An Overview on Slag Re-usability - Current Scenario & Future Prospects

Contents

Chapter 1: Introduction .pg 3 Importance of the topic Objective of the studyChapter 2: Solid waste scenario .... pg. 6 International Scenario National ScenarioChapter 3: Solid Waste Generation . pg. 15 Quantification CharacteristicsChapter -4: Data Analysis & interpretation. pg. 28 Tata Steel SAILChapter 5: Newer Direction of Research & Development..pg 34 Innovative applications of Slags Need for additional funding .Chapter 6: Summary of the Studypg 44

Chapter 7: Recommendations..pg 46 Chapter 1 Introduction

1.1 Importance of this topic The iron and steel industries around the world are responsible for the generation of large amount of waste materials mainly because they process huge quantity of raw materials. Neither the governments nor the society have forced the industries to develop ways and means of managing the waste in a creative way. However, with very little land available for disposal of wastes and also because whatever was a waste material two decades ago cannot be considered a waste today due to ever increasing shortage of natural resources including ores, minerals and fuels, the pattern of thinking of scientists and technologists have changed. Newer materials and products are now being developed from wastes generated from different process industries including metallurgical industries. The concept of utilization of solid wastes in iron and steel industries embraces the three basic principles of recovery, recycling and converting to high value added products. The utilization of wastes has attained in more recent years fourth and most important dimension in its relation to environment and problem of disposal. A fifth dimension lies in the domain of research and development and relates to the addition of values to wastes so as to make them into economical and useful products. As has been mentioned in various literatures recycling is an integral feature of modern steel plant operations. Of the materials recycled, dust from various operations is recycled from the economic and environmental point of view. Recovery of values from dust and slag has been receiving considerable attention internationally in recent years. Some of the well attempted examples by various countries are recovery of phosphorous, niobium and manganese from slags, recovery of zinc from blast furnace and BOF dust etc. Besides recycling and recovery, continuous efforts are being made by many foreign institutions and industries to convert solid wastes into value added marketable products namely various types of ceramic based products, composites and low cost building materials etc.

Fig 1.1 Landfills using blast furnace slag

2.2 Objective of the study

In this study, the aim is to present the development of a few products manufactured from solid waste generated from iron & steel industries including captive power plants. Some of these products are wear resistant ceramic lining materials, refractory aggregate for high alumina cement cast-able, ceramic floor & wall tiles, etc. The theoretical aspects behind development of these products have also been touched upon. Extensive discussion of Blast Furnace and Electric Arc Furnace slag will be made and the environmental hazards that arise from wasteful disposal of these wastes. Fig1.2 pollution of a local water body due to dumping of slag

