Initial Cd Concentration Research Articles

Adsorption isotherms and removal of lead (II) and cadmium (II) from aqueous media using nanobiochar and rice husk

Removal of Cd(II) and Pb(II) from aqueous solutions is a challenging task and the search for novel adsorbents is underway. This study examined the efficiency of nanobiochar (NB) and rice husk (RH) in the adsorption and removal of Cd(II) and Pb(II) from water. The effect of various physicochemical parameters such as initial pH, initial Cd and Pb concentration, adsorbent dosage, and contact time were tested. SEM/EDX images confirmed the adsorption of Pb and Cd with surface physical and chemical changes. The maximum Pb removal was noted at pH 6 using NB (96%) and at pH 8 for RH (90%), and the maximum Cd removal by NB was recorded at 8 pH (91%) and by RH at pH 6 (87%). The decline in adsorption intensity at lower pH suggested protonation of the adsorbent surface causing cation-cation repulsion. Most of the adsorption occurred within the initial 60 min. A continuous gradual increase in the adsorption with time suggested multilayer formation. Of the three isotherms, the Freundlich model fits the present data best, implying an infinite surface coverage and indicating the potential for multilayer adsorption of Pb and Cd on the surfaces of RH and NB adsorbents. In conclusion, this study highlights the promising potential of NB as a cost-effective adsorbent for the removal of Cd and Pb ions from aqueous solutions.

UV-modified biochar-Bacillus subtilis composite: An effective method for enhancing Cd(II) adsorption from water

The adsorption of Cd(Ⅱ) in sewage by single-modified biochar systems have limitations, whereas composite modification can enhance the efficiency. In this study, reed straw biochar and Bacillus subtilis were used as raw materials. UV radiation was employed to modify the biochar, and subsequently, Bacillus subtilis was loaded onto the biochar by adsorption, creating modified biochar composites. The Cd(II) adsorption performance and removal efficiency of these composites were then investigated. It was characterized by BET, SEM-EDS, FT-IR, XRD and ZETA potential analysis. Adsorption experiments were conducted under varying conditions (initial Cd(Ⅱ) concentration, UV radiation time, initial pH, etc.), with adsorption isotherms and kinetic models used. Results indicated that 24 hours UV radiation significantly enhanced adsorption performance, increasing the biochar’s surface area by 40 % and pore volume by 20 %, and introducing numerous pores and oxygen-containing functional groups to the biochar's surface. Significantly enhancing the saturation adsorption capacity for Cd(II) from 23.98 mg/g to 49.93 mg/g after UV- Modified biochar was loaded with Bacillus. Modified biochar composites performed better compared to single-modified biochar across different initial Cd(Ⅱ) concentrations, particularly in slightly alkaline environments. The primary adsorption mechanisms were chemical adsorption, such as ion exchange and surface precipitation. The synergistic effect of UV radiation and microbial loading significantly enhanced Cd(Ⅱ) adsorption efficiency. This study demonstrates that composite modification is a more efficient method, aiding in the removal of heavy metal ion Cd(Ⅱ) from water.

Simultaneous removal of heavy metals and electricity generation from wastewater in constructed wetland-microbial fuel cells

Constructed wetlands (CWs) are environmentally friendly and cost-effective methods for wastewater treatment. Recently, there have been innumerable efforts to integrate CWs with microbial fuel cells (MFCs) to enhance the removal of pollutants while generating electricity. Constructed Wetland-Microbial Fuel Cells (CW-MFCs) are engineered systems incorporating physical, chemical, and biological processes for wastewater treatment. However, the application of CW-MFCs to remove multiple heavy metals from wastewater is still an active area of research. The present study explores for the first time the utilization of different types of CW-MFCs, including CW-MFC-planted, CW-MFC-unplanted, and CW-sand-filter for simultaneous removal of different concentrations of organic pollutants and multiple heavy metals such as zinc (Zn), cadmium (Cd), copper (Cu), and lead (Pb) from wastewater while generating electricity. The study employed nine CW-MFC microcosms, some of which were planted with Phragmites australis. The initial concentrations of Cu, Pb, Zn, and Cd were maintained at 2, 10, and 30 mg/l, respectively, while initial COD concentrations were 120, 500, and 1000 mg/l. Remarkably, the maximum removal rates achieved were 98.83 %, 95.74 %, 92.91 %, and 90.75 % for Cu, Pb, Zn, and Cd, respectively, and the maximum removal rate of COD was 97.96 % at 10 mg/l of Cu, Pb, Zn, Cd, and 500 mg/l of COD in CW-MFC-planted. The attained highest voltage, current, and power densities reached 687 mV, 4000 mA/m3, and 785.86 mW/m3, respectively, in CW-MFC-planted. This study demonstrates the significant impact of CW-MFC-planted systems on wastewater treatment and electricity generation.

