2nd International Slag Valorisation Symposium | Leuven | 18-20/04/2011 313 Additions of industrial residues for hot stage engineering of stainless steel slags (original) (raw)

Additions of industrial residues for hot stage engineering of stainless steel slags

The disintegration of stainless steel slags, due to the beta to gamma dicalcium silicate transformation, hinders the valorisation and increases the landfilling cost considerably. In this work, two industrial wastes, namely boron residues from the dressing of boron minerals and fly ash from lignite's combustion, have been used as additives in order to produce physically stable stainless steel slags. Results indicate that 1 wt% of boron residue is sufficient, however, 22 wt% of fly ash is required for a synthetic slag of basicity (CaO/SiO 2) = 2. The practical implications in terms of valorisation of the produced slags are also discussed.

Construction Materials from Stainless Steel Slags: Technical Aspects, Environmental Benefits, and Economic Opportunities

Journal of Industrial Ecology, 2015

State-of-the-art technologies that implement the 'Industrial Ecology' concept only make it to the market if environmental gains and economic benefits are significant. Therefore, the paper investigates, in an interdisciplinary way, two innovative technologies that valorize Stainless Steel (SS) slags as block masonry (bricks): carbonation and thermo-alkali-activation. The technical, environmental and economic features of three SS bricks-solid bricks, perforated bricks and lightweight aerated blocksare compared to commercially available construction materials. Although the produced bricks meet industrial standards, technical challenges such as optimization of alkali addition and use of metal molds should be dealt with before upscaling to industrial production. A cradle-to-gate Life Cycle Analysis (LCA) that aggregates the results of the various impact categories shows that the environmental impact of solid and perforated SS bricks is lower than the impact of conventional clay-baked bricks thanks to the avoidance of additives for slag stabilization and energy consumption for sintering clay. The impact of aerated SS bricks was found to be similar to the commercially available aerated blocks. More specifically, the CO2 uptake from carbonation reduces the overall environmental impact whereas use of alkalis increases the impact. A SWOT analysis highlights the economic advantages of SS bricks originating from lower energy requirements, reduced dependence on primary resources and improved metal recovery from slag. However, in order to apply the innovative technologies at industrial scale, challenges related to processing conditions, feedstock variability and potential competition from existing brick suppliers have to be overcome. used as aggregates, mostly in road construction, kept in temporary storage or landfilled (Nielsen 2008). However, use as road aggregate is a low-value application for the slag. Moreover, borate additions increase the risk of leaching (Shen and Forssberg 2003), posing a further environmental and legal challenge for the use of this slag (JRC 2010). Use of SS slag as construction material not only avoids slag disposal, but also, to some extent, limits the utilization of virgin resources for the production of construction materials. Construction materials from the current raw material sources and processes account for a large portion of the global anthropogenic carbon dioxide (CO2) generation. For example, the production of ordinary Portland cement (OPC) contributes to about 5-8% of the total global CO2 emissions (van Deventer et al. 2010; The World Business Council for Sustainable Development,www.wbcsd.org.). As a result, the "Cement and Technology Roadmap 2009" has laid a task for a 50% reduction by 2050 of global CO2 emissions from cement production (WBCSD 2009). Also, yearly emissions of the ceramic industry are estimated at 400 Mtons of CO2 (IEA 2013). Considering this, the production of construction materials from alternative sources like SS slag is an ambitious and promising option. Recent technical research has developed construction materials in the form of masonry bricks from fine AOD and CtCs SS slag by applying two innovative processes (Salman et al 2014): 1) thermo-alkali-activationa process where the latent hydraulic (binding) property of the slag is activated by use of alkalis and high temperature and 2) carbonationa process where CO2 is used to bind the slag particles together by the formation of stable carbonates. Fig. 1 illustrates that, in line with the 'Industrial Ecology' paradigm, both technologies unlock slag properties in order to substitute energy and primary material consuming production processes (Graedel and Allenby 1995; Lifset and Graedel 2002).

Valorisation of Stainless Steel Slags as a Hydraulic Binder

Acta Metallurgica Slovaca, 2013

This work is focused on exploring various cold and hot stage treatment paths of stainless steel slag as a tool to improve its hydraulic properties. At a cold stage, mechanical and chemical activation was applied on industrial stainless steel slag; and it was found that both activation methods effectively improve the reactivity of the studied slag. In addition, the detailed investigation of hydration on two major phases, γ -C 2 S and merwinite, revealed that their hydration resulted in the formation of C -S -H gel, typically formed during the hydration of OPC. Regarding the hot stage treatment, the combination of the chemistry modification with the addition of fly ash at 30 wt. % and fast cooling by means of water quenching resulted in a complete amorphisation of the material. Ultimately, the produced material possessing similar properties to granulated blast furnace slag could be used as a latent hydraulic material in blended cements.

