| At present,there are many researches on the application of rare earths in the field of new materials,especially in the catalytic function,but rare earth is used to prepare silicon aluminum oxide as the starting material for the aluminosilicate hydrate of kaolinite,?Na,K?-PSS in the synthesis of polysilicon?sodium,potassium?-silicas and the mechanisms of its action are rarely reported.Incorporations of rare earth nitrates into metakaolin and its catalytic mechanism is still in blank state for alkali leaching and geomaterial synthesis.Rare earths can reduce reaction activation energies and promote the reactions.Therefore,the use of rare earth properties to activate aluminum silicon raw materials and catalytic bonding conditions in the strong alkali conditions,will improve the performances of polymers and expand application areas.In this paper,XRD,FTIR and SEMEDS were used to study the effects of rare earth lanthanum nitrate on alkali leaching processes and mechanical properties of metakaolinite.The main conclusions are as follows:1)Appropriate increase of alkali leaching temperature can accelerate the process of MK-750 alkali solution.When leaching temperature was 25 ?,NaA zeolite was the maximum,while leaching temperature was 45 ?,the formation of hydroxysodalite was the best;La?NO3?3 significantly accelerated the progress of the formation of zeolite and hydroxysodalite,and the NaA zeolite and hydroxysodalite in the alkali leaching products were rapidly appeared and increased in a short time,and the zeolite phase was promoted.Reasonable control of the liquid-to-solid ratio allows the crystal phase of the MK-750 alkali leaching product to develop to a greater degree of zeolite or hydroxysodalite to varying degrees,at a lower liquid to solid ratio?2:1?NaA zeolite,in a certain range to improve the liquid-solid ratio can speed up the process of MK-750 alkaline solution.Formation of hydroxysodalite is best when liquid to solid ratio is 4:1;NaOH solution concentration play a decisive role in dissolution,polycondensation and hydroxy dodecylstone of active aluminum-silicon and formation of NaA zeolite and hydroxysodalite,while dissolution of quartz is almost the same.2)La?NO3?3 significantly increased the progress of formation of NaA zeolite and hydroxysodalite,while promoting the transition of NaA zeolite to the hydroxysodalite phase when the ratio of NaOH solution in the alkali system was higher than 70%.Leaching time affects not only the dissolution of active aluminum-silicon components in MK-750,but also the formation of slag phase and liquid phase in alkali leaching products.The crystal phases of La-100-MK-750 alkali-soluble products were obtained by reasonable extension of the leaching time and La?NO3?3 was added.The crystallization of the MK-750 alkali-leaching product was controlled by reasonable control of the liquid-solid ratio.When liquid-solid ratio was higher than 4: 1,the products with lower crystallinity can be obtained,and the liquid-solid ratio accelerated in a certain range will promote leaching progresses.Dissolution of quartz is not sensitive to the liquid-solid ratio.La?NO3?3 improved the crystallinity in lower liquid-solid ratio conditions,suggesting that a critical point existed between the liquid to solid ratio of 4: 1 and 6: 1;Appropriate increase in alkali temperature can accelerate MK-750 leaching.Addition of La?NO3?3 to the La-100-MK-750 alkaline solution resulted in the formation of the crystal phases in a shorter time,and at leaching temperature of 45 ?,hydroxysodalite was the best.3)Both addition sequence of La?NO3?3 had little effect on MK-750,which promoted crystallization.The effect of La?NO3?3 on the properties of the geopolymer was not significant at room temperature,and the activation process of MK-750 was slightly enhanced.The effect of La?NO3?3 on the geopolymer in the oven was very small,which promoted the dissolution,rearrangement and polymerization of MK-750.Under the curing box the role of La?NO3?3 on the geopolymer was not obvious,which was slightly conducive to MK-750 alkali activation process.4)Appropriate amount of La?NO3?3 can help to improve the strength of MK-750 base geopolymer.Excess La?NO3?3 reduced the strength of geopolymer,especially in the early time,and the middle and late was not that obvious.La?NO3?3 had little effect on the phase of MK-750,and the crystallinity of the composites,which was detrimental to geopolymer properties,and was decreased with the increase of content of La?NO3?3.With the increase of La?NO3?3,the compressive strength of the clay for 3 days was the highest at La-200 and then decreased.With the La-100 as the critical point,as La?NO3?3 increased,the compressive strength of the geopolymer for 7 days increased first and then decreased.With La-50 as the critical point,as La?NO3?3 increased,the compressive strength of the clay after 28 days increased first and then slightly decreased. |
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