Study On The Leaching Process And Kinetics Of Aluminum And Iron In Fly Ash

Fly ash is a kind of solid waste generated from the combustion of pulverized coal.It has large emission and low utilization rate.It is mainly used in construction,agriculture,materials,and sewage treatment industries.Long-term accumulation of fly ash will cause soil,water,gas,and Radioactive pollution.Therefore,relevant national policies put forward strict requirements for the comprehensive utilization of fly ash to enterprises.Kunming Power Plant's fly ash contains a large number of metal oxides,from which can extract alumina,and iron oxide,however,the separation of aluminum and iron is difficult.In this paper,fly ash of Kunming Power Plant is treated by using the sodium bicarbonate activator to activate raw material at high temperature,and leacheing with nitric acid.The filtration liquid provides the aluminum-iron metal ions to the aluminum-iron composite flocculant,and the residue can prepare silica.This is a new technology for treating fly ash.Firstly,the feasibility of activating fly ash with sodium bicarbonate during the calcination process is investigated by thermodynamic calculation and analysis.The results show that sodium bicarbonate can not react with mullite in the tempreture range where sodium bicarbonate can keep stable.The product of sodium bicarbonate decomposition--Sodium carbonate and mullite gradually reacted to get NaAlSiO₄ above 700K,and gain NaAlSi₃O₈?NaAlSi₂O₆ over 900K.The analysis of raw materials and clinker by SEM and XRD shows that the crystalline phase of the mullite in the fly ash is almost completely destroyed and converted into sodium aluminosilicate with good acid solubility.The optimum process conditions of activating fly ash with sodium bicarbonate are got as follows:mass ratio of sodium bicarbonate to fly ash is 0.7:1,the calcination temperature is 800?,and the roasting time is 45min.Under these conditions,the leaching rate of aluminum and iron is 94.78%and 91.55%respectively.Secondly,the thermodynamic calculation and analysis of activated clinker's acid solubility show that sodium aluminosilicate,iron mine were completely dissolved in pH<3.66,pH<0.46 acid solution respectively.The existing forms and conditions of the dissolved products in the nitric acid solution system are analyzed by Pourbaix diagram.Analysis results show that when pH of the slurry after decomposition reaction adjust to less than 2,the generation of ferric hydroxide and aluminum hydroxide are hindered and the filtering strength is improved.It is studied that process of the leaching rate of aluminum and iron by leaching of clinker with nitric acid.The optimum leaching conditions are got as follows:the concentration of nitric acid is 25%wt,the liquid-solid mass ratio is lOg/g,the leaching temperature is 80?,the leaching time is 1.5h,and the stirring rate is 380r/min.In these technological conditions,the leaching rate of aluminum and iron is 93.93%and 90.55%respectively.The leaching residue is analyzed by SEM,XRD and EDS,and it is found that the residue is mainly amorphous silica,with the purity is over 90%.In the end,I studied the key factors and dynamic characteristics in the process of acid leaching aluminum and iron.The results show that the acid leaching process of the clinker is a liquid-solid phase reaction process.The process of aluminum extraction by nitrate acid leaching clinker,and in 1?5min,this process is controlled by chemical reaction process,the chemical activation energy equation of aluminum is Ea?o=14.255kJ/mol,dynamic model is:1-?1-x?1/3 =8.8013e-14255/RTt,chemical reaction series is 0.765;in 5?25min,this process is controlled by diffusion process,the chemical activation energy-20672 equation isEa?=20.672kJ/mol,dynamic model is:1 + 2?1-x?-3?1-x?2/3=18.6753e-20672/RTt,chemical reaction series is 0.7206.The process of aluminum extraction by nitrate acid leaching clinker,and in 1?5min,this process similarly is controlled by chemical reaction process,the chemical activation energy equation of iron is Ea =23.966kJ/mol,dynamic model is:1-3?1-x?1/3=298.89e-23966/RTt,chemical reaction series is 0.4421.