Retention, kinetics and thermodynamics profile of cadmium adsorption from iodide medium onto polyurethane foam and its separation from zinc bulk

The sorption behaviour of 2.5 × 10⁻⁵ M solution of Cd(II) on polyurethane foam (PUF) from iodide medium have been investigated. The conditions were optimized from aqueous solutions of different pH (1-10) and of acids of varied concentration (0.01-1.0 M). The maximum concentration of KI was found to be 0.24 M and equilibration time was established to be 20 min. The data successfully followed the Freundlich and Dubinin-Radushkevich (D-R) isotherms at low metal ion concentration while Langmuir isotherm followed at higher metal ion concentration. The Freundlich parameter 1/n = 0.66 ± 0.02 have been evaluated whereas D-R isotherm yields the sorption free energy E = 10.5 ± 0.1 kJ mol⁻¹ indicating ion exchange type chemisorption. The monolayer coverage (XL) constant of Langmuir isotherm was found to be 23.7 ± 0.4 mg g⁻¹. The numerical values of thermodynamics parameters enthalpy (ΔH), entropy (ΔS) and Gibbs free energy (ΔG) indicated the endothermic and spontaneous nature of sorption. The Scatchard plot analysis was tested to evaluate the binding sites of the PUF and stability constants of sorption were determined. On the basis of these parameters, the sorption mechanism was discussed. Among the foreign ions tested, Pb(II), Hg(II), cyanide and nitrite should be absent. The clean separation of Cd(II) from Zn(II) ions in the ratio 1:250, respectively, was achieved by column chromatography.     

Preconcentration and separation of iron, zinc, cadmium and mercury, from waste water using Nile blue a grafted polyurethane foam

The present work describes a novel method for the incorporation of Nile blue A into polyurethane foam matrix. This foam material was found to be very suitable for the extraction of metal ions from aqueous solutions. The characterization of Nile blue A grafted foam and the effect of halide concentration, pH, shaking time, extraction isotherm and capacity have been investigated. This foam material was found to be suitable for the separation and preconcentration of iron (III), zinc (II), cadmium (II) and mercury (II) from waste water. The extraction was accomplished in (15-20) minutes. Iron was separated from acid medium (2-4 M HCl), zinc from (3-5 M HCl), cadmium from (4-6 M HCl) as thiocyanate complexes and mercury was separated from (1-2 M HCl) as chloride.     

X-ray fluorescence spectrometric determination of germanium after extraction with polyurethane foam

Germanium is extracted onto polyurethane foam as molybdogermanate, and determined by X-ray fluorescence spectrometry in the dried foam. The extraction is effective between pH 0.5 and 3.7 and as little as 7 μg of germanium can be detected in 100 ml of aqueous solution.     

Preconcentration and separation of acaricides by polyether based polyurethane foam

This paper reports the preconcentration of some dissolved organic phosphorous and chlorinated acaricides in water by porous polyether based polyurethane foam. Preliminary screening tests on the retention of the tested compounds, i.e., dicofol and bromopropylate, by polyether foams indicated that a very high percent removal of the tested species was obtained. The retention rate was found fast and reaches equilibrium in a few minutes. The various parameters, e.g., pH, extraction media, shaking time, salt effect, temperature and sample volumes affecting the preconcentration of the tested species by the unloaded foam, trioctylamine and trimethylphosphate treated foam have been optimized via batch modes of separation. The unloaded foams were employed in column modes for the retention and recovery of the tested species. The sorption efficiency and recovery of the compounds by the unloaded foams column were found to be up to 97.5%. The height equivalent to a theoretical plate (HETP) obtained by the unloaded foam was found to be in the range 1.1-1.3 ± 0.2 mm. The sorption mechanism of the tested compounds by the foams was discussed.     

