A generic plasma-arc process for toxic waste destruction with co-generation of high value construction materials .

In the project research tasks various feed materials have been used. The fly ashes obtained from the Nofer Institute of Occupational Medicine in Lodz and the fly ashes and carbon filter deposits from the Belchatow power plant have been tested. The composition and quantity of the additives such as the sludge wastes from the chemical industrial plant producing sodium chromate (post-chromium sludge) and the sewage sludge from a municipal wastewater treatment plant from Lodz have been also determined. The tested ashes were consisted of inorganic compounds, mostly SiO2 and Al2O3. The medical ash was grey with dark-grey and black elements and it contained needles and glass pieces. The ash from Belchatow power plant was loose and powdery, but not homogenous and its colour was grey-brown. The ashes were separated into specific fractions. The post-chromium sludge, used in the project, contained mainly CaO, Fe2O3, MgO, SiO2 as well as chromium at various oxidation states (III and VI). The total chromium content in the sludge was 16,34 % of dry mass. This sludge was of a loose homogenous mixture of brown-grey-black colour. In the case of the municipal wastewater sludge simple three oxides (P2O5, CaO and MgO) were the main inorganic compounds. This sludge was exceptional because of the organic matter dominated in it. This sludge was a loose, heterogeneous mixture with pieces of organic matter of a grey-black colour. The sludge was also separated into specific fractions. All these feed materials were recognized as applicable for plasma processing. Even if all the tested feeds had different compositions they were still applicable for thermal plasma vitrification due to a large content of glass generating oxides. The vitrificates were chemically stable (leachability tests) and they had a homogenous structure and a high mechanical resistance.

The project originality was to identify of two independent waste stream types that can be treated with plasma simultaneously to receive non-toxic, friendly to environment and added value product. The waste streams were: - Inorganic materials i.e. waste materials composed almost entirely of inorganic substances, such as medical & industrial waste incineration residues: ash, filtration deposits and sediments. - Organic materials, i.e. hazardous fluid/solid chemical wastes: polychlorinated biphenyls (PCB`s), oil-solid mixed wastes (filters), pesticides, spend chemical reagents etc. The plasma treatment and computer simulation exercise has been demonstrated mainly for medical ash representing inorganic stream and PCBs containing transformer oil representing organic hazardous waste stream. The interesting conclusion of this research was that the main solid component - carbon converts into silicon carbide SiC above certain temperature. The SiC amount increases nearly linearly with the increase of the organic admixture. This increases the product hardness. The conversion temperature matches well the range of smelting process temperatures. In the range of temperature 1000 - 3000K the off gas is rich in hydrogen. Carbon monoxide together with hydrogen creates the most caloric off gas in the 2100-2400K temperature range. The total amount of this off gas depends on the quantity of PCB-oil in the hospital ash. To get the melt of the same viscosity value higher operating temperature is needed for moist ash compared to the dry one. The higher the amount of oil added the lower the operating temperature required for smelting. Generally in the pyrolysis conditions the more oil added the more energy is required. The development of plasma technology for inorganic wastes is well established and in widespread commercial use but for organic wastes it is an emerging technology with enormous potential application.

In order to determine the degree of feed decomposition/transformation in different processing conditions, and to get information about the formation of hazardous compounds during cooling of hot plasma gases, thermodynamic and thermo chemical calculations have been performed by computer codes ASTRA 4.0 and FactSage, respectively. Equilibrium compositions were determined for the thermal plasma treatment of following models in the temperature range of 293-6000K: Inorganic wastes (WASTASH): - Steel-making dust containing iron-oxide, zinc-oxide, lead?oxide and silicon-dioxide as main components; - Red mud from bauxite processing, which contains iron-oxide, aluminum-oxide, silicon-dioxide and sodium-oxide as main components. Organic wastes (HAZCHEM): - Aliphatic and aromatic hydrocarbons (n-hexane, toluene); - Chlorinated aliphatic hydrocarbons (chlorinated and fluorinated ethane derivatives); - Polychlorinated aromatic hydrocarbons as models of pesticides (hexachloro-benzene); - Amino-aromatic compounds as models of waste transformer oils (aniline). It has been proved that all models as above can be decomposed and transformed to non-hazardous solid, liquid and gaseous products during thermal plasma treatment. Based on results particular calculations, the actual decomposition conditions to be tested in the experiments have been fixed. Special attention was devoted to excluding formation of hazardous by-products on cooling of plasma gases.

