Cadmium Ions In Solution Research Articles

Converting wastes to resource: Preparation of NiO@γ-Al2O3 sludge composite from aluminum-containing sludge for cadmium removal from wastewater

Solid sludge waste and heavy metal water pollution have attracted great interest due to the adverse impacts on the ecological environment, which remains a significant challenge to environmental protection. Herein, with the concept of converting wastes to resources, this work presents a general procedure to fabricate NiO@γ-Al2O3 sludge composite derived from aluminum-containing sludge for efficient cadmium removal. During the procedure, the unstable metal compounds were converted into chemically stable metal oxides, and the organic components in sludge are decomposed via high-temperature treatment. Then, the NiO@γ-Al2O3 sludge composite was obtained by in situ growth of NiO nanocrystals using the calcined sludge as raw materials, followed by calcination to form a porous structure. The as-obtained NiO@γ-Al2O3 sludge composite with hierarchical porosity comprises self-assembled NiO nanosheets with sizes ranging from 1 to 3 μm. Compared with raw sludge particles, the specific surface area of NiO@γ-Al2O3 sludge composite is enhanced significantly (116.27 m2/g), revealing that the preparation procedure is favorable for the improvement of the surface properties of the sludge. The cadmium adsorption results showed that the maximum cadmium adsorption capacity of the sludge composite could attain 160.12 mg/g, and cadmium removal efficiency could reach 99.9% with an optimal dose of 1.5 g/L. Meanwhile, the sludge composite showed high adsorption capacity at the neutral pH condition, which was attributed to the exchange of cadmium ions in solution with the surface protons on the adsorbent. Significantly, a simple regeneration operation was used for the desorption of cadmium ions to realize the regeneration of adsorbents, and the regenerated sludge composite can be recyclable for continuous use. This work provides a waste-to-resource strategy for resource utilization of solid waste sludge and presents an adsorbent material with high surface activity for cadmium adsorption, which may inspire the development and application of other solid waste for wastewater treatment.

Высшие грибы как сорбенты ионов кадмия

It is known that fungal chitin exhibits high sorption properties with respect to heavy metal ions, while it is practically not absorbed in the human body, which makes it a promising sorbent. The aim of this work was to evaluate the sorption abilities of the mushrooms of Agaricus bisporus and Russula atropurpurea with respect to cadmium ions. The use of the potentiometric method for measuring the potential of the ion-selective electrode, which depends on the concentration of cadmium ions in solution, made it possible to register in detail in real time the kinetic curves of sorption of cadmium ions by mushrooms. During the experiment, it was found that the kinetics of sorption of cadmium ions from a solution with initial concentrations (0.2-2.0)·10-5 M by the preparations of fruit bodies of mushrooms A. bisporus and R. atropurpurea is well described by the pseudo-second order equation, according to which the limiting stage of the process is chemical interaction of sorbent and sorbate (1:1 ratio). At relatively low initial concentrations of cadmium ions in solution ((0.2-0.6)·10–5 M), the sorption rate was 1.5-2.5 times higher for R. atropurpurea compared to A. bisporus. At higher concentrations of cadmium ions in solution ((0.8-2.0)·10-5 M) the speed and capacity of sorption were very close for different types of mushrooms. Moreover, the rate of sorption by mushrooms exceeds 5-10 times the rate of sorption of activated carbon and micromycetes of the genus Fusarium. It was revealed that the sorption isotherm of cadmium ions by mushrooms is well described by the Dubinin-Radushkevich equation, according to which R. atropurpurea is characterized by the highest sorption compared to A. bisporus. Thus, R. atropurpurea has the highest sorption activity with respect to cadmium ions.

