Screening Of Uranium Autotrophic Microorganisms And Mechanism Of Aspergillus Niger To

The heterotrophic microorganisms can grow by obtaining energy from organics, andthey can produce multiple kinds of organic acids in their metabolite including citric acidoxalic acid, acetic acid, malic acid, lactic acid, succinic acid, gluconic acid, and so on,which can be used to leach the oxide ores, sulfide ores and high acid consuming ores. Theheterotrophic microorganisms have the following advantages, they could use the wastes ofthe industry and agriculture as the energy source, the high leaching pH during the leachingprocess, the produced organic acids can be decomposable by the microorganisms in natureand they are friendly to the environment. The heterotrophic microorganisms could betteradapt to increasing environmental pressure and the present situation characterized by theshortage of resources, thus increasing attentions are focused on the heterotrophicmicroorganisms which can be used to leach ore. However, the available strains for studyare limited, the present understanding of the leach mechanism is not studied in depth, andespecially the leach mechanism of the uranium ore by the heterotrophic microorganisms islittle researched, all these factors hampers the development of the uranium leachingtechnology with the heterotrophic microorganisms.This paper firstly isolated and purified the heterotrophic microorganism for oreleaching by using a several kinds of medium,43strains of the heterotrophicmicroorganisms with the capacity to produce acid or alkali were obtained, and then theperformance of uranium leaching was investigated. Five strains of fungi, acid producingbacteria and uranium leaching alkali producing bacteria were screened which have a betterperformance on leaching uranium ore. The physiological identification, biochemicalidentification and ribosomal DNA identification techniques were employed to identifythese five strains and their growth characteristics were studied. The relationship of the ratioof the organic acids, the concentrations of organic acids and the uranium leaching rate wasstudied with the analytically pure organic acids, which provided reference to the optimizing the incubation conditions of the fungus and improving uranium leaching rate.Uranium leaching mechanisms by the Aspergillus niger and the produced organic acidwere researched by using the micro and macro analysis techniques. The recovery of thecomplexes of the organic acidic and uranium was preliminary investigated by the ionexchange technology.The detailed contents of the paper were concluded as the following aspects:1. Isolation and purification of the heterotrophic microorganisms and the screen ofthe uranium leaching heterotrophic microorganisms43strains of the heterotrophic microorganisms with the potential to bioleaching theores were acquired with the PSA medium, glucose+corn steep liquor medium, LBmedium, nutrient broth medium, DOX medium, DOX+corn steep liquor medium and newfermentation medium as the isolation medium, and using the bromocresol purple,phenolphthalein as the indicators. Among the acquired strains,23strains belonged to thefungal,16strains belonged to the yeasts,2strains belonged to the acid-produced bacteriaand2strains belonged to the alkaligenous bacteria.The results of uranium leaching with the isolated heterotrophic microorganismsshowed all of them had the capability of uranium recovery, the uranium leachingperformance of these strains were related to the incubation medium, and the strainsincubated with the PSA medium performed the highest uranium recovery rate. Strain H1and strain Q5have the highest leaching rates when incubated on the PSA medium with therates of66.75%and54.41%, respectively. When incubated on the PSA medium, theuranium leaching rates of the acid-produced strains SJ9and SJ10amounted to46.35%and33.27%, respectively. The isolated yeast strain J5had the highest leaching rate with49.05%when incubated on the PSA medium. The alkaligenous strains of JLI and JR11showed higher uranium leaching rate on the nutrient broth medium compared with the LBmedium, and the strain JL1obtained the highest leaching rate of27.68%. 