Sorption of chromium(III) and chromium(VI) on lead sulfide

The sorption of chromium(III) and chromium(VI) on lead sulfide has been investigated in dependence on pH, time of sorption and the concentrations of sorbate and sorbent. The mechanisms of the sorption of Cr³⁺ and CrO ₄ ^2– traces on lead sulfide are discussed; a difference between CrO ₄ ^2– sorption on PbS and -Fe₂O₃ has been found. Sulfates and molybdates affect the removal of chromates from aqueous solutions. Lead sulfide carrier prepared in this work was also used for the preconcentration of chromium(III) and chromium(VI) from tap water.     

Sorption of chromium(VI) on ion-exchange resins and sorbents

Sorption of Cr(VI) on AV-17 and EDE-10P anion exchangers, KU-2 and KB-4 cation exchangers, activated charcoal, and foamed graphite (STRG) is studied.     

Sorption of hydrolytic products of iron(III), aluminium(III) and chromium(III) on the silica column and its analytical use

Summary The influence of pH upon the sorption of hydrolytic products of Fe³⁺, Al³⁺, and Cr³⁺ on silica was studied under kinetic conditions. The capacity of the silica column and the influence of ionic strength upon the sorption were investigated. The results obtained are utilized for the pre-concentration of trace amounts of Al³⁺, and Fe³⁺ and their separation from an excess of several other metals (e.g. Cr, Cu, Zn, Co) at pH 4.5. The separation of Al³⁺ traces from an excess of Fe³⁺ was achieved by reduction and masking of Fe with thioglycollic acid.

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Zusammenfassung Es wurde eine Untersuchung durchgeführt über die Sorption von Hydrolyseprodukten von Fe(III), Al(III) und Cr(III) an Silicasäulen und die Abhängigkeit vom pH-Wert, von der Kapazität der Säule und der Konzentration an Fremdsalzen (KCl, KNO₃) wurde geprüft. Analytische Anwendungsmöglichkeiten ergaben sich in der Anreicherung von Al³⁺- und Fe³⁺-Spuren und ihrer Trennung von anderen Elementen (z.B. Cr, Cu, Zn, Co) sowie in der Trennung von Al³⁺-Spuren von überschüssigem Fe³⁺, wobei letzteres mit Hilfe von Thioglykolsäure reduziert und maskiert wurde.

     

Sorption of small amounts of europium(III) on iron(III) hydroxide and oxide

The sorption of small amounts of europium(III) on iron(III) hydroxide and oxide has been studied as a function of pH. The mechanism of sorption is discussed. Optimum conditions have been found for the preconcentration of small or trace amounts of europium(III) by iron(III) hydroxide and oxide. The influence of complexing agents (EDTA, oxalate, tartrate and 5-sulfosalicylic acid) on the sorption of small amounts of europium(III) on iron(III) oxide has also been studied.     

Novel chromium(III)/(VI) adducts of XPS-determined mixed valence,from electroreduced chromium(VI)

Summary Conditions of chromium(VI) and acidity have been found at which a novel brown deposit from electroreduction. Its 11 chromium(III):chromium(VI) composition, and the 21 ratio of the alkali-leached product, were established by XPS. The composition bounds for electrodeposition of the 11 solid and the competing insulative chromium(III) film were established electrochemically. Earlier reported chromium(III) and chromium(VI) solid or gels, some deposited from alkali, differ in colour and composition properties.     

Ultrafast concentration and speciation of chromium(III) and (VI)

There is an increasing need to know the concentrations of chromium(III) and (VI) separately rather than only the total chromium content. A method is described for accomplishing this very quickly using only low-cost, portable equipment. Two small, resin-loaded extraction disks are placed one on top of the other in a plastic holder. Then a syringe containing the aqueous sample is attached to the holder and the sample is pushed through the disks. In a matter of seconds, all of the chromium(VI) is retained on the top anion-exchange disk and chromium(III) is extracted by the second cation-exchange disk. The concentrations on each disk are several hundredfold higher than they were in the original sample. The amounts of chromium(III) and (VI) extracted are measured directly on the surface of the respective disks by diffuse reflectance spectroscopy (DRS). Despite the low molar absorptivity of chromium(III) in aqueous solution, the concentration on the upper most layer on the extraction disk is high enough to permit the determination of chromium(III) in samples at the low mg/L range. Chromium(VI) can also be determined at low to sub-mg/L concentrations. A study of the cation-exchange disks was undertaken to compare the performance characteristics of disks containing sulfonated resins and those with iminodiacetate functionality. In addition, data are presented to show the effects of heating the iminodiacetate disks after the initial extraction. The disks were heated in hot water for 15-30 min to complete the slow complexation reaction on the surface.     

