Determination of Fluoride Ions by Diffuse Reflectance Spectrometry Using Chromaticity Functions of Adsorbates of the Thorium Complex of Arsenazo I

Diffuse reflectance spectrometry in combination with chromaticity measurements was used for the determination of trace fluoride ions. The determination method was based on a decrease in the color intensity of the thorium complex of Arsenazo I. Silica gel Silochrom-120 was studied as the substrate. The linearity ranges were determined for chromaticity functions (chromaticity coordinates X, Y, and Z in the X, Y, Z system; lightness L; chromaticity coordinates A and B in the CIELAB system; color saturation S; yellowness G; hue T; whiteness W; and total color difference E); in a homogeneous system, for the sorption on silica gel and in the presence of a surfactant, the linearity ranges are 10–40, 5–20, and 2–15 g of fluoride per 25 mL of the solution, respectively. The sensitivity of the chromaticity functions as analytical signals and the measurement errors were examined. The procedure was used for the analysis of tap water and toothpaste.     

Determination of Aluminum and Beryllium by Diffuse Reflectance Spectrometry with the Use of Chromaticity Functions

Immobilized Eriochrome Cyanine R was used for the direct determination of trace aluminum and beryllium by diffuse reflectance spectrometry. Anion exchanger AV-17, silica gel Silochrom C-120, Chromaton N-Super, octadecyl silica gel, and cellulose were examined as supports. Optimal sorption conditions were found. The dependence of chromaticity functions (chromaticity coordinates, lightness, color saturation, yellowness, and whiteness) on different factors was studied. Advantages of the use of chromaticity functions rather then the diffuse reflectance coefficient were demonstrated. A method is developed for the separate determination of aluminum and beryllium using cellulose as the support; the method was used for the analysis of real samples and tested with standard samples. When solution samples of 50 and 100 mL were used, the determination limit was 0.004 g/mL for aluminum and 0.0002 g/mL for beryllium.     

Optical and Chromaticity Characteristics of Cobalt and Palladium 4-(2-Pyridylazo)resorcinates

Optical and chromaticity characteristics (diffuse reflectances, chromaticity coordinates, lightness, color saturation, yellowness, color tint, and whiteness) of cobalt and palladium complexes of 4-(2-pyridylazo)resorcinol were determined at pH 7.2–7.9 and in 1 M H₂SO₄. The conditions of the separate determination of cobalt and palladium in the presence of each other by changing the order of the addition of reagent and using bifunctional chromaticity measurements and two-wavelength spectrophotometry are specified. The advantages of the chromaticity measurements are demonstrated. The proposed procedures were used for the analysis of model mixtures, binary cobalt–palladium alloys, and cobalt and palladium catalysts.     

Complexation of Lanthanum(III) and Terbium(III) with 5-Br-PAAP in the Presence of Surfactants

The complexation of lanthanum(III) and terbium(III) with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PAAP) in the presence of surfactants was studied by spectrophotometry. Optimal conditions of interaction and chemical and analytical characteristics of the resulting complexes were determined. Molar absorptivities are 7.8 × 10⁴ (La) and 8.7 × 10⁴ (Tb). The effect of the ionic strength of the solution and concentration of the organic solvent on the conditions of complexation in the presence of surfactants was considered. Correlation equations relating all chromaticity characteristics to the concentration of lanthanum, terbium, and erbium in the range 5–25 g per 25 mL were deduced. It was demonstrated tat the use of the most sensitive chromaticity functions (yellowness, chromaticity coordinates, color saturation, etc.) increases the sensitivity of the determination by a factor of 25–100 in comparison with the photometric method.     

Selective adsorption of thorium on activated charcoal from electrolytic aqueous solution

The adsorption of thorium on activated charcoal has been studied as a function of shaking time, amount of adsorbent, pH, concentration of adsorbate and temperature. Adsorption of thorium obeys the Langmuir isotherm. H⁰ and S⁰ were calculated from the slope and intercept of ln K_D vs. 1/T plots. The influence of different anions and cations on thorium adsorption has been examined. The adsorption of other metal ions on activated charcoal has been studied under specified conditions to check its selectivity. Consequently, thorium was removed from Cs, Co, Ba, Cr, Sr, Cd, Cu, Mn and Zn. More than 98% adsorbed thorium on activated charcoal can be recovered with 55 ml 3M HNO₃ solution. Wavelength dispersive X-rays fluorescence spectrometer was used for measuring thorium concentration.     

