Aqueous Cd Research Articles

Insights into the mechanisms of aqueous Cd(II) reduction and adsorption by nanoscale zerovalent iron under different atmosphere conditions

Nanoscale zero-valent iron (NZVI) can effectively remove and recover Cd(II) from aqueous solutions. However, the oxygen effects on Cd(II) removal by NZVI have been overlooked and not well studied. In this research, the Cd MNN auger lines obtained by X-ray photoelectron spectroscopy (XPS) revealed that Cd(II) adsorbed on the NZVI surface could be reduced to Cd(0) by the Fe(0) core under anaerobic conditions. With coexisting oxygen, the Cd(II) removal efficiency declined significantly, and Cd(II) reduction was inhibited by the thickened surface γ-FeOOH layer. Furthermore, the post-oxygen intrusion corroded the generated Cd(0) and led to the dramatic leaching of Cd(II) ions. According to the density functional theory (DFT) simulation, the adsorbed Cd(II) was preferably coordinated via a monodentate model on the surface of Fe3O4 and γ-FeOOH, which are the dominant surface species of NZVI under anaerobic and aerobic conditions, respectively. Thus, γ-FeOOH with doubly coordinated hydroxyl groups provided fewer adsorption sites than Fe3O4 for Cd(II) ions. Overall, the atmospheric conditions of subsurface remediation and wastewater treatment should be considered when applying NZVI for Cd(II) removal. Favorable atmospheric conditions would improve the efficiency and cost-effectiveness of NZVI-based technologies for the practical remediation of Cd(II) pollution.

Tailored design of well-defined hierarchical nitrogen-doped carbon via salt-confined strategy for selective Cd(Ⅱ) adsorption

Efficient cadmium (Cd) removal is vital to ensure freshwater safety, yet it still lacks high-efficiency treatment technologies, especially for the technique with simple-operation and eco-friendliness. Herein, three different carbon-based nanomaterials of hierarchical nitrogen-doped carbon (h-NC-750, h-NC-800 and h-NC-850) were successfully synthesized, via carbonizing the sealed ZIF-8 particles in NaCl crystals at various carbonization temperatures of 750, 800 and 850 °C in Ar atmosphere. Amongst them, the acquired dual-carbon of h-NC-800 harvesting a total nitrogen content of 15.5% rendered the maximum Cd(Ⅱ) adsorption capacity of 356.4 mg g−1, which was 12.5 and 48.3% higher than that of h-NC-750 and h-NC-850 counterparts. The density functional theory (DFT) simulations in combination with characterizations unveiled that the exceptional Cd(Ⅱ) removal of h-NC-800 was derived from the harmonized edge- to graphitic-nitrogen ratio that strengthened the binding energies between Cd(Ⅱ) and h-NC. Impressively, thus-optimized adsorbents afforded the favorable and stabilized removal efficiency (>92%) toward Cd(Ⅱ) in realistic water and five-consecutive regeneration cyclicality. This work is anticipated to offer an innovative insight into the molecular-level architecture design of h-NC with well-defined nitrogen doping and controllable edge- to graphitic-nitrogen ratio, targeting high performance in aqueous Cd(Ⅱ) removal.

Effect of varying pH and co-existing microcystin-LR on time- and concentration-dependent cadmium sorption by goethite-modified biochar derived from distillers’ grains

Cadmium (Cd) is one dangerous and widespread heavy metal that of great environmental concern. To cost-efficiently adsorb aqueous Cd under influence of various factors, this study succeeded in fabricating goethite-modified biochar (GBC) derived from distillers’ grains (DGs) for Cd sorption of different concentrations (10–100 mg L−1) at pH of 3, 6 and 8 with and without microcystin-LR (MC-LR). Sorption kinetics and isotherms data revealed that Cd sorption capacity of GBC and unmodified BC increased as pH elevated from 3 to 6 but stabilized when pH further elevated to 8. Pseudo-second-order and Langmuir models more accurately fitted to sorption data for both BCs, implying monolayer chemisorption of Cd onto BCs. GBC exhibited more robust sorption for each Cd concentration than unmodified BC, with the maximum sorption capacity of around 28 mg g−1 at neutral and weak alkaline pH. Notably, goethite-modification obviously increased bulk polarity, specific surface area, porosity and surface oxygenic group abundance of BC, thus strongly enhancing Cd sorption by creating more sorption sites mainly via pore-filling, electrostatic attraction, and also via complexation and cation exchange. Co-existing MC-LR of 100 μg L−1 did not obviously affect Cd sorption by both BCs for most Cd levels at each pH, mostly because sorption mechanisms diverged between MC-LR and Cd to largely avoid their competition for sorption sties. Thus, goethite could modify DG-BC as promising and cost-efficient sorbent for Cd even with co-existing MC-LR, especially at neutral and weak alkaline pH that common in the nature. This study was greatly implicated in modifying and applying DG-BC for Cd immobilization in MC-LR laden waters with various pH circumstances.

