Study On The Preparation Process And Mechanism Of Alumina From Coal Gangue Acid Soluble Matter

Coal is one of the most important energy materials in our country.Coal gangue is symbiotic with the coal measure surface,and it is a solid waste produced in the process of coal mining,mining,washing,processing,etc.,which is about 10%?20%of the output of raw coal.With the rapid development of society,the accumulation of coal gangue is increasing,which brings great harm to the atmosphere,soil,water quality and geological disasters.Coal gangue is a kind of solid waste rich in aluminum and silicon,and the content of aluminum is 16%?48%(mainly kaolinite),which can be used to extract aluminum.It has great significance for the resource utilization of coal gangue.In this paper,the acid soluble substances of coal gangue in Liuzhou,Shanxi Province was taken as the research object.Firstly,the feasibility and trend of the reaction were judged by the thermodynamic analysis of the pure aluminum sulfate carbothermal reduction reaction,and the reaction kinetics was studied.Secondly,according to the composition of the solid of coal gangue acid solution,different kinds of sulfate were added to study the effect of different kinds of sulfate on the carbothermal reduction of aluminum sulfate and study its reaction kinetics.Then,the transition to the real system--coal gangue acid solid carbon thermal reduction system research,and with the help of the relevant characterization of the mechanism.Finally,the solid carbon thermal reduction products of coal gangue acid were dissolved by alkali,and the optimum technological conditions were obtained by single factor experiment.The following conclusions are drawn:(1)The results of thermodynamic calculation under different atmospheres showed that aluminum sulfate was the most difficult to decompose under oxidized atmospheres,and the initial decomposition temperature was as high as 800?.Under H₂ reduction and weak reduction atmosphere of anthracite,the decomposition reaction is easy to be carried out.Under H₂ reduction atmosphere,it can be carried out at room temperature,while under weak reduction atmosphere of anthracite,the initial decomposition temperature is 60?.From thermodynamics analysis results,the reaction temperature on carbon thermal reduction aluminum sulfate reaction rate effect is very significant,high temperature stage(450?600?)is mainly Al₂(SO₄)₃be restored generated CO dominant reaction,reaction of CO and Al₂(SO₄)₃.Temperature rising rapidly system is conducive to reducing C and Al₂(SO₄)₃generation CO reaction,which can improve response speed and shorten the carbon and aluminum sulfate reaction time required to completely.According to the kinetic analysis results,when the reaction temperature at the range of 450?600?,the reduction reaction rate is controlled by the interface chemical reaction and the apparent activation energy is 227.488 k J/mol.The kinetic equation can be expressed by Erofeev equation (?).The XRD diffraction patterns,FTIR spectra and SEM images of the products at 600?and 2 h showed that the products were amorphous aluminum oxide with obvious Al-O-Al bond tensile vibration and small particle size,which provided a good theoretical basis for the preparation of metallurgical grade aluminum oxide by alkali solution of the later reduction products.(2)The activation energies of potassium sulfate,sodium sulfate,calcium sulfate,magnesium sulfate,iron sulfate and titanium sulfate doped were 191.395 k J/mol,197.799 k J/mol,217.755 k J/mol,220.073 k J/mol,206.422 k J/mol and 213.049 k J/mol,respectively.By comparing the activation energy of the three systems,it can be seen that potassium sulfate,sodium sulfate,calcium sulfate,magnesium sulfate,iron sulfate and titanium sulfate,as dopants,are easier to conduct carbon thermal reduction reaction than the undoped system(pure material aluminum sulfate).The dopants all have similar"catalytic"effect,and their"catalytic"performance is K₂SO₄>Na₂SO₄>Fe₂(SO₄)₃>TiOSO₄>Ca SO₄>Mg SO₄.From XRD and SEM analysis of the true system,it can be seen that in the range of 450?600?,with the increase of temperature,the XRD peaks of the reduction products gradually become disordered and the amorphous degree becomes higher and higher.However,the temperature is too low to ensure the conversion rate of aluminum sulfate.Therefore,the carbon thermal reduction temperature should not be lower than 500?.Moreover,the carbon thermal reduction products of coal gangue acid solubors are relatively small,which provides convenient conditions for alkali solution operation in the later stage..(3)The optimum technological conditions for alkali solution of coal gangue acid soluble solid carbon thermal reduction products are as follows:carbon thermal reduction reaction temperature is 600?,reaction temperature is 200?,reaction time is 80 min,liquid-solid ratio is 1:1,Na OH concentration is 200 g/L.Under this condition,the dissolution rate of alumina was 97.73%.XRD and SEM analysis of the alkali soluble products showed that the alkali soluble products were?-Al(OH)₃,and the product particles were regular globules,further proving that alumina has better reactivity in the reduction product.The quality of aluminum hydroxide product meets the AH-1 requirements in GBT 4294-2010.