Statistical modeling and optimization of heavy metals (Pb and Cd) adsorption from aqueous solution by synthesis of Fe3O4/SiO2/PAM: isotherm, kinetics, and thermodynamic

In this study, magnetic material was synthesized using iron salts, then silicon-specific material was used to gain porosity, straight-chain polyacrylamide (PAM) was modified to give the surface functional properties, and the final product synthesized Fe3O4/SiO2/PAM nanocomposite material. Heavy metal (Pb and Cd) removal studies were carried out with the synthesized composite material, considering the central composite design and response surface methodology (CCD-RSM) optimization model. The effects of various parameters, for example, the initial concentration, pH, adsorbent dose, temperature and contact time, were investigated as a part of this study. To optimize these parameters, the CCD-RSM model was applied to design the experiments. Analysis of variance (ANOVA) was applied to evaluate statistical parameters and investigate interactions of variables. In the designed experimental set, the amount of adsorbent (30 mg), pH 7.0 value, temperature (40 °C), initial concentration of Pb (80 mg/L) and Cd (20 mg/L) and 90 min contact time were determined as the optimum conditions. The high coefficient of determination of both metals showed good agreement between experimental results and predicted values (R2 0.99; 0.95). TEM, SEM, XRD, FTIR, BET and Zeta potential analyses were performed to characterize the structure and morphology of the adsorbent. In Pb2+ and Cd2+ heavy metal removal studies, maximum adsorption capacities were determined as 66.54 and 13.22 mg/g, respectively. Additionally, adsorption isotherms, adsorption kinetics and thermodynamic modeling studies were conducted. Features such as large surface area and high adsorption capacity of the synthesized nanoparticles were observed. In this study, Fe3O4/SiO2/PAM demonstrated its potential as an effective adsorbent for the removal of heavy metal ions present in simulated wastewater samples. In particular, we can say that the material has a strong selectivity, as well as a high affinity for Pb(II) ions.

Cadmium Removal by Adsorption on Biochars Derived from Wood Industry and Craft Beer Production Wastes

Cadmium pollution is a serious environmental issue that has an impact on both the ecosystem and human health. As a result, its removal from water is essential. Agro-industrial wastes are suggested as a sustainable adsorbent option, as they are among the most readily available renewable sources worldwide. Biochar is a carbonized biomass that has been shown to be a viable and novel adsorbent. This article compares the results of cadmium adsorption on biochars derived from wood industry and craft beer production wastes. Biochars were characterized before and after adsorption. Batch adsorption results of 0.18 mmol/L Cd(II) concentration solutions indicated adsorption percentages (A%) of 99.7% and 92.2% for sawdust biochar and barley biochar, respectively. For this cadmium concentration, the sawdust biochar presented an adsorption capacity (qm) of 0.0172 mmol/L, while the barley biochar presented a value of 0.0159 mmol/L. The influence of initial Cd(II) concentration on single and multimetal solutions was studied, and a decrease in Cd(II) adsorption on sawdust biochar was observed in the presence of Ni(II) and Zn(II). The Freundlich isotherm model was found to be the best fit to the data for Cd(II) adsorption isotherms on both biochars. According to the results of this article, sawdust biochar has the best performance as an adsorbent and can be safely disposed of in building bricks at the end of its useful life.

