Fixed-bed Column Experiments Research Articles

Removal of hexavalent chromium using activated and magnetic Ziziphus Jujube seed biochar — a column study

ABSTRACT In this study, activated and magnetic biochar prepared from Ziziphus Jujube Seeds (ZJS) is used to remove Hexavalent Chromium (Cr(VI)) using Fixed Bed Column Experiment. Physicochemical characteristics of the activated and magnetic biochar such as functional groups, surface area, morphological study, and magnetic properties were analyzed. The column experiment was carried out for varying bed heights (2, 4, 6, 8, 10 cm), flow rates (20, 30 ml/min), and initial chromium concentrations (40, 60, 80 ppm) to determine adsorption performance of the studied biochar. The characteristic study found that magnetic biochar (MB) has good magnetic properties and crystallinity nature with essential functional groups such as C-O, FeO. The study found that Magnetic Biochar (MB) effectively removed 99% of hexavalent chromium through column adsorption under optimal conditions, including bed height of 6 cm, 60ppm Chromium concentration, and flow rate of 20 ml/min. Kinetic model study showed that Magnetic Biochar (MB) showed very good agreement with Adam Bohart Model, with R2 of 0.97, which is best fit model than other model studies whereas the other model showed a lesser R2 value. The study reveals that magnetic biochar from Ziziphus Jujube Seed is optimal adsorbent for removal of Cr(VI) through column adsorption experiment.

Eco-friendly and cost-effective synthesis of hierarchical porous HKUST-1 from thin waste electric cables for enhanced cationic dye removal

HKUST-1, as a type of metal-organic framework (MOF), has attracted significant interest for various applications. However, its use for adsorption applications is hindered by its microporous structure, which negatively impacts the diffusion and mass transfer of large particles (> 2 nm). Concurrently, waste electric cables from discarded vehicles and electronic equipment pose significant environmental challenges. To address these issues, we developed a novel recycling method using copper hydroxide recovered from waste-thin electric cables as the metal source for synthesizing hierarchical porous HKUST-1 (W) using a green approach at a low temperature. The resulting HKUST-1 (W) exhibited interesting properties compared to the typical HKUST-1 (C) synthesized from commercial precursors, showing a microporous-mesoporous structure with enhanced molecular mass transport, while HKUST-1 (C) exhibited only micropores. Moreover, the waste-derived HKUST-1 (W) formed interconnected small particles with enhanced methylene blue (MB) removal properties compared to HKUST-1 (C), mainly due to its hierarchical porous structure facilitating easy mass transfer of MB. To evaluate the industrial potential of our adsorbent, we conducted a fixed-bed adsorption column (FBAC) experiment, which showed that HKUST-1 (W) achieved a high removal efficiency of 99 %, confirming its effectiveness as a dye adsorbent in both batch experiments and a FBAC. This approach opens new perspectives in applying upcycled waste-based materials in synthesizing hierarchical porous MOFs.

Understanding the transitional phase of nitrate removal in three different specialty adsorbents for stormwater treatment

Excess nitrogen input from nonpoint sources driven by hydrologic and anthropogenic disturbances has become a significant ecological challenge in receiving water bodies. Moreover, nitrate removal by cost-effective filtration media has still not performed up to expectation because of the knowledge gap in the transitional phase from physicochemical to microbiological processes. This study developed three cost-effective, sustainable, and adaptable green sorption media (GSM), namely CPS (clay–perlite with sand sorption media), ZIPGEM (zero-valent iron and perlite green environmental media), and BIPGEM (biochar, zero-valent iron, and perlite-based green environmental media), made of readily available and recyclable materials, to compare nitrate removal methods for stormwater treatment and elucidate the transitional phase. The primary adsorption mechanism was chemisorption, and subsequent biofilm growth sustained removal efficiency for a long-lasting period. Adsorption kinetics, adsorption equilibrium, material characterization, and fixed-bed column experiments with a 2-stage cultivation approach were undertaken to characterize the transitional phase in these GSM, based on breakthrough curves, maximum adsorption capacity, and microbial population dynamics for nitrification and denitrification. As shown in the column study, BIPGEM had the highest adsorption capacity (7.637 mg∙g−1), followed by ZIPGEM (2.16 mg∙g−1), and CPS (0.1798mg∙g−1). The biochar in BIPGEM provides a better cultivation environment for nitrifying and denitrifying bacteria, contributing sufficient electron donors. Biofilm production and maturation enabled the BIPGEM to maintain 30 % nitrate removal in a steady state even after 2000 h of operation in the first stage. When the biofilm reached maturation, BIPGEM’s nitrate removal percentage was up to 70 % via denitrification in the second stage.

