In this study chemical leaching with sulphuric acid has been performed on 10 selected oxidic by-products in order to determine their neutralising capacity. The ultimate aim with this work is to replace the lime or limestone normally used in bioleaching operations to maintain pH at 1.5, the optimum pH-level for bioleaching microorganisms, with oxidic by-products. The investigated by-products includes three ashes from combustion for energy production, five slag samples from ore and scrap based steelmaking, an EAF dust and mesa lime from a paper and pulp industry, slaked lime (Ca(OH)2) was used as reference material. The neutralising potential of the by-products were evaluated by leaching them with sulphuric acid and comparing the amount of acid needed to that of the reference. Most of the by-products examined had good neutralisation potential and some had even higher capacities than Ca(OH)2. Neutralisation kinetics were lower for some slag products due to slow dissolution of some of the silicates present, but kinetics are considered good enough since stirred tank bioleaching is a relatively slow process. Zinc recoveries from the zinc containing materials were high, which thus is an additional benefit if these materials were to be used for neutralisation in a bioleaching process for zinc recovery.

In acidic biological and chemical leaching processes for base metal recovery, iron is dissolved in addition to the desired metal values. Prior to valuable metal extraction iron has to be removed. This is usually achieved through hydroxide precipitation of ferric iron by the addition of lime or limestone to a pH of approximately 3 whereby ferric hydroxide is formed. The aim of this work has been to investigate the possibility to substitute lime or limestone with oxidic industrial by-products for neutralisation and precipitation of iron from leaching solutions. The neutralisation potential for 10 selected oxidic by-products like slags, ashes and dusts were examined and compared with slaked lime.Experiments were performed by decreasing pH to 3 by additions of H2SO4 to slurry of respective by-product at an S/L ratio of 1/10 at 25 °C and continued till no changes in pH were observed during 10 days. Original samples, residues and solutions were analysed by ICP-MS and XRD in order to identify potential harmful elements for the subsequent metal recovery steps.Characterisation of the by-products revealed high concentrations of oxides such as lime, calcite and metal oxides as well as different forms of silicates in the materials which all dissolved at pH 3. The neutralising potential was found to be high for most of the by-products investigated and in the case of Ladle slag it was even higher than for slaked lime. Slags generally had higher neutralisation potential and long-term effects while the ashes had high initial reactivity which is important for continuous neutralisation in stirred tanks with limited retention times. The most reactive materials were Bioash and Mesa lime which both contained considerable amounts of calcite. Replacement of the conventional lime and limestone with oxidic by-products for neutralisation of acidic leaching solutions has the potential to save costs, environmental resources, reduce CO2 emissions and to recycle metal values like zinc contained in the by-products.

Four types of steel slags, a ladle slag, a BOF (basic oxygen furnace) slag and two different EAF (electric arc furnace) slags, were characterized and modified by semi-rapid cooling in crucibles and rapid cooling by water granulation. The aim of this work was to investigate the effect of different cooling conditions on the properties of glassy slags with respect to their leaching and volume stability. Optical microscopy, X-ray diffraction, scanning electron microscope and a standard test leaching (prEN 12457-2/3) have been used for the investigation. The results show that the disintegrated ladle slag was made volume stable by water granulation, which consisted of 98% glass. However EAF slag 1, EAF slag 2 and the BOF slag formed 17%, 1% and 1% glass, respectively. The leaching test showed that the glass-containing matrix did not prevent leaching of minor elements from the modified slags. The solubility of chromium, molybdenum and vanadium varied in the different modifications, probably due to their presence in different minerals and their different distributions.

Based on modified Bogue calculations, steelmaking slags were combined in order to produce a belite-rich clinker activated with sulphoaluminate. The experiments were conducted on two different mixtures based on steelmaking slags together with additives, namely MixA and MixB. The objective of the present study was to investigate the hydraulic properties of the specimens, using conduction calorimetry, X-ray diffraction and differential scanning calorimetry, and also to measure the mechanical strength of the specimens when hydrated for 2 and 28 days. The compressive strength was satisfactory in relation to the estimated compositions. Both mixtures behaved the same with regard to heat development as well as the amount of ettringite formed during the first 24 h of the hydration.

