Monazite Sand Research Articles

Preconcentration and recovery of uranium and thorium from Indian monazite sand by using a modified fly ash bed

Adsorption of uranium, as UO2 2+, and thorium, as Th4+, has been studied using a modified fly ash bed. Effects of pH and various ions like La3+, Fe3+, Ce4+, SiO3 2- etc., have been examined. Synthetic mixtures of UO2 2+ and Th4+ in different concentrations were passed through the bed and eluted separately with various selective reagents viz. ammonium carbonate, sodium carbonate and acetic acid-sodium hydroxide buffer. Separations of these elements at ppm level are shown to be very effective. The separation of uranium and thorium in the presence of lanthanides in monazite sand has been studied successfully. In the analysis of monazite sand, the oxalate precipitation has been avoided. The method is simple and of very low cost. The modified fly ash bed can also be used to remove uranium from contaminated water.

Selective Extraction and Separation of Thorium from Monazite Using N-Phenylbenzo-18-crown-6-hydroxamic Acid

A method for the liquid–liquid extraction, separation, preconcentration and trace determination of thorium with N-phenylbenzo-18-crown-6-hydroxamic acid (PBCHA) is described. Thorium is extracted from the dichloromethane solution of PBCHA at pH 4.5 which gives a colourless extract (λmax 375 nm, e=1.5×104 L mol−1 cm−1, linear range following Beer’s law 0.77–18.48 µg mL−1). The extract is directly inserted into the plasma for ICP-AES measurements of thorium. A linear calibration graph was obtained between 10 and 130 ng mL−1 of thorium. The proposed method has been applied for the separation and determination of thorium in the presence of several ions in monazite sand, rare earths, sand and sea water samples. The thorium-PBCHA complexes are very stable, having the formation constant (log β2) 13.45 compared to lanthanum (log β2) 2.95, cerium (log β2) 2.95 and uranium (log β2) 3.80. Hence, thorium can easily be separated and determined in monazite sand.

Column chromatographic separation of thorium(IV) from ascorbic acid medium using poly-(dibenzo-18-crown-6)

A simple separation method has been developed for thorium(IV) using poly-(dibenzo-18-crown-6) and column chromatography. The separation was carried out from ascorbic acid medium. The adsorption of thorium(IV) was quantitative from 0.001-0.01M ascorbic acid. The elution of thorium(IV) was quantitative with 4.0-8.0M HCl, 3.0-6.0M HClO4, 4.0-8.0M H2SO4 and 1.0-8.0M HBr. The capacity of poly-(dibenzo-18-crown-6) for thorium(IV) was found to be 1.379±0.01 m.mol/g of crown polymer. Thorium(IV) was separated from a number of cations in binary as well as in multicomponent mixtures. The method was extended to the determination of thorium in monazite sand. It is possible to separate and determine 5 ppm of thorium(IV) by this method. The method is very simple, rapid, selective and has good reproducibility (approximately ±2%).

Polymer supported calix[4]arene-semicarbazone derivative for separation and preconcentration of La(III), Ce(III), Th(IV) and U(VI)

The new “upper-rim” functionalized 11,23-disemicarbazono-26,28- n-dipropoxy-25,27-dihydroxy calix[4]arene has been synthesized by condensing 11,23-diformyl-26,28- n-dipropoxy-25,27-dihydroxy calix[4]arene with semicarbazide hydrochloride. This calix[4]arene-semicarbazone derivative was then covalently linked with commercially available Merrifield’s peptide resin at the “lower-rim” to obtain polymeric chelating resin and its analytical properties were investigated. The resin was then used successfully for the separation and preconcentration of lanthanum(III), cerium(III), thorium(IV) and uranium(VI) prior to their determination by spectrophotometry and inductively coupled plasma atomic emission spectroscopy. The resin exhibits good separating ability with maximum sorption between pH 2.5–4.5 for Th(IV) and between pH 5.5–7.0 for U(VI) whereas La(III) and Ce(III) were found to have maximum sorption between pH 6.5–8.5. The elution studies were carried out with 0.01 M HCl for La(III) and Ce(III), 2.0 M HCl for Th(IV) and 0.25 M HCl for U(VI). The preconcentration factors for La(III), Ce(III), Th(IV) and U(VI) were 125, 130, 102 and 108, respectively. The resin shows good stability along with faster rate of equilibrium for all the metal ions. The influence of several ions (cations and anions) on the resin performance is also discussed. The relative standard deviation was between 96 and 98% with good analytical reliability. The proposed method was applied for the determination of metal ions in monazite sand and some standard geological materials.

