Proceedings of XV BALKAN MINERAL PROCESSING CONGRESS Sozopol, Bulgaria, June 12 16, 2013

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2 Proceedings of XV BALKAN MINERAL PROCESSING CONGRESS Sozopol, Bulgaria, June 12 16, 2013 V O L U M E II Edited by Ivan Nishkov, Irena Grigorova, Dimitar Mochev 2013

3 ISBN All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publisher. Papers are reprinted as they were submitted. The content of the papers is the sole responsibility of the authors. The publisher is not responsible as a body for the facts and opinions advanced in any of its publications. The publisher takes no responsibility for typographical or other errors. Printed in Bulgaria. Publishing House St. Ivan Rilski Sofia, Bulgaria For the Publisher: Eng. Teodora Hristova Technical Editor: Eng. Maya Grigorova

4 STRUCTURE OF NEW BUILDING CERAMICS WITH HIGH CRYSTALLINITY FROM INDUSTRIAL WASTES AND KAOLIN Stela Atanasova-Vladimirova, Bogdan Ranguelov, Georgi Avdeev, Emilia Karamanova, Alexander Karamanov Institute of Physical Chemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Block 11, 1113 Sofia, Bulgaria ABSTRACT. New building ceramics, obtained by sintering at o C of huge amounts of Blast Furnace Slag or bottom ashes from Municipal Solid Waste Incinerator (MSWA) mixed with kaolin, are characterised. The phase compositions and the amounts of formed crystal and amorphous phases are estimated by XRD analysis. The structures of the final samples (both surface and fractures) and the morphology of the formed crystal phases are characterized with SEM coupled with EDS. The open and closed porosities are evaluated by water absorption and density measurements with gas pycnometer. The results elucidate that the new ceramics are characterised with low open ( vol %) and high closed (10-20 vol%) porosities as well as with wt % fine-crystalline anorthite solid solutions, pyroxene and some residual quartz. The observed structures and phase compositions are untypical for the traditional ceramics and are comparable to ones of the glass-ceramics from industrial wastes, which are produced by a more complicated and more expensive technology cycle. Keywords: structure, phase composition, ceramics, industrial wastes INTRODUCTION The traditional tiling ceramics are heterogeneous materials, obtained by mixing and sintering of three main types of natural raw materials (i.e. sands, feldspars and clays). The clay-based minerals provide plasticity and workability of the ceramic greens. The feldspars melt during the firing and thus supply the formation of liquid phase, which governs the densification process. The quartz, because of its dissolution, helps to balance the viscosity of formed melt and also has structural functions in both green and finished products. Since the thermodynamic equilibrium can not be reached during an industrial firing the finished products commonly contain residual quartz (at about 15-25%) and traces of feldspars. At the same time the fine clay s crystals completely disappear and participate in the formation of primary or/and secondary mullite (3Al 2O 3.2SiO 2) in amount of about 10-20%. The formed liguid phase, which assures the sintering process, during the cooling vitrified into % amorphous phase (Hlavac J., 1983, Kingery W.D. et al., 1976). The formation of high amount liquid phase leads to good degree of densification, low or zero water absorption and 5-10 % closed porosity. The formed pores usually are spherical, sized between 5 and 15 µm and with a smooth surface (Dondi M. et al., 2005). Due to the significant variations in chemical and phase compositions of the ordinary raw materials, the traditional ceramics are produced in a wide range of composition, which could tolerate the usage of different alternative raw materials or various inorganic industrial wastes (Carbonchi G. et al., 1999, Ergul S. et al. 2007, Gennaro R. et al., 2003, Kurama S. et al., 2006). Among the above-mentioned raw materials the feldspars are the most expensive and therefore its replacement would represent a significant reduction in the final costs. For this reason many works, related to the usage of different alternative fluxing agents, were realized. Promising results were obtained using soda lime glass