During gasification of refuse derived fuel (RDF) to produce syngas in a system in which a melt is also produced, the gasified organic fraction of the RDF is in contact with the molten inorganic fraction, i.e. a slag. Examples of such systems are plasma gasifiers, in which crude syngas is further cracked in a plasma converter. Depending on the degree of gas–slag interaction, their compositions may vary and influence the valorisation potential of both resources. To evaluate the influence of this interaction, a pseudo-kinetic model was developed based on local thermodynamic equilibrium between the gas phase and part of the slag phase. The interaction level was accounted for by varying the amount of the slag that equilibrates with the gas. The valorisation potential of the resulting gas and slag phases was evaluated in terms of the heat of combustion and the mineralogy after cooling, respectively. Engineering of the slag composition was made through lime-rich addition. The influence of waste composition on the gas/slag properties and the production of a metal phase was investigated.

In this study, the copper bearing particle of a fayalitic copper slag was assessed using quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN) and X-ray computed tomography (CT). The copper content of the slag was, similar to 0.87 wt-%. Copper in this slag was present as sulphidic droplets. The content and particle size distribution of the major sulphide phases (bornite, chalcopyrite and chalcocite/digenite) were quantified using QEMSCAN. The copper bearing particles had a wide particle size distribution from a few micrometres up to millimetre level. Large copper bearing particles (> 100 mu m) were composed mainly of bornite and chalcocite/digenite and tended to accumulate in the lower part of the slag layer. As characterised with CT, similar to 70% of the copper value was present in these large copper bearing particles.

Slags from non-ferrous metallurgy are Fe rich, with Si as a minor constituent, and with low levels of Al. Due to variations in the slag cooling practice, they can exist as semi-amorphous or as crystalline solids. Considering that both higher Al in the slag and a higher cooling rate during solidification would have an impact on the availability of Al and ultimately on the formation of linkages in the inorganic polymer, we study the microstructure and reactivity of a Fe and Al rich slag cooled in different ways. Results show that high cooling rates lead to a predominantly amorphous material. For lower cooling rates the content of amorphous phase varies from 52wt.% to 12wt.%. Spinel is the primary phase precipitating, whereas, for the lowest cooling rate investigated, pyroxenes form as well. Dissolution tests in a 10M NaOH solution for 96h reveal that approx. 54wt.% of Al and 33wt.% of Si of the total content become available for the highly amorphous slag. On the contrary, the dissolved Al and Si are below 5wt.% when slag pot cooling is applied. The above strongly influence the resulting inorganic polymers with the ones originating from the amorphous slag being superior in mechanical properties.

This chapter contains sections titled: Introduction Materials and Methods Results and Discussion Conclusions Acknowledgements

This work explores the possibility of transforming secondary steelmaking slags to a cementitious binder by: a) high cooling-rate solidification and b) mechanical activation via high energy milling in a bead mill. Industrially produced and synthetic slags with various basicities were used in the experiments. Hydraulic activity was evaluated by means of isothermal calorimetry, scanning electron microscopy (SEM), thermogravimetry (TGA) and quantitative X-ray diffraction analysis (QXRD). For the study of the cooling path, a melt spinning granulation device was employed in addition to water quenching experiments. Results demonstrate that the beta to gamma-2CaO.SiO2 transformation can be suppressed and that the end product is hydraulically active upon mixing with water. For the mechanically activated samples, 2h and 6h milling resulted in partial amorphisation and significant increase of hydraulic activity compared to the as-received slags. The work concludes with a proposed hydration behavior for the major slag phases.

TMS has forged cooperative agreements with several carefully selected organizations that actively work to benefit the materials science community. In this occasional series, JOM will provide an update on the activities of these organizations. This installment features the Center for Resource Recovery & Recycling (CR3), a research center established by Worcester Polytechnic Institute, Colorado School of Mines, and K.U. Leuven.

Options to Prevent Dicalcium Silicate-Driven Disintegration of Stainless Steel SlagsIn this paper, a short overview is given on the strategy for high dicalcium silicate stainless steel slags stabilisation along with some results from work done and currently being performed at the K.U. Leuven.

