The Study Of Structural Modification, Organic Intercalation, And Microwave Expansion Of Vermiculite

Vermiculite is an important raw materialfor many functional materials, due to itsgood cation exchange capacity, expandability, and absorption capacity. Inrecent years,many endeavors have been devoted to the study of vermiculite. However, thestructural change of vermiculite during acid processing and microwave treatment stillneed to be investigated. In this work, studiesof structural changes of vermiculite aftermodification and intercalation were carried out. The results are as following:1. The effect of HCltreatmenton the structure and property of vermiculite werestudied and the relevant mechanisms were elucidated. The results show thatdissolution of Si, Mg, and Cacould occur at a lower HCl concentration of0.003mol/L.The Si comes from tetrahedralof vermiculite, whilethe Mg and Ca are derived fromthe interlayer of vermiculite. When the HCl concentration increasedto0.05mol/L, allcations are dissolved witha significant increasein Al, Mg, and Fe, suggesting thatportions of octahedralstart to be destroyed. During the acid treatingbothSi and Al aredissolvedwith dissolution of Si startedprior to Al andtetrahedral Al prior to octahedralAl. The CEC of vermiculite increasedfirst and then decreased, but the interlayerresidual charge increased generally as the HCl concentration increased.2. The organic intercalation into vermiculite and its relevant mechanism wereinvestigated. CTAB, TTAB and DTAB are all effective to intercalate into the raw andacid-treated vermiculite. The increase of the interlayer distance of vermiculite bythese organic cations followed: CTAB>TTAB>DTAB and increased with the dosageincrease. An improved intercalation was found with the acid-treated vermiculite atHCl concentration of0.003mol/L. The raw vermiculite showed a similar result withthe sample treated with0.01mol/L HCl.However, the vermiculite treated with0.1mol/L HCl did not result in any intercalation. These results suggest that a larger CECvalue of vermiculite would makethe intercalation process easier and a higher mount ofintercalation would produce a larger inter layer distance. 3. The variation of charge distribution after HCl treatment, the interactionbetween the organic cations of different chain lengths and vermiculite, and thedistribution of organic cations in the interlayer were simulated. The resultsshowedthat with the dissolution of Al or Si after the acid treatment, the positivecharge surrounding these sites decreased, while other sites might carry more positivecharges. The acid treatment enhanced the interaction between vermiculite and organiccations in the interalyer, resultin a closer distance between the organic cations and thevermiculite sheets. When organic cations were intercalated to the same acid-treatedvermiculite, the longer the organic cations were, the larger the amount ofintercalations was. However, their interlayer arrangements were similar.Somewereparallel to the lamella, while others inclined with a certain angle. The main drivingforce of intercalation into vermiculite is cation exchange,originatedfromelectrostaticattraction.4. The effect of expansion under microwave and its relevant mechanism werestudied. The results indicated that the vermiculite could be expanded well undermicrowave condition. And the microwave frequency and particle size of vermiculiteare the key factors. The expansion of vermiculite that has the larger particle sizedisplayed the better performance than that of the smaller particle size. Theexpandability of vermiculite increased with the increasing microwave frequency andthe heating time with a maximum of expansion achieved after60sec heat treatment.At a fixed heating time (e.g.60sec) the expandability of both vermiculite andacid-treated vermiculite increased with an increased frequency. However, theexpandability of the acid-treated vermiculite is smaller than that of the rawvermiculite. The different binding force between the interlayercations and watermolecules is the main cause for the different expandability of acid-treated vermiculite.The binding force between Na+and water molecule is relative weak, so the expansionof NaCl modified vermiculite is much larger under low frequency conditions. Whilethe interlayercations of Mg and Ca had a strong binding force for water molecules,they showed large expansibilityonly under high microwave frequency conditions.