Recycling Aluminum From The Surface Of Waste Aluminized Plastic Film By Acidophilic Bacteria

Due to different kinds of material performance each are not identical,single one or a layer of packing material is difficult to meet the requirements of the product,so people usually used the technology of dry type composite make two or more packaging materials into composite packaging.Electronic products packaging aluminum plating film is made up of polyethylene terephthalate?PET?,polyethylene?PE?and aluminum?Al?,It has the function of plastic and aluminum properties.its light quality,good abrasion resistance,good thermal stability,easy processing and forming characteristics,convenient people's life,at the same time also brought hidden trouble.Especially with the continuous updating of electronic products,the aluminum foil packaging materials are gradually increasing.In the absence of effective recycling methods and processes,the aluminized film is either treated as household waste or incinerated or landfill.Incineration can release a large amount of toxic and harmful gases,even causing carcinogens such as dioxins.The landfill causes soil and plant life to be suppressed,and the soil and groundwater are contaminated with prolonged rain.At present,there are mainly mechanical,chemical or mechanical-chemical methods.Mechanical method is the use of aluminium melting point is different to the plastic gasification aluminum-plastic separation,in order to achieve its disadvantage is that energy consumption is large,and the emission of harmful gases such as CO₂,the second is the only recycling of aluminum,and plastic can only be in the form of heat energy recycling,use value is not high.The chemical method is mainly used to dissolve the aluminum layer through acid or alkali,but strong acid and alkali has corrosive effect on the equipment,and there is a secondary pollution problem.Typical waste aluminum-plastic separation machinery-chemical method is mainly waste aluminum-plastic first under the action of wind,into the reaction tank with separating agent,after a clockwise and counterclockwise rotation feeding,finally through two-stage separation screen will aluminous model for separation and recovery.As a result,it is imperative to seek an effective separation process of aluminum.At present,microbial method because of its environmentally friendly,low energy consumption to achieve widespread attention,the more study focus on using Acidthiobacillus ferrooxidans,?hereinafter referred to as A.f bacteria?,Acidithiobacillus thiooxidans?hereinafter referred to as A.t bacteria?to bioleaching metals.The metal can be leached by ferric oxide.In this study,because of eosinophilic acid and aluminum ions in acidic conditions can coexist and it can be used for the separation of aluminum plasticine.Selective domesticated A.f and A.t bacteria strains resistant to high concentrations of aluminum ions,and through the continuous cycle training,explores this technology processing packaging aluminum plating film experiment effect and technical conditions and the mechanism of leaching is analyzed,so as to provide certain technical support of industry in the future to remove aluminium.The following conclusions are obtained:?1?Using the Nitrate and hydrochloric acid digestion method,The packaging of different particle size between 0.5-3mmwas digest.The content of aluminum in different particle size is different.With the decrease of particle size,the content of aluminum increases gradually.When the particle size is less than 0.5mm,the increase of aluminum is not significant,accounting for 18%of the aluminum film,indicating that it has good value for the recovery of aluminum resources.However,because of the secondary pollution problem,it is necessary to use the microorganisms without secondary pollution to make the separation of aluminumand plastic.?2?Through a gradual increase of the volume of aluminum plating film to be added,the domestication training for A.f and A.t bacteria,finally attained domesticated strains of Al³⁺high tolerance,selected fifth generation domesticated strains as experimental strains,analyze and compare the processing efficiency of different treatment methods under different conditions.The leaching rate of aluminum is 79.42%,57.24%and 68.96%,respectively,when the particle diameter is less than 0.5mm.The leaching rate of the control group was 16.24%,10.39%and 12.96%respectively.Under the condition of the same solid concentration,The leaching rate of aluminum under the optimum solid concentration was 83.29%,64.58%and72.33%,respectively,The leaching rate of the control group was 19.58%,13.76%and 15.23%respectively.Under the same initial pH of the medium,the