Chromaticity characteristics of chromium(VI) solutions

The light-absorption spectra of solutions of chromium(VI) in the form of dichromate (pH 1–5) and chromate (pH 7–9) have been studied. The solutions have maxima of light absorption at 360 and 380 nm and molar extinction coefficients of 155 ± 7 and 935 ± 27 for Cr₂O ₇ ^2? and Cr O ₄ ^2? respectively. The chromaticity functions of these chromium(VI) forms have been investigated and it has been shown that they are 1.0–1.5 orders of magnitude higher than the molar extinction coefficients. In all cases, the yellowness is maximal.     

Sorption–Optical Determination of Nitrite Ions in Sea Water with Chromotrope 2B

The Chromotrope 2B reagent was used as an analytical reagent for the direct determination of nitrite ions by sorption chromaticity measurements, diffuse reflectance spectrometry, and solid-phase spectrophotometry. The silochrom C-120 silica gel and the AV-17 anion exchanger were used as supports. Optimum conditions were found for the formation and sorption of Chromotrope 2B. The dependence of the chromaticity characteristics (chromaticity coordinates, lightness, color saturation, yellowness, and whiteness) on the concentration of nitrite ions was examined. The advantages of the use of chromaticity characteristics over the diffuse reflection coefficient were demonstrated. A procedure was developed for the test and sorption–optical determination of nitrite ions in sea water.     

Selective Extraction and Inductively Coupled Plasma Atomic Emission Spectrophotometric Determination of Thorium Using a Chromogenic Crown Ether

A method for the preconcentration and trace determination of thorium with crown hydroxamic acid (NHDTAHA) is described. The thorium is extracted from the chloroform solution of NHDTAHA at pH 4 which gives a colourless extract, _max = 365 nm; = 9.4·10^–3 l·mol^–1·cm^–1. The extract is directly inserted in the plasma for ICP-AES measurements of thorium. A linear calibration graph was obtained between 15–150 ng·ml^–:1 of thorium. The proposed method has been applied for the determination of thorium in the presence of several diverse ions in monazite sand, rare earth sand and in sea water.     

Estimation of natural thorium in low level effluents from processing plants

This is a report of simple estimations of natural thorium in low level effluents generated during the reprocessing of irradiated Th/ThO₂ rods for the recovery of²³³U. The method involved co-precipitation of thorium with ceric iodate at pH 1.29±0.01 and subsequent photometric determination. Conditions were optimised to eliminate the interferences of other ions present in the effluent. Approximately 15 mg each of phosphate, fluoride, and sulphate, 10 mg of iron, and 300 g zirconium did not interfere in the estimation of 2–5 g Th/100 ml of the effluent. Average thorium recovery was around 101.9%±2.6% when nearly 10 g of thorium were spiked.     

Liquid-liquid extraction of thorium/IV/ with LIX-54 and its mixtures

Solvent extraction of thorium/IV/ by a commercially available chelating extractant LIX-54 /a -diketone derivative/ /HA/ and its mixtures with tri-n-butyl phosphate /TBP/, thenoyltrifluoroacetone /HTTA/ and tri-n-octyl phosphineoxide /TOPO/ in benzene as the diluent have been studied. Quantitative extraction of thorium/IV/ by the mixture of 10% LIX-54 and 0.1M TOPO was noticed at pH 2.8. Influence of various concentrations of HTTA and TOPO in their mixtures with LIX-54 on the extraction of the same metal ion has been investigated and pronounced synergism was observed. Slope analyses determination shows the extracted species to be possibly of the type [Th/TTA/₂/A/₂] in case of extraction by mixtures of HTTA and LIX-54. Slopes of the linear plots were computed employing regression analysis, and variance in results has been shown.     

Uptake of thorium ions from aqueous solutions by a molecular sieve (13X type) powder

The adsorption of thorium(IV) ions on molecular sieve (13X type) powder from aqueous solutions has been studied as a function of shaking time pH, thorium ion concentration and temperature. The conditions of maximum adsorption of thorium ions obeys Langmuir and D-R isotherms over the entire concentration range studied. Thermodynamic quantities such as H, G and S have been calculated fromK _D values determined at various temperatures. The results show endothermic heat of adsorption, but negative free energy value indicates that the process of thorium adsorption on molecular sieve powder is favored at high temperature. The influence of various cations and anions on thorium(IV) ion adsorption was examined. A wavelength dispersive X-ray fluorescence spectrometer was used for measuring the thorium ion concentration in solutions.     

