Precipitation of metal ions by organic acids as a mean for metal recovery and decontamination of wastewater

The dicarboxylic and oxycarboxylic acids known as complexing agents for metal ions under the conditions when the amount of metal ions exceeds that in metal complexes, act as precipitants for metal ions. The completeness of precipitation, depends on the kind of metal and organic acid, pH and the concentrations of substances. The abundance of metals in metal finishing industry enables to use such precipitation for regeneration and decontamination of the complexing agents containing solutions.     

One-pot aqueous solution syntheses of iron oxide nanostructures with controlled crystal phases through a microbial-mineralization-inspired approach

Iron-oxidizing bacteria produce trivalent iron oxides with the controlled crystal phases outside of their cells. Herein we have synthesized iron oxides with controlled oxidation states and crystal phases through a microbial-mineralization-inspired approach in an aqueous solution at low temperature. Trivalent iron oxides, such as lepidocrocite, ferrihydrite, goethite, and hematite, are selectively obtained from an aqueous solution containing divalent iron ions below 90 °C. The presence of a chelating agent facilitates the control of the oxidation states through the ligand-controlled approach because the precipitation of the divalent iron species is inhibited by the complexation between divalent iron ion and a chelating agent. The control of the crystal phases is achieved by the tuning of the synthetic conditions, such as the initial pH, the concentration of a chelating agent, and the reaction temperature. Furthermore, the resultant iron oxides have hierarchically organized structures consisting of nanoscale objects. The microbial-mineralization-inspired approach by using a chelating agent has potentials for the further morphological control of iron oxides and the further application to aqueous-solution syntheses of other metal oxides.     

Synthesis of bifunctional chelating agents based on mono and diphosphonic derivatives of diethylenetriaminepentaacetic acid

Bifunctional chelating agents (BFCAs) are small molecules containing a chelating unit, able to strongly coordinate a metal ion, and a reactive functional group, devised to form a stable covalent bond with another molecule. BFCAs are widely employed since their conjugation to a suitable biomolecule (e.g., a peptide or an antibody) allows the synthesis of diagnostic or therapeutic agents that specifically target diseased tissue with metals or radiometals. For this reason, BFCAs find application in diagnostic imaging, molecular imaging, and radiotherapy of cancer. The synthesis of new BFCAs based on a diethylenetriaminepentaacetic acid (DTPA) structure in which one or two carboxylic groups are replaced with phosphonic units is described. The phosphonic group, aside from being a classical isostere of the carboxylic acid in coordination chemistry, allows to modulate the physico-chemical properties of the ligands and of the corresponding complexes.     

微波辅助制备螯合纤维及其对汞的吸附性能

在微波辅助下,以聚丙烯腈纤维(PANF)为基体材料,二乙烯三胺(DETA)和硫化钠为改性试剂,通过两步接枝反应快速制备了含有大量硫原子的螯合纤维吸附剂。利用傅里叶变换红外光谱仪(FT-IR)和热重分析仪(TGA)对改性前后的纤维进行表征,同时考察了pH值、初始浓度、吸附时间和温度对螯合纤维吸附汞离子的影响。结果表明,微波辅助是一种高效、节能、经济和绿色的改性方法,改性过程在无毒的水环境中进行,试剂用量少,且改性时间大大缩短。改性纤维对汞离子的吸附是一个准二级动力学过程,较好的符合Langmuir吸附模型。在pH=7的条件下,螯合纤维对汞离子的最大吸附容量达到333.1mg/g,是一种有效的去除水中汞污染的吸附材料。     

Metal ion separations using cellulose phosphate as an ion-exchanger

Cellulose phosphate is used as a chelating ion-exchanger to effect the separation of several metal ions. Its exchange rate is much more rapid than that of a chelating ion-exchanger containing phosphonic acid groups on a polystyrene matrix. Weight distribution coefficients as a function of hydrogen ion concentration on cellulose phosphate are given for several metal ions. Successful separations of rare earths and alkaline earths, alkaline earths and alkali metals and aluminium and alkaline earths have been achieved on cellulose phosphate columns.     

Determination of nanogram levels of zirconium by chelating ion exchange and on-line preconcentration in flow injection UV-visible spectrophotometry

Trace quantities of zirconium were preconcentrated on a series of chelating resins. The experimental conditions for preconcentration such as pH, time and metal ion concentration were optimized for the batch processes. Continuous flow manifolds were developed for the on-line preconcentration of zirconium using microcolumns containing chelating resins. Calibration plots were obtained with correlation coefficients of 0.9990 +/- 0.0008. The determination of zirconium was performed using Xylenol Orange at 535 nm. Binary and ternary mixtures of zirconium, thorium and titanium did not show any cross-contamination during column chromatographic separation.     