Efficient removal of cadmium from aqueous solution by chitosan grafted pillared bentonite

Developing an environmentally friendly adsorbent with high adsorption capacity and economic advantages is crucial for the treatment of cadmium (Cd)-contaminated wastewater. In this study, Bentonite (Bt), which is widely distributed in nature, was used to prepare a new type of chitosan (CS)-grafted polymerized aluminum-pillared bentonite (i.e., Al@Bt): CS@Al@Bt. This new material effectively addresses the issues of chitosan’s poor mechanical strength, limited load capacity, and the weak adsorption properties of raw bentonite for Cd. The effects of synthesis conditions on Cd adsorption by modified bentonite were investigated through batch experiments. The adsorption mechanism was revealed by characterization tests such as X-ray diffraction (XRD), N2 adsorption-desorption experiments, Scanning and Transmission electron microscopy (SEM-TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The results showed that compared to raw Bt, when the ratio of Al in polymerized aluminum to the cation exchange capacity (CEC) of Bt was increased to 5 (i.e., Al/CEC=5), the specific surface area (SSA) of Bt increased from 78.46 m²/g to 195.99 m²/g. Additionally, the interlayer spacing and total pore volume increased by 1.22 and 1.13 times, respectively. After grafting chitosan onto Al@Bt, CS@Al@Bt reached adsorption equilibrium rapidly within 15 min, achieving a removal rate of up to 99.82% (initial concentration of Cd(II) was 20 mg/L, and the solid-liquid ratio was 1 g/L). Additionally, CS@Al@Bt showed good adsorption performance over a wide pH range. The rich pore structure of CS@Al@Bt and the complexation between amino (-NH2) and hydroxyl (-OH) groups with Cd(II) were the main mechanisms for the removal of Cd(II) from the solution. The application showed that CS@Al@Bt effectively reduced Cd-containing mining wastewater from class V to class II quality, underscoring its significant potential for treating Cd(II)-contaminated wastewater.

Phosphorylated chitin from shrimp shell waste: A robust solution for cadmium remediation

In this work, chitin (CT) was isolated from shrimp shell waste (SSW) and was then phosphorylated using diammonium hydrogen phosphate (DAP) as a phosphorylating agent in the presence of urea. The prepared samples were characterized using Scanning Electron Microscopy (SEM) and EDX-element mapping, Fourier Transform Infrared Spectroscopy (ATR-FTIR), X-Ray Diffraction (XRD), Thermogravimetric Analysis (TGA/DTG), conductometric titration, Degree of Substitution (DS) and contact angle measurements. The results of characterization techniques reveal the successful extraction and phosphorylation of chitin. The charge content of the phosphorylated chitin (P-CT) was 1.510 mmol·kg−1, the degree of substitution of phosphorus groups grafted on the CT surface achieved the value of 0.33. The adsorption mechanisms appeared to involve electrostatic attachment, specific adsorption (CdO or hydroxyl binding), and ion exchange. Regarding the adsorption of Cd2+, the effect of the adsorbent mass, initial concentration of Cd2+, contact time, pH, and temperature were studied in batch experiments, and optimum values for each parameter were identified. The experimental results revealed that P-CT enhanced the Cd2+ removal capacity by 17.5 %. The kinetic analyses favored the pseudo-second-order model over the pseudo-first-order model for describing the adsorption process accurately. Langmuir model aptly represented the adsorption isotherms, suggesting unimolecular layer adsorption with a maximum capacity of 62.71 mg·g−1 under optimal conditions of 30 °C, 120 min, pH 8, and a P-CT dose of 3 g·L−1. Regeneration experiments evidenced that P-CT can be used for 6 cycles without significant removal capacity loss. Consequently, P-CT presents an efficient and cost-effective potential biosorbent for Cd2+ removal in wastewater treatment applications.

Competitive Adsorption of Cd(II) and Zn(II) on Biochar, Loess, and Biochar-loess Mixture

