Bioleaching Of Uranium Ore From Xiangshan Deposit And Preliminary Study On Its Mechanism

Xiangshan uranium deposit,which is set with hydrometallurgy as a whole,is one of the biggest uranium exploitation mines in China.The unranium ores of Xiang deposit are complex with high content of clay minerals.Currently,high-grade uranium ore from this deposit is leached bya conventional agitation hydrometallurgical way,but the production costs are high and economic efficiency is poor.On the other hand,low-grade uranium ore is leached by percolation leaching method,while the fine ores in it cause the heap compacted,clayed and the penetrate ability decreased.In this thesis,heap bioleaching and CSTR bioleaching are conducted in-depth study,as well as a preliminary study on its mechanism during the bioleaching process.The research makesboth the role and characteristics during the microbial leaching of uraniumto be understood more deeply.The technology is a better to solve those problems such as high acid consumption,easy compactionand long leaching period.Boths of the technological process and technological parameters of microbial leaching of uranium are obtained through the study.The results can provide good referencesfor industrial applications of the microbial leaching of uranium oresuch as Xiangshan uranium deposits.It can aslo enrichoururanium mining technology and uranium mining theory.The main research content and results are as shown follows.According to the material compositions of Xiangshan uranium deposit,the uranium minerals are brannerite and pitchblende mainly.The refractory native brannerite accounts for about half content of the uranium minerals.These uranium minerals are often associated with pyrite and fluorite,and are semi-wrapped with them or at their edges.The uranium ore contains many apatite and illite,which can product mud and clay in the heap.They can cause compaction easily during leaching.Furthermore,there is a significant positive correlation between chemical sulfur content and uranium content in the ore.This indicates that there exists a close relationship between uranium and pyrite in production.Thus the study suggests that Xiangshan uranium ore is suitable for bacterial leaching due to its mineralogy.Through the study from bioleaching pilot test,a heap bioleaching technology is developed and those process parameters areoptimized.The main factors,which affect process of uranium bioleaching,are analyzed as well.It is found that most of acid is consumed in pre-leaching acidification stage.The acid consumption is controlled by the total acid minerals,but not affected by the leaching ways.The hexavalent uranium is prioritily leached in the early stage.The consumption of acid substances presence in the ore have bad impact on the uranium leaching,while acidification with higher acid in the early stage can promote uranium leaching significantly.It is shown that the bioleaching of uranium gets better results than the acid leaching does.The turned column technology is one of the important methods to solve uneven of ore in the column during bioleaching process.This technology can avoid the compaction problem of ore basically.The leaching result shows that the acid consumption is low to 6.8%and the leaching rate is high to 90%.The leaching period is around 126 days.Through batch tests of fine uranium ore bioleaching in stirred-tank reactor,a technology of continuous-flow stirred-tank reactor(CSTR)bioleaching,which adopts to leach Xiangshan uranium ore,has been obtained.Those parameters of stirred-tank reactor bioleaching are obtained,of which the acidification acidity ranges from 30 g/L to 60 g/L,and the acid consumption ranges from 8%to 15%,and the purple density ranges from 20%to 40%,and the initial ferric concentration ranges from 7 g/L to 10 g/L,and the optimum leaching period is around 10 hours.Through a pilot bioleaching in CSTR,it is showed that CSTR can improve the uranium recovery.After three tanks in series,the uranium recovery is more than 91%and the leaching period is about 20 hours.In this leaching system,those parameters,such as Eh value,ferric,ferrous,ratio of ferric to ferrous,are the main factors of influence uranium leaching rate.In this thesis,the mechanism of uranium bioleaching is preliminary discussed.According to the characteristic of bioleaching process and thermodynamic principle,a potential-pH diagram for bacteria-pyrite-uranium-water system is created.The role of bacterial leaching of uranium is analyzed by the diagram.By the thermodynamic principles,the mechanism of bacterial leaching was clarified that the indirect action holds the leading status in uranium leaching process.The consumption of acid for mineral is calculated and the acid consumption mechanism is explained clearly too.Through the study of the chemical composition change during the leaching process,it is proved that the uranium leaching is related to the pyrite leaching closely.The leaching of pyrite has good benefit for leaching of uranium.The uranium bioleaching is under indirect action mainly.In short,according to the material composition of uranium ore from Xiangshan deposit,the theme put forward a heap bioleaching technology and a bioleaching technology in stirred-tank reactor for coarse and fine uranium ore respectively.Systematic research.of bioleaching of uranium ore in stirred-tank reactor is the first time in Xiangshan area.A diagram of potential-pH for bacteria-pyrite-uranium-water is createdinnovatively.It provides a new methodology for in-depth discussion of the mechanism of microbial action during bioleaching.