Batch Sorption Experiments Research Articles

Convenient sorption of uranium by Amidoxime-functionalized mesoporous silica with magnetic core from aqueous solution

The use of inexpensive and biocompatible sorbents for effective removal of uranium from water environment is still an open challenge for many researchers. Herein, the magnetic amidoxime-functionalized mesoporous silica (MMS-AO) has been prepared by a combination of soft template method and co-condensation method in weak alkali oil/water phase. A feature of MMS-AO is core–shell configuration with Fe3O4 service as core, which makes the material easy to be recovered by an external magnetic field after sorption. Various characterization techniques of SEM, TEM, N2 sorption–desorption, FT-IR, TGA, Zeta potential and VSM were applied to evaluate MMS-AO. Batch sorption experiments confirmed that there were some good behavior to U(VI) removal on MMS-AO from aqueous including sorption capacity, selectivity and reusability. The experimental data fitted well to Langmuir isotherm model and the pseudo-second-order kinetic model. The maximum sorption amount at 298 K and pH 5.50 was 236.70 mg·g−1 and the dynamic equilibrium can be reached in 90 min. The sorption process is spontaneous and endothermic via thermodynamic study. The analysis of XPS provided three insights on mechanism based on the chelation of U(VI) with amidoxime groups.

Modified oyster shell powder with iron (II) sulfate heptahydrate to improve arsenic uptake in solution and in contaminated soils.

Arsenic is a metalloid whose presence can be due to natural or anthropological causes. It is considered as a toxic chemical that puts human health at high risk. In this study, we evaluated a novel modified oyster shell (MOS) that was coated with iron (II) sulfate heptahydrate using two different proportions through batch sorption experiments in an arsenic solution and in arsenic-contaminated soils. The arsenic solution was prepared using As(III)-standard solution. The arsenic contaminated soils were extracted from a contaminated site in Cheonan, South Korea, where the average arsenic concentration of the soil was reported as 136.28mg/kg. Different doses of oyster shell and modified oyster were used to understand the effect of the addition of iron (II) sulfate heptahydrate via sorption batch experiments in solution and sorption tests in soils. The sorption tests were conducted with 50g of contaminated soil; then, 150g of soils was used for the pot cultivation tests, and finally, 150g of contaminated soils was used for column percolation test. Through the experiments, the authors observed a comparable improvement of arsenic stabilization from 10 to 60% with the addition of iron (II) sulfate heptahydrate to oyster shell.

Adsorptive removal of hazardous crystal violet dye onto banana peel powder: equilibrium, kinetic and thermodynamic studies

In this study, banana peel powder (BPP) was used to remove carcinogenic crystal violet (CV) dye from aqueous solution. The BPP adsorbent was characterized by Fourier-Transform Infrared (FTIR) spectroscopy and Scanning Electron Microscopy (SEM). In batch sorption experiments, the maximum removal of CV was recorded 93% at optimum levels of operating parameters, i.e., pH 7.0, adsorbent dosage 0.1 g, contact time 10 min, initial adsorbate concentration 90 ppm and temperature 20 C o . The kinetics of the adsorption process was found best to follow the pseudo first order model with high value of R 2 (0.9999) and low values of error functions. The Langmuir isotherm model was the best fit with high R 2 (0.9552) low values of error models. The plots of Freundlich and D-R isotherms confirmed the feasibility ( n = 1.3109 L g − 1 ) and the physisorption nature ( E s = 0.1107 kJ mol − 1 ) of the process respectively. The negative values of thermodynamic parameters ( Δ G & Δ H ) revealed that the adsorption was spontaneous and exothermic in nature respectively. The results of the desorption study showed that 91% of the adsorbent was regenerated. The novelty of the present research is that no work has been reported till date to remove crystal violet dye by using banana peel specifically. The high adsorption and desorption efficiencies (>90%) suggest that BPP possesses characteristics to be used as an effective, fast and low-cost adsorbent for adsorption of CV dye from industrial effluents. HIGHLIGHTS Adsorption technique was employed to remove crystal violet dye by using banana peel powder. The hydroxyl ( OH − ) & carboxylate ( OH − ) groups on adsorbent surface provided excellent binding with adsorbate molecules. Equilibrium attainment in 10 min at neutral pH. 93% adsorption and 91% desorption.