Evaluation of sorption and desorption characteristics of cadmium, lead and zinc on Amberlite IRC-718 iminodiacetate chelating ion exchanger

A chelating type ion exchange resin (Amberlite IRC-718), containing iminodiacetate groups as active sites, has been characterized regarding the sorption and subsequent elution of Cd, Zn and Pb, aiming to metal preconcentration from solution samples of different origins. The methodology developed is based on off-line operation employing mini columns made of the sorbent. The eluted metals were determined by flame atomic absorption spectrometry. The effect of column conditioning, influent pH and flow rate during the sorption step, and the nature of the acid medium employed for desorption of the retained metals were investigated. Working (breakthrough) and total capacities were measured under dynamic operating conditions and the results compared with those obtained with Chelex-100, a resin extensively employed for analytical preconcentration. Structural information on the complexation of metals by the chelating groups was obtained by Fourier Transform infrared spectrometry. The analytical response of the Amberlite sorbent was assessed for the analysis of water samples and digestates of marine sediments.     

Chelating Sorbents Prepared by the Modification of Silica Gel, Lichroprep RP-8 and Lichroprep RP-18 with Calcon and Their Application in the Analysis of Some Metal Ions

 Two new chelating sorbents for metal ions were prepared by the impregnation of chemically modified silicas LiChroprep RP-8 and RP-18 with ion pairs composed of the cation of Aliquat 336 and the anion of Calcon. The sorbents were compared with an analogous sorbent with a plain silica carrier containing the same ion pairs. A hypothesis for binding this ion pair by the surfaces of the applied carriers was presented. A higher stability of the two sorbents in comparison with that of the plain silica chelating sorbent was demonstrated. The sorbents obtained were applied for chromatographic separations of some chosen mixtures of some metal ions and for additional purification of aqueous solutions of alkali metals from trace amounts of heavy metals. The multiple use of the sorbents based on RP-8 and RP-18 in sorption–desorption processes of metal ions without deterioration of their sorption capacities was demonstrated. Received March 8, 2000. Revision March 5, 2001.     

Supramolecular aggregates of amphiphilic gadolinium complexes as blood pool MRI/MRA contrast agents: physicochemical characterization

In this paper, we present the development of a new potential blood pool contrast agent for magnetic resonance imaging applications (MRA/MRI) based on gadolinium complexes containing amphiphilic supramolecular aggregates. A novel amphiphilic unimer, containing the DTPAGlu chelating agent covalently bound to two C18 alkylic chains, has been synthesized. DTPAGlu is a well-known chelating agent for a wide number of ions such as the paramagnetic metal ion Gd3+ used as contrast agent in MRA/MRI. The wide aggregation behavior of this surfactant, as free base or as gadolinium complex, has been studied and compared by means of dynamic light scattering, small-angle neutron scattering and cryogenic transmission electron microscopy techniques. Near neutral pH in both cases, the dominant aggregates are micelles.The high negative actual charge of the surfactant headgroup causes a strong headgroups repulsion, promoting the formation of large and high curvature aggregates. By decreasing pH and less markedly increasing the ionic strength, we observe a micelle-to-vesicle transition driven by a decreased electrostatic repulsion. A straightforward switch between different aggregation states can be particularly useful in the development of pH-responsive MRA/MRI contrast agents.     

Heavy metal ion uptake properties of polystyrene-supported chelating polymer resins

Metal ion uptake properties of polystyrene-supported chelating polymer resins functionalized with (i) glycine, (ii) hydroxy benzoic acid, (iii) Schiff base and (iv) diethanol amine have been investigated. The effects of pH, time and initial concentration on the uptake of metal ions have been studied. The uptake of metal ion depends on pH. The resins are more selective at pH 10 for Pb(II) and Hg(II), whereas at pH 6 they are found to be Cd(II) and Cr(VI) selective. Metal ion uptake properties of resins follow Freundlich’s equation. The resins are recyclable and are therefore employed for the removal of heavy metal pollutants from industrial waste water.     

