Aqueous Cd Research Articles

Adsorption of aqueous Cd2+, Pb2+, Cu2+ ions by nano-hydroxyapatite: Single- and multi-metal competitive adsorption study

Being an inexpensive but efficient adsorbent, hydroxyapatite is extensively used for decontaminating wastewater and soils polluted by heavy metals. However, its solubility and grain size can affect its remediation effectiveness. This study investigated the ability of nano-hydroxyapatite (nano-HAP) to adsorb aqueous Cd, Pb and Cu ions from single-metal and multi-metal ions reaction systems. Langmuir and Freundlich isotherm equations were employed to study the sorption constants. Based on the sum of squares errors (SSE), results showed that the Langmuir isotherm better fits sorption data than the Freundlich equation. The sorption affinity of nano-HAP for Pb(II) is always higher than that for Cu(II) and for Cd(II); the sorption maxima for the Cd, Pb and Cu follow the order Pb2+ > Cu2+ > Cd2+. This could be inversely proportional to the hydrated ionic radii as Pb2+ (4.01 angstrom) > Cu2+ (4.19 angstrom) > Cd2+ (4.26 angstrom). The measured selectivity coefficients in multi-metal (Cd-Pb-Cu) reaction systems shows that Pb has the highest sorption selectivity on nano-HAP among the metals investigated. This sorption selectivity coincided well with the sorption affinity order in mono-metal reaction systems. The pH of the solution is an important parameter in controlling Cd, Pb and Cu ions sorption on nano-HAP. Indeed, the nano-HAP sorption capacity increases with increasing pH up to a value of 6.25. This implies that the removal of metals from the solution is recommended for pH 6.25 or below, during remediation using nano-HAP as a sorbent.

CdCu3(OH)6(NO3)2: An S = 1/2 Kagomé Antiferromagnet

The cadmium copper hydroxide nitrate, CdCu(3)(OH)(6)(NO(3))(2).0.5H(2)O, is furnished from oxygenated suspensions of Cu(2)O in aqueous Cd(NO(3))(2). The compound possesses the kagome structural motif and shows no evidence of magnetic ordering to temperatures as low as 5 K, despite exhibiting a Curie-Weiss temperature of Theta = -114 +/- 27 K, thus giving a spin frustration parameter, f = 22.8.

Preparation of a hydroxyapatite film and its application in the removal and regeneration of aqueous cations

Aqueous Pb 2+, Cd 2+, Co 2+, and Cu 2+ were continuously removed and regenerated using a bulk powder of calcium hydroxyapatite (Ca 10(PO 4) 6(OH) 2, CaHAp) and a glass plate coated with a thin film of CaHAp. Although use of CaHAp effectively removed aqueous Pb 2+ from the wastewater, lead cations immobilized on CaHAp could not be regenerated in an aqueous solution due to the formation of lead hydroxyapatite (Pb 10(PO 4) 6(OH) 2), which is insoluble in water at acidic and neutral pH. In contrast, Co 2+ and Cu 2+ immobilized on CaHAp were easily regenerated in an aqueous solution by treatment with an acidic aqueous solution containing Ca(NO 3) 2, as previously reported for the CaHAp-Cd 2+ system. We found that the combination of the removal of the aqueous divalent cations by the CaHAp film and subsequent regeneration of the immobilized divalent cations from the film allowed for recycling of the film and for removal and regeneration of aqueous Cd 2+, Co 2+, and Cu 2+.

