| A large number of waste electronic products are produced due to the continuous acceleration of the iteration of the renewal of electronic products.Printed Circuit Board(PCB),as the core component of electronic products,accumulates in large quantities with the increase of the number of waste electronic products.The discard of PCB would threaten the environment and cause a great waste of metal resources.At present,the main methods for recovering metals in PCB contained pyrolysis,mechanical crushing,chemical and biological leaching.Among them,bioleaching has become the most popular approach for metal recovery from PCB due to its unique characteristics such as low-cost,environmentally friendly and simple process.In this study,the diversity of Iron oxidizing bacteria(IOB)in volcanic ash from Northeast China(Changbai Mountain in Jilin province,Maanshan and Gushan in Heilongjiang Province,and Ashan in Inner Mongolia)were analyzed through high-throughput sequencing technology.The enrichment of acidophilic IOB with high Fe(?)oxidation activity,high concentration of copper and nickel ion tolerance,and high metal leaching efficiency enriched and obtained.Accordingly,the IOB strains were isolated from the acidophilic IOB enrichment.The inoculum with the best performance were selected from IOB enrichment and strains as PCB leaching bacteria,the immobilization conditions of IOB to volcanic rocks were optimized,and the effect of magnetic field intensity on cell immobilization was explored.Under the optimal conditions of cell immobilization strengthened by magnetic field,the optimum leaching conditions of copper and nickel were obtained by single factor combined with response surface method.Thereafter,the current intensity to enhance the leaching efficiency is determined,and the process of leaching of copper and nickel by IOB from PCB strengened by magnetic field and electric field coupling is established.The following conclusions are drawn:(1)There are significant differences in physical and chemical factors in volcanic ash from different sites in Northeast China.The redox potential and sulfate content of Maanshan volcanic ash are the highest,and the contents of ammonia nitrogen,sulfate,total iron,Fe(?),sulfide and phosphate in Changbai Mountain volcanic ash are the highest.The IOB diversity of volcanic ash in different locations in Northeast China is similar,and it is distributed in 9 genera at the genus level: Sphingomonas,Acidithiobacillus,Gaiella,Rhodoplanes,Massilia,Nitrosospira,Nitrospira,Sulfuriferula and Pseudarthrobacter.The common dominant IOB bacteria were Sphingomonas and Acidithiobacillus.The dominant IOB bacteria were Acidithiobacillus(6.7%and 6.2%)in Maanshan and Gushan mountains,and Sphingomonas(9.2% and 9.6%)in Changbai Mountains and Arshan Mountains.Acidithiobacillus is the dominant IOB strain in the experiment,and its diversity was positively related to p H and sulfate content in volcanic ash.(2)Acidophilic IOB in volcanic ash from different sites in Northeast China was enriched with 9K culture medium,and 18 Acidophilic IOB cultures were obtained.Acidophilic IOB cultures MA and CB were selected through the comparison of Fe(?)activity,metal tolerance and leaching ability,and A.ferrooxidans MA-Y1 and A.ferrooxidans CB-Y1 were isolated from Acidophilic IOB cultures MA and CB.The Fe(?)activity,metal tolerance and leaching ability of A.ferrooxidans MA-Y1,A.ferrooxidans CB-Y1,Acidophilic IOB cultures MA and CB were compared.A.ferrooxidans MA-Y1 has higher Fe(?)oxidation activity(98.32%),copper and nickel metal leaching ability in PCB(52.06% and 62.48%).The tolerance of copper and nickel ions is 2-7% higher than that of the Acidophilic IOB culture from Maanshan volcanic ash.(3)Taking the oxidation rate of Fe(?)as an index,single factor experiments were conducted to investigate the effects of temperature(20-35 ?),volcanic stone particle size(0.3-1.2 cm),ventilation(0.2-0.8 L/min)and immobilization time(3-9 d)on the immobilization of A.ferrooxidans MA-Y1.The significant conditions were obtained by single factor analysis of variance,and the best immobilization process was obtained by response surface experiment.On this basis,the magnetic field(0-30 m T)was added to explore the effect of magnetic field intensity on the immobilization effect.The operating conditions of the magnetic field strengthening system were as follows: the gas flow rate was 0.5 L/min,the particle size of volcanic stone was 0.75 cm,the immobilized time was 6 d,and the magnetic field was 20 m T.The highest Fe(?)oxidation rate of the immobilized cells was 99.67%.(4)According to the basis of(3),single factor experiments were conducted to investigate the effects of PCB particle size(2-4 cm),pulp concentration(PCB addition 60-100 g L/min),temperature(25-35 ?)and liquid flow rate(1.2-3.6 L/min)on the leaching rate of copper and nickel in PCB.The conditions with significant influence were obtained by single factor analysis of variance,and the best leaching process was obtained by response surface experiment.The effect of electric field intensity on the leaching rate of copper and nickel in PCB was investigated by adding electric field(0-150 m A),and the magneto-electric coupling enhancement system for A.ferrooxidans MA-Y1 leaching of copper and nickel in PCB was established.The operating conditions of the electric field strengthening system are as follows:the addition amount of the circuit board is 80 g / L,the diameter of the circuit board is 4 cm,the liquid flow rate is 2.0 L/min,the leaching rate of copper is 67.27% and the leaching rate of nickel is 75.28% under the intensity current of 70 m A.Compared with the group that without strengthening treatment,the magneto-electric coupling enhanced process can increase A.ferrooxidans MA-Y1 15.21% and 12.8% leaching rate of copper and nickel by leaching PCB,and it is estimated that 0.52 yuan can be gained by dealing per 100 g PCB.This study can provide available technology,good economic and environmental benefits for the recycling of waste PCB,promote scientific and technological progress and improve the competitiveness of the industry.It plays an important role in promoting the healthy development of industrial economy.The follow-up research will continue to optimize the leaching process by other ways,improve the leaching rate,and provide data support for the application of bioleaching process and equipment. |
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