Some Aspects of the Spontaneous Solubility Equilibria of Solid Carbonates

In order to adequately carry out the laboratory procedures usually taught in a general analytical chemistry course, students must master the subject of multiple equilibria in aqueous solution, both conceptually and mathematically. The use of a computer program to solve the concentrations of all species at equilibrium with a slightly soluble compound is frequently recommended in the chemical education literature, due to its simplicity and quickness. But, when this calculation procedure fails to consider other important reactions aside from the solubility equilibrium itself, significant differences in the numerical results may be obtained. For several metal carbonates, the usual procedure to calculate their solubilities is to consider carbonate ion hydrolysis as the only additional reaction.In this paper it is shown numerically and graphically that for magnesium and silver carbonates, the precipitation reaction of metal (hydr)oxides would occur at the pH value calculated from the carbonate dissolution plus the anion hydrolysis equilibria. An analytical procedure to solve these complex multiple equilibria system is presented. The final solution to the problem is obtained through a high-order equation that is easily solved by a simple iterative method. The correct solubility-pH curve for the metal carbonates is calculated, and the pH values for the metal hydroxide precipitation onset for several important representative and transition metal carbonates are shown. It is concluded that the overall procedures to solve these multiple equilibria problems are not beyond the comprehension of any chemistry student with a acceptable background in general, inorganic, and analytical chemistry, and that by focusing on tasks such as these, important critical-thinking skills can be obtained.     

Histidine as the functional group for a chelating ion exchanger

In the chelating ion exchanger synthesized, the amino group of histidine is attached chemically via the azide method to the carboxyl group of Amberlite IRC-50. A flow system based on a spectrophotometric detector, with 4-(2-pyridylazo) resorcinol as reagent, is described for fast assays of eluted cations. The pH dependence of the metal extraction is reported for Ag(I), Au(III), Cu(II), Fe(III), Hg(II), Ni(II) and Zn(II) ions. The resin exhibits no affinity for the alkali or alkaline earth metals. The uptake of traces of the specified elements from synthetic samples by a short (90 mm) column of the histidine-containing resin was in the range 94–100% and the retained metals were readily eluted by means of 2 M hydrochloric or hydrobromic acid. In column operation, mercury was quantitatively recovered even in the presence of large excesses of various ligands. The recoveries of the trace metals were good at the usual pH of natural waters.     

Atomic Absorption Detector for Liquid-Liquid Chromatography

Abstract

A detector system specific for the measurement of chelating agents and applicable to liquid-liquid chromatography has been developed. A solution containing the chelating agent is passed over a short column of chelating ion exchange resin in the copper form, and directly into the aspirator of a recording atomic absorption spectrophotometer set to measure copper. A quantity of copper proportional to the quantity of the chelating agent is stripped from the column and recorded as a peak. Precision and accuracy compare with normal atomic absorption techniques, with an average mean standard deviation of 3%, and a corresponding accuracy. The detection limit for this method is 5x10-⁷ millimoles of EDTA or NTA. Determinations are rapid and reproducible in solutions having a pH in the range of 4 to 9. The role of interfering ions is considered. The applicability of the method as a specific detector system for liquid-liquid chromatographic separations of chelating agents is discussed. Recovery of chelating agents from solutions with an ionic strength approximating natural fresh waters is demonstrated.     

The effect of chelating agent on the separation of Fe(III) and Ti(IV) from binary mixture solution by cation-exchange membrane

The competitive transport of Fe(III) and Ti(IV) ions and the effect of chelating agents on separation from binary mixture solutions through charged polysulfone cation-exchange membrane (SA3S) has been studied under Donnan dialysis conditions. The amount of chelating agent was taken as an equimolar of Fe(III) ion in the feed phase. In this process, the membrane separated two electrolyte solutions: the feed solution, initially containing metal salts (Fe, Ti), or metal salts solution, containing a chelating agent, and the other side (receiver solution) being HCl solution. An external potential field is not applied. It was observed that the chelating agents affect the metal transport; the transport of Fe(III) is decreased and the transport of Ti(IV) is increased.     

Desorption of Heavy Metals from Typical Soil Components (Clay,Peat) with Glycine

Abstract

Natural organic chelating agents take part in the mobilization and translocation of heavy metals in unpolluted and polluted soils. They also have to be considered as possible extracting agents for the decontamination of heavy metal polluted soils. For an assessment of the desorption capability of glycinc, heavy metals (Cd, Cu, Ni, Pb, Zn) were adsorbed onto typical soil components (bentonite and peat). The metal loaded sorbents were resuspended in aqueous solutions of glycine at pH 7.0 and 4.5 and the quantities of the desorbed metals were analysed in the liquid phase. Furthermore, the dependency of the desorption rate on the duration of experiments and the metal content were investigated. The remobilization of heavy metals from bentonite by glycine at pH 7.0 decreases following the order Cu > Ni > Zn > Cd > Pb and ranges from 95% to 9.5%. The desorption rate was significantly lower at pH 4.5 and in suspensions of peat.     