cullet (Matteucci F. et al., 2002, Tucci A. et al., 2004), cathode ray tube of TV or PC monitors (Andreola F. et al., 2008) and granite cutting sludge (Torres P. et al., 2004). In theses studies it was elucidated that the optimal percentage of addition is between 10 and 15 wt % and that the final structure and phase composition of these new ceramics are similar to the traditional ones. Other works examine the possibility to use industrial streams as Blast Furnace Slag, MSW ashes, fly ashes from thermal stations and various sludges. Usually, these residues are added as inert materials and the sintering process is related mainly to the presence of traditional ceramic fluxes (Andreola F. et al., 2002, Barbieri L. et al. 2002, Dana K., Das S. K., 2004). However, if the melting temperatures of the used wastes are reached they also start to melt which drastically changes the sintering behaviour, the phase composition and the structure of final ceramic. In some cases this feature gives the unique possibility for a total removal of the feldspars and for usage of huge amount of wastes in the batch (Karamanova E. et al., 2011, Schabbach L.M. et al., 2012). In addition, these innovative ceramics are characterised with higher crystallinity and improved mechanical properties. Practically, their chemical and phase compositions are fairly similar to these of the glass-ceramics, obtained by industrial wastes (Rawlings R. D. et al., 2006). However, the glass-ceramics are produced by a much more expensive technology, including glass melting and subsequent two step crystallization heat- treatment. The aim of the present work is to study and discuss the specific structures of four new ceramics, obtained without traditional fluxes and with high amounts of industrial wastes. Two of these compositions are prepared using Blast Furnace Slag and two - by means of bottom ashes from Municipal Solid Waste Incinerators. EXPERIMENTAL The first of studied ceramics (labelled as CSK-70) was obtained by mixing 70 wt% granulated Blast Furnace Slags (BFS) with 30% refractory kaolin (K), while the second (labelled as CSSK-30) - by mixing 30 % BFS, 40 % quartz sand (S) and 30% K. The other two compositions were prepared using 40% clays and 60% of two different fractions of bottom ashes from Municipal Solid Waste Incinerators (F fine, below 3 mm and L large, above 3 mm, respectively). The last two ceramics are labelled as CLK-60 and CFK- 60. In order to prepare suitable press-powders all raw materials were ground and sieved below 75 μm. Each batch composition was prepared by dry-grinding and then humidified with 6 wt.% distilled water; after that green samples were pressed at 40 MPa. The sintering process was studied with dilatometry (Netzsch 402 ED and Misura HSML ODLT 1400), while the thermal behaviour was determined by DTA-TG (Netzsch STA 409). Then samples (50 x 5 x 4 mm) were sintered for various times at different temperatures and at 10 C/min heating and cooling rates. The apparent, ρ a, skeleton, ρ s, and absolute, ρ as, densities of the sintered samples, as well as their water absorption, W, were determined and the results were used to evaluate closed, P C, and open P O porosity: P O W x a as s P C 100 x as ρ a was estimated by precise micrometer, while ρ s and ρ as - by gas pycnometer (AccyPy1330, Micromeritic) before and after crashing and milling the samples below 26 μm, respectively. W was measured after 3 h boiling in distillate water. The chemical compositions of ceramics and the corresponding optimal firing temperatures are summarized in Table 1. Details about the chemical compositions of used industrial wastes and information for the sintering behaviours of ceramics and the related phase transformations were reported elsewhere(karamanova E. et al., 2011, Schabbach L.M. et al., 2012). X-ray powder diffraction patterns for phase identification were recorded in the angle interval o (2 ), on a Philips PW 1050 diffractometer, equipped with Cu K α tube and scintillaition detector. Data for Rietveld refinements were collected in -2, step-scan mode in the angle interval from 8 to 110 o (2 ), at steps of 0.03 o (2 ) and counting time of 3 s/step. The amorphous content in samplea was determined with a Rietveld refinement by addition of a crystalline standard phase with HighScore Plus software package. 1083