Temperature dependence of Cd and Pb binding onto bacterial cells

We measured aqueous Cd and Pb adsorption onto bacterial surfaces at 5 °C, 50 °C, and 80 °C. We performed the adsorption experiments using one Gram-positive species, Bacillus subtilis, and one Gram-negative species, Pseudomonas mendocina. We use a surface complexation approach to determine the thermodynamic stability constants for the important metal–bacterial surface complexes for each temperature and each bacterial species. Our results indicate that temperature affects metal adsorption onto the surfaces of Gram-positive and Gram-negative species differently. B. subtilis exhibits little difference in its metal-binding capacity over the temperature range of this study. At elevated temperatures, Pb(OH) + is the dominant form of Pb that binds to the surface while Pb 2+ adsorption predominates at lower temperatures. However, the overall extent of Pb adsorption does not vary significantly with temperature. Conversely, the extent of both Cd and Pb adsorption onto P. mendocina is higher at 5 °C relative to the 50 °C and 80 °C data, but only under low pH conditions. The temperature dependence of metal adsorption onto bacteria depends upon both the metal and the bacterial species involved in the reaction. For both bacterial species studied here under circumneutral conditions, there is no significant temperature dependence to the extent of Cd adsorption or to the speciation of the important Cd–bacterial surface complexes. Therefore, a single set of averaged stability constant values can be used to account for Cd adsorption onto the cells as a function of temperature. Conversely, Pb more readily hydrolyzes in solution with increasing temperature than does Cd. Therefore, although the extent of total Pb adsorption does not change with temperature above pH 5, the speciation of the important Pb–bacterial surface complexes does vary with temperature. For metals such as Pb, the effect of temperature on the identity and stability constants of the bacterial surface complexes must be determined in order to accurately model metal speciation and transport as a function of temperature in bacteria-bearing geologic systems.

Cd adsorption onto Pseudomonas putida in the presence and absence of extracellular polymeric substances

The role of bacterial extracellular polymeric substances (EPS) in metal adsorption was determined by studying Cd adsorption onto the gram-negative bacterial species Pseudomonas putida with and without enzymatic removal of EPS from the biomass material. A range of experimental approaches were used to characterize the Cd adsorption reactions, including bulk proton and Cd adsorption measurements, FTIR spectroscopy, and fluorescence microscopy. The proton-reactivities of the biomass samples with EPS are not significantly different from those obtained for EPS-free biomass. Similarly, the presence of EPS does not significantly affect the extent of Cd removal from solution by the biomass on a mass-normalized basis, based on bulk Cd adsorption measurements conducted as a function of pH, nor does it appear to strongly affect the Cd-binding groups as observed by FTIR. However, fluorescence microscopy indicates that Cd, although concentrated on cell walls, is also bound to some extent to EPS. Together, the results from this study suggest that the P. putida EPS can bind significant concentrations of Cd from solution, and that the nature and mass-normalized extent of the binding is similar to that of the cell wall. Therefore, the EPS-bearing systems do not exhibit enhanced mass-normalized removal of Cd from solution relative to the EPS-free systems. The presence of the EPS effectively increases the viability of cells exposed to aqueous Cd, likely due to sequestration of the Cd away from the cells due to Cd-EPS binding.

Preparation of CdS Nanocrystals within Supramolecular Self-Assembled Nanoreactors and Their Phase Transfer Behavior

A new strategy for the synthesis of CdS nanocrystals (NCs) within supramolecular self-assembly nanoreactors has been described. The self-assembly nanoreactors were readily constructed through the electrostatic interactions and ion pairs between palmitic acid and the terminal amine groups of hyperbranched polymer. In a chloroform/water two-phase system, aqueous Cd (2+) ions were spontaneously encapsulated into the cavities of self-assembly nanoreactors in chloroform. After reaction with S (2-) ions, the CdS NCs with high stability were obtained. By the addition of excess triethylamine, CdS NCs formed in the self-assembly nanoreactors were transferred from organic phase into aqueous phase. After dialysis and rotorary evaporation, aqueous CdS NCs could be redispersed into chloroform solution containing palmitic acid.

Influence of synthetic surfactants on the uptake of Pd, Cd and Pb by the marine macroalga, Ulva lactuca

Uptake of Pd, Cd and Pb by the marine macroalga, Ulva lactuca, has been studied in the presence of an anionic (sodium dodecyl sulphate, SDS), cationic (hexadecyltrimethylammonium bromide; HDTMA) and non-ionic (Triton X-100; TX) surfactant. Compared with the surfactant-free system, metal sorption was reduced in the presence of SDS or TX. Neither surfactant, however, had any measurable impact on cell membrane permeability, determined by leakage of dissolved free amino acids (DFAA), or on metal internalisation. We attribute these observations to the stabilisation of aqueous Cd and Pb by SDS and the shielding of otherwise amenable sorption sites by TX. Presence of HDTMA resulted in a reduction in the extent of both sorption and internalisation of all metals and a significant increase in the leakage of DFAA. Thus, by enhancing membrane permeability, HDTMA exerts the greatest influence on metal behaviour in the presence of U. lactuca.