Chapter 2 Solid Waste scenario

2.1 Global ScenarioAs early as 350 B.C., the Greek philosopher-physician Aristotle prescribed iron slags for healing wounds. Around 1589, Germans were making cannon balls cast from iron slag and records are available which indicate that cast iron slag stones were used for masonry work in Europe of the 18th century. The history of slaguse in road building dates back to the time of Roman empire, some 2000 years ago, when broken slag from the crude iron-making forges of that area were used in base construction. Roads made from slag were first built in England, blocks cast of slag were in general use forstreet paving in Europe and the US. Today slag is a nuisance it dumped and is a valuable material if properly processed. The target of current steel industry is to recycle and utilize all their by products. Slag is the important waste and by products of steel industry, which have been treated, recycled and used worldwide. Zero slag processlowers the amount of slag generated through hot metal pretreatment, thereby expanding the range of slag utilization . Almost a century ago, the term waste product aptly described slag. Slag was considered to be essential in the production of iron, but once it served its purpose in refining the metal, it was strictly a nuisance with little or no use. The use of slags became a common practice in Europe at the turn of the 19th century, where the incentive to make all possible use of industrial byproducts was strong and storage space for byproducts was lacking. Shortly after, many markets for slags opened in Europe, the United States, and elsewhere in the world. The Portland Cement Association is promoting slag use in Portland cement production. The potential for a carbon tax levy on CO2 emissions may provide the cement producers with incentives to find ways of reducing unit CO2 emissions in Portland cement production, where the combustion of fuel and decomposition of carbonates in the raw feed contribute to CO2 emissions. Texas Industries Inc. has developed a process for cement clinker production involving the use of steel slag. In this process, which is called CemStar, steel slag is fed into the rotary kiln as a part of the raw meal. Replacing a part of the limestonein the raw deal directly with slag results in the lowering of CO2emissions as well as increasing cement production directly proportional to the quantity of slag used. Refinements of theprocess started in 2000 have continued throughout 2001 (RobertD. Rogers, President, Texas Industries Inc., oral commune, 2001).Based on 2011 data on hazardous solid wastes regulated under the RCRA, the EPA found that iron and steel mills and ferroalloy manufacturing activities ranked fifth for the 50 largest quantities of hazardous waste generated in the U.S. (around 1.4 million tons.). More than 56% and 24% of the produced steel slag have been utilized as sinter material in USA and German respectively. In China, Baoshan Iron and Steel Group (Bao Steel) began to reused steel slag for sintering in 1996, now having a stable reusing amount of 15,000 tons. Lianyuan Iron and Steel Company (Lianyuan Steel) have been utilizing steel slag as sinter material while in recent years the amount for sintering has deceased because of either the increase of phosphorus content in iron ore and hot metal or the decrease of CaO and Fe content in steel slag. In Germany, about 400,000 tons of steel slag per year is used as aggregate for the stabilization of rive bankers and river beds against erosion. Nippon Slag Association in Japan has since 1993 been involved in application technology research for the use of steelmaking slag as a material for ground improvement in port and harbor construction and in 2008 published the Guide to the use in port and Harbor Construction. JFE Steel Corporation in Japan manufactured artificial reefs for sea wood/coral breeding (Marine block) using carbonated steel slag. The Artificial reefs show a high stability in seawater due to the fact that it consists of CaCO3, like shells and coral, and they act as great breeding habitats for seaweeds and coral. In China, Xu manufactured concrete armor blocks for sea coast projects, partially replacing sand with steel slag and cement with fine slag powder, and the concrete blocks has been applied practically in East China sea coast reclamation works and Luchao port project. Li, et al prepared high strength of artificial reefs concrete with 79% granulated high furnace slag ,15% steel slag , 5% flue gas desulphurization gypsum and 1% mixture as cementitious material and steel slag grains as its fine and coarse aggregates. Approximately 60% of slag is used for road engineering in Japan and European countries, and even 98% of that is utilized as aggregates of cement and bituminous pavement in UK. More than 25 years ago in Germany test roads were built using steel slag as an aggregate for unbound and bituminous bound mixtures. Ahmedzadea investigated the influences of the utilization of steel slag as a coarse aggregate on the properties of hot mix asphalt. The results showed that steel slag used as a coarse aggregate improved the mechanical properties of asphalt mixtures. Moreover, volume resistivity values demonstrated that the electrical conductivity of steel slag asphalt mixtures were better than that of limestone asphalt mixtures. Asi observed that asphalt concrete mixes containing 30% steel slag had the highest skid number followed by Superpave, SMA(Stone Mastic Asphalt), and Marshall mixes, respectively. Ameri, et al. evaluated the effectiveness of steel slag as a substitute for virgin aggregates on mechanical properties of cold mix recycling asphalt pavement. The results showed that the use of steel slag could enhance Marshall stability, resilient modulus, tensile strength, resistance to moisture damage and resistance to permanent deformation of CIR (Cold In Place Recycling) mixes. Steel slag presents porous structure and large surface area; in addition, it is easy to separate from water due to its high density. Therefore, the application of steel slag in industrial waste water treatment has received intensive attention in recent years. Shi, et al. studied the treatment of mercury-containing sea water with steel slag and the high adsorption capacity of steel slag for mercury was observed. Chamteut used steel slag as a low-cost adsorbent for arsenic in aqueous system, showing 95-100% removal efficiency near initial pH=2. The removal mechanism included the co-precipitation and adsorption of CaCO3. Kim, et al. investigated the removal mechanism of copper using steel slag and the results confirmed that the major mechanisms were adsorption and precipitation. In addition, steel slag as a separated adsorbent can be used to remove aqueous ammonium nitrogen, phosphorous and phenol .The combined use of steel slag and H2O2 can decompose organic pollutions due to the ferrous ion produced from FeO in steel slag reacting with hydrogen peroxide to form Fenton's reagent that has strong oxidation .Steel slag can also be used as raw material for coagulant preparation . Steel slag contains fertilizer components CaO, SiO2, and MgO. In addition to these three components, it also contains components such as FeO, MnO, and P2O5, so it has been used for a broad range of agricultural purposes. Its alkaline property remedies soil acidity .In developed countries such as Germany, USA, France and Japan, converter slag is used to produce siliceous fertilizer, phosphorus fertilizer and micronutrient fertilizer. In Europe, due to expertise and agreements with environmental authorities in various countries ,some of the slag types are recognized as non-wastes, products or by-products (e.g., in Belgium, Finland, Germany, Austria and the United Kingdom) but still have a waste status in some other countries. Steel slags in particular are often considered as waste, especially inthe liquid state and before treatment. The following figures give the utilization of iron and steel slags in Europe in the year 2010.