Natural Clay Minerals as Potential Arsenic Sorbents from Contaminated Groundwater: Equilibrium and Kinetic Studies

Arsenic (As) contaminated groundwater is a worldwide concern due to its chronic effects on human health. The objectives of the study were to evaluate natural inexpensive raw laterite (RL) and kaolinite (RK) for their potential use as As sorbents and to understand the As sorption on laterite and kaolinite by employing sorption and kinetic models. Raw laterite and RK were tested for EC, pH, XRF and CEC as basic parameters. Batch sorption and kinetic experiments data were fitted in the sorption (Langmuir and Freundlich) model and kinetic (pseudo-first and pseudo-second order) reaction equations, respectively. Morphological and structural changes were observed in RL and RK samples before and after As saturation by employing FTIR and SEM. The major constituent in RL was Fe and Al oxides while in RK major oxides were silica and Al. The Freundlich sorption model well explained the experimental data, indicating a greater sorption capacity of RL on a hetero-layered surface compared to RK. The kinetic reaction equations showed that equilibrium was achieved after a contact time of 240 min and the adsorption was chemisorption in nature. The RL and RK were found to be effective sorbents for As removal, however, RL showed maximum As adsorption and thus superior in comparison with RK. Structural and morphological characterization reveals the role of Fe and Al oxides in the case of RL, and Al oxides in the case of RK, in the adsorption of As. Hence this study concludes that these naturally occurring inexpensive resources can be used as sorbent agents for As-contaminated drinking water treatment.

Effective Removal of Phosphate from Waste Water Based on Silica Nanoparticles

This study explored the potential application of silica nanoparticles (SiNPs) prepared from rice husk ash (RHA) to reuse phosphate from aqueous solution. The physicochemical analysis illustrated that the SiNPs, which were extracted from waste biomass, have a nonuniform shape with a size range of a few nanometer to hundreds of nanometers, a surface area of 15.56 m2·g−1, and an adsorption pore width of 4.06 nm. Those results carried out the possibility to utilize the SiNPs for removal of phosphate. Findings from the batch sorption experiments showed that the phosphate adsorption was controlled by experimental parameters, i.e., pH, adsorbent dosage, concentration of adsorbate, and adsorption time. The experimental results showed that the maximum phosphate adsorption capacity of SiNPs was achieved at around 9.08 mg·g−1 at adsorption conditions, i.e., pH 7, SiNPs dosage of 0.3 g, and adsorption time of 90 min. The phosphate removal based on SiNPs will offer several benefit such as an effective and low cost method, reliable to reuse as an effective slow release phosphate fertilizer.

Experimental Evidence from the Field that Naturally Weathered Microplastics Accumulate Cyanobacterial Toxins in Eutrophic Lakes.

Freshwater ecosystems with recurring harmful algal blooms can also be polluted with plastics. Thus the two environmental problems may interact. To test whether microplastics influence the partitioning of microcystins in freshwater lakes, we examined the sorption of four microcystin congeners to different polymers of commercially available plastics (low-density polyethylene, polyethylene terephthalate, polyvinyl chloride, and polypropylene). We conducted three experiments: a batch sorption experiment in the laboratory with pristine microplastics of four different polymers, a second batch sorption experiment in the laboratory to compare pristine and naturally weathered microplastics of a single polymer, and a 2-month sorption experiment in the field with three different polymers experiencing natural weathering in a eutrophic lake. This series of experiments led to a surprising result: microcystins sorbed poorly to all polymers tested under laboratory conditions (<0.01% of the initial amount added), irrespective of weathering, yet in the field experiment, all polymers accumulated microcystins under ambient conditions in a eutrophic lake (range: 0-84.1 ng/g). Furthermore, we found that the sorption capacity for microcystins differed among polymers in the laboratory experiment yet were largely the same in the field. We also found that the affinity for plastic varied among microcystin congeners, namely, more polar congeners demonstrated a greater affinity for plastic than less polar congeners. Our study improves our understanding of the role of polymer and congener type in microplastic-microcystin sorption and provides novel evidence from the field, showing that naturally weathered microplastics in freshwater lakes can accumulate microcystins. Consequently, we caution that microplastics may alter the persistence, transport, and bioavailability of microcystins in freshwaters, which could have implications for human and wildlife health. Environ Toxicol Chem 2022;41:3017-3028. © 2022 SETAC.