Combined heavy metal contamination in soil is a common phenomenon. Biochar amendment into the soil is considered to be an alternative for immobilization remediation of soil contaminated with heavy metals due to its adsorption and alkalization. However, much attention has been paid to the adsorption and immobilization of single heavy metals by biochar. In this paper, the competitive adsorption of Cd(II) and Zn(II) on biochar derived from cotton straw and pig manure at 500℃ (BCS500 and BPM500), loess and biochar-loess mixtures were investigated using the batch equilibrium method. The results showed that the adsorption capacities of biochars, loess, and biochar-loess mixtures to Cd(II) and Zn(II) in the mixed Cd-Zn systems increased with the increase of initial metal concentrations of Cd(II) and Zn(II). The adsorptive capacities of BCS500 and BPM500 to Cd(II) in mixed Cd-Zn system were 33% and 35% less than those in the single Cd(II)systems, while the adsorptive capacities to Zn(II) were 62% and 56% less than those in the single Zn(II) systems. The adsorptive capacities of loess to Cd(II) and Zn(II) in mixed Cd-Zn systems were 29% and 55% less than those in the single metal systems. The adsorptive capacities of loess-BCS500 (LBCS) and loess-BPM500 (LBPM) to Cd(II) in mixed Cd-Zn system were 40% and 38% less than those in the single Cd(II) systems, while the adsorptive capacities to Zn(II) were 63% and 60% less than those in the single Zn(II)systems. Moreover, the competitive adsorptive capacity of Cd(II) is greater than that of Zn(II). It can be seen that when heavy metal pollution with similar nature of multiple elements exists in soil, the amount of adsorbent should be increased to resist the possible weakened adsorption caused by competitive adsorption in order to guarantee an effective absorption treatment.

Corncob-supported calcium oxide nanoparticles from hen eggshells for cadmium (Cd-II) removal from aqueous solutions; Synthesis and characterization

This study investigated the efficient removal of cadmium ions from aqueous solutions using calcium oxide nanoparticles (CaO NPs) synthesized from waste hen eggshells using a Sol-gel method and supported on corncob bio-adsorbent. The synthesized CaO NPs were characterized using FT-IR, XRD, specific surface area, and TGA. Batch adsorption experiments were conducted to examine the influence of process parameters such as adsorbent dosages, initial Cd (II) concentrations, pH values, and contact times. XRD analysis revealed that the synthesized CaO nanoparticles had a size of 24.34 nm and a specific surface area of 77.4 m2/g. The optimal conditions for achieving the highest percent removal of cadmium (99.108%) were found to be an initial concentration of 55 ppm, pH 7, adsorbent dose of 0.75 g, and contact time of 50 min. The experimental removal efficiency closely matched the predicted value (99.0%), indicating the suitability of the method used in optimizing the removal of Cd (II) ions from aqueous solutions. These findings, corroborated by predicted values, underscore the efficacy of our method in optimizing cadmium removal. Based on these findings, it can be concluded that corncob-supported CaO NPs are optimized for their highest efficiency and hold great promise as a cost-effective and environmentally friendly solution for wastewater treatment with a focus on cadmium removal.

Screening and characterization of novel biosorbent for the removal of Cadmium from contaminated water

Presence of trace metal pollutants in the aquatic system is a worldwide foremost concern. The present investigation was an attempt to find out the novel biosorbent for the removal of Cadmium(CdII) from contaminated water. The leaf of Sesbania bispinosa was screened out as a potential Cd(II) removing biosorbent from thirty different natural biomasses by physico-chemical and sorption process characterizations. Biosorption capacity of S. bispinosa was determined by batch mode biosorption method with the functions of solution pH, contact time, biosorbent dose and initial Cd(II) concentration. Obtained results were analyzed for isotherm and kinetic study. The S. bispinosa biosorbent exhibited the biosorption equilibrium of Cd(II) uptake in 30 min. At pH 4, biosorbent dose of 1 g/L was sufficient for maximum Cd(II) uptake. Scanning Electron Microscopy (SEM) images and Fourier Transform Infrared Spectroscopy (FTIR) spectra confirmed the favourable sorption surface characteristics. The data also demonstrated that Freundlich isotherm (R2=0.998) is the better fitted model compared to Langmuir model and the maximum sorption capacity was found to be 33.33 mg/g. Suitabilty of pseudo second order reaction pathway was observed during the kinetic study. Most especially, The selected biosorbent is ascertained effective in removing multimetals [Cd(II) - 67.51 %, Cr(VI) – 40.36 %, Pb(II) – 100 % and Cu(II) – 59.01 %] from a quaternary aqueous solution of Cd(II), Cr(VI), Pb(II) and Cu(II) mixture and spent biosorbent can be easily regenerated by applying 0.1 M HCl solution as a desorbing agent. It, therefore, could be concluded that leaves of S.bispinosa might be a low-cost and environmentally sound novel biosorbent for the treatment of Cd(II) contaminated water.

