improved due to its low specific surface area. In addition, HPP treatment efficiently reduced the particle size of KP and increased its total and soluble dietary fiber content by 17% and 63% at 600 MPa/10 min, respectively. Scanning electron microscope micrographs demonstrated that the surface of HPP-treated KP was rough and porous, and the specific surface area increased with increasing pressure and processing time. To conclude, the results obtained in the present study suggest that HPP is a promising processing method for improving the functionality and structural characteristics of KP and provide a theoretical basis for the utilization of HPP-treated KP as a fiber-rich ingredient in the functional food industry.

EDTA functionalized Mg/Al hydroxides modified biochar for Pb(II) and Cd(II) removal: Adsorption performance and mechanism

This study has successfully synthesized layered double hydroxide (LDH) biochar (E-Mg/Al-LDH BC) with ethylenediaminetetraacetic acid (EDTA) and examined its adsorption capabilities towards Pb(II) and Cd(II). The results demonstrate that the kinetics of heavy metal removal can be well described by the pseudo-second-order model. The intraparticle diffusion model indicates that the controlling steps for Pb(II) and Cd(II) are not uniform. The adsorption isotherm for Cd(II) conforms to the Langmuir model, while for Pb(II), it adheres to the Freundlich model. The distribution coefficient (Kd) shows that Pb has a significantly higher competitive adsorption capacity than Cd(II). Therefore, in comparison to single adsorption, the maximum adsorption capacity of Cd(II) in competitive adsorption decreased by 58.86%, while Pb(II) only decreased by 13.54%. Surface complexation, cation exchange, chemical precipitation, electrostatic interaction, and cation-π bonding are the inherent mechanisms by which E-Mg/Al-LDH BC removes heavy metal ions. E-Mg/Al-LDH BC has the potential to remediate heavy metal-contaminated water, and it also provides insights for the application of modified biochar in the treatment of multi-metal water pollution.

Biochar Derived from Urban Green Waste Can Enhance the Removal of Cd from Water and Reduce Soil Cd Bioavailability.

The beneficial utilization of potentially increasing urban green waste (UGW) is critical for sustainable urban development in China. In this study, UGW was pyrolyzed at different temperatures, and the resulting biochar was used to amend Cd-contaminated soils to grow cabbage. Our results showed that the Cd adsorption capacity of UGW-biochar was positively correlated with the surface area, O/C, and (O+N)/C value of biochar. Furthermore, UGW-biochar was incorporated into three Cd-contaminated soils, including one acidic soil and two neutral soils, to assess its impact on the availability of Cd. The most substantial reduction in the concentration of available Cd was observed in the acidic soil, of the three tested soils. In the neutral soils, a more substantial reduction was found in the heavily Cd-contaminated soil compared to the lightly Cd-contaminated soil. UGW-biochar amendments to the three Cd-contaminated soils resulted in an increase in the cabbage biomass in acidic soil, whereas in neutral soils, it increased in lightly contaminated soils but decreased in heavily contaminated soils. Additionally, the Cd bioaccumulation factor (BCF), translocation factor (TF), and removal efficiency (RE), as impacted by the biochar application, were calculated in the lightly Cd-contaminated soil-cabbage system. The BCF decreased from 5.84 to 3.80 as the dosage of the UGW-biochar increased from 0% to 3%, indicating that the UGW-biochar immobilized Cd and reduced its bioaccumulation in cabbage roots. Based on our investigations, UGW-biochar effectively immobilizes Cd by reducing its mobility and bioavailability in a lightly contaminated environment matrix.

Synthesis, structural, magnetic property, and Cd(II) adsorption behavior of Ca-substituted MgFe2O4 nanomaterials in aqueous solutions.