Application of pressurized fluid extraction to determine cadmium and zinc in plants

A procedure for the determination of Cd and Zn in plants is proposed. The metals are extracted by pressurized fluid extraction (PFE). Operational conditions are: pressure 1500 psi, temperature 75 °C, static time 5 min, flush volume 35%, purge time 60 s, cycles 1 and 1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (CDTA) 0.01 M at pH 4.5 as extracting solution. Determination of Zn is carried out by flame atomic absorption spectroscopy and depending on the concentration level, Cd content is determined by flame or electrothermal atomic absorption spectroscopy. Certified samples of Virginia tobacco leaves, tea leaves, spinach leaves, poplar leaves, a commercial spinach sample (Spinacea oleracea) and genetically modified Arabidopsis thaliana were analysed by the proposed procedure and also by microwave acid digestion and extraction with HCl-Triton X-100. Confidence intervals for Cd and Zn content obtained by the proposed procedure overlap with the certified values. The other procedures, however, provide inaccurate results for Cd. Recoveries obtained for a confidence level of 95% are 96 ± 6% and 95 ± 5% for Zn and Cd, respectively. Reproducibility of Zn by the proposed procedure is 7% (n = 8), similar to the other tests and the detection limit is 2.6 μg. For Cd reproducibility is 8.5% (n = 8), better than with HCl-Triton X-100 and similar to acid digestion, the detection limit is 3.5 ng of Cd.     

Preconcentration and separation of some organic water pollutants with polyurethane foam and activated carbon

Summary Although pesticides and phenols, cause reproductive failure in many areas of the world, there is a no effective means of treating waste water containing these compounds. This work deals with the adsorption of insecticides and phenols from aqueous solution by untreated porous polyurethane foam and activated carbon. Static experiments showed that in comparison with activated carbon a reasonable percentage of the compounds was adsorbed by the foam. Attempts were therefore made to extract these species from aqueous solution by foam column chromatography.The results showed that the adsorption of the compounds was brought about by a mechanism similar to that of solvent extraction. The effect of various experimental conditions such as temperature, extracting medium, pH, contact time, volume of sample flow rate, compound concentration, and eluting solvents on the retention and separation of the compounds has been determined. The height equivalent to a theoretical plate (HETP) was calculated from breakthrough capacity curves and from chromatograms obtained from polyurethane foam columns for the insecticide Dyfonate; values were in the range 2.1–2.3 mm at 10–15 ml min^–1. Extraction of the compounds from natural water, and subsequent recovery, were both found to be complete. The high capacity of polyurethane provides advantages over activated carbon; in particular, large sample volumes can be analyzed at high flow rates.     

On-line preconcentration system using a minicolumn of polyurethane foam loaded with Me-BTABr for zinc determination by Flame Atomic Absorption Spectrometry

In the present paper, an on-line system for preconcentration and determination of zinc by Flame Atomic Absorption Spectrometry (FAAS) is proposed. It is based in the sorption of zinc(II) ions on a minicolumn packed with polyurethane foam loaded with 2-[2′-(6-methyl-benzothiazolylazo)]-4-bromophenol (Me-BTABr) reagent. Chemical and flow variables as pH effect, sample flow rate and eluent concentration were optimized using univariate methodology. The results demonstrated that zinc can determinate using the sample pH in the range of 6.5-9.2, sample flow rate of 6.0 ml min⁻¹, and the elution step using 0.10 mol l⁻¹ hydrochloric acid solution at flow rate of 5.5 ml min⁻¹. In these conditions, an enrichment factor of 23 and a sampling rate of 48 samples per hour were achieved. The detection limit (DL, 3σ) as IUPAC recommendation was 0.37 μg l⁻¹ and the precision (assessed as the relative standard deviation, R.S.D.) reached values of 5.9-1.8% in zinc solutions of 1.0-10.0 μg l⁻¹ concentration, respectively. The method was successfully applied to the determination of trace amounts of zinc in natural water samples from Salvador (Brazil).     