Application of biological soil crusts for efficient cadmium removal from acidic mine wastewater

Utilizing an acid-resistant biological soil crust (BSC) species that we discovered, we developed a device capable of efficiently removing cadmium (Cd) from mine wastewater with varying levels of acidity. Our research has demonstrated that this particular BSC species adapts to acidic environments by regulating the balance of fatty acids and acid-resistant enzymes. At a Cd concentration of 5 mg/L, the BSC grew well. When the initial Cd concentration was 2 mg/L, and the flow rate was set at 1 mL/min (at pH levels of 3, 4, and 5), BSC had a high removal rate of Cd, and the removal rate increased with the increase of pH (from 90% to 97%). Chemisorption is the primary removal mechanism in the initial stage, where the functional groups and minerals on the surface of the BSC play a significant role. In addition, BSC also adapts to Cd stress by changing bacterial community structure. It was discovered through infrared spectroscopy and two-dimensional correlation analysis that hydrophilic groups, specifically phosphate and carboxyl groups, exhibited the highest reactivity during the Cd binding process. Protein secondary structure analysis confirmed that as the pH increased, the adsorption capacity of the BSC increased; making biofilm formation easier. This study presents a novel approach for the treatment of acidic wastewater.

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.

Eco-friendly magnetic biochar from Leb Mu Nang banana peel: Response surface methodology optimization for Cd(II) adsorption from synthetic wastewater

Magnetic biochar derived from Leb Mu Nang banana peel waste is introduced as a novel precursor for Cd(II) removal from synthetic wastewater. This study comprehensively evaluates and optimizes variable factors, including initial Cd(II) concentration, magnetic biochar (MLP) dosage, adsorption time, and initial pH level, using the Response Surface Methodology (RSM). A Cd(II) removal efficiency of up to 93.4 % is reached under the conditions of a 50 mg/L initial concentration, 5 g/L MLP dosage, 24 h of adsorption time, and a solution pH of 8. The pseudo-second-order and Langmuir models accurately represent the kinetics and isotherm adsorptions, highlighting ion exchange, surface complexation, and precipitation as primary adsorption mechanisms. The magnetic biochar derived from Leb Mu Nang banana peels shows promise for efficient Cd(II) removal with easy post-adsorption separation.

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.

Equilibrium Kinetic and Thermodynamic Adsorption of Ni and Cd Ions from Waste Water Using Orange Peel

The aim of this study is to evaluate fresh orange peels as low cost available adsorbent for removing nickel and cadmium ions from laboratory solutions and record the adsorption capacity, which represents the amount of up take per amount of fresh orange peels (FOP). Fourier-Transform Infrared Spectroscopy (FTIR) analyses of FOP was carried out and comparing with the peaks of standard FTIR of cellulose matter to show functional groups and finger print that found in FOP formula. Batch experiments were carried out at different conditions: Ni and Cd ions initial concentration are (10, 20, 30, 40, and 50) ppm, FOP dosage (0.5, 0.75, 1, and 1.5) g, pH (3.5, 5, and 6), contact time (30 to 240) min and temperature (28, 35, and 45) oC where recorded. The results showed that the removal percentage of Ni and Cd increased with increasing FOP dosage. Initial Ni and Cd concentration, pH, and contact time. The best Ni and Cd Removal% where 64% and 80%, respectively at optimum conditions with FOP dosage of 1 g, pH of 6, initial concentration of 50 ppm and contact time of 120 min, where the calculated adsorption capacity was 2.9 mg/g for Ni and 4 mg/g for Cd. In case of the thermal study, best result was obtained at 45 oC with removal% of 65% for Ni and 78% for Cd and adsorption capacity of 2.8 mg/g and 3.7 mg/g for Ni and Cd, respectively.