5 Tabl. 1 Chemical compositions of the studied ceramics and (wt %) the high percentages of CaO, MgO and iron oxides, are not common for the traditional ceramics. In fact, similar phases are usual for the glass ceramics by industrial wastes (Rawlings R. D. et al. 2006). Tabl. 2 Phase composition (wt.%) of the final ceramics The microstructure and the crystal morphology of the final samples (both surface and fracture) were observed by Scanning Electron Microscopy (JEOL JSM 6390) coupled with an energy dispersion spectroscopy equipment (EDS, INCA 350, OXFORD). RESULTS AND DISCUSSION Quartz, as one of the main phases, is presented only in composition CSSK-30, which is the ceramic with lowest percentage of industrial waste. The SiO 2 content in this composition is maximal and the sum of CaO + MgO + Fe 2O 3 is minimal. In this ceramics some crisobalite and relatively high quantity of amorphous phase are also observed. Another composition, where undissolved quartz remains is CLK-60. This cermics also is characterised with relatively low sum of CaO + MgO + Fe 2O 3 and SiO 2 percentage is about 60 %. In this composition the maximum percentage of 59% amorphous phase is observed. In other two compositions the quartz phase is negligible and the main crystal phases are pyroxenes (in CSK-70) and anorthite s.s. (in CFK-60). Here the amounts of amorphous phases are lower and their percentages were estimated as 45% and 47%, respectively. Tabl. 3 Density (g/cm 3 ), porosity (vol %) and water absorption of the final samples Fig. 1 XRD spectra of final ceramics (Q quartz, P pyroxene, A anorthite s.s., C cristobalite, H -hematite) The XRD spectra of final new ceramics are presented on Fig. 1, while the results about the amounts of main phases in the materials are summarized in Tab. 2. These phase compositions are untypical for the traditional tiling ceramics. The presented anorthite solid solutions and pyroxenes as main crystal phases, which are results of Table 3 shows the obtained results for density and porosity. The apparent densities and open and closed porosities for samples CSSK- 30 and CLK-60 are somewhat similar to these of monofired earthenware (terracotta) (Kingery W.D. et al., 1976, Hlavac J., 1983). CSSK-30 is characterized with less then 3 % W and with a minimal closed porosity. In CLK-60 the open porosity is lower, which can be explained by the higher amount of formed liquid phase, while some increasing in the closed porosity is observed. The results of other two samples are fairly different. The absolute densities of ceramics CSK-70 and CFK-60 are significantly higher then ρ as of the traditional tiling ceramics (Dondi M. et al., 2005, Andreola F. et al., 2008), which can be related to their higher crystallinity and to the elevated densities of formed pyroxenes ( g/cm 3 ) and anorthite ( g/cm 3 ) phases. At the same time, the apparent densities are significantly lower than ones of porcelain stoneware and earthenware tiles, which is result of elevated closed porosities. Here can be noted that the minimal open porosity of samples CSK- 70 and CFK-60 is in apparent contradiction with their high crystallinity, because usually % liquid phase is required to ensure formation of samples with minimal or zero water absorption. The high closed porosity, couplet with a minimal open porosity in these two compositions can be explained with partial melting of anorthite and pyroxenes during the sintering and a subsequent crystallization process during the cooling. Similar peculiarities can lead to some overfiring during the sintering and to formation of crystallization induced porosity during the cooling. The overfiring (due to narrow sintering interval and relatively low viscosity of formed melt) might be identified by formation of larger pores, while the crystallization induced porosity, contrary, can be related with formation of additional tiny pores with polycrystalline surface. The formation of crystallization induced porosity was confirmed in both ceramics CFK-60 and CSK-70. Ceramic CFK-60 was studied by optical dilatometry and hot-stage XRD at heating and cooling. The XRD results, obtained at heating, demonstrate anorthite formation in the interval o C and its partial melting at o C. This data is in a good agreement with the corresponding dilatometric curve, which shows some shrinkage at o C and intensive sintering process at o C 1084