In the present study, magnetic nanomaterials (Mg1-xCaxFe2O4, 0.0 ≤ x ≤ 0.8) were prepared via a simple sol-gel method. The samples were characterized using XRD, TEM, SEM, EDX, FTIR, BET, and VSM. The structural and magnetic properties of prepared nanomaterials (NMs) were investigated, and the adsorption capacity of Cd2+ from aqueous solution was evaluated via flame atomic absorption spectroscopy (AAS). The impact of several factors on Cd2+ adsorption such as contact time (1-60 min), pH (3-8), dose (0.003-0.03 g), and initial concentration of Cd2+ (5-60 mg L-1) has been assessed. The adsorption capacity of Cd2+ for the prepared NMs followed the pseudo-second order. Several isotherm models were analyzed, and the Langmuir model was found to be the best fit for NMs. Among as-prepared NMs, Mg0.8Ca0.2Fe2O4 (MCF2, cubic 97%, orthorhombic 3%, qe 100 mg g-1) and Mg0.2Ca0.8Fe2O4 (MCF8, cubic 18%, orthorhombic 83%, qe 90 mg g-1) samples exhibited the highest adsorption performance at conditions, viz., contact time 20 min, pH 7, NM dosage 3 mg, and ions at a concentration 60 mg l-1. Cd removal percentages were achieved 93 and 75 for MCF2 and MCF8, respectively. Overall, the prepared MCF2 and MCF8 NMs could be used as effective adsorbents to eliminate toxic Cd2+ from polluted aqueous solution.

Screening of cadmium-chromium-tolerant strains and synergistic remediation of heavy metal-contaminated soil using king grass combined with highly efficient microbial strains

The present study involved the isolation of two cadmium (Cd) and chromium (Cr) resistant strains, identified as Staphylococcus cohnii L1-N1 and Bacillus cereus CKN12, from heavy metal contaminated soils. S. cohnii L1-N1 exhibited a reduction of 24.4 % in Cr6+ and an adsorption rate of 6.43 % for Cd over a period of 5 days. These results were achieved under optimal conditions of pH (7.0), temperature (35 °C), shaking speed (200 rpm), and inoculum volume (8 %). B. cereus strain CKN12 exhibited complete reduction of Cr6+ within a span of 48 h, while it demonstrated a 57.3 % adsorption capacity for Cd over a period of 120 h. These results were achieved under conditions of optimal pH (8.0), temperature (40 °C), shaking speed (150 rpm), and inoculum volume (2–3 %). Additionally, microcharacterization and ICP-MS analysis revealed that Cr and Cd were accumulated on the cell surface, whereas Cr6+ was mainly reduced extracellularly. Subsequently, a series of pot experiments were conducted to provide evidence that the inclusion of S. cohnii L1-N1 or B. cereus CKN12 into the system resulted in a notable enhancement in both the plant height and biomass of king grass. In particular, it was observed that the presence of S. cohnii L1-N1 or B. cereus CKN12 in king grass led to a significant reduction in the levels of Cd and Cr in the soils (36.0 % and 27.8 %, or 72.9 % and 47.4 %, respectively). Thus, the results of this study indicate that the combined use of two bacterial strains can effectively aid in the remediation of tropical soils contaminated with moderate to light levels of Cd and Cr.

Effects of ultrasounds and microwaves on the morphology and adsorption capacity of calcium alginate

Three non-conventional strategies have been used to prepare calcium alginate (CaAlg) from sodium alginate (NaAlg) by a batch process: ultrasound (US); microwave (MW) and combined US-MW. The calcium alginates obtained were used to remove Pb(II) and Cd(II) from single and binary aqueous solutions. The resulting adsorption capacities were compared to those obtained by conventional synthesis of calcium alginate. Scanning electron microscopy (SEM) revealed that the use of microwave and ultrasound produced CaAlg beads with roughened surfaces and consequently with increased specific surface area. The optimum parameters for the removal of Pb(II) and Cd(II) ions from single and binary solutions were determined in terms of pH, contact time, adsorbent dose and initial heavy metal concentration. A significant increase of the maximum adsorption capacity of Cd(II) and Pb(II) ions determined from Langmuir isotherm model was recorded in the case of CaAlg particles prepared in the combined microwave and ultrasound system. These values are 1.7389 ± 0.0585 mmol/g for Cd(II) and 1.5872 ± 0.0657 mmol/g for Pb(II) compared to 0.9305 ± 0.0926 mmol/g and 0.9735 ± 0.0572 mmol/g, respectively recorded for CaAlg particles prepared and matured using the conventional method. The differences between the values of the adsorption capacity of CaAlg-C-C for Pb(II) compared to Cd(II) ions is due to the Pb(II) ions characteristics (ion radius, hydrated ion radius, electronegativity). Thus, it can be stated that use of a combination of microwave and ultrasound improved the adsorption capacity of CaAlg for the removal of heavy metal ions from polluted effluents.