Development and demonstration of foam glass process: - Porous tiles ; - Porous granules. The fundamentals of the technology, of thermo insulating foam glass production, which utilizes vitrified ash formed in the process of toxic waste in plasma arc destruction, have been elaborated. The foam glass obtained is highly porous material of closed pores (porosity 92%) it does not absorb water (absorbility below 5%), it is inflammable, and does not emit toxic fumes, light (app. density 180 - 225 kg/m³), strength (compression str. about 2.4MPa) posses thermoinsolation 0.06W/mK, and high chemical and biological durability. Thus it represents a highly valuable material for various applications mainly in building industry and engineering. So far foam glass has been produced from one kind of raw material, mainly container glass cullet. Addition of other raw materials differing from glass in their chemical composition and properties have not been used. It refers particularly to toxic ash plasma vitrified, which, unlike the glass, contains small amounts of silica and sodium but great amounts of calcium, aluminium and iron, it crystallize easy and melts with difficulty. The result of the project is the development of the thermo insulating foam glass technology by elaborating the fundamentals of the thermal foaming of mixtures of various glassy wastes. It has been established that it is possible to obtain foam glass from a mixture containing 30 wt.% of plasma vitrified ash and waste container or flat glass cullet of low quality, not suitable for the production of glass. It allows processing the glassy waste incineration products, including plasma process vitrified toxic ashes, into valuable product. The result of the project is also the development of the technology principles of porous thermo insulating tiles production from mixtures composed of vitrified waste incineration ash and waste glass cullet, adjusted to the specific properties of components of the mixture, i.e. the softening and foaming temperatures, which are higher than those for traditional raw materials and very narrow interval of foaming temperatures. This technology enables partial recrystallization of the product, which results in the improvement of its mechanical properties. The foam glass tiles obtained under laboratory condition by foaming in steel moulds demonstrates properties described above. The tiles can be coated with paint, coloured plasters used in building industry as well as vitreous enamel. As a material not absorbing water, chemically and bacteriologically resistant, it can be used for thermal insulation of the foundation of buildings on waterlogged areas, for the foundation of motorways, for insulation of pipelines. It is flowing on the surface of water and can be used to collect the petrol contaminations. As an inflammable, heat resistant to the temperature 5000 C it can be used for fire barrier in public buildings, as well as for lining of factory chimneys, through which chemically aggressive substances are emitted including those used in energetic for desulfurization of the combustion gases. Another result of the project is the elaboration of the fundamentals of the technology of production of porous material in the form of granules of various dimensions. The granules can be used as aggregate for light weight concrete in the building industry, for renovation of the old historical buildings, for the grounds of motorways and others. Elaborated technologies are waste consuming, giving valuable products and they can improve the economy of process of waste incineration.

A detailed conceptual design of a plasma-based commercial waste treatment plant has been completed, including piping and instrumentation diagrams, process flow diagrams, thermal and thermodynamic calculations and detailed equipment description. This plant is designed to process a mixture of organic and inorganic waste materials and produce a stable solid by-product and a synthetic gas (syn gas) with a retained heating value. The design is based on an organic content in the waste of between 0 and 20% and with water at up to 20% in order to give a plant with a range of operating regimes. The composition of the solid by-product can be adjusted by the careful mixing of waste materials in the appropriate ratios to give a material suitable for granulation and crushing as a ceramic raw material. The syn gas can be used for heat recovery in the form of hot water and/or steam or for the generation of electrical power. Economic evaluations have been made of the concept design at throughputs of between 500 and 2500kg/h, including assessments of capital and operating costs and the credits available from the sale or use of solid by-products. This has given a cost of treatment, including capital charges, of between 350 Euros/tonne of waste and 150/tonne of waste including credits from the sale of the slag, depending on the plant size. Economic analysis suggests that at lower throughputs the capital and labour costs dominate, but this is reversed at higher plant throughputs. It also suggests that the capital cost of the plants vary in proportion to the throughput raised to the power of 0.35, which is consistent with other chemical engineering processing plants, of similar complexity and throughput. These aspects of the result provide a ready reference for potential investors in the technology, with detailed information on plant design, plant descriptions, process economics and the dependence of all these things with changing plant throughput. The waste treatment cost figures suggest that plasma treatment will be competitive with alternative disposal methods, especially when comparisons are made at similar throughputs.

Various feed materials were analysed: medical ash, ash from the Belchatow power plant, post-chromium sludge and the municipal wastewater sludge. From these materials plasma treated vitrificates have been made. The investigated materials were characterised and tested for moisture content, pH and mass decrement. Leaching tests were also made for feed materials and vitrificates. The obtained results were compared with the EU Directive pr EN 12457-3, which includes specific standard requirements for hazardous wastes. The analysis of the moisture content of materials showed the largest level of water adsorbed in the municipal wastewater sludge (78,04%). The Belchatow power plant ash contained only 7,90% of water. The pH of the Belchatow power plant ash and the post-chromium sludge was around 10. Only pH of the municipal waste water sludge was acidic. The feed materials were also tested for mass decrement. The medical ash had the highest mass decrement (9,3%) and the municipal wastewater sludge had the lowest decrement. Leachability tests were also made for feed materials. The results of the leachability tests showed that the medical ash is the most dangerous because the leachibility of heavy metal (Crtotal, Zn, Cd) exceeded the required concentrations. All the feed materials were vitrified. The vitrificates were analysed and put to the tests on leachability. According to the requirements of the European Standards the vitrificates can be recognised as inert wastes for the transient period (16 July 2002 to 16 July 2005). Almost all the heavy metal concentrations had not exceed the required concentrations for those metals except Pb where the required concentration after the transient (regulations) period would be 0,3mg/kg. Only the vitrificates from medical ash can be recognised as inert wastes after the transient period - the leaching tests showed that those types of vitrificates are safe. Leachability of metals was also checked for final products i.e. foam glass (from UMM) and tiles (from GLASS). The leachability of metals from these products was within standard requirements with the only exception of tiles that had been coloured red. There the content of Cd was above standard requirement (0,148 [mg/kg] compared to standard value 0,03[mg/kg]).

