The term ‘slag’ is applied to two main types of industrial materials: unprocessed waste from mining operations and process residues from metal-winning and refining. A new report from Smithers Apex focuses on the most important slags from metal-winning and refining: ferrous slags and residues from the iron and steel industry.
The Future of Ferrous Slag to 2025 examines the factors affecting ferrous slag production to provide a basis for forecasting the quantities likely to be produced up to the year 2025. It looks at current and possible future applications of slag and describes the trends in regulations affecting the market.
In the past, most slags were regarded as waste and disposed of as such, in dumps close to steelworks. As the size of these dumps increased at an alarming rate in industrial areas, ways of treating slags were devised to make them suitable for use in a variety of applications, leaving only a small proportion to be disposed of as true waste.
The first by-product, and still among the most important, was crushed crystalline slag – used as ballast, or aggregate in the place of crushed rock or gravel, predominantly in road making. The most valuable by-product is the result of super-cooling liquid slag as it leaves a blast furnace (or from similar ironmaking equipment). Super-cooling results in a granular, non-crystalline, amorphous material, referred to as granulated blast furnace slag or GBS/GBFS.
The current potential market supply of blast furnace slag is estimated to be 446.8 million tonnes, of which almost 295–300 million tonnes is GBS. The making of steel from blast furnace iron through oxygen conversion (or basic oxygen furnace, BOF) contributes a further 140–145 million tonnes of slag, and the alternative route to steelmaking through electric arc furnaces (EAF) supplies more than 50 million tonnes.
Figure 1: World EAF output, 2009-14 (‘000 tonnes)
Source: Worldsteel and Smithers estimates (*includes Turkey)
According to the report, the total output of ferrous slag is expected to increase only slowly, or to stagnate and decline marginally, because EAF steelmaking capacity is expected to grow faster than BF-BOF steelmaking capacity. This effect can already be seen in the US, where the tonnage of steel produced by EAF works overtook the tonnage produced by BF-BOF works in the 1990s. Since then, further decline in BF-BOF output has led cement and aggregate companies to start importing slag and to invest in new coastal slag treatment installations dependent entirely on imported supplies.
Changes in the Chinese steel industry will contribute substantially to this rising share of EAF steel in world supply. China produces half of world crude steel and BF-BOF steelworks account for over 80% of China’s steel output. The Chinese government is campaigning to replace small and inefficient steelworks with EAF installations.
In the current market it is estimated that total production of ferrous slag of all types amounts to $24.5 billion. While it is possible that supply will increase only slowly, if at all, there is growing demand for slag products, which is likely to ensure that the value per tonne of slag products will increase. The growth in demand has been accelerated by environmental legislation and by direct intervention from governments and international bodies.
Ferrous slag is not only a by-product, but it can also be used as a substitute for products that have high environmental impact. For example, GBS is valued as a substitute for cement clinker. Other products of ferrous slag act as filtering agents for purifying water, for enhancing the productivity of land and for improving marine environments. Slag also provides an insulation material that can replace toxic asbestos.
Demand for slag products has been affected by market cycles. The collapse of construction activity in Europe, as a consequence of the financial crisis, reduced sales of slag for cement and aggregate use. Over the medium term there is every prospect that demand will outrun supply. Currently GGBS meets only an estimated 17% of world cement supply. Slag products as aggregate substitutes meet only 1–1.5% of total demand. These are the largest items of supply; the market share of slag is equally small in the markets served by smaller tonnage slag products (such as filtering gravels and soil improvers).
While environmental considerations potentially extend the market for ferrous slag, realisation of new market opportunities depends on clearing away technical barriers that have hindered the use of some slag products in the past; and on revising regulatory systems, so as to acknowledge the difference between unusable or positively toxic wastes and residues that are essentially by-products.
The Future of Ferrous Slag to 2025 is available now for £4,200. For more information, please contact Stephen Hill on +44 (0)1372 802025 or at firstname.lastname@example.org