Phytoextraction of cadmium by Ipomoea aquatica (water spinach) in hydroponic solution: Effects of cadmium speciation

Phytoextraction is a promising technique to remediate heavy metals from contaminated wastewater. However, the interactions of multi-contaminants are not fully clear. This study employed cadmium, Triton X-100 (TX-100), and EDTA to investigate their interactions on phytotoxicity and Cd phytoextraction of Ipomoea aquatica (water spinach) in simulated wastewater. The Cd speciation was estimated by a chemical equilibrium model and MINEQL+. Statistic regression was applied to evaluate Cd speciation on Cd uptake in shoots and stems of I. aquatica. Results indicated that the root length was a more sensitive parameter than root weight and shoot weight. Root elongation was affected by Cd in the Cd-EDTA solution and TX-100 in the Cd-TX-100 solution. Both the root length and the root biomass were negatively correlated with the total soluble Cd ions. In contrast, Cd phytoextraction of I. aquatic was correlated with the aqueous Cd ions in the free and complex forms rather than in the chelating form. Additionally, the high Cd bioconcentration factors of I. aquatica (375–2227 l kg −1 for roots, 45–144 l kg −1 for shoots) imply that I. aquatica is a potential aquatic plant to remediate Cd-contaminated wastewater.

Modelling coupled water flow, solute transport and geochemical reactions affecting heavy metal migration in a podzol soil

Many or most subsurface pollution problems at the field scale involve such simultaneous processes as water flow, multicomponent solute transport, heat transport and biogeochemical processes and reactions. Process-based models that integrate these various processes can be valuable tools for investigating the mobility of a wide range of inorganic and organic contaminants subject to different hydrologic and geochemical conditions. The HP1 reactive transport simulator, obtained by weak coupling of HYDRUS-1D and PHREEQC-2, was developed and designed to address multicomponent geochemical transport processes in the vadose zone. In this paper we discuss a hypothetical HP1 application involving the transport of major cations and heavy metals in a soil during transient flow over a period of 30 years. Results show that variations in water content and water fluxes can significantly influence the speciation, and thus the mobility and availability, of elements. Decreasing water contents near the soil surface lowered pH of the soil solution and produced new cation exchange equilibrium conditions. The upward transport of Cl during summer due to increased evapotranspiration, and subsequent accumulation of Cl near the soil surface, caused an increase in the total aqueous Cd concentration because of the formation of Cd–Cl complexes. Coupled reactive transport codes for the unsaturated zone, such as HP1, are promising tools to unravel the complex interaction between soil physical and biogeochemical processes for all kinds of problems, including the impact of natural processes and antropogenic activities on soil evolution.

An ion-imprinted silica-supported organic–inorganic hybrid sorbent prepared by a surface imprinting technique combined with a polysaccharide incorporated sol–gel process for selective separation of cadmium(II) from aqueous solution

Ion-imprinting concept and polysaccharide incorporated sol–gel process were applied to the preparation of a new silica-supported organic–inorganic hybrid sorbent for selective separation of Cd(II) from aqueous solution. In the prepared shell/core composite sorbent, covalently surface coating on the supporting silica gel was achieved by using a Cd(II)-imprinting sol–gel process starting from an inorganic precursor, γ-glycidoxypropyltrimethoxysiloxane (GPTMS), and a functional biopolymer, chitosan (CS). The sorbent was prepared through self-hydrolysis of GPTMS, self-condensation and co-condensation of silanol groups (Si-OH) from siloxane and silica gel surface, in combination with in situ covalent cross-linking of CS with partial amine shielded by Cd(II) complexation. Extraction of the imprinting molecules left a predetermined arrangement of ligands and tailored binding pockets for Cd(II). The prepared sorbent was characterized by using X-ray energy dispersion spectroscopy (EDX), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Batch experiments were conducted to study the sorption performance by removal of Cd(II) when present singly or in binary system, an aqueous Cd(II) and Zn(II) mixture. The ion-imprinted composite sorbent offered a fast kinetics for the sorption of Cd(II) and the maximum capacity was 1.14 mmol g −1. The uptake capacity of the imprinted sorbent and the selectivity coefficient were much higher than that of the non-imprinted sorbent. The imprinted sorbent exhibited high reusability. The prepared functional sorbent was shown to be promising for the preconcentration of cadmium in environmental and biological samples.

