Microwave Vitrification of Model Heavy Metals Carriers From Wastewaters Treatment
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Microwave Vitrification of Model Heavy Metals Carriers From Wastewaters Treatment Milota Kovacova, Michal Lovas, Stefan Jakabsky, Maximina Romero 1 and Jesus Ma. Rincon1 Institute of Geotechnics, Slovak Academy of Sciences, Watsonova 45, 043 53 Kosice, Slovakia 1 Group/Lab of Vitreous and Ceramic Materials, Instituto E. Torroja de CC Construccion (IETcc, CSIC), Madrid, Spain
ABSTRACT The metallurgical industry of ferrous and non-ferrous metals produce huge amount of wastes. In Slovakia, the factory for nickel production was closed in 1993, but around 5.5 kt of wastes remain in a dump. This waste was used as a model sorbent of heavy metals (Cu, Cd, Co) from wastewater treatments. The TCLP (Toxicity Characteristic Leaching Procedure) test of precipitated heavy metals on waste materials has confirmed the necessity of waste stabilization. The microwave vitrification was applied because of a high content of iron in waste. After vitrification, the chemical durability and microhardness by indentation have been tested in the glassy and glassceramics obtained.
INTRODUCTION Microwaves are a form of electromagnetic radiation with frequencies in the range of 0.3 – 300 GHz. The frequency used for microwave heating are 915 and 300 MHz. Microwave heating is fundamentally different from the conventional heating, which rely on conduction and convection, as the microwaves rapidly penetrate and deposit energy directly within the material. The absorption of microwave energy depends on the dielectric properties of material. The temperature inside the material heated by microwave is higher than the surface temperature, resulting in an inverted temperature gradient as compared to conventional heating. Moreover, the unique internal heating phenomenon associated with microwave energy can lead to products that cannot be achieved using conventional method [1]. Microwave energy has wide use in waste technologies [2]. In waste stabilisation was applied mainly for radioactive waste [3], but also for stabilisation of asbestos material [4] and contaminated soil [5]. This paper is aimed to the application of microwave energy for vitrification of waste from industrial activity with high content of iron, which was used as a model sorbent of heavy metals from wastewater treatment. The mechanical properties and chemical durability of vitrified waste was studied.
EXPERIMENTAL DETAILS Table I shows the chemical composition of nickel leaching residue (NLR), glass and dolomite. Glass and dolomite were added to the mixture for obtaining glass with adequate properties, because the waste (NLR) does not contain enough glass-network forming and modifier agents. The theoretical composition of vitrified mixtures is described in table II. Heavy
metals (Cu, Cd, Co) were precipitated with nickel leaching residue in concentration 10 mg of ions per 1 g of waste. Table I. Chemical composition of the raw materials used in mixtures (wt%) NLR glass dolomite SiO2 15.21 72.4 0.59 Al2O3 4.72 1.7 0.34 Fe2O3 67.98 0.05 0.29 FeO 23.13 CaO 3.55 9.6 29.61 MgO 2.67 1.7 22.47
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