Construction Of Pseudomonas Biofilm,Cyanogen Production Characteristics And Its Leaching Effect On Precious Metals From Electronic Waste

With the rapid development of science and technology,the renewal frequency of electronic products has been accelerating,resulting in a large amount of electronic waste.In view of the large amount of precious metals in e-waste,the research and development of its recycling,disposal and resource utilization technology has attracted widespread attention.At present,mechanical recycling,pyrometallurgy,hydrometallurgy and biometallurgy are commonly used e-waste resource recycling methods.Among them,bio-metallurgy has shown great development potential in the utilization of e-waste resources,because of the advantages of low environmental pollution and low energy consumption.Previous studies have found that cyanide-producing bacteria under suspension culture conditions can leach precious metals from e-waste.However,due to the poor resistance of bacteria in the suspension culture state and insufficient ability to continuously produce cyanide,the leaching efficiency of precious metals from electronic waste is greatly reduced.Biofilm,as a microbial community growing on the surface of the carrier,has stronger resistance to stress than suspension culture bacteria.Therefore,this article studies the construction of cyanogen-producing bacteria biofilms,the characteristics of cyanogen production and the leaching rules of precious metals,which provide a basis for the realization of high-efficiency biological recycling of precious metals from electronic waste.The main research conclusions are as follows:(1)There are differences in the biofilm formation ability of the 17 tested Pseudomonas cyanogenes,and the biofilm formation ability of most strains shows an upward trend with the extension of the culture time.Strains 24-3 and 113 were selected based on the cyanide production and biofilm formation ability of the strains for the optimization test of biofilm formation conditions.The results showed that strain 113 had the strongest biofilm formation ability at 25℃ under the four culture temperature conditions of 15℃,25℃,30℃ and 35℃,while strain 24-3 did not have a clear optimal temperature for biofilm formation.As the pH value increased from 7 to 11,the biofilm formation ability of the two strains showed a downward trend.Under three medium concentration conditions of 1/50 NB,1/25 NB and NB.NB medium is conducive to the formation of strain 24-3 biofilm,and 1/25 NB medium is conducive to the formation of strain 113 biofilm.In addition,the formation of two bacterial biofilms is inhibited by high concentrations of copper ions(1000 ppm,2000 ppm)and silver ions(10 ppm),and promoted by low concentrations of silver ions(2,5 ppm).However,the response to low concentrations of copper ions(500 ppm)is differentiated,which shows that strain 113 is promoted while strain 24-3 is inhibited.(2)Considering the strain’s cyanide production capacity,biofilm formation and its response characteristics to environmental factors,strain 113 was selected to study the biofilm cyanide production capacity and its influencing factors.Single factor test showed that the Pseudomonas cyanogen-producing biofilm has the ability to produce cyanide,and compared with ceramsite,polyethylene particles are more suitable as a biofilm carrier.The best cyanogen production conditions for strain 113 biofilm were 20℃,pH 7,100 rpm and 1/25 NB medium.High concentrations of copper ions and silver ions are toxic to biofilms,while low concentrations of copper ions and silver ions will promote cyanide production by biofilms,and the peak value of cyanide production by biofilms at a copper ion of 500 ppm is as high as 24.26 mg/L.(3)Based on the above test results,the semi-continuous culture method was used to study the leaching dynamics of silver from simulated electronic waste particles by cyanogen-producing biofilm.The results showed that:in the semi-continuous culture,the proportion of silver in simulated e-waste particles was 0.05%,0.10%,0.15%,and 0.20%,and the silver leaching rate was 19.23 μg/L/h,22.38 μg/L/h,23.81 μg/L/h and 28.60 μg/L/h.In addition,a continuous culture method was used to initially construct an e-waste precious metal leaching reactor based on continuous cyanide-producing biofilm.The continuous cyanogen production system of the reactor was stable at 2～4 mg/L under the conditions of rotating speed 30 rpm,temperature 25℃ and no aeration.The silver leaching rate of the precious metal leaching system reached 40.67 μg/L/h at a stirring rate of 150 rpm,aeration rate of 0.5 L/min,pH 11 and room temperature,which was 42%higher than that of semi-continuous culture.