Study On Bioleaching The Heavy Metals From Municipal Solid Waste Incineration Fly Ash

Increasing municipal waste results in a large number of incineration fly ash,Incineration fly ash contains a variety of environmentally harmful heavy metals,and the removal of heavy metals in it has become a widespread concern.Pyro and hydro metalslurgical process are the traditional methods of extracting heavy metals from the solid phase,which suffer from large energy consumption,high equipment requirements,harsh operating conditions and other defects.Bioleaching is one of the economically effective,safe and environmental methods to solve this problem.In this work we bioleach the heavy metals from municipal solid waste incineration fly ash,select and optimizate strain system,explore relatively optimum microbial culture process and leaching process conditions.What’s more,it is quite important to study on recycling process,in order to develop a new technology for dealing with the heavy metals of municipal solid waste incineration fly ash.The bioleaching results show that Acidthiobacillus thiooxidans,Leptospirillum ferriphilum and Acidithiobacillus ferrooxidans bacteria mixed systerm is significantly better than other single strain system on acid producing efficiency and leaching efficiency.Reduction mechanism and acid-soluble oxidation mechanism are coexist through the whole bioleaching progress.Three different kinds of municipal solid waste incineration fly ash(solid-liquid ratio of Huzhou fluidized bed fly ash is 6%,solid-liquid ratio of Huzhou grate fly ash is 4%,solid-liquid ratio of Beijing grate fly ash is 2%)all have accorded with GB16889-2008 after the bioleaching of mixed culture system.In order to achieve the success of recycling process,contact bioleaching must be required to transfer into non-contact bioleaching.It is necessary to compare the target metals leaching rate of contact and non-contact biological leachate and make sure that the target metals ion concentration in leachate(non-contact bioleaching residual disposed according to HJT300-2007)is also lower than the standard concentration in GB16889-2008.Then we optimize the acid production efficiency,and explore relatively appropriate parameters of bioleaching solid-liquid ratio(consistent with the above conclusions),bioleaching temperature(30℃)and bioleaching time(3h).Finally,we study on the recycling process which based on non-contact bioleaching.The results indicate that Huzhou fluidized bed fly ash leachate recycles 20 times,Huzhou grate fly ash leachate recycles 19 times and Beijing fluidized bed fly ash leachate recycles 6 times.We study the heavy metals and Cl-,F-accumulation concentration of the three kinds of fly ash.It turned out that the Ni which accumulated in Beijing fluidized bed fly ash cycling leachate worth recycling to some extent,and the concentration reaches 133.79mg/L after 6 times of cycling.The following study analyzes the toxic effects of high concentration of Cl-on microbial growth.On the basis of the above research we can domesticate the existing strains or finding new strains to improve the ability of resistance to high concentration chloride ion,and so as to achieve the purpose of enriching metals as much as possible.