6 (Schabbach L.M. et al., 2012). The XRD results on cooling elucidate increasing of the amount of anorthite, while the parallel dilatometric traces highlight flat line with no crystallization shrinkage. These results clearly indicate that the volume changes, related to the phase formation during cooling, can lead to formation of addition porosity. Fig. 2 XRD spectra of CSK-70 cooled (c) and quenched (q) samples (Q quartz, P pyroxene, A anorthite s.s.) In CSK-70 the crystallization during cooling were studied with XRD, comparing the spectra of specimens cooled in the furnace and rapidly quenched in air, respectively. The spectrum of sample, quenched after 30 min holding at 1210 o C, and one of final ceramic (30 min holding at 1210 o C and cooling at 10 o C/min) are presented in Fig. 2. The analyses of results highlights an increasing of the crystallinity during the cooling (mainly due to pyroxene formation) with ~15 %. The measurements of apparent and skeleton densities of these two CSK-70 samples demonstrate comparable ρ s and ρ a values, which means that no densification carries out during the cooling. At the same time, due to supplementary crystallization during the cooling the absolute density in the cooled sample increases with g/cm 3 ; this leads to formation of additional 3-4 % closed crystallization induced porosity. It is interesting to note, that identical experiments, made with CSSK-30 samples (Karamanova E. et al., 2011), show equal XRD spectra, densities and porosities of both cooled and quenched samples (i.e. in this ceramic no densification, crystallization and porosity formation carried out during the cooling). These differences demonstrate that phase formation during cooling and the related formation of crystallization induced porosity may be expected mainly in composition with high crystallization trend (i.e. ceramics with superior amounts of CaO, MgO, Al 2O 3 or iron oxides). In addition, these compositions are characterised with inferior SiO 2 percentage, which can leads to relatively lower viscosity of the formed melts and thus to an higher tendency for overfiring. The XRD and porosity results were confirmed by the made SEM analysis. Some typical photos of the surfaces and fractures of studied four ceramics are summarised in Figures 3-6. The image of CSSK-30 surface (Fig. 3-a) shows an uncompleted densification and some open pores, mainly with irregular shape and size of m; the way out of a typical open pore, at higher magnification, is presented in Fig.3-b. The fracture of this sample is elucidated in Fig.3-c, which show a satisfactory degree of sintering and presence of both open and closed pores in the bulk of ceramic. The closed pores are spherical, whit a smooth surface and with size of µm. Together with the pores two other subjects, which details are presented in Fig. 3-d and 3-e, respectively, were identified in the bulk of CSSK-30 sample. Fig. 3-d highlights a zone, enriched in Si and Al, which XRD analysis is reported in the inset of figure. These fine crystalline formations are very similar to preliminary mullite (Hlavac J., 1983, Kingery W.D. et al., 1976), which however is not distinguished in a definite manner in the made XRD analyses. In fact, due to overlapping with the peaks of quartz and other phases, the identification of low amount of mullite is quite difficult. Even in traditional ceramics, where only quartz and mullite are formed, the XRD evaluation of mullite requires serious and accurate studies (Martín-Márquez J. et al. 2009). Fig. 3-e presented a typical Image and EDS analyses of residual quartz grain with size of µm. The irregular shape of the observed quartz crystals can be explained by their partial dissolution. In fact, the evaluated final percentage of the quartz (see Table 2) is at about two time lower than the initial 40 wt % sand in the initial CSSK-30 batch. Images of other slag sample CSK-70 are summarized in Fig. 4 and show significant differences in both surface and fracture. The surface of sample is very well sintered and minimal number of open and