Ferroalloys are added during secondary steelmaking to impart special properties to the steel. Depending upon the ferroalloy quality this may lead to the formation of inclusions. The present knowledge lacks in the exact content of the individual elements and the nature of inclusions dispersed in the ferroalloys. In order to broaden the knowledge concerning ferroalloy quality, eight different ferroalloys (i.e. FeMo, FeNb, HCFeMn, LCFeMn, FeTi70, FeTi35, FeSi75 and FeP) were characterised for their impurity content. The samples were investigated for chemical analysis ( inductively coupled plasma atomic emission spectroscopy and Leco combustion technique) and microstructural analysis (SEM energy dispersive spectroscopy). These impurities are linked to the ferroalloy manufacturing route. The inclusions observed in the microstructure are in good agreement with the inclusions extracted by the dissolution technique. In the present manuscript, the possible influence of ferroalloy quality over steel cleanliness is evaluated in the context of the impurities extracted and observed in the ferroalloys.

The flue gas cleaning system of a MSW incinerator with a capacity of 350 kt/year was changed to improve the HCl elimination efficiency. Instead of the semi-wet operating spray reactor and subsequent baghouse, a two-step wet flue gas cleaning was added behind the baghouse. Elemental composition, X-ray powder diffraction patterns and TGA measurements showed that the resulting APC residue was totally different from the former residue. As a consequence, leaching characteristics of both residues also differed and another treatment was required prior to disposal. For the former residue, mainly leaching of Pb (>100 mg/l), necessitated treatment prior to landfilling. The lower alkalinity of the new residue resulted in a leachate pH of 9.7 and a Pb concentration of 0.8 mg/l. The leachate pH of the former residue was 12.4. The leaching of Pb and Zn increased above 100 mg/l when immobilising the new residue with cement. Better results were obtained when immobilising with micro silica. The high CaCl2 x 2H2O content of the new residue brought along clogging of the bag filter system. Adding 1.4% of CaO (or 1.9% of Ca(OH)2) to the residue already improved these inconveniences but again significantly changed the leaching behaviour of the residue.

This paper covers the Flemish legislative tools concerning the management of bottom ash, fly ash and APC residue from municipal waste incinerators, with respect to their contamination with heavy metals. The situation in Flanders is compared to the one in the Walloon region, The Netherlands, Germany and France. Waste management in the countries considered differs on the level of available management options, of leaching tests and of limit values. To make an indicative comparison of leaching tests and limit values in the different countries, leaching tests were carried out on bottom ash and fly ash, and the results are compared to the relevant limit values for recycling and landfilling of the different countries. The comparison of legislations as well as the leaching results show that discrepancies in waste management between the different regions and countries exist. Recently, European limit values for landfilling became available. European legislation on recycling, however, has not been developed and urgently needs to be considered and drafted as the market for recycling can be expanding rapidly.

Cement as agent for immobilising Pb from air pollution control residues is compared with the use of different silica-containing materials. The DIN 38414-S4 leaching test was used to control Pb leachability and to compare obtained Pb leachate concentrations with the landfill limit of 2 mg/l for Pb. Firstly, one scrubber residues was treated with cement and micro-silica. With cement, the Pb leachability could be reduced with a factor ranging from 3 to 50 depending on the type and amount of cement used and depending on the curing time. The landfill limit of 2 mg/l was, however, never attained. From all tested silica-containing additives, aerosil could reduce the initial Pb leaching (101.3mg/l) to below the detection limit at a dosage of 0.13 g aerosil/g residue. Second best and an economically preferable silica-containing additive was micro-silica: a reduction from 101.3 to 0.7 mg/l was observed at a dosage of 0.4 g micro-silica/g residue. The formation of Ca-silicates was found to be responsible for the decreased Pb leachability. To generalise the findings, the Pb leachability of five cement-treated and five micro-silica-treated air pollution control residues were compared. For three scrubber residues, 2-20 times lower Pb leachate concentrations were measured for micro-silica-treated samples (cured for 5 weeks) than cement-treated samples. For a fly ash and a boiler ash the difference was, respectively, 48 and 17 times. pH-dependent leaching tests showed that at pH=2.5, Pb leaching is 250 times lower for the micro-silica-treated residue than for the cement-treated residue and almost seven times lower at pH 12.4.

