Cadmium (Cd) is toxic for humans, but its effects on the yield and quality of rice under contaminated irrigation conditions remain uncertain. In this study, paddy soils in the Red River Delta (Vietnam) were selected for experiments with the purpose of understanding the effects of Cd contaminated irrigation water on growth, yields, and grain Cd accumulation. In addition, biochar was produced from rice husk (BRH) and rice straw for preventing Cd infiltration into rice was also studied in this experiment. A field experiment was established with applicated BRH and straw into polluted paddy soil, as a result the Cd content in grains reduced significantly. The Cd contaminated soil was added to the BRH and rice straw (RS) with six ratios, including: (1) RS 2.5%, (2) BRH 2.5%, (3) RS-BRH: 1.25-1.25%, (4) RS 5.0%, (5) BRH 5.0%, (6) RS-BRH: 2.5-2.5%, (w:w). Besides, three content levels 0.01-0.05-0.5 mg/L of Cd in irrigation water were applied throughout crop season. The results showed that the Cd accumulation in rice was in the following order: roots > stems > seeds. With 3 contaminated irrigation levels which were applied, the Cd concentrations of 0.05 mg/L and 0.5 mg/L affected plant height and yield. However, the Cd content in grains under contaminated soil condition can be controlled from 82.47-83.94% by applying a BRH ratio from 2.5-5% (w:w).
Design, construction and operation of a pilot for processing uranium containing ores are important stages in the process of project development of uranium production from ores because uranium contained minerals and the composition of minerals are unstable factors. In this case, pilot needs to be a simulation of a plant in the future, but with upgrade equipment compared that at laboratory scale. Results of lab research were used to select the most appropriate process for ore processing and selection of equipment for each stages. In the circumstance when there has been a lack of experience in processing uranium ores in Vietnam, the design and construction of such a pilot with completed technological procedures are essential. The main purpose of this work is to verify results of lab researches and optimize operational parameters of the process. In addition, several purposes were also considered such as study on the effects of solution circulation/recycling and accummulation of impurities in a long run; obtain necessary and sufficient information for design, cost estimate for investment and operation... The pilot only can achieve the expected objectives when ore sources (including reserves and characteristics) are determined; a complete technological process for obtaining technical uranium (yellowcake) is designed; investment and operational capitals are estimated and these estimates show the costs and benefits of the process. In this article, the authors will focus on the presentation of research results, including data on ore, process technology, material balance, pilot scale, the basic parameters of equipments, installation diagram of equipments, construction, power and water needs identification, preliminary calculation of investment and operational costs.
Ion exchange is one of the most popular techniques for recovery and purification of uranium from sulfuric acid leaching solution, especially for recovery of uranium from a low uranium containing solutions. Resins commonly used are strong base or weak base anion resins with amine functional group. The anionic form of resins may be NO3-, Cl- , SO42- or OH-. The selection of a resin depends on the uranium total exchange capacity, selectivity and the cost. The previous studies often use Amberlite IRA-420 for concentration and purification of uranium solution from Pa Lua sandstone ores. This is a good and suitable resin but high price. To diversify the resins and reduce the costs, instead of IRA-420, the authors tested two commercial resins Indion GS300 (India) and Purolite A400 (UK) in the processing of uranium solution from sandstone ores. The results showed that the uranium total exchange capacity of these resins is only about 80 - 85% over Amberlite IRA-420, but these resins should be able to be used instead of Amberlite IRA-420 due to their low cost and availability in Vietnam.
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