One-pot synthesis of iron oxides decorated bamboo hydrochar for lead and copper flash removal

A novel one-pot codeposition strategy was developed by employing bamboo hydrochar as precursors to fabricate magnetic porous char (MPC) with Fe 3 O 4 or α-Fe loading. The synthesized MPC with well dispersed magnetic phase and high thermal stability displayed excellent adsorption capacities and flash adsorption rate for Cu(II) and Pb(II). The batch sorption experiments showed that MPC had the best performance with Langmuir adsorption capacities as high as 125.06 mg/g for Cu(Ⅱ) and 153.85 mg/g for Pb(Ⅱ), respectively. More importantly, the short time of adsorption reaching 90 % equilibrium within 10 min was considerably beyond previous study. Also, a synergistic mechanism of the chemical complexation and physical adsorption for the higher adsorption capabilities and flash removal rate of the synthesized MPC was proposed. The regeneration investigation revealed that the sorption efficiencies remained at high level with above 92.4 % for Cu(II) and 94.1 % for Pb(II) after five cycles. Thus, the MPC were expected to be a promising candidate for high-efficient and rapid removal of heavy metal contaminants from wastewater in future practical utilization . • Highly porous and thermal stable magnetic biochar were synthesized by one-pot method. • The adsorption capacities were 125.06 mg/g for Cu(Ⅱ) and 153.85 mg/g for Pb(Ⅱ), respectively. • The adsorption reached 90 % of the adsorption equilibrium within 10 min. • The sorption efficiencies of regeneration remained above 92.4 % for Cu(II) and 94.1 % for Pb(II) after five cycles.

KMnO4 modified biochar derived from swine manure for tetracycline removal

Abstract Tetracycline (TC) is widely used in the livestock industry, but undigested TC is excreted with livestock waste and accumulates in the environment. In this study, swine manure-derived biochar (SBC) was modified with KMnO4 (MnOx-SBC), and used to remove TC. SEM-EDS, FTIR, XPS and elemental analysis all indicated that ultrafine MnOx particles were attached to the biochar surface. The surface properties and composition of the oxygen-containing functional groups were enhanced by KMnO4 modification. Batch sorption experiments showed that MnOx-SBC's TC-adsorption capacity was 105.9 mg·g−1, 46.4% higher than SBC's. The TC-adsorption onto MnOx-SBC agreed well with the pseudo-second-order model and Freundlich isotherm. A new platform is proposed for reusing swine manure while solving the livestock industry's antibiotic pollution risk by ‘treating waste with waste’.

Artificial aging induced changes in biochar,s properties and Cd2+ adsorption behaviors.

Fresh biochar has been widely applied to the remediation of heavy metals in soil by its property of adsorption, but the changes in its physicochemical properties and in situ adsorption performance over time cannot be ignored. In this study, the sorption of Cd2+ by corn straw biochars (CB) and municipal sludge biochars (SB) produced at 350 °C and 650 °C before and after H2O2 oxidation, and dry-wet and freeze-thaw aging were investigated using batch sorption experiments. The changes of physicochemical properties of biochar before and after aging were analyzed by various characterization methods. Based on these results, the impact of aging on the Cd2+ adsorption behavior could be clarified, which showed that CB650 was able to display the highest adsorption capacity in fresh biochars. Aging treatments reduced the ash content and pH value of CB, and significantly diminished the adsorption performance of Cd2+. These changes indicated that precipitation was a critical factor in the adsorption of Cd2+ on CB. The adsorption capacity of SB was enhanced after H2O2 oxidation, but weakened after dry-wet and freeze-thaw aging. This was closely related to the increase or decrease in the content of oxygen-containing functional groups, which in turn enhanced or inhibited its ability to compound with heavy metals. These results are of great significance for evaluating its long-term application prospects in the natural environment.