Response surface modelling and optimization for copper removal from acid mine drainage using oxidized Himalayan pine needle biochar

ABSTRACT This study aims to investigate and compare the adsorption behaviour of pine needle biochar (PNB) and H2O2-oxidized PNB (OPNB) in eliminating Cu(II) from acid mine drainage. The PNB and OPNB adsorbents undergo comprehensive characterization through various techniques (BET, FTIR, SEM, and pHPZC). A central composite design was employed for designing experiments and optimizing the impact of process factors (metal concentration, adsorbent doses, contact time, and pH) on adsorption capacity. Pseudo-first-order, pseudo-second-order, and intra-particle diffusion kinetics models as well as Langmuir, Freundlich, and Temkin isotherm models were used to analyze the experimental data. Langmuir isotherm best fit (R2 > 0.99) the experimental data and adsorption capacities of 29.49 and 102.04 mg/g, were determined for PNB and OPNB, respectively. Under optimized experimental conditions, desorption studies revealed the reusability of OPNB about 80% even after four cycles. Fixed-bed column experiments were conducted at ambient temperature with an initial Cu(II) concentration of 125 mg/L and 5.0 g of adsorbent, utilizing a flow rate of 1 mL/min for both PNB and OPNB. These results indicate that oxidized biochar, synthesized for Cu(II) remediation, not only addresses Himalayan pine needle concerns sustainably but also exhibits potential applicability for removing other metal ions from aqueous environments.

Xanthium Strumarium based activated carbon as low cost bioadsorbent for efficient removal of antidepressant drug Imipramine

Abstract Although, the pharmaceutical industries have contributed to improve the quality of human lifestyle. However, due to the extensive growth in living standards of modern society is one of the reasons that reinforce to millions of peoples to follow unhealthy lifestyle that leads to several health issues (like mental illness, disability and several metabolic problems etc.) it reinforces the over-dependency on pharmaceutical drugs. Among various pharmaceuticals, the tricyclic antidepressants (TCAs) have consumed significantly for the treatment of psychiatric disorders. The drug Imipramine (IMP) is one of the potential candidates among these TCAs, which is frequently used drug across the globe. That is why these TCAs are frequently detected pharmaceuticals in environment and negatively affect living organism. The levels of contamination of these TCAs in the environment have increased due to COVID-19 pandemic which consequently increased psychiatric disorders such as anxiety and depression in a significant population. The Imipramine contamination has harmful impact on human such as hypotension, cardiac arrhythmias, convulsions and hypothermia. The present study witnessed an effective removal of the Imipramine contamination from aqueous effluent using Xanthium Strumarium based low cost bio-adsorbent. The thermal activation was done to produce powdered bioadsorbent (XPT1) for Imipramine removal from its aqueous phase. The batch experiments were performed to access adsorption parameters like contact time (2 hours), maximum adsorption capacity (3.74 mg/g), optimum pH (less than 5 and more than 9) and adsorption capacity dependence on concentration and temperature of produced bioadsorbents. The fixed-bed column experiment was carried out to attain saturation time (626 minutes), adsorption capacity (64.9 mg.g−1) with 90.08 % of total removal percent of Imipramine. The adsorption isotherm data were best fitted to Freundlich model at low temperature 303 K, while at higher temperature the Imipramine adsorption is well fitted with both Langmuir and Freundlich models.

Fixed bed column adsorption systems to remove 2,4-Dichlorophenoxyacetic acid herbicide from aqueous solutions using magnetic activated carbon

The widespread use of 2,4-Dichlorophenoxyacetic acid (2,4-D) as a weedkiller has resulted in its persistence in the environment, leading to surface and groundwater pollution. In this study, the fixed bed column experiments were performed to remove 2,4-D from aqueous solutions using magnetic activated carbon derived from Peltophorum pterocarpum tree pods. The evaluation was done on effects of operating parameters such as bed depth (2–4 cm), influent flow rate (4.6–11.4 mL/min), and 2,4-D concentration (25–100 mg/L) on the breakthrough curves. The data fit well with the Yoon-Nelson and Thomas models, exhibiting high R2 values. Results indicated that lower flow rates, lower 2,4-D concentrations, and greater bed depths enhanced adsorption capacity, achieving up to 196.31 mg/g. Reusability studies demonstrated the material's potential for repeated use, while toxicity studies with Vigna radiata seeds confirmed the effectiveness of Fe3O4-CPAC in removing 2,4-D. This investigation highlights the promising application of Fe3O4-CPAC in fixed bed adsorption systems for efficient 2,4-D removal.