Highly efficient Cd(Ⅱ) removal using 3D N-doped carbon derived from MOFs: Performance and mechanisms

Cadmium (Cd) removal is imperative to ensure the safety of aquatic-ecosystem, yet its effective removal technology has remained elusive by far. To address this concern, three-dimensional N-doped carbon (NC) polyhedrons affording ample porosity is fabricated based upon the thermal carbonization and KOH activation of zeolitic imidazolate framework-8 (ZIF-8) precursor. Thus-derived activated NC (a-NC) adsorbent not only overcomes the inherent instability of ZIF-8 but also harvests a maximum Cd(Ⅱ) adsorption capacity of 370.2 mg g−1, which evidently surpasses those of bare NC counterpart as well as previously reported adsorbents. Impressively, a-NC achieves ca. 100% removal of aqueous Cd(Ⅱ) in a broad working pH range (5−9), and particularly attains stable performances (81−92%) in various realistic water. Theoretical calculations in combination with experimental characterizations further offer mechanistic insight into the enhanced removal exerted by a-NC. Notably, owing to the increased specific surface area (3041 vs. 389 m2 g−1) and enhanced sp2 carbon content (91.7 vs. 68.8%) of a-NC as compared to NC, advanced Cd(Ⅱ) adsorption via a-NC can be exhibited. Our designed a-NC material harnessing favorable recycling capability would be in particular attractive in the realm of practical Cd(Ⅱ) remediation.

Up-flow anaerobic column reactor for sulfate-rich cadmium-bearing wastewater purification: system performance, removal mechanism and microbial community structure.

This study constructed an up-flow anaerobic column reactor fed with synthetic sulfate-rich cadmium (Cd(II))-bearing wastewater, for investigating its Cd(II) removal performance and mechanism. Long-term experiment results manifest that introducing Cd(II) into influent led to an enhanced sulfate removal but did not increase the effluent sulfide concentration, implying the CdS formation. When influent Cd(II) concentration was shifted from 50 to 100mg/L, the median Cd(II) removal rate was increased from 13.6 to 32.2mg/(L·d). Batch tests indicate that the uptake and sequestration function of anaerobes merely led to a small portion of Cd(II) removal. A majority of aqueous Cd(II) (86.3%) was eliminated by precipitation reactions. The generated precipitates were found to be dominantly presented in carbonate, Fe-Mn oxide, sulfide bound and residue forms, which account for 92.6-93.9% of total Cd content of sludge obtained at diverse operation phases. The crystallographic CdS (i.e., residue fraction) particles have nano-scale sizes, and the relatively high atomic ratio of S to Cd was likely due to the adsorption/deposition of other sulfides. The dominant sulfate-reducing bacteria (SRB) were recognized as Desulfurella, Desulforhabdus and Desulfovibrio, and the primary competitor with them for substrate utilization were identified to be methanogens.

