Study on activity evaluation of activated coal-gangue and the hydration process

Journal of Harbin Institute of Technology( New Series),Vol. 14,No6,2007tudy on activity evaluation of activated coal-gangue andthe hydration processZHANG Hong-tao, DENG Hong-wei, FENG Qi., WANG Pei-ming张洪涛,邓宏卫,冯奇王培铭(1. HIT University Science Park Co., Itd., Harbin 150001, China; 2. School of Materials Science and Engineering, Harbin Institute of TechnologyHarbin 150006, China; 3. School of Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin 150090, China4. School of Science and Engineering of Materials, Tongji University, Shanghai 200092,ChinaAbstract: Chemical compositions, mineral compositions and the activated mechanism of the coalwere analyzed. And pozzolana activities of the coal-gangue were evaluated after activated. Moreover, hydrationheat and hydration compositions of activated coal-gangue-calcium oxide system, as well as hydration degree andhardened paste microstructures of activated coal-gangue-cement system were studied. Results show that pozzola-1a activities of the activated coal-gangue root in amorphous Sio, and activated Al2O,. With the exciting of gyp-sum, the reaction of activated coal-gangue and Ca( OH)2 would produce hydration products as ettringite, calci-um silicate hydrate, and calcium aluminate. The relationship between the curing age and the content of Ca(OH)2 in coal-gangue-cement system was ascertained. Unhydrated particles in the coal-gangue-cement pastewere more than that in the neat cement paste at the same hydration periods, and even existed at the laterof hydration. Furthermore, the activated coal-gangue could inhibit growth and gathering of the calciumcrystal, and improve the structure of hardened cement paste.ey words: activated coal-gangue; cement; pozzolana activity; hydration; function mechanismCLC number: TB321Document code: AArticle ID:10059113(2007)060855-06Coal-gangue is a solid waste produced in thecoal production, and the discharge amount is up to 1 Analysis on the Coal-gangueabout 10% of the output of coal In China, with coalexploitation the coal-gangue has discharged increasing 1. 1 Compositions and the Mechanism of Activanumbers; However, the current comprehensivetion of the Coal-ganguelization is less than 15%121. and effectiveness of itsThe coal-gangue was produced from Xuzhou.Itsilization is also inapparent. Abroad people pay atten- main chemical compositions are shown in Tab. 1,andtion to the utilization of coal-gangue. Starting the study its XRD is shown in Fig. 1. The coal-gangue was com-very early, they have logged up a remarkable series of posed of siallite minerals. Its mineral compositions weregains in the usage of coal-gangue, and the utilization as follows: Kaolinite, Quartz, Siderite,Orthoclaseratio remains ahead of chinaStudy on the com- Muscovite, Calcite and othersprehensive utilization of the coal-gangue could betraced in 1950 in China5). Coal-gangue has beenTab 1 Chemical composition of coal-ganguenow used in the field such as agriculture, chemical inAl2O, Fe203 MgO Cao K20 50, TiOdustry,environment, contracture, engineering, etc6-9149.914.912.20.93Despite this, compared with other solid wastes such asslag and fly ash, theoretical investigations and applicaKaolinite(AL2O3·2SiO2·2H2O) in the coaltions of the coal-gangue are very limited in China. gangue is a phyllosilicate mineral of the 1: I typSo, for accelerating development and utilization in which is composed of a Silicon-Oxygen tetrahedron laythe construction industry, this paper took the study re- er and an Aluminum-Oxygen octahedron layer. Itslated with the coal-gangue, i. e. compositions and acti- structural minelayers are absolutely the same, hydrogenvated mechanism of the coal-gangue were analyzed bonds are connectors of layers, and there's nopozzolana activity was evaluated as well as hydration moleIn the Kaolinite coordinprocess and the effect on cement hydration were illumnatedYH中国煤化工ely4and6. HydroxCNMHGthe temperature roseReceived 2005-11-15ponsored by the National Basic Reasearch Program of China( Grant No. 2001CB610704)855Journal of Harbin Institute of Technology( New Series), Vol. 14, No 6, 2007Fig 1 XRD patterns of the coal-gangueto 400-600 C. After this, the kaolinite remained the acid at 80 C for 2 h, under the condition of uniformlyinherent layer structure, but major dislocations had oc- agitating. Relative mass of the digested Al2O,curred among atoms, so the Kaolinite varied to be the measured as the content of the activated Al,O,, in theMetakaolinite(Al, O3. 