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Separation of Cr(III) and Cr(VI) using melamine-formaldehyde resin and determination of both species in water by FAAS

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Abstract

A method is described for the determination of Cr(VI) and total chromium by FAAS. Cr(VI) is separated from Cr(III) by adsorption on melamine-formaldehyde resin. After elution of Cr(VI) with 0.1 mol/l NaAc solution, it is analysed by FAAS. Total chromium is determined by FAAS after conversion of Cr(III) to Cr(VI) by oxidation with hydrogen peroxide, total Cr(VI) is concentrated as above. If the total concentration of chromium is sufficient, the determination can be directly made by FAAS. Cr(III) can then be calculated by subtracting Cr(VI) from the total Cr. This method was successfully applied to the determination of chromium in lake water.

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... Cr(VI) can easily penetrate the cell wall and exert its noxious influence in the cell itself, being also a source of various cancer diseases [3,4]. One of the routes of Cr incorporation into the human body is by ingestion [5,6]. Several analytical methods have been developed in order to separate and determine Cr(III) and Cr(VI) species in water samples [4,5]. ...
... One of the routes of Cr incorporation into the human body is by ingestion [5,6]. Several analytical methods have been developed in order to separate and determine Cr(III) and Cr(VI) species in water samples [4,5]. Various preconcentration procedures for the determination of chromium have been reported [6][7][8][9][10][12][13][14][15][16], including, among others, chelation, precipitation, co-precipitation, liquid-liquid extraction and ion-exchange. ...
... Among these methods, adsorption is highly effective and economical. Many adsorbents such as various activated carbon123456781011121314, agricultural waste including chitosan, orange peel and various hell, barley straw and grape bagasse [15]; industrial products including lignin, waste slurry, silica gel [16,17], polymeric ion exchange resins [18] and polymeric chelating resins19202122232425; natural materials including zeolites, clay and lignite, [16,26] have been used for the heavy metals removal. Among these materials, the low-cost adsorbents such as agricultural waste, industrial waste slurry and natural materials are unquestionable interesting compared to expensive commercial activated carbon due to higher the quality. ...
... Among these materials, the low-cost adsorbents such as agricultural waste, industrial waste slurry and natural materials are unquestionable interesting compared to expensive commercial activated carbon due to higher the quality. While polymeric chelating resins such as chemically modified melamine chelate resins with functional groups of sulfur and nitrogen donor atoms are very efficient for heavy removal of Fe(II), Fe(III), Cr(III), Cr(VI), Cu(II), Ag(I) and Ni(II) with a high selectivity1920212223242527,28]. The importance of chelating resins are usually greater than carbonaceous adsorbents with good selectivity to metal ions, make them very attractive candidates for heavy metal removal, but the expensive costs at capital and operation limit the application in industrial scale. ...
Article
Tetraoxalyl ethylenediamine melamine chelate resin grafted-coconut active charcoal (MFT/AC) was fabricated for Ni(II), Pb(II) and Cd(II) removal using a convenient pressure relief-dipping-ultrasonic synthesis method firstly. Under the aid of vacuum pressure relief, chemicals could be quickly implanted the intrinsic porous of AC in aqueous solution, the processes involved three steps, ethylenediamine was modified at AC, tetraoxalyl ethylenediamine was grafted at the amine function, then melamine, formaldehyde and tetraoxalyl ethylenediamine could be polymerized at AC in suit to form MFT/AC. The present materials were carefully examined by fourier transform infrared spectroscopy, field emission scanning electron microscope and X-ray photoelectron spectroscopy. MFT/AC showed excellent uptake effects for Ni(II), Pb(II) and Cd(II) removal with a pseudo-second order model. The Langmuir, Freundlich, Temkin and Dubinin–Radushkevich models well described the equilibrium isotherm. Thermodynamic parameters showed that adsorptions were feasible, spontaneous and endothermic; these suggested that both electrostatic adsorption and chemisorption were involved. The results indicated that MFT/AC could well be used as a high performance sorbent for the heavy metal ions removal from aqueous solution with a list of Ni(II) > Pb(II) > Cd(II).