Electroanalytical sensing of Cd2+ based on metal–organic framework modified carbon paste electrode

This paper reports, for the first time, the fabrication and characterization of sensitive electrochemical sensor for the efficient detection of cadmium ion using metal organic framework (MOF). TMU-16-NH2 ([Zn2(NH2-BDC)2(4-bpdh)]·3DMF) a kind of metal organic frame works was used as a modifier. The interaction between cadmium and amine groups of TMU-16-NH2 are conditioned by dative attachment that caused Cd2+-N complexation by soft–soft interactions. To achieve the highest efficiency of the sensor, effective factors on analytical response such as pH, deposition potential and deposition time have been optimized. Under optimal experimental conditions, the oxidation current increased by the addition of cadmium in the sample and dynamic ranges obtained from 0.7 to 120 by differential pulse voltammetry (DPV). This method exhibited a lower limit of detection (LOD) of 0.2μgL−1 (S/N=3). The presented work demonstrates that the MOFs are effective materials to fabricate efficient electrochemical sensors for the easy and costly effective detection of cadmium ions in solutions.

Sno2 quantum dots as novel platform for electrochemical sensing of cadmium

This paper reports, for the first time, the fabrication and characterization of highly sensitive and selective electrochemical sensor for the efficient detection of cadmium ion using SnO2 quantum dots (QDs). The SnO2 QDs were prepared by simple and facile low-temperature hydrothermal process and characterized by several techniques. The detailed characterizations revealed that the QDs are pure SnO2, prepared in large quantity with the average size of 2–4nm and possessing well-crystallinity with tetragonal crystal structure. Further, the prepared SnO2 QDs were used as potential scaffold to fabricate highly sensitive, selective and reproducible electrochemical sensor for the efficient detection of cadmium ions. The fabricated sensor exhibited a high sensitivity of ∼77.5×102 nA ppm−1 cm−2, a low detection limit of ∼0.5ppm and response time of <2s. The presented work demonstrates that the SnO2 QDs are effective electron mediators to fabricated efficient electrochemical sensor for the easy, cost effective and accurate on-site detection of cadmium ions in solution.

Development of a multifunctional membrane for chromatic warning and enhanced adsorptive removal of heavy metal ions: Application to cadmium

In this study, a multifunctional membrane for visual warning and enhanced adsorptive removal of cadmium ions in aqueous solutions was prepared and examined. 5,10,15,20-Tetrakis (1-methyl-4-pyridinio) porphyrin tetra (p-toluenesulfonate), an optical indicator ligand for cadmium ions, was immobilized onto a porous chitosan/cellulose acetate blend base membrane through the polymer brushes grafted on the membrane surface via a surface-initiated atom transfer radical polymerization (ATRP) method. The prepared membrane was found to be capable of displaying distinctive color changes in response to the presence of cadmium ions in aqueous solutions. In addition, it also showed significantly enhanced performance for adsorptive removal of cadmium ions. Experimental results indicated that the developed membrane can exhibit quick (within 2 min) color change (from yellow to green) when it was in contact with cadmium ions in a solution even at relatively low concentrations (e.g. 5 mg/L). The interference study revealed that the functionalized membrane also possessed selectivity towards cadmium ions when other cationic species such as K +, Na +, Ca 2+ and Mg 2+ ions existed together in the solutions. Hence, the development in this study demonstrated the prospect to make porous membranes truly multifunctional with added advantages for adsorptive removal as well as for chromatic warning of heavy metal ions in the solutions that are treated.

Identification of a metallothionein in Synechococcus by capillary electrophoresis hyphenated with inductively coupled plasma mass spectrometry.

A home-made system hyphenating capillary electrophoresis with an inductively coupled plasma mass spectrometer (CE-ICP-MS) for cadmium speciation of protein-binding and free cadmium ions in solution is presented. The CE-ICP-MS interface consisted of an acrylic block with an internal volume ca. 20 microL in which a platinum electrode, a capillary column, and a connection to an ICP nebulizer were inserted. A make-up electrolyte solution containing 50 mmol L(-1) Tris-HCl buffer solution (pH 9.0) was continuously flowed through the interface to the ICP nebulizer. The separation of free Cd ions, Cd-cysteine, and Cd bounded to metallothionein (MT) isoforms from rabbit liver was carried out by capillary electrophoresis, and the analytes were detected by ICP-MS. The feasibility to isolate metallothionein compounds extracted from the cyanobacterium Synechococcus PCC7942 was demonstrated. The Cd binding proteins were induced in Synechococcus PCC7942 and further analyzed by CE ICP-MS.

