Dissolution Factors of Ta, Th, and U Oxides Present in Pyrochlore

Abstract

Air pollution can be a problem in industrial processes, but monitoring and controling the aerosols in the work place is not enough to estimate the occupational risk due to dust particle inhalation. The solubility in lung fluid is considered to estimate this risk. The aim of this study is to determine in vitro specific dissolution parameters for thorium (Th), uranium (U), and tantalum (Ta) associated to crystal lattice of a niobium mineral (pyrochlore). Th, U, and Ta dissolution factors in vitro were obtained using the Gamble solution (simulant lung fluid, SLF), particle induced X-ray emission, and alpha spectrometry as analytical techniques. Ta, Th, and U are present in the pyrochlore crystal lattice as oxide; however, they have shown different dissolution parameters. The rapid dissolution fraction (f r ), rapid dissolution rate (λ r ), slow dissolution rate (f s ), and slow dissolution fraction (λ s ) measured for tantalum oxide were equal to 0.1 and 0.45 and 0.00007 day −1 , respectively. For uranium oxide, f r was equal to 0.05, λ r was equal to 1.1 day −1 , and λ s was equal to 0.000068 day −1 . For thorium oxide, f r was 0.025, λ r was 1.5 day −1 , and λ s was 0.000065 day −1 . These results show that chemical behavior of these three compounds in the SLF could not be represented by the same parameter. The ratio of uranium concentration in urine and feces samples from workers exposed to pyrochlore dust particle was determined. These values agree with the theoretical values of estimated uranium concentration using specific parameters for uranium oxide present in pyrochlore.

Atomic spectrometry update. Environmental analysis

“…Using ion chromatography, they found that 99% of S in particles smaller than 2 mm was soluble ammonium sulfate. Brazilan researchers, 42 in a study evaluating the occupational risk due to dust particle inhalation, determined the solubility of Ta, Th and U oxide species contained in pyrochlore (a niobium mineral) dust particles when subjected to a simulant lung fluid (Gamble solution). These experimentally derived dissolution factors were in broad agreement with calculated dissolution factors from worker exposure studies involving air monitoring and subsequent biomonitoring using faecal and urine samples.…”

Source and Nature of Inhaled Atmospheric Dust from Trace Element Analyses of Human Bronchial Fluids

“…In anthropized areas people are exposed to the almost constant inhalation of lithogenic and anthropogenic atmospheric dust delivered from natural sources, automotive traffic, and/or industrial activities. Effects on human health related to the inhalation of these atmospheric particulates are mainly recognized as precursors of silicosis, asbestosis, and cancers, whereas only a scarce literature is available focused on effects of the dissolution of atmospheric dust in the presence of human bronchial fluids. − This represents a lack of knowledge since environmental solids are often a source of concentrated metallic elements that can be released in biological fluids, and the amplitude of trace elements leachable from these solids depends from their composition and nature. , …”