Experimental Study On The Promotion Of Plagioclase Weathering By Bacillus Safensis HR-2 And Aspergillus Aculeatus FS-4

The interaction between microorganisms and minerals is closely related to geological evolution,element cycle and the coordination of ecological environment.The products of mineral weathering at the presence of microorganisms is an important source of forming secondary minerals in the soil,and the dissolution of minerals can provide nutrients for plants.Studying the weathering of silicate minerals can provide important clues to scientific issues such as global climate changes and the global carbon cycle in the geological time scale.In the existing studies on the microbial weathering of silicate minerals,predecessors often focused on the role and effects of microorganisms or on the dissolution rate and sequence of elements.Both the dissolution process and the formation mechanism of secondary minerals need further investigation.In addition,fungi are far less important than bacteria.This article carried out two groups of weathering experiments using Bacillus safensis HR-2,Aspergillus aculeatus FS-4 and plagioclase.Determination of ion concentration of K,Al,Fe,Na,Ca,Mg and Si in supernatant by inductively coupled plasma optical emission spectrometer;Measure the concentration of low molecular weight organic acids using high performance liquid chromatography.In addition,the liquid phase indicators such as the content of extracellular polysaccharides,bicarbonate ions and carbonic anhydrase activity were also measured.According to stoke's law,the granular component of<2 ?m in the solid phase product was extracted.The mineral species,surface morphology and elemental composition of solid phase products were observed and analyzed using X-ray diffraction technology,electron scanning microscope and energy dispersive spectrometer.The dissolution rate and sequence of elements in plagioclase under the action of bacteria and fungi were analyzed,and the formation mechanism of secondary minerals was discussed.This article mainly gained the following knowledge:(1)Both the strain HR-2 and FS-4 can promote the weathering of plagioclase.We obtained on the basis of Si that the weathering rate of plagioclase promoted by strain FS-4 is about 12 times that of strain HR-2.(2)In terms of the elements position in the plagioclase,the dissolution sequences of the elements during the experiments of strain HR-2 and FS-4 both are:elements filled in the gaps between the skeletons of Si-O tetrahedrons(K,Na,Ca and Mg)?elements in the skeletons of Si-O tetrahedrons(Fe,Al and Si).This result shows that microbial species affect the weathering rate of plagioclase,but not the dissolution sequence of elements in plagioclase.(3)Both strain HR-2 and FS-4 can promote the weathering of plagioclase by secreting low molecular weight organic acids and extracellular polysaccharides,and the concentration of oxalic acid secreted by the strain FS-4 is 244 times that of the strain HR-2.According to the correlation analysis results,the correlation coefficients of the concentration of Al³⁺,Ca²⁺,Fe³⁺,K⁺,Na⁺,Si⁴⁺and the content of extracellular polysaccharide in bacterial experiments were 0.64,0.63,0.78,0.68,0.64,0.81 respectively.Except for Fe³⁺and Al³⁺,the correlation coefficients of the concentration of Ca²⁺,K⁺,Mg²⁺,Na⁺,Si⁴⁺with extracellular polysaccharide were 0.70,0.98,0.56,0.79,0.73 in fungal experiments.And the correlation coefficients of their concentrations with oxalic acid are 0.76 and 0.93,0.64,0.78 and 0.79 respectively.It is speculated by comprehensive considerations that the strain HR-2 mainly promotes the dissolution of plagioclase by secreting extracellular polysaccharides.Strain FS-4 promotes it by secreting oxalic acid and extracellular polysaccharide.(4)By analyzing the XRD pattern of the solid phase product with a particle size of<2?m,the bacterial experiment showed diffraction peaks of illite on the 50th day,and a diffraction peak of gypsum was observed on the 100th day.The diffraction peaks of illite were observed on the 50th day during the experiments with strain FS-4.The author speculated that illite may be formed by the dissolution-precipitation model.