Alexander Karamanov

Chemical durability of glasses obtained by vitrification of industrial wastes

The vitrification of zinc-hydrometallurgy wastes, electric arc furnace dust (EAFD), drainage mud, and granite mud was shown to immobilize the hazardous components in these wastes. Batch compositions were prepared by mixing the wastes with glass-cullet and sand to force the final glass composition into the glass forming region of the SiO2-Fe2O3-(CaO, MgO) system. The vitrification was carried out in the 1400-1450 degrees C temperature range followed by quenching in water or on stainless steel mold. The United States (US) Environmental Protection Agency (EPA) toxic characterization leaching procedure (TCLP) test was used as a standard method for evaluating the leachability of the elements in the glasses and glass-ceramics samples made with different percentages of wastes. The results for EAFD glasses highlighted that the chemical stability is influenced by the glass structure formed, which, in turn, depends on the Si/O ratio in the glass. The chemical durability of jarosite glasses and glass-ceramics was evaluated by 24 h contact in NaOH, HCl and Na2CO3, at 95 degrees C. Jarosite glass-ceramics containing pyroxene (J40) are more durable than the parent glass in HCl. Jarosite glass-ceramics containing magnetite type spinels (J50) have a durability similar to the parent glass and even lower in HCl because the magnetite is soluble in HCl.

Crystallization phenomena in iron-rich glasses

Abstract In this study, results of the crystallization of iron-rich glasses are summarized. Thermogravimetry (TG)–differential thermal analysis (DTA) were utilized to explain the phase formations and the surface oxidation of FeO to yield Fe2O3. The crystal phases fraction was evaluated utilizing X-ray diffraction analysis (XRD). Low angle XRD technique was used to investigate the distribution of the crystal phases on the surface and in the bulk as a function of the heat treatment. Transmission electron microscopy (TEM) was employed to detect the evolution of the crystalline structure and to determine the variation of the residual glass composition. The crystallization kinetics were investigated in isothermal conditions by measuring the variation of the density. The activation energy of crystal growth was calculated using isothermal and non-isothermal methodologies. The values of 377 and 298 kJ/mol were obtained for the temperature ranges 620–660°C and 720–780°C, respectively. Similar values, 368 and 321 kJ/mol, were estimated for the energy of viscous flow in the same temperature ranges. The results indicate that magnetite and pyroxene are the main crystal phases and that the kinetics of pyroxene formation can be explained as growth on a fixed number of magnetite nuclei. In powder samples, heat-treated in air, the crystallization is inhibited by the surface oxidation of Fe2+ to yield Fe3+ and a layer of haematite is formed on the surface.

Vitrification of electric arc furnace dusts.

Electric arc furnace baghouse dust (EAFD), a waste by-product of the steelmaking process, contains the elements that are volatilized from the charge during the melting (Cr, Pb, Zn, Cu and Cd). The results of leaching tests show that the concentration of these elements exceeds the regulatory limits. Consequently, EAFD cannot be disposed of in ordinary landfill sites without stabilization of the heavy metals. In this work, the vitrification of EAFD, from both carbon and stainless steel productions, were studied. The vitrification process was selected as the inertizing process because it permits the immobilization of the hazardous elements in the glass network and represents an environmentally acceptable method for the stabilization of this waste. Classes of various compositions were obtained by mixing EAFD with glass cullet and sand. The EAFD and the glass products were characterized by DTA, TG, X-ray analysis and by the TCLP test. The results show that the stability of the product is influenced by the glass structure, which mainly depends on the Si/O ratio. Secondary crystallization heat-treatment were carried out on some samples. The results highlighted the formation of spinel phases, which reduced the chemical durability in acid media. The possibility to recover Zn from carbon steel production EAFD was investigated and about 60-70% of metal recovery was obtained. The resulting glass show higher chemical stability than glasses obtained without metal recovery.

Evaluation of the degree of crystallisation in glass-ceramics by density measurements

A theoretical procedure has been developed with the aim of obtaining an accurate and rapid estimation of the degree of crystallisation in jarosite glasses by measuring the densities of the parent glass and, after the thermal treatment, of the glass-ceramic. Compositions were prepared by mixing jarosite waste with granite scraps and glass cullet, yielding three different glass-batchs, melted at 1450°C, quenched and thermal treated to obtain glass-ceramics with different degrees of crystallisation. Density measurements were carried out by means of a helium displacement pycnometer. The results were compared with the degree of crystallisation as evaluated by XRD and showed a good agreement. The method is applicable if the variation of density connected to the phase transformation is sufficiently large. In the formation of pyroxene and magnetite phases, with large density variation compared to the parent glass, it is precise and easily applicable.

The kinetics of surface induced sinter crystallization and the formation of glass-ceramic materials

A thorough analysis is given of a process which is of great importance for the formation of many present day glass ceramic materials: sinter-crystallization. In the first part of the paper the problems determining surface induced nucleation of glasses are analyzed, emphasis being given to the influence of elastic strains and surface contamination by active substrates. The second stage of the analysis is centred on the dependence of crystal growth and overall crystallization kinetics on the mean size of an ensemble of sintering glass grains. Here a formalism is derived, connecting overall crystallization with the mean size of the crystallizing system of glass particles. In the third part the interdependence sintering – crystallization is investigated. Several cases of this interrelation are analyzed in details for different mechanisms of growth of nuclei, athermally formed on the grain surface.