Influence of metal exposure history on the bioaccumulation and subcellular distribution of aqueous cadmium in the insect Hydropsyche californica

The influence of metal exposure history on rates of aqueous Cd accumulation, elimination, and subcellular distribution was examined in the aquatic insect Hydropsyche californica. Specimens were obtained from a reference site and a metal-contaminated site and returned to the laboratory where they were continuously exposed to aqueous Cd (518 ng/L, nominal) for 6 d, followed by 9 d of depuration. Rates of Cd accumulation and elimination were similar in insects from the two sites. Efflux rate constants, k((e), ranged from 0.20 to 0.24/d (t 1/2 approximately 3 d). Immediately following exposure, the cytosol accounted for 40% of the body burden in insects from both sites; however, 89 +/- 2% of the cytosolic Cd was associated with metallothionein-like proteins (MTLP) in insects from the contaminated site, compared to 60 +/- 0% in insects from the reference site. The concentration of Cd bound to non-MTLPs (representing potentially Cd-sensitive proteins) was significantly greater in the insects from the reference site (134 +/- 7 ng/g) than in those from the contaminated site (42 +/- 2 ng/g). At the end of the depuration period, 90% of the accumulated Cd body burden had been eliminated, and Cd concentrations in MTLPs and non-MTLPs were similar between the sites. Results suggested that differences in exposure history had no influence on the bioaccumulation of Cd, but did affect the concentrations of Cd bound to MTLP during Cd exposure in these insects.

One-dimensional structure ofcatena-poly[tetraethylammonium [tetracyanoiron(III)-μ-cyano-[bis(ethylenediamine)cadmium(II)]-μ-cyano] tetrahydrate

The title compound, {(C8H20N)[CdFe(CN)6(C2H8N2)2]·4H2O}n, was isolated from the aqueous system Cd2+/ethyl­ene­diamine (en)/[Fe(CN)6]3− in the presence of [Et4N]Br. The crystal structure is dominated by a one-dimensional motif, viz. a negatively charged 2,2-CT (cis–trans) [–Cd(en)2—NC—Fe(CN)4—CN–]nn− chain. The Cd and Fe atoms of the anion and the N atom of the cation all lie on twofold axes. The ethyl groups of the cation are equally disordered over two orientations. The cationic building block of the chain consists of a CdII atom coordinated by two chelating en ligands, and the distorted octa­hedral coordination is completed by two bridging cyano ligands in cis positions. The anionic building block is an [Fe(CN)6]3− anion in which the FeIII atom is octa­hedrally coordinated by six cyano ligands; two of the cyano ligands, in trans positions, are bridging. The uncoordinated water mol­ecules link neighbouring chains through O—H⋯N and N—H⋯O hydrogen bonds.

EXAFS Studies about the Sorption of Cadmium Ions on Montmorillonite

Abstract We investigated local structures around cadmium (Cd) sorbed on montmorillonite at various pH values by EXAFS (extend X-ray absorption fine structure). We found two sorption types, an outer-sphere complex and a surface precipitate. The outer-sphere complex was mainly formed at a lower pH which had an identical structure to aqueous Cd2+, while the surface precipitate was found at high pH which had a one-layer Cd5(OH)8(NO3)2(H2O)2-like structure.