Natural and environmentally friendly rhamnolipid functionalized luffa fibers for adsorptive removal of pharmaceutical contaminant: Batch and fixed-bed column studies

This study aims to explore the potential of utilizing rhamnolipid functionalized luffa fibers as an environmentally sustainable solution for removing pharmaceutical contaminants from water. The efficiency of the developed adsorbent for removing acetaminophen has been investigated in batch and fixed bed column modes. The adsorbent has been characterized via FTIR, XRD, and SEM analyses which revealed the rhamnolipid nanomicelles formation with bi-pyramidal morphology and the presence of functional groups on the surface of the adsorbent. The optimum conditions have been reported (pH: 5.0, adsorbent dosage 2 g/L, initial acetaminophen concentration: 20 mg/L, and contact time: 80 min). The highest adsorption capacity for acetaminophen was 37.03 mg/g at the optimized conditions. Fixed-bed column experiments examined flow rate and initial acetaminophen concentration effects, with the Thomas model assessing column performance. This research investigates the potential of RL-LF for effective water remediation, offering insights into practical applications and optimization strategies.

Characterization and Performance of Peanut Shells in Caffeine and Triclosan Removal in Batch and Fixed-Bed Column Tests.

Peanut shells' adsorption performance in caffeine and triclosan removal was studied. Peanut shells were analyzed for their chemical composition, morphology, and surface functional groups. Batch adsorption and fixed-bed column experiments were carried out with solutions containing 30 mg/L of caffeine and triclosan. The parameters examined included peanut shell particle size (120-150, 300-600, and 800-2000 µm), adsorbent dose (0.02-60 g/L), contact time (up to 180 min), bed height (4-8 cm), and hydraulic loading rate (2.0 and 4.0 m3/m2-day). After determining the optimal adsorption conditions, kinetics, isotherm, and breakthrough curve models were applied to analyze the experimental data. Peanut shells showed an irregular surface and consisted mainly of polysaccharides (around 70% lignin, cellulose, and hemicellulose), with a specific surface area of 1.7 m2/g and a pore volume of 0.005 cm3/g. The highest removal efficiencies for caffeine (85.6 ± 1.4%) and triclosan (89.3 ± 1.5%) were achieved using the smallest particles and 10.0 and 0.1 g/L doses over 180 and 45 min, respectively. Triclosan showed easier removal compared to caffeine due to its higher lipophilic character. The pseudo-second-order kinetics model provided the best fit with the experimental data, suggesting a chemisorption process between caffeine/triclosan and the adsorbent. Equilibrium data were well-described by the Sips model, with maximum adsorption capacities of 3.3 mg/g and 289.3 mg/g for caffeine and triclosan, respectively. In fixed-bed column adsorption tests, particle size significantly influenced efficiency and hydraulic behavior, with 120-150 µm particles exhibiting the highest adsorption capacity for caffeine (0.72 mg/g) and triclosan (143.44 mg/g), albeit with clogging issues. The experimental data also showed good agreement with the Bohart-Adams, Thomas, and Yoon-Nelson models. Therefore, the findings of this study highlight not only the effective capability of peanut shells to remove caffeine and triclosan but also their versatility as a promising option for water treatment and sanitation applications in different contexts.

Nanoconfined Fe(II) releaser for long-term arsenic immobilization and its sustainability assessment

Ferrous (Fe(II))-based oxygen activation for pollutant abatements in soil and groundwater has attracted great attention, while the low utilization and insufficient longevity of electron donors are the primary challenges to hinder its practical applications. Herein, we propose a nanoconfined Fe(II) releasing strategy that enables stable long-term electron donation for oxygen activation and efficient arsenic (As) immobilization under oxic conditions, by encapsulating zero-valent iron in biomass-derived carbon shell (ZVI@porous carbon composites; ZVI@PC). This strategy effectively enhances the generation of reactive oxygen species, enabling efficient oxidation and subsequent immobilization of As(III) in soils. Importantly, this Fe(II) releaser exhibits strong anti-interference capability against complex soil matrices, and the accompanying generation of Fe(III) enables As immobilization in soils, effectively lowering soil As bioavailability. Soil fixed-bed column experiments demonstrate a 79.5 % reduction of the total As in effluent with a simulated rainfall input for 10 years, indicating the excellent long-term stability for As immobilization in soil. Life cycle assessment results show that this Fe(II) releaser can substantially mitigate the negative environmental impacts. This work offers new insights into developing green and sustainable technologies for environmental remediation.