Accessibility of ENaC extracellular domain central core residues

The epithelial Na+ channel (ENaC)/degenerin family has a similar extracellular architecture, where specific regulatory factors interact and alter channel gating behavior. The extracellular palm domain serves as a key link to the channel pore. In this study, we used cysteine-scanning mutagenesis to assess the functional effects of Cys-modifying reagents on palm domain β10 strand residues in mouse ENaC. Of the 13 ENaC α subunit mutants with Cys substitutions examined, only mutants at sites in the proximal region of β10 exhibited changes in channel activity in response to methanethiosulfonate reagents. Additionally, Cys substitutions at three proximal sites of β and γ subunit β10 strands also rendered mutant channels methanethiosulfonate-responsive. Moreover, multiple Cys mutants were activated by low concentrations of thiophilic Cd2+. Using the Na+ self-inhibition response to assess ENaC gating behavior, we identified four α, two β, and two γ subunit β10 strand mutations that changed the Na+ self-inhibition response. Our results suggest that the proximal regions of β10 strands in all three subunits are accessible to small aqueous compounds and Cd2+ and have a role in modulating ENaC gating. These results are consistent with a structural model of mouse ENaC that predicts the presence of aqueous tunnels adjacent to the proximal part of β10 and with previously resolved structures of a related family member where palm domain structural transitions were observed with channels in an open or closed state.

Evaluation of aqueous Cd2+ and Pb2+ removal by natural loess using spectral induced polarization and microscopic characterization.

Mining and landfill activities can cause serious soil and groundwater contamination with lead (Pb) and cadmium (Cd). Loess soils are common and have been reported as effective for the removal of heavy metals. The spectral induced polarization (SIP) technique has been approved for its nondestructive ability to characterize the contaminant transport process and surface geochemical properties in porous media. In the present study, SIP was applied to monitor Pb2+ and Cd2+ removal processes using loess through column flow-through experiments. The outflow aqueous geochemical analyses indicated a better retention capability of loess for Pb2+, which was through precipitation induced by calcite dissolution and aqueous pH increment, as confirmed by SEM-EDS and XRD results. Cd retention took place mainly through ion exchange with Ca2+ and Mg2+ on the loess surface. The SIP signals showed a continuous decrement on the magnitude of imaginary conductivity during both Pb2+ and Cd2+ flow-through, which was attributed to the total surface area and decrement of polarizable surface charges. The SIP signals differentiated the interactions between loess and Pb2+/Cd2+ by displaying a peak shift to a higher frequency on the imaginary conductivity spectra during Pb2+ flow-through, which was attributed to calcite dissolution and proved by the high correlation (R2 = 0.9366) between the estimated dissolved calcite mass and the peak of imaginary conductivity. The above results suggest that loess has a great potential for field heavy metal remediation applications, and the SIP technique displays a promising capability of monitoring the remediation performance.

An efficient PET-based probe for detection and discrimination of Zn2+ and Cd2+ in near-aqueous media and live-cell imaging

A newly designed and synthesized quinoline-based chemosensor (DDTQ) is reported for the detection of Zn2+ and Cd2+. The ligand is characterized by all possible spectroscopic techniques. From a pool of different metal ions in aqueous medium, Zn2+ and Cd2+ ions are simultaneously detected by the probe, giving an excellent enhancement in the fluorescence intensity at 445 nm. The fluorescence intensity of DDTQ-Cd is higher than that of DDTQ-Zn. Cd2+ and Zn2+ can be distinguished by using Cu2+ as a tool for sequential quenching where, DDTQ-Zn is responsive towards Cu2+ while DDTQ-Cd is not. It is noteworthy that the novel probe has shown a nanomolar level detection limit of 154 and 126 nM for Zn2+ and Cd2+ respectively. The binding modes of the complexes are also verified by HRMS, Job’s analysis, and by single crystal-XRD analysis. Fluorescence lifetime measurements of the complexes show lifetime values of 28 ns and 26 ns for DDTQ-Zn and DDTQ-Cd complexes respectively. Photoinduced electron transfer (PET) and chelation enhanced fluorescence (CHEF) mechanisms are proposed to be responsible for the enhancement of the fluorescence intensity. The fluorescence intensity of DDTQ in presence of Zn2+ or Cd2+ is stable in the physiological pH range and this prompted us to explore the bioimaging applications in live Vero cells to demonstrate its potential for real-life applications.