... 24% of all pretreatments employed for the speciation analysis of chromium [3]. The sorption of Cr(VI) has been achieved using column filled with melamine-formaldehyde [14], melamine-urea-formaldehyde [15], sodium dodecyl sulfate-coated alumina [16], C18-bonded silica reversed-phase sorbent with DDC [17] and Amberlite XAD-2010 [18]. On the other hand, Cr(III) may be sorbed selectively using polyaminophosphonic acid [19], quinolin-8-ol or imminodiacetate [20] and quinolin-8-ol complexed macroporous resin [21]. ...
... 2-Naphthol-3,6-disulfonic acid [22] and azophenylcarboxylate [23] functionalized polystyrene-divinylbenzene copolymer resins were reported to sorb Cr(III) and (IV) at different pH. Each method has many advantages but in general the time length of preparation, the lower sorption capacity and the use of expensive organic reagents [14][15][16][17][18][19][20][21][22] are the common disadvantages. The use of modified ion-exchange resins in separation and/or preconcentration solved these difficulties, but suffers from the presence of electrolytes [23]. ...
Article
Trivalent and hexavalent chromium have been successfully separated and estimated from different solutions using 1-(3,4-dihydroxybenzaldehyde)-2-acetylpyridiniumchloride hydrazone (DAPCH) loaded on Duolite C20 in batch and column modes. The obtained modified resin [DAPCH-Duolite C20] was identified by C, H and N analyses and infrared spectra. The presence of multi-active chelating sites gives the ability for DAPCH to bind more chromium, Cr(III) by forming stable complex and chromate by forming ion pair molecule [H(2)DAPCH-Duolite C20](2+)[Cr(2)O(7)](2-) (H(2)DAPCH-Duolite C20 is the protonated form in acidic medium). The extraction isotherms were measured at different pH. The pH was found to be the backbone for the separation procedure in which the Cr(VI) and Cr(III) ions are sorbed selectively from aqueous solution at pH 2 and 6, respectively. The sorbed ions can be eluted using different concentrations of HCl. The saturation sorption capacity (41.6 and 20.05 mg g(-1)), the preconcentration factor (150 and 200) and the detection limit (13.3 and 10.0 ppb) were calculated for Cr(III) and (VI). The loaded resin can be regenerated for at least 50 cycles. The utility of the modified resin was tested in aqueous samples and shows R.S.D. value of <4% reflecting its accuracy and reproducibility.
... Various methods are being effectively used for the removal of metal ions such as coprecipitation (Rao et al. 2005), solvent extraction (Subramanian 1988), and electrochemical (Demirata et al. 1996;Li et al. 2005). These metal ions were removed from wastewater having inherent advantages and limitations (Tuzen et al. 2005). ...
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Selective and rapid determination of procedure for Cd²⁺ and Pb²⁺ samples using MWCNT surfaces can be modified by loading ligands such as D2EHPA and Cyanex 272 which is described. The adsorbent was modified with D2EHPA and Cyanex 272. Effect of pH, amount of adsorbent, contact time for adsorption, and the optimum eluent for the quantitative recovery of Cd²⁺ and Pb²⁺ were investigated and the subsequent determination by FAAS. The adsorption was found to be mainly due to the chemical interactions between the metal ions and functional groups –COO⁻ and –OH which were characterized by FT-IR. The adsorption of metal occurs at pH 4.5 with 500 mg of MWCNTs. The enrichment factor was 40 and 30. The detection limit was 0.03 and 0.05 μg L⁻¹. The quantitative recovery of metal ion used 1 mol L⁻¹ HNO3. The thermodynamic parameter of Langmuir and Freundlich adsorption isotherm revealed that the adsorption of free energy (ΔG) was spontaneous and the monolayer adsorption of Cd²⁺ and Pb²⁺ was mainly on the surfaces. The adsorbent performance of R² in the range of 0.93–0.99 and also the identified adsorption efficiency of Cd²⁺ and Pb²⁺ are linear or non-linear curves respectively. The proposed method was applied to heavy metals from environmental samples. Graphical Abstract
... Many investigations have been carried out to improve selective retention with different partitioning mechanisms using different solid sorbents, such as ion exchangers, chelating resins or immobilized functional group on solid sorbent materials, alumina and TiO 2 (Baffi et al., 1992;Sule et al., 1996;Cespon-Romero et al., 1996;Sperling et al., 1992a;Manzoori et al., 1996;Marqués et al., 2001;Vassileva et al., 2000;Yu et al., 2001). Cr(VI) is retained by using columns with melamine-formaldehyde, C18 bonded silica reversed phase sorbent with diethyldithiocarbamate as complexing agent, zirconium (IV) oxide modified silica, Amberlite and several other anion-exchange resins (Demirata et al., 1996;Sperling et al., 1992b;Li et al., 2002;Dyg et al., 1994;Naranjit et al., 1979). Retention of Cr(III) has been carried out using chelating resins and cation-exchange resins such as Chelex 100 or Lewatit TP207 (Cespon-Romero et al., 1996;Pasullean et al., 1995;Baffi et al., 1992). ...