Fixed Bed Column Adsorption System for the Removal of 2,4-Dichlorophenoxyacetic Acid Herbicide from an Aqueous Solution

The intensive use of 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide has resulted in the presence of its residues in the environment, which leads to contamination of surface and groundwater. In this study, a fixed-bed column experiment was conducted for the removal of 2,4-D from an aqueous solution using termite mound soil (TMS). Scanning electron microscopy (SEM), Fourier transform infrared (FTIR), atomic absorption spectrometry (AAS), and Brunauer–Emmett–Teller (BET) techniques were used to characterize the adsorbent. The effect of significant variables, such as the initial 2,4-D concentration (50 mg/L and 75 mg/L), flow rate (2.5 ml/min and 5 ml/min), solution pH (2, 4, and 6), and bed height (3, 6, and 9 cm), on the breakthrough characteristics of the adsorption system was assessed. In addition, the Thomas and Yoon–Nelson models were applied to predict the breakthrough curves and to determine the characteristic parameters of the column that are useful for process design. The findings showed that at a lower pH (2), a lower flow rate (2.5 ml/min), a lower 2,4-D concentration (50 mg/L), a higher bed depth (9 cm), and 840 min breakthrough time, a higher removal percentage (80.2%) of 2,4-D was achieved. The experimental data were in good agreement with the Thomas and Yoon–Nelson models. For the Yoon–Nelson model, the rate constant increased with an increase in the flow rate, initial ion concentration, and bed height. The time required for a 50% breakthrough decreased with an increase in the flow rate, bed height, and initial ion concentration. For the Thomas model, the rate constant increased with an increase in the flow rate but decreased with an increase in bed height and initial concentration. Overall, the study showed that termite mound soil in a fixed-bed column adsorption system presents an excellent potential for removing 2,4-D from aqueous solutions.

Facile synthesis of MIL-88A/PVA sponge for rapid tetracycline antibiotics degradation via sulfate radical-advanced oxidation processes

MIL-88A is a metal–organic framework (MOF) material known for its excellent performance in advanced oxidation processes (AOPs). However, due to its powdery nature, MIL-88A may undergo loss during catalytic degradation in flowing solutions, making continuous degradation removal challenging. Herein, we report the synthesis of MIL-88A/PVA sponge composite material by the in-situ integration of MIL-88A with PVA sponge. The composite sponge exhibits excellent removal efficiency of tetracycline antibiotics under the conditions of sulfate radical-advanced oxidation processes (SR-AOPs), achieving a degradation rate exceeding 99.0% within 2 min. Additionally, through fixed-bed column experiments, 1 kg of MIL-88A/PVA can treat 2160 L of wastewater within 24 h, indicating promising industrial applicability. It’s worth noting that this material can be customized into any desired block shape as needed. This work offers a highly promising solution for the application of MOF-based bulk-type catalysts in the treatment of antibiotic pollution using SR-AOPs.

Sustainable Banana-Waste-Derived Biosorbent for Congo Red Removal from Aqueous Solutions: Kinetics, Equilibrium, and Breakthrough Studies

This study investigates the adsorption of Congo red (CR) dye from wastewater using banana peel biochar (BPBC) in both batch and fixed-bed column modes. BPBC was characterized using FTIR, SEM, XRD, TGA, and BET analysis, revealing a predominantly mesoporous structure with a surface area of 9.65 m2/g. Batch adsorption experiments evaluated the effectiveness of BPBC in removing CR, investigating the influence of the BPBC dosage, initial CR concentration, and solution pH. Results showed optimal CR removal at pH levels below 4, suggesting a favorable electrostatic interaction between the adsorbent and the dye. Furthermore, a pseudo-first-order kinetic model best described the adsorption process. The Freundlich isotherm provided a better fit compared to the Langmuir and Dubinin–Radushkevich (D-R) models, implying a heterogeneous adsorption surface. The calculated maximum adsorption capacity (Qm) from the Langmuir model was 35.46 mg/g. To assess continuous operation, breakthrough curves were obtained in fixed-bed column experiments with varying bed heights (1–3.6 cm). The results demonstrated efficient CR removal by BPBC, highlighting its potential for wastewater treatment. Finally, this study explored the feasibility of BPBC regeneration and reuse through four adsorption–desorption cycles.