Sorption of Sn and Nb on montmorillonite at neutral to alkaline pH

ABSTRACT The distribution coefficient (K d) value of radionuclides is an important parameter in the radionuclide migration analysis in the safety assessment of the geological disposal of high-level radioactive waste. To improve the reliability of safety assessment, the K d values must be extensively evaluated, particularly under conditions where they might be decreased. In this study, the pH dependence of the K d values for Sn and Nb on montmorillonite was evaluated using batch sorption experiments at neutral to alkaline pH, which might be caused by the leaching of cementitious materials and the corrosion of carbon steel. The K d values were determined in the range 8 < pH < 12 by the experiments and were found to decrease with increasing pH. A model calculation using a thermodynamic sorption model was conducted on the measured pH dependence of the K d values. Two different sorption sites were required to describe the pH dependence of the K d values of Sn in the model calculation, whereas one sorption site was considered predominant in the sorption of Nb.

Adsorption behaviour and mechanism of polycyclic aromatic hydrocarbons onto typical microplastics in a soil solution

ABSTRACT Microplastics (MPs) have a tremendous potential to sorb hydrophobic organic contaminants in the soil environment. The effects of MPs in the soil systems, however, remain largely unexplored. The objective of this study was to investigate the impact of polyethylene and polystyrene MPs on the transport of the benzo[a]anthracene (BaA) and benzo[a]pyrene (BaP) in soil matrices. In this study, we investigated the sorption process of BaA and BaP in batch sorption experiments in a laboratory and systematically evaluated the particle sizes of MPs (0.8, 50, 200, and 500 μm) and the environmental factors, such as pH, ionic strength, and humic acid (HA) concentration on adsorption behaviour. The results showed that the adsorption of PAHs onto MPs reached equilibrium within 24 h. The adsorption kinetics of PAHs onto MPs were fitted well with the pseudo-first-order kinetic model. The adsorption isotherm modelling showed a better fit of the adsorption results to the Freundlich model. The thermodynamic research indicated the adsorption of BaA and BaP as spontaneous and endothermic processes. Additionally, the adsorption capacity of BaA and BaP reached the highest when polyethylene and polystyrene MPs with a particle size of 0.8 μm and 50 μm, respectively. The sorption of BaA and BaP on PE and PS MPs was significantly influenced by pH and the peaking at pH 5.0 and 7.0, respectively. Furthermore, the adsorption mechanisms of the BaA and BaP on MPs were dominated by electrostatic interaction, π–π interactions, and hydrophobic interaction.

Preferential sorption of polysaccharides on mackinawite: A chemometrics approach

Marine sediments represent the most important sink for natural organic matter (NOM) across geological time spans. Strong associations between minerals, including iron oxides, and organic matter reaching the seafloor play a fundamental role in this preservation and have been known for some decades. Despite the importance of this protective mechanism in the balances of the global carbon budget, very little is known about the affinity of NOM for reduced iron species such as mackinawite (FeS) in the anoxic layers of sediment. In this study, equilibrium partition coefficients (Kd) for three types of NOM (soil extract, corn leaf extract and plankton extract) on FeS were determined through batch sorption experiments. Models were then built via multiple linear regression (MLR) and partial least squares regression (PLSR) in order to predict sorption Kd’s based on the chemical characteristics of the NOM. Investigation of the PLSR regression coefficients indicates that functional groups characteristic of polysaccharides are the greatest positive predictors of NOM sorption onto FeS at marine sediment porewater pH. This conclusion was independently verified by analyses of NOM FTIR spectra pre- and post-sorption. PLSR outperformed MLR with a lower root mean square error of prediction (RMSEP) of 53.4 L/kg compared to 64.0 L/kg. To our knowledge, this research presents a novel machine-learning approach to the quantitative modelling of NOM sorption to minerals found in anoxic marine environments.

Investigating the role of bentonite clay with different soil amendments to minimize the bioaccumulation of heavy metals in Solanum melongena L. under the irrigation of tannery wastewater.