Spectrophotometric determination of chromium(III, VI) by use of chromium(III, VI)-Chrome AzurolS-cetylpyridinium bromide-hydroxylamine hydrochloride-zinc(II) system

This paper shows that the sensitivity of the Cr(III, VI)—Chrome Azurol S (CAS)-cetylpyridinium bromide (CPB)—hydroxylamine hydrochloride system can be increased and the wavelength of maximum absorption slightly shifted by addition of zinc(II) and that the analytical data are practically identical for both Cr(III) and Cr(VI), indicating that under the conditions used both initial oxidation states of chromium yield the same final oxidation state, Cr(III). On the basis of the Cr(III, VI)—CAS—CPB—NH₂OH·HCl—Zn systems a new, highly sensitive and selective method for spectrophotometric determination of microamounts of Cr(III, VI) has been developed, with molar absorptivity of 1.27 × 10⁵ 1. mole⁻¹ . cm⁻¹ for the complex at 620 nm and linear calibration up to 0.4 μg/ml chromium. Various foreign ions do not interfere. The method can be applied to direct determination of chromium in steels.     

Speciation studies by capillary electrophoresis- Simultaneous determination of chromium(III) and chromium(VI)

A method for the simultaneous determination of chromium(III) and chromium(VI) by capillary electrophoresis (CE) has been developed. The chromium(III) has been chelated with 1,2-cyclohexanediaminetetraacetic acid (CDTA) in order to impart a negative charge and similar mobility to both the chromium(III) and the chromium(VI) species. The effects of the amount of the reagent, pH and heating time required to complete the complexation have been studied. Factors affecting the CE behaviour such as the polarity of electrodes and the pH of electrophoretic buffer have been investigated. The separated species have been monitored by direct UV measurements at 214 nm. The detection limits achieved are 10 microg/l for Cr(VI) and 5 microg/l for Cr(III) and linear detector response is observed up to 100 mg/l. The procedure has been applied to the determination of both chromium species in industrial electroplating samples and its accuracy was checked by comparing the results (as total chromium) with those of atomic absorption spectrometry. No interference occurred from transition metal impurities under optimized separation conditions. The method is also shown to be feasible for determining Cr(III) as well as other metal ions capable to form complexes with CDTA (like iron(III), copper(II), zinc(II) and manganese(II)) in pharmaceutical preparations of essential trace elements.     

Speciation studies by capillary electrophoresis- Simultaneous determination of chromium(III) and chromium(VI)

A method for the simultaneous determination of chromium(III) and chromium(VI) by capillary electrophoresis (CE) has been developed. The chromium(III) has been chelated with 1,2-cyclohexanediaminetetraacetic acid (CDTA) in order to impart a negative charge and similar mobility to both the chromium(III) and the chromium(VI) species. The effects of the amount of the reagent, pH and heating time required to complete the complexation have been studied. Factors affecting the CE behaviour such as the polarity of electrodes and the pH of electrophoretic buffer have been investigated. The separated species have been monitored by direct UV measurements at 214 nm. The detection limits achieved are 10 g/l for Cr(VI) and 5 g/l for Cr(III) and linear detector response is observed up to 100 mg/l. The procedure has been applied to the determination of both chromium species in industrial electroplating samples and its accuracy was checked by comparing the results (as total chromium) with those of atomic absorption spectrometry. No interference occurred from transition metal impurities under optimized separation conditions. The method is also shown to be feasible for determining Cr(III) as well as other metal ions capable to form complexes with CDTA (like iron(III), copper(II), zinc(II) and manganese(II)) in pharmaceutical preparations of essential trace elements.     

Thermal analysis of chromium(III) and chromium(VI) systems with silica and sodium silicate

Sodium silicate, or a mixture of silica and sodium carbonate, reacts with chromium(III) oxide in the presence of oxygen to give sodium chromate, within the approximate temperature range 300–900°. Above 900° the reaction is reversed and chromium(III) oxide regenerated.

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Zusammenfassung Natriumsilikat oder eine Mischung von Siliziumdioxid mit Natriumkarbonat ergeben bei der Reaktion mit Chrom(III)oxid in Gegenwart von Luft im Temperaturbereich zwischen 300° und 900° Natriumchromat. Über 900° wird die Reaktion umgekehrt und Chrom(III)oxid zurückgebildet.

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Résumé Le silicate de sodium ou un mélange de silice et de carbonate de sodium réagissent, en présence d'oxygène, avec l'oxyde de chrome trivalent pour former le chromate de sodium, approximativement entre 300 et 900°. Au-dessus de 900°, la réaction s'inverse et l'oxyde de chrome(III) est régénéré.

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(III) , 3002900°. 900° .

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We thank Messrs. Albright and Wilson for a grant (to D. A. F.)     