Selective solid-phase extraction of trace cadmium(II) with an ionic imprinted polymer prepared from a dual-ligand monomer

A novel dual-ligand reagent (2Z)-N,N′-bis(2-aminoethylic)but-2-enediamide, was synthesized and applied to prepare metal ion-imprinted polymers (IIPs) materials by ionic imprinted technique for selective solid-phase extraction (SPE) of trace Cd(II) from aqueous solution. In the first step, Cd(II) formed coordination linkage with the two ethylenediamine groups of the synthetic monomer. Then the complex was copolymerized with pentaerythritol triacrylate (crosslinker) in the presence of 2,2′-azobisisobutyronitrile as initiator. Subsequently, the imprinted Cd(II) was completely removed by leaching the dried and powdered materials particles with 0.5 M HCl. The obtained IIPs particles exhibited excellent selectivity for target ion. The distribution ratio (D) values of Cd(II)-IIPs for Cd(II) were greatly larger than that for Cu(II), Zn(II) and Hg(II). The relative selective factor (α_r) values of Cd(II)/Cu(II), Cd(II)/Zn(II) and Cd(II)/Hg(II) were 25.5, 35.3 and 62.1. The maximum static adsorption capacity of the ion-imprinted and non-imprinted sorbent for Cd(II) was 32.56 and 6.30 mg g⁻¹, respectively. Moreover, the times of adsorption equilibration and complete desorption were remarkably short. The prepared Cd(II)-IIPs were shown to be promising for solid-phase extraction coupled with inductively coupled plasma atomic emission spectrometry (ICP-AES) for the determination of trace Cd(II) in real samples. The precision (R.S.D.) and detection limit (3σ) of the method were 2.4% and 0.14 μg L⁻¹, respectively. The column packed with Cd(II)-IIPs was good enough for Cd(II) separation in matrixes containing components with similar chemical behaviour such as Cu(II), Zn(II) and Hg(II).     

The chromatographic behavior of group (IIB) metal ions on polyurethane foam functionalized with 8-hydroxyquinoline

Polyurethane foam functionalized with 8-hydroxyquinoline has been prepared by coupling the foam matrix with 8-hydroxyquinoline (oxine) through an azo spacer. The oxine-bonded foam (Ox PUF) was characterized by use of different tools (UV–Vis spectra, IR spectra, density, and stability). Ox PUF was found to be very suitable for separation and preconcentration of trace metals, e.g. Zn(II), Cd(II), and Hg(II) ions, from wastewater in the pH ranges 2–12, 9–12, and 3–6, respectively. Various conditions influencing the sorption of these metal ions on to Ox PUF were optimized. Extraction of the metal ions was accomplished in 15 to 20 min. Study of the variation of the sorption of the tested metal ions with temperature yielded average values for H, S, and G of 41.99, 158.23, and –5.1 kJ mol^–1, respectively. The capacities of the foam material were 0.27, 0.16, and 0.09 mmol g^–1 for Zn(II), Cd(II), and Hg(II), respectively. Preconcentration factors >50 were achieved (RSD6.18). The quantitative results were obtained from experiments performed using certified reference materials.     

镉基体中微量锌的富集与分离研究

提出了一种用于富集分离镉基体中的微量锌的分离体系,研究了从镉基体中富集分离微量锌的可行性——采用二安替比林甲烷(DAM)作为络合剂,与硫氰酸铵、锌在盐酸介质中形成三元离子缔合物,用三氯甲烷作为萃取剂,最后用氨水作为反萃剂将有机相中的锌洗脱出来与镉分离。试验发现,当15%的硫氰酸铵用量为1.5mL,DAM的用量为1.5mL,加入20mL4mol/L的盐酸时,用20mL的三氯甲烷萃取两次,10mL1:3的氨水反萃两次,锌的回收率达到95%以上,相对误差小于0.5%。     

The determination of molybdenum in water and biological samples by graphite furnace atomic spectrometry after polyurethane foam column separation and preconcentration

A system for molybdenum separation and enrichment aiming its determination in water and biological samples by graphite furnace atomic absorption spectrometry (GFAAS) is proposed. The procedure is based on the sorption of the molybdenum (VI) thiocyanate complex onto a mini-column packed with polyurethane foam (PUF). The elution is accomplished by a 3.0 mol l⁻¹ nitric acid solution. Flow variables were optimized and an enrichment factor of 10 as well as a limit of detection (LOD) (3 s) of 0.08 μg l⁻¹ in the sample solution were achieved. The coefficient of variation showed values of 3 and 2% for molybdenum solutions of 2.0 and 10.0 μg l⁻¹, respectively. The accuracy of the method was confirmed by the good concordance between found and certified values in the analysis of certified reference materials (CRMs) (CASS-3 Nearshore Seawater, NIST 1547 Peach Leaves, NIST 1515 Apple Leaves and NIST 1572 Citrus Leaves). The procedure was also applied for the molybdenum determination in mineral waters as well as in produced water samples. The results obtained for the mineral water samples compared well with those obtained by ICP-MS. Concerning the produced water samples, in spite of their large salinity, recoveries of 90 to 120% at the 1 μg l⁻¹ were observed.     