Wastewater from tanneries is a major source of heavy metals in soil and plants when used for crop irrigation. The unavoidable toxicological effects of this contamination, however, can be minimized through two independent steps discussed in the present study. In the first step, a batch sorption experiment was conducted in which Cr was adsorbed through bentonite clay. For this purpose, DTPA extraction method was used to analyze Cr concentration in the soil after regular time intervals (0.5, 1, 2, 6, 8, 9, 10.5, 11.5, and 20.3 h) which reduced Cr concentration from 38.542 mgL–1 for 30 min to 5.6597 mgL–1 for 20.3 h, respectively, by applying 1% bentonite. An increase in the contact time efficiently allowed soil adsorbent to adsorb maximum Cr from soil samples. In the second step, a pot experiment was conducted with 10 different treatments to improve the physiological and biochemical parameters of the Solanum melongena L. irrigated under tanneries’ wastewater stress. There were four replicates, and the crop was harvested after 30 days of germination. It was seen that the application of wastewater significantly (P < 0.01) reduced growth of Solanum melongena L. by reducing root (77%) and shoot (63%) fresh weight when compared with CFOP (Ce-doped Fe2O3 nanoparticles); chlorophyll a and b (fourfolds) were improved under CFOP application relative to control (CN). However, the deleterious effects of Cr (86%) and Pb (90%) were significantly decreased in shoot through CFOP application relative to CN. Moreover, oxidative damage induced by the tannery’s wastewater stress (P < 0.01) was tolerated by applying different soil amendments. However, results were well pronounced with the application of CFOP which competitively decreased the concentrations of MDA (95%), H2O2 (89%), and CMP (85%) by efficiently triggering the activities of antioxidant defense mechanisms such as APX (threefold), CAT (twofold), and phenolics (75%) in stem relative to CN. Consequently, all the applied amendments (BN, BT, FOP, and CFOP) have shown the ability to efficiently tolerate the tannery’s wastewater stress; results were more pronounced with the addition of CFOP and FOP+BT by improving physiological and biochemical parameters of Solanum melongena L. in an eco-friendly way.

Assessment and optimization of As(V) adsorption on hydrogel composite integrating chitosan-polyvinyl alcohol and Fe3O4 nanoparticles and evaluation of their regeneration and reusable capabilities in aqueous media

A modified chitosan-polyvinyl alcohol (PVA) hydrogel was developed by incorporating Fe3O4 nanoparticles. Four chitosan-Fe3O4 (ChFe) hydrogel types were developed based on chitosan:Fe3O4 ratio as 1:0, 1:1, 1:0.5 and 1:0.25. Batch sorption experiments were conducted with different pH, dosage, kinetics, and isotherms. The exhausted ChFe hydrogels were evaluated for their regeneration and reuse capability with different acids and bases. The best hydrogel for arsenic (V) [As(V)] adsorption was 1:0.5 ratio ChFe hydrogel. The highest As(V) adsorption (89 %) was at pH 4 and the adsorption capacity gradually decreased with increasing solution pH. Within the pH 4–6 range, the hydrogel surface became positively charged due to protonation of NH2 and OH groups in the polymer chain and the positive surface attracted H2AsO4− and HAsO42− oxyanions. The experimental kinetic data was well-fitted to the Elovich model (R2 of 0.99) while the Freundlich isotherm model best described the isotherm data (R2 of 0.97). The models predicted chemisorption mechanisms on ChFe hydrogel composites. Electrostatic attractions with NH3+ and OH2+, ligand-exchange inner-sphere complexes formation and bidentate corner-sharing (2C) and bidentate edge-sharing (2E) trimetric surface complexes formation have been proposed as the adsorption mechanism of As(V) into ChFe hydrogel. 0.1 M CH3COOH showed the best regeneration pattern with 75, 96, 81, 53 and 43 % of 1st, 2nd, 3rd, 4th and 5th adsorption respectively. Because of this re-usable capability, the As(V) adsorption capacity is not a single value from one adsorption cycle, but a cumulative value of several adsorption cycles and it was 17.39 mg/g for five adsorption cycles. Open for regeneration and reuse, no post-treatment is needed for adsorbent-water separation, allow applications of the ChFe hydrogel composite in a wide range of applications such as water filtration and purification systems. The modification with ChFe further expands the application capacity since the ChFe can remove other contaminants as well.