New insight into the co-removal of arsenic and cadmium from wastewater by using thiol-functionalized UiO-66: A mechanistic study and real water test

Industrial wastewater is normally a complex matrix, and few reported MOFs have considered the co-removal of anion and cation contaminants from wastewater. In this study, we synthesized a highly stable thiol-functionalized MOF (UiO-66-SH) to achieve the coadsorption of As(V) and Cd(II) in an aqueous solution. The morphology, functional groups and thermal properties of UiO-66-SH were examined. The prepared UiO-66-SH possessed an octahedral structure (size: 0.8–2 μm) with a large surface area (224 m2/g). TEM-EDX mapping showed a uniform distribution of S and Zr throughout UiO-66-SH. The FT-IR spectra showed peaks for -SH at 2566 cm-1, indicating that -SH was successfully incorporated into UiO-66. Adsorption batch experiments showed that both As(V) and Cd(II) were rapidly taken up by UiO-66-SH in the first 6 h, and the removal rates were over 70% and 88%, respectively, after 24 h. The maximum As(V) and Cd(II) adsorption capacities were 52.31 and 77.42 mg/g. The optimum pH values for As(V) and Cd(II) adsorption were 3 and 5, respectively. Except for Pb(II) and phosphate, anions, cations, and humic acid had almost no effect on As(V) and Cd(II) co-removal by UiO-66-SH. Spectral analysis indicated that surface hydroxyl groups (Zr-OH) and -SH groups played vital roles in As(V) and Cd(II) adsorption by participating in inner-sphere coordination interactions. A real water test showed that a very small amount of UiO-66-SH could decrease the concentration to below the emission standard within 6 h. Our study demonstrated that UiO-66-SH is a promising adsorbent for treating As- and Cd-cocontaminated mining wastewater, ensuring the environmental safety of wastewater emission.

Synthesis and characterization of bio-nanocomposite based on chitosan and CaCO3 nanoparticles for heavy metals removal

Water is a vital component of life; therefore, it is critical to have access to pure water for various life-sustaining activities including agriculture and human consumption. An eco-friendly nanocomposite based on chitosan (Cs) and nanomaterials (CaCO3-NPs) were combined to amalgamate the advantages of biopolymers and nanomaterials to overcome the problems of instability, poor mechanical properties, and low removal percentage of biopolymers. The as-prepared samples were characterized and were used for the removal of heavy metal from wastewater. X-ray diffractometer, Fourier transform infrared spectroscopy, and transmission electron microscope were used to distinguish the prepared absorbents. The absorption of the heavy metals by as-prepared samples was examined at different conditions. The kinetic and isotherm models of the adsorption process were also studied. The data showed that the removal percentages of Cd, Cu, Pb, Zn, Cr and Ni by the composite were 98.0, 94.8, 99.0, 97.9, 97.4 and 98.3 %, respectively. The kinetic and isothermal studies showed that the absorption of these metal ions by the samples obeyed a pseudo-second-order mechanism and Langmuir isotherm model, respectively. In addition, the maximum adsorption capacities of Cd, Cu, Pb, Zn, Cr, and Ni ions by as-prepared nanocomposite were 83.33, 47.84, 98.03, 89.28, 62.11, and 63.69 mg/g, respectively.

Myrica esculenta Leaf Extract-Assisted Green Synthesis of Porous Magnetic Chitosan Composites for Fast Removal of Cd (II) from Water: Kinetics and Thermodynamics of Adsorption.