Fig 2.1 Utilization of BF slag in European countries in the year 2010

Fig 2.2 Utilization of Steel Slag in Europe in 20102.2 Indian scenario As per the Report of the Working Group on Cement Industry for the 12th Plan, around 10 million tones BF slag is currently generatedin the country from iron & steel industry. The BF slag in India is used mainly in the cement manufacture and in other unorganized work, such as, landfills and railway ballast. A small quantity is also used by the glass industry for making slag wool fibers. Cement plants in thecountry producing slag cement require BF slag in granulated forms.Commonwealth Scientific & Industrial Research Organization (CSIRO) carried out investigations for value-added method for slag and proved a number of technically viable and commercially interesting applications of slag. The applications include (i) base course and top course to asphalt roads, (ii) anti-skid surfacing for roads on accident-prone intersections, (iii) low-strength concrete for footpaths (iv) controlled low strength fill for backfill required for trench stabilization and (v) concrete sub-base for rigid pavements. Most leading steel plants sell part of blast furnace slag to private cement manufacturers for granulation, the remaining being air cooledand dumped. The amount of GBFS added to cement is higher only if the glassy content of the slag is 90 to 96 per cent, which in turn is possible if temperature of the slag is above 1200C. Cast house granulation in some of the blast furnaces at these steel plants have taken care of slag temperature. The Indian Road Congress (IRC) and the Bureau of Indian Standards (BIS) accept air cooled blast furnace slag as a substitute of store aggregate /chips for making purposes. Necessary efforts are required to be made for its utilization in road making in the steel townships and inside the plants. Utilization of thecrystalline air cooled blast furnace slag also requires persuasion and follow up with various road making authorities - Central, State, Local bodies - so that it is included in the schedule for economic transportation. Studies on slags for their use as substitute for stone aggregates in road making have been conducted. Based on the report an experimental road patch is going to be constructed soon at Rourkela with the active participation of RSP, CRRI and state road authorities. The outcome of this trial is expected to help in popularizing the slags for road making purposes.

Fig 2.3 Slag processing plant

Some steel plants are preparing for necessary supply of crushed and sized slag to the customer. The finer size of the BF Slag can be used as a substitute for sand in concrete/mortar making. RDCIS is conducting a study with jointly with Central Road Research Institute, New Delhi and is trying to develop a suitable combination for making high density -heavy duty roads with Steel Plants wastes.

Fig. 2.4 Solid Waste utilization pattern in Indian steel plantsAvenues to utilize blast furnace slag in the form of boulders for arresting erosion of the embankment of Hooghly and Digha shore lines are also being explored by nearby steel plants. Rajkot (Gujarat) is well known for its small scale industries for long time and one of the fastest developing cities of India is hub of steel and allied industries.. Rajkot itself produces blast furnace slag of amount 2500T/month from its 2000 steel processing units. This enormous quantity of blast furnace slag is generally dumped in unscientific manner create environmental issues and little is used for landfill purpose without any technical input.

Chapter 3 Solid Waste Generation

3.1 Quantification In an integrated steel plant, 2 4 tons of wastes (including solid, liquid and gas) are generated for every ton of steel produced. Accordingly, today the emphasis is on the avoidance of waste generation, recycling and reuse of waste, and minimizing the adverse impact of disposal on the environment. Among all the solid/liquid wastes, slag generated at iron making and steel making units are created in the largest quantities. Some

3.2 Characterization In this study, our topics of discussion are mainly BF slag and EAF slag, so we discuss their physical and chemical characteristics. The figure given below gives us an idea about the steps of generation and processing of blast furnace and steel slag.

