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Journal of Material Cycles and Waste Management https://doi.org/10.1007/s10163-018-0711-z

REVIEW

Review on the innovative uses of steel slag for waste minimization

Yogesh Nathuji Dhoble1 · Sirajuddin Ahmed1

Received: 11 May 2017 / Accepted: 1 February 2018 © Springer Japan KK, part of Springer Nature 2018

AbstractPiles of steel slag, a solid waste generated from the iron and steel industry, could be seen due to no utility found for the past century. Steel slag has now gained much attention because of its new applications. The properties of slag greatly influence its use and thus had got varied applications. The chemical composition of steel slag varies as the mineral composition of raw material such as iron ore and limestone varies. This paper reviews the characteristics of steel slag and its usage. The paper reviews recent developments in well-known applications to the steel slag such as aggregate in bituminous mixes, cement ingredient, concrete aggregate, antiskid aggregate, and rail road ballast. This paper also reviews novel uses such as mechanomutable asphalt binders, building material, green artificial reefs, thermal insulator, catalyst and ceramic Ingredient. The review is also done on utilization of solid waste for waste management by the novel methods like landfill daily cover material, sand capping, carbon sequestration, water treatment and solid waste management. Review also shows recovery of pure calcium carbonate and heavy metals from slag, providing opportunity for revenue generation. Steel slag once traded as free to use by steel industries is now sold in the market at some price. Its utilization is of great economic significance as it also contributes to the reduction of solid waste.

Keywords Steel slag · Use · Properties · Patents

Introduction

Steel slag is a mixture of metal oxides and silicon dioxide and may contain metal sulphide along with metal in the ele-mental form. Steel slag output is approximately 20% by mass of the crude steel output [1]. It is found that over 2000 years ago during the times of Roman Empire, slag was used in building roads. Around 1589, cannon ball casts were made from iron slag and iron slag stones were found being uti-lized in masonry work in Europe [2]. Increase in production capacity of steel production also increases the production of the steel slag. Global slag production was 250 Mt from the 1.6 bn tonnes of steel production in 2014 [3]. Asia alone contributes to 60% of steel slag production. It is estimated that steel slag produced by VISL, DSP and BSP plants in India produces 8 Mt of steel slag and the price of granulated

slag at the cement factory was in the range of INR 450–856 for the financial year 2014–2015. India exports its slag to countries like China, Philippines and Bhutan. India also imports the slag from Germany, Sri Lanka and Lithuania [4].

On an average, US and developed countries use 70–80% of the steel slag, Australia utilizes 60–70%, whereas India utilizes less than 20% of its slag generated [5].

Analysis of publications reveals that China is most actively working in this research area and next is Japan.

Figure 1 shows that research picked up in the area of steel slag in the early 2000s and more recently the researchers are publishing their work in patent and not publishing them in non-patent publications. Therefore, review of utilization of steel slag without consideration of patent publication is incomplete. Earlier reviews [6–8] had not included patent publications. Table 1 indicates that most of the patents are filed (since 2000 till date) by the China and the applicants for most of them are universities. Japanese and Korean com-panies are also found patenting in the area of steel slag [9].

Disposal of slag is the major issue for the steel industries as huge space is required for its dumping. Dumping of slag on the agricultural land often creates protest by farmers for the disposal of the slag waste by the industry [10]. Near

* Yogesh Nathuji Dhoble yogesh.ipu@niscair.res.in

Sirajuddin Ahmed suahmed@jmi.ac.in

1 Dept. of Civil Engineering, Jamia Millia Islamia (Central University), New Delhi 110025, India

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Jamshedpur in India, where most of the steel industries are established, the people with low- to very low income reside near those waste dumping yards. People residing near were also found laying foundation of their houses on aged slag dumps.

Characteristic of steel slag

Chemical composition

The chemical composition of steel slag varies as the mineral composition of raw materials such as iron ore and limestone varies. Olivine, merwinite, C3S, C2S, C4AF, C2F, RO phase (CaO–FeO–MnO–MgO solid solution) and free-CaO are the main mineral phases found in the steel slag [11].