Synthesis and characterisation of macromolecules containing multiple tetrazole functionalities

The synthesis of tetra-tetrazole macromolecules, containing various aromatic cores including benzene, pyridine and pyrazine directly attached to the tetrazole moieties, is described. This variation allowed for the generation of ligands with greater potential for metal ion complexation. Metal ion complexation reactions of the tetra-tetrazole macromolecules with the chelating pyridyl-tetrazole arms result in the formation of metal complexes where the metal ion was bound at the pendant arms rather than at the central core.     

Analysis of Nonionic Surfactants by High Performance Liquid Chromatography

Abstract

This review discusses the principles of immobilized metal ion affinity chromatography (IMAC) and its applications to protein separations. IMAC functions by binding the accessible electron-donating pendant groups of a protein - such as histidine, cysteine, and tryptophan - to a metal ion which is held by a chelating group covalently attached on a stationary support. A common chelating group is iminodiacetate. The ions commonly used are of borderline or soft metals, such as Cu²⁺, Ni²⁺, Co²⁺, and Zn²⁺. Protein retention in IMAC depends on the number and type of pendant groups which can interact with the metal. The interaction is affected by a variety of independent variables such as pH, temperature, solvent type, salt type, salt concentration, nature of immobilized metal and chelate, ligand density, and protein size. Proteins are usually eluted by a decreasing pH gradient or by an increasing gradient of a competitive agent, such as imidazole, in a buffer. There are still several unresolved issues in IMAC. The exact structures of protein-immobilized metal complexes need to be known so that retention behavior of proteins can be fully understood and sorbent structures can be optimized. Engineering parameters, such as adsorption/desorption rate constants, sorbent capacities, and intraparticle diffusivities, need to be developed for most protein systems. Engineering analysis and quantitative understanding are also needed so that IMAC can be used efficiently for large scale protein separations.     

Simultaneous recovery of cadmium and lead from aqueous effluents by a semi-continuous laboratory-scale polymer enhanced ultrafiltration process

Performance of a semi-continuous polymer enhanced ultrafiltration (PEUF) process has been investigated for the simultaneous recovery of cadmium and lead from binary mixtures. This method uses poly(acrylic acid) as water-soluble polymer to bind these metals. Experiments have taken place in a laboratory-scale system. Loading ratio (mg total metal ions/g polymer) and pH values for separation of cadmium and lead have been studied by means of preliminary experiments, analyzing their influence on permeate flux, metal rejection coefficients and separation factor.The proposed process includes three different stages: total retention of metal ions, selective separation and polymer regeneration. Operating pH values for total retention of metal ions and polymer regeneration processes are 5 and 2, respectively. Selective separation has been investigated working at an intermediate pH value. In this way, if a stream containing 12.5 ppm of each metal ion (1:1 in weight) is treated in the first stage, two different streams enriched in each metal ion are obtained in the second stage. Permeate stream is enriched in cadmium with a proportion near 5:1 in weight, and retentate is enriched in lead with a similar proportion.Finally, the three stages have been modelled successfully with a mathematical model based on conservation equations and chemical reactions taking place in solution.     

Measurement of Chelating Agent Levels in Media with High Concentrations of Interfering Metal Ions

Abstract

An ion-exchange method for the measurement of levels of chelating agents in media with high levels of metal ions has been developed. The test solution is passed through a specially prepared ion-exchange column, which both removes metal ion interferences, and places the chelating agent in the copper form. The copper levels in the column effluent are then measured by flame atomic absorption methods, the copper levels corresponding in a 1:1 ratio to the levels of chelating agent in the sample. The detection limit for this method is on the order of 1 ppm copper equivalent chelating capacity, and is applicable in situations where the interfering metal ions are at concentrations in the range of 10^?2 M. The method is reproducible in the pH ranges of 4 to 9 Precision and     

Determination of copper, nickel, zinc, cobalt and manganese in seawater by chelation ion chromatography

Preconcentration and determination of trace elements in seawater by chelation ion chromatography (CIC) was studied. For the retention of metal ions (0.25–0.30 M), ammonium acetate (at pH 4.8–5.1) and macroporous iminodiacetate chelating resin were used. This system (CIC) permits trace and ultra-trace determination of metals in a variety of complex matrices, in particular those with a high content of alkali and alkaline earth metals. Detection limits range from 0.1 to 0.5 ng. Satisfactory results are obtained in the range 0.05–0.5 μg/1 when 60 ml of sample are preconcentrated. In this work the contents of zinc, copper, nickel, cobalt and manganese in seawater from the Venice lagoon are presented. The results obtained by chelation ion chromatography are compared with those obtained using preconcentration of metals with dithizone and ammonium pyrrolidinedithiocarbamate in chloroform and analysed by graphite furnace atomic absorption spectrometry.