closed pores are observed. At lower magnification the surface looks fairly smooth (Fig. 4-a), but at higher magnification a high crystallinity and some individual crystals are well notable. Fig. 4-b elucidates a typical open pore in the surface, while the image from Fig. 4-c demonstrate a closed surface pore with a well distinguished single crystal in the center; the corresponding EDS spectrum, reported in inset, corresponds to Mg-reach pyroxene. The fracture of CSK-70 (Fig. 4-d) demonstrates mainly closed spherical pores with size between 20 and 100 µm, which are characterized with rough and polycrystalline surface. The presence of bigger pores (> µm), which are not observed in sample CSSK- 30, elucidates some overfiring. In addition, tiny pores with 3-5 μm size, which can be associated to the crystallization at cooling, are observed. Fig. 4-e presents a typical crystallization induced pore with hexagonal crystals having anorthite composition (according to corresponding EDS result). Details of the structure of CLK-60 are summarised in Fig. 5. The image from Fig. 5-a highlights a surface with minimal porosity, while the image from Fig. 5-b shows a singe open pore, which is very similar to ones formed in ceramic CSSK-30 (see Fig. 3-b). At the surface mainly hexagonal anorthite crystals were identified, together with some needle-like structures. One typical pine crystal is well seen in the centre of image Fig. 5-b; its EDS spectra corresponds to wollastonite (CaO.SiO 2) solid solution. The fracture of ceramic CLK-60 demonstrate mainly closed pores, sized between 20 and 60 μm, together with few bigger open pores whit size reaching μm. Typical open and closed pores are presented in Figs. 5-d and 5-e, respectively. The open pores have irregular form and in many cases inside the open pore different individual crystals may be identified. Together with the typical anorthite crystals (right inset in Fig. 5-e) pyroxene formation was also identified (left inset). The closed pores are similar to these in composition CSSK-30 and are characterised with smooth surface. This fact can be explained with the lower crystallinity of these two samples and the absence of phase formation during cooling. The structure of composition CFK-60 is shown in Fig. 6. Notwithstanding of its low open porosity, the surface of this ceramic (Fig. 6-a) is not flat as ones of CLK-60 and especially CSK-70, which can be related to the superior crystallinity of ceramic CFK-60. Fig. 6-b demonstrates the outside part of a well formed open canal pore, whereas the inset shows an image of the pore, made at superior depth of focus. It is well seen that the fine polycrystalline structures of the surface and of the pore are identical. The only nonhomogeneities, observed on the surface of this sample were some zones of hematite formation. An example is presented in BSE image from Fig. 6-c and the associated EDS spectrum. The CFK-60 fracture is presented in Fig. 6-d and shown well sintered body with closed spherical and semi-spherical pores between 20 and 120 μm, as well as small crystallization induced pores (similar to these in ceramic CSK-70) with size between 3-10 μm. An typical spherical pore, elucidating the elevate crystallinity of this ceramic, is demonstrated in the image from Fig. 6-e. The formed anorthite crystals have similar shape and size as these in ceramics CSK-70 and CLK-60, but their EDS analysis highlights that some Fe (between 2 and 4 atom%) takes part in the crystal composition. This is consequence of the highest iron oxides content in this ceramics and the possibility for substitution of a part of Ca 2+ ions by Fe 2+ in anorthite structure (Sclar C. B., Kastelic, R. L., 1979). 1085

7 Fig. 3 SEM images of ceramic CSSK-30 Fig. 4 SEM images of ceramic CSK

8 Fig. 5 SEM images of ceramic CLK-60 Fig. 6 SEM images of ceramic CFK