Fig 3.1 Steps of slag production3.2.1 BF slag Blast furnace slag is a nonmetallic by-product produced in the process of iron making (pig iron) in a blast furnace and 300kg of Blast furnace slag is generated when 1 ton of pig iron produced. In India, annual productions of pig iron is 70-80 million tons and corresponding blast furnace slag are about 21-24 million tons. Blast furnace slag is mildly alkaline and exhibits a pH in solution in the range of 8 to 10 and does not present a corrosion risk to steel in pilings or to steel embedded in concrete made with blast furnace slag cement or aggregates. The blast furnace slag could be used for the cement raw material, the roadbed material, the mineral admixture for concrete and aggregate for concrete, etc. Now in India, resources of natural sand are very lacking, it is necessary that the new fine aggregate was sought. The property of blast furnace slag is similar to natural sand, the price is cheap and the output is large too, could be regarded as the substitute of the natural sand. But there is no experience about application of blast furnace slag fine aggregate in concrete and the reports about the research are also few. The main uses of blast furnace slag are given as follows:-

Fig 3.2 main uses of BF Slag Ground granulated blast furnace slag (GGBS) is a by-product from the blast-furnaces used to make iron. These operate at a temperature of about 1,500 degrees centigrade and are fed with a carefully controlled mixture of iron-ore, coke and limestone. The iron ore is reduced to iron and the remaining materials form a slag that floats on top of the iron. This slag is periodically tapped off as a molten liquid and if it is to be used for the manufacture of GGBS it has to be rapidly quenched in large volumes of water. The quenching optimizes the cementitious properties and produces granules similar to coarse sand. This 'granulated' slag is then dried and ground to a fine powder. It is a glassy granular material. GGBS cement is added to concrete in the concrete manufacturer's batching plant, along with Portland cement, aggregates and water. The normal ratios of aggregates and water to cementitious material in the mix remain unchanged. GGBS is used as a direct replacement for Portland cement, on a one-to-one basis by weight. Replacement levels for GGBS vary from 30% to up to 85%. Chemical composition of GGBS may vary from plant to plant owing to difference in raw material composition, process routes etc. Table 3.1 given below highlights this fact as it draws a comparison between chemical compositions of GGBS from two different Steel Plants.

Table 3.1 Comparative composition of GGBS generated from Bokaro Steel Plant and Tata Iron & Steel Plant Typically 40 to 50% is used in most instances. GGBS concrete cement sets more slowly than concrete made with ordinary Portland cement, depending on the amount of GGBS in the cementitious material, but also continues to gain strength over a longer period in production conditions. This results in lower heat of hydration and lower temperature rises, and makes avoiding cold joints easier, but may also affect construction schedules where quick setting is required. GGBS is used to make durable concrete structures in combination with ordinary Portland cement and/or other pozzolanic materials. GGBS has been widely used in Europe, and increasingly in the United States and in Asia (particularly in Japan and Singapore) for its superiority in concrete durability, extending the lifespan of buildings from fifty years to a hundred years.

Fig 3.3 Chemical composition of BF slag (% weight)

3.2.2 Steel SlagModern integrated steel plants produce steel through basic oxygen process. Some steel plants use electric arc furnace smelting to their size. In the case of former using oxygen process, lime (CaO) and dolomite (CaO.MgO) are charged into the converter or furnace as flux. Lowering the launce, injection of higher pressurized oxygen is accomplished. This oxygen combines with the impurities of the charge which are finally separated. The impurities are silicon, manganese, phosphorous, some liquid iron oxides and gases like CO2 and CO. Combined with lime and dolomite, they form steel slag. At the end of the operation liquid steel is poured into a ladle. The remaining slag in the vessel is transferred to a separate slag pot. For industrial use, different grades of steel are required. With varying grades of steel produced, the resulting slag also assume various characteristics and hence strength properties. Grades of steel are classified from high to medium and low depending on their carbon content. Higher grades of steel have higher carbon contents. Low carbon steel is made by use of greater volume of oxygen so that good amount carbon goes into combination with oxygen in producing CO2 which escapes into atmosphere. This also necessitates use of higher amount of lime and dolomite as flux. These varying quantities of slag known as furnace slag or tap slag, raker slag, synthetic or ladle slag and pit or clean out slag. The Steel Slag is crushed to get the desired size of aggregates. The slag had grayish white color. Steel slag must be allowed to undergo the weathering process before using as an aggregate in construction because of its expansive nature. This is done in order to reduce the quantity of free lime to acceptable limits. The steel slag is allowed to stand in stockpiles for a period of at least 4 months and exposed to weather. During this weathering process, the steel slag is required to be in contact with water so that the hydration process between lime and water takes place. Hydration of free lime (CaO) or free magnesia (MgO) is responsible for expansive nature of steel slag.

