Experimental study on radon retardation effect of modular covering floats in radon-containing water.

Radon-containing water bodies in uranium mining areas inevitably release radon gas, polluting the surrounding environment via radiation. Thus, it is particularly important to develop devices with the ability to retard the radon release from such water bodies. Based upon theories of radon exhalation in water, a radon exhalation retardation device (RERD) with flexible, modular floats (a flexible polyvinyl chloride material module that floats on water) was designed and manufactured. To study the modular surface-covering floats' effectiveness in retarding radon release from water surfaces, an experimental setup was constructed to simulate radon release from water bodies, using a granular uranium ore sample from a uranium mine as sediment material. Closed-loop measurements were taken to determine the radon exhalation rate on the exposed surface of the water in uncovered and covered conditions. Radon retardation rates were also compared for different area coverage (29.6%, 59.1%, and 88.7%) and immersion depths (0.02 m and 0.04 m) in unperturbed and perturbed water bodies. The results show that: 1) the greater the area coverage, the greater the radon retardation rate in both unperturbed and perturbed water bodies; 2) under the same coverage conditions, the surface radon exhalation rate and the radon transfer velocity at the gas-liquid interface of the perturbed water are larger than those of the unperturbed water; 3) The immersion depth of modular surface-covering floats has a stronger effect on the radon retardation rate in unperturbed water bodies than in perturbed water bodies. The study shows that the proposed modular floats are effective in retarding radon release from both perturbed and unperturbed water bodies.

A laboratory method for concurrently determining diffusion migration parameters and water saturation effects of thoron in uranium tailings.

Environmental humidity has a significanteffect on changes in free 220Rn (thoron) production rate and effective diffusion coefficient of 220Rn in uranium tailings. To understand such changes, a closed cavity containing porous 220Rn media with finite thickness was studied. Based on the 220Rn diffusion migration theory in porous media with finite thickness, a model for calculating the uniform 220Rn activity concentration in a closed container with porous media of finite thickness was established. A laboratory method for concurrently determining free 220Rn production rate and effective diffusion coefficient of 220Rn was proposed and a corresponding experimental setup was made. With samples taken from a uranium tailing impoundment in southern China, water content, free 220Rn production rate, and effective diffusion coefficient of 220Rn in uranium tailings were determined under certain environmental temperature and humidity conditions. Results show that: (1) The method and experimental setup presented in this study can simultaneously determine free 220Rn production rate and effective diffusion coefficient of 220Rn in porous media such as uranium tailing; (2) The free 220Rn production rate in uranium tailings increases linearly with water saturation. Effective diffusion coefficient of 220Rn, on the other hand, decreases exponentially with the increase in water saturation.

Transport of uranium(VI) in red soil in South China: influence of initial pH and carbonate concentration.

Uranium-contaminated wastewater associated with uranium (U) mining and processing inevitably releases into soil environment. In order to assess the risk of U wastewater contamination to groundwater through percolation, U adsorption and transport behavior in a typical red soil in South China was investigated through batch adsorption and column experiments, and initial pH and carbonate concentration were considered of the high-sulfate background electrolyte solution. Results demonstrated that U adsorption isotherms followed the Freundlich model. The adsorption of U to red soil significantly decreased with the decrease of the initial pH from 7 to 3 in the absence of carbonate, protonation-deprotonation reactions controlled the adsorption capacity, and lnCs had a linear relationship with the equilibrium pH (pHeq). In the presence of carbonate, the adsorption was much greater than that in the absence of carbonate owing to the pHeq values buffered by carbonate, but the adsorption decreased with the increase of the carbonate concentration from 3.5 to 6.5 mM. Additionally, the breakthrough curves (BTCs) obtained by column experiments showed that large numbers of H+ and CO32- competed with the U species for adsorption sites, which resulted in BTC overshoot (C/C0 > 1). Numerical simulation results indicated that the BTCs at initial pH 4 and 5 could be well simulated by two-site chemical non-equilibrium model (CNEM), whereas the BTCs of varying initial carbonate concentrations were suitable for one-site CNEM. The fractions of equilibrium adsorption sites (f) seemed to correlate with the fractions of positively charged complexes of U species in solution. The values of partition coefficients (kd') were lower than those measured in batch adsorption experiments, but they had the same variation trend. The values of first-order rate coefficient (ω) for all BTCs were low, representing a relatively slow equilibrium between U in the liquid and solid phases. In conclusion, the mobility of U in the red soil increased with the decrease of the initial pH and with the increase of the initial carbonate concentrations.

Experimental study of the effect of water level and wind speed on radon exhalation of uranium tailings from heap leaching uranium mines.

Water level and wind speed have important influences on radon release in particle-packing emanation media. Based on radon migration theory in porous media under three water level conditions, an experimental setup was designed to measure the surface radon exhalation rate of uranium tailings from heap leaching uranium mine at different water levels and wind speeds. When the water level was at 0.3 m (overlying depth 0.05 m), radon transfer velocities at the gas-liquid interface were also measured at different wind speeds. Results show that when the water level was equal to or lower than the surface of the sample, the radon exhalation rate increased with increasing wind speed and decreased with increasing water level. When the water level was higher than the surface of the sample, radon exhalation rate of the water surface increased with increasing surface wind speed. The wind speed, however, was less influential on the radon exhalation rate as the depth of the overlying water increased, with a dramatic decrease in radon release. That said, at different wind speeds, radon transfer velocities at the gas-liquid interface were consistent with literature. On the other hand, changes in wind speed had significant influences on the radon transfer velocity at the gas-liquid interface, with the effect less pronounced at higher wind speeds.

Experimental study on radon exhalation behavior of heap leaching uranium ore column with dilute sulfuric acid.