Chemical microsensors based on chalcogenide glasses for the detection of cadmium ions in solution

Chemical microsensors for the detection of Cd 2+ ions in solution were prepared. The sensitive membranes are chalcogenide glasses from the CdSAgISb 2S 3 system. Physical, chemical and electrochemical characteristics of the sensors are presented. Quasi-nerstian responses over five orders of magnitude associated to a limit of detection lower than 10 −6 mol/l were observed. Selectivity of the sensitive membranes versus several cations was studied. While low selectivity coefficients were obtained when the interfering cations were Co 2+, Ni 2+, Zn 2+or Ca 2+the present sensing device appears to be non selective against Pb 2+and Cu 2+.

Optical fibre fluorosensor for cadmium with diethylaminoethyl-Sephadex as a substrate

An optical fibre fluorosensor for cadmium ion was prepared by immobilizing 8-hydroxy-7-iodoquinoline-5-sulfonic acid on diethylaminoethyl (DEAE) Sephadex. Owing to the lowest excited singlet changing from n–π* to π–π*, complexation between cadmium ion and the immobilized reagent resulted in a weakly fluorescent ligand becoming a strongly fluorescent complex. Based on the fluorescence intensity change of the immobilized phase at 505 nm, cadmium ion in solution was determined. The characteristics of the fluorosensor were studied by using both the kinetic and equilibrium methods. As DEAE-Sephadex is a colourless and transparent gel containing diethylaminoethylglucan with a low transfer resistance in water, the fluorosensor reached 90% of the steady-state response in 10 s. The relationship between the response and the logarithm of cadmium ion concentration was linear in the range of 2.0 × 10–7–7.0 × 10–5 mol dm–3. The detection limit for CdII was 8.0 × 10–8 mol dm–3. Using KI solution, the sensing layer saturated by cadmium ion can be regenerated, but the immobilized 8-hydroxy-7-iodo-quinoline-5-sulfonic acid was not destroyed. The results of this study demonstrate that DEAE-Sephadex is a good substrate for an optical fibre fluorosensor for cadmium ion. With appropriate separation it can be applied to the determination of cadmium ion in flour samples.

Uptake of zinc and cadmium by two different populations of shore crabs Carcinus maenus at different salinities

Effects of salinity on the accumulation of Zn and Cd in the haemolymph (relative indices of Zn and Cd uptake rates) of 2 populations of shore crab Carcinus maenas (L.) were investigated. Zn accumulation rates in the haemolymph of the Scottish (high salinity) crabs were higher than those of the Danish (low salinity) crabs. Decreases in salinity significantly decreased the Zn accumulation rate in the Scottish crabs but increases in salinity did not change the Zn accumulation rates in the Danish crabs significantly. Scottish crabs also showed a higher Cd accumulation rate, as well as elimination rate, than those of the Danish crabs. The highest Cd accumulation rate in Scottish crabs was found at 33 ppt salinity. In contrast the Cd accumulation rate of Danish crabs was highest at 15 ppt. It is proposed that exposure of the crabs to low salinity probably involves changes to crab permeability (e.g. apparent water permeability), thereby off-setting physico-chemical changes promoting the availabilities of free zinc and cadmium ions in solution which would otherwise increase metal uptake rates.

