Thermal behaviour of clay mixtures with bauxite residue for the production of heavy-clay ceramics

"Bauxite Residue", BR, is the main by-product of the alumina-producing Bayer cycle. Aiming at its utilisation in the production of heavy-clay ceramics, the thermal behaviour of clay body mixtures with BR was investigated. The process parameters examined were the calcite content in the clay body mixture and the firing temperature, in relation to different BR additions in the clay body mixture. The firing process was studied by means of DTA-TG and dilatometry whereas the mineralogy was determined by XRD. The DTA-TG curves did not reveal cross-reactions between body mixture and BR. However, in the mixtures with BR, sintering initiated at a lower temperature and the firing shrinkage was increased. Moreover, a second shrinkage zone was observed for high BR content and firing temperature above 950 degrees C, suggesting the development of a low viscosity liquid phase. The main mineralogical phases present in the BR modified mixtures after firing were quartz, hematite, clinopyroxenes, gehlenite and plagioclase. The formation of clinopyroxenes and gehlenite seems to be dependant on all process parameters examined, i.e. calcite content in the clay body mixture, BR addition and firing temperature. (c) 2006 Elsevier Ltd. All rights reserved.status: publishe

Analysis of potential field anomalies in Lavrion mining area, Greece

Mining activities in Lavrion began during the first millennium B.C, after the decline of ancient Athens and then restarted more deliberately during the nineteenth century. Aeromagnetic data from a 1967 survey of the mining area was recompiled, processed, and interpreted for the present study. The original flight lines were digitized and leveled, and the international geomagnetic reference field (IGRF) was removed. The data were inverted by means of a terracing technique that defines separate domains of uniform distribution of physical properties that cause the magnetic anomalies. The log power spectrum was computed; along with the results of terracing, it suggested the existence of two sources of the magnetic anomaly. The long-wavelength anomaly reflects a large, concealed body that is most probably a granitic intrusion, consistent with local geological evidence. The source of the short-wavelength anomaly is a strongly magnetized body attributed to the net effect of various thin, magnetite-bearing sulfide zones. The anomalies were then separated in the wavenumber domain. Magnetic susceptibility measurements were made in situ on the exposed parts of the local formations. Three-dimensional models whose effect simulates the observed anomalies were calculated. Results of the modeling show that the large magnetic body is buried at 0.68 km depth. The small, relatively shallow body is about 0.035 km thick and buried at 0.6 km depth. The bodies do not show any corresponding gravity anomaly on the regional Bouguer gravity anomaly map

Valorisation of different types of boron-containing wastes for the production of lightweight aggregates

Four boron-containing wastes (BW), named as Sieve (SBW), Dewatering (DBW), Thickener (TBW) and Mixture (MBW) waste, from Kirka Boron plant in west Turkey were investigated for the formation of artificial lightweight aggregates (LWA). The characterisation involved chemical, mineralogical and thermal analyses as well as testing of their bloating behaviour by means of heating microscopy. It was found that SBW and DBW present bloating behaviour whereas TBW and MBW do not. Following the above results two mixtures M1 and M2 were prepared with (in wt.%): 20 clay mixture, 40 SBW, 40 DBW and 20 clay mixture, 35 SBW, 35 DBW, 10 quartz sand, respectively. Two different firing modes were applied: (a) from room temperature till 760 °C and (b) abrupt heating at 760 °C. The obtained bulk density for M1 and M2 pellets is 1.2g/cm(3) and 0.9 g/cm(3), respectively. The analysis of microstructure with electron microscopy revealed a glassy phase matrix and an extended formation of both interconnected and isolated, closed pores. The results indicate that SBW and DBW boron-containing wastes combined with a clay mixture and quartz sand can be valorised for the manufacturing of lightweight aggregates.status: publishe

Synthesis, characterization and properties of calcium ferroaluminate belite cements produced with electric arc furnace steel slag as raw material

This study investigated the use of 10 (M1), 17 (M2) and 27 wt.% (M3) electric arc furnace steel slag (EAFS) as a raw material in the production of calcium ferroaluminate belite cement clinker, after firing at 1320 C. The thermal behavior of the raw meals was studied by TG/DSC and XRD whereas for the analysis of the clinkers, XRD/QXRD, SEM/EDS and EPMA were employed. The resulting clinker was co-grinded with 5 and 20 wt.% Flue Gas Desulfurization (FGD) gypsum and the properties were determined by a series of tests in accordance to EN standards. The evolution of hydration was investigated by SEM and the development of compressive strength. The results revealed that the formed phases in the clinkers were C2S, C4AF and C 4A3Ŝ. The main hydration products were ettringite, AFm and hydrogarnet. The leached CrVI was below 1 ppm in M3. Compressive strength in cements with 5 wt.% FGD gypsum was (in MPa): 18.3 for M1, 14.3 for M2 and 7.8 for M3 at 28 days, whereas for 20 wt.% FGD gypsum, the values were almost doubled.© 2013 Elsevier Ltd. All rights reserved.publisher: Elsevier articletitle: Synthesis, characterization and properties of calcium ferroaluminate belite cements produced with electric arc furnace steel slag as raw material journaltitle: Cement and Concrete Composites articlelink: http://dx.doi.org/10.1016/j.cemconcomp.2013.08.002 content_type: article copyright: Copyright © 2013 Elsevier Ltd. All rights reserved.status: publishe

Valorization of Electric Arc Furnace Steel Slag as raw material in the production of low energy FA- belite cement