Isolation of heavy metal-immobilizing and plant growth-promoting bacteria and their potential in reducing Cd and Pb uptake in water spinach

Heavy metal-immobilizing bacteria are normally capable of stabilizing metals and affecting their absorption by plants. However, few studies have elucidated the mechanisms employed by novel heavy metal-immobilizing and plant growth-promoting bacteria to immobilize Cd and Pb and reduce their uptake by vegetables. In this study, polyamine (PA)-producing strains were isolated and their effects on biomass and metal accumulation in water spinach (Ipomoea aquatica Forssk.) and the underlying mechanisms were investigated. Two PA-producing strains, Enterobacter bugandensis XY1 and Serratia marcescens X43, were isolated. Strains XY1 and X43 reduced the aqueous Cd and Pb levels (49%–52%) under 10 mg L−1 Cd and 20 mg L−1 Pb because of metal ion chelation by bacterially produced PAs and cell adsorption. Further evidence showed that Cd and Pb were bound and precipitated on the bacterial cell surface in the form of Cd(OH)2, CdCO3 and PbO. Compared with strain-free water spinach, greens inoculated with strains XY1 and X43 showed 51%–80% lower Cd and Pb contents. The rhizosphere soil pH and PA contents were significantly higher, and lower contents of the rhizosphere soil acid-soluble fractions of Cd (18%–39%) and Pb (31%–37%) were observed compared to the noninoculated control. Moreover, inoculation with XY1 reduced the diversity of the bacterial community, but the relative abundances of plant growth-promoting and PA-producing bacteria in rhizosphere soil were enriched, which enhanced water spinach resistance to Cd and Pb toxicity. Our findings describe novel heavy metal-immobilizing bacteria that could be used to improve the habitat of vegetables and reduce their uptake of heavy metals.

Mechanistic insight into the removal of aqueous Cd using an immobilized ZIF-8 and microflora cooperative composite

Biotechnology and metal-organic-frameworks (MOFs) materials have been investigated intensively for the removal of heavy metal from wastewater. However, the cooperative effect of bacteria and MOFs on heavy metal adsorption was less reported. Considering this, this study has screened out microflora with cadmium (Cd) adsorption ability. Furthermore, it was combined with zeolitic imidazolate framework-8 (ZIF-8) to form a ZIF-8 and microflora complex (ZMC). Moreover, ZMC was further immobilized to improve its Cd adsorption effect and reusability. Results revealed that the immobilized ZMC exhibited 99.91% and 78.83% Cd adsorption rate for 20 mg L−1 and 300 mg L−1 Cd, respectively. Meanwhile, the immobilized ZMC maintained a relatively stable adsorption effect under varied external pH. The reaction mechanism was summarized as covalent binding accompanied with a small amount of electrostatic attraction. Microflora could enhance the surface electronegativity of ZIF-8. ZIF-8 could strengthen the response of antioxidant activity of microflora and augmented the affinity of microflora secretions for Cd. This proposed method may provide a new insight for the removal of heavy metal contaminants in water.

Efficient Removal of Cd (II) from Aquatic Media by Heteronanostructure MgO@TiO2@g‐C3N4

MgO@TiO2@g‐C3N4 heteronanostructure was synthesized using a simple ultrasonication technique and assessed potentially to remove Cd (II) from aqueous environments. X‐ray diffraction analysis confirms composite formation with mean crystallite size in the range of 4‐17 nm while transmission electron microscopy analysis reveals nanosheet‐like nanoparticles with the homogeneous elemental distribution. N2 adsorption‐desorption measurements indicate the formation of a mesoporous structure with a BET surface area of about 107 m2/g. Fourier‐transformed infrared elucidates the presence of O–H, amino groups, triazine, Mg–O, and Ti–O vibrations modes. At the same time, X‐ray photoelectron spectroscopy analysis manifests the presence of Mg, O, N, Ti, and C elements. For aqueous Cd (II) ions, the MgO@TiO2@g‐C3N4 nanostructure displays a superior adsorption efficiency, reaching 99.94% Cd (II) elimination with an optimum adsorption capacity of 515.86 mg/g in a short duration of 16 min. This study demonstrates the capability of using the MgO@TiO2@g‐C3N4 nanostructure as an efficient and reusable adsorbent for the uptake of Cd (II) ions in wastewater treatment and potentially for the removal of other heavy metal ions.