Nitrate removal from aqueous solution by glucose-based carbonaceous adsorbent: Batch and fixed-bed column adsorption studies

In the present study, the glucose-based carbonaceous adsorbent was prepared from glucose, melamine and urea by using ZnCl2 activation and heated at 550°C under N2 flow. The sample was treated for the 1st, 2nd and 3rd activation process, and they were characterized by N2 adsorption and desorption isotherms, elemental analysis and X-ray photoelectron spectroscopy (XPS). The results showed that the content of nitrogen increased and that of oxygen decreased with the increasing of the number of activation process. The adsorbent obtained after the 2nd activation showed the best adsorption properties and was used in batch and fixed-bed column adsorption studies. In batch adsorption experiments, we investigated the factors affecting nitrate adsorption such as initial concentration, solution pH, adsorption isotherms and adsorption kinetics. The isotherm data and kinetic data were fitted well to the Langmuir isotherm model and pseudo-second-order model, respectively, and the maximum adsorption capacity calculated by Langmuir model was 1.58 mmol/g at pH 3. The adsorption performance of the adsorbent in industrial application mode was also investigated by fixed-bed column experiments. The breakthrough time of the packed column was 160 min for the initial nitrate concentration of 200 mg/L at pH 3. The saturated column could be regenerated by 1 mol/L HCl and reused for at least 5 adsorption-desorption cycles. The column showed good adsorption performance in both coexisting ions solution and real contamination water.

Efficient selective uptake of Hg(Ⅱ) using a porous organic polymer rich in N and S atoms

The escalating issue of mercury (II) ions (Hg2+) pollution in water, primarily due to human activities, poses a significant environmental and health risk. Addressing the urgent need for efficient Hg2+ removal, this study introduces a novel porous organic polymer (TpTHU) synthesized through Schiff base condensation of thiourea (THU) and 1,3,5-Triformylphloroglucinol (Tp). TpTHU, enriched with sulfur and nitrogen, facilitates soft–soft interaction with Hg2+, offering a potent solution for mercury contamination. Our experimental results demonstrate TpTHU's remarkable adsorption capacity for Hg2+, reaching 1250 mg/g, attributed to its dense complexation sites. The adsorption behavior aligns well with the Brouers-Sotolongo model. Notably, TpTHU achieves 99.25% mercury removal within 120 min over a broad pH range (4 to 10), underscoring its rapid action. Additionally, in fixed-bed column experiments, TpTHU effectively lowers Hg2+ concentrations in industrial wastewater from 10.0 mg/L to below 5 μg/L, surpassing industrial emission standards. Through XPS analysis and density functional theory calculations, we elucidate the adsorption mechanism, affirming TpTHU's efficiency. With its straightforward synthesis, high efficacy, and excellent reusability, TpTHU emerges as a promising candidate for mitigating Hg2+ pollution in industrial wastewater.

Pesticides’ low-cost removal from polluted groundwater using charcoal from “Salix mucronata” trees activated by gold nitrate

ABSTRACT Used pesticides result in soil pollution, which potentially seep into groundwater, posing risks to human and animal health. The current study examines the use of a new cheap material for removing four commonly used pesticides from polluted groundwater before use for drinking. These pesticides are Malathion, Methomyl, Abamectin, and Thiamethoxam. Activated charcoal obtained from the trunk of “Salix mucronata” trees is introduced for removing these pesticides by surface adsorption. Activation treatment using gold-nitrate solution is introduced to enhance the charcoal adsorption capacity, because removal of pesticides is difficult due to their large-sized molecules and lack of obvious surface electrostatic charges. Physical and chemical properties of the studied pesticides and the activated charcoal were determined. Batch experiments tested the effects of solution pH, contact time, dose of charcoal, and initial concentrations on the charcoal adsorption capacity. Langmuir adsorption linear isotherm test was done to use for the prediction of adsorption behavior. Fixed-bed column experiments tested clean-up of polluted water using charcoal filter under steady flow. Gold-nitrate activated charcoal adsorption capacities were almost three times higher than other charcoals for the same pesticides at the same initial concentrations. Maximum adsorption capacities achieved in the current study were 16.17, 14.59, 9.55, and 8.99 mg/g, respectively, at the initial concentrations of 50.0 mg/l. Meanwhile, treatment times in steady-flow fixed-bed columns were much lower compared to other studies. Preparation cost of gold-nitrate activated charcoal in the current study was lower than other adsorbents. The charcoal introduced in this study is recommended for use in low-cost removal of pesticides from polluted groundwater on the national scale, including small treatment units for rural communities with limited facilities.