Chemical and mineralogical composition of the basic oxygen furnace (BOF) slag is similar to the electric-arc fur-nace (EAF) slag obtained during basic steelmaking opera-tion. Calcium oxide and iron oxide are the two major chemi-cal constituents of both EAF and BOF slags as shown in Table 2. As lime or dolomitic lime is used in BOF, the CaO content of the slag is found to be more than 35% and the free lime content can be as high as 10%.

The composition of the ladle slag (LD) differs from those of BOF and EAF slag. EAF slag also contains free CaO and MgO but the FeO content of EAF may be as low as 0.5%. On the other hand, the Al2O3 and CaO contents are typically higher for LD slag.

Physical characteristics

Physical characteristics play a major role towards the utiliza-tion of the steel slag. BOF, EAF, granite and flint gravel are compared for their physical properties [13]. Porous struc-tures can be observed in the magnified view of the steel slag as shown in Figs. 2 and 3. Table 3 shows the high bulk density of steel slag 3.3 g/cm3 which qualifies steel slag as a construction material for hydraulic structures. The high level of strength is described by the impact value, and crushing value along with its rough surface texture makes steel slag furnace as a very useful engineering material. High polish-ing (PSV) and a binder adhesion qualifies slag as a very suitable aggregate for high-traffic road material especially for asphaltic surface layers.

When remelted slag is subjected to semi-rapid cooling as well as rapid cooling it is found that semi-rapid cooled steel slag produced large pieces whereas rapid cooling produced granular slag making it brittle, porous and volumetric sta-ble and more suitable for cement industry [14]. Improved cementitious properties are found in finer slag [15]. Higher basicity and proper cooling provide better properties to the slag for its utilization in cement industry [16].

Use of steel slag

Once considered as waste material it has now become a use-ful raw material for many industries and is almost 100% utilized in some part of the world. US, Europe and other developed countries utilize up to 70–80% of the slag it gen-erates, whereas slag utilization in China is 22% [6] and in

Fig. 1 Trends in publication of patent and non-patents in the research area of steel slag

Table 1 Applicants for patents in the area of steel slag

Sr. no. Name of applicant No. of patents

1 Peop Rep China 2412 Wuhan Iron and Steel (Group) Corp, Peop Rep China 623 Nippon Steel Corp, Japan 594 Wuhan University of Technology, Peop Rep China 465 Shanxi Taigang Stainless Steel Co Ltd, Peop Rep China 376 Jfe Steel Corp, Japan 347 POSCO, S Korea 348 Mcc Baosteel Technology Service Co Ltd, Peop Rep China 329 University of Science and Technology Beijing, Peop Rep China 3210 Central Research Institute of Building and Construction Co Ltd MCC

Group, Peop Rep China31

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India it is less than 20% [17]. Most of the slag (50%) is used in road projects, sintering, iron-making and in recycling in steel making plant [18].

The paper reviews the progressive research trend in well-known uses such as aggregate in bituminous mixes, Ta

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Fig. 2 Steel slag SEM at ×2.71 magnification

Fig. 3 Steel slag SEM at ×2.71 magnification

Table 3 Technical properties of processed BOF and EAF in compari-son with naturally occurring aggregate [13]

Characteristics BOF EAF Granite Flint gravel

Bulk density (g/cm3) 3.3 3.5 2.5 2.6Shape—thin and elongated

pieces (%)< 10 < 10 < 10 < 10

Impact value (%/wt.) 22 18 12 21Crushing value (%/wt.) 15 13 17 2110% fines (KN) 320 350 260 250Polishing (PSV) 58 61 48 45Water absorption (%/wt.) 1 0.7 < 0.5 < 0.5Resistance to freeze–thaw (%/

wt.)< 0.5 < 0.5 < 0.5 < 1

Binder adhesion (%) > 90 > 90 > 90 > 85

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cement ingredient, concrete aggregate, antiskid aggregate and railroad ballast. This paper also reviews novel uses such as mechanomutable asphalt binders, building material, green artificial reefs, thermal insulator, catalyst and ceramic ingre-dient. The review is also done on utilization of solid waste for waste management by the novel uses like Landfill daily cover material, sand capping, carbon sequestration, water treatment and solid waste management. Review also shows recovery of pure calcium carbonate and heavy metals from slag, providing opportunity for revenue generation. Table 4 provides the classification of slag usages according to the volume of slag that can be used. It is observed that major-ity of the slag can be utilized in the area of building and construction.