Preparation and characterization of new magnetic chitosan-glycine-PEGDE (Fe3O4/Ch-G-P) beads for aqueous Cd(II) removal

The growing threat to human health caused by cadmium pollution urges industry to conduct proper and efficient wastewater treatment. For that purpose, chitosan could be employed as an excellent adsorbent for the cadmium removal, however, requiring some modifications. This present work aimed to develop chitosan beads, by means of glycine grafting, PEGDE crosslinking, and magnetic Fe3O4 filler embedment. Characterizations of the prepared Fe3O4/Chitosan-Glycine-PEGDE (Fe3O4/Ch-G-P) beads were carried out using Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), thermogravimetry analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscope (SEM). Batch adsorption of Cd2+ was optimized with parameters of contact time and solution pH. The regeneration of Fe3O4/Ch-G-P was also studied. Batch adsorption of Cd2+ on Fe3O4/Ch-G-P was found optimum after 30 min contact time at initial pH 5 with removal percentage of more than 98%. Isotherm studies suggested the adsorption was Langmuir isotherm model dependent (adjusted-R2 = 0.992) with qm = 171.06 mg/g. Further investigation using three-parameters isotherm model, Sips, revealed a better fitness with adjusted-R2 = 0.999. The experimental data followed pseudo-second-order kinetic model (adjusted-R2 = 0.796, 0.911, and 0.981 for initial Cd2+ concentrations of 20, 25, and 30 mg/L, respectively) indicated the adsorption was determined by chemisorption. In conclusion, the addition of PEGDE improved the ability of magnetic glycine-grafted chitosan in Cd2+ removal from aqueous solution.

Multiplexed detection of aqueous Cd2+, Pb2+ and Cu2+ ions at mercury-on-graphene film modified electrode by DPASV

With the ever-increasing influence of heavy metal ions in environmental pollution, it is highly desirable to develop facile, rapid, and low-cost methods for the multiplexed detection of heavy metal ions in aqueous media sensitively and quantitatively. In this study, we report a facile electrochemical method for the selective, quantitative and multiplexed detection of cadmium (Cd2+), lead (Pb2+), and copper (Cu2+) ions in aqueous media. In this method, a glassy carbon electrode (GCE) is modified first with reduced graphene oxide(rGO) microflaks followed by the controlled in situ electro-deposition of a very thin mercury film. The final working electrode, denoted as (Hg|rGO)film|GCE, was employed as the detector for reported multiplexed detection of multi-ions, taking advantages of the well-established polaragraphic principles. The rGO layer was known to be capable of significantly increasing the heterogeneous interface electron-transfer rate and therefore the detection sensitivity, while the highly dispersed over-potentials of heavy metal ions on mercury allowed the multiplexed detection of several heavy metals ions at different working potentials. The differential pulse anodic stripping voltammetry (DPASV) was employed as the detection mode to further boost up the detection sensitivity. Very good quantitative relationships were observed between the peak current in DPASV and the concentration of the ions being detected. The cross-interference in the multiplexed detection was found negligible. The limit of detections (LODs) of Cd2+, Pb2+, and Cu2+ ions in aqueous phase at the (Hg/rGO)film/GCE working electrode were found to be 0.17, 0.18 and 0.69 μg/L, respectively.

Utilization of dredged river sediments to synthesize zeolite for Cd(II) removal from wastewater

Resource utilization of dredged sediments has been an urgent issue in recent years in China. To solve this problem, an approach of zeolite synthesized by dredged sediment was proposed for the first time in this study. Then the optimum conditions for sediment-based zeolite (SZ) synthesis and its adsorption performance of aqueous Cd (Ⅱ) were investigated. The results showed that the optimal parameters of SZ synthesis were 3–6 mol/L HCl as the extracting agent, a NaOH/RM ratio of 1.4:1–2.1:1, and 80–100 °C and 12–24 h as the crystallization temperature and reaction time. The specific surface area of the SZ (516.36 m2/g) was much larger than that of the initial sediment (9.51 m2/g), while the adsorption equilibrium of Cd (Ⅱ) by SZ could be achieved within 120 min. Moreover, the maximum adsorption capacity was 206.64 mg/g at the optimal condition of pH = 5.0 and a SZ concentration of 1.5 g/L. In addition, ion exchange between Cd(II) and Na+ was demonstrated to be the predominant mechanism for Cd(II) adsorption by SZ. Other functional groups including –OH or –CH on the surface of the SZ could combine with Cd(II) to form complexes to remove Cd(II) as well. Furthermore, the SZ was successfully regenerated in this work. The findings confirmed that SZ could be reused as an effective adsorbent for the treatment of Cd(II)-polluted wastewater, which could provide a new and feasible approach to the resource utilization of dredged sediments.