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Chromium speciation in the presence of organic chromium(III) complexes was investigated using solid-phase extraction. The adsorptions of Cr(VI) and Cr(III) on alumina and pumice powder were studied. Maximum sorption of Cr(VI) was obtained by alumina (90.22%), while Cr(III) was highly adsorbed onto pumice powder (86.65%). This result shows that pumice may be a new and promising adsorbent for Cr(III). The experimental equilibrium data for Cr(VI) adsorption onto alumina and Cr(III) sorption onto pumice were analysed using Langmuir and Freundlich isotherms. The separation and adsorption of Cr(VI), Cr(III) and five organic chromium(III) complexes onto pumice and alumina at different pH values were evaluated. Ethylenediaminetetraacetate (EDTA), oxalate, citrate, glycine, alanine and 8-hydroxyqinoline were used as ligands. Sorption of alanine and ethylenediaminetetraacetate complexes was higher onto alumina than pumice at pH>3. The enhancement of adsorption of chromium(III) complexes onto pumice was achieved by surface modification of pumice using a surfactant, namely hexadecyltrimethylammoniumbromür (HDTMA). The presence of surfactant enhanced the adsorption of Cr(III) citrate, oxalate, glycine and 8-hydroxyquinoline complexes onto pumice. However, the adsorption of EDTA and alanine complexes decreased, with ratio of 13.40% and 4.00% respectively. Here we demonstrate that chromium speciation methods depending on adsorption onto various adsorbents including alumina may lead erroneous results. Analytical measurements were performed by flame AAS, data were obtained by standard addition method.
... Melamineformaldehyde (MF) resins were not widely studied for metal ions removal purpose. Few publications were reported in this area of application, for example MF resins were used for the separation and preconcentration of Cr(VI)/Cr(III) (Dixon et al., 1947;Demirata, 1996) and Fe(III)/Fe(II) from natural water (Filik et al., 1997). MF-diethylenetriaminepentaacetic acid resin was prepared as a new adsorbent for removing heavy metals from wastewater effluents (Baraka et al., 2007). ...
Article
Two modified melamine resins has been prepared and investigated, the modification process took place through the treatment with thiourea to produce R1 or tetraoxalyl ethylenediamine to produce R2. The adsorption behavior of the obtained resins towards Ag(I) and Cu(II) from their aqueous solutions has been studied using batch method. The obtained resins were tested for selective separation between Cu(II) and Ag(I) form their binary mixtures. Resin R1 showed high selectivity towards Ag(I) from Cu(II) solution, while R2 gave a promising results for the selective separation of Cu(II) from Ag(I) solution. Both kinetic and thermodynamic parameters of the adsorption process were obtained. Thermodynamic data indicated that the adsorption process is endothermic spontaneous reaction. Kinetic analysis showed that the adsorption of Ag(I) on R1 is perfectly fit pseudo-first order model, while the adsorption of Cu(II) on R2 is perfectly fit pseudo-second order one. The interaction mechanism between metal ion and active sites has been interpreted as chelation. Durability of resins was estimated from column studies. These parameters indicated that the prepared resins have a good efficiency for repeated use.
