Study On Leaching Low-grade Phosphate Ore By Moderate Thermophilic Bacteri

The distribution of phosphate rock resources in China is uneven and the grade is low.More and more attention has been paid to the efficient utilization and development of medium and low grade phosphate rock resources.Bioleaching technology is suitable for the treatment of low-grade phosphate rock due to its advantages of economy and environmental protection.However,there are some problems in the leaching process of mesophilic bacteria,such as local heat release,low leaching rate,long leaching period and strain tolerance.Microbial leaching of phosphate rock has a strong development and application prospect.Microbial leaching should be strengthened.In this paper,thermophilic acid-sulfur bacillus was used to leach a low-grade phosphate rock.The ore characteristics of low-grade phosphate rock and the physiological morphology of thermophilic acid-sulfur bacillus were studied,and the microbial growth conditions were optimized.The microbial leaching of low-grade phosphate rock was studied by different leaching methods to explore the influence of various factors on the leaching rate.By exploring the adsorption behavior of microorganisms in the leaching process,the changes in the morphology of phosphate rock before and after leaching,the particle size analysis of different leaching periods,the infrared spectra of thiobacillus thermophilus and phosphate rock before and after leaching,and the Zeta potential and contact angle changes before and after leaching,the leaching mechanism was explored to obtain better microbial growth conditions and better leaching process.The research results are as follows:The research on low-grade phosphate rock shows that the composition,structure and dissemination size characteristics of a low-grade phosphate rock are as follows:the grade of the phosphate rock is 14.12%,and there are many impurities.The main components are Ca（PO₄）₃F,Ca₅（PO₄）₃（OH）,Si O₂and Ca Mg（CO₃）₂,which belong to siliceous and calcareous low-grade minerals with layered structure.The growth behavior test of Thiobacillus thermophilus showed that the color of the solution changed from clear and transparent to turbid and finally to milky white with the prolongation of culture time in the liquid medium.In the solid medium,it could be seen that the size and shape were different,showing milky white colonies.Acidithiobacillus thermophilus was in a slow growth period at 0-36h,a logarithmic growth period at 36-96h,a stable period at 96-120h,and a decline period after 120h.Microorganisms cultured for 36h and 96-120h were selected for one-step and two-step leaching,respectively.Through single factor experiment,the optimum growth conditions of microorganisms were as follows:initial p H 2.8,temperature41°C,inoculation amount 9%,initial sulfur addition amount 15g/L,and the highest microbial concentration culturedafter 96h culture was 6.85×10⁸m L^-1,7.21×10⁸m L^-1,7.87×10⁸m L^-1,8.24×10⁸m L^-1,respectively.The results of orthogonal experiment are as follows:temperature>initial sulfur addition>p H>inoculation amount,temperature 42°C,initial p H 2.8,microbial inoculation amount 9%,sulfur addition1.7g/100m L.Under these conditions,the bacterial concentration was 8.95×10⁸m L^-1.The experimental study on the leaching of low-grade phosphate rock by thermophilic acid-sulfur bacillus showed that the leaching rates of acclimated and unacclimated thermophilic acid-sulfur bacillus phosphate rock during one-step leaching were 81.56%and 70.5%,respectively.The doses of Tween 20,Tween 60 and Tween 80 were 10g/m³,10g/m³and 100g/m³,respectively.The final leaching rates of phosphate rock were 82.88%,86.78%and 84.65%,respectively.The leaching rates of glucose,sucrose and starch were 86.8%,83.9%and 80.6%,respectively.The better leaching conditions for two-step leaching are as follows:culture time 5d,pulp concentration 3%,ore particle size 0.075mm,shaking speed 175 r/min,14h leaching rate 76.1%,80.21%,82.5%,84.15%.Orthogonal experimental results:ore particle size>slurry concentration>shaking speed,shaking speed 125r/min,slurry concentration 2%,ore particle size 0.075mm,phosphate rock leaching rate 89.32%.The leaching mechanism study shows that:microorganisms and phosphate rock before and after leaching indicate that there is not only physical adsorption but also chemical adsorption by microorganisms during the leaching process.During the leaching process,the particle size of phosphate rock decreases in the early and middle stages of leaching,and increases in the later stages.The wetting contact angle of phosphate rock measured by contact angle is 43.7°.After microbial action,the wetting contact angle of phosphate rock surface was 68.5°,and the hydrophobicity is significantly enhanced,not conducive to leaching.