Fluorimetric determination of uranium in certain refractory minerals,environmental samples and industrial waste materials

Summary A simple sample decomposition and laser fluorimetric determination of uranium at trace level is reported in certain refractory minerals, like ilmenite, rutile, zircon and monazite; environmental samples viz. soil and sediments; industrial waste materials, such as, coal fly ash and red mud. Ilmenite sample is decomposed by heating with ammonium fluoride. Rutile, zircon and monazite minerals are decomposed by fusion using a mixture of potassium bifluoride and sodium fluoride. Environmental and industrial waste materials are brought into solution by treating with a mixture of hydrofluoric and nitric acids. The laser induced fluorimetric determination of uranium is carried out directly in rutile, zircon and in monazite minerals and after separation in other samples. The determination limit was 1 μg ^. g^-1 for ilmenite, soil, sediment, coal fly ash and red mud samples, and it is 5 μg ^. g^-1 for rutile, zircon and monazite. The method is also developed for the optical fluorimetric determination of uranium (determination limit 10 μg ^. g^-1) in ilmenite, rutile, zircon and monazite minerals. The methods are simple, accurate, and precise and they require small quantity of sample and can be applied for the routine analysis.     

Determination of ultra traces amount of uranium in raffinates of Purex process by laser fluorimetry

A simple and rapid, laser fluorimetric method for the determination of uranium concentration in raffinate stream of Purex process during reprocessing of spent nuclear fuel has been developed. It works on the principle of detection of fluorescence of uranyl complex formed by using fluorescence enhancing reagent like sodium pyrophosphate. The uranium concentration was determined in the range of 0–40 ppb and detection limit of 0.2 ppb. The optimum time discrimination is obtained when the uranyl ion is complexed with sodium pyrophosphate. Need of preconcentration step or separation of uranium from interfering elements is not an essential step.     

Total reflection X-ray fluorescence analysis of fly ash from Bulgarian coal-fired power plants

The contents of Cl, Ca, K, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Rb, Sr, Ba and Pb in raw coal fly ash from five Bulgarian power plants were determined by total reflection X-ray fluorescence (TXRF), using gallium as the internal standard. The samples were analysed as in slurry form in Triton? X-114. The experimental parameters, such as grain size, concentrations of fly ash slurry and excitation time were optimised. For validation of the method, the certified reference material BCR-176R fly ash was used. The precision of the results obtained is characterised by a relative standard deviation of approximately 10%. The resulting data confirm the suitability of TXRF for the simultaneous determination of major, minor and trace elements in coal fly ash samples. Further advantages provided by TXRF are easy sample preparation (no sample dissolution) and the small sample amount required for analysis.     

Comparison of fluorescence-enhancing reagents and optimization of laser fluorimetric technique for the determination of dissolved uranium

Results from tests aimed at optimizing an instrumental procedure for the direct and fast determination of uranium in solution by laser fluorescence are presented. A comparison of sample fluorescence measured using different fluorescence enhancing reagents was performed: sodium pyrophosphate, orthophosphoric acid, sulphuric acid and a commercially available fluorescence enhancer were tested for the determination of uranium. From the experimental results, 0.01 M Na₄P₂O₇·10H₂O showed the best performance. Effects of reagent pH, different matrices, different concentrations of dissolved Th, and sample volume were investigated. Applications of the improved procedure for the determination of uranium in samples arising from UO₂-based high level nuclear waste dissolution studies are described.     

褐煤SHELL气化飞灰黏附影响因素的研究

通过激光粒度仪、X射线荧光光谱仪、扫描电子显微镜等现代化分析测试技术对褐煤样、飞灰样以及换热废锅中的积灰样进行了粒度分布、化学组成、晶体矿物组成、微观形貌、微区化学组成等特征的分析,研究影响飞灰黏附特性的因素。并通过引入富集系数,描述各个元素在煤灰、正常飞灰、废锅积灰中的迁移富集情况。结果表明,在废锅积灰中有含铁矿物的生成,同时Na、K、Fe、S、P元素在废锅积灰中发生富集,在飞灰与积灰颗粒边缘处有大量的Fe、Na元素的富集。     

Determination of cadmium,mercury and lead in coal fly ash by slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry

Ultrasonic slurry sampling electrothermal vaporization isotope dilution inductively coupled plasma mass spectrometry (USS-ETV-ID-ICP-MS) has been applied to the determination of Cd, Hg and Pb in coal fly ash samples. Thioacetamide (TAC) was used as the modifier. Since the sensitivities of the elements studied in coal fly ash slurry and aqueous solution were quite different, isotope dilution method was used for the determination of Cd, Hg and Pb in these coal fly ash samples. The isotope ratios of each element were calculated from the peak areas of each injection peak. This method has been applied to the determination of Cd, Hg and Pb in NIST SRM 1633a coal fly ash reference material and a coal fly ash sample collected from Kaohsiung area. Analysis results of reference sample NIST SRM 1633a coal fly ash agreed satisfactorily with the certified values. The other sample determined by isotope dilution and method of standard additions was agreed satisfactorily. Precision was better than 6% for most of the determinations and accuracy was better than 4% with the USS-ETV-ID-ICP-MS method. Detection limits estimated from standard addition curves were in the range of 24–58, 6–28 and 108–110 ng g⁻¹ for Cd, Hg and Pb, respectively.     

Certified reference materials for the quality control of fluorine in coal, fly ash and clay

A group of laboratories has worked in various intercomparisons in the frame of the BRC-programme (European Commission) to improve their methods for fluorine determination, especially for coal analysis. These exercises allowed to detect and remove sources of error. Methods were improved to such an extent that the certification of fluorine and chlorine in different materials could be envisaged and the BCR consequently decided to produce coal, fly ash and clay materials certified for their F content. In addition, chlorine was certified in the fly ash CRM.     

A study of the chemical forms or species of manganese found in coal fly ash and soil

The chemical speciation of manganese of environmental and toxicological interest was undertaken in coal fly ash and soil. Hard coal used in combustion creates considerable quantities of waste ash. The greatest quantities of industrial ashes are stored in the form of waste-heaps, which create a serious problem as the source of inorganic pollution. It is necessary to identify physical and chemical properties of ash, especially when analyzing the pollution of soil by trace metals, which are potentially mobile in environment. In this work, a new analytical method has been developed and used successfully for identification and determination of chemical forms of manganese in coal fly ash and soil. The basic chemical forms of metals contained in the environmental samples (fly ash and soil) can be described by using sequential extraction method. To identify Mn ions, the UV-VIS spectrophotometric method was used by means of comparative analysis of spectrophotometric spectra of appropriate Mn ions in the standard solutions and solutions obtained after extraction. The concentration of manganese in all solutions was determined by the Flame Atomic Absorption method. The experimental approach and analytical method developed in this study appear adequate for this purpose and can therefore be used for similar research.     

Fluorescence determination of trace amounts of uranium(VI) in various materials by a repetitive laser technique

A laser-induced fluorescence method (LFM) is described for determination of trace amounts of uranium(VI), with a detection limit of 4 x 10(-11) g/ml. A repetitive pulsed laser, time discrimination and an averaging technique are used. The optimum time discrimination is obtained when the uranyl ion is complexed with phosphoric acid or sodium polysilicate. LFM does not need a preconcentration step or separation of uranium from interfering elements. The time needed for analysis is only 1-2 min.     

Determination of Ga, Ge, As, Se and Sb in fly ash samples by ultrasonic slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry

Ultrasonic slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry (USS-ETV-ICP-MS) has been applied to determine Ga, Ge, As, Se and Sb in fly ash samples. The influences of instrument operating conditions and slurry preparation on the ion signals were reported. Pd and ascorbic acid were used as the mixed modifiers to enhance the ion signals. This method has been applied to determine Ga, Ge, As, Se and Sb in NIST SRM 1633a and 1633b coal fly ash reference materials and a fly ash sample collected locally. Since the sensitivities of the elements studied in slurry solution and aqueous solution were different slightly, analyte addition technique was used for the determination of Ga, Ge, As, Se and Sb in these samples. The As and Se analysis results of the reference materials agreed with the certified values. The results for which no certified value was available were also found to be in good agreement between the ETV-ICP-MS results and the reference values. The reference value was obtained by digesting the samples and analyzing the digested sample solutions by pneumatic nebulization Dynamic Reaction Cell™ (DRC) ICP-MS. The method detection limits estimated from analyte addition curves were about 0.23, 0.13, 0.17, 0.25 and 0.11 μg g⁻¹ for Ga, Ge, As, Se and Sb, respectively, in original fly ash samples.     

