Natural radionuclide-free phosphoric acid production

High-uranium phosphate rock from Itataia, Brazil, was milled for wet-process phosphoric acid production using the dihydrate method. Uranium contained in the phosphoric acid was recovered by solvent extraction. The distribution of long-lived natural radionuclides of the ²³⁸U and ²³²Th decay series involved in these operations was evaluated. ²²⁶Ra, ²²⁸Ra and ²¹⁰Pb were found to predominate in the phosphogypsum, while ²²⁸Th, ²³⁰Th and ²³²Th in the uranium-free phosphoric acid. Thorium is removed from the phosphoric acid by solvent extraction to produce a NORM-free phosphoric acid.     

Removal of radionuclides from acid mine waters by retention on adsorbing materials

Summary This study proposes a method for decontamination of acid drainage water from a uranium mine, as an alternative process to lime treatment. The research embodied the recovery of uranium with an ion-exchange resin, treatment of effluent resin with lime, or with inorganic adsorbents and biosorbents. The uranium decontamination level using the resin process was 94% and allowed the recovery of this element as a commercial product. Among the inorganic adsorbents studied, phosphogypsum was effective for ²²⁶Ra, ²²⁸Ra, and ²¹⁰Pb removal. Among the biosorbents, Sargassum sp.was superior in relation to its specific capacity to accumulate and remove ²²⁶Ra.     

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.     

Dentinal surface-cutting efficiency using a high-speed diamond bur,ultrasound and laser

We compare an ultrasound bur with a conventional one and an Er:YAG laser for cavity preparations. Human molars were embedded in resin and sliced for this study. The surface abrasion was performed by a high-speed instrument and ultrasound. The cavity preparation was initially performed with a high-speed diamond bur. After this, a 2.94-μm laser with 400 mJ/pulse at 4 Hz, and a pulse width from 250–500 μs was applied to the tooth surface for 30 s in a sweeping motion. The samples were analyzed by SEM. The abrasion surface with a conventional bur showed structure removal with different grooves, a smear-layer presence, and occluded dentinal tubules. The abraded surface with the CVD bur suggested a removal process in layers. The laser-irradiated surface showed a rough aspect with opened tubules and the absence of a smear layer. The results of this study suggest that a high-speed diamond bur, ultrasound, and laser were able to perform cavity preparation. However, the CVD bur presented a higher surface quality.     

Teeth characterization using ion beam analysis

Summary A collaboration project between the School of Dentistry and the Institute of Physics of the University of S?o Paulo has been established to measure elemental concentrations in teeth by proton induced X-ray emission (PIXE) and heavy ion elastic recoil detection analysis (HI-ERDA) techniques. Data on trace elements in human, bovine and swine teeth, analyzed by PIXE with a 2.4 MeV proton beam, were compared and concentrations for several elements were obtained with tens of mg/g sensitivity. HI-ERDA measurements employing a 52 MeV Cl beam were done to evaluate changes in elementary concentration in dental enamel after bleaching treatment with different products in 25 bovine incisors teeth. This non-destructive technique allowed the measurements of Ca, P, O and C concentrations above the limit of 100 mg/g.     

Synthesis of nanocrystalline tetragonal zirconia by a polymeric organometallic method

A polymeric precursor method based on the Pechini process was successfully used to synthesize zirconia–12 mol% ceria ceramic powders. The influence of the main process variables (citric acid—ethylene glycol ratio, citric acid—total oxides ratio and calcination temperature) on phase formation and powder morphology (surface area and crystallite size) were investigated. The thermal decomposition behavior of the precursor is presented. X‐ray diffraction (XRD) patterns of powders revealed a crystalline tetragonal zirconia single‐phase, with crystallite diameter ranging from 6 to 15 nm. The BET surface areas were relatively high, reaching 95 m² g⁻¹. Nitrogen adsorption/desorption on the powders suggested that nonaggregated powders could be attained, depending on the synthesis conditions. Copyright © 1999 John Wiley & Sons, Ltd.