Study On The Behavior And Mechanism Of Selective Bio-desilication From Fly Ash By Bacillus Amyloliquefaciens

Fly ash is fine particulate matter produced by coal,in which oxides such as Si O₂,Al₂O₃,Fe₂O₃,Ca O,Mg O,Na₂O,K₂O and trace heavy metals and a variety of rare elements are mostly existing with the form of crystalline or amorphous silicate.Applicating silicate bacteria to bio-leaching of fly ash containing a large number of crystals and amorphous silicate compounds has the advantages of energy saving,environmental protection,simple process and controllable cost;The silicon in the slurry can be used as raw materials for core plate,water glass and silica gel after separation and purification,and meanwhile improve the grade of some elements in the leaching residue;The leaching residue can also be researched and utilized as an adsorbent owing to its looseness and porosity.In this study,a bacteria strain with desilication ability on fly ash was isolated from the soil and identified as Bacillus amyloliquefaciens by biological method and named ZGW-12 that was used for the bio-leaching treatment.The experiment conditions of bacteria growth and fly ash bio-leaching desilication were researched.The experiment determined that the most suitable carbon and nitrogen sources for the culture medium were sucrose and sodium nitrate,respectively;The culture conditions of the strains were to inoculate 5 m L bacteria in 100 m L Czapek's culture medium with the p H of 7.2,maintain a constant temperature of 30?and cultivate at 125 r/min for 4 days reaching a stable growth period;The best conditions for bio-desilication of fly ash are determined that 5 m L bacteria was inoculated in 7.5%concentration of 100 m L sterile slurry and it was bio-leaching at 30?and 150 r/min.The experiment found that the strains are suitable for growth in a neutral or weakly alkaline environment,and have a certain adjustment effect on the culture environment to make them tend to be neutral,but the addition fly ash can promote strains secreting more acidic substances;In addition,the fly ash particle size has a great influence on leaching,as its less than 75?m has a better bio-desilication effect.XRD,HPLC,SEM-EDS and FTIR were used to analyze the bacteria culture medium,ore slurry and leaching residue to study the bio-leaching mechanism of ZGW-12.The fly ash was leached for 31 days during experimental optimization conditions,and the concentrations of Si²⁺and Al³⁺in the slurry were determined to reach 306 mg/L and 0.5 mg/L,respectively,indicating that the bacteria have the effect of selective leaching silicon.In bio-leaching process,a large amount of bacteria was adsorbed on the surface of the fly ash particles;After bio-leaching process,obvious erosion of the fly ash particles surface occurred,and Si-O fractured,making the proportion of Si and Al content from 25%and 20.53%to 22.93%and 21.81%,respectively;However,the diffraction peak of the silicate crystalline compound did not change significantly,so the main component that dissolved during the bio-leaching process was the amorphous compound in fly ash.The analysis found that the types and contents of acidic metabolites in the slurry were much higher than the bacteria culture medium;According to the analysis results of the types and contents of organic acids and amino acids,a single factor experiment was carried out on the fly ash,which showed that the leaching effect of organic acids was better than acidic amino acids,and the leaching ability of organic acids from strong to weak was citric acid>lactic acid>succinic Acid>acetic acid>fumaric acid.Study shows that Bacillus amyloliquefaciens ZGW-12 has two mechanisms of direct cell adsorption and indirect leaching of metabolites in the bio-leaching experiment.Studies shows that Bacillus amyloliquefaciens ZGW-12 has two mechanisms of direct cell adsorption and indirect leaching of metabolites in the bio-leaching experiment;Acidic metabolites produced by bacteria growth and metabolize are excreted to extracell due to the mineral particles changing the permeability of cell membrane,and undergo acidolysis with amorphous components in the fly ash,and selectively form soluble complexes with Si²⁺,that achieve leaching silicon while retaining aluminum.