Heavy metal contamination in water resources is a major issue worldwide. Metals released into the environment endanger human health, owing to their persistence and absorption into the food chain. Cadmium is a highly toxic heavy metal, which causes severe health hazards in human beings as well as in animals. To overcome the issue, current research focused on cadmium ion removal from the polluted water by using porous magnetic chitosan composite produced from Kaphal (Myrica esculenta) leaves. The synthesized composite was characterized by BET, XRD, FT-IR, FE-SEM with EDX, and VSM to understand the structural, textural, surface functional, morphological-compositional, and magnetic properties, respectively, that contributed to the adsorption of Cd. The maximum Cd adsorption capacities observed for the Fe3O4 nanoparticles (MNPs) and porous magnetic chitosan (MCS) composite were 290 mg/g and 426 mg/g, respectively. Both the adsorption processes followed second-order kinetics. Batch adsorption studies were carried out to understand the optimum conditions for the fast adsorption process. Both the adsorbents could be regenerated for up to seven cycles without appreciable loss in adsorption capacity. The porous magnetic chitosan composite showed improved adsorption compared to MNPs. The mechanism for cadmium ion adsorption by MNPs and MCS has been postulated. Magnetic-modified chitosan-based composites that exhibit high adsorption efficiency, regeneration, and easy separation from a solution have broad development prospects in various industrial sewage and wastewater treatment fields.

Surface-loaded magnesium and phosphorus-modified lignite adsorbents: Efficient adsorption and immobilization for remediation of Cd-contaminated water and soil

Lignite is a resource-rich material with favorable adsorption properties and can be used as an environmentally friendly material for removing heavy metals. In this study, we loaded magnesium and phosphate ions onto the surface of lignite (LM) by using chemical modification to generate modified lignite materials, Mg-LM and P-LM, which were used for the adsorption and immobilization of Cd (II) in polluted water and soil. Characterization analysis showed the introduction of exchangeable Mg ions and enhancement of the pore structure in Mg-LM; the increase in the number of oxygenated functional groups and, exchangeable calcium ions and P content of P-LM may favor the adsorption and immobilization of Cd (II). Cd (II) adsorption on Mg-LM and P-LM was consistent with the pseudo-secondary kinetics and Langmuir isotherm models. The maximum adsorption capacity of Cd (II) on Mg-LM and P-LM was 1033 mg/g and 55 mg/g, respectively. The reduction in the soil DTPA-Cd content (32.9%) was greater under P-LM treatment than under Mg-LM (20.2%) and LM (11.1%) treatments. In addition, successive BCR extractions confirmed that Mg-LM and P-LM promoted the transformation of unstable Cd fractions to stable Cd fractions in the soil. The XRD, FTIR, and XPS results indicated that electrostatic interactions, ion exchange, surface complexation and precipitation might be the main mechanisms involved in the adsorption and immobilization of Cd (II) by Mg-LM and P-LM. Our results suggest that Mg-LM is more suitable than P-LM for the remediation of Cd-contaminated water, and less applicable than in Cd-contaminated soil.

Co-utilization of sepiolite and ferromanganese ore reduces rice Cd and As concentrations via soil immobilization and root Fe-Mn plaque resistance

Cadmium (Cd) and arsenic (As), common toxic elements in farmland soil, are easily absorbed by rice and accumulate in grains. Combined amendment is likely to ameliorate Cd-As-contaminated soil; however, studies on this aspect are limited. Therefore, we explored the effects of co-utilizing sepiolite and ferromanganese ore (SF) on Cd-As accumulation in rice by conducting pot experiments on Cd-As-contaminated paddy soil. The results showed that 4 g kg−1 SF (4SF) reduced Cd (55.9 %/48.5 %) and As (82.9 %/64.7 %) concentrations in grain in early and late rice. The Fe concentration in Fe-Mn plaque (IMP) (FeIMP) first decreased and then increased, and the Mn concentration in IMP (MnIMP) increased with an increase in the SF addition amount. This resulted in the 4SF treatment maximizing the Cd adsorption capacity of IMP, whereas the 2 g kg−1 SF treatment (2SF) minimized the As adsorption capacity of IMP. More importantly, when the total Cd and As were 9.7 mg kg−1 and 304.2 mg kg−1, respectively, in the soil, 4SF application reduced CaCl2-extractable Cd (80.5 %/87.9 %), and 2SF reduced available As (24.0 %/20.9 %) in early and late rice. Additionally, SF decreased the Cd and As ion contents in soil pore water. Overall, SF has good immobilization and sustained effect on Cd-As and can be used as an effective material for remediation of Cd-As-contaminated soil.