The immobilization of MSWI-scrubber residues with soluble PO43− was studied and compared to the immobilization using cement. The DIN 38414-S4 leaching protocol and pH dependent leaching were used to evaluate the leaching of Pb and Zn. Four different scrubber residues from MSW combustion (Pb concentration: 2.8–4.8 mg/g; Zn concentration: 3.0–12.3 mg/g) were mixed with water and cement or Na2HPO4 as source of soluble PO43− at dosages of at least 0, 0.1, 0.2, 0.3 and 0.4 g per g residue. With cement as well as with PO43− a reduction in Pb and Zn leaching was observed. With 0.4 g cement per g residue, the Pb leaching was reduced by a factor ranging from 70 to 100, but still exceeded the Pb landfill limit of 2 mg/l. With PO43− the Pb leaching was reduced with a factor of 100–300 to below 2 mg/l. The Zn landfill limit (10 mg/l) was only exceeded by one untreated residue. Adding 0.2 g cement or 0.1 g PO43− per g of that residue was enough to reduce leaching below 10 mg/l. However, when 0.6 g Na2HPO4 per g residue was added to a lime based scrubber residue, an increase in Zn leaching up to 12.5 mg/l was observed due to an increase in pH of up to 13.0. When using NaH2PO4 and H3PO4 no such increase in Zn leaching was observed. pH dependent leaching performed on one of the four residues showed that in the pH range of 2.5–6, Pb leaching was 100–50 times lower with Na2HPO4 treatment than with cement. In the pH range from 7–11, almost equal results were obtained for cement treated and Na2HPO4 treated residue. Above a pH of 12, Pb leaching was three times lower for the PO43−-treated residue than for the cement treated residue. With soluble PO43−, Pb leaching below 2 mg/l could be attained at a dosage of 0.27 g PO43−/g residue. With cement, Pb leaching was never below 2 mg/l.

The contribution of the emission of PCBs by a municipal waste incinerator in Wilrijk, a relatively industrialized district in the largest city of Flanders, to the total emission to air and to the total human intake was estimated. Therefore it was compared to the emission of PCBs by evaporation from PCB containing applications (transformers, capacitors, paint, ink, etc.) and to the intake of PCBs with food. As there was a lack of PCB data from the incinerator, the PCB emission concentration was estimated using three different approaches. A PCB measurement of the incinerator emission, performed later on, fell within the predicted range of 0.0004-0.005 ng TEQ/Nm3. Emission of PCBs from PCB containing applications and intake from food were deduced from information available on Flemish and European level. The results indicate a PCB contribution from the incinerator to local emissions between 0.3% and 3% of the emission from PCB containing applications and a contribution to human intake less than 6 x 10(-4)% of the intake from food.

: When using waste material in construction applications, the leaching of heavy metals can pose an environmental problem. In Flanders the construction material should comply with requirements regarding total concentration and leaching. The leachability of heavy metals from monolithical materials is determined using the Dutch diffusion test (NEN 7345) and the availability test (NEN 7341). In order to assess the long term release of heavy metals, so-called inert compounds like Na, K and Cl are used in the diffusion test to determine whether leaching from the monolith is diffusion-driven or not. A necessary assumption in this procedure is that these compounds are highly soluble. Results from several investigations indicate however that this assumption may not always hold for Na and K. Interpretation of leaching mechanisms based on leaching of these inert compounds may thus be difficult. INTRODUCTION MATERIAL AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

When a fly ash waste material from a copper refining process containing large amounts of As2O3 is solidified using cement and lime, the arsenic concentration in the leachate can be lowered to ca. 5 mg/l in a saturated solution of Ca(OH)2. It is shown that the decrease of the concentration in the leachate, mainly of As(III), is due to the formation of insoluble CaHAsO3 in the leachate in the presence of Ca(OH)2. This method is compared with a method whereby use is made of oxidation of the waste before solidification to oxidise As(III) to As(V) using H2O2. The arsenic concentration in the leachate of the extraction test of an oxidised S/S sample was lowered to ca. 0.5 mg/l, a factor of 10 below the one for a non-oxidised sample. It is shown that the decrease of the concentration in the leachate mainly of As(V) is due to the formation of insoluble Ca3(AsO4)2 in the presence of Ca(OH)2. Extensive use was made of the speciation program MINTEQA2, to clarify the immobilisation of arsenic.