Simultaneous determination of uranium(VI) and thorium(IV) with carminic acid by derivative spectrophotometry

The reactions of uranium(VI) and thorium(IV) ions with carminic acid have been investigated. These ions react with carminic acid in neutral medium, forming colored complexes. The dark purple or red wine complexes show a high absorption in the visible region (597 nm U(VI) and 616 nm Th(IV)). Chemical variables that affect the reaction have been optimized. The spectral overlapping of the color of complexes has been resolved by first-derivative spectrophotometry. The simultaneous determination of uranium(VI) and thorium(IV) mixtures is accomplished by taking the derivative signal (zero crossing) at 597 nm for U(VI) determination and at 616 nm for Th(IV) determination, respectively. The method has been applied to Tyuyamonite ore, containing in the matrix both ions.     

Adsorption of thorium (IV) by amorphous silica; response surface modelling and optimization

The amorphous SiO₂ (200–300 nm) was synthesized as an absorbent and thorium adsorption of SiO₂ was investigated using experimental and RSM method. The SiO₂ particles were made for the adsorption of thorium from aqueous solutions, and characterized by particle size measurement, XRD and SEM. The adsorption of thorium process was optimized with RSM method. The correlation between four variables was modeled and studied. Under optimum conditions, the adsorption capacity of SiO₂ particles was found to be 134.4 mg/g, the correlation coefficient (R²) and the F value was obtained 0.96 and 1.98?×?10^?6, respectively. In addition, the adsorption isotherms were examined.     

Development of a method for recovery of 233U from thorium oxalate cake in reconversion step of reprocessing of irradiated thorium rods

A method is developed for the selective leaching of ²³³U from a thorium oxalate cake. The leaching capacity of ammonium carbonate and nitric acid have been investigated, showing that (NH₄)₂CO₃ leads to higher recovery. The maximum leaching efficiency is obtained using 0.5% ammonium carbonate, with a minimal thorium pick-up. A uranium recovery of 94% is obtained after three consecutive contact experiments in carbonate media, with minimal thorium uptake in the leachate. This process was applied to an actual plant stream, allowing the reduction of the ²³³U -activity from 5.64 to 0.3 Ci/g of thorium oxalate cake.     

Neutron activation analysis of thorium after separation of233Th by isotopic ion exchange

The procedure for thorium determination in ammonium diuranate (ADU) and rocks, by neutron activation analysis after chemical separation of²³³Th, is presented. The separation of²³³Th from the interfering radioisotopes is based on the retention of²³³Th by a resin saturated with thorium (isotopic exchange) and on the elution of the interfering radioisotopes by a dilute solution of thorium in 0.5M HCl (ion exchange). The determination limit of thorium in rocks and ADU was found to be 0.56 and 9.3 g, respectively, when a 20% relative standard deviation was assumed as acceptable. The highest value obtained for the determination limit of thorium in uranium compounds, on account of the²³⁴Th activity present, is discussed.From a thesis submitted by C. S. Munita to the Instituto de Pesquisas Energéticas e Nucleares (CNEN/SP) University of São Paulo, in partial fulfillment for a Doctor of Science's Degree. Work supported by the Brazilian Atomic Energy Commission.     

Spectrophotometric Determination of Thorium with Disodium Salt of Arsenazo-III in Perchloric Acid

A rapid and sensitive spectrophotometric method has been developed for the determination of thorium using 0.04% Arsenazo-III in a 2M perchloric acid solution. Absorbance was measured in 1 cm cell and the complex has a sensitive absorption peak at 654 nm. The complex is formed instantly in perchloric acid and remains stable for 45 minutes with constant absorbance. Beer's law is obeyed in the range 1–60 g·g^–1 of thorium concentration with a molar absorptivity at 654 nm = 3.07·10⁵ M^–1·cm^–1 at 24±2°C. The foreign ions interference in thorium determination have been checked. The cations were tested at >60-fold excess of thorium, Mn(II), Fe(III), Co(II) and Ni(II) interfere negatively, whereas only Ce(III) has increased the absorbance. Among the anions, cyanide, phosphate, thiocyanate and acetate at 150-fold excess of thorium cause significant interference. However, thorium can bedetermined in the presence of nitrate, chloride, oxalate, tartrate, ascorbate, thiosulphate and citrate. The method has been applied on certified reference material for thorium determination after extractive separation and the result was found in good agreement with the certified value. The method has been also applied successfully to determine thorium at g·g^–1 level in local ore samples with a precision of ±0.04%.     