The effect of Cr2O3 as a nucleating agent in iron-rich glass-ceramics

In this work, the eAect of Cr2O3 as a nucleating agent, in iron rich glasses has been investigated by means of DTA, XRD and density measurements. By Cr2O3 addition, from 0. 4t o 1.0wt%, a lowering of the crystallisation peak temperature resulted in the DTA trace, the maximum eAect corresponding to 0.7wt%. By evaluating the degree of crystallisation of the glass at 0.7wt% Cr2O3, the highest eAciency in the nucleation process also corresponds. The optimum values for the nucleation and crystallisation time and temperature, determined for 0 . 7wt% Cr2O3 addition, have been 70min at 630C and 30 min at 800C. The crystalline phases formed at different thermal treatment temperatures of the parent glass have been investigated by XRD; the spinel is the only phase after the nucleation; pyroxene is the major phase after the crystallisation. The results of this study have highlighted that a small percentage of Cr2O3 strongly aAects the spinel formation thereby reducing the time and temperature of the thermal treatment and enhancing the degree of crystallisation of high iron content glasses. # 1999 Elsevier Science Limited. All rights reserved

The crystallisation kinetics of iron rich glass in different atmospheres

The crystallisation kinetics of powder and bulk iron-rich glass, based on zinc hydrometallurgy hazardous waste, were investigated in air and nitrogen atmospheres. The activation energy of crystal growth, EC, and the Avrami parameter, n, were estimated by means of diAerential thermal analysis. The kind and amount of crystal phases, formed during the thermal treatment and their relative ratio were evaluated by X-ray diAraction analysis. The kinetics results sustain that the pyroxene phase grows on a fixed number of magnetite nuclei. The activation energy of crystal growth on the surface and in the bulk are similar in air and nitrogen atmospheres. When the powder glass sample is heat-treated in air, surface oxidation of Fe 2+ into Fe 3+ inhibits crystallisation resulting in the decrease of the percentage of crystal phase and the change of the Avrami parameter value. # 2000 Elsevier Science Ltd. All rights reserved.

Kinetics of phase formation in jarosite glass-ceramic

The crystallisation behaviour of an iron-rich glass was studied by means of density measurements, Differential Thermal Analysis and X-ray DiAraction. The results highlighted that there is no typical nucleation process in which the number of nuclei is influenced by the thermal treatment and influence the crystallisation process. The kinetics of phase formation was investigated in isothermal and non-isothermal conditions; the Avrami parameter value, 1 . 5, is indicative of a three dimensional diAusion controlled growth of the pyroxene crystals on a fixed number of nuclei. The activation energy of crystal growth, obtained by the isothermal and non isothermal methods, resulted in being 377kJmol ˇ1 and 298kJ mol ˇ1 , respectively. Considering the diAerent temperature range, these values are in fair agreement and consistent with values reported by other authors. Using TEM-EDS analysis the high immiscibility of the initial glass was highlighted; the two liquid phases, one richer in Fe and the other in Si and Ca, promote the formation of magnetite and pyroxene during the thermal treatment, respectively. # 1999 Elsevier Science Limited. All rights reserved

Glass-ceramic frits from fly ash in terracotta production

Preliminary results of an investigation into the possible use of glass-ceramic frits from fly ash and glass cullet in terracotta (stoneware) tile manufacture are reported. Two new ceramics were studied and compared with a plant composition, containing 45 wt.% sodium feldspar. In the first ceramic batch 20% of the feldspar was substituted by frits and in the second the whole amount of feldspar was eliminated and replaced by 35% frits and 10% refractory waste. It was found that the addition of low viscous glass-ceramic frits decreased the sintering temperature by 50—100 °C. At the same time, due to formation of an additional crystal phase (i.e. pyroxene or anorthite) the new ceramics showed an improvement of 25—50% in bending strength.

Vitrification and Sinter-Crystallization of Iron-Rich Industrial Wastes

Results about the vitrification of several hazardous iron-rich industrial wastes (from productions of Zn and Cu metals, as well as EAFD and MSWA) and the usage of obtained glasses for synthesise of sintered glass-ceramics are summarises. It is shown that the appropriated method of sinter-crystallization mainly depends on the crystallization trend of used glasses. When the parent composition is characterised by formation of a moderate amount of crystal phase low temperature sintering with short crystallization step in the interval 800-900 °C can be used. In addition, attractive granite-like building glass-ceramic can be obtained by mixing fine and coarse glass frits and “free” sintering in refractory moulds at 1000-1050 °C. Contrary, when intensive phase formation carries out the crystallization inhibits the sintering resulting in specimens with scarce degree of densification. However, in some cases a secondary densification process occurs at temperatures near to the eutectic ones, leading to well sintered samples with higher crystallinity and improved mechanical properties. It is also highlighted that the preventing of Fe2+oxidation by using inert atmosphere during the heat-treatments leads to a decreasing of sintering temperature, finer crystalline structure and additional enhancement of the mechanical properties.