Metamorphosis of two amphibian species after chronic cadmium exposure in outdoor aquatic mesocosms

Amphibian larvae at contaminated sites may experience an alteration of metamorphic traits and survival compared to amphibians in uncontaminated conditions. Effects of chronic cadmium (Cd) exposure on the metamorphosis of American toads (Bufo americanus) and southern leopard frogs (Rana sphenocephala) were determined. The two species were reared separately from shortly after hatching through metamorphosis in outdoor mesocosms (1,325-L polyethylene cattle tanks) that simulated natural ponds and enhanced environmental realism relative to the laboratory. Both species exhibited a decrease in survival with increasing initial nominal aqueous Cd concentration. Cadmium treatment did not influence mass at metamorphosis for either species when survival was included as a covariate, but increased the age at metamorphosis for the American toads. The whole body Cd content of metamorphs increased with aqueous Cd treatment level for both species, and the American toads tended to possess more elevated residues. Cadmium quickly partitioned out of the water column and accumulated in and altered the abundance of the tadpoles' diet. Cadmium-contaminated sites may produce fewer metamorphs, and those that survive will metamorphose later and contain Cd. Interspecific differences in the response variables illustrate the importance of testing multiple species when assessing risk.

Synthesis and Evaluation of an Ion‐Imprinted Functionalized Sorbent for Selective Separation of Cadmium Ion

An ion‐imprinted functionalized sorbent for selective separation of Cd2+ from aqueous solution was prepared by molecular imprinting technique in combination with the sol‐gel process. The procedures involved the synthesis of mesoporous silica through hydrolysis of tetraethoxysilicate with cetyltrimethylammonium bromide as the structure director, the complex formation between Cd2+ and 3‐mercaptopropyltrimethoxysilane, and subsequent co‐hydrolysis and co‐condensation of the complex with the mesoporous silica. After template Cd2+ was removed with hydrochloric acid, specific cavity for selective recognition of Cd2+ was left. The selectivity of the sorbent was investigated by a batch competitive ion‐binding experiment using an aqueous Cd2+ and Pb2+ mixture. The largest selectivity coefficient for Cd2+ in the presence of Pb2+ was found to be over 67, the largest relative selectivity coefficient between Cd2+ and Pb2+ over 18. The uptake capacity and selectivity coefficient of the imprinted functionalized sorbent are higher than those of the nonimprinted sorbent. The sorbent offered a fast kinetics for the extraction/stripping of Cd2+ and good recyclability.

Efficient Immobilization of a Cadmium Chemosensor in a Thin Film: Generation of a Cadmium Sensor Prototype

[reaction: see text] The development of an ion-selective chemosensor for Cd(2+) allows generation of a "real-time" sensor. Immobilization of the chemosensor on quartz was achieved in a simple monolayer and in a thin film using a polymer intermediary. As intended, the thin film contains much more chemosensor than the monolayer and provides measurable responses to aqueous Cd(2+) concentrations below 1 microM. Alkali and alkaline earth ions do not interfere with Cd(2+) sensing; Zn(2+) and Cu(2+) are potential interferents.

Ionic strength effect on the liquid–liquid extraction of zinc(II) and cadmium(II) from sulphate medium by 1-phenyl-3-methyl-4-benzoylpyrazol-5-one in chloroform

The liquid–liquid extraction of zinc(II) and cadmium(II) from sulphate medium by 1-phenyl-3-methyl-4-benzoylpyrazol-5-one (HPMBP) in chloroform is studied. The ionic strength effect of the aqueous phase shows that the extraction of the metal increases with decreasing concentration of sulphate. At initially of about 10−4 M with three different sulphate concentrations 0.033, 0.16 and 0.33 M in the aqueous phase, Zn(II) and Cd(II) are extracted as the complexes Zn(PMBP)2 and Cd(PMBP)2. Sulphate complexes of Zn(II) and Cd(II) are formed in the aqueous phase. The metal–sulphate interaction has been made in evidence by using the Debye–Huckel extended limiting law of ionic activity coefficient.

An imprinted organic--inorganic hybrid sorbent for selective separation of cadmium from aqueous solution.