The American Society for Testing Materials (ASTM) has studied and evaluated the benefits of using industrial mate-rials in civil engineering applications. ASTM made stand-ard specification such ASTM C 150, ASTM C 311, ASTM C 595, ASTM C 618, and ASTM C 989 for using fly ash and ground-granulated blast furnace slag in cement manu-facturing and concrete in buildings. The Bureau of Indian Standard, in India specified the quality of granulated slag in Portland slag cement under IS: 12089-1987 and guidelines for utilization and disposal of solid wastes from integrated steel plants under IS 10447-1983 which show the possible use as soil conditioner for acidic soil, and source of flux in the blast furnace either directly or through the sinter. China developed around 31 standards for the utilization of the slag

under different categories [19]. The standards developed help in implementation of new uses and attracts investments.

Aggregate in bituminous mixes

The feasibility study of steel slag as an aggregate in asphalt pavement using coarse BOF slag and common natural fine aggregate together to design and prepare the steel slag stone matrix asphalt mixtures (Smix) concludes that steel slag can be used as an asphalt mixture aggregate in expressway con-struction [31].

Steel slag obtained by hot-sprinkling method is a very suitable aggregate with porous structure for preparing stone mastic asphalt mixtures after 3 years ageing. The ability of resisting permanent deformation at high temperature was found enhanced. The test roads showed excellent perfor-mances even after 2 years of service, with abrasion and fric-tion coefficient of 55 British Pendulum Number (BPN) and surface texture depth of 0.8 mm [43].

Slag usually has high stability, high skid resistance, longer heat retention after mixing, and ease of compaction without “shoving” in front of a roller compactor. Steel slag aggregates have potential for volumetric expansion due to the fast occurring hydration of CaO and the slower hydra-tion of MgO found in steel slag. The percent swell of the steel slag specimens is also within tolerable limits. Field pavements also had performed satisfactorily [44]. Slag can also be used for pavement surfaces (wearing and binder

Table 4 Classification by slag utilization

Volume of slag utilization

Uses of steel slag Property References

High Railroad ballast Slow cooled slag, Permanent deformation resistant [20]Concrete aggregate Improved early crack resistance, long-term durability [21, 22]Aggregate in bitumen mix High-temperature stability, fatigue resistant [23]Cement ingredient High later strength, slight expansion, good resistance to

sulphate, CO2, sea water[24]

Antiskid aggregate Surface properties [25]Building material (putty/plastering mortar) Good permeability, high adhesion strength [26]

Medium Sand capping Iron source for seaweeds [27]Landfill daily material Long-term stability [28]Crop enhancer Slag-based silicon fertilizer [29]Mechanomutable asphalt binder Source of micro-iron particles [30]Thermal insulator High melting point, non-combustible [31, 32]Ceramic ingredient High density, better strength and corrosion resistant [33, 34]Slag as filler in constructed wetland Physicochemical properties [28]

Low Carbon sequestration Calcium content in slag [35]Pure calcium carbonate Calcium content in slag [36]Wastewater treatment (phosphorus, heavy metals,

chloro-compounds, COD removal)Physicochemical properties [36–40]

Catalyst [41]Solid waste management [42]

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courses), bases, surface treatments, seal coats, slurry coats and cold patch. Mix of bitumen (6.0–6.8 weight %), BOF slag (87.1–87.9 weight %) and mineral filler (6.0–6.1 weight %) is a better bituminous coating composition for roadway covering and pavement [45]. In another study, mix of steel slag coarse aggregate, natural stone, coarse aggregate, fine aggregate, filler and rubber asphalt shows low-temperature crack resistance, high-temperature stability, and normal-tem-perature fatigue resistance [23]. Further studies are required to evaluate the use of steel slag aggregate along with it’s life cycle assessment [46].