Treatments and Recycling of Metallurgical Slags

Recovery and Utilization of Metallurgical Solid Waste [Working Title], 2018

Steelmaking plants continuously strive to reduce the environmental load in the steelmaking process, resulting in the recycling of energy, water, and other byproducts. In this chapter, techniques for the treatment and recycling of metallurgical slags are described. Metallurgical slags are considered secondary raw materials and are used or added during the process to improve steelmaking practice. Steelmaking slag added into ladle slags makes it possible to minimize slag line wear. BOF-converter slags are also applied in buildup, foaming, or slag splashing practices carried out to prolong the lifespan of refractory lining. Also, EAF slags are commonly used to avoid refractory wear and decrease energy consumption. It is known that cement concrete is one of the most common building materials. Blast furnace crystallized slags are used in cement production, in different percentages. In this sense, understanding the properties of slags is a prerequisite to apply them in different functions. This chapter deals with the measurement and modeling of thermochemical properties of slags, thermophysical properties, and interproperty correlations. Different experimental tests applied in slag characterization are also detailed.

Overview of Steel Slag Application and Utilization

MATEC Web of Conferences, 2016

Significant quantities of steel slag are generated as waste material or byproduct every day from steel industries. Slag is produced from different types of furnaces with different operating conditions. Slag contains Ferrous Oxide, Calcium Oxide, Silica etc. Physical and chemical properties of slag are affected by different methods of slag solidification such as air cooled, steam, and injection of additives. Several material characterization methods, such as X-ray Diffraction (XRD), Scanned Electron Microscopy (SEM) and Inductive Coupled Plasma (ICP-OES) are used to determine elemental composition in the steel slag. Therefore, slags can become one of the promising materials in various applications such as in transportation industry, construction, cement production, waste water and water treatment. The various applications of steel slag indicate that it can be reused and utilized rather than being disposed to the landfill. This paper presents a review of its applications and utilization

Stabilization of Stainless Steel Slag via Air Granulation

Journal of Sustainable Metallurgy, 2019

In stainless steel production, slag from argon oxygen decarburization (AOD) converters is dumped on to the ground and then slowly cooled. The slag undergoes phase transformation from β-dicalcium silicate (β-C 2 S) to γ-dicalcium silicate (γ-C 2 S) at approximately 500 °C to 450 °C, resulting in slag volume expansion, disintegration, and dust generation. The dusty slag leads to challenges in material handling, metals recovery, and emissions control. Some operations use slag additives to stabilize slag, but this solution is expensive and can limit the end use of slag due to inclusion of toxic elements. Air granulation was hypothesized as a water-free method for stabilizing AOD slag via rapid quenching. Pilot-scale experiments at Sandvik Materials Technology (SMT) with silicon-reduced AOD slags confirmed that air granulation can produce products which are stable and dust free. Mineralogical analyses further indicated that these air-granulated stainless slags contained either no or low content of γ-C 2 S and are therefore stable.

Hot stage processing of metallurgical slags

Resources, Conservation and Recycling, 2008

Slags are an indispensable tool for the pyrometallurgical industry to extract and purify metals at competitive prices. Large volumes are produced annually, leading to important economical and ecological issues regarding their afterlife. To maximise the recycling potential, slag processing has become an integral part of the valorisation chain. However, processing is often directed solely towards the cooled slag. In this article, the authors present an overview of the scientific studies dedicated to the hot stage of slag processing, i.e. from the moment of slag/metal separation to complete cooling at the slag yard. Using in-depth case studies on C 2 S driven slag disintegration and chromium leaching, it is shown that the functional properties of the cooled slag can be significantly enhanced by small or large scale additions to the high temperature slag and/or variations in the cooling path, even without interfering with the metallurgical process. The technology to implement such hot stage processing steps in an industrial environment is currently available. No innovative technological solutions are required. Rather, advances in hot stage slag processing seem to rely primarily on further unravelling the relationships between process, structure and properties. This knowledge is required to identify the critical process parameters for quality control. Moreover, it could even allow to consciously alter slag compositions and cooling paths to tailor the slag to a certain application.

STUDY OF IRON AND STEEL SLAG AS A PRODUCT WITH RESPECT TO PHYSICAL-CHEMICAL PROPERTIES

International Journal of Advanced Engineering Technology, 2017

This paper review the generation of slag from an integrated steel plant; focusing on, slag generated in blast furnace during process of iron making and through EAF / BOF during process of steel making .The slag generated from BF and EAF/BOF are having different characteristic. The different type of slag having different chemical and physical properties, this depends on the chemical properties of input raw material charged in process of iron/steel making and this slag used in different process as raw material. Blast Furnace slag production ranges from about 220 to 370 kilograms per metric ton of pig iron produced; although lower grade ores may yield much higher slag fractions. Steel making process in electric arc furnaces generates up to 15 % of slag, which is, based on its properties, classified as non-hazardous waste. Disposal of such material requires large surfaces and it is rather unfavorable in economic terms.

Potential beneficial uses of steel slag wastes for civil engineering purposes

Resources, Conservation and Recycling, 1991

Large tonnages of slag wastes are produced in the iron and steel industry and space for dumping them has become a problem.-Any means of utilizing the slag would be welcome. Although blast furnace slags are known to be widely used in the manufacture of cement , the use of steel slags for civil engineering purposes has not been given much encouragement in the literature. This communication reports efforts to assist the Nigerian steel industry to ease the problem of waste disposal. An effort has been made to make their slag potentially useful in civil engineering with, hopefully, some revenue earned from the disposal of the now unwanted material.