Study On The Influence Of Brominated Flame Retardants On The Bioleaching Of Copper From Waste Printed Circuit Boards

As the main component of E-waste, the number of the discarded and eliminated Waste Printed Circuit Boards(WPCBs) increases with the accelerated rapid of replacement of electronic products which could cause seriously environmental issues. Due to the continuous improvement of environmental laws, regulations and the concept of building a green and environment-friendly society, researching the recovery of metals which in the WPCBs is the key to solve the environmental pollution and ease the resource crisis. In this paper, the BFRs in WPCBs were as the research objects and the influence of BFRs on bioleaching the Cu from WPCBs were studied.The solid-liquid extraction technique is adopted for removing the BFRs in the WPCBs. Four factors were researched to find the optimum conditions of extracting BFRs in the WPCBs, which are different amount of WPCBs, different particle size of WPCBs, extraction time and extraction times when we take CCl4 as the extraction agent. To get the impact on the growth of Thiobacillus ferrooxidans by Tetrabromobisphenol A(TBBPA) and copper leaching efficiency difference after extraction by Thiobacillus ferrooxidans in the WPCBs with difference amount of WPCBs and difference content of BFRs, we did further research. The extracts after extraction were added to the circuit board in the WPCBs after extraction and effect on the ability of leaching of Cu was observed. Get the following main conclusions:1) The result shows that more WPCBs are added, more BFRs are obtained with extracting and the maximum value is 11 mg/g. The content of BFRs decreases after the first increase with decreasing particle size. The higher content of BFRs in the WPCBs is, the better extract result obtains and the maximum removal rate reaches 38.5%. The extraction efficiency is getting better with time increases, but increases slowly later. Increasing the number of extraction times can improve extraction efficiency, but increase margin is not obvious.2) The extraction efficiency and removal ratio of Br(about 30%) is good. The extracts have a more single component and the mass content of the Br is 94.47%.3) TBBPA did has effect on the growth of Thiobacillus ferrooxidans by analyzing the trend of microbial biomass with time after adding TBBPA. When the addition amount of TBBPA is 15g/L, the biomass is low in the solution and organic nitrogen is 25 mg/L; the addition amount of TBBPA is 15g/L, biomass is higher in the solution and organic nitrogen is 40 mg/L.4) Different add quantity of WPCBs have different influence on microorganisms’ leaching efficiency of Cu. The results show that the greater amout of added WPCBs are, the lower Cu leaching efficiency of Thiobacillus ferrooxidans is. For example, adding 5 g/L of WPCBs, the Cu removal rate is 98.39% after 144 h; adding 15 g/L of WPCBs, the Cu removal rate is 80.42% after 144 h; adding 25 g/L of WPCBs, the Cu removal rate is 18.73% after 144 h.5) When the addition amount of WPCBs is 5 g/L, the content of BFRs has no significant impact on the capacity of leaching copper of microbial. When the addition amount of WPCBs is large, reducing the content of BFRs can improve the efficiency of leaching copper of microbial. However, the content of the metal exceeds the tolerance range of microorganisms and we cannot obtain a high improvement rate. For example, if the addition amount of WPCBs is 25g/L, removal rate of the group after extraction is only 2% higher than the group without extraction when remove 30% BFRs. When the addition amount of WPCBs is 15 g/L, reducing content of BFRs in WPCBs can significantly improve the efficiency of leaching Cu, with an average increase of 12%.6) Comparing the Cu leaching efficiency by microorganism as following groups, the group of before extraction, the group of after extraction and the group of after extraction with extractions, we can get the following conclusion. The content of BFRs and the contact area with microbial both effect microorganism. If the content of BFRs decreases 30%, the second group’s Cu leaching efficiency is 12% higher than the first one. If the contact area between microorganism and BFRs, the Cu leaching efficiency of the third group is 16% lower than the first one.The above study shows that as an important component of WPCBs, BFRs can inhibit the growth activity of microorganisms and reduce copper leaching efficiency. Therefore, in order to promote the development of microbial metallurgical processes and ease the resource crisis, it is essential to consider the impact on growth of microbial by BFRs for improving the efficiency of metal recovery during recovering the metals in WPCBs.