Quantitative extraction of organic tracer compounds from ambient particulate matter collected on polymer substrates

Organic compounds in ambient particulate matter (PM) samples are used as tracers for PM source apportionment. These PM samples are collected using high volume samplers; one such sampler is an impactor in which polyurethane foam (PUF) and polypropylene foam (PPF) are used as the substrates. The polymer substrates have the advantage of limiting particle bounce artifacts during sampling; however these substrates may contain background organic additives. A protocol of two extractions with isopropanol followed by three extractions with dichloromethane (DCM) was developed for both substrate precleaning and analyte extraction. Some residual organic contaminants were present after precleaning; expressed as concentrations in a 24-h ambient PM sample, the residual amounts were 1 g m⁻³ for plasticizers and antioxidants, and 10 ng m⁻³ for n-alkanes with carbon number lower than 26. The quantification limit for all other organic tracer compounds was ≈0.1 ng m⁻³ in a 24-h ambient PM sample. Recovery experiments were done using NIST Standard Reference Material (SRM) Urban Dust (1649a); the average recoveries for polycyclic aromatic hydrocarbons (PAHs) from PPF and PUF substrates were 117±8% and 107±11%, respectively. Replicate extractions were also done using the ambient samples collected in Nogales, Arizona. The relative differences between repeat analyses were less than 10% for 47 organic tracer compounds quantified. After the first extraction of ambient samples, less than 7% of organic tracer compounds remained in the extracted substrates. This method can be used to quantify a suite of semi- and non-polar organic tracer compounds suitable for source apportionment studies in 24-h ambient PM samples.     

Determination of Hg from Cu concentrates by X-ray fluorescence through preconcentration on polyurethane foam

A methodology was developed for the separation and determination of microamounts of mercury from copper concentrate samples by wavelength dispersive X-ray fluorescence (WDXRF) after solid-phase extraction of mercury from iodide medium using polyurethane foam (PUF). The best sorption conditions for the Hg-KI-PUF system were settled using X-ray fluorescence technique after collection of ground PUF on a filter paper by vacuum filtration and direct measurement of the intensity signal of the sorbed mercury on PUF. The main parameters of sorption such as iodide concentration, pH, shaking time and sample dilution effect were studied. The system shows rapid kinetic sorption and maximum X-ray intensity signal was achieved after shaking for 2 min a 0.01 mol l⁻¹ iodide solution containing microamounts of mercury in the pH range from 1.0 to 9.0. Effective sorption up to a volume of 0.9 l allows preconcentration of mercury. A linear fit up to 50 μg mercury was obtained by the plot of the initial mercury mass in the bulk solution (0.5 l) vs. its respective XRF intensity signal measurement on ground PUF after the sorption process. The calibration sensitivity, quantification and detection limits found were 9.09 CPS μg⁻¹, 9.0 and 2.7 μg, respectively. The sorption of many elements was also evaluated under the best conditions. High concentrations of Cu(II) and Fe(III) interfere seriously. Mercury-selective separation could be achieved using citrate or EDTA as masking agent; no interference due to copper matrix samples was observed in citrate medium. This methodology was evaluated by recovery for mercury determination in copper concentrate ore samples supplied by a mining industry and copper sulfate salts; the results were between 98% and 106%.     