Efficient adsorption of phosphorus by macroscopic MOF/chitosan composites and preliminary investigation of subsequent phosphorus recovery through electrochemically-driven struvite precipitation

The proper management of phosphorus (P) from wastewater is crucial for sustainable development consideration. Herein, we developed a strategy which combines adsorption via tailored adsorbents and electrochemically-driven struvite precipitation (ESP) for P recovery. Novel polydopamine-modified Ce-MOF/chitosan composite beads (PDA@Ce-MOF-CS) were prepared by a facile in situ growth of Ce-MOF crystals incorporated natural polymers and PDA coating. The physicochemical properties of PDA@Ce-MOF-CS were characterized. Both batch and fixed-bed column experiments were conducted to evaluate its adsorption performances. Representatively, PDA@Ce-MOF-CS performed good selectivity for P removal and exhibited a maximum adsorption capacity of 161.13 mg P/g at pH 3 and 318 K. Meanwhile, the developed adsorbent showed great reusability after ten regeneration cycles as well as good adsorption stability. The dominant mechanism for efficient P adsorption included electrostatic attraction, surface precipitation and ligand exchange. Interestingly, PDA@Ce-MOF-CS exhibited a remarkable adsorption capacity of 92.86 mg P/g by treating real P-rich electroplating wastewater, and the desorbed P in the eluate could be effectively recovered and converted into a solid fertilizer as struvite via ESP. Overall, this work provided a new research direction for P recovery from wastewater as struvite by combined technologies with the help of macroscopic MOF architectures.

In-situ growth of Al/Ni layered double hydroxide onto polyaniline-wrapped sisal fibers for highly efficient removal of pharmaceutical Ketoprofen and Ibuprofen contaminants: Batch and fixed-bed column studies

The present study focuses on the in-situ growth of Al/Ni layered double hydroxide onto polyaniline/sisal fibers (SF/PANI/LDH). The main purpose is investigating the effectiveness of this composite material in removing non-steroidal anti-inflammatory artificial pharmaceutical contaminants (ketoprofen (KTP) and ibuprofen (IBP)). The present investigation involves conducting batch and fixed-bed column experiments. Various analytical techniques, namely SEM, FTIR, and XRD, were conducted to analyze prepared adsorbent features. These analyses indicated that Al/Ni layered double hydroxide was successfully coated on the polyaniline-wrapped sisal fibers. The batch study was mainly focused on assessing influencing parameters (solution pH, adsorbent dosage, pollutant concentration, and time), equilibrium curves, kinetic behavior, and the determination of thermodynamic parameters. In particular, the findings illustrate that adsorption results were well correlated to the pseudo-second-order kinetic and Temkin isotherm models, in which the maximum adsorption capacities for IBP and KTP were measured to be about 86.03 and 38.68 mg/g, respectively. The adsorbent showed having an acceptable efficiency even after six cycles of regeneration, where adsorption capacity decreased <15 % compared to primary adsorbent. In addition, the fixed-bed column study was conducted, and the results revealed that the service volume reduced with the increase in the flow rate.

