Optimization of Environmental Conditions for Microbial Stabilization of Uranium Tailings, and the Microbial Community Response

Uranium pollution in tailings and its decay products is a global environmental problem. It is of great significance to use economical and efficient technologies to remediate uranium-contaminated soil. In this study, the effects of pH, temperature, and inoculation volume on stabilization efficiency and microbial community response of uranium tailings were investigated by a single-factor batch experiment in the remediation process by mixed sulfate-reducing bacteria (SRB) and phosphate-solubilizing bacteria (PSB, Pantoea sp. grinm-12). The results showed that the optimal parameters of microbial stabilization by mixed SRB-PSB were pH of 5.0, temperature of 25°C, and inoculation volume of 10%. Under the optimal conditions, the uranium in uranium tailings presented a tendency to transform from the acid-soluble state to residual state. In addition, the introduction of exogenous SRB-PSB can significantly increase the richness and diversity of endogenous microorganisms, effectively maintain the reductive environment for the microbial stabilization system, and promote the growth of functional microorganisms, such as sulfate-reducing bacteria (Desulfosporosinus and Desulfovibrio) and iron-reducing bacteria (Geobacter and Sedimentibacter). Finally, PCoA and CCA analyses showed that temperature and inoculation volume had significant effects on microbial community structure, and the influence order of the three environmental factors is as follows: inoculation volume > temperature > pH. The outcomes of this study provide theoretical support for the control of uranium in uranium-contaminated sites.

Application Analysis of Radial Basis Function Neural Network Algorithm of Genetic Algorithm for Environmental Restoration and Treatment Effect Evaluation of Decommissioned Uranium Tailings Ponds

A new analysis method for the environmental stability of uranium tailing ponds is established in this paper, and the stability intervals and environmental stability rates of indicators are defined in precise mathematical language and analyzed with examples. The results show that the overall environmental stability of this uranium tailings pond is still in a poor state after the first phase of decommissioning treatment, and special decommissioning treatment should be carried out for factors such as pH and radionuclides Po and Pb. Using the powerful nonlinear mapping function of the artificial neural network, a radial basis function neural network algorithm was constructed to predict the environmental stability of the uranium tailing pond. It provides a new feasible method for the comprehensive evaluation technology of uranium tailings ponds. Accuracy in DOA Estimation. The research work in this paper mainly analyzed the environmental stabilization process and stability of decommissioned uranium tailings ponds, proposed a new concept of environmental stability with ecological and environmental protection concepts and gave it a new connotation, established an environmental stability evaluation index system for decommissioned uranium tailings ponds through index screening by using rough set theory, comprehensively considered the influence of environmental factors such as external wastewater and exhaust gas, and realized the multifactor. The system of evaluation indexes for the stability of decommissioned uranium tailings ponds was established by combining multiple factors, and the long-term monitoring and modeling of the environmental stabilization process of decommissioned uranium tailings ponds was carried out by using mathematical methods. The results show that the RBFNN-GA algorithm can reduce the training error of the random radial basis function neural network, improve the generalization ability of the network, and make it capable of handling large data sets.

Radioecological Assessment of Uranium Tails Deposits (Sumsar, Shekaftar, Terek-Sai)

The article presents the results of radio ecological studies of the territories of uranium tailings in Kyrgyzstan (Sumsar, Shekaftar and Terek-Sai), as well as their current state and assessment of the radioactive contamination’s potential risks. The ore field of this region is characterized as an extremely complex structure and covers about 30 ore occurrences of lead and rare metals. Starting from the Precambrian period both applicative and disjunctive disturbances within its boundaries have been widely developing and being manifested many times throughout the history of geological development. Oxidized and sulfide ores have been developed within the deposit. Unfortunately, serious miscalculations were made. As result of natural disasters; such as earthquakes, landslides, mudflows, etc., several uranium tailing dumbs have been damaged. Day by day, the risk of destruction and the threat of radioactive contamination of the Kyrgyz Republic territory are increasing. There are eight tailing dumps on the territory of Shekaftar uranium natural-technogenic province, the total volume of which is 1194 thousand m3 of radioactive waste. There are 15 mountain dumps of substandard ore with an ore volume of 4585.6 thousand m3. Hour, in local areas it exceeds 500 μR/h.

Response and Dynamic Change of Microbial Community during Bioremediation of Uranium Tailings by Bacillus sp.