Development and demonstration of tiles process consists in: - Nucleation and crystallisation of original glass; - Processing of tiles; - Coloration of tiles. Nucleation and crystallisation of original glass: As is nowadays useful for the production of glass-ceramics, the determination of nucleation rate of crystals at different temperatures (700- 750ºC) and several heating rates from the vitreous slag coming from the arc- plasma processing of wastes has been carried out by DTA analysis. This has given convex curves from where determination of maximum nucleation is possible. To ascertain the predominant crystallization mechanism for such type of original glass from plasma, the DTA experiments were made in bulk monolite and fine powdered samples (< 35µm), calculating the activation energy for crystallization. Static (quenched) TTT curves have been also determined from the pressed powder of original glass due to the dominant surface crystallization mechanism here discovered for this type of glass. After thermal treatments in the 800-1000ºC range, the crystalline phases have been identified in the final products, viz: Gehlenite, akermanite and wollastonite, being at higher temperatures only the wollastonite (CaSiO3) the dominant phase. Microstructure analysis carried out by SEM/ EDX show compacted crystallization of wollastonite fibres embedded in the residual glassy matrix. The information given by this result is of high relevance for the definition of the processing of glasses coming from plasma and possible recycling into the production of wastiles. Processing of tiles: After crushing and sieving of the vitreous slag coming from the arc-plasma processing, axial pressing operations have been carried out followed by thermal cycling. Several small prototypes of wastiles (50x 0x5mm) have been obtained in the laboratory scale from different wastes. Optimisation of compositional design is a very critical step for overcoming the composition heterogeneities of original glasses. Optimum tiles depict a full sintered and vitrified texture with brown colour and glassy brilliant surface. A wide range of aspects was obtained between 800- 1000ºC and very short times of heating. Physical, mechanical and leaching analysis gives values in the range (or improved) of conventional commercial tiles. After testing of processing of tiles in the laboratory scale heating in electric furnaces at normal atmosphere, the processing was repeated on industrial scale roller furnace (reducing atmosphere) with the obtaining of 120x150x7mm tiles brown colour. The mechanical properties were in the range of: Microhardnes: 5.0-5. 6GPa; Modulus of Elasticity = 90 -138GPa and toughness = 1.0 -2.0 Mpam1/2. The flexural strength for this type of tiles are in the range of s F: 70- 80MPa. Coloration of tiles: In order to wide the commercial capabilities of wastiles as construction materials for coverings or pavements of buildings and/or even civil engineering applications, have been obtained several shapes and colours of wastiles from the plasma processing by using commercial ceramic pigments applied to the same processing. That is: a) Bulk coloured wastiles; b) Surface coloured glazed tiles and c) Mosaic coloured glass-ceramics. In the case of a) tiles, colours with graduated tonalities were obtained: green, brown and dark-yellow. Large size coloured tiles of 120x150x7mm were obtained at industrial scale roller furnace. From the b) tiles glazed: blue, green, brown, pearl, grey and purple, even developing a specific glass- ceramic glaze for this application. From c) tiles (shaped in small triangles of 30x30x30mm and thickness of 3mm) colours: granate, orange, dark-yellow, green, dark-blue and violet. A proposal of design has been presented as several combinations of these tiles for external/internal wall coverings producing a wide range of decoration possibilities which should be developed more specific applications in construction via a demonstration project running after this project. Leaching properties have been determined accomplishing these products the EPA standards.

A composition of slag has been selected which meets the following criteria. - High fluidity at plasma treatment temperatures for good mixing and pouring - Ability to synthesise almost entirely from a mixture of readily available waste materials - Correct nucleation and crystallisation behaviour in the vitrified form for ceramic product manufacture. The establishing of this composition will provide the raw materials for a novel class of ceramic materials to be manufactured from readily available waste products, having superior properties and firing characteristics than equivalent conventional materials. This has the potential to improve the economic viability of a range of waste processing techniques, especially plasma treatment, and to increase the recycling and reuse of waste materials in a safe and beneficial way, leading to greater sustainability in the field of ceramic materials production. The chosen slag chemistry has been optimised as far as possible within the programme but further refinements to aid the three criteria above are both possible and desirable to achieve the full potential of the waste treatment and ceramic manufacture. Future European research activities are being actively considered for this purpose in collaboration with leading in ceramics production and plasma techniques.

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