Synthesis and characterization of lanthanum acetate for application as a catalyst

The use of precursors based upon the rare earths is of considerable interest for the manufacture of catalysts. Starting with a rare earths fraction depleted in cerium (a low cerium carbonate, LCC) produced locally by the industrial processing of monazite sand as raw material, a very pure concentrate of lanthanum was prepared. The rare earth chloride solution was loaded into a strong cationic ion-exchange resin and then eluted using the ammonium salt of EDTA. No barrier ion was used. The lanthanum fraction was separated from the EDTA and then precipitated as oxalate and fired to lanthanum oxide. The lanthanum oxide was fairly easily dissolved using only acetic acid from which lanthanum acetate was crystallized. The solid salt was characterized via thermal analysis, chemical analysis, X-ray diffraction, inductively coupled plasma optical emission spectrometry and infrared spectroscopy. An aqueous solution of lanthanum acetate was prepared to be added to alumina microspheres support, especially sinthesized by the sol–gel process for use as a catalyst. Further work will involve the preparation of a highly specific surface lanthanum oxide via lanthanum acetate to be used as a catalyst and to be compared with the alumina–lanthanum oxide catalyst.

The areas of high natural radioactivity and TENORM wastes

There are many areas of high natural radioactivity (HINAR) throughout the world. To mention a few, the monazite-bearing sands in the Kerala coast in India and in the coastal regions of the states Espirito Santo and Rio de Janeiro in Brazil; the mineralized volcanic intrusives in the Brazilian states of Minas Gerais and Goiás; the hot springs in Ramsar, Iran; the primitive, granitic, schistous and sandstone areas of France; and selected areas in Zaire. Some HINAR areas are such that there are sources of economically feasible ores geologically associated with naturally occurring radioactive materials (NORM). In Brazil, the main technologically enhanced naturally occurring radioactive materials (TENORM) waste-producing ores are the rare earth-rich monazite sands; phosphate rocks; and gold, lead, silver, copper, tin, tantalum and niobium associated with uranium and/or thorium. Some of these orebodies are in HINAR areas which were never investigated; while, on the other hand, some others are in HINAR areas which have been extensively studied. This work discusses the advantage of using the exposure baseline in the Brazilian HINAR areas, whenever available, for the interpretation of exposures to TENORM resulting from the extraction and/or industrial processing of orebodies bearing NORM.

The influence of urbanization on natural radiation levels in anomalous areas

This paper verifies the effects of urbanization on the original levels of environmental gamma radiation in an anomalous area. The fieldwork was done in the city of Guarapari, on the seacoast of the state of Espírito Santo, Brazil. This place was chosen because the whole region is naturally rich in monazite sand, which contains thorium and uranium. A similar study was also carried out in the 1960s. The measurements were done using an inorganic NaI scintillometer detector with Cu+Pb filters coupled to a scaler. The methodology of measurements used was similar to the one applied in the fieldwork carried out in the 1960s. In addition, a simulation was performed in the laboratory, to determine the attenuation of the materials used in the urbanization of the region. The results of this work clearly show that there was a reduction in the levels of external radiation in the streets and squares of Guarapari. It was concluded that the reduction was due to attenuation by the materials used in the urbanization.

Extraction of uranium, thorium and lanthanides using Cyanex-923: Their separations and recovery from monazite

The extraction behavior of uranium, thorium and lanthanides, represented by cerium and ytterbium, by Cyanex-923 has been investigated. The effect of different variables like the concentration of acids, metal ion and extractant, nature of diluent and temperature has been studied. A composition for the extracted U(VI) and Th(IV) species has been proposed. Based on the partition data some important binary and ternary separations involving the aforesaid metal ions have been achieved. The proposed procedure has been applied for the recovery of uranium, thorium and lanthanide fraction from monazite sand. The stability and regeneration capacity of the extractant have been evaluated.

Abnormal high natural radium concentration in surface waters

Unexpected high 228Ra concentrations, up to 2 Bq l −1, were found in waters of a coastal lagoon close to a monazite sand separation plant. Due to their use as process waters in this plant, the initial supposition was a contamination related to its operation. However, it was concluded that these abnormal radium concentrations had a natural origin, springs at the lagoon head area with high 228Ra and 226Ra concentrations. The strong relationship among radium and light rare-earth elements (LREEs), the observed 228Ra/ 226Ra activity ratio and the rare-earth element pattern in the spring waters suggested that monazite is the main source of nuclides for water, indicating the disturbance of monazite chemical stability by the combined effects of low pH and high salinity. Both factors combined allow relatively low mobility of thorium, but, on the other hand, a relatively high mobility of radium and LREEs.

