Study On Synthesis Of Cordierite From Blast Furnace Slag

With the degradation of iron ore, more high-alumina iron ore is used in smelting.and a larger amount of blast furnace slag with high Al2O3is produced. The totalcomponents of Al2O3, MgO and SiO2in the high-alumina slag account for55%ormore. This research explored a new process of preparing cordierite powders from theindustrial waste high-alumina blast furnace (BF) slag in a sol-gel route through aseries of steps such as acidolysis, leaching, sol-gel, drying and calcining. Cordierite isone of inorganic materials with good thermal characteristics. This study not onlyrecycles blast furnace slag with high added value, but also provides a new path forcordierite synthesis. The technological process and equipment are simple, and the costis low. As a result this method can be used to replace the original production ofcordierite, and has certain application value. The work is based on one complicatedsilicic acid-sulfuric solution system containing cations of Al3+and Mg2+from theleaching of the slag as raw materials of the cordierite. The main findings from thestudy are as follows:(1) Through the experiment of using the pure reagents for the simulation of blastfurnace slag leaching solution as the raw materials of the cordierite synthesis, we canconclude that the use of sulfate as the material to synthesize cordierite is feasible. Dueto the higher decomposition temperature of magnesium sulfate, we will generate amain phase of cordierite product at the temperature of1200℃keeping for2h.(2) Through the pretreatment to modify the raw slag for high activity, we canmake the slag completely acidolysis by using slag whose particle size is less than80μm and the dilute sulfuric acid solution is1.1mol/L while the ratio between acidand slag is1:15.(3) After a long time exploration, we have known that the successful process forpreparing cordierite by a sol-gel method using blast furnace slag as raw materials: aparticle size of less than80μm of blast furnace slag, an ratio between acid and slag of1:15, using a1.1mol/L dilute sulfuric acid solution, filtered and washed three times toremove the by-product of calcium sulfate. The TEOS-ethanol solution(1+4) andaluminum sulfate in deionized water was added to the filtrate in accordance withstoichiometric proportion of cordierite, and then the solution was adjusted to pH= 2.5-3. The sol-gel process was accomplished under60℃keeping36h and dried at105℃for12h. After the dried gel calcined at900℃the relatively pure cordieriteproducts can be obtained by calcined at1200-1300℃for2h.(4) The product was subjected to TG/DSC, XRD, FT-IR, and SEM/EDS analysis.According to the TG/DSC thermal analysis on the product calcined at900℃, wefound that a cordierite crystal phase is formed must over1200℃when themagnesium decomposed completely. From XRD and FT-IR analysis results whichconfirmed each other, we can conclude that the the main crystal phase of the productscalcined through1200-1300℃is cordierite, and the product using slag as material isthe same as the product prepared using pure reagents. In the graphs of SEM/EDSspectra of the cordierite powders prepared from the high slag and pure reagents, wefind that they are both irregular product. But some clusters generated in the surface ofthe sample particles of a pure reagent and the surface of the particles of the productprepared by the high slag is smoother. There is no big difference on the physicalproperties and microstructure between using slag and pure reagents as the rawmaterial by the same sol-gel method. EDS and X-ray fluorescence spectroscopy of theproduct from slag calcined at1300°C showed that the chemical composition of thesynthetic cordierite (Si: Al: Mg=(5.02-5.56):(3.72-3.84):2) is closed with thetheoretical composition (Si: Al: Mg=5:4:2) relatively. The further analysis of thesynthetic cordierite indicates that it is poor-aluminum and rich-silicon type.(5) On the basis of the XRF results, we found some impurities such as calcium,titanium, sodium, iron, potassium and other elements in the product prepared by slag.Since the content is too little, they cannot affect the form of cordierite main phase.(6)The sum content of the CaO, MgO, Al2O3and SiO2in the high alumina slag ismore than99%of slag and the magnesium aluminosilicate component which is usedfor the production of cordierite accounts for more than55%. In addition, thebyproduct calcium sulfate is high purity and its particle diameter is about10μm withgood economic value. In general the blast furnace slag has good utilization in thisexperiment.At last we made some preliminary exploration on the preparation of honeycombcordierite ceramic by slag and tested its performance. Under the range of1200-1300℃the temperature has no great impact on the synthesis of the cordieritepowder. But on the aspect of the performance of the honeycomb cordierite ceramic,the results are different in the three different temperature conditions of1200,1250 and1300℃. So if we want to prepare honeycomb cordierite ceramic with the slag, weneed to determine the best temperature for cordierite synthesis. There is also a need tostudy on the impact of calcium, titanium, sodium, iron, potassium and other elementsin the product. If you want to determine the best ceramic calcine temperature or otherpreparation process optimization, we require further experiments and detailed analysisof the sample testing.