Bacillus sp. is widely used in the remediation of uranium-contaminated sites. However, little is known about the competitive process of microbial community in the environment during bioremediation. The bioremediation of uranium tailings using Bacillus sp. was explored, and the bacterial community was analyzed by high-throughput sequencing at different stages of remediation. Bacillus sp. reduced the leaching of uranium from uranium tailings. The lowest uranium concentration was 17.25 μg/L. Alpha diversity revealed that the abundance and diversity of microorganisms increased with the extension of the culture time. The microbial abundance and diversity were higher in the treatment group than in the control group. The dominant species at the phyla level were Firmicutes and Proteobacteria in the uranium tailings environment, whereas the phylum of Proteobacteria was significantly increased in the treatment group. Based on the genus level, the proportions of Arthrobacter, Rhodococcus and Paenarthrobacter decreased significantly, whereas those of Clostridium sp., Bacillus and Pseudomonas increased dramatically. Hence, the remediation of uranium contamination in the environment was due to the functional microorganisms, which gradually became the dominant strain in the treatment, such as Desulfotomaculum, Desulfosporporosinus, Anaerocolumna, Ruminiclostridium and Burkholderia. These findings provided a promising outlook of the potential for remediation strategies of soil contaminated by uranium. The dynamic characteristics of the microbial community are likely to provide a foundation for the bioremediation process in practice.

A study on waterproof capabilities of the bentonite-containing engineered barrier used in near surface disposal for radioactive waste

Study of nuclear fuel cycle in Vietnam at the aspect of domestic production, the exploitation and process of uranium ore were began. These processes generated large amounts of radioactive waste overtiming. The naturally occurring radioactive material and technologically enhanced radioactive material (NORM/TENORM) waste, which would be large, needs to be managed and disposed reasonably by effectivemethods. It was therefore very important to study the model of the radioactive waste repository, where bentonite waterproofing layer would be applied for the low and very low level radioactive waste in disposal site. The aim of this study was to obtain the preliminary parameters for low-level radioactive waste disposal site suitable with the conditions of Vietnam. The investigation of the ratio between soil and bentonite was interested in the safety of the uranium tailings disposal site. The experiments with some layers of waterproofing material with the ratio of soil and bentonite are 75/25; 50/50; 25/75 were carried out to test the moving of uran nuclide through these waterproofing material layers. Waterproofing layers containing bentonite combined with soil were compacted into PVC pipes. One end of the plastic tube is sealed, the other end is embedded in a solution containing uranium nuclide. Analyzing the uranium content in each layers (0,1 cm) of material pipe is to determine the uranium nuclide adsorption from solution into the material in the different ratios at the different times: 1, 2 and 3 month. The results showed that the calculated average speeds of the migration of uranium nuclide into the soil- bentonite layer are 5.4.10-10, 5.4.10-10 and 3,85.10-10 m/s and thickness waterproofing layer (for 300 years) are 4,86 m, 4,86 m and 3,63 m for layer with the ratio of soil and bentonite are 75/25; 50/50; 25/75 respectively

Draft Genome Sequence of Arthrobacter sp. Strain 260, Isolated from a Uranium Tailings Management Facility in Northern Saskatchewan, Canada

The 3.9-Mbp draft genome sequence of Arthrobacter sp. strain 260, which was isolated from a uranium tailings management facility, is reported. The sequence may help determine the bioremediation potential of this strain and facilitate further research aimed at a better understanding of the hypertolerance of this genus to extreme conditions.

Physical-mechanical Properties and Radon Exhalation of Fiber-reinforced Uranium Tailings Geopolymer Solidified Bodies

Uranium tailing ponds are a potential major source of radioactive pollution. Solidification treatment of uranium tailings can control the diffusion and migration of radioactive elements in uranium tailings to safeguard the surrounding ecological environment. Literature review and field investigation were conducted in this study prior to fabricating 11 solidified uranium tailings samples with different proportions with PVA fiber, basalt fiber, metakaolin, and fly ash. The samples’ pore structure, volume resistivity, compressive strength, and radon exhalation rate variations were analyzed. The pore size of the solidified samples is mainly between 1–50 nm, the pore volume is between 0.726–1.750 cm3/g, the volume resistivity is between 1411.33-1937.33 Ω·m, and the compressive strength is between 20.61–36.91 MPa. The radon exhalation rate is between 0.0397–0.0853 Bq·m2·s− 1, which is lower than the national standard. Based on a comprehensive analysis of the physical and mechanical properties and radon exhalation rate of the solidified samples, the basalt fiber is found to outperform PVA fiber overall. The solidification effect is optimal when the 0.6% basalt fiber is added.