Cold dissolution method for the determination of uranium in various geological materials at trace levels by laser fluorimetry

A cold dissolution procedure for the determination of uranium in various geological materials like rocks, minerals, soils etc., has been described. Samples are allowed to react with HF and HNO(3) at room temperature overnight. Boric acid is added to complex excess fluoride ions. From the clear solution thus obtained, uranium is determined directly in laser fluorimeter after the addition of fluorescence enhancing reagents. The results of few standard reference materials analysed by the present method agree with the certified values. This methodology does not require platinum or teflon ware, exhaust system and time consuming solvent extraction step. Hazardous acid vapours are not left in air, so there is no air pollution. Chemicals consumption is minimal. Therefore the method is economical. The method can be employed for high sample throughput which is the prerequisite for exploration geochemists.     

Direct determination of Ge in hot spring waters and coal fly ash samples by hydride generation-ETAAS

A method for Ge determination in hot spring water and acid extracts from coal fly ash samples involving hydride generation, trapping and atomisation of the hydride generated from Ir-treated graphite tubes (GTs) has been developed. Hydride was generated from hydrochloric acid medium using sodium tetrahydroborate. Several factors affecting the hydride generation, transport, trapping and atomisation efficiency were studied by using a Plackett-Burman design. Results obtained from Plackett-Burman designs suggest that trapping and atomisation temperatures are the significant factors involved on the procedure. The accuracy was studied using NIST-1633a (coal fly ash) reference material. The detection limit of the proposed method was 2.4 μg l⁻¹ and the characteristic mass of 233 pg was achieved. The Ge concentrations in fly ash and hot spring samples were between 6.25-132 μg g⁻¹ and 12.84-36.2 μg l⁻¹.     

ICP-MS multielement determination in fly ash after microwave-assisted digestion of samples

A microwave assisted digestion procedure has been developed for dissolution of fly ash samples prior to the inductively coupled plasma-mass spectrometric determination of their elemental composition. The developed methodology was validated by carrying out the analysis of two high-silicate containing reference materials (CRM 134R sewage amended soil and NIES JR 1 rock) and by means of the comparison between results found by microwave-assisted digestion and ICP-MS of fly ash samples with those found by neutron activation analysis (NAA) for Sb, Cs, Cr, Co, Fe, U and Zn determination. The method developed can be recommended for routine multielement analysis of fly ash.     

Fly ash based zeolite analogues: versatile materials for energy and environment conservation

Fly ash is combustion residue from burning of pulverised coal in electric utility generating stations. The annual production of fly ash in India is around 100 MTPA and is responsible for several environmental hazards, which is quite well documented. There are stringent norms for its land disposal and hence utilisation of fly ash is imperative. Fly ash has more than 85% of SiO₂ and Al₂O₃ content and is therefore a tailor made raw material for production of zeolite. An innovative process has been developed for synthesis of zeolites using fly ash as a substitute for conventional raw materials viz. sodium silicate and aluminate. The process consists of three major steps viz. fusion of caustic soda and fly ash for optimal extraction of silicate and aluminate, aging step which provides time for formation of nuclei and hydrothermal crystallization resulting in activation of nuclei into well defined crystals. Low temperature operation, simplicity of process and optimal recycling of unused reactants and process water are special features of these processes. Zeolites have high internal and external surface areas and also exhibit high exchange capacities, which makes them versatile materials for targeting wide range of pollutants, ranging from cationic to anionic and hydrophilic to hydrophobic molecules. The major uses of zeolites are in adsorption, ion exchange and as catalysts. The use of zeolites in environmental remediation is restricted due to procurement problem and prohibitive cost, which can be overcome by using low cost fly ash based zeolites (FAZs). The synthesis of FAZ-A and FAZ-Y and their modifications either by transition metal incorporation or by surfactant treatment for various environmental applications in air, water and soil remediation are addressed in this review.     

The determination of traces of cadmium,lead and thallium in fly ash by potentiometric stripping analysis

The suitability of potentiometric stripping analysis for the determination of cadmium, lead and thallium in fly ash and in waters polluted by leaching of fly ash is assessed. By an appropriate choice of medium and of electrolysis potential and by employing a rotating working electrode, it is possible to eliminate interferences from electroactive species often found in fly ash in high concentrations. The accuracy obtained in a study of a certified coal fly ash (SRM 1633a) is satisfactory.     