2. Identification and the growth characteristics of the uranium leachingmicroorganismsPhysiological and biochemical methods as well as ribosomal DNA analysis were usedto identify the screened5strains of heterotrophic microorganisms. The strain JR11wasidentified as Staphylococcus sciuri; strain SJ9was identified as Sphingobacteriummultivorum; strain JL1was identified as Brevundimonas dimimuta; strain H1wasidentified as Aspergillus niger; strain Q5was identified as Penicillium funiculosum.Then the effects of medium, initial pH value, culture temperature and inoculum sizeon the growth and the production of organic acids of the5strains of heterotrophicmicroorganisms were studied. The PSA medium, glucose+corn steep liquor medium,DOX medium (pH=6.5), DOX+corn steep liquor medium and LB medium (natural pH)were suitable to incubate the Aspergillus niger and Penicillium funiculosum to produce theorganic acids.The new fermentation medium, DOX medium (natural pH), DOX medium (pH=6.5),DOX+corn steep liquor medium (natural pH), DOX+corn steep liquor medium (pH=6.5)and the glucose medium were appropriate organic acid producing mediums for theSphingobacterium multivorum. The production of the organic acids by Aspergillus nigerand Sphingobacterium multivorum could be influenced by the temperature of theincubation process, and the incubation at25℃showed most beneficial to the production ofthe organic acid. However, the difference of the capability of the strains to produce theorganic acid did not change with the temperature.The best incubation condition of the Aspergillus niger: the initial pH of the mediumwas7.0, the incubation temperature was37℃, and the inoculation concentration was0.1%(OD600of spore suspension was1.0);The best incubation condition of the Penicillium funiculosum: the initial pH of themedium was3.0, the incubation temperature was28℃, the inoculation concentration was 1.5%(OD600of the mother liquor was1.0);The best incubation condition of Staphylococcus sciuri: the initial pH of the mediumwas8.0or9.0, the incubation temperature was30℃, and the inoculation concentration was1.5%(OD600of the mother liquor was1.0);The best incubation condition of Brevundimonas dimimuta: the initial pH of themedium was7.0, the incubation temperature was30℃, and the inoculation concentrationwas2.5%(OD600of the mother liquor was1.0);The best incubation temperature of the five strains for growth were different with thetemperature for uranium leaching.3. The relationship between the ratio of the organic acids and uranium recoveryThe different compositions and contents of the mixed organic acids influenced theuranium leaching rates. With more kinds and concentrations of the organic acids, theuranium leaching rates could be increased and the acid consumption could be decreased.The oxalic acid and citric acid played a major role during the leaching process. In addition,the appropriate composition of the organic acids could contribute to increase the uraniumleaching rate.4. The mechanism of uranium leaching by Aspergillus nigerThe metabolite of Aspergillus niger showed the higher uranium leaching rate, the bestleaching performance of the metabolite of Aspergillus niger was obtained at25℃with themedium pH2.3, and the uranium leaching rate amounted to83.09%. The difference of theorganic acids ratio resulted the different leaching rates, and the main factors influencingthe organic acids ratio produced by Aspergillus niger were the types of the mediums,incubation temperature and the pH of the medium. The best leaching temperature ofAspergillus niger was not in accordance with the best one of growth.The existence of the uranium ore could inhibit the production of organic acids ofAspergillus niger and resulted the decreasing of the leaching rate. The major mechanism of the uranium ore leaching by Aspergillus niger was the effectof direct destroy to the crystal structure of the ore, the effect of adoption, and thedisplacement and complexation of the organic acids proton.5. Column leaching and uranium recovery from the leach solutions by ion exchangeThe uranium leaching rate of the Aspergillus niger by the metabolite and the sulphuricacid was81.76%and83.90%, with the leaching time of14days and15days, respectively.The total ratio of liquid versus solid were1.4:1and1.5:1, respectively. The Eh of theleaching system of the metabolites in Aspergillus niger tended to decrease, while Eh of thesulfuric acid leaching system tended to increase. The ion exchange characteristics of theleachate of the metabolites in Aspergillus niger was completely different with the S type ofthe sulphuric acid, which was a wavy shape, while the elution curve of the two systemswere similar.408(II)-type strongly alkalescency anion-exchange resin was not suitable foruranium recovery from the leach solutions by ion exchange.