The selective cleanup of complex matrices and simultaneous separation of benzo[a]pyrene by solid-phase extraction with MgO microspheres as sorbents

A new method for the selective cleanup of complex matrices and simultaneous separation of benzo[a]pyrene (BaP) was developed in this study. This method was based on solid-phase extraction (SPE) using magnesium oxide microspheres as sorbents, and it eliminated interferences from various impurities, such as lipids, sulphur, pigments, halobenzenes, polychlorodibenzo-p-dioxins and polychlorodibenzofurans. Several parameters, including the volume of rinsing and eluting solvents, the type of loading solvents and SPE sorbents, were optimized systematically. The capability for impurity removal was verified by gel permeation chromatography, gas chromatography, and liquid chromatography. Compared to commercial sorbents (silica gel, florisil and alumina), MgO microspheres exhibited excellent performance in the selective isolation of BaP and removal of impurities. The proposed method was applied to detect BaP in complex samples (sediments, soils, fish, and porcine liver). The limit of quantification (LOQ) was 1.04 ngL(-1), and the resulting regression coefficient (r(2)) was greater than 0.999 over a broad concentration range (9.5-7600 ngL(-1)). In contrast to traditional methods, the proposed method can give rise to higher recovery (85.1-100.8%) and better selectivity with simpler operation and less consumption of organic solvents (20-40 mL).     

Determination of bismuth and cadmium after solid-phase extraction with chromosorb-107 in a syringe

The determination of bismuth and cadmium by graphite furnace atomic absorption spectrometry (GFAAS) after solid-phase extraction (SPE) on Chromosorb-107 filled in a syringe was described. To retain the analytes, the sample solution treated with and without ammonium pyrolidine dithiocarbamate (APDC) was drawn into the syringe filled with Chromosorb-107 and discharged back manually. Bismuth and cadmium were quantitatively sorbed at pH ≥ 6 irrespective of whether the analyte was complexed with APDC prior to passing through the Chromosorb-107. Analyte elements sorbed on the resin were quantitatively eluted with 3.0 M of HNO₃ again drawing and discharging the eluent into the syringe and ejected it back. Optimum flow rates of sample or eluent for sorption and elution processes were 20 ml min⁻¹ for drawing and 20 ml min⁻¹ for discharging in all cases. Bismuth and cadmium were analyzed by graphite furnace atomic absorption spectrometry. The elements could be concentrated by drawing and discharging several portions of sample successively but eluting only one time. The validity of the proposed method was checked with standard reference materials (NIST SRM 1515 Apple-Leaves, CWW-TM-E Waste Water and CRM-SW Sea Water). The analyte elements were quantitatively (>95%) recovered from different matrices irrespective of treated samples with APDC. Detection limits (δ) were 0.8 and 1.2 μg l⁻¹ for Bi and Cd, respectively. The method can be characterized with fastness, simplicity, quantitative recovery and high reproducibility.     

Chemical enrichment and separation of uranyl ions in aqueous media using novel polyurethane foam chemically grafted with different basic dyestuff sorbents

The new type of the grafted polyurethane foam sorbents were prepared by coupling polyether polyol, toluene diisocyanate and basic dyestuff (Methylene blue, Rhodamine B and Brilliant green). The Me.B-PUF, Rh.B-PUF and Br.G-PUF were characterized using UV/vis, IR and TGA. The adsorption properties and chromatographic behaviour of these new adsorbents for preconcentration and separation of uranium(VI) ions at low concentrations from aqueous thiocyanate media were investigated by a batch process. The maximum sorption of U(VI) was in the pH ranges 1-4. The kinetics of sorption of the U(VI) by the Grafted-PUF were found to be fast with half life of sorption (t_1/2) in 2.43 min. The average sorption capacity of different sorbents 0.124 meq g⁻¹ for uranyl ions, enrichment factors ≈40 and the recovery 98-100% were achieved (R.S.D. ≈ 0.73%). The basic dyestuff Grafted-PUF could be used many times without decreasing their capacities significantly. The value of the Gibbs free energy (ΔG) for the sorbents is −7.3 kJ mol⁻¹, which reflects the spontaneous nature of sorption process. The sorption mechanism of the metal ion onto Grafted-PUF was also discussed.     