Simultaneous and sequential determination of chromium(VI) and chromium(III) by unsegmented flow methods

Summary Several different configurations for simultaneous and sequential photometric speciation of Cr(VI) and Cr(III) based on the reversed flow injection analysis and completely continuous modes are proposed in this paper. The determination of these species at theg · ml^–1 level is achieved with sampling frequencies between 30 and 100 h^–1 and an r.s.d. of less than ±1% for simultaneous methods and of less than ±3% for the sequential method. The proposed methods are suitable for chromium speciation in waters. A simulation of the continuous monitoring of Cr(VI) and periodical of Cr(III) in natural and waste waters has been performed. The most frequent interferents in these types of samples have been investigated.

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Simultane und sequentielle Bestimmung von Chrom(VI) und Chrom(III) durch unsegmentierte Durchflußmethoden

Zusammenfassung Verschiedene Arten der simultanen und sequentiellen photometrischen Cr(III)- und Cr(VI)-Bestimmung nach der Technik der reversed-flow Injektionsanalyse werden beschrieben. Die relative Standardabweichung für die Bestimmung dieser Chromspezies im g/ml-Bereich bei einer Probenfrequenz von 30 bis 100 je Stunde beträgt weniger als +1% für die Simultan- und weniger als +3% für die sequentiellen Methoden. Eine simulierte kontinuerliche Überwachung von Chrom(VI) sowie eine periodische von Chrom(III) in natürlichem Wasser und Abwasser wird beschrieben. Die häufigsten Störungen werden diskutiert.

     

Neutron activation analysis for chromium(III) and (VI) in lixiviated liquid through a calcined chromium(VI) adsorbed hydrotalcite

Summary Electrophoresis followed by neutron activation analysis was utilized to determine chromium(III) and (VI) in mixed solutions. These solutions proceeded from Cr(VI) adsorbed hydrotalcites heated at 800 °C to partially immobilize Cr in the Mg-Al oxide solid solution. Immobilization was studied by Cr lixiviation with NaCl solutions through the heated hydrotalcites. The results have shown that Cr lixiviated was in the form of CrO₄^2- ions, mainly because some Cr(VI) was not completely reduced to Cr(III) during heating. Chromium lixiviated from HT-Cr sample, heated at 800 °C and γ-irradiated at 1000 kGys, was found, as well, in the form of CrO₄^2- ions. Although γ-irradiation increases Cr immobilization in the solid, it does not reduce completely all CrO₄^2- ions present in the solid and, therefore, some Cr is lixiviated through the solid in the form of CrO₄^2- ion.     

Spectroscopy of multisites chromium (III) in yttrium aluminium garnet

Cr³⁺ multisites in an yttrium aluminium garnet host have been observed. The absorption, emission and excitation spectra and decay curves have been recorded. With the help of a high-resolution dye laser, the ²E and ⁴A₂ splittings were measured.     

Retention of chromium(III) and chromium(VI) in rat tissues after different drying procedures

Losses of chromium(III) and chromium(VI) during freeze-drying and ovendrying at different temperatures from various rat tissues and feces containing the radioactive isotopes are assessed. Significant loss of chromium(III) occurs from fur samples (hair with skin) on freeze-drying. Oven-drying at 80°C does not cause losses of either form of chromium but at 105°C there are minor losses from kidney and feces samples. At 120°C, chromium(III) is lost from all samples to varying extents whereas losses of chromium(VI) are less significant.     

Sorption of chromium hydroxide sol on silica studied by radiotracing

This study was undertaken to investigate the sorption behavior of chromium hydroxide sol on silica type adsorbent in aqueous solution. Radioisotopic tracer method was used to assess data. This technique allowed sensitive kinetic and equilibrium measurements in both direction: sorption and desorption, which are strongly dependent on solution conditions, such as pH, ionic strength or the presence of complexing species. Total removal of sol particles could not be achieved, even under the most favorable experimental conditions (acidification).     

Sorption of trace concentrations of gallium(III) and iodide ions on tin(II) hydroxide

Summary The results of sorption measurements for gallium (III) and iodide ion traces onto tin(II) hydroxide from aqueous heterogeneous systems are given. Since only tagged sorbate was used (⁶⁷Ga and 1311), in the determination of sorption by radioactive tracer method, it was necessary to establish the pH interval of tin(II) hydroxide in/stability. This was done by a turbidimetric method and the pH region of instability between 3 and 9 was found.The sorption results indicate a difference in sorption ability of gallium(III) and iodide as it appears from the dependence of the amount sorbed on contact time between heterogeneous reactants (sorbentsorbate). The amounts sorbed increase with increasing contact times at higher pH values for Ga(III) but remain unaffected for iodide sorption. Thus the sorption of iodide ions seems to be restricted to the solid surface while the sorption results for gallium(III) indicate the diffusion of sorbate into sorbent as a possible parallel mechanism. Those processes could be taken as compatible with the porous-double-layer mechanism which has been proposed in literature for aqueous heterogeneous oxide systems.