Mechanomutable asphalt binders

A successful use of steel slag to replace iron microparti-cles for the making of mechanomutable asphalt binders, a smart material, had shown change in mechanical properties of binder under the effect of a magnetic field [47]. Steel slag properties can be altered through the manipulation of pro-cess control and carbothermic reduction to give iron micro-particles of desired size for the mechanomutable asphalt binders [30].

Cement ingredient

The use of grounded blast furnace slag as cementicious material dates back to 1774. Both the steel slag and the blast furnace slag are composed of particles that are very hard. To use slag in cement, hydraulic properties should be known. Chemical composition is one of the important parameters determining the hydraulic properties of slag. In general, it is assumed that the higher the alkalinity, the higher the hydraulic properties and is considered as suitable cementi-tious material [24].

The main limitation with using steel slag as cement ingre-dient is due to presence of free lime, especially large-sized components of heated undissolved limestone, because when it hydrates, its volume increases and this swelling can lift the top layers. However, emerging new technologies overcome the problem of free lime and MgO making it 100% replace-ment to the ordinary sand.

This type of cement has the advantages of lower energy cost, higher abrasion resistance, lower hydration heat evo-lution and higher later strength development, but it has the disadvantage of longer setting time and lower early strength when compared with Portland cement. Steel slag cement can be used for general construction use, especially suitable for mass concrete and pavement applications due to its special features.

Samples with higher lime saturation factor developed higher C3S content and better mechanical properties [48]. Steel slag cement is characterized by high lateral strength, slight expansion, good resistance to harmful materials such

as sulfate, CO2 and sea water. It also has high tolerance to alkali–aggregate reaction [24]. It is shown that the physical and mechanical properties of the resulting concrete from BOF slag are acceptable as per Turkish Standards Institute [49]. It is found that particle size less than 20 µm has bet-ter cementicious properties than the slag which has particle size of more than 20 µm [50]. Self-cementitious properties of steel slag are found improved when gypsum is added to the mix [51].

Steel slag-based cement clinker production is done by crushing and screening steel slag and is fed along with the lime at the feed end of the kiln [52]. Speciality cement for oilfield well cementation is composed of 40–60% of steel slag powdered oilfield cement to form steel slag cement slurry [53].

Concrete aggregate

The quality of coarse aggregate has a significant effect on the compressive strength of concrete. Specific gravity of the steel slag is higher than that of normal aggregate. Percent-age absorption of sand and steel slag is smaller than coarse aggregate making it suitable for the use as a concrete aggre-gate [21].

The modulus of elasticity of steel slag aggregate con-cretes is highest after 28 days of curing, while that of calcar-eous limestone aggregate concrete is lowest [54]. The use of steel slag as fine aggregate in concrete mixes has improved both compressive and tensile strengths; hence, introducing it in concrete will eliminate one of the environmental prob-lems created by the steel industry [21]. Concrete mix having coarse steel slag aggregates (40–65%) and fine steel slag aggregates (20–60%) provides later-stage volume stability, improved early-stage crack resistance, and long-term dura-bility [22].

Building material

A synthetic building material is produced for indoor and outdoor decoration, plastering mortar which has 600 mesh surface area comprises mineral slag, steel slag, furnace slag, fly ash, desulphurization gypsum, iron ore tailings and mar-ble waste [55]. Exterior wall putty is prepared using 65 to 90% of modified slag powder, cement along with additives which provides high adhesion strength and good perme-ability [26]. Addition of 30% Al2O3 with LD slag generates near-homogeneous coatings and improves the interfacial adhesion which is good for surface coating [56].

Green artificial reefs

Green artificial reef concrete mainly made from blast fur-nace slag (70%), steel slag (10%), clinker (10%) and flue-gas

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gypsum (10%) provides 28-day compressive strength of 72.6 Mpa [57]. It helps in attachment growth of algae near the coastline. The reefs developed also avoid development of fouling organisms [58]. Artificial reef developed by add-ing 50% steel slag, 16% Portland cement clinker, 25% dry river sand with other additives have high density, strength and abrasion [59]. Reef is also developed without the use of cement having ingredients steel slag, gypsum, and building waste aggregate [60].