Analytical aspects of some azo dyes from chromotropic acid

Summary Nitroso-SNADNS-4, itself a yellow coloured dye in acid medium forms a reddish-pink colouration with thorium in weakly acid solution. The colour is stable for about 24 hours and to a temperature up to 50C. The thorium complex shows maximum absorbance at the wave length 520 m, while that of the dye occurs at 430 m. The maximum intensity of colour of the thorium complex is shown at aph 2.5. The colour system conforms to Beer's law in a wide range of concentration of thorium and presents a reliable method for the spectrophotometric determination of the metal even in presence of a large number of common ions, the ions interfering are: tin, iron, nickel, cobalt, cerium(IV), zirconium, gold, phosphate and fluoride. The average percentage of deviation of the absorbance index in the determination of thorium is 1.14.Part VI: See Z. analyt. Chem. 167, 105 (1959)     

A study on the hydrolytic behavior of thorium (IV) and dioxo-uranium(VI) in the absence and presence of fluoride ions

The hydrolytic behavior of thorium(IV) and dioxo-uranium(VI) was studied in the absence as well as in the presence of small concentration of fluoride in the pH range of 2.0 to 4.0 and 2.0 to 5.5, respectively. Effects of metal ion concentration and time dependence of the hydrolytic process were also investigated. The log values of ₁₁ ^* and ₁₃ ^* computed from the best model of species distribution were found to be -3.51±0.03, and -10.75±0.14 for thorium(IV). Similarly, the best model for dioxo-uranium consisted of ₂₂ ^*, ₄₆ ^* and ₄₇ ^* species having values -6.15±0.05-18.43±0.09 and -23.36±0.07, respectively. Recently developed HYPERQUAD computer program was used for analyzing the various aspects of solution equilibrium species. Different models of chemically possible species distribution were invoked to identify the best model for which HYPERQUAD yields the best fitting of experimental data with least errors. The best model was also decided on the basis of chemical feasibility of the reaction. The species distribution of hydrolytic product remained unaffected in the presence of small quantity of fluoride ions (~1% of thorium and uranium concentration). Moreover, fluoride was found to be helpful in suppressing the early polymerization and colloid formation at the metal ion concentrations investigated. The small amounts of fluoride did not seem to affect the response of glass electrode significantly. The formations of fluoride containing ternary complexes were also not observed at 1% fluoride concentration.     

Studies on the Complexation Behavior of Thorium(IV). 1. Hydrolysis Equilibria

The stability constants of thorium(IV) hydrolysis species have been measured at15, 25, and 35°C (in 1.0 mol dm^–3 NaClO₄) using both potentiometry and solventextraction. The results indicate the presence of the monomeric speciesTh(OH)³⁺, Th(OH)²⁺ ₂, Th(OH)⁺ ₃, and Th(OH)₄, in addition to the polymericspecies Th₄(OH)^{8+ 8} and Th₆(OH)⁹⁺ ₁₅. The polymeric species were found to beimportant, although the total thorium concentration was limited to 0.01–0.1mmol-dm^–3. The solvent extraction measurements required the use of acetylacetone.As such, the stability constants of thorium(IV) with acetylacetone were alsomeasured using both potentiometry and solvent extraction. All logarithms of thestability constants were found to be linear functions of the reciprocal absolutetemperature indicating that H ^o and S^o of reaction are both independent oftemperature (over the temperature range examined in the study).     

Separation and spectrophotometric determination of thorium contained in uranium concentrate

A method for the determination of thorium in uranium concentrate by spectrophotometry with Arsenazo III has been developed. Preliminary solvent extraction procedures were used to eliminate interfering species. Samples were dissolved in nitric, perchloric and sulfuric acid and the uranium extracted from the solution using tri-octylamine. The aqueous layer was evaporated to dryness and the residue re-dissolved with hydrochloric acid, thorium was extracted by tri-n-octyl phosphine oxide and stripped with oxalic acid. For a typical uranium concentrate produced from the phosphate rock of Itataia, Brazil, concentrations of thorium as low as 5 g·g^-1 can be determined.