... Hence, the speciation of chromium has special importance in several fields of life. Up to now, several methods for speciation of chromium(VI ) and chromium(III) have been investigated and published in different journals such as catalytic cathodic stripping voltammetry (CCSV) [5], X-ray absorption near-edge structure (XANES) spectroscopy [6] , the separation or preconcentration methods using capillary electrophoresis [7], sorption [8, 9], liquid-liquid extraction [10, 11] , extraction using ion-pair formation [12, 13], coprecipitation [14], extraction using supported liquid membranes (SLM) [15], solid phase extraction [16, 17, 19], ion exchange [18], cloud point extraction [20] followed by instrumental analysis such as UV-Vis [7, 13] , energy dispersive X-ray fluorescence spec- trometry [9], GFAAS [10, 11,151617, FAAS [14, 19], ion chromatography [18] , and high-performance liquid chromatography (HPLC) [20]. The flow injection methods with conjunction by several detection techniques were also applied for the chromium speciation [3, 4,2122232425262728. ...
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In this approach, a pneumatic flow injection-tandem spectrometer system, without a delivery pump, has been developed to study chromium speciation. In this system, suction force of pneumatic nebulizer of a flame atomic absorption spectrometer has been used for solution delivery through the manifold. Cr(VI) and total Cr concentrations were determined using UV-Vis and FAAS spectrometers, respectively. The Cr(III) was determined by difference. The calibration curves were linear up to 10 mug mL-1 and 20 mug mL-1 for Cr(VI) and total Cr with detection limit of 0.12 mug mL-1 and 0.07 mug mL-1 for Cr(VI) and Cr(III), respectively. The midrange precision and accuracy are less than 1.98% and +/- 2.50% for two species, respectively, at a sampling rate of 100 h-1. This system was applied for the determination of the chromium species in spiked and natural waters as well as industrial waters.
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Magnetic melamine-formaldehyde resin was prepared via water-in-oil emulsification approach by entrapping Fe3O4 magnetic nanoparticles as the core. The preparation of the magnetic resin was optimized by investigating the amount of polyethylene glycol 20000 and Fe3O4 nanoparticles, the concentration of the catalyst (hydrochloric acid), as well as the mechanical stirring rate. The prepared material was characteristic of excellent anion-exchange capacity, good water wettability, and proper magnetism. Its application was demonstrated by magnetic solid-phase extraction of nonsteroidal anti-inflammatory drugs coupled to high performance liquid chromatography-UV analysis. Under the optimal conditions, the proposed method showed broad linear range of 1–5000 ng mL–1 of milk and urine samples, satisfactory reproducibility with intra-day and inter-day relative standard deviations less than 12.4% and 9.7%, respectively, and low limits of detection of 0.2 ng mL–1 for the studied nonsteroidal anti-inflammatory drugs. The developed method was successfully used for the determination of the nonsteroidal anti-inflammatory drugs in spiked urine and milk samples. The magnetic melamine-formaldehyde resin was promising for the sample pretreatment of acidic analytes via anion-exchange interaction with convenient operation from complex sample matrix. Graphical abstractMagnetic solid-phase extraction based on melamine-formaldehyde resin
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A rapid, sensitive and accurate method for the separation, preconcentration and determination of Cr(III) and Cr(VI) in water samples is described. Chromium species can be separated by biosorption on Saccharomyces cerevisiae immobilized on sepiolite and determined by flame atomic absorption spectrometry (FAAS). The optimum conditions for separation and preconcentration (pH, bed height, flow rate and volume of sample solution) were evaluated. Recovery of the chromium was 96.3+/-0.2% at 95% confidence level. The breakthrough capacity of the adsorbent was found as 228 mumol g(-1) for Cr(III). The proposed method was applied successfully to the determination of Cr(III) and Cr(VI) in spiked and river water samples.