Antiskid aggregate

The resistance to skidding of a road surface is one of the fundamental requirements that highway engineers look for in the pavement design to provide a safe travel. Skid-resistant pavements are specially required on a specific section of the road such as sharp slope, sharp curve or ramps, which requires a braking distance, to prevent vehicles from skid-ding on the road. In the case of asphalt pavements, their skid resistance is governed by the properties of the aggregate in the wearing course of the surface layer [25].

Slag, which has an inherited irregular surface with many vesicles, is dominantly composed of metal oxides. The micro-texture of the rock is formed by interlocking large crystals of the metal oxides which provide cohesion to the material and, therefore, good surface friction. Since they polish hard, these oxides effectively protect the smaller per-ovskite and pyroxene crystals located between them from abrasion during the polishing process, while still providing a surface relief that has a rough microtexture and, therefore, is a better skid resistance [61]. Antiskid composition can be produced using tire waste, reducing agent, ceramic waste and steel slag [62]. BOF slag coarse aggregates with particle size of 4.75–16 mm show better antiskid properties of stone mastic asphalt mixture [63].

Thermal insulator

Thermal insulator is manufactured from slag wool by add-ing auxiliary raw materials to air-cooled blast furnace slag, adjusting constituents, melting the mixture in a cupola or an electric arc furnace and finally fiberizing it with special devices like spinner. The fibres are elongated by jet of air, steam or flame. The fibres are non-combustible and have melting point over 1100 °C, they are used in protection against fire [31].

Typically, slag wool may contain silicon oxide (20–30%), aluminium oxide (20–36%) and magnesium oxide (15–36%) for the manufacture of heat-resistant, fire-resistant and/or alkali-resistant fibre material [32]. The fibrous structure and high density of slag wool insulation also offer excel-lent sound absorption properties [43]. Aggregate foam con-crete also prepared by the mixture of cement (20–40%), slag

fine aggregate material (50–70%), water (10–20%), and the blowing agent in an amount of 1.0–1.8 kg/m3 had shown excellent heat-preserving and insulating properties [64] .

Ceramic ingredient

Slag is becoming value-added engineering material and utilized to develop vitreous ceramic tiles. Slag (30–40%) with other conventional raw materials when heated up to 1100–1150 °C showed relatively higher density and better strength properties for the production of tiles [33].

Ceramic composition of ceramic tiles having slag (35–44%) with silica, clay, talc and other materials provides high strength, corrosion resistance, good decorative effect [34].

Another composition describes the use of converter steel slag (30–50%) with muscovite, asbestos powder, talc, kaolin, waste glass powder, hydroxyethyl cellulose, methyl, water glass powder, zinc oxide, brown sugar, and polyvinylpyr-rolidone to provide good thermal insulation effect, which enhances the muscovite and green glaze compatibility and improves product quality [65]. High-performance glass ceramic composition is also prepared by compounding steel slag (30 to 65%) and red mud [66].

Railroad ballast

Ballast as it is known is another important part of railroad infrastructure. Ballast allows proper drainage of water away from the rails and keeps down vegetation that might interfere with the track structure. The sharp corners and rough pit-ted surface of the steel slag grip the ties firmly and prevent shifting of the tracks on the curve. Its electrical resistance does not interfere with the interlocking signal system [67]. Slow cooled steel slag can be better utilized in the railroad ballast. Further results confirmed 27% increase in lateral resistance of track with steel slag ballast with respect to that of limestone ballast [20].

Landfill daily cover material

Landfill daily cover helps in controlling vectors, fire, and odour. Long-term stability of steel slag within the final cover and the effect of ageing process are studied at laboratory scale. Leaching of aged steel slag showed trace elements below detection limits and hence it is suitable for use as a landfill cover material [28]. Landfill cover material is also produced by comminuted steel slag along with plasticizer and silica gel [68]. In full-scale studies for non-hazardous waste landfill top cover liners having 50% EAF slag and 50% cementitious LD slag (LS) are found to meet the Swedish infiltration criteria [27].