2SiO2)which had a bad crys- filtrated liquor by ICP. Results represented that thetallinity 10, Il.The atom arangement in the Metaka- content of the activated AL, O, in the activated coalalinite is irregular; the Metakaolinite is in a thermo dy- gangue was 9. 24 %. The crystallinity is represented bynamical metastable condition and it is a mineral which the percentage, the crystalline gross of the mineralhas pozzolana activities.gross. The crystallinity can be worked out in twoActivation of the coal-gangue, i. e. removing ways 6: a) by the integral area of the diffractionhydroxide radicals from the Aluminum-Oxygen octahed- curve. For that any phase, no matter in what stateron, makes the coordination number of Al vary from 6 has a diffraction characteristic curve corresponding to4 or 5. Simultaneously, the Kaolinite with a regular the corresponding state. The rystallinity is the area ra-structure varies to be the Metakaolinite which has an ir- tio that the integral area of the crystalline phase be diregular structure. The heat treatment of calcinating was vided by the total integral area; b)by other methodschose as the activation mode heresuch as the FWHM of the diffraction peak. Five-finger1.2 Pozzolana Activities of the Activated Coal-gangue peak in the Quartz Crystal is a characteristic diffractionK. Takemoto and H. Uchikawa defined the peak; its morphology reflects crystal statuspozzolana activity or chemical activity a criterion for the ple and the stale of the system. With the tested 2132degree of reaction which is generated by pozzolana ma- peak(20 is from 67 to 69), corresponding a and bterials and water at the normal temperature. Test meth- were worked out. Basing on CI=10F. a/b(F isods commonly used to appraise pozzolana activities of 1. 67); the crystallinity could be worked out Thematerials are as follows the lime absorbing method, activated coal-gangue was given an X-ray diffraction a-the pozzolana testing method, intensity method, the nalysis. The scanning speed was 0.01%/s, the scan-ISO method, and the method of determining the quanti- ning range was from 65 to 70, and the XRD graph isty of the soluble matter in the pozzolana, in the alter- shown in Fig. 2. Ultimately, the crystallinity of thenate treatment by acid and alkali or the acid treat- SiO, in the activated coal-gangue was worked out to bement( 13, 14. The composition of the activated coal- 6.91, and the content of amorphous Si02 in the activa-gangue that has pozzolana activities is the Metakaolin- ted coal-gangue was examined to be 30. 90%ite.So, the experiment digesting soluble matter of theFrom the above analysis, it can be concluded thatacid treated Al,O, was done and the crystallinity of the the pozzolana activity of the activated coal-gangue is gotSio, was determined, the digesting quantity of the acti- as the following: the content of( the activated Al, 0,)+vated AL, O,and the content of the noncrystalline state the content of amorphous SiO,)=24. 66%SiO2 were taken to represent pozzolana activities of theactivated coal-gangue 5J2 Hydration Study on the Activated Coal-gangueThe activated coal-gangue contains a great deal ofCa(Oh), SystemQuartz, which has no activity at the normal temperature中国煤化工and only exerts the function of a fine aggregate in ce-CNMHhannel microheat ma-ment pastes. Metakaolinite is the main source of pozzo- chinheats of the followinglana activities of the activated coal-gangue. The activa-two compound systems: G+CH system: m( activatedted coal-gangue was dunked in 4 mol/L hydrochloric Coal-gangue )/m( analytically pure Ca( OH)2)/Journal of Harbin Institute of Technology(New Series),Vol 14, No 6, 