9 CONCLUSIONS The phase compositions of studied ceramics are completely different from these of traditional tiling ceramic materials. The main crystal phases in the new compositions, instead quartz and mullite, are anorthite solid solution and pyroxenes. In addition the amounts of residual vitreous phase are inferior than these in the well sintered traditional ceramics. The compositions with lower crystallisation trend are characterised with water absorptions similar to earthenware and with some unreacted quartz. In this case the formed closed pores are spherical and with smooth surface, but their size is bigger than ones in the traditional tiling ceramics. The compositions with higher crystallization trend show regular fine-polycrtalline structure in surface, fracture and pores. These samples are characterised with a negligible open porosity and high (at about vol %) closed porosity. A part of this closed porosity can be related to phase formation during the cooling, which leads to creation of tiny crystallization induced pores. ACKNOWLEDGMENTS The authors are grateful for the financial support of Project BG051 PO funded by OP Human Resources Development of EU Structural Funds. The work was also supported by Project DID-02/40 (Bulgarian Ministry of Science and Education). REFERENCES Andreola, F., Barbieri, L., Corradi, A., Lancellotti, I. & Manfredini, T. (2002). Utilisation of municipal incinerator grate slag for manufacturing of porcelainized stoneware tiles manufacturing. Journal of the European Ceramic Society, 22, Andreola, F., Barbieri, L., Karamanova, E., Lancellotti, I. & Pelino, M. (2008). Recycling of CRT panel glass as fluxing agent in the porcelain stoneware tile production. Ceramics International, 34, Barbieri, L., Corradi, A., Lancellotti, I. & Manfredini, T. (2002). Use of municipal incinerator bottom ash as sintering promoter in industrial ceramics. Waste Management, 22, Carbonchi, G., Dondi, M., Morandi, N. & Tateo, F. (1999). Possible Use of Altered Volcanic Ash in Ceramic Tile Production. Industrial Ceramics, 19, Dana, K. & Das, S. K. (2004). Partial substitution of feldspar by B.F. slag in triaxial porcelain: Phase and microstructural evolution. Journal of the European Ceramic Society, 24, Dondi, M., Ercolani, G., Guarini, G., Melandri, C., Raimondo, M., Rocha, E. (2005). The role of surface microstructure on the resistance to stains of porcelain stoneware tiles. Journal of the European Ceramic Society, 25, Ergul, S., Akyildiz, M. & Karamanov, A. (2007). Ceramic material from basaltic tuffs. Industrial Ceramics. 2, Gennaro, R., Cappelletti, P., Cerri, G., Gennaro, M., Dondi, M., Guarini, G., Langella, A.,& Naimo D. (2003). Influence of zeolites on the sintering and technological properties of porcelain stoneware tiles. Journal of the European Ceramic Society, 23, Hlavac, J. (1983). The Technology of Glass and Ceramics: an Introduction, Elsevier, Amsterdam. Karamanova, E., Avdeev G., Karamanov A., (2011). New Building Ceramics based on Blast Furnace Slag, Journal of the European Ceramic Society, 31, Kingery, W.D., Bowen, H. K. & Uhlmann, D.R. (1976). Introduction to Ceramics, John Willey & Sons, New York. Kurama, S., Kara, A. & Kurama, H. (2006). The effect of boron waste in phase and microstructural development of a terracotta body during firing. Journal of the European Ceramic Society, 26, Matteucci, F., Dondi, M. & Guarini G. (2002). Effect of soda-lime glass on sintering and technological properties of porcelain stoneware tiles. Ceramics International, 28, Martín-Márquez, J., De La Torre, A.G., Aranda, M.A.G., Rincón, J.M. & Romero, M. (2009). Evolution with temperature of crystalline and amorphous phases in porcelain stoneware. Journal of the American Ceramic Society, 92, Rawlings, R. D., Wu, J. P. & Boccaccini, A. R. (2006). Glass-ceramics: Their production from wastes-a review. Journal Materials Science, 41, Schabbach, L.M., Andreola F., Barbieri L., Lancellotti I., Karamanova E., Ranguelov B. & Karamanov A. (2012). Post-treated incinerator bottom ash as alternative raw material for ceramic manufacturing, Journal of the European Ceramic Society, 32, Sclar, C. B. & Kastelic, R. L. (1979). Iron in Anorthite: an Experimental Study. Lunar and planetary science, 10, Torres, P., Fernandes, H. R., Agathopoulos, S., Tulyaganov, D. U. & Ferreira, J. M. F. (2004). Incorporation of granite cutting sludge in industrial porcelain tile formulations. Journal of the European Ceramic Society, 24, Tucci, A., Esposito, L., Rastelli, E., Palmonari, C. & Rambaldi E. (2004). Use of soda-lime scrap-glass as a fluxing agent in a porcelain stoneware tile mix. Journal of the European Ceramic Society, 24,