Management of production residues

Radioactivity in scrap

[ 51, UN ECE 2006 ] [ 215, BSS 2007 ] [ 260, Germany 2007 ] [ 373, Eurofer 2007 ]

Control of radioactivity of input scrap is an important issue, which is followed in detail by an expert group from the United Nations Economic Commission for Europe (UNECE). The UNECE Group of Experts developed in 2006 provide a framework of recommendations and examples of good practice which is based, as much as possible, on existing national, regional and international instruments and standards and on national experience. Their works include:

• recommendations on monitoring and response procedures for radioactive scrap metal

• international training and capacity building strategy for monitoring and response procedures (2007)

• Report on the Improvement of the Management of Radiation Protection Aspects in the Recycling of Metal Scrap, ISBN 92-1-116789-2 (2002). These guidelines represent the industrial reference for handing this issue, which is not exclusive to the steel companies but to all the stakeholders involved, from the administration departments to recovery and recycling in metal industries (www.unece.org/trans/radiation/radiation.html).

Source:[ 243, Eurofer 2007 ]

Figure 2.11: Example for the management of production residues such as by-products and wastes in an integrated steelworks

2.3.2.1 Internal use of integrated steelworks residues

Most of the residues arising within an integrated steelworks have a high content of iron, carbon, calcium and other useful components and can replace primary raw materials such as iron ores, coal, slag formers, heavy oil and cokes. Indeed, the management of residues in an integrated steelworks is characterised by the application of advanced integrated processing techniques designed to retain, as much as possible, all of the useful components contained in residues within the steelmaking process.

The identification and separate collection by material categories (e.g. by chemical composition, particle size, or oil content) are necessary preliminary conditions to ensure proper use inside the steelworks without negative effects in terms of production efficiency, product quality and environmental protection.

The iron-bearing fraction of the various types of crude slag, iron- and carbon-bearing dusts and sludges from gas cleaning systems, used oil, new scrap and scale can be recirculated back through sinter plants, pellet plants, coke ovens, blast furnaces, and BOF plants. The fine materials tend to be recirculated through the sinter plant, whereas coarser materials are more often returned to the blast furnace or BOF plant. In order to return certain fractions to the blast furnace and BOF plant, briquetting plants are often employed, where all sorts of fine graded residues are combined into cold bonded bricks/briquettes that are easier to handle and can be used elsewhere within the process. In particular, the dusts or sludges from the steelmaking plant can be briquetted or pelletised and afterwards used in the steelmaking plant when the non- ferrous content is not too high.

In Section 2.5.4.4 specialised recycling facilities for iron-rich residues are described. Some of these facilities make the direct recovery of liquid iron possible; others serve as a pre-treatment stage to reuse the residues in the blast furnace or the electric arc furnace. The presence of high concentrations of unwanted compounds such as alkalis, heavy metals and mineral oil sets limits on the recycling of iron-rich residues.

Table 2.7 shows a compilation of different uses for steel slags in Europe.

Table 2.7: Use of steel slags in Europe

Use of steel slags (¹) % Amount

Cement production 1 152

Road construction 45 6840

Hydraulic engineering 3 456

Fertiliser 3 456

Internal recycling 14 2128

Interim storage 17 2584

Final deposit 11 1672

Other 6 912

Total 100 15200

(¹) ‘Steel slags’ refers to slags from BOF, secondary metallurgy and EAF.

NB: Figures are from 2004 and correspond to 12 EU member states (AT, BE, DE, DK, ES, FR, FI, LU, NL, UK, SE, SK).

Source: [ 174, Euroslag 2006 ].

2.3.2.2 External applications of integrated steelworks residues

Zinc-rich sludges and dusts are generated during BOF gas cleaning and BF gas cleaning.

Nevertheless, the zinc content is not high enough to make reuse economical. Only some of these sludges and dusts can be used, so almost all iron and steel plants have a large deposit of zinc- rich sludges and wastes.

If the non-ferrous metal content of the dusts or sludges arising in the integrated steelworks is sufficiently high to ensure its technical and economic feasibility, some non-ferrous metals can be recovered in external metal production and recycling plants. For example, steelmaking dusts with enriched zinc concentrations can be used as a raw material within the zinc sector instead of zinc ores.

2.3.2.3 Disposal of integrated steelworks residues

Small parts of the overall quantity of residues from an integrated steelworks have no economic use (either internally, within the installation, or externally) and some disposal is inevitable.

Materials usually requiring disposal include:

• fine dust/sludge from BF gas cleaning

• runner refractory rubble from the BF

• fine dust from BOF gas scrubbing (if a wet cleaning process is used)

• in some cases, the dust which contains high amounts of alkali chlorides and heavy metal chlorides from the last field of electrostatic precipitators, bag filters or scrubbers used to treat the off-gas from sinter strands.

Many integrated steelworks have their own internal, certified landfill facilities whilst other companies rely on external landfill sites. In all cases, landfill sites must be authorised to receive the particular wastes.