Integration of silicate minerals for ammonium and phosphate removal with an on-site wastewater treatment prototype

Inadequately treated wastewater exiting from on-site water treatment systems (OWTS) contains high levels of ammonium and phosphate, which contribute to environmental nutrient pollution. Nutrient removal in small-scale OWTS can be challenging because the most effective known methods are designed for large-scale systems and rely on biological processes. This work focuses on the implementation of two natural silicate-based minerals, clinoptilolite and Polonite, as non-biological sorptive media for nutrient removal in an OWTS. Lab-scale batch sorption experiments showed that Polonite performance is maximized after suspended solids have been removed from blackwater via ultrafiltration. In contrast, clinoptilolite shows robust performance even with untreated blackwater. With both minerals installed in our full-scale OWTS prototype, nutrient removal performance increased from 47.5 ± 15.0% to 84.1 ± 6.3% removal for total N and from 32.3 ± 2.3% to 78.9 ± 5.9% removal for total P. Nevertheless, the target removal performance (&gt;80%) for total P was only achieved with high Polonite loading, which increased effluent pH outside the target range of 6 &lt; pH &lt; 9. Additionally, no loss in nutrient removal performance was observed when the OWTS was restarted after a 150-day idle period. To investigate the potential for media reuse and nutrient recovery, various media regeneration solutions were evaluated. For clinoptilolite, 1 M HCl, NaCl, and KCl all showed good regeneration ability at 2 h contact time, with KCl showing the highest (&gt;86%) ammonium recovery. For the first time, we demonstrated that a minor fraction (30–40%) of binding sites in Polonite can be regenerated using 1 M NaOH or KOH. We also found that the same 1 M HCl regeneration solution could be reused for four clinoptilolite regeneration cycles with no loss in performance. From these results, we discuss opportunities and limitations for implementing these materials in small-scale OWTS.

SOIL-SOIL SOLUTION DISTRIBUTION COEFFICIENT OF RADIOIODINE IN SURFACE SOILS AROUND SPENT NUCLEAR FUEL REPROCESSING PLANT IN ROKKASHO, JAPAN.

The soil-soil solution distribution coefficient (Kd) of radioiodine in soil samples with various total carbon (TC) contents was measured in a batch sorption experiment using 125I tracer spiked as I-. The log values of Kd-125I and TC concentration in low-TC soils (< 10g kg-1) were positively correlated, whereas those of Kd-125I in TC rich soils (> 10 g kg-1) and dissolved organic carbon (DOC) in liquid phase were negatively correlated. The proportion of 125I in the < 3 kDa fraction in the liquid phase is negatively correlated with the log of DOC, implying that 125I is primarily combined with high-molecular-weight organic matter in soil solutions rich in DOC. The results suggest that Kd-125I in soil with high soil organic material (SOM) content is governed by DOC via the combination of 125I and DOC. In contrast, Kd-125I in soils with a low SOM content was governed by SOM because the anion exchange capacity of SOM was vital for the sorption of 125I-.

Sorption Mechanism and Site Energy Distribution of Acetaminophen on Straw-derived Biochar

As one of the large dosages of pharmaceutical and personal care products (PPCPs), acetaminophen is widely present in the water environment and presents potential environmental risks. Therefore, it is necessary to study the removal mechanism of acetaminophen from the environment. Based on the high-value conversion demand of agricultural straw resources in China, straw-derived biochar prepared by pyrolysis has a good application prospect for the sorption and purification of acetaminophen in water. However, the sorption process and mechanism of straw-derived biochar for acetaminophen remain unclear. Four types of straw (rice, wheat, maize, and bean straw) were chosen as raw materials, and straw-derived biochars were prepared through the pyrolysis method at 400℃ and 500℃. The batch sorption experiments were used to study the sorption of acetaminophen to different sources and different pyrolysis temperature biochars. The effect of humic acid and pH on the sorption process was also studied. The results showed that:based on the Freundlich and site energy distribution models, the sorption of acetaminophen on biochar at 500℃ biochar was significantly higher than that at 400℃ biochar (the sorption coefficient KF was 1.16-2.53 times higher), and 500℃ biochar had more high-energy sorption sites. For high-temperature pyrolysis biochar, the primary sorption mechanism was pore sorption and π-π effect; for low-temperature pyrolysis biochar, the primary sorption mechanism for removing acetaminophen was H-bonding. The presence of humic acid enhanced the sorption of acetaminophen, which was attributed to the strong interaction between the humic acid selected in the experiment and acetaminophen, thus promoting adsorption. The decrease in sorption capacity of biochar caused by the increasing pH was mainly attributed to the pore blockage resulting from the aggregation of acetaminophen molecules. The pore sorption and π-π interaction of acetaminophen on straw-derived biochar could be promoted by increasing pyrolysis temperature. These experiments on humic acid and pH show that straw-derived biochar is not affected by humic acid and has good sorption performance in a low pH environment.

