Study On The Bioleaching Of Metal Concentrates Of Waste Printed Circuit Boards In The Bioreactor System

Valuable metal resource is abundant in waste printed circuit boards. If those wasteprinted circuit boards cannot be properly dealt, the living environment will suffer a powerfulinfluence. In recent years, The bioleaching technology get more and more extensive usage inthe recovery of metals from waste printed circuit boards, because its low-cost, less energyconsumption, simple operation and pollution-free etc. advantages. But, the technology is nowat the stage of lab research and flask-shaking experiments. In order to improve thebioleaching performance in the process of bioleaching and implementation the practicalproject applications of the technology of bioleching, on the basis of our preceding work, atwo-steps bioleaching bioreactor was built which was simple to operate, Acidithiobacillusferrooxidans Z1was used as the species resources in the course of the experiment. In thispaper the bioleaching characteristics of valuable metals from waste circuit boards wereinvestigated, the optimum operation conditions of bioleaching reactor also determined. Thisresearch also studyed the feasibility of gauze as the carrier immobilized Acidithiobacillusferrooxidans Z1. Finally, the feasibility of bioleaching of metal concentrates of waste printedcircuit boards using Acidithiobacillus ferrooxidans immobilized on the cotton guaze wasdiscussed. The main conclusions were as follows:(1) The influences of aeration rate, retention time, stirring speed and powder dosages onthe performance of two-steps homemade bioleaching bioreactor were investigated. Resultsshow that, the optimum operation conditions of the reactor were: aeration rate1L/min,retention time30h, stirring speed300r/min and powder dosages12g/L. Under the conditions,90.24%copper leaching efficiency was achieved in101h. Meanwhile,93.06%of magnesium,85.59%of zinc,85.59%of aluminium and64.51%of nickel was bioleached in197h,respectively. Therefore, the bioleaching reactor can effectively provided experimentalevidence for the practical application of the technology.(2) Selected the best immobilization carrier by comparison with the immobilizedAcidithiobacillus ferrooxidans effects of cotton guaze, zeolite and activated carbon. Theresults showed that cotton gauze is the most appropriate carrier to immobilizeAcidithiobacillus ferrooxidans cells in comparison with zeolite, activated carbon andcarrier-free. Additionally, the cotton gauze immobilized Acidithiobacillus ferrooxidans bygravity dehydration can achieve a mean ferrous iron oxidation rate of0.55g/(L h) and amaximum oxidation rate of0.92g/(L h). Furthermore, the ferrous iron oxidation ratios under the bioreactor of continuous batch operation has maintained above97.83%.(3) Based on the above, the conditions of bioleaching of metal concentrates fromWPCBs by using the technology of immobilized Acidithiobacillus ferrooxidans cells oncotton gauze were investigated further. The results showed that the highest extraction rate ofcopper achieved91.68%after96hours in the presence of retention time6h,1L/min aerationrate and12g/L of metal powder. Meanwhile,95.32%zinc,90.32%magnesium,86.31%aluminum and59.07%nickel could also be extracted after96h. In continuous batch operation,the copper leaching efficiency can maintain above91.12%.