Mechanism of Cd(II) and Cu(II) Adsorption onto Few-Layered Magnetic Graphene Oxide as an Efficient Adsorbent.

Heavy metal contamination caused by industrial discharge is a challenging environmental issue. Herein, an efficient adsorbent based on few-layered magnetic graphene oxide (FLMGO) was fabricated, characterized, and utilized to remove aqueous Cd(II) and Cu(II). Results present that the two components graphene oxide (GO) and Fe3O4 of FLMGO promote mutually, enabling FLMGO to outperform either GO or Fe3O4. Specifically, FLMGO adsorbs Cd(II) and Cu(II) with adsorption quantities of 401.14 and 1114.22 mg·g–1 in 5 and 7 min, respectively. Moreover, FLMGO can be readily recovered via magnetic separation using a hand-held magnet. Adsorptions are spontaneous, endothermic, and entropy increasing, which are the best described by the Freundlich and pseudo-second-order model. The interaction mechanism is as follows: lone pair electrons in C=O- and C–O-related groups were coordinated toward Cd(II) and Cu(II) to induce chemical interaction. The high adsorption efficiency endows FLMGO with encouraging application potential in heavy metal remediation.

Cadmium bioaccumulation and distribution in the freshwater bivalve Anodonta woodiana exposed to environmentally relevant Cd levels

Anodonta woodiana is a globally distributed freshwater bivalve, which is a unique bioindicator in the “Freshwater Mussel Watch” project. Numerous countries have used A. woodiana for biomonitoring the aqueous cadmium (Cd) contamination. However, the bioaccumulation and distribution characteristics of environmentally relevant Cd concentrations in the bivalve were unknown. In this study, A. woodiana was exposed to aqueous Cd concentrations (1.1, 2.6, and 5.5 μg/L) for 30 days. The concentrations of Cd in the whole soft tissues were linearly and positively correlated with the aqueous Cd concentrations and exposure time (P < 0.05). Analysis of the organic bioaccumulation and distribution showed that Cd concentrations and proportions in the gills and mantle were linearly and positively correlated with aqueous Cd concentrations and with the Cd concentrations in the whole soft tissues (P < 0.05). Analyses of the subcellular fractions showed that Cd concentrations and proportions in the metal-rich granule (MRG) were linearly and positively correlated with aqueous Cd concentrations and with the Cd concentrations in the whole soft tissues (P < 0.05). This suggests that the gills and mantle could be the main target organs for Cd bioaccumulation, and that the MRG could be the major site for Cd bioaccumulation and distribution. These results improve our understanding of the bioaccumulation and distribution mechanisms of Cd in bivalves.

Adsorption of Cd2+ Ions from Aqueous Solution Using Biomasses of Theobroma cacao, Zea mays, Manihot esculenta, Dioscorea rotundata and Elaeis guineensis

In this work, the mechanisms of cadmium (Cd2+) adsorption on residual biomasses from husks of yam (Dioscorea rotundata), cassava (Manihor esculenta), cocoa (Theobroma cacao), corn (Zea mays) and oil palm bagasse (Elaeis guineensis) were studied in order to evaluate the effect of temperature, adsorbent dose and particle size in a batch system. Isotherms and adsorption kinetics were determined and adjusted to different models. The biomaterials were characterized using the techniques of Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS). Results reveal that the possible mechanisms of Cd2+ adsorption in bioadsorbents were ion exchange and complexation with -COOH and -OH groups. From the experimentation, it was found that best conditions were presented at 55 °C, particle size 0.5 mm and 0.03 g adsorbent. The following biomass performance was obtained in terms of adsorption capacities: cocoa husk (CH) &gt; corn cob residues (CCR) &gt; cassava peel (CP) &gt; palm bagasse (OPB) &gt; yam peel (YP), according to the Langmuir and Dubinin- Radushkevich (D-R) models. The equilibrium of Cd2+ adsorption over YP and OPB was well described by Langmuir’s isothermal model, while for CH, CCR and CP the model that best fit experimental data was Freundlich’s model. The results of D-R model suggested that the process is controlled by physisorption mechanism with strong interactions among active sites and Cd2+ ions. The kinetics for all systems studied fit the pseudo-second order model. The values of the thermodynamic parameters established that cadmium removal is of endothermic nature and not spontaneous using YP and CP, and exothermic, spontaneous and irreversible when using OPB, CH and CCR. The results suggest the use of YP, OPB, CH, CP and CCR residues for the removal of aqueous Cd2+.

