BIOLEACHING OF URANIUM PDF

Table 1 Chemical and mineralogical composition of the ore sample used in column bioleaching. Back-scattered electron image shows that the uranium minerals are located in the tiny fractures of the ore and they are accompanied by pyrite as shown in Figure 1. This indicates that once pyrite is leached; the surface area of those uraninite and coffinite minerals will be greatly increased. Those tiny fractures around uranium minerals will be enlarged as well.

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Table 1 Chemical and mineralogical composition of the ore sample used in column bioleaching. Back-scattered electron image shows that the uranium minerals are located in the tiny fractures of the ore and they are accompanied by pyrite as shown in Figure 1. This indicates that once pyrite is leached; the surface area of those uraninite and coffinite minerals will be greatly increased. Those tiny fractures around uranium minerals will be enlarged as well.

Furthermore, when the pyrite is dissolved or, more precisely, is oxidized, ferric iron is produced which can offer good oxidizing for those reduced-type uranium minerals. Iron oxidizing bacteria are a good worker who can do this job. In our study, a strain of mesospheric iron oxidizing bacteria Acidithiobacillus ferrooxidans mixed with Leptospirillum ferriphilum, named B3mYP1Q provided by our university was used throughout the investigations.

Acidithiobacillus ferrooxidans is Gram-negative bacteria [ 8 ], characterized by nonsporulating rods, 0. The bacteria are also known to be motile by means of a single polar flagellum. All of these characteristics were observed during the isolation of the strain used.

The compositions of the nutrient growth medium are from PLS at this deposit. Experimental Bioleaching Leaching system consists of serial organic glass columns with a diameter of mm and a height of 2 m. In the bottom of each column gravel and pebbles were cushioned at 10 cm height. The ratio of the internal diameter of the column to the height of ore is important for the leaching solution percolates more efficiently. It has been established that this ratio must be greater than 4 and not in excess of 20 in order to avoid any effects of the wall [ 9 , 10 ].

As a consequence, a ratio of 10 was adopted in these experiments. In each column, the ore is built up cm high and on top there are loading cobble and gravel 10 cm high. Plastic film was covered on the top of both leaching column and liquid collecting tank to reduce evaporation. The irrigation is powered by a peristaltic pump. The speed of pump is changed in the test to control the time and intensity.

Test process is d for the uranium leaching cycle, consisting of four columns as shown in Figure 2. The test process and the specific implementation process are as follows: 4 columns are, respectively, set, first column acid leaching stage and domestication stage , second column bioleaching stage , third column bioleaching stage , and the last column final leaching stage. Each column acidification stage is 30 d, and domestication stage is 30 d, and bioleaching stage is 30 days and final leaching stage is 30 days.

Afer d of leaching, the last column was unloaded out of this system and a new column was added in. Before irrigation of the former column, the pH of PLS should be adjusted to 1.

For comparison, a single column test is conducted at the same time. Sample volumes of liquid were extracted periodically and the pH and redox potential Eh were measured.

Figure 2 Schematic of continued multicolumn bioleaching system. Results and Discussion 3. Acid Consumption during Bioleaching There exist consumptive acid minerals such as calcite chemical analysis of the weight of CO2 1. Thus, during bioleaching, the pH of irrigating solution in the column will be increased. When the pH value of irrigating solution reaches over 2. As shown in Figure 3 , the pH values of PLS in the first 5 leaching days decrease very fast but are still greater than 4.

In the next five days, pH values decrease slowly compared with the former 5 days and reach around 2. This indicates that during this stage most easily consumptive acid minerals such as calcite of this ore are almost reacted by acid in the large fractures. However, some consumptive acid minerals in small fractures will be reacted more slowly. On the other hand, the mesospheric iron oxidizing bacteria of Acidithiobacillus ferrooxidans and Leptospirillum ferriphilum which are used in this experiment are more active in pH of 1.

Therefore, the pH of irrigating solution cannot be lower than 1. When pH is lower than 1. These type of precipitations are difficult to be dissolved by strong acid and that will decrease the permeability of the column [ 12 ].

The uranium minerals will be wrapped up by them. As a consequence, they hinder the irrigating solution to react with the uranium minerals and the uranium recovery is decreased. In acidification stage, therefore, the acid concentration should be decreased as well.

Under these circumstances, the precipitation of both goethite and jarosite-type basic compounds will not occur in the next bioleaching stage and the bacterium will grow in the column as bacteria are adapted to this pH and the culture from the irrigating solution PLS of pH adjustment. Figure 3 pH value of the PLS in the first 40 days.

In the next 20 days, acid consumption increases still fast but it is lower than that in the first 10 days. And then in the next bioleaching stage, acid consumption still increase slowly because some acid needs to be added in the bacteria domestication pond for pH adjustment and there are still some consumptive acid minerals in tiny fracture which are not reacted by acid in the former stage.

The total acid consumption of 1st column is highest and that of the last column is lowest. Moreover, the acid consumption of the 1st column and that of the 2nd column are very similar. Because the first column is the initial column in this type of system and the acid amount of PLS from the 1st column is small, the irrigating solution of 2nd column needs to add more acid for pH adjustment using PLS from the 1st column.

The acid of the 3rd and 4th column, however, can accumulate acid from the former columns. It is found that the acid consumption of the later columns will be lower than that of the former ones. Redox potentials of from 1st column to 4th column are presented in Figures 5 a , 5 b , 5 c , and 5 d. During the acidification process of leaching of uranium, the redox potentials of leaching solution are low and varied between mV and mV versus SCE.

In this type of ore, many minerals such as pyrite and urinate belong to reduced substances. In the leaching progress, they can be oxidized by ferric iron or O2 of the solution [ 13 ].

EL SUEO LUCIDO PDF

Uranium Bioleaching

Bioleaching of non-sulfidic ores such as pitchblende also uses ferric iron as an oxidant e. Sulfidic iron ores can be added to speed up the process and provide a source of iron. Bioleaching of non-sulfidic ores by layering of waste sulfides and elemental sulfur, colonized by Acidithiobacillus spp. The copper is removed by bonding to a ligand, which is a large molecule consisting of a number of smaller groups , each possessing a lone electron pair.

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Bioleaching

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Continued Multicolumns Bioleaching for Low Grade Uranium Ore at a Certain Uranium Deposit

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