Luminescence determination of europium microquantities after its preconcentration on polyurethane foam

Sorption of the mixed-ligand complexes of europium(III) with thenoyltrifluoroacetone (TTA) and 1,10-phenanthroline (Phen) on polyurethane foam (PUF) has been studied by a luminescence method. The optimum conditions of sorption have been found. The sorbate composition on PUF has been determined (the Eu:TTA:Phen ratio was 1:3:1). Luminescence spectra of the europium complexes in solution and on PUF at 77 K have been investigated. It was concluded that the character of the Eu³⁺ coordination both in solution and on the sorbent is the same. Stability constants for the complexes in solution (lg K = 8.4) and on the sorbent (lg K = 5.5) have been calculated. The decrease of the stability of the complex on PUF is explained by the deformation of the complex molecule in the sorbent phase. Sorption coefficients for europium (245) and scandium (2.35) and the coefficient of selectivity for europium in Sc₂O₃ (102.3) have been determined. A method for the sorption-luminescence determination of europium in Sc₂O₃ with a lower limit of contents determined of 1 × 10⁻⁶⁰% has been developed.     

Sequential solid-phase extraction with cyanopropyl bonded-phase cartridges for trace enrichment of PCBs and chlorinated pesticides from water samples

Summary Gas chromatography of polychlorinated biphenyls and chlorinated pesticides in water samples has been performed after adsorption from a 50–250 mL sample on to a cartridge containing 100 mg cyanopropyl-bonded porous silica. The PCBs are desorbed with 500 μL ethyl acetate, which is concentrated and analysed by gas chromatography with electron-capture detection (GC-ECD). The average recovery of 1 ppb PCB congeners at from distilled water and from Marta river water is ≥95% (standard deviation ≤2.5). The average recovery of 20 ppb Aroclor 1260 from Marta river water was ≥91% (standard deviation ≤3.5). In the separation of the PCBs from the chlorinated pesticides only aldrin, heptachlor and 4,4′-DDD are adsorbed with the PCBs by the CN Sep-Pak cartridge. The method proposed is rapid, simple and reproducible.     

Synthesis of Zn(II) ion-imprinted solid-phase extraction material and its analytical application

Zn(II) ion-imprinted polymer materials used for solid-phase extraction (SPE) column were prepared by the copolymerization of 8-acryloyloxyquinoline (8-AOQ) monomer and a crosslinker ethylene glycol dimethacrylate (EGDMA) in the presence of 2,2′-azobisisobutyronitrile (AIBN) as an initiator. After removing Zn(II) ion from the polymer, molecularly imprinted polymers (MIPs) capable of selectively rebinding Zn(II) ion were obtained. The maximum adsorption capacity of Zn(II) on MIPs beads was about 3.9 mg g⁻¹. The effect of pH and flow rate for quantitative enrichment was also investigated. The Zn(II)-imprinted microbeads have a greater affinity for Zn(II) with respect to Cu(II), Co(II) and Ni(II) ions. A detection limit of 0.65 μg L⁻¹(3σ) and a relative standard deviation (R.S.D., n = 7) of 2.9% were obtained. The MIPs-SPE preconcentration procedure showed a linear calibration curve within concentration range from 0.65 to 130 μg L⁻¹. Zn(II) ion-imprinted beads enabled the selective extraction of zinc ions from a complex matrix, and after 20 times of adsorption and desorption cycle, the recovery of adsorption capacity of Zn(II) on MIPs beads was only decreased 3.2%. The results suggested that these MIPs can be used several times without considerable loss of adsorption capacity.     

Improving chemical recycling rate by reclaiming polyurethane elastomer from polyurethane foam

Flexible polyurethane foam was decomposed into a polyol mixture by an extruder with diethanolamine (DEA) as a decomposing agent. The resulting decomposed product could be used as an alternative virgin polyol in reclaiming polyurethane. In the case of reclaiming elastomer by using the decomposed product without any purification, virgin polyol could be alternated by the decomposed product up to 80%. It is a great improvement compared with the reclamation to foam, whose percentage was maximum 5%. Furthermore, the percentage could be improved up to 100% by purifying the decomposed product. We have found that physical properties of reclaimed polyurethane elastomer, such as tensile strength, hardness, and elongation, can be regulated by the ratio of unrefined/refined polyol. Whereas the tensile strength and the hardness increased as the content increased, the elongation decreased.