23
2
Waste from Metal
Processing Industries
M. Balakrishnan, V.S. Batra, and J.S.J Hargreaves
CONTENTS
2.1 Iron and Steel .................................................................................................. 24
2.1.1 Slag .....................................................................................................25
2.1.1.1 Slag Utilization ....................................................................25
2.1.1.2 Hot Processing .....................................................................27
2.1.1.3 Recovery of Iron and Other Compounds .............................29
2.1.1.4 Cement and Concrete ...........................................................29
2.1.1.5 Ceramics (Bricks, Tiles) ......................................................30
2.1.1.6 Adsorbent ............................................................................. 31
2.1.1.7 Others ................................................................................... 31
2.1.2 Sludge .................................................................................................32
2.1.2.1 Recycling of Sludge Back in Process ...................................32
2.1.2.2 Metal Recovery ....................................................................33
2.1.2.3 Other Applications ...............................................................33
2.2 Aluminium ......................................................................................................33
2.2.1 Red Mud .............................................................................................35
2.2.1.1 Civil and Building Construction and Ceramics ...................37
2.2.1.2 Catalysis and Gas Scrubbing ...............................................38
2.2.1.3 Water Treatment and Use as a Soil Additive .......................40
2.2.2 Dross ................................................................................................... 44
2.2.2.1 Refractory Materials and Cements ......................................46
2.2.2.2 Chemicals and Catalysts ...................................................... 47
2.2.2.3 Metal Production, Metal Casting, and Composites .............48
2.2.2.4 Others ...................................................................................49
2.2.3 Salt Cake .............................................................................................49
2.2.4 Spent Pot-Lining (SPL) ....................................................................... 50
2.2.4.1 Developments in SPL Utilization ......................................... 51
2.3 Copper............................................................................................................. 52
2.3.1 Slag .....................................................................................................53
2.3.2 Floatation Waste .................................................................................55
2.4 Nickel ..............................................................................................................55
2.5 Other Metal Wastes ........................................................................................55
References ................................................................................................................56
24 Conversion of Large Scale Wastes into Value-added Products
Metal ores are complex mixtures of compounds and several steps are used to
obtain the respective metals from them. Pyrometallurgical, hydrometallurgical, or
electrolytic methods are used to extract the metals from the ore and to rene them
depending on the end-use requirements. These steps involve generation of wastes
in large quantities whose properties and hazardous nature vary considerably. With
increasing environmental awareness and rising disposal costs, these wastes are
being seen as raw materials for other applications. In this chapter, the status of use
of wastes generated from different metal industries is discussed and the trends in
research in this area are presented. In case of wastes such as slag where utilization
levels are high, the current common applications are covered. However, for wastes
like red mud, the focus is more on literature studies since the utilization levels are
still low and many exploratory studies on their use are underway.
2.1 IRON AND STEEL
Iron is produced in a blast furnace (BF) where iron ore, coke, and limestone are
charged from the top. In a series of reactions, the iron oxide is reduced to iron by
the reducing gases from the coke and the limestone ux reacts with the impurities
mainly comprised of silica and alumina to form low melting slag. The molten metal
is then taken for steel making. In a basic oxygen furnace (BOF) (or basic oxygen
converter), the molten iron is subjected to the addition of ux and blowing of oxygen.
This oxidizes the impurities like silicon, which react with the ux to form slag. Steel
is also made in an electric arc furnace (EAF) where uxes are added which react
with impurities to form slag. Inaddition to slag, there are also other wastes gener-
ated as part of the ue gas cleaning system, furnace feed preparation, etc. Figure2.1
shows a ow chart for iron and steel making with the waste generation points.
Sintering to
make pellets
Blast furnace
Pig iron
Steel for continuous casting
Steelmaking
(BOF or EAF)
Iron ore, fines
Iron ore
pellets,
coke,
flux
Slag
Sludge
Slag
Sludge
FIGURE 2.1 Iron and steel making process showing the wastes generated.

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