Mechanisms of cadmium adsorption by ramie nano-biochar with different aged treatments

Biochar (BC) has proven to be very effective against the remediation of cadmium contamination. However, aged treatment is inevitable and variations in the adsorption mechanism caused by ageing remain unclear. In this study, different treatments (i.e., photo-aged (nano-PBC) and chemical treatment (nano-NBC)) were used on the nano-BC. The nano-BC as well as the two aged nano-BCs were characterized separately to examine their surface morphology, functional groups, and variations in phase composition. The aged nano-BCs exhibited larger specific surface area and mesopore volume. The nano-NBC produced more surface functional groups (i.e., carboxyl groups, lactone groups, and phenolic hydroxyl groups) compared to the nano-BC and nano-PBC. In addition, the study revealed the effect of aged treatment on the adsorption mechanism of the nano-BCs by adsorption kinetic model and adsorption isotherm model, respectively. The fitted consequences revealed that the adsorption of Cd by the three nano-BCs was consistent with the pseudo-second order kinetic model and the Langmuir adsorption isotherm model. The aged nano-BCs have higher Cd adsorption capacity, which was more effective for the nano-NBC. In addition, different adsorption conditions (i.e., pH, ionic strength, coexisting cations, and initial nano-BCs addition concentration) were performed to explore the optimal adsorption capacity. The results showed the optimal adsorption efficiency of 93.24 % was achieved for nano-NBC at pH 7, a background solution of 0.001 M Na+, and an initial nano-BC addition concentration of 50 mg L−1. The different aged treatments did not significantly affect the adsorption mechanism of the nano-BCs, but changed the chemisorption mode and enhanced the physical adsorption (pore size filling and hydrogen bonding). Namely, aged treatment significantly enhanced the adsorption capacity of the nano-BCs on Cd.

Preparation and Characterization of Mercapto-Functionalized Calcined Attapulgite and Its Removal of Pb (II) and Cd (II) Solution

To enhance the sorption efficacy of attapulgite for heavy metals, mercapto-functionalized attapulgite (ATP-SH) was synthesized with mercaptan functional groups. When the mass-to-volume ratio of calcined attapulgite (ATP-C) to 3-Mercapropyltrimethoxysilane (MPTMS) was 1 g:0.5 mL (ATP-SH-0.5) and the pH was set to 8, a strong adsorption capacity for Cd (II) and Pb (II) was demonstrated. This indicates excellent adsorption performance for these heavy metals. ATP-SH-0.5 exhibited a maximum adsorption capacity of 43.81 mg/g and 274.83 mg/g for Cd (II) and Pb (II), respectively, in a single ion system. In a binary ion system, the maximum adsorption capacity was 31.86 mg/L and 254.45 mg/L for Cd (II) and Pb (II), respectively. Various characterizations and experiments showed that the adsorption of Cd (II) and Pb (II) onto ATP-SH-0.5 involves ion exchange reactions involving hydroxyl and thiol functional group complexation reactions. This adsorption process follows a single-molecule layer adsorption mechanism. XPS results indicate that hydroxyl and grafted thiol functional groups on the surface of mercapto-functionalized attapulgite participated in surface complexation reactions with Cd (II) and Pb (II), resulting in the formation of Cd-S and Pb-S species. Overall, this study provides a promising mercapto-functionalized modification material for the remediation of polluted water and soil.