Polymer supported calix[6]arene hydroxamic acid, a novel chelating resin

A new polymer-supported calix[6]arene hydroxamic acid has been synthesised by reacting the acid chloride 37,38,39,40,41,42 hexahydroxy 1,8,13,19,25,31 hexacarboxy calix[6]arene with poly(styrene β-hydroxylamine). The synthesised resin was characterised by elemental analysis, FT-IR and mass spectra. Physicochemical properties viz. swelling, wet-density, void-volume, exchange capacity etc. were determined. The resin has 4.46 mmol/g exchange capacity for rare elements. The resin was used for the chromatographic separation of U(VI), Th(IV) and Ce(IV) by the judicious adjustment of pH 4.0, 6.0 and 7.5, respectively. The thorium and cerium were eluted with 0.1 M HCl while uranium was eluted with 2 M HCl. These rare elements were preconcentrated and determined in the presence of each other, monazite sand and environmental samples.

Preparation of highly pure thorium nitrate via thorium sulfate and thorium peroxide

A simple alternative and selective method has been proposed for the preparation of thorium nitrate using as raw material a hydrated crystalline technical grade thorium sulfate. This salt was produced industrially [1] from the alkaline chemical processing of monazite sand in S. Paulo. From a crude thorium hydroxide as the raw material containing uranium and rare earth elements was prepared a technical grade thorium sulfate [Th(SO 4) 2.9H 2O]. A typical analysis of this salt had shown the following composition: ThO 2 47–53%, R 2O 3 (rare earth oxides) 0.5–0.9%, and UO 3 0.01% and minor amounts of iron, titanium, phosphorus, and silicon oxides. The thorium sulfate is dissolved into water and the thorium peroxide is precipitated from acidic medium by addition of hydrogen peroxide. The thorium peroxide is filtered, washed and finally dissolved with nitric acid. Samples of the thorium peroxide were dried and fired to ThO 2 and aliquot of the thorium nitrate solution was evaporated to dryness and calcined to obtain the ThO 2. Both ThO 2 have high purity (>99.5%). The content of total rare earth elements is very low (0.23% as oxide). Uranium was not detected. The great majority of the RE is precipitated and recovered from the filtrate by oxalic acid.

Methodologies for the analysis of rare earth elements and their relevance to reference materials.

India has the third largest resources of rare earth elements (REE) in the world. These resources are essentially the monazite sand present in the beaches of southwest, south-east, and mid-eastern coasts of India. Therefore, analytical methodologies for the determination of REE in sea water and high-purity materials were developed. An overview of this work and its relevance to the preparation of standard reference materials of REE in sea water, marine sediments, and high-purity materials in the future is given.

Pre-concentration, separation and trace determination of lanthanum(III), cerium(III), thorium(IV) and uranium(VI) on polymer supported o-vanillinsemicarbazone

A nonionic polymeric adsorbent styrene divinylbenzene, Amberlite XAD-4 was functionalized with o-vanillinsemicarbazone and its analytical properties have been studied. The synthesized resin was utilized for selective column separation, pre-concentration and trace determination of lanthanum(III) (La(III)), cerium(III) (Ce(III)), thorium(IV) (Th(III)) and uranium(VI) (U(VI)). The resin exhibits good chemical stability, reusability and faster rate of equilibrium for their determination by spectrophotometry and their simultaneous confirmation of the results by inductively coupled plasma-atomic emission spectrometry (ICP-AES) and graphite furnace-atomic absorption spectrometry (GF-AAS). Both, the uptake and stripping of these metal ions were fairly rapid, indicating a better accessibility of the chelating sites. The proposed method has been applied to sequential chromatographic separation of their binary and ternary mixtures. Uranium(VI) has been determined from simulated river water sample with good analytical reliability. The detection limit of these metal ions on the resin is 100 ng cm −3 with recovery upto 96–98%. The method is also applied for their determination in monazite sand and some standard geological materials.

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, λmax = 365 nm; e = 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.

Solvent extraction and spectrophotometric determination of uranium(VI) with pyridine-2-carboxaldehyde 2-hydroxybenzoylhydrazone

Pyridine-2-carboxaldehyde 2-hydroxybenzoylhydrazone (PAHB) is proposed as an extractant for the separation and spectrophotometric determination of uranium(VI). The optimum extraction conditions have been evaluated by studying various parameters such as pH, diluents, equilibration time and reagent concentration. PAHB forms yellow colored complex with uranium(VI) in the pH range of 3.5-4.6 which can be extracted by isobutyl methyl ketone. The extracted complex exhibits an absorption maximum at 375 nm. Beer's law was obeyed in the concentration range 1.0-5.6 ppm of uranium(VI). The nature of the extracted species (1:2) was determined by log D-log c plot. The proposed method permits selective separation of uranium(VI) from its binary mixtures. The method is also applied for the estimation of uranium in multicomponent mixtures and monazite sand.