A hierarchical double-imprinting concept was applied to the preparation of a new organic-inorganic hybrid sorbent for selective separation of Cd(II) from aqueous solution. In the prepared hierarchically imprinted sorbent, both Cd(II) and surfactant micelles (cetyltrimethylammonium bromide) were used as templates. The sorbent was prepared through self-hydrolysis, self-condensation, and co-condensation of the cross-linking agent (tetraethoxysilicate) and the functional precursor (3-(2-aminoethylamino)-propyltrimethoxysilane) in an alkaline media followed by gelation. The selectivity of the sorbent was investigated by a batch competitive ion-binding experiment using an aqueous Cd(II) and Zn(II) mixture. The largest selectivity coefficient for Cd(II) in the presence of Zn(II) was found to be over 100; the largest relative selectivity coefficient between Cd(II) and Zn(II), over 200. The uptake capacity of the prepared hierarchically imprinted sol-gel sorbent and the selectivity coefficient are much higher than those of the sorbent prepared in the absence of CTAB-template. The sorbent possesses a fast kinetics for the removal of Cd(II) from aqueous solution.

β-Ionone cyclodextrins inclusion complexes: [formula omitted] NMR study and photolysis

Complexes of β-ionone (BI) with β-cyclodextrin (β-CD), 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) and 2-hydroxypropyl-γ-cyclodextrin (HP-γ-CD) were studied by 1 H NMR spectroscopy in aqueous and methanolic solutions. From the dependence of chemical shifts of the BI protons on CD concentration (Job’s plot), it was concluded that BI forms 2:1 inclusion complexes (CD:BI) with β-CD and HP-β-CD, but a 1:1 complex with HP-γ-CD. The stability constants in water are K 21 (BI/β-CD) ≥ 2×10 6 M −2; K 21 (BI/HP-β-CD) = 5×10 6 M −2; K 11 (BI/HP-γ-CD) = 1×10 4 M −1. In 1:1 water/methanol solution the stability constants decrease by about two orders of magnitude compared to those in water. For example, for BI/HP-β-CD complex, K 21=8×10 4 M −2 in this case. Photolysis of trans-β-ionone in water and aqueous CD solutions leads to only one final product, retro-γ-ionone. Other isomers, cis-β-ionone and racemic α-pyran, are formed at earlier stages of the photolysis. The role of cyclodextrin in this process is discussed.

Synthesis and spectroscopic and structural studies of a new cadmium(II)-citrate aqueous complex. Potential relevance to cadmium(II)-citrate speciation and links to cadmium toxicity.

The presence of cadmium in the environment undoubtedly contributes to an increased risk of exposure and ultimate toxic influence on humans. In an effort to comprehend the chemical and biological interactions of Cd(II) with physiological ligands, like citric acid, we explored the requisite aqueous chemistry, which afforded the first aqueous Cd(II)-citrate complex [Cd(C(6)H(6)O(7))(H(2)O)](n)() (1). Compound 1 was characterized by elemental analysis, and spectroscopically by FT-IR and (113)Cd MAS NMR. Compound 1 crystallizes in the orthorhombic space group P2(1)2(1)2(1), with a = 6.166(2) A, b = 10.508(3) A, c = 13.599(5) A, V = 881.2(5) A(3), and Z = 4. The X-ray structure of 1 reveals the presence of octahedral Cd(II) ions bound to citrate ligands in a molecular crystal lattice. Citrate acts as a tridentate binder promoting coordination to one Cd(II) through the central alcoholic moiety, one terminal carboxylate group, and the central carboxylate group. In addition, the central carboxylate binds to three Cd(II) ions. Specifically, one of the oxygens of the central carboxylate serves as a bridge to two neighboring Cd(II) ions, while the other oxygen binds to a third Cd(II). A bound water molecule completes the coordination requirements of Cd(II). (113)Cd MAS NMR studies project the spectroscopic signature of the nature of the coordination environment around Cd(II) in 1, thus corroborating the X-ray findings. Collectively, the data at hand are in line with past solution studies. The latter predict that other similar low molecular mass Cd(II)-citrate complexes may exist in the acidic pH region, thus influencing the uptake of cadmium by living (micro)organisms, their ability to metabolize organic substrates, and possibly Cd(II) toxicity.