Adsorption of Cd(II) ions on magnetic graphene oxide/cellulose modified with β-cyclodextrin: Analytical interpretation via statistical physics modeling and fractal like kinetic approach

In the present study, β-cyclodextrin modified magnetic graphene oxide/cellulose (CN/IGO/Cel) was fabricated for removal of Cd(II) ions. The material was characterized through various analytical techniques like FTIR, XRD, TGA/DTA, SEM, TEM, and XPS. The point of zero charge of the material was obtained as 5.38. The controllable factors were optimized by Taguchi design and optimum values were: adsorbent dose-16 mg, equilibrium time-40 min, and initial concentration of Cd(II) ions-40 mg/L. The material shows high adsorption capacity (303.98 mg/g). The good fitting of Langmuir model to adsorption data (R2 = 0.9918–0.9936) revealed the monolayer coverage on adsorbent surface. Statistical physics model M 2 showed best fitting to adsorption data (R2 > 0.997), suggesting the binding of Cd(II) ions occurred on two different receptor sites (n). Stereographically n > 1 confirming vertical multi-molecular mechanisms of Cd(II) ions adsorption on CN/IGO/Cel surface. The adsorption energies (E1 = 23.71–28.95 kJ/mol; E2 = 22.69–29.38 kJ/mol) concluded the involvement of physical forces for Cd(II) ions adsorption. Kinetic data fitted well to fractal-like pseudo first-order model (R2 > 0.9952), concluding the adsorption of Cd(II) ions occurred on energetically heterogeneous surface. The kinetic analysis shows that both the film-diffusion and pore-diffusion were responsible for Cd(II) ions uptake. XPS analysis was utilized to explain the adsorption mechanism of Cd(II) ions onto CN/IGO/Cel.

Biomass-derived carbon/iron composite (FexOy-BC (RM)) with excellent Cd(II) adsorption from wastewater – Red mud resource utilization

Red mud is an industrial by-product produced in the process of alumina refining. It contains many iron elements, and the traditional resource utilization method is to extract it. This study took an alternative approach by using red mud's iron content as the substrate to synthesize a novel iron-biochar adsorbent for removing heavy metals from wastewater. Walnut shell biochar was reacted with the iron in red mud via an in-situ reduction–oxidation process to produce an iron-carbon composite adsorbent (FexOy-BC). A series of characterization analyses (e.g., SEM, FTIR, XPS, etc.) and batch adsorption experiments were conducted to investigate the properties and Cd(II) removal performance of the adsorbent, respectively. Response surface methodology was further employed to optimize the adsorption conditions, identifying the ideal 6 g/L adsorbent dose, 10 mg/L initial Cd(II) concentration (C0), and pH 6. The optimized quadratic model demonstrated excellent fit, with an average Cd(II) removal efficiency of 92.59 % under optimal conditions. The adsorption mechanism, renewability, and preliminary cost-benefit analysis indicate that FexOy-BC has the potential to be a highly efficient and sustainable adsorbent. In summary, the new method can recover resources from red mud waste and synthesize heavy metal adsorbents, which comprehensively solves two long-standing problems of industrial waste.

Optimal synthesis of dolochar derived faujasite zeolite X for highly effective Cd(II) removal

Cadmium-induced water pollution is a major environmental issue because of its persistent nature and adverse ecological impacts. Adsorption is a highly favored method due to its versatility and high efficacy in cadmium removal. Hence, the present work aims to develop a low-cost, highly effective adsorbent-dolochar-derived nanoporous zeolite to easily and effectively purify Cd(II) polluted water. The work focuses on the Cd(II) batch adsorption study using the optimal hydrothermal synthesis of a crystalline faujasite Zeolite X (ZX) from dolochar. The synthesis parameters were optimized using Response Surface Methodology, specifically Box Behnken Design (RSM-BBD), to maximize the crystallinity percentage. Variables such as initial Cd(II) concentration, solution pH, dosage, time, and temperature were studied for the Cd(II) batch adsorption study. The optimum conditions for synthesizing ZX include NaOH/Dolochar, crystallization temperature, and crystallization time of 1.375, 100 °C, and 11 h, respectively. The resultant XRD structure exhibited an average crystal size and crystallinity of 0.79 μm and 87.231 %, respectively. The average pore size, micropore volume, micropore area, and total surface area were 3.316 nm, 0.311 cc. g−1, 567.226 m2 g−1, and 583.117 m2 g−1, respectively. The maximum removal was accomplished with optimum conditions of 0.25 g.L−1 dosage, 80 min, at 313.15 K, and 6.5 pH. Adsorption isotherm results agreed with those hypothesized by Freundlich isotherm, with a maximum adsorption capacity of 714.285 mg g−1, and the pseudo-second-order kinetic model describes the adsorption kinetics well. The relevance of the results highlights the importance of using this dolochar-derived nanoporous zeolite as an adsorbent to effectively treat Cd(II) containing wastewater.