Fig 3.3 Microstructure of steel slag The chemical and physical data for the above steel slag is presented as follows. The tests on Steel Slag are as per Indian Standard Codes.

Table 3.2 Physical properties of steel slag Aggregates Absorption Specific Gravity L.A.Absorption

Steel Slag 2.5 2.91 27

Table3.3 Chemical properties of steel slag (sample)Component Sample slag composition (%)Composition provided by NSA (%)

FeO1- 2.5 24

CaO 45-50 42

SiO2 20-22 15

MgO 10-15 8

Al2O3 4-8 1-5

3.3 Electric Arc Furnace (EAF) Slag Demand and production of steel is increasing day by day and all the developing countries like China, India are increasing their production capacity significantly. Total world steel production has crossed 1200 million metric tons and the leader China is producing more than onethird of it. Steel production by electric arc furnace route has gained momentum after eighties and consists of around 50% of the total steel production by advanced countries. This route of steel production has several advantages over the conventional blast furnace and converter route. These are mainly: Low capital cost and lower energy requirement per ton of steel, allows the utilization of waste steel scraps, precise control on chemistry and temperature of steel, flexibility in the size of the furnace (can be very small for special alloys) and very high temperature may be achieved by arcing. But due to this change in the steel making technology, there appears a new by-product: electric arc furnace (EAF) slag (also commonly called as black slag).Electric Arc Furnace Slag (EAFS) that contains low percentage of amorphous silica and high content of ferric oxides and consequently has low pozzolanic activities in comparison with Blast Furnace Slag (BFS), is not appropriate to be used in blended cement production. But it has been widely employed as aggregate, mainly in base, sub-base and bituminous pavement for road construction ,breakwater blocks, foundations, shoring walls, noise barriers, andradiation insulators, in which EAF slag provides many advantages in comparison with natural aggregates.

Fig 3.4 Generation of EAF slag The Electric Furnace Slag is an excellent material to be used in the ceramics industry for the production of construction items. The slag enriches these products with firefighting phases, giving the final product:- Increased mechanical strength Small shrinkage of dimensions during drying and roasting Zero water permeability Good behavior in testing of strength in frost Decreased energy cost, due to the decreased percentage of moisture demanded for their production.The Electric Furnace Slag is an excellent raw material replacing the silica sands in the ceramic industry for the production of construction tiles and bricks, with an increase of about 40% of their mechanical strength without an increase of the roasting temperature. This means that is now possible for tiles and bricks with thinner walls to be produced, therefore a more economical use of the raw material and decrease of the energy consumption is achieved, plus a lighter and easier to handle product. The products have zero level permeability. Furthermore, if the tiles are roasted at a temperature 30 oC higher than usual, they obtain a glassy texture which makes them fine for external (visible) construction sections. The firefighting Fetling masses are broadly used in metallurgical smelting furnaces(electric furnaces, transportation buckets etc.), an effort to reduce the wear of the permanent firefighting tiles. The demand in the firefighting properties of the Fetling masses is low, for their easier cementation with the furnace walls at its operation temperatures. Therefore the high firefighting masses produced from domestic low iron magnesite deposits are not proper for this use. The addition of the high Fe2O3 slag of can reduce the firefighting properties of the mixture. A comparison of physical properties between naturally occurring aggregates and EAF slag are as given in the table below. The testing method has been specified.

