Bioleaching Of In From Waste Liquid Crystal Displays (LCDs) By Mixture Bacteria And Its Recovery

The liquid crystal displays(LCDs)have been one of the most incomparable device,due to high display characteristics,low cost,easy to carry and no electromagnetic radiation.However,many of them are rejected by their end-users because of their short life span,which will be a serious threat to the environment and human health.Moreover,it contains some rare metals known as indium.Therefore,it is critical to recover the indium from waste LCDs.Bioleaching have been increasingly reported for the treatment of e-waste,due to its eco-friendly soundness.To our knowledge,there is no available reports concerning the bioleaching of indium from waste LCDs mediated by microorganisms.Therefore,the aims of this project were to investigate the effect of different microorganisms on the bioleaching of indium from waste LCDs and elucidate the feasibility about In3+ recovery from bioleaching solutions by electrodeposition method.The main contents of this study are listed as follows:(1)On the basis of domestication,we have designed the bioleaching experiment,setting four different bioleaching systems,which referred to as IOB(iron-oxidizing bacteria),SOB(sulfur-oxidizing bacteria),MSB1(mixed energy sources-bacteria)and MSB2(IOB+SOB),respectively.The concentration of the indium,the change dynamics of each parameter and sediments were detected during the bioleaching period.The results showed that the concentration of In3+ by these four systems could be negligible.Four systems showed different performances in indium bioleaching.In the MSB2 system,the maximum indium leaching rate of 97%was achieved after 8 days;Indium was harvested with a maximum extraction efficiency of 77%using the SOB system;Whereas,the leaching rate of indium were 50%and 2%in the MSB1 and IOB systems,respectively.Therefore,acid dissolution was the main bioleaching mechanism of indium in waste LCDs.Owe to the combination of acid dissolution and oxidation by Fe3+,the bioleaching rate of indium by the MSB2 system was significantly higher than that of SOB system.(2)The microbial community structure of the initial sludge and the changes of microbial community structure during the bioleaching process were analyzed by high-throughput sequencing method based on the metagenomic.The results showed that the number and richness of microbes changed obviously in each system after the domestication under different conditions.Actinobacteria were predominant in the four bioleaching systems.The species in the four systems were decreased comparing to the original sludge,indicating that the microbes displayed the selectivity towards the bioleaching conditions.In the four bioleaching systems,g3,g5,g6 and gll were predominant.G5 was predominant in the IOB,SOB and MSB2 systems.However,the bioleaching efficiency by IOB was only 2%,because of its energy material which could not produce acid.Based on the above data,we could conclude:① In these four systems,acid dissolution in the bioleaching mechanism of indium was a main-form;② The predominant bacteria may not have the function of bioleaching;③ G5,which belonged to Actinobacteria,Actinobacteria,Actinobacteria,ACK-M1,could not only use Fe2＋but also S as energy;④ Furthermoer,it could suggest that g6 used Fe2+ as the main energy material.(3)The artificial bioleaching solutions was determined by cyclic voltammetry method and chronoamperometry.The results showed that the suitable conditions for the deposition of indium was at pH=2.5.Under this condition,it belongs to diffusion control in the deposition of indium.Foremore,the deposition efficiency of indium at pH=2.5 was 87%after 8 hours.