2007n(H,O)=50: 50: 100; G+CH Gypsum system: sically the same. There were Ca( OH )2, ettringitem(activated Coal-gangue )/m( analytically pure AFt), Calcium Silicate Hydrate(CSH), Calcium ACa(OH)2)/m( gypsun)/m(H2O)=50:45:5:100luminate Hydrate( CAHjo) and those derived from primary materials just as Calcite( CaCO, )and a-Quartzcreased. the content of the Caha distinctly increasedtheof the AFt almostd thethe CSh could be hardly detected by XRD in the multiThe phase analysis of products represented that, with67.067267467.667.868.068.268.468.6the stimulation of gypsum, the activated coal-ganguecould react with the Ca(oH)2 and produce hydratesFig. 2 XRD patterns of activated coal-gangueuseful for the strength development. Conclusions canbe extrapolated from this, if added into the cementThe hydration heat curve is shown in Fig 3. Fig. paste, the activated coal-gangue could generate a sec-3(a) shows that when no gypsum is in, the heat re- ondary hydrating reaction with cement hydrates andlease time of the hydration produced by the activated promote the hydration of the cement pastecoal-gangue and the Ca( oh)2 is as short as about 3 hand the hydrating speed basically holds the line at thelater stage; when some gypsum is added in, the time--·G+Cextends to 30 h. Fig. 3(b)shows that the total exo-G+CH+gypsumtherm of the compound system containing gypsum is always higher than that free of gypsum. This proves thatthe hydrating speed and the degree of the hydrationthe former system are both higher than the laterthe gypsum can stimulate pozzolana activities of thehydrating reaction generated by the activated coala)Hydrated velocitygangue and cement hydratesBasing on the above results of hydration heat, theXRD analysis of the G+CH+ Gypsum system will bethe only object studied thereinafter. The activated coalgangue,the Ca(oH)2 and the natural pure gypsumG+CHwere mixed together, and then the mixture was agitatedG+CH+gypsumuniformly with water. The mixture was closely conserveed for3d,7dand28d,at20±2℃ and thedampness of 95%. The XRD analysis was taken and( b)Tolal hydrated hethe results are shown in Fig. 4. Phases of the com- Fig 3 Hydrated heat experimental result of coal-gangue.und system hydrated for 3 d, 7 d and 28 d were baCa( oh), system- Ca(OH)2CaCO中国煤化工CNMHGFig 4 XRD patterns of coal- gangue-Ca( Oh)2"gypsum systemJournal of Harbin Institute of Technology( New Series), Vol. 14, No 6. 2007energy spectrum analysis ): when the age upped to 283 The Reaction Degree and the Microstructure of d, the platelike Ca( OH), was formed and there were athe Activated Coal-gangue- cement Systemlarge abound of preferred orientations( Fig. 6(a))This microstructure certainly caused the stress concen-Two kinds of pastes were studied. The pure ce- tration, produced micro cracks and made the structurement system: cement and water were mixed at the wa- uneven. To macro properties, the structure caused theter-cement ratio of 0. 4, the cement was the 52.5 Sili- decrease of the intension and the durability. As thecate cement provided by Lafarge( Beijing ), and the photo shows, there're some micro cracks and pores incompositions were CaO 65. 2%, Si02 21. 3%, AL,O,the harden cement paste, and shapes of hydrates are4.2%, Fe20, 2. 7%, S0, 3. 5%, Mg0 2. 1% and oth- uneven. Fig. 6(c) shows, when the hydration age upsers l.0%: Activated coal-gangue-cement system: theto 7 d, the Caleium Sulphoaluminate Hydrate of single-activated coal-gangue was mixed with the cement and sulfur type(AFm)are produced. Compared with thewater,therein the activated coal-gangue replaced 30% AFt, the AFm has less constitutional water and a largerof the cement, and the water-solid ratio was 0.4. After density. So the constitutional water will be increased.even agitation, these two kind mixtures had been closethe density will be decreased and sizable cubic dilataly conserved at20±2℃ with the dampness of95%tion occurs, when the AFm varies to be the aft be-amples were respectively taken when the age reached cause of coming in contact with so, 2 of all sources7h, I d, 3 d, 7d, 14 d, 28 d, and they were given The AFm is a main factor that causes volumetric chan-the thermal analysis and the microstructure analysis of ges of the cement paste[ I8Jthe hardened paste.3. 