The Screening And Breeding Of Bacteria And Key Technologies Of Bioleaching Of High Fluoride Uranium Ores

It is well known that uranium is important energy and strategic resources.For the reason that about 60%of uranium resources lies in granite and volcanic type uranium deposit with high fluoride in China,it is of importance to develop an efficient extraction technology of uranium from high fluoride-contained uranium ores in order to solve the problem of shortage of uranium resource.Nowadays,the uranium bioleaching technology has been focusing on advantages,such as cost saving,high utilization rate of resources and eco-friendly.On the other hand the leaching liquid of high concentration fluoride inhibits the bacteria activities and affects the leaching efficiency,which hindered the uranium bioleaching technology to be promoted and applied in industry.745 uranium ore in Guangdong Province are analyzed in detail in this paper,with regard to bioleaching bacteria breeding,experiments on parameter optimizing and active cultures matching and study of the leaching mechanism carried out.In the end,a typical demonstration project on 10,000 tons ore was set up successfully in China.To solve the key problems in bioleaching of the fluoride-contained uranium ore,the present study has achieved the following results:The geological and geochemical bases of bioleaching of high fluoride uranium were provided by the study of ore properties in 745 uranium ore such as uranium ore chemical composition,mineral constitutes,uranium occurrence state and dissemination characteristics of uranium minerals.Uranium grade,fluorine and reduced sulfur content were about 0.20%,2.15%and 0.24%in 745 uranium ore,respectively.Uranium minerals were mainly pitchblende and coffinite,followed by brannerite and uranothorite,which mainly existed in the form of micro-vein,massive and gelatinous in ore microfissures and gaps of gangue mineral crystal.Particle size of uranium minerals was less than 0.1 mm.Due to the high fluorine content and low content of pyrite ore,it is very important to breed high fluoride resistant bacteria and join the ferrous sulfate to the bacterium fluid.This paper is based on the study of the screening and breeding of bacteria which adapted to the high fluoride uranium ore and raffinate,and obtained suitable strains of bioleaching of high fluoride uranium.The uranium leaching consortium,B_3mYP1Q-C,which was isolated and enriched from the ore slag,was mainly composed of Leptospirillum ferriphilum and Acidithiobacillus ferrooxidans.It was domesticated with uranium raffinate of 3.5 g/L high fluorine and was able to oxidize 4.75 g/L Fe²⁺in 21 hours lastly.After ultrasonic mutation for 60min,a new consortium B_3mYP1Q-C-UW60-300 was obtained.The average ferrous iron oxidized rate could reach to 2.20 g/L in modified 9K medium with 300 mg/L NaF after 3 inoculations and cultivation.The optimum process conditions of uranium bioleaching in 745 uranium ore were studied by column leaching with batch experiments.Firstly,uranium minerals are acidified by H₂SO₄solution with concentration of 40 g/L fresh water irrigated on minerals to pH≤2.0 of leachate in accordance with the irrigation intensity of 10%at acidified leaching stage.Then culture solution of B_3mYP1Q-C and raffinate solution were irrigated alternatively with the irrigation intensity of5%till Fe³⁺concentrations in leachate more than in the spray liquid at bioleaching stag.And then,liquid of series column was irrigated with the irrigation intensity of 5%till uranium concentrations in leachate was less than 50 mg/L.Finally,uranium raffinate used as irrigation solution to irrigate with uranium concentrations was less than 20 mg/L.Four series column experiment showed that the average slag uranium leaching rate was 89.79%and the average acid consumption was 3.85%after 135 days leaching.Minerals composition,morphology and microbial community changes before and after bioleaching were analyzed by EPA（electron probe analyzer）,SEM（scan electron microscope）,XRD（X ray diffraction）and molecular methods（RFLP,restriction fragment length polymorphism）.Leptospirillum ferriphilum and Acidithiobacillus ferrooxidans were advantageous bacterium group of bioleaching system in 745 uranium ore,and microbial community successions related to sampling depth,leaching stage,spray condition.Microbial diversity attached on ore surface was more abundant than that of free in the leachate.Uranium as pitchblende and coffinite outside quautz in the fissure of ore were easier to be bioleached,and brannerite and uranium packaged by quartz are difficult to be bioleach.Al₂O₃,FeO,Fe₂O₃,CaCO₃ and CaF₂ were dissolved in ore in the processing of bioleaching.Morphology of tailings after bioleaching showed that the surface was rough,uneven,and gypsum crystals were precipitated on the surface of the slag.Therefore,the formation of gypsum crystals through bioleaching of high fluoride uranium was elucidated on the basis of these data.According to the optimized process parameters,multiple heap series bioleaching test of industrialization was carried out in 745 uranium ore set up a typical demonstration project in China.The results showed that work bacteria liquid was produced after three level expansions which adapt to local environmental condition.Periods were 129 days and 122 days,the acid consumption were 4.97%and 4.77%,and the slag uranium leaching rate were 90.4%and 90.5%in two bioleaching heaps,respectively.Compared with the other two acid leaching heaps with similar uranium grade,work periods were shorten by 18%and 28%,the acid consumption was decreased by 10%and 13%,and the slag leaching rate was increased by 0.7%and 0.4%,respectively.