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Sand capping

Sludge layers are capped with sand to mitigate the effects of organic decomposition that lowers the amount of oxygen dissolved in the water. Sand capping is a technique used in the eutrophication of seawater. The studies showed that significantly more organisms lived in the slag-covered sea bottom area than in the sediment-covered area [69]. In Japan, sea desertification had extensively destroyed seaweed beds along the costal lines. BOF slag is used as an iron source to restore seaweed beds successfully [27].

Carbon sequestration

Capturing carbon dioxide (CO2) from large point sources and storing it instead of releasing it into the atmosphere is called carbon sequestration. A modern conventional power plant could reduce CO2 emissions to the atmosphere by approximately 80–90% compared to a plant without carbon sequestration [70]. Maximum CO2 sequestration capacity of grounded steel slag carbonated in aqueous suspensions based on the total Ca content of the slag sample is found to be 0.25 kg of CO2/kg of steel slag [35]. Another study also confirms the formation of carbonate crystals in the slag dur-ing carbon sequestration [71].

Pure calcium carbonate

The dissolution of calcium from steel converter slag using acetic acid as a solvent and the precipitation of pure cal-cium carbonate from the resulting solution is experimen-tally investigated. It is found that while strong solutions of acetic acid dissolve most of the calcium from the slag, weak acetic acid solutions dissolve calcium selectively. Calcium conversion from the solution into the precipitate is as high as 86% and the purity of the precipitate is over 99% [36]. In another method, slag is extracted with ammonium salt for the calcium-rich solution which is further reacted with CO2 to form calcium carbonate. It is also suggested that lesser the particle size of the slag, more is the extraction of the calcium [72]. It is also suggested that sonication helps in enhanced extraction [73].

Water treatment

Laboratory studies on basic oxygen furnace slag shows that slag can be utilized to remove more than 99% of phosphorus from a solution within 1 h [74]. Adsorption of phosphate is largely dependent on pH [75]. BOF slag is found to be a better media for phosphorus removal in terms of both batch and continuous flow passive treatment systems [37].

Steel slag is found to be effective in removal of hexa-valent chromium from groundwater [76]. Adsorbing slag

flotation removes heavy metal ions from acid streams and provides promising result in the treatment of an acid mine drainage [77]. In another investigation it is found that adsorption carried out in multi-element system with Pd, Cu, Zn, and Cd has the selectivity in the order of Pb > Cu > Zn > Cd [38]. Slag fines when blended with the soil is capable to immobilize Zn, As(III), As(V), Cd, Ni, W, Cu, P, Se(IV), Se(VI) and Pb. 1% use of pulver-ized slag fines in the acidic soil helps increase the rice yield and from leaching studies it is found that slag better immobilizes heavy metals then natural soil, gravel and sand [77–80]. Steel slag is also found to help increase the yield in coffee plants [29].

Chlorinated organic compounds get released into the groundwater in the industrial area. Removal of chloro compounds such as tetrachloroethylene from the ground-water up to 81% is attainted by BOF slag as a catalyst to enhance fenton-like oxidation [39]. Removal of perchlo-rate in subcritical water in the presence of steel slag is also possible without leaching of heavy metal [81].

COD removal up to 90% is achieved in the coking wastewater by the use of steel slag and hydrogen peroxide [40, 82, 83]. COD, NH3-N, total N and other pollutants are removed from sewage water by microaerophilic expanded granular sludge-bed reactor [84].

Slag as a filler in constructed wetland for the treatment of pollutant in sewage treatment in rural areas is found to have better adsorption capacity than bamboo charcoal and limestone [85, 86].

Recovery of heavy metals

Recovery of metals such as Al, Nb, Ta, Au, Pb, Zn, Fe, Cr, Cu, Co, Ni, and Ag is possible either by magnetic separa-tion, crushing, grinding, floatation, eddy current separa-tion or by leaching or roasting [87]. Steel slag when passed into DC reactor through the hollow electrode metals such as Fe, Mn, V and Cr are obtained and the treated slag is having better mechanical properties [88]. Recovery of Fe and phosphorus is done by carbothermal reduction [89]. Leached out vanadium from the steel slag at highly alka-line condition can be removed or recovered up to 57–72% from the anion-exchange resin. The resin used can be reused for 20 times without loss of efficacy [47]. Bioleach-ing by Acidithiobacillus thiooxidans culture supernatant provides recovery of Mg (28–75%), Zn (14–60%) and Cu (11–27%) [90]. Selective leaching of Cr with NaOH in the presence of NaOCl under temperature-controlled extrac-tion, followed by water leaching is able to give 99.9% recovery rate [91]. It is evident that metal recovery would help stabilize the steel slag when it is sent for disposal.