石嘴山电厂煤中微量元素的迁移释放行为

应用电感耦合等离子体质谱（ICP-MS）和原子荧光光谱（AFS）对中国西北部石嘴山电厂的原煤、底灰和飞灰中Hg、As、Se、Pb、Cr、Cd、Mo、Ni、Co、U和Th 11种微量元素的含量进行了测定。根据底灰和飞灰的产率, 结合微量元素在底灰和飞灰中的含量计算了电厂燃煤过程中微量元素的挥发性。结果表明, Hg、Cd、Se、As四种元素在燃煤过程的挥发率均在50%以上, 最高可达70%。通过对底灰和飞灰在酸性介质下的柱淋滤实验研究了底灰和飞灰中微量元素在60h内的迁移释放行为。Mn、Ni、Co、As四种元素的最大淋出率均超过2.0%, 最高接近10.0%, 并且还未达到淋滤平衡。根据微量元素的挥发和淋滤释放特性建立了电厂煤中有害微量元素在燃烧和淋滤过程中的释放分配模型。结果显示, 燃煤过程中的挥发是微量元素释放的主要形式, 部分元素的淋滤释放也可对周围水环境造成污染。
     

Composition and morphology of stack emissions from coal and oil fuelled boilers

Instrumental neutron activation analysis (INAA) together with scanning electron microscopy (SEM) have been used in the study of fly ash from large electric power and heating plants. Two basic kinds of fly ash originating either from brown coal or heavy-oil combustion can be characterized both by morphology and trace element composition. INAA technique used consisted of both short (1 min) and long (2 h) activations to ensure the determination of 30–40 elements in each fly ash sample. The average composition and determination limits obtained by INAA for coal fly ash produced in several electric power plants burning two kinds of brown coal have been compared with those obtained for fly ash originating from heating plants burning heavy-oil. Coal fly ash showed much higher concentrations of many elements especially of Sc. La, Th, Cs, Ce, Sm, Rb and Al in comparison with oil fly ash. On the other hand, the latter contained relatively high concentrations of V and Ni. The results of INAA of fly ash samples can be used for the projection of efficient separating devices and for the evaluation and prediction of contamination levels in the vicinity of large emission sources.     

激光-时间分辨荧光法测定U3O8中痕量硼

本文提出了一种测定U3O8中痕量硼的激光-时间分辨荧光法, 在适当介质中, 用小型氮分子激光器激发硼与二苯甲酰基甲烷配合物的荧光, 发现此配合物的荧光寿命为2ms, 它比铀的荧光寿命长得多, 从而可将荧光的时间分辨技术应用于铀中硼的测定, 不经分离基体铀即可进行测定, 方法简单而快速, 检测下限达到0.02ng.mL^-^1(硼),当取样10mg铀时, 能测定0.01ppm的硼。用本法分析了含量在0.04-0.5ppm几个U3O8样品, 结果与其他方法相符。     

Determination of trace elements in fly ash samples by FAAS after applying different digestion procedure

The fly ash samples obtained from Kangal Power Plant were prepared for FAAS analysis by a new approach. The trace elements of the fly ash samples were leached with appropriate solvents under suitable conditions. The leaching method is known as an effective technique for substances dissolving very hard and refractory materials. The leaching effects of solvents and their mixtures were investigated on fly ash samples that are used largely in analysis of soil and sediment samples.The fly ashes mainly consist of glassy aluminosilicates. The major components of the samples are SiO₂, Al₂O₃, CaO and Fe₂O₃. Therefore, decomposition of the silicate lattice of the fly ash is required for liberation of trace elements. The dissolution process can be completed by using a mineral acid such as concentrated HCl. This technique has an advantage that the fly ash can be dissolved without any oxidation at room temperature.Maximum element recoveries were obtained by the procedure of 37% HCl leaching after the samples were treated with 2.0 ml of concentrated HF. It was also observed that maximum mass loss occurred in this procedure. The effect of the four leaching reagents, which are HCl, HNO₃, HClO₄ and HNO₃ + HClO_4, were investigated on fly ash samples that were treated with concentrated HF. An optimum leaching method was determined based on the confidence of analytical results and element recovery rates.     

Certification of a new NIST fly ash standard reference material

In June 1993 the National Institute of Standards and Technology (NIST) released the third version of Constituent Elements in Coal Fly Ash Standard Reference Material (SRM 1633b). This material is intended for quality assurance purposes in evaluating the analytical methods used for the determination of constituent elements in coal fly ash or in materials with similar matrices. It has been certified for 23 major, minor and trace elements using ten different analytical techniques. For an element to be certified in a NIST SRM, its concentration is usually determined by at least two independent analytical techniques. The concentrations of additional 24 elements are provided for information only purposes in the new fly ash. Current plans are to certify the concentrations of a number of rare earths upon completion of additional analytical work now in progress. Homogeneity testing was accomplished using instrumental neutron activation analysis and X-ray fluorescence. This presentation summarizes the preparation of this new material and the analytical results used for certification.