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A rapid, sensitive and accurate atomic absorption method for Cr(III) and Cr(VI) ions was developed based on the cloud-point extraction (CPE) technique. Cr(III) reacts with a new Schiff's base ligand to form the hydrophobic complex, which is subsequently entrapped in the surfactant micelles. The Cr(VI) assay is based on its reduction to Cr(III) by the addition of concentrated H2SO4 and ethanol to the sample solution. The condensed surfactant phase containing the metal chelates is introduced into an atomic absorption spectrometer. The relative standard deviations were 2.1% for both species and the limits of detection were around 0.17 microg l(-1).
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The synthesis of a new stable chelating resin from the polystyrene divinylbenzene copolymer is reported. The polystyrene is first functionalized with a phenolic group and then allowed to couple with diazotized anthranilic acid through the --N==N-- bond. The resulting polymer containing azophenolcarboxylate with an ONO chelating environment has been characterized by elemental analysis, hydrogen ion capacity, and water regain value. Its stability towards thermal and different chemical environments has been evaluated. The sorption capacity of the chelating resin for Cr(III) and Cr(VI) as a function of pH has been studied. The interesting point is that chromium(III) is selectively retained at ca. pH 5.0 and chromium(VI) at ca. pH 2.0. When packed in a column, the new material is able to separate Cr(III) from Cr(VI). Five replicate determinations of 10 microg Cr(III) and 10 microg Cr(VI) present in 100 mL solution gave recoveries of 96.9+/-2.9% (for Cr(III)) and 96.2+/-2.1% (for Cr(VI)) at the 95% confidence level. Calibration graph was linear over the concentration range of 0-250 microg L(-1) of chromium species with correlation coefficient (R) of 0.99994. The detection limits based on 3sigma criterion were determined to be 0.6 microg L(-1) for Cr(III) and 0.9 microg L(-1) for Cr(VI). The developed method was successfully used for the speciation of chromium in wastewater.
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As a result of recent studies, a clearer understanding of the nutritional requirements for chromium, and of the levels of chromium in the serum and urine of normal subjects is available. Recent developments in technology have provided analytical techniques with sufficient sensitivity for both these determinations, although serum chromium at the lowest levels is still a difficult determination for routine hospital laboratories without specialized facilities. Recent developments in analytical techniques are reviewed in the light of clinical requirements both now and in the foreseeable future.
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Disposable commercial C18 mini-cartridges are treated with tributyltin chloride (TBTCl) and used for selective pre-concentration of CrVI from aqueous solutions. The accumulated CrVI-TBTCl adduct is eluted with 5 ml of methanol and measured using electrothermal atomic absorption spectrometry. Pre-concentration factors of 100-fold are readily achieved for 0.100 ng ml–1 samples of CrVI with an average recovery of 98 ± 8%.
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A two-step method for the determination of CrVI and CrIII in natural waters was developed. The method is based on the variation of the coprecipitation yields with Pb(PDC)2(PDC = pyrrolidine dithiocarbamate) as a function of pH. By using two different pH values both species can be determined separately. Firstly, CrVI was coprecipitated at pH 4.0 and then CrIII was separated at pH 9. Total chromium was determined by reduction of CrVI followed by coprecipitation at pH 9. The validity of the procedure was checked with the National Institute of Standards and Technology Standard Reference Material 1643b Trace Elements in Water and the result was found to be in good agreement with the certified value.