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Utilization of EAF metallurgical slag in “green” belite cement

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Evolution of microstructure, mineralogy and properties during firing of clay-based ceramics with borates

The effect of sieve boron waste (SBW) and borate-containing Evansite® on the thermal behaviour, microstructure and properties of a clay-based body was investigated. SBW and Evansite® were introduced in quantities that correspond to 0.6 wt.% B2O3 addition in the dry body for both cases. Cylindrical samples were extruded and fired at three different peak temperatures 900, 950 and 1000 °C. The reference body, R, and the body with SBW, RB, demonstrate a comparable dilatometric behaviour whereas the densification for the body with Evansite®, RV, initiated 50 °C approximately lower and resulted in higher firing shrinkage. After firing at 900 °C, the physico-mechanical properties as well as the microstructure are comparable. Nonetheless, åkermanite is formed in RB, whereas hercynite and mullite, the latter at 1000 °C, are formed in RV. For firing at 1000 °C, the role of borates is intensified. Water absorption is reduced by 16.1% and 18.0%, whereas bending strength increased by 27.6% and 40.8%, for RB and RV respectively, compared to the reference formulation. This is attributed predominantly to the enhanced vitrification that took place in the boron-containing bodies.status: publishe

Valorisation of electric arc furnace steel slag as raw material for low energy belite cements

In this paper, the valorisation of electric arc furnace steel slag (EAFS) in the production of low energy belite cements is studied. Three types of clinkers were prepared with 0 wt.% (BC), 5 wt.% (BC5) and 10 wt.% (BC10) EAFS, respectively. The design of the raw mixes was based on the compositional indices lime saturation factor (LSF), alumina ratio (AR) and silica ratio (SR). The clinkering temperature was studied for the range 1280–1400°C; firing was performed at 1380°C based on the results regarding free lime and the evolution of microstructure. In order to activate the belite, clinkers were cooled fast by blown air and concurrent crushing. The results demonstrate that the microstructure of the produced clinkers is dominated by belite and alite crystals, with tricalcium aluminate and tetracalcium-alumino-ferrite present as micro-crystalline interstitial phases. The prepared cements presented low early strength development as expected for belite-rich compositions; however the 28-day results were 47.5 MPa, 46.6 MPa and 42.8 MPa for BC, BC5 and BC10, respectively. These values are comparable with OPC CEMI 32.5 N (32.5–52.5 MPa) according to EN 197-1. A fast setting behaviour was also observed, particularly in the case of BC10, whereas soundness did not exceed 1 mm.status: publishe

Use of boron wastes in the production of heavy clay ceramics

Colemanite, ulexite and tincal are the main boron ores found in Turkey and account to 63% of the world estimated reserves. The production route of boron products results in significant amounts of different types of Boron Wastes, BW. Their open field disposal raises substantial environmental concerns in fear of leaching and groundwater pollution. The heavy clay ceramic industry can potentially absorb substantial quantities of BW. In the present study, BW produced from Kirka borax plants in Turkey, with 12.6 wt.% B2O3 was introduced in 0 wt.%, 5 wt.% and 15 wt.% in a heavy clay body mixture. Four peak temperatures, 800 degrees C, 850 degrees C, 900 degrees C and 950 degrees C, were examined for the dry pressed samples. The thermal behaviour analyzed by dilatometry and TGA shows that major loss in weight starts about 600 degrees C and continues to 700 degrees C approximately. For 5 wt.% BW addition and firing at 900-950 degrees C, the sintered bodies present comparable or improved physical and mechanical properties with respect to the reference formulation. The microstructure was analyzed by SEM whereas the main crystalline phases were identified by XRD. Samples fired at 900 degrees C with 5 wt.% BW present comparable properties with the reference ones. At 950 degrees C, the obtained properties were improved. Deformation occurs for samples with 15 wt.% BW when fired at >900 degrees C.status: publishe

Use of scrap soda-lime-silica glass in traditional ceramics

Alternatives ways of recycling soda-lime-silica scrap glass (SLS) glass, apart from remelting can offer certain advantages and may be implemented when glass production is not suitable. For the ceramics industry, the incorporation of glass into the ceramic body may improve the quality of fired products and save energy Mixtures of SLS glass and ceramic raw materials used for the production of porcelain stoneware tiles and heavy-clay products were developed and examined. In the case of porcelain stoneware tiles, several modified mixes were prepared by replacing different amounts of the fluxing component, sodium,feldspathic sand For roofing tiles, SLS glass was added at a fixed percentage in the body mixes. The fired samples were characterised in terms of linear shrinkage, water absorption, flexural strength and reliability Microstructure and the main phase transformations in the fired samples were examined by x-ray diffraction and by scanning electron microscopy along with EDS microanalysis. The results, for the porcelain stoneware body mix, shou, that a substitution of the fluxing component in the range of 5-10 wt% is feasible The new formulations had lower water absorptions, adequate flexural strengths and a consistent increase in reliability due to improved homogeneity. For substitutions exceeding 10 plagioclase was crystallised, which inhibited the formation of mullite and did not favour densification. The results regarding the modified body mix for heavy clay products have shown that a glass additions up to 30 wt% are feasible. New crystalline phases were developed within and at the interface of the glass grains. The particle size distribution of the glass and the firing temperature both influenced the physical and mechanical characteristics whereas they had a minor effect on the mineralogy. The fired products demonstrated improved characteristics in terms of water absorption and bending strength.status: publishe