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Catalyst

Mn-loaded catalytic particle electrode is developed from steel slag waste through ultrasound impregnation–calcina-tion strategy to degrade Rhodamine B [92].

Steel slag catalyses glycerol transesterification with dime-thyl carbonate for the synthesis of valuable glycerol carbon-ate with 97% yield. The catalyst is used five times without deactivation [41]. CeO2-loaded porous alkali-activated steel slag-based photocatalyst (CeO2–PASSP) is used for pho-tocatalytic water-splitting for hydrogen production [26]. Molecular sieve catalyst obtained by processing smelting waste steel slag is found to have high catalytic activity [93]. Solidified slag as a catalyst is used to produce synthetic gas of desired quality by reforming hydrocarbons [94].

Solid waste management

Converter slag solidification (CSS) technology is used for the solidification of digested sewage sludge using converter slag as the solidifying agent and quick lime as the solidifying aid. CSS technology can minimize the hazard of heavy metal leaching from the solidified sludge [95]. Composted sewage sludge and steel slag when used on unfertile soil help in improving quality of soil in urban area and tree growth [42].

Conclusion

Utilization of steel slag is more centred towards its physical and chemical properties. It is observed that granulated slag is preferred for utilization in many applications. Slag has an inherited irregular surface with many vesicles which acts as a good anti-skidding aggregate and a better adsorbent. Slag with low free lime and higher C3S content having bet-ter mechanical properties is preferred for its cementitious properties.

Steel slag has tremendous potential for exploration of new utilities as evident from the present publication trend. Steel slag is the best alternative to the natural resources.

Steel slag has tremendous potential for exploration of new utilities as evident from the present publication trend. Steel slag is the best alternative to the natural resources. The research trends show the innovations are done in well-known uses such as aggregate in bituminous mixes, cement ingre-dient, concrete aggregate, antiskid aggregate and railroad ballast towards maximizing the utilization of steel slag by the use of modifiers or fillers or by alteration of physical and chemical properties of the slag. Standardization of methods for the use of steel slag has helped in increasing the utiliza-tion of the steel slag for those uses. Recently, novel uses are also reported such as mechanomutable asphalt binders, building material, green artificial reefs, thermal insulator,

and ceramic ingredient. New approaches towards utilization of slag for waste management such as landfill daily cover material, sand capping, carbon sequestration, water treat-ment and solid waste management are also reported. Recov-ery of minerals and heavy metals from slag and use of steel slag as catalyst are the new areas of research. The rapidly increasing trend of patenting in this area shows the steel slag is gaining commercial interest. Most of the recently devel-oped utilities require cases studies on pilot-scale towards its acceptability for those uses. Therefore, decrease in research publications in this area is a matter of concern. The output of the research plays a big role in making standards for the utilization of the steel slag which eventually helps in increas-ing the percentage utilization of the steel slag.

References

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https://www.ipcc.ch/pdf/special-reports/srccs/srccs_wholereport.pdfhttps://www.ipcc.ch/pdf/special-reports/srccs/srccs_wholereport.pdf

Review on the innovative uses of steel slag for waste minimizationAbstractIntroductionCharacteristic of steel slagChemical compositionPhysical characteristics

Use of steel slagAggregate in bituminous mixesMechanomutable asphalt bindersCement ingredientConcrete aggregateBuilding materialGreen artificial reefsAntiskid aggregateThermal insulatorCeramic ingredientRailroad ballastLandfill daily cover materialSand cappingCarbon sequestrationPure calcium carbonateWater treatmentRecovery of heavy metalsCatalystSolid waste management

ConclusionReferences