Amelioration Of Alumina Extracting Process And The Study On Synthesis Of Ettringite By Using Leaching Residue

Alumina is an important industrial raw material,which is widely used in various industries such as aerospace,automobile,construction,and semiconductor industries.Alumina with high purity and high specific surface area is used as an adsorbent or nano-adsorbent material for environmental pollution treatment.At present,the process of producing alumina in my country still uses the traditional Bayer process,of which bauxite is the mainly raw materials.However,in the face of declining aluminum resources,how do we use the limited aluminum resources to support the unlimited development of mankind?The thesis takes a large amount of aluminum dross(AD)produced by the aluminum industry as the research object,and extracts alumina from the AD by using the ameliorative alkali sintering leaching method,to recover most of the aluminum resources from AD in the form of high-purity alumina.The remaining residue is used as a raw material for the synthesis of solidified heavy metal ettringite.In this paper,through the study of the pretreatment of aluminum dross,alkali sintering and alumina leaching,the leaching of alumina in the aluminum dross in a high-purity form was realized;secondly,the leaching dynamic models fitting were used to find out the control step of leaching process of alumina and silica during the leaching process,and their leaching mechanism;finally,this thesis studied the recycling of the leaching residue in the process,and the mixtures of the leaching residue and calcium-based compounds(Ca O and Ca SO₄)can be used to prepare Ettringite material,which has the ability to solidify heavy metals.Studies have found that in the process of denitrification and salt removal,temperature had a greater impact on the hydrolysis reaction of aluminum nitride.Within a certain temperature range,the higher the system temperature,the faster the decomposition rate of aluminum nitride.In this study,with a solid-to-liquid ratio of 1/15 g/m L and heating at 100°C for 100 minutes,84.5%of aluminum nitride in the AD was decomposed.The calcination temperature of the material,the ratio of Na₂O/Al₂O₃(alkali ratio),the ratio of Ca O/(Si O₂+Fe₂O₃)(calcium ratio),the leaching temperature during the leaching process,the leaching time,and the liquid-to-solid ratio all had effect on the leaching of aluminum oxide and silicon oxide.The most direct effect of the calcination process parameters was reflected in the sintered phase of the material,that is,when the calcination temperature,alkali ratio or calcium ratio is low,alumina and silicon oxide will easily generate Na₂Al₂Si O₄;when the alkali ratio is high and the calcium ratio was high or low,sodium ferrite will be formed in various forms(Na₈Fe₂O₇,Na Fe O₂,Na4Fe O₇,etc.);when the calcination temperature was low or the calcium ratio is high,calcium oxide was easy to form calcium aluminate(Ca₂Al₂O₅and Ca₄Al₆O₁₃)with alumina under high temperature conditions.The research showed that the best parameter values of calcination temperature,sodium ratio and calcium ratio are 1000?,1.4 and 2.0 respectively;the best parameter values of leaching temperature,time and liquid-solid ratio are 60?,40min and 25/1 m L/g.The introduction of calcium sulfate into the leachate system can effectively remove 90%of the soluble silicon in the solution,and the usage amount is 1.5 g/m L.The study of leaching kinetics showed that the leaching reaction of alumina and silica were mainly controlled by the internal diffusion step.The apparent activation energy of their leaching kinetic reaction were 11.4010 k J/mol and 2.0556 k J/mol,respectively;The leaching mechanism was that the alumina leaching process was accompanied by the dissolution of silica,and silicate can react with aluminate and calcium aluminate to form insoluble minerals such as sodalite and garnet,thereby affecting the leaching fraction of alumina.The solidified material synthesized by the leaching residue can effectively solidify Pb,Mn,and Cd into heavy metals-ettringite.The solidification thresholds are:1.0%?6.0%,1.0%?4.0%and 0.5%?2.0%.