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The polarographic behaviour at the dme of chromate and dichromate is investigated within the concentration limits 0·2 – 2·0 mM. In acid solutions, 2 waves are observed representing the reduction to Cr(III) and Cr(II). In neutral unbuffered solutions, 4 waves are obtained for chromate, whereas dichromate gives 5 waves. In NaOH, 3 or 1 waves are observed at lower and higher alkalinities respectively. In buffer solutions, the shape of the polarograms depends essentially on the pH. The nature of the waves is discussed. Some media were found to be suitable for the polarographic determination of Cr(VI).RésuméEtude du comportement polarographique à l'électrode de mercure gouttante, du chromate et du bichromate dans les limites de concentrations 0·2 – 2,0 mM. En solution acide, on observe deux vagues représentant la réduction de Cr(III) et Cr(II). En solutions neutres non tamponnées, on obtient 4 vagues pour le chromate, tandis que le bichromate en donne 5. Dans NaOH, on observe trois ou une vagues pour des alcalinités respectivement inférieure et supérieure. En solutions tamponnées, la forme des polarogrammes dépend essentiellement du pH. La nature des vagues est discutée. Quelques milieux sont sélectionnés pour la détermination polarographique de Cr(VI).ZusammenfassungMan untersucht das polarographische Verhalten von Chromat und Bichromat mittels einer Quecksilber-Tropfelektrode im Konzentrationsbereich 0,2 – 2,0 mM. In sauren Lösungen sind zwei Wellen zu beobachten, welche den beiden Reduktionsstufen Cr(VI)Cr(III) und CR(III)Cr(II) entsprechen. In neutralen, nicht gepufferten Lösungen treten beim Chromat vier, beim Bichromat fünf Stufen auf. Enthalten die Lösungen NaOH, so ergeben sich sowohl bei starker wie auch bei schwacher Alkalinität drei Stufen. In gepufferten Lösungen hängt die Form der Polarogramme vom pH ab. Man diskutiert den Verlauf der Kurven und findet, dass sich einige der verwendeten Lösungssysteme fäur die polarographische Bestimmung von Cr(VI) eignen.
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Trace amounts of Cr(VI) have been enriched from aqueous solutions by exchange of Cr(VI) on melamine-formaldehyde resin. The exchange capacity increased at lower pH-values. The material was used to preconcentrate Cr(VI) very efficiently from 0.1 µg ml-1 solutions of chromate. After the Cr(VI) adsorbed on the column is eluted, it is analysed by atomic absorption spectroscopy and almost 100% recovery was achieved in every instance. The effect of other anions was examined and it was observed that the adsorption of Cr(VI) was not significantly affected by the presence of other anions.
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The comparative acute toxicity of potassium chromate and dichromate salts to six aquatic species including both freshwater and marine forms was investigated. A thermodynamic equilibrium model was developed to aid in interpreting toxicity data with respect to hexavalent chromium speciation. Although parallel acute toxicity tests conducted with both salts yielded similar LC50 values, toxicity differences tended to become more pronounced as the sensitivity of the test species to the chemical decreased. Observed changes in pH and predicted changes in chromium speciation that occurred between the two salts in tests with less sensitive species were postulated to explain these findings. The implication of the aqueous chromium species to the relative toxicity of the hexavalent chromium are discussed. If hexavalent chromium is widely adopted as a standard reference toxicant for aquatic toxicity testing then the chromate salt should be used since it does not appreciably alter the initial pH of the dilution water and subsequent speciation to the extent that would be expected if the dichromate salt was employed. Standardization of the source of hexavalent chromium used in reference tests will facilitate intralaboratory comparison of toxicity data.
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A method for the determination of chromium(III) and (VI) species has been studied and applied to mineral water samples. The chromium(III) was chelated with 0.1 mol/l 8-hydroxyquinoline in methyl alcohol, extracted in isobutyl methyl ketone and determined by ETA-AAS. The effects of the pH, extraction and heating time and amounts of the reagents required for the extraction were studied. A method for the determination of total chromium was optimized too, and the chromium(VI) can be calculated. The precision, sensibility, accuracy, graphite furnace program and interferences for both methods were also investigated.
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Thermodynamic considerations suggest that the ions Cr(H2O)4(OH)2+ and CrO42− are the major forms of trivalent and hexavalent chromium in sea water. Cr (VI) should predominate in water in solubility equilibrium with the atmosphere but analysis shows that theoretically unstable Cr (III) species are often dominant.
Chromium in the natural and human environment
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Chromium in the natural and 10. Demirata B (1992)
  • J O Nriagu
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