Binding of cadmium by cyanobacterial growth media: Free ion concentration as a toxicity index to the cyanobacteriumNostoc UAM 208

A quantitative study of cadmium binding to three different growth media for nitrogen-fixing cyanobacteria was done with the aid of a solid state ion-specific electrode. Kratz and Myers modified medium and Arnon medium bound large amounts of Cd2+, BG11o medium had less binding capacity. Of the media components, phosphate ion showed the greatest ability to bind Cd2+. Different pHs, the size of cell inoculum and two buffers (Tricine and HEPES, 25 mM) also changed the availability of free cadmium ion in solution. The effect of free Cd2+ ion towards the cyanobacterium Nostoc UAM 208, isolated from a heavy metal polluted environment, also was tested. The effective concentration affecting 50% of population (EC50), at 120 h of exposure, was less for nitrogenase activity (0.26 microgram/mL) than for growth (0.55 microgram/mL), suggesting that this enzyme activity is more sensitive to cadmium than growth. Furthermore, cadmium toxicity was influenced by the addition of buffers to the growth medium. In the presence of buffer, Tricine (25 mM), growth and nitrogenase activity was reduced by 50% at a total cadmium concentration of about 115 micrograms/mL, although no free ion was detected in this case. These results suggest that although generally cadmium toxicity is a function of free metal ion concentration, this can also vary in the presence of complexing agents.

A laboratory study of the immobilisation of cadmium in soils

Traces of cadmium ion in solution, alone and together with different cadmium bonding agents (K 2CO 3, CaCO 3, KH 2PO 4, Ca 3(PO) 4, Fe(NO 3) 3 and Fe(OH) 3), were added to three soils of pH 5·0, 7·0 and 7·6, respectively, and incubated aerobically at 45°C for 6 days. The extent to which the different binding agents immobilised cadmium in the treated soils was determined by measuring the amounts extracted by CH 3COONH 4, CaCl 2, NH 4Cl, Ca(NO 3) 2, (CH 3COO) 2Ca or KNO 3 solutions. The extracted cadmium was determined by AAS. Recoveries by the different extractants, which are representative of those proposed for the determination of ‘available cadmium’ in soils, showed a systematic variation for each of the treated soils. The extent to which these differences arise from pH and the complexation of the cadmium is discussed. Markedly different amounts of cadmium were immobilised in the different soils, under the same conditions and treatments. CaCO 3 and Ca 3(PO 4) 2 were the most efficient in immobilising cadmium in the acid soil, K 2CO 3 and Ca 3(PO 4) 2 were best with the neutral soil and Fe(NO 3) 3, Fe(OH) 3 and Ca 3(PO 4) 2 with the calcareous soil. Thus, under the aerobic conditions likely to be found in dry farmlands, the cadmium immobilisation mechanisms appear to be associated with precipitation on carbonate and phosphate surfaces; in calcareous soils, the surface hydrolysis of cadmium on ferric hydroxide seems most important.

CADMIUM SPECIES IN BASIC SOLUTION

The principal cadmium-containing species in basic solutions varies with the concentration of hydroxide ion such that the solubility of cadmium hydroxide can be satisfactorily expressed, in solutions of high ionic strength, in terms of [Cd(OH)+] = 3.0 × 10−9[OH−]−1, [Cd(OH)2]soln = 1.0 × 10−6, [Cd(OH)3−] = 1.2 × 10−6[OH−], and [Cd(OH)42−] = 3.1 × 10−6[OH−]2. Since the solubility 10 varies from 10−4 to 10−6M, the predominant species at high concentrations of hydroxide ion is Cd(OH)42−; at low concentrations of hydroxide ion Cd(OH)+ is the principal cadmium-containing ion in solution. There is little free cadmium ion in solutions whose hydroxide ion concentration is greater than 10-4M.

Polarographic studies of ion binding in solutions of pepsin. I. Binding of cadmium ions

AbstractThe results of the application of the modified polarographic method to the study of binding of cadmium ions in solutions of pepsin are reported. Isoionic solutions of pepsin were converted by suitable treatment with a cation‐exchange resin to solutions of cadmium pepsin. As in previous cases, i.e., in solutions of synthetic polyelectrolytes, the extent of ion binding was obtained by assuming that only free, i.e., unbound, ions contribute to the diffusion and migration currents, respectively. It has been furthermore shown that cadmium ions are bound to pepsin ionically as well as covalently, and the relative amounts of cadmium in either state of binding have been determined.