| Fe3+ ion is an important natural oxidant in acid leaching of uranium,in order to accelerate the leaching rate of uranium,it is necessary to increase the concentration of Fe3+ in the solution.In order to make full use of the Fe2+ ion in the adsorption tail liquid,in production,the high cost H2O2 is mainly added to the dispensing pool for oxidation of Fe2+ ion.To reduce production costs,in the acid leaching of uranium mines,domestic scholars have used Acidithiobacillus ferrooxidans instead of H2O2 as oxidant to convert Fe2+ ion into Fe3+ ion in adsorbed tailings.Some progress has been made,but the technology has not yet been applied to large-scale industrialization.There are many factors that restrict its industrial application.First,The optimum growth temperature of the common mesophilic bacteria(Acidithiobacills ferrooxidans ? Acidithiobacills thiooxidans ?Leptospirillum ferriphilum?Acidithiobacills caldus)is about 25~35 ?,this result in poor growth activity of mesophilic bacteria in low temperature(10~20 ?)adsorption tail liquid.Second,in the previousstudy,many organic materials,such as elastic nylon with low specific surface area and poor adsorption performance,were used as carrier of bacteria immobilization.They brought the problems of poor immobilization effect,slow growth of bacteria,low rate of oxidized Fe2+ion,etc.Third,most of the bioreactor were reaction pools which had some shortcomings: large area,low air utilization,high investment costs.In view of the problems appeared when bacteria was used as oxidant in the acid-leaching uranium ore in previous research.First of all,Acidithiobacillus ferrivorans was selected as oxidant instead of the mesophilic bacteria used in previous studies.The effects of the factors such as inoculation amount,temperature and initial Fe2+ content on the growth activity of the bacterium during the process of oxidative Fe2+were studied,and this bacteria had been domesticated for acid-resistant.Secondly,a new type of mobile bed bioreactor which has the advantages of small footprint,high air utilization ratio and a new moving bed biological reactor has been redesigned and processed.The biological ceramsite with strong acid resistance,large specific surface area and about 3~5 mm in diameter was screened as the carrier of the biofilm.Finally,the immobilized bacteria were cultured in the moving bed biological reactor,and then the Fe2+ ion in the adsorption tail liquid was continuously oxidated.The effects of aeration volume,adsorption tail liquid flow rate and temperature on the oxidation Fe2+ of bacteria werestudied.The specific research results mainly include the following three aspects.1 Growth characteristics and acid-resistant acclimation of Acidithiobacillus ferrivorans.The experimental result indicated the appropriate inoculum quantity of this bacterium was controlled at about 10%;When the initial concentration of Fe2+ was 0.3~0.5 g/L,the bacteria still maintained a fast rate of oxidation;At the temperature of 5 ~ 25 ?,oxidation rate of Acidithiobacillus ferrivorans was higher than Acidithiobacillus ferrooxidans,namely Acidithiobacillus ferrivorans was more suitable for leaching solution at low temperature environment;at the temperature of25 ?,the addition of extra isoleucine in the culture medium has little effect on the growth activity of bacteria.Acidithiobacillus ferrivorans could maintain good oxidative characteristics in nutrient fluid(p H=0.31)after domesticated in acid condition.2 Immobilization culture and continuous oxidation Fe2+ test of Acidithiobacillus ferrivoransA thicker biofilm could be observed in the SEM images of the Bio-ceramic,and the oxidation rate of Fe2+ of synergistic interaction between immobilized bacteria and dissociative bacteria was about 3.4times that of dissociative bacteria.and continuous oxidation rate of Fe2+by bacteria up to 0.21 g/(L·h).3 Field test of Fe2+ in adsorption tail liquid of rapid oxidation of Acidithiobacillus ferrivoransThe results showed that the selected bio-ceramsite has these characteristics of high porosity,high water permeability,high adsorption and high specific surface area,and the bio-ceramsite has good adsorption and fixation effect on bacteria.These characteristics was beneficial to the growth and reproduction of bacteria.Therefore,the oxidation rate of bacteria on Fe2+ was also enhanced.Bio-ceramsite had strong acid-fastness and stability in the adsorption tail fluid with p H 1.6 ~1.7.When the aeration volume and temperature,flow rate of adsorption tail was 20 L/h and 17 ~ 19 ?,500 L/h,respectively,the continuous oxidation rate of Fe2+ in bioreactor could reach 0.85 g/(L·h).Compared to H2O2,The bioreactor has the advantages of good running stability,small footprint,high air utilization rate and low maintenance cost.Acidithiobacillus ferrivorans as the oxidant can save about 72.63% of the cost,which provides a powerful basis for the industrial application of bacteria as oxidant.The subject of this paper originates from the production practice,and the stage results of the experimental research provide the theoretical basis and practical guidance for the later industrialization application,which lays a foundation for the realization of the industrial application of the Acidithiobacillus ferrivorans as oxidant in the acid leaching uranium mountains. |
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