Table 3.4 Physical properties of EAF slag (aggregate)

Table Physical properties of EAF slag (powdered)

The EAF steelmaking process is essentially a steel scrap recycling process. Therefore, the chemical composition of EAF slag depends significantly on the properties of the recycled steel. Compared to BOF slags, the main chemical constituents of EAF slags can vary widely. Typically, the FeO, CaO, SiO2, Al2O3, and MgO contents of EAF slags are in the 1040%, 2260%, 634%, 314%, and 313% ranges, respectively. Other minor components include other oxidized impurities, such as MgO, MnO, and SO3. EAF slags also contain free CaO and MgO along with other complex minerals and solid solutions of CaO, FeO, and MgO. The FeO content of EAF slags generated from stainless steel production processes can be as low as 2% . Table 3.5 Chemical Composition of EAF slags

The above slag can be used as a soil enhancer due to high percentage of iron oxide and calcium oxide.

Chapter 4Data Analysis & Interpretation

4.1 Introduction Utilization solid wastes which include blast furnace slag, LD sludge, fly ash etc. This section deals with a few case studies: the plant data for slag generated by some of the leading steel producing plants in India.

4.2 Case Studies 4.2.1 Tata Steel With the steel making production capacity now at 9.7 MTPA approximately 6 MTPA of solid waste is generated. The waste primarily comprises two major components BF Slag and Sludge - produced during iron making - and LD Slag and Sludge - generated during steel making. Various operating units also generate other wastes such as Flue Dust, Mill Scale and Sludge, Muck and Refractory Wastes. This huge volume of waste not only requires proper handling or storage but more importantly minimization and efficient utilization. Currently nearly all solid waste materials generated at the Steel Works are utilized or stored for future processing and usage. Sustained utilization of LD Slag, which constitutes more than 30% of the solid waste, is a major vulnerability.

Table 4.1 Solid waste generation of Tata SteelYear 2011-12 2012-13 2013-14

Waste generated (mill. tones) 4.45 5.25 5.99

A project focuses on processing LD Slag at the Waste Recovery Plant (crushing and magnetic separation), making it phosphorous free and then reusing it in the steel melting shops as well as in sinter making.LF slag is rich in CaO (~50%) and thus can be used to replace direct addition of Lime. The Company commissioned a facility to condition LD Slag and improve its utilization, which has already increased from less than 30% in 2011-12 to nearly 100% in 2013-14. Most of this processed waste is likely to be used as construction aggregate.Improvement projects led to higher waste utilization of LD Slag in sinter making - from 42 Ktpa to 165 Ktpa, replacement of limestone and sand in the cast-house with LD slag, a 20-fold increase of LD Slag usage in the Cement sector (58 Ktpa in 2013-14) and higher utilization of waste at its waste management site. Trials were undertaken to replace sand with slag in underground mine stowing.Trials are also being conducted using a mix of LD Slag, Fly Ash and Granulated Blast Furnace Slag, with Alkali (NaOH and Silicate) as binder, to develop paver blocks. Discussions are also underway to market this product. A study of solid waste best practices across the world revealed the possibility of Air granulation of LD Slag. Once granulated the slag can be used for road construction or in the cement industry. This method has added advantage of better metal recovery from slag hence it is being evaluated for implementation. Tata Steel is engaging with the Jharkhand State Government, Department of Agricultural to promote the iron rich LD Slag as a soil conditioner. Over 93% of the blast furnace slag is granulated before being sold to the cement industry as a clinker substitute, eliminating the need to use Limestone to produce clinker. This reduces CO2 emission in cement production. Tata Steel supplies most of this granulated and dried Blast Furnace Slag to cement makers around its Steel Works at Jamshedpur.

4.2.2 SAILSolid wastes in steel plants are essentially by products generated during various processing steps involved in the production of iron and steel. The quantities of such wastes are enormous and their nature quite varied and diverse. Some wastes like BF and SM Slags as well as fly ash, constitute a major fraction of the total generation, whereas mill scale and flue dust contribute comparatively smaller fraction. The solid waste generation in SAIL plants in kg/t of crude steel for 1994-95 is given in Table below