Solvent extraction of uranium(VI) using dibenzo-18-crown-6 in nitrobenzene from ammonium thiocyanate medium

Solvent extraction of uranium(VI) from aqueous solutions of ammoniumthiocyanate has been investigated in the presence of dibenzo-18-crown-6. Uranium(VI)was quantitatively extracted from 1.0M ammonium thiocyanate using 0.01M dibenzo-18-crown-6in nitrobenzene. Back extraction of U(VI) was quantitative with various strippingagents. Separation of U(VI) from other elements was achieved from binary aswell as multicomponent mixtures. Uranium was determined in monazite sand andsyenite rock samples. The method is very simple, rapid and highly reproducible(approximately ±2%).

Effects of Surfactant PDFO on Photoluminescence of Porous Silicon

On the performance of the hydrogen peroxide method for Th-determination we encountered some difficulties, namely the formation of the insoluble matter occured in the nearly neutral solution after evaporation. We carried out the Th-determination in the mixture of the Th and some kind of the rare earth, and found that the insoluble matter was not formed in case of the mixture of Th and some kind of rare earth, but formed in case of Monazite. The formation of the insoluble matter in the case of Monazite sand, however, could be avoid by using the beaker instead of the evaporating dish and by adding the water repeatedly before it was completely evaporated to dryness.

Determination of thorium in environmental and workplace materials by ICP–MS

The paper outlines the advantages of the use of Inductively Coupled Plasma Mass Spectrometry (ICP–MS) over radiometric techniques to measure natural thorium, 232Th. Experimental parameters that must be taken into account in the sample digestion, preparation and ICP–MS analysis of environmental (soils, rocks, sediments) or workplace (thorium oxide, reference solutions) materials are described. The methods presented are applied to various reference materials, with the aim of providing suitable procedures to be useful for other important thorium containing materials (such as monazite sands or welding electrodes). The participation in a European Commission intercomparison exercise is detailed and a comparison with alpha spectrometry is made.

Separation of Thorium(IV) from Associated Elements Using Poly-(Dibenzo-18-Crown-6) and Column Chromatography from Picric Acid Medium

A simple column chromatographic method has been developed for the separation of thorium(IV) from associated elements using poly-(dibenzo-18-crown-6). The separations are carried out from picric acid medium. The adsorption of thorium(IV) was quantitative from 0.0005–0.05M picric acid. Amongst the various eluents tested, 2.0–8.0M HCl, HBr, 1.0–6.0M HClO4 and 5.0M acetic acid were found to be particularly efficient for the quantitative elution of thorium(IV). The capacity of poly-(dibenzo-18-crown-6) for thorium(IV) was found to be 1.29±0.01 mmol/g of crown polymer. Thorium(IV) was separated from a number of cations in binary mixtures in which most of the cations showed a very high tolerance limit. It was possible to separate thorium(IV) from a number of cations such as lanthanum(III), yttrium(III), uranium(VI), beryllium(II) and barium(II) in multicomponent mixtures. The method was extended to the determination of thorium in monazite sand. It is possible to separate and determine 5 ppm of thorium(IV) by this method. The method is very simple, rapid, selective and has good reproducibility (approximately ±2%).

Background Contribution to Internal Contamination

The northern part of the state of Rio de Janeiro is characterised by the presence of large deposits of monazite sand. In this region a monazite sand extraction plant is located, which has been in operation for more than 25 years. In order to analyse the background contribution to the internal contamination, 72 inhabitants of this region were monitored by excreta analysis. Some people have contributed with more than one sample to the study. In the high background radiation area it was possible to detect significant amounts of 232 Th in urine samples suggesting a chronic thorium incorporation. In 'normal' background areas, as in the city of Rio de Janeiro, the amount of 232 Th excreted in urine is not significant. The average 232 Th concentration in faeces of the non-exposed population is about one third of the average of 232 Th concentration in faeces samples from the workers and twice the average concentration in faeces samples from inhabitants of the city of Rio de Janeiro. The results indicate that the thorium intake is influenced by the place of residence and show how important it is to characterise the region where workers live when occupational control is carried out.