Sorption mechanism of cadmium on soils: A combination of batch experiment, path analysis, and EXAFS techniques

• The sorption mechanism of Cd(II) in 49 soils was fully explored. • Cd(II) sorption capacities were closely related to soil physicochemical properties. • Cd in soils was mainly bound to metal (hydro)oxides or existed as CdCO 3 . Soil cadmium (Cd) contamination has emerged as an alarming environmental issue worldwide. Chemical reactivity and bioavailability of Cd in soils are highly dependent on soil properties. However, the sorption mechanism of Cd(II) on soils is not yet fully explored. For this purpose, batch sorption experiments, statistical analysis, and extended X-ray absorption fine structure (EXAFS) spectroscopy were integrated to elucidate the Cd(II) sorption mechanism by investigating the Cd(II) sorption behaviors in 49 soils with contrasting physicochemical characteristics and to figure out the influence of soil properties on Cd(II) sorption in soils. The outcomes of this study revealed that the soils from different areas had large differences in their abilities to adsorb Cd(II), while the differences were closely related to the physicochemical properties of soils. Cd(II) sorption capacities were controlled together by pH, metal (hydro)oxides, organic matter, and cation exchange capacity. The soil pH was the most critical factor in connecting Q max with soil properties. EXAFS results indicated that Cd(II) adsorbed on soils was mainly bound with metal (hydro)oxides or existed as CdCO 3 precipitate. The findings of this study provide a theoretical basis for predicting the risk of soil Cd contamination.

Combining batch experiments and spectroscopy for realistic surface complexation modelling of the sorption of americium, curium, and europium onto muscovite

For a safe enclosure of contaminants, for instance in deep geological repositories of radioactive waste, any processes retarding metal migration are of paramount importance. This study focusses on the sorption of trivalent actinides (Am, Cm) and lanthanides (Eu) to the surface of muscovite, a mica and main component of most crystalline rocks (granites, granodiorites). Batch sorption experiments quantified the retention regarding parameters like pH (varied between 3 and 9), metal concentration (from 0.5 µM Cm to 10 µM Eu), or solid-to-liquid ratio (0.13 and 5.25 g·L−1). In addition, time-resolved laser fluorescence spectroscopy (TRLFS) using the actinide Cm(III) identified two distinct inner-sphere surface species. Combining both approaches allowed the development of a robust surface complexation model and the determination of stability constants of the spectroscopically identified species of (S-OH)2M3+ (logKo −8.89), (S-O)2M+ (logKo −4.11), and (S-O)2MOH (logKo −10.6), with all values extrapolated to infinite dilution. The inclusion of these stability constants into thermodynamic databases will improve the prognostic accuracy of lanthanide and actinide transport through groundwater channels in soils and crystalline rock systems.

High efficient removal of molybdenum(VI) from aqueous solution by starch-acrylamide/nanohalloysite composite

In this paper, poly(starch-acrylamide/nanohalloysite) [P(St-AAm/NH)] was prepared by grafting acrylamide onto starch using gamma rays as an initiator. Physical characteristics of the newly synthesized nanocomposite were studied using FT-IR, TGA, DTA and SEM. P(St-AAm/NH) was evaluated for adsorption of Mo(VI) radionuclide from aqueous solution using batch sorption experiments. Factors affecting adsorption of Mo(VI) radionuclide, such as pH, contact time, and metal ion concentration were extensively investigated. P(St-AAm/NH) composite shows high sorption capacity of 524 mg g−1 towards Mo(VI) radionuclide. Finally, Mo(VI) radionuclide sorption was best represented by the pseudo-second-order kinetic model. As well, it was best fitted to Langmuir model, which suggests the chemisorption mechanism.