Study On Bacterial Leaching For Low-grade Chalcopyrite Intensified By Static Magnetic Field

It is studied in this thesis that the bacterial leaching for the low-grade chalcopyrite is intensified by static magnetic field.The bacteria strain used in this study is thiobacillus ferrooxidans.Growth conditions of bacteria,leaching conditions and the effect of magnetic field on bacterial growth and bacterial leaching are mainly studied.Furthermore,a discussion on the mechanism of bacterial leaching for the low-grade chalcopyfite intensified by static magnetic field is presented on the basis of research reports and relative basic theories of the magnetized water and solution.In order to get the static magnetic field,a long straight solenoid has been designed as the magnetic field generator provided by a direct current power supply with stabilized voltage/constant current.Its technical parameters are as follows: magnetic induction intensity range(continuously variable):0～20mT;uniform region:785cm³;uniformity:10%.It shows a good linear relationship between the magnetic induction intensity and the current intensity measured by gauss meter,thus ensures the accuracy of the magnetic induction intensity in magnetization.The effects of some conditions on bacterial ability to oxidize ferrous ion are investigated.It is indicated that bacteria grow best when the temperature is 30℃,the pH value is 2.0 and the concentration of Cu²⁺in 9K culture medium is below 1.00 g·L^-1.Based on that condition,the bacteria have gradually adapted to low-grade chalcopyrite sample used as culture medium by means of domestication,which can be beneficial to subsequent leaching process.By using the orthogonal experimental design method,the conditions of bacterial leaching are optimized.The results show that under the conditions of pulp density 5%, inoculum 10%,pH 2.0,the leaching rate of Cu in low-grade chalcopyrite is optimal.A comparative study concerning leaching process with and without bacteria is performed.As a result,the leaching with bacteria obtains higher leaching rate(16.35%) of Cu than that without bacteria(5.73%)by shaking leaching for 30 days.It can arrive at a conclusion,in terms of thermodynamic calculation of the leaching reaction,that chemical leaching reaction without bacteria can not go on spontaneously,however,the leaching reaction with bacteria can be carried out readily.Studying on the bacterial leaching for the low-grade chalcopyrite intensified by static magnetic field,the results show that the 9K culture medium after magnetization treatment can promote bacterial breeding and oxidation activity and that the optimum conditions of magnetization are as follows:magnetic induction intensity:8mT, magnetization time:30min.Furthermore,the maximum bacterial leaching rate of Cu and Fe in low-grade chalcopyrite without magnetization is 16.35%and 21.79% respectively for 30 days.Nevertheless,the maximum bacterial leaching rate of Cu and Fe with magnetization is raised to 21.56%and 26.19%respectively.With the increase of magnetic induction intensity,the leaching rate of Cu is boosted gradually,but changes are not obvious when magnetic induction intensity is more than 8mT. Underlying mechanism of comprehensive leaching by magnetization treatment is that the structure of water could be changed in the existence of magnetic field,that the dissolution of oxygen and mineral ingredient could be promoted and that the penetrability of biological membrane in bacterial cell could be increased.