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Zusammenfassung In der Arbeit werden Ergebnisse von Sorptionsmessungen für Ga³⁺- und j-Spuren an Zinn(II)-Hydroxid aus wäßrigen heterogenen Systemen berichtet. Zur analytischen Erfassung wurden radioaktives⁶⁷Ga und 131 J verwendet. Die Stabilität von Zinn(II)-Hydroxid wurde durch Trübungsmessungen untersucht. Im pH-Bereich von 3–9 ist das Zinn(II)-Hydroxid als kolloide Suspension instabil.Ga³⁺ und J^– verhalten sich bei der Adsorption unterschiedlich. Die adsorbierte Menge steigt mit zunehmender Kontaktzeit bei hohen pH-Werten von Gallium, bleibt jedoch für Jod unverändert. Die Unterschiede werden gedeutet durch die Annahme, daß Jod nur an der festen Oberfläche adsorbiert wird, während die Galliumionen auch in das Sorbens diffundieren können. Man könnte die Ergebnisse als verträglich mit einem porösen Doppelschichtmechanismus ansehen; ein solcher Mechanismus ist in der Literatur für wäßrige heterogene Oxidsysteme vorgeschlagen worden.

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With 4 figures     

Heterotri- and -tetrametallic alkoxides of chromium(III) containing aluminium(III), gallium(III) and niobium(V)

CrCl₃ · 3THF reacts with two equivalents of potassium alkoxometallates K{M(OPr ⁱ ) _x } [M = Al(A), Ga(B), x = 4; M = Nb(C), x = 6] to give heterobimetallic chloride isopropoxides [Cr{M(OPr ⁱ ) _x }₂Cl(THF)] [M = Al(A – 1), Ga(B – 1), and Nb(C – 1)], in which the replacement of the chloride with an appropriate alkoxometallate (tetraisopropoxoaluminate, tetraisopropoxogallate, or hexaisopropoxoniobate) results in the formation of novel heterotrimetallic derivatives. The 'single pot synthesis of an heterotetrametallic isopropoxide [Cr{Nb(OPr ⁱ )₆}{Al(OPr ⁱ )₄}{Ga(OPr ⁱ )₄}] (7) has been carried out by the sequential addition of (A), (B), and (C) to a benzene suspension of CrCl₃ · 3THF. Alcoholysis of [Cr{Al(OPr ⁱ )₄}₂{Nb(OPr ⁱ )₆}] (1) and [Cr{Al(OPr ⁱ )₄}₂{Ga(OPr ⁱ )₄}] (5) with t-BuOH has also been studied and the derivatives characterized by elemental analyses, molecular weight determinations, spectroscopic [Electronic, i.r., ²⁷Al-n.m.r.] and magnetic susceptibility studies.     

Effect of the anionic composition and pH on the dissolution kinetics of chromium(III) oxide and chromium(III) hydroxide oxide in acids

Based on an experimental investigation of the effects of the pH and anionic composition on the dissolution rate of chromium(III) oxide α-Cr₂O₃ and chromium(III) hydroxide oxide α-CrOOH and subsequent modeling of the process, it is demonstrated that, depending on the pH, the rate-controlling stage of the dissolution is the CrOH²⁺ or CrHSO ₄ ²⁺ sobulization.     

Determination of antimony(III) by titration with chromium(VI)

Summary There is no need for a catalyst in the potentiometric or spectrophotometric titration of antimony(III) with chromium(VI). The failure of titrations using indicators is due to slowness of the oxidized indicator-Sb(III) reaction; the indicator reaction can be catalysed by iodine. The spectrophotometric titration yields accurate results, and shows that the Sb(III)-Cr(VI) reaction is rapid. Slowness in the potentiometric titration is due to unfavourable electrode kinetics.

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Titration von Antimon(III) mit Chrom(VI)

Zusammenfassung Bei der potentiometrischen oder spektrophotometrischen Titration von Sb(III) mit Cr(VI) bedarf es keines Katalysators. Der Fehler bei Titrationen unter Verwendung eines Indikators hat seine Ursache in der langsam verlaufenden Reaktion zwischen dem oxydierten Indikator und Sb(III); die Indikator-Reaktion kann mit Jod katalysiert werden. Die spektrophotometrische Titration gibt genaue Resultate und zeigt, daß die Sb(III)-Cr(VI)-Reaktion rasch abläuft. Die Langsamkeit der potentiometrischen Titration ist durch die ungünstige Kinetik der Elektrode verursacht.