Furthermore, control tests were performed to demonstrate the effect of A. ferrooxidans in uranium bioleaching process and showed that the addition of this . PDF | This review describes the involvement of different microorganisms for the recovery of uranium from the ore. Mainly Acidithiobacillus forrooxidans. initial work on uranium bioleaching in the early s was taken to prevent oxidation rate of iron that may affect uranium’s microbial leaching.
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To receive news and publication updates for Journal of Nanomaterials, enter your email address in the box below. This is an open access article distributed under the Creative Bioleachihg Attribution Licensewhich permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Bioleaching has lots of advantages compared with traditional heap leaching.
In industry, bioleaching of uranium is still facing many problems such as site space, high cost of production, and limited industrial facilities.
Bioleaching of low-grade uranium ore using Acidithiobacillus ferrooxidans
In this paper, a continued column bioleaching system has been established for leaching a certain uranium ore which contains high fluoride.
The analysis of chemical composition of ore shows that the grade of uranium is 0. However, the fluoride content 1. This can be toxic for bacteria growth in bioleaching progress. In our continued multicolumns bioleaching experiment, the uranium recovery These results indicate that continued multicolumns bioleaching technology is suitable for leaching this type of ore.
The uranium concentration of PLS can be effectively improved, where uranium recovery can be enhanced by the iron exchange system. Furthermore, this continued multicolumns bioleaching system can effectively utilize the remaining acid of PLS, which can reduce the sulfuric acid consumption.
The cost of production of uranium can be reduced and this benefits the environment too. Biological metallurgy technology does not have a long history in leaching minerals.
Bioleaching is one of the most active technologies [ 1 ].
Continued Multicolumns Bioleaching for Low Grade Uranium Ore at a Certain Uranium Deposit
For introduction of bacterial leaching process at uranium leaching can enhance the kinetics of leaching and strengthen its process, bioleaching has been paid great attention in uranium industry in recent years. By this technology, the leaching time can be shortened and the recovery of minerals can be improved and the production costs can be reduced. This technology has been used in the production [ 23 ] or is still in the laboratory research stage [ 4 ].
Leaching in columns simulates percolation leaching because the conditions are very similar to those in the heap [ 5 ].
In China, bioleaching has been greatly improved in uranium industry. In China, hard-rock-type uranium such as granite-type deposits are using heap leaching widely in industry.
In this paper, one of the biggest granite uranium deposits located in south China with high fluoride mineral is selected for study. However, the uranium concentration of pregnant bioleacging solution PLS is low. This affects the adsorption efficiency.
The company who owns this deposit needs a new technology to solve this problem. So we try to use continued multicolumns bioleaching in uranium to model multiheaps bioleaching as to improve the production efficiency and reduce the production cost. A solid sample of uranium ore from the normal production of biolsaching in this deposit plant was used.
This type of uranium ore is mainly distributed in Taoshan Zhuguangshan mineralization belt. It has a relationship with the granite of Yanshan period in space and genesis. Uranium mineralizations are product in low level bioleadhing of tectonic fault, which mainly contain pitchblende, coffinite, fluorite silicate uranium, lead, and zinc.
Table 1 shows the chemical and mineralogical composition of the sample. Fluoride element analysis of the sample by potassium hydroxide digestion and measurement by fluoride electrode indicated that fluoride weight is high 1. This indicates these ores contain lots of fluoride mineral.
It can have certain influence on the growth of microorganisms. The sulfur weight is 0. This uranium ore belongs to a low grade type. Back-scattered electron image shows that the uranium minerals are located bioleachingg 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 bioleachingg 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 bioldaching growth medium are from PLS at this deposit.
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 [ 910 ]. As a consequence, a ratio of 10 was adopted in these experiments. 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. The test process and the specific implementation process are as follows: Afer d of leaching, the last column was unloaded out of this system hioleaching 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 ov and the pH and redox potential Eh were measured.
There exist consumptive acid minerals such as calcite chemical analysis of the weight of CO 2 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 3the pH values of PLS in bioleachhing 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, uramium 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.
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. During this experiment, both redox potentials of irrigating solution and PLS are measured in each day. Redox potentials of from 1st column to 4th column are presented in Figures 5 a5 b5 cand 5 d.
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 O 2 of the solution [ 13 ].
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After bioleaching period, redox potentials of PLS are significantly higher than the correspondence leaching solutions. This indicates that the bacteria grow well in these columns.
They enhance the ferrous oxidizing and produce ferric iron to oxidize pyrite and uraninite as shown in the following equations [ 14 ]: During bioleaching period, redox potentials increase and uranium concentrations are also increased as shown in Figures 5 and 6. With the variation of Eh of irrigating solution, the uranium concentration is varied too. Therefore, high Eh value is good benefit for oxidizing fourth valence uranium [ 15 ].
In this type of system, one purpose is the increasing redox potentials of this system; the other purpose is that the bioleacuing oxidizing bacteria can grow in the column. Irrigation method is that one day we use bacteria as irrigation solution after domestication by air in 24 hours for increasing the activity of bacteria and also increasing the redox bbioleaching, and the next day we use PLS from the former column which contains ferrous iron as the nutrition for those iron oxidizing bacteria in order to help the bacteria grow in the ore.
The redox potential of PLS is much lower than that of bacteria culture. For the bacteria culture and the PLS as irrigation solution changed in turns, the red curves of irrigation solution are more fluctuant than blue curve of PLS. In the acidification period, there occurs a uranium concentration peak. Most of sixth valence uranium minerals are leaching because they can dissolve in acid normally.
In this period, the redox potential and the concentration of uranium have no correlation relationship which are presented in Figure 6 a.
There is a big peak for uranium concentration for each column in the fifth day. However, the peak of 4th column is the highest one and that of the 3rd column is the second. The peaks uraniun the control column and the 1st column are much lower than the later columns.