Table 4.2 Slag products of SAIL plantsSolid by-product BSP DSP RSP BSLIISCO

Air-cooled BF Slag 1081 265 222 1479 332

Granulated BF slag 833 273 217 205 128

SMS slag-THE/OHF 438 133 74 _ 33

SMS Slag-LD/BOF 254 74 193.3 754 _

Generation of "Solid Wastes" from a steel plant fully depends on the quality of raw materials available for its process which is around 12(X) kg. for each tons of steel produced in SAIL steel plant. The steel plants abroad operating of on superior raw materials produce in the order of 550 kg of wastes for each tons of steel produced.The quality of slag fly ash is of most importance in formulating management strategy for its effective utilization and disposal. The quality varies with physical and chemical characteristics of raw materials, process technology, operating practice and type of end products. The slag quality governs the extent of slag reuse in metal recovery and utilization by mixing with other materials. Part of BF Slag can be recycled to blast furnace and sinter plant. The magnesium content in the converter slag may be useful as a slag conditioner. The fly ash generated in SAIL plants are high in SiO2 content of the order of 45-50% and alumina content of 14-28% in different units. The usual practice of managing these solid wastes is to dump them in openspace and excavated land which creates environmental pollution in the form of dusts and leachates. Beside, these also need huge investment in dumping . As a age old practice, SAIL was also following the same method. The solid by products generated in SAIL steel plants can become profitable when disposed as saleable products. Out of total solid waste generated in our steel plants 16% are sold , 21% recycled and rest 63% are dumped. The utilization of granulated BF Slag (GBFS) is 99.4% and that of rest of wastes such as air cooled BF slag, fly ash have been insignificant. This has resulted in the continuous increase of dumps and related environmental problems. At the present level of production it is estimated that over 10 million tons of solid wastes are generated every year by SAIL steel plants. Out of this about 8 million tons areestimated to be dumped annually, the dumps of accumulated slags alone may account for over 100 million tons in our major steel plants. Technologies for utilization of these and other wastes are available from national institutes and laboratories including RDCIS (SAIL). These technologies are in the areas of : (i) Utilizations of fly ash in brick making, pellet making and in agricultural field, (ii)Utilizations of ferruginous wastes through micro pelletisation sinter making route,(iii) Utilizations of salvaged refractories in production of remming mass, mortar etc. and (iv) Recovery of acid from waste acid sludge. In DSP, parties have been identified to manufacture bricks from Fly ash using CFRI technology. Land, water/raw materials and power will be supplied to entrepreneurs by DSP. The parties will have to identify the market for it. Each of them will be manufacturing 8000 bricks/day initially

Chapter 5Newer Direction of Research & Development : INNOVATIVE uses

5.1 Innovative applications of EAF slagsWhile blast furnace slag can be easily recycled following cooling and treatment before granulation, to be utilized by the cement industry(mainly),steel slags are particularly difficult to recycle, especially EAF slags .This chapter deals with the more innovative approach of utilizing slags, namely EAF slags. A few such cases are considered as follows

5.1.1 EAF Steel Slag Filters for Phosphorus Removal from MilkThe treatment technologies that are utilized for municipal and industrial wastewater are complex and very expensive. Chemical dosing, for example, a traditional P removal technology, is an energy intensive method that requires constant monitoring and manipulation . Agricultural producers lack the capital, manpower and technical training to build and maintain such systems. Steel slags, a co-product of steel production, have demonstrated the greatest capacity to remove P from a variety of wastewaters. Thus for specific study, Parlor Effluent Electric arc furnace (EAF) steel slag filters were investigated for their efficiency at reducing the concentration of phosphorus (P) from dairy farm wastewater in Vermont. The primary objective for this study was to examine the use of in series design on filters performance in P removal from dairy farm wastewater at subzero temperatures. During much of the first feeding cycle the EAF steel slag filters were operated under subzero temperatures. Many steps were made to reduce the incidence of freezing in the filter system, and the few times that freezing did occur it was mostly in the connecting piping between filters, which were more exposed. This demonstrates that with simple design modifications to provide insulation and protection from cold, an EAF steel slag filter system can function effectively in cold climates.

