| Fly ash is a solid waste mainly consisting of silicon dioxide,aluminum,etc.The fly ash is main dericed from coal-fired power plants in the from of spherical glass beads.A dense layer of Si-O-Si,Si-O-Al network structure constitute the crystal structure of glass beads in the surface of fly ash,so chemical properties of fly ash is very stable state,lead to having high chemistry stability.The metal elements contained therein are mostly encapsulated in such crystal structures.Due to the existence of these special properties,not only difficult to dispose fly ash as a solid waste,but also brings many challenges to the comprehensive utilization of fly ash.Especially as it is tried to recycle rare metals and produce a sustained-release fertilizer for improving mine.Currently,the comprehensive utilization via recover rare metals from fly ash,used more physical and chemical methods in general.Industrial methods such as hydrometallurgy,pyrometallurgical,pyrolysis and chloride distillation methods,etc,used a large number of inorganic acids,and high temperature produce low the effect of extraction in recovery process of rare metals in fly ash.However,these methods not only impose excessive demands on the extraction equipment and energy sources,but also pollute the environment and thus have limited economic benefits.Biological extraction methods also exist many limitations,such as low biological adaptability,suitable for biological leaching of microorganisms,biological leaching rate is low.One of the main factors limiting the bioleaching rate is the stable chemical structure of fly ash.Moreover,the solid waste of fly ash after recycling metal is still a major problem.Therefore,in this study,we designed trials to improve low bioleaching rates,overcome difficulties in handling fly ash solid wastes.We used fly ash from a coal-fired power plant in Chongqing as a research object,first conduced a sries of experiments via combined physical and chemical pretreatment,then recover the rare metals with microbial leaching method,to investigate the Feasibility of obtaining rare metals from fly ash;Then,the fly ash waste residue is properly pretreated and then combined with soil beneficial microorganisms to make the sustained release microbial fertilizer;Finally,laboratory simulation experiments were designed via testing growth situation of plants Pseudodrynaria coronans,Buxus sinica and Photiniaxfraseri,such as plat heigh,root lengh and analyzing soil fertility indicators,such as soil microbial community structure and soil enzymes.Using the fly ash micro-manure fertilizer to improve the soil fertility in the process of greening the mines.Under laboratory conditions,this study not only solved two problems of low bioavailability and low leaching rate during leaching of fly ash,but also solved the problem of solid waste utilization after leaching.Throughout the research process,the solid waste of fly ash has been fully utilized,which has no waste residue,the process is environment-friendly.The main results are as follows:1、After hydrothermal high-temperature and high-pressure via acid-base pretreatment of fly ash,the dense glass bead structure is destroyed in differnt degrees,which increases the specific surface area of fly ash and the metal compounds was exposed.Prerequisites for the contact of microorganisms and their secondary metabolites with metal compounds.Acidithiobacillus thiooxidans(T.t)and Aspergillus niger(A-n)can stable growth in 20% high concentration of fly ash medium via domestication.The results showed that the maximum yield of sulfuric acid was 0.004 mol / L after the domestication for T.t meanwhile pH reduced to 1.65.And the cell significantly in different fly ash culture system comparedwith that pure culture cell growth.After reaching the plateau,the maximum amount of bacterial protein in the pure ash,alkali-treated ash and acid-treated ash systems were 0.615,0.445 and 0.608 mg / ml respectively,it increased 1.81,1.31,and 1.78 times,respectively,compared with that pure culture.The amount of organic acids produced via domesticating A-n has also been greatly improved,and the yields of oxalic acid,citric acid,acetic acid,and alpha-ketoglutaric acid were 12.671,2.032,4.251,and 2.927 mg/ml,respectively.The plateau reached the growth stage on the 6th day.The maximum amount of bacteria in the pure ash,alkali treated ash and acid treated ash system were 3.409,3.505 and 3.690 mg / ml,respectively.it increased 2.33,2.39,and 2.58 times,respectively,compared with pure culture.2、The results of section 2 showed that the effect of hydrothermal alkali treatment is better than hydrothermal acid treatment and one-step leaching method overall better than the two-step leaching method.In the bioleaching of fly ash,the main metabolite of T.t is sulfuricacid.The bacteria contributes less to the leaching process(except for metal Ti).Alkali-treated fly ash is more conducive to the leaching of five metals V,Ni,Sr,Y and Ce by the one-step leaching method.Compared with pure culture,the leaching tate increased 40.39%,41.64%,47.83% and 10.50% respectively.The two-step leaching method is more conducive to the leaching of La and the leaching rate is increased by 14.60% compared with the pure fly ash.Acid-treated fly ash is more suitable for the leaching of Ti,Ni and La metals by one-step leaching.Compared with pure culture,the leaching tate increased 0.40%,11.88 % and 11.40% respectively.The two-step leaching method V,Y,Ce four metals leaching more advantage and the leaching rate is increased 6.60%,10.51% and 14.50% respectively compared with the pure fly ash.3、The results of section 3 showed that in the bioleaching of fly ash with A-n bacteria,the major metabolite of organic acids from A-n is the main role.Alkali-treated is more conducive to the leaching of three metals Ti,Sr,and Ba by the one-step leaching method.Compared with pure culture,the leaching tate increased 89.20%,54.30%,and 35.40% respectively.Acid-treated is more suitable for the leaching of Ti and Sr metals by two-step leaching.Compared with pure culture,the leaching tate increased 0.90% and 0.40% respectively.The one-step leaching method is more conducive to the leaching of Ba and the leaching rate is increased by 14.60% compared with the pure fly ash.4、In order to make full use of fly ash,it was made into sustained-release bacterial manure to use for mine green via experiment in lab.The results show that the loose porous structure was formed on the fly ash surface after vacuum sintering.It not only provides a "habitat" for the attachment of microorganisms,but also solves the problem of incompatibility between fly ash and microorganisms in the process of producing manure.The prepared fly ash fertilizer are good moldability,and slow hydrolysis,reaching the purpose of sustained release.Simulation test shows that the effect of retrieved green has been improved via combining abandoned mine soil and microorganisms as slow release fertilizer in the cultivation of pot experiment,with Pseudodrynaria coronans,Buxus sinica and Photiniaxfraseri.The addition of fly ash fertilizer increased many kinds of microorganisms beneficial to plant growth in marginal soils of mines,increased soil microbial population abundance and biodiversity,increased the content of many kinds of active enzymes in soil,and effectively increased,and improved soil fertility. |