Removal of aqueous Cd(II) and Ni(II) by aminopyridine functionalized magnetic Fe3O4 nanocomposites

Aminopyridine functionalized Fe3O4 nanocomposites (HE-Fe3O4@SiO2-AP and HO-Fe3O4@SiO2-AP) were prepared by the general method and simple one-pot method. They were employed as adsorbents for removing aqueous Cd(II) and Ni(II). The factors that influence the adsorption behavior was tested and the optimum condition was determined. The best adsorption was achieved under pH 6 for the two ions. The uptake of Cd(II) and Ni(II) can achieve saturation at 270 and 260 min. Kinetic process is controlled by film diffusion and follows pseudo-second-order (PSO) model. The adsorption prefers high concentration and temperature. It is a chemical process and can be depicted with Langmuir model. The adsorption mechanism is demonstrated by experimental technique and density functional theory (DFT) simulation. The adsorption is the synergistic effect of the nitrogen atoms of aminopyridine group, the oxygen atom of ether linkage, and hydroxyl oxygen atom. The nitrogen atoms of aminopyridine group play a leading role in the adsorption. The regeneration performance shows the nanocomposites can be regenerated and recycled.

The impact of an Amberlite XAD-16-based chelating resin for the removal of aqueous Cd(II) and Pb(II)ions

The main objective of this study is to investigate the influence of the Amberlite XAD-16-based chelating resin, 1,8-(3,6-dithiaoctyl)-4-polyvinylbenzenesulphonate (dpvbs), for the removal of the highly lethal Pb(II) and Cd(II) from aqueous solutions. The extractor`s behavior is examined, as adsorbent as well as coordinating agent showing structural changes upon the interaction with the targeted metal ions. Elemental analyses, FTIR, electronic spectra, EDS and XPS were used to provide a close image of the composition, structural and morphological changes upon the interaction with Pb(II) and Cd(II). Thermal behavior of the sorption products, compared with the coordinating resin, were also, studied and the estimated thermodynamic parameters indicated an endothermic spontaneous sorption mechanism. The BET surface area, BJH desorption volume and the pore diameters increased upon chelation with Cd(II) and Pb(II), indicating the destruction of the cross-linking of the free resin. SEM and AFM studies confirmed the surface morphological change of dpvbs, after sorption processes. The sorption effectiveness was examined utilizing batch and column methods, showing high removal efficiency with an average sorption of 99.9%. dpvbs was tested for the removal of metal ions from tap watershowing a metal uptake of almost the same after 3 cycles, with an efficiency of 98–99%.

Adsorption and (induced) desorption of Cd(II) from the corrosion scales of water distribution pipes, following a deliberate contamination event

Abstract Intrusion of toxic heavy-metal cations into water-distribution systems (WDS) may cause severe adverse health-effects on large populations, along with an undesirable psychological impact. The corrosion (scale) layer, that invariably develops on the pipes’ inner walls, is capable of adsorbing a significant mass of metal-cations and releasing them thereafter via diffusion to the water once operation is resumed, thereby causing a secondary contamination event. To overcome this, the contaminant should be completely removed, in a controlled fashion, from both the aqueous and scale phases, with minimum damage to the pipe's physical stature. This study determined the range of the Cd(II) adsorption capacity of corrosion-scales and quantified alternative treatments for desorbing it, using an assortment of metal water-pipes, extracted from the WDS. Batch, water-recirculation and flow-through experiments were conducted to determine the extent of Cd(II) adsorption and the best way to desorb it. Corrosion-scales showed substantial Cd(II)-absorption capacity (up to 0.75 mg Cd(II)/g scale) with an approximately linear relation between the aqueous Cd(II) concentration and the adsorbed mass. Desorption experiments included dosages of various acids. Sequential rinsing (eight pipe-volumes) by pH3 solution was found to be the best approach, releasing close to ∼100% of the adsorbed Cd(II), with only a minor effect on the pipes’ integrity.