Study On Strengthening Effect Of Exogenous Substances On Bioleaching Of Valuable Metals In Circuit Board

Biological leaching technology can be used to recycle waste circuit boards,and has good economic,social and environmental benefits.But at present,the technology is mostly in the scale of laboratory shake flasks,and its leaching efficiency is one of the important reasons that affect the actual industrial application.The research on improving the leaching efficiency mostly focuses on the types of microorganisms,leaching process conditions,but rarely involve the simple and convenient way of adding exogenous substances,especially the types of recyclable glass beads,low-cost organic acids,and environmentally friendly biodegradable chelating agents.Based on the preliminary research in the laboratory,this paper studies the effect of the addition of exogenous substances on the bioleaching of valuable metals in the printed circuit board.First,screen out potential exogenous additives that can promote the bioleaching of waste printed circuit boards;then the application conditions were optimized to establish a exogenous promotion system for bioleaching of waste circuit boards,and verify the promoting effect;finally,the role of potential exogenous additives in the process of bio-leach waste circuit board was explored to determine the reason why exogenous could play a facilitating role.The results are as follows:?1?Through the experiment of bioleaching west circuit board with the addition of organic acids,glass beads,and chelating agents,the effect of different kinds of exogenous substances on the leaching rate of copper in the metal-rich powder of the circuit board was investigated.The results show that tartaric acid,citric acid and malic acid can only promote the early leaching period or increase the maximum copper leaching rate,but inhibit the copper leaching later.Glass beads only promote leaching at a concentration of 3g/L,too much or too little will limit the copper leaching of the powder.The chelating agent has a promoting effect on biological leaching,which is EDDS,GLDA,IDS,and EDTA in descending order.Among them,the leaching rate of copper is over 90%after leaching for 72h after adding EDDS.Therefore,it is proposed to use the selected chelating agent EDDS as a potential exogenous addition.?2?By investigating the effect of different dosing time and dosing amount of EDDS on the promotion of leaching copper from the printed circuit board,optimized and strengthened leaching conditions..The results show that the earlier the EDDS is added,the stronger the leaching promotion effect,and the best copper leaching rate is obtained under the condition of0.1%EDDS dosage.Under preferred conditions,the leaching rate of copper reached 93.78%at4d,and the leaching rates of zinc,nickel,and lead reached 88.27%,93.69%,and 87.32%,respectively.Thus,an exogenous additive promotion system was established for bioleaching waste circuit board?3?Adding EDDS during the cultivation of Acidithiobacillus ferrooxidans,designing biological leaching,EDDS leaching,and biological leaching experiments with EDDS added for comparison to explore the reasons why EDDS can enhance leaching.The results show that EDDS can help maintain the dissolved state of Fe³⁺in the solution,improve the contact between the bacteria and powder,and reduce the production of jarosite precipitation.In other words,EDDS can strengthen the bioleaching of valuable metals in the printed circuit board by affecting the leaching mechanism,chelating heavy metals,reduce precipitation and metal loss.