leaching rate of aluminum under the optimum pH was 92.86%,71.37%and 83.93%,respectively.The leaching rate of the control group was 33.21%,27.36%and 29.68%,respectively.With the extension of time,the dealuminized amount of the three kinds of treatment increased gradually,and in the 8th day,the leaching rate of the three types of inoculation was 94.36%,66.43%and 79.87%respectively.Control group without bacteria leaching rate were 15.78%,4.99%,11.21%.under different test conditions in combination with three kinds of treatment of aluminum ions concentration,draw A.f bacteria leaching effectively on the surface of aluminum in the aluminum plating film,followed by A.f and A.t in all cultures,is again A.t bacteria.?3?Optimized test conditions,it is concluded that A.f bacteria bioleaching best conditions:FeSO₄·7 H₂O dosing amount to 60 g/L,the particle size of 0.5-1.0 mm,ratio of solid and liquid was 40 g/L,bacteria inoculation quantity was 10%,9 k medium initial pH of1,leaching time is 8 d,metal aluminum leaching rate of 93.86%,60.3%higher than unvaccinated processing;The A.f bacteria significantly increased the leaching rate of aluminum.The initial pH of culture medium,size of particle size and ratio of solid and liquid have significant influence on the leaching process.The optimal range of each factor was determined by experiment,and the initial pH of culture medium is 0.5,1 and 1.5;size of particle size is<0.5mm,0.5-1.0mm,1.0-2.0mm;the solid-liquid ratio is 30g/L,40g/L and50g/L;as the level of the response surface experiment.?4?On the basis of single factor experiment,the response surface analysis is conducted.Under the condition of the best addition amount of ferrous was 60g/L,bacteria inoculation amount was 10%and culture time was 8d,analysis of interaction influence of the different initial pH,different particle size,different solid-liquid ratio on leaching process,through the response surface analysis,the best experiment condition of the factors with significant influence on aluminum leaching is the initial pH is 1.13,the size of the particle size is0.74-1.24 mm,solid-liquid ratio is 41.51 g/L,the initial pH of culture medium is significant for aluminum leaching,followed by solid-liquid ratio,the particle size is once again.Under this condition,the leaching rate of aluminum is 96.41%.The optimum leaching conditions are used to verify the experiment.The experimental conditions were set to the initial pH 1.2,the size of the particle size was 0.8-1.2mm,the solid-liquid ratio was 41g/L,and the amount of FeSO₄·7H₂O was 60g/L,the inoculation quantity was 10%and the incubation time was 8d,and the actual leaching rate was 95.99%.Under this condition,the dealumination rate of the inoculation group was optimal,and it was much higher than that of the non-grafting group.?5?according to the different culture under the condition of parameters such as pH,ORP of variation over time and the result of SEM images,and combined with the leaching rate of aluminum,the pH rise faster or ORP reduction of the sooner,the microbiological leaching rise faster.Compared with the control group,It was found that that inoculation of A.f bacteria accelerate leaching of aluminum in aluminum film.The toxicity of plastics in the process of dealuminizing of acidophilic bacteria has no effect on the bacteria.It's possible leaching mechanism of is Fe²⁺/Fe³⁺and O₂/H₂O exists oxidation reduction potential,ferrous oxide can released electronic,When the pH is 1-2.5,the ferrous oxide will spontaneously oxidize to produce trivalent iron.Therefore,a large amount of ferric oxide can bring the biomass to a higher level.Since the A.f bacteria for aerobic bacteria,the culture medium of bivalent iron ions can be used as electron donor,it allows the electrons to transport electrons from the outside of the cell to a carrier in the cell membrane,to perform the function of the electron donor.RUS necessary element in the electron transport chain can effectively absorb every electrons on the outer membrane,which is located in the outer membrane of electron acceptor remain completely oxidation state,may at any time to obtain ferrous oxide release electrons,in the end,the ferrous ion oxidation degree will reach the highest.Under the action of A.f.,the divalent iron is oxidized to produce trivalent iron ions.The REDOX of Fe²⁺/Fe³⁺to present a positive electrode potential,as electron acceptor oxygen under acid condition,accept electronic oxygen generating water.And with the continuous transfer of electrons,the elemental aluminum is transferred from the solid phase to the leaching solution.Then the oxidant Fe³⁺receives the electron to be reduced,circulating to supply A.f bacteria for growth and use.