1 The Thermal AnalysisConsidering the preferred orientation growth of theCa(OH)2, the DSC was used to analyze contents ofthe Ca( oh)2 at different hydration periods in the pucement system and activated coal-gangue-cement sys-tem. The content of the Ca(OH), produced (or con-umed)in the hydration was proportional to the energyabsorbed when decomposing the Ca(OH)2, also it was7d(16.68%proportional to the area below the DSC curve. The ex-14d(17.55%)perimental result the number in brackets of the pic3d(14.76%)ture is the exact content of the Ca( OH)2) is shown in1d(1144%)28dAs the age increased, the content of theCa( OH)2 in products of the pure cement system con-(a) The neat cement pastetinuously grew, and it reached the highest when theage was 28 d; the content of the Ca(OH)2 in activatedcoal-gangue-cement system reached the highest as theage was 3 d. That is to say: if the age was less than3 d, the Ca(oh)2 produced by the cement hydrationwas much more than that consumed in the secondaryhydrating reaction with the activated coal-gangue;positely if more than 3 d, the Ca( oH), consumed was1d(254%more than that produced. The consumption reached the14d(3.07%)highest when the age was from 3 d to 7 d, and tended28d(262%)7d(509%)to be smooth when the age was 28 d3d(1005%)3. 2 The Microstructure of the Hardened PasteSamples were respectively taken from the pure ce-ment system and activated coal-gangue-cement systemb)The activated coal-gangue- cement systemwhen the age was 3 d, 7 d and 28 d, their new sec-中国煤化工 of the systemtions were observed by SEM then. In the pure cemesystem,when the hydration age upped to 3 d, someCNMHGCa(OH)2 crystals were generated( Fig. 6(a)); when cement system, almost no platelike Ca(OH), and nothe age upped to 7 d, platelike crystals of the preferred orientation Ca( OH)2 can be observed. WhenCa(OH)2 were formed( Fig. 6(b), derived from the the age was 7 d( Fig. 7), although there were someJournal of Harbin Instiute of Technology(New Series),Vol14,No6,2007platelike Ca(OH), produced, the surfaces were ad-hered to with products, and the edge angles becamesmooth. These represented that the Ca( OH)2 hadbeen partly consumed by active compositions of thecoal-gangue. When the hydration had been run for 28d( Fig. 7(c)), many unhydrated particles were still inthe hardened paste. But in the products, the CaOH)2 decreased, the CalciumHydrate GelCSH) and the Calcium AlurCAHo )increased, furthermore the products werecomparativelyeven and there was no obvious microcrack and no big pore. Hydrates on surfaces of the(e)7doal-gangue particles(G on Fig. 7(c)) were likely tobe products of the self secondary hydrating reactionalso they could be adhesive substances of cement hydrates. But shown by the form, interfacial adhesionsbetween coal-gangue particles and hydrates seem wellFig. 7(d)is a photo of products in a big pore( the ap-erture is about 80 um) in the harden paste. It can beobserved that the pore is filled by the CSH, the CAH,oand the AFt to erase the stress concentration of theharden paste and inhibit developments of micro cracksHence,adding the activated coal-gangue can improvethe microstructure of the harden cement paste, de-(d)28dcrease adverse effects of the Ca( OH )2, increase the Fig. 6 SEM Pictures of hydrated products of the pure ce-content of the gelatin that is useful for macro propertiesment pasteof the hardened cement paste, and can homogenizeforms of hydrates中国煤化工CNMHG(b)7d859Journal of Harbin Institute of Technology(New Series), Vol. 14, No 6, 2007References[1 Leng F G. Study and applications about the comprehensiveutilization of the coal-gangue. Si Chuan Building Scienceeach, 2000(6): 44-46( in Chinese)2] Liang A Q, Kuang S P, Ding H. The discussion of compre-hensive utilization of coal gangue. China Resources Comprehensive Utilization, 2004(2): 11-14( in Chinese)[3] Vence T D, Powers D L. Resource recovery systems, Part1. 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