Adsorptive performance of a new magnetic hydrochar nanocomposite for highly efficient removal of cadmium ions from water: Mechanism, modeling, and reusability studies

In this study, a novel and effective magnetic watermelon seed hydrochar (MWSHC) was successfully synthesized via hydrothermal carbonization technique and in situ co-precipitation method. The prepared magnetic watermelon seed waste hydrochar has been utilized for the elimination of cadmium ions from the aqueous environment. The structural morphology, surface properties, and thermal stability of MWSHC adsorbent were characterized using FTIR, SEM, XRD, BET surface area, and TGA analysis, which demonstrated the successful synthesis of MWSHC. An extensive study of Cd(II) adsorption was conducted by assessing the influence of contact time, adsorbent mass, pH, initial Cd(II) concentration, temperature, and coexisting cations on the adsorption process of Cd(II). The results revealed that the removal efficiency of Cd(II) was 96.60% achieved at pH 7.0, time: 300 min, and dosage: 0.01 g, T: 298 K. Adsorption isotherm and kinetic parameters were estimated. The results indicated that the Cd(II) adsorption onto MWSHC followed the Freundlich and pseudo-second-order models. Based on the Langmuir equation, the MWSHC has a maximum adsorption capacity of 347.2 mg/g at 298 K. The reusability of magnetic hydrochar nanocomposite was studied, revealing that around 84.4% Cd(II) was still removed after four cycles. In conclusion, the newly- prepared MWSHC adsorbent has the advantages of high adsorption capacity, cost-effectiveness, and easy separation, thus having promising applications in effectively removing cadmium(II) from the aqueous environment.

Cadmium immobilization during nitrate-reducing Fe(II) oxidation by Acidovorax sp. BoFeN1: Contribution of bacterial cells and secondary minerals

Microbially nitrate-reducing Fe(II) oxidation (NRFO) is widespread in anoxic environments at circumneutral pH, in which Fe(II) oxidation is considered to be mainly catalyzed by nitrite via chemodenitrification after microbial nitrate reduction. Cadmium (Cd) is toxic to organisms, and its availability is strongly affected by iron (oxyhydr)oxides and/or bacteria. However, it remains unclear how NRFO affects the fate of Cd with environmentally relevant concentrations, and the relative contributions of microbes and secondary minerals to Cd immobilization during NRFO. Here, Acidovorax sp. BoFeN1, a typical NRFO bacterium, was used to investigate the Cd immobilization during NRFO at pH 7.0 with 0.1, 0.5, and 1.0 mg/L Cd, respectively. Higher initial Cd concentration resulted in a higher amount of Cd immobilized in precipitates, but showed stronger inhibition on nitrate reduction, acetate metabolism, and cell growth. The presence of Cd barely influenced the Fe(II) oxidation during NRFO or chemodenitrification, but retarded the mineral transformation to secondary crystalline minerals, i.e., lepidocrocite and goethite. The extracellular polymeric substances deposited in the bacteria-mineral precipitates were rich in tyrosine-like and tryptophan-like proteins with negatively charged amino and carboxyl groups. The STEM-HAADF images with EDX mapping demonstrated that Cd was strongly co-localized with Fe on the cell surface and in the periplasm. Cadmium immobilization experiments with bacterial cells or during chemodenitrification indicated that the bacterial cells and secondary minerals formed during chemodenitrification are comparably important for Cd immobilization in the Cd0.1 treatment, while the secondary minerals played a predominant role in Cd immobilization in the Cd0.5 and Cd1.0 treatments. These results suggested that Cd was likely associated with the secondary iron minerals, which precipitated with the proteins on the cell surface and in the periplasm. Our findings provide a comprehensive understanding of the roles of Cd, bacterial cells, and secondary minerals formed via chemodenitrification, as well as their interactions during the complicated NRFO process at circumneutral pH.