| With the innovation and development of science and technology and the increasing pursuit of material life,the speed of upgrading electronic and electrical products is also accelerating.As the core component of electronic and electrical products,the number of circuit boards eliminated and abandoned is also increasing.At present,the main methods to deal with electronic waste are:heat treatment,mechanical and physical methods,chemical wet method and biological method,each method has its own advantages and disadvantages.Biological method has a good development prospect in the treatment of electronic waste because of its green environmental protection and economic simplicity.In this paper,a series of complete treatment processes of waste circuit board were carried out by using Thiobacillus ferrooxidans（Acidithiobacillus ferroxidans,A.f）,including the removal of components on the surface of circuit board and the leaching of valuable metals in component powder.And the leaching of valuable metals from the circuit board powder.Through the analysis of the changes of pH,ORP and metal content in the leaching solution during the leaching process,the optimum leaching conditions under each process condition were explored respectively.It provides a certain research basis for the future biological treatment of electronic waste.The main conclusions are as follows:（1）the analysis of pH,ORP and metal content in the leaching solution of circuit board surface components by A.f bacteria shows that eosinophilic bacteria have a significant effect on the removal of mobile phone circuit board surface components;The optimum leaching conditions were as follows:initial pH1.0,solid-liquid ratio 3:50,inoculum size 15%,temperature 30℃,rotating speed 125 r/min.by the 7th day of leaching,the surface components of mobile phone circuit board had been completely removed.The soldering foot between the components of the mobile phone and the circuit board is dissolved in the leaching solution,Among them,Ni,Zn and other elements exist in the leaching solution in the form of ions,and Sn,Pb and other elements are leached and precipitated.（2）the pH and ORP of the experimental leaching solution of valuable metals from the powder of components and the changes of valuable metals in the leaching solution were analyzed by A.F bacteria+NCNTs modified electrode,and the results showed that the NCNTs modified electrode+A.f bacteria could extract the powder of components.The valuable metal in the end has a significant effect.the initial pH was2.0,the ratio of solid to liquid was 1:50,the inoculum size was 15%,and the modified amount of 2.5mg/cm2 was NCNTs,and on the 7th day,The leaching rates of Cu,Ni,Zn and Al in the leaching solution are 90%,52%,63.5%and 60.3%respectively.（3）the leaching of valuable metals from circuit board powder by external electric field+NCNTs modified electrode+A.f bacteria showed that the applied electric field+NCNTs modified electrode had a significant catalytic effect on the leaching of valuable metals from A.f circuit board.The NCNTs modified electrode can significantly increase the electron transfer rate in the leaching solution and improve the leaching efficiency of valuable metals in the leaching solution.When the current intensity is30mA,the solid-liquid ratio is 1:50,the modification amount of NCNTs is 2.5mg/cm2,and the diameter of carbon rod is 8mm,the leaching solution has the best leaching effect on valuable metals in the circuit board.Among them,the extreme difference of solid-liquid ratio is the largest,which has the greatest influence on the leaching results,followed by the current intensity,and the diameter of carbon rod and the amount of NCNTs modification have the least effect.On the 5th day,the leaching rates of Cu,Ni,Zn and Al were 98.9%,99.3%,94.9%and 50.1%,respectively.Through the experimental study in this paper,it can be seen that A.f bacteria has a significant effect on the removal of valuable metals from the surface components of mobile phone circuit boards and the powder of leaching components and circuit board powders.through the first stage of indirect action,A.f bacteria can remove Fe2+from the leaching solution.The strong oxidation property of Fe3+,Fe3+can oxidize the valuable metals in the component powder or circuit board powder to the corresponding ionic state.The applied electric field+NCNTs modified electrode has a significant catalytic effect on the leaching of valuable metals from the circuit board powder by A.f bacteria.The NCNTs modified electrode can increase the electron transfer rate of the leaching solution,and the Cu ion in the leaching solution can be precipitated directly in the cathode carbon rod by the action of applied electric field.at the same time,the activity of A.f bacteria can be stimulated by the action of a certain intensity of electric field.Improve its leaching efficiency.Through the analysis of the change of metal content in the leaching process,it can be seen that the catalytic effect of the applied electric field on the valuable metals in the circuit board powder of the leaching solution is greater than that of the bacteria in the leaching process for 01 day.After 15 days of leaching,the effect of A.f on the leaching of valuable metals from PCB powder was greater than that of applied electric field. |
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