Adsorption of metal ions by oceanic manganese nodule and deep-sea sediment: Behaviour, mechanism and evaluation

Deep-sea mining disturbs the sediment on the seabed to form plumose flows, carrying metal ions that are transmitted through the food chain, posing a serious threat to marine ecosystems and human health. In this study, two types of marine raw materials were screened: Oceanic Manganese Nodules (OMN) and Deep-sea Sediments (DSS), and prepared the spherical regenerative adsorption materials OMN@SA, DSS@SA and OMN&DSS@SA using sodium alginate (SA) by sol-gel method. Preliminary investigations on the adsorption effect of metal ions were carried out. OMN@SA exhibited the best adsorption capacity, with the adsorption quantities for Cu2+, Co2+ and Ni2+ reaching 31.12, 21.11 and 16.66 mg/g, respectively. The adsorption behaviour is consistent with the Langmuir, pseudo-second-order kinetics and particle diffusion model, indicating that the adsorption process is mainly spontaneous, monolayer chemical adsorption, and the adsorption rate is mainly controlled by internal particle diffusion. SEM-EDS, XRD, FTIR and XPS analyses suggest that the adsorption mechanism includes surface physical adsorption, ion exchange, functional group complexation, electrostatic attraction and precipitation. The fixed bed column experiment shows that OMN@SA can effectively remove metal ions Cu2+, demonstrating excellent stability, safety and good regenerability. This study paves a new direction for the design of efficient and sustainable materials for heavy metal adsorption. More importantly, as marine primordial materials, OMN and DSS have strong technical and economic feasibility for future use in in-situ fixation of metal ions in seafloor sediments and restoration of the original seabed environment.

Adsorption of pharmaceutical pollutants on ZnCl2-activated biochar from corn cob: Efficiency, selectivity and mechanism

The occurrence of pharmaceuticals in water bodies and drinking water poses risks for the environment and human health, thus it is necessary to study methodologies that allow the efficient removal of these contaminants. In this work, corn cob-derived biochar was obtained by ZnCl2-activation, and subsequent carbonization at 700 °C. The effect of contact time, temperature, pH, and initial concentration on the adsorption capacity of acetaminophen (ACE) and amoxicillin (AMX) was determined through batch experiments. In addition, the kinetics, isotherms, and thermodynamics parameters were determined. The activated biochar exhibited a maximum adsorption capacity of 332.08 mg/g for ACE and 175.86 mg/g for AMX. The adsorption kinetics and adsorption isotherm of ACE corresponded to the pseudo-second order and Langmuir model, respectively. Meanwhile, pseudo-first-order kinetics and the Freundlich isotherm model were well-fitted to AMX adsorption. The ACE and AMX co-adsorption had a synergistic effect on AMX but an antagonistic effect on ACE removal, achieving a maximum adsorption capacity of 193.51 and 184.58 mg/g, respectively. On the other hand, fixed-bed column experiments showed that the adsorption capacity depends on the influent concentration, and the breakthrough curve fits the Thomas and Yoon-Nelson model. The mechanism adsorption studies showed that surface interactions (hydrogen bonding formation and n-π interactions) are the main driving forces for the adsorption process, and pore filling is the rate-limiting step. In this way, the prepared biochar exhibits a high potential for the adsorption of pharmaceutical compounds from water.

A novel Chitosan-Barbituric acid hydrogel supersorbent for sequestration of chromium and cyanide ions: Equilibrium studies and optimization through RSM

The objective of this study is to transform chitosan biopolymer by crosslinking with barbituric acid into an amine-rich product that could be applied as a water treatment agent. Chitosan-barbituric acid (CBA) was synthesized by lyophilization process and characterized using FT-IR, XRD, TGA-DTA, SEM-EDX, BET surface area and BJH pore size distribution analysis. The pHpzc was found to be 7.7 indicating applicability towards both cations and anion adsorption. The CBA was used for seizure of CrVI and CN– from aqueous solutions in batch adsorption as well as fixed bed column experiments. Response surface methodology (RSM) was used as a statistical tool to optimize the functioning parameters resulting in more than 90 % removal of these ions. As shown by isotherm and kinetics data, Langmuir isotherm and pseudo second order kinetics exhibited a good fit for the adsorption process. The maximum adsorption capacities of CBA towards CrVI and CN– evaluated using Langmuir isotherm fitment were 534.75 mg g−1 and 251.66 mg g−1 at pH 4.0 and 6.0 respectively. Thermodynamic studies indicated spontaneous and enthalpy driven course with large negative enthalpy changes of −56.39 and −31.81 kJ mol−1 respectively. Fixed bed column studies showed that the material could be used for larger sample volume treatment even at 200 mg/L CrVI and 100 mg/L CN−1 concentration. Regeneration studies of adsorbent was conducted over five adsorption–desorption cycles with removal efficiency more than 50 %indicating reusability of the adsorbent. Analysis of adsorbent sustainability revealed that the synthesis was eco-friendly as indicated by low value of E-factor of 0.32.