Fig 5.1 Porous nature of slag that makes it an excellent water filter

5.1.2 Steel Slag Filtration For Extensive Treatment Of Mining WastewaterThe mining industry faces major environmental concerns, if itdischarges effluents that have the potential to damage ecosystems and human health. The various composition of mining wastewaters has led to the development of several treatment systems. Systems for leachate from abandoned mines have to be efficient for a long period of time and cost effective, as they are often implemented as a condition of post-closure plans. Use of EAF slag to remove fluoride, phosphorous and heavy metals is notable under specific restriction of pH and this is an area which may have huge scope for research. 5.1.3 Use of Steel Slag in Agriculture and for Reclamation of Acidic Lands

As discussed in the previous chapter, steel slags contains significant concentrations of Ca and Mg. These elements occur in the form of silicates, ferrites, aluminates, oxides and some free CaO and MgO. Steel slag is alkaline, with pH in the range of 8-10, but values of 12 or higher are possible if the free CaO content is high enough (CaO reacts with water to form Ca(OH)2 which has a maximum pH of 12.5). While Calcium silicate is alkaline and will act as a long-term liming agent in soil, the immediate liming effect comes from the free CaO and MgO. The liming materials in steel slag comprise water-soluble and less water-soluble Ca and Mg compounds. Free Ca in slag reacts rapidly with water to form Ca(OH)2. The Ca(OH)2will react rapidly with soil acidity. The less soluble silicate compounds will react more slowly with soil acidity and will provide more long-term buffering of soil pH. It is expected that Ca(OH)2, formed when the CaO in the slag reacts with soil moisture, will cause an immediate increase in soil pH, but not to the desired pH. The desired pH will be achieved over time as the less soluble liming constituents in the slag react with the soil. It is recommended that a lime reaction test be conducted for a specific slag. The lime reaction test involves mixing one or more representative acid soils with the rate of steel slag determined from the buffer lime test and observing changes in soil pH over time. The frequency of application would be based on the time that the slag was able to maintain the desired pH.Use of steel slag for reclamation of acidic mine land is an excellent use for this material. Application rates to neutralize total potential acidity of mine land are high and reapplication of lime may not be technically or economically feasible.

5.1.4 Production of Sintered Ceramic Tiles Produced from Steel SlagCharacteristics of the raw materials indicate that EAF slag contains very high amount of iron oxide, lime, silica and magnesia. Presence of very high amount of iron oxide may restrict the use of this material in a ceramic composition, as it may reduce the firing temperature and vitrification range. Silica, lime and magnesia may be accommodated in the ceramic compositions. The developed tiles are having relativelyhigher density value due to presence of heavier iron oxide. Again use of EAF slag showed relatively short vitrification range for all the compositions, even on the use to the extent of 3040 wt% in the composition. Presence of higher amount of feldspar and also higher amount of low alumina containing clay showed further reduced vitrification range for the compositions. A little reduced flexural strength was obtained when complete vitrification was obtained, which may be associated with grain growth and re-crystallization. In the microstructural study quartz was found to be unreacted at 1125C for all the compositions and iron oxide rich portion (remnant of slag) and alumina, lime, silica containing compound was found as the other microstructural constituents.

5.1.5 Slag usage in thermal and insulator manufacturingSlag wool is manufactured by adding auxiliary raw materials to air cooled blast furnace slag, adjusting constituents, melting the mixture in a cupola or an electric arc furnace and finally fiber zing it with special devices like spinner. The fibers are elongated by jet of air, steam or flame. The product is cured in ovens and formed in-to familiar insulation bats and blankets or chopped in- to lose-fill insulation used home, commercial and industrial buildings. The slag wool has a wide range of applications as heat insulating material, fire-proof wall material for houses, heat reserving and sound absorption materials for industrial applications. The fibers are noncombustible and have melting point over 1100 oC; they are used in protection against fire. The fibrous structure and high density of slag wool insulation offer excellent sound absorption properties, making these products an outstanding part of overall wall system designed to reduce sound transmission. It resists the growth of mild, fungi and bacteria because it is inorganic. Competitive advantages of BF slag insulators are as follows: Because of using less silica compared with similar kinds of hasnt danger of pulmonary disease and doesnt cause sensitiveness for skins. Standard amount of SiO2 in insulators shows that its not harmful for environment and can return to ecosystem. Low heat conduction coefficient of insulators has caused their high insulating power.

Fig 5.2 Slag wool sample5.1.6 Ceramic pipe manufacturing by using of molten BF slagIn the first stage, moltenBF slag cast in sand mould, later it cast in centrifugal mould BF slag is usually melilite (solid solution series of gehlenite, 2CaO.Al2O3.SiO2, and akermanite, 2CaO.MgO.2SiO2) with a small amount of calcium sulphide (oldhamite)