Currently, about 75% of end-of-life vehicle's (ELV) total weight is recycled in EU countries. The remaining 25%, which is called auto shredder residues (ASR) or auto fluff, is disposed of as landfill because of its complexity. It is a major challenge to reduce this percentage of obsolete cars. The European draft directive states that by the year 2006, only 15% of the vehicle's weight can be disposed of at landfill sites and by 2015, this will be reduced to 5%. The draft directive states that a further 10% can be incinerated. The quantities of shredder fluff are likely to increase in the coming years. This is because of the growing number of cars being scrapped, coupled with the increase in the amount of plastics used in cars. In Sweden, some current projects are focusing on recycling of ASR material. In this paper some different alternatives for using this material are reported. The hypothetical injection of ASR into a blast furnace concentrating on ASR's effect to some blast furnace (BF) parameters has been completed using a blast furnace mass balance model. As a result, in principle, ASR can be used as reducing agent in the BF process if certain conditions are met. The particle size of ASR material must be controlled to ensure optimal gasification of the material in the raceway. Regarding the chemical composition of ASR, the non-ferrous content can affect the pig iron quality, which is difficult to rectify at a later point. The most attractive recycling alternative is to use the products obtained from pyrolysis of ASR in appropriate metallurgical processes.

In the present study, slags from the steelmaking industry are described and considered as a potential raw material within the field of sulphoaluminate belite cement. The objective of the study was to investigate the possibility of using a substantial amount of steelmaking slags as raw meal in the manufacture of a sulphobelitic clinker. A further aim was to compare the influence of different slags in relation to the formation of sulphoaluminate and the other clinker phases required. The behaviour of high temperature reactions was investigated by using thermogravimetric analysis coupled with a quadrupole mass spectrometer. Mineralogical observations were carried out through X-ray powder diffraction, and scanning electron microscopy. Three different mixtures and a single ladle slag were prepared using modified Bogue calculations, which are characterised by the assessment of a potential phase composition in order to produce belite-rich cement activated with sulphoaluminate. The results so far prove that steelmaking slags have the potential to be used as raw material, since sulphoaluminate along with polymorphs of dicalcium silicate and ferrite phases were detected after firing at 1200 degrees C in an air atmosphere.

The agglomeration of iron ores or fine-grained recycled high-grade iron materials is an essential part of the integrated iron and steelmaking process. The 15 European countries produce more than 100 Mt of sinter per year. However, environmental regulation is becoming more stringent, and therefore, sintering plants are under pressure to minimize their generated emissions, because they are the most polluting processes. Different possibilities have been suggested to solve this problem, e.g. using imported pellets or briquettes in blast furnace or to use EAF process. Such changes are very expensive and also delete the recycling route of the by-products, thereby creating an additional treatment or disposal problem. In this paper, different methods for minimizing emissions generated from sinter strands are reviewed.

To apply a decision-making scheme using a statistical classification while conforming to the meaning of representativeness as defined by the US EPA, we propose an equation defining the representativeness of a sample. To utilize this equation, the batch must be homogenized. This requires analyzing the constitution and distribution heterogeneities. The equation relates the sample weight ms to its representativeness R either by a statistical approach or by a physical approach using the following equation:ms={4/(1-R)2}·[K+ke(1-2te)/te] In the equation, K and ke are the heterogeneity factors determined from a descriptive analysis. This equation is applicable to solid waste with majority constituents such as automobile shredder residue (ASR) and domestic waste. This analysis was applied to a sample of ASR in the framework of a verification for France. The results of the analysis showed that the sample weight must be at least 140 kg to have a representativeness of 90%.