In order to study the radon release behavior when heap leaching uranium ores with dilute sulfuric acid, unleached uranium ores from a uranium mine in southern China were selected as test samples. Adopting parameters from leaching processes commonly used in uranium mines, a laboratory experiment was carried out for 21 days with a one-dimensional acid heap leaching experimental column. The surface radon exhalation rate of uranium ore column was determined by static accumulation method while spraying with deionized water and dilute sulfuric acid. The uranium leaching rate and ore column height for all 21 days of the experiment were also measured. The results show that (1) when sprayed with a leaching agent, the surface radon exhalation rate of uranium ore column initially increased with time sharply. After a maximum value was reached, the rate gradually decreased and stabilized. When the spraying stopped, the surface radon exhalation rate of uranium ore column initially decreased, before increasing until it tended to stabilize. (2) During the entirety of the 21-day leaching experiment, the cumulative leaching rate of uranium increased gradually with time. On the other hand, the surface radon exhalation rate of uranium ore column fluctuated, but the leaching of uranium from uranium ores had almost no effect on the radon exhalation rate. (3) There was no linear correlation between the surface radon exhalation rate and the residual height of ore column during leaching, but the collapsing event of ore column was the direct inducing factor of the fluctuation of surface radon exhalation rate.

Transformation of uranium species in soil during redox oscillations.

Redox oscillation is commonly found in near-surface environment, where soils are often polluted with many redox active contaminants, including uranium (U). In order to investigate the transformation of U species in near-surface soil under redox oscillations conditions, redox oscillations and reduction experiments were performed, biogeochemical parameters and native microbial community composition were monitored, main elements on the surface of solid-phase were analyzed by XPS, and labile U(IV) species and stable U(IV) species in solid-phase were provisionally defined using an anoxic 1 M sodium bicarbonate extraction. It was found that redox oscillations slightly increased the water-soluble U but significantly increased the stable U(IV) species (P < 0.05) in soil. In reduction experiment, there was upper limit value for percentage of stable U(IV) species, and the labile U(IV) species could not transform to stable U(IV) species in a short period of time under reduction conditions. The redox transition of Fe enriched on the surface of soil and the conversion of microbial community composition played a major role in speciation transformation of U under redox oscillations conditions. In addition, sequential extraction revealed that the increase of stable U(IV) species content reflected the U speciation transition from acetate extract to more recalcitrant hydroxylamine extract. The finding provides a potential method for improving the stability of U when bio-reduction is used to remediate the U-contaminated soils.

Modeling and experimental examination of water level effects on radon exhalation from fragmented uranium ore.

In this study, a one-dimensional steady-state mathematical model of radon transport in fragmented uranium ore was established according to Fick's law and radon transfer theory in an air-water interface. The model was utilized to obtain an analytical solution for radon concentration in the air-water, two-phase system under steady state conditions, as well as a corresponding radon exhalation rate calculation formula. We also designed a one-dimensional experimental apparatus for simulating radon diffusion migration in the uranium ore with various water levels to verify the mathematical model. The predicted results were in close agreement with the measured results, suggesting that the proposed model can be readily used to determine radon concentrations and exhalation rates in fragmented uranium ore with varying water levels.

Biomedical molecular of woody extractives of Cunninghamia Lanceolata biomass.

Extractives, important compounds from wood, provide abundant resources for woody medicine. In this study, the three extractives from Cunninghamia lanceolata wood were removed by method of three-stage extraction with alcohol, petroleum ether, and alcohol/petroleum ether and their chemical components were analyzed by gas chromatography-mass spectrometry (GC-MS). Thirteen chemical components were discovered in the first-stage extractives, including: 4-((1e)-3-hydroxy-1-propenyl)-2-methoxyphenol (36.80%), α-(2-phenylethenyl)-1-piperidineacetonitrile (15.39%). One-hundred chemical components were discovered in the second-stage extractives, including: [1s-(1α,4aα,10aß)]-1, 2,3,4,4a,9,10,10a-octahydro-1,4a- dimethyl-7-(1-methylethyl)-1- phenanthrenecar-boxylic acid (15.16%), 1,3-dimethoxy-5-[(1e)-2- phenylethenyl]-benzene (6.99%). Seven chemical components were discovered in the third-stage extractives, including: 1,3-dimethoxy -5-[(1E)-2-phenylethenyl]-benzene (32.88%), stigmasta-4,6,22-trien-3α-ol (17.83%). And both the main retention time of the first-stage and which of third-stage extractives are 20-30 minutes, and the main retention time of the second-stage extractives is <10 minutes. Besides, the three extractives contained many biomedical molecular, such as [1s-(1α,4aα,10aß)]-1,2,3,4,4a,9,10,10a-octahydro-1,4a-dimethyl-7-(1-methylethyl)-1-phenanthrenecar-boxylic acid, squalene, stigmast-4-en-3-one and γ-sitosterol and so on, which means that the three extractives from Cunninghamia lanceolata wood have huge potential in biomedicine.

Molecular characteristics of woody extracts of Buxus microphylla.

As one of famous shrubs in China, Buxus microphylla is considered as the important wattle. However, the constituents of Buxus microphylla stem extracts aren't used effectively. Therefore, the molecules of stem extracts in Buxus microphylla are analyzed to further utilize the resources. The results show that the optimal extraction time of ethanol/methanol extraction, petroleum ether/ benzene extraction, and benzene/alcohol extraction are 7h, 7h, and 5h, respectively. The HK-61, HK-63, HK-73, HK-81, HK-82 stem extracts are obtained 1, 9, 1, 27, and 1 components, respectively. The stem extracts of Buxus microphylla is rich in drug and biomedical activities. Buxus microphylla stem is fit to extract 1,5-hexadien-3-yne, squalene, and dibutyl phthalate.