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Mass Flow Analysis of Chromium and Chromium Compounds

2 Chromium use in Denmark

2.1 Iron and steel

Chromium is used as an alloy metal in ferrous chromium, a metal which contains very large amounts of chromium. It is also used in iron and various types of steel, primarily stainless steel. The use of metallic chromium in Denmark has been determined on the basis of information from Statistics Denmark on the registered foreign trade in Denmark and the registered sales in Denmark of products of Danish manufacture. The consumption of metallic chromium in industrial products has been determined on the basis of supply information from the Statistics Bank provided by Statistics Denmark. This information was divided into so-called Broad Economic Categories (BEC).⁷ The information from the Statistics Bank has been compared with information about stainless steel contents in various product types (The Danish EPA's Product Database). All figures are for the period 1998–2000. Table 2.1 shows the supply of metallic chromium on the basis of production, import and export of finished goods, raw materials and semi-finished goods made from iron, steel and ferrous chromium.

2.1.1 Products and semi-finished goods made from iron and steel

Ferrous chromium is a chromium-iron alloy with a chromium content of 60–65%. It is produced by reducing chrome iron ore with coke and/or silicon at high temperatures in furnaces. This alloy is primarily used in the manufacture of stainless steel, a process accounting for up to 90% of the total consumption of ferrous chromium.

The designation stainless steel covers a wide variety of alloys, including chromium steel (which contains 12–13% chromium), the widely used austenitic steel or 18/8 steel (18% chromium and 8% nickel), and particularly heat-resistant special steel containing 25–30% chromium and up to 15% nickel. Austenitic steel accounts for 70–90% of the stainless steel used in Denmark (Sandvik Steel Denmark, 2002; Avesta Polarit, 2002; Aco-drain, 2002).

As stainless steel contains relatively large quantities of chromium, certain significant product groups containing stainless steel have been included in the calculations of the metallic chromium supply in Denmark. Large portions of the finished goods which contain steel are included in calculations along with many other materials. As a result, the estimated flows in and out of Denmark are subject to considerable uncertainty.

The designation alloyed steel covers hundreds of steel types where steel is alloyed with other metals. The main reason for alloying steel is a desire for greater hardness and strength. Many types of alloyed steel contain chromium, but the relative quantities vary from 0.1% to 12.5%. A US study sets the chromium contents in the steel alloys used at 0.68+0.11% (US Bureau of Mines, 1994). It has not been possible to confirm this figure with people within the iron and steel industry in Denmark. The reason was that none of the people asked felt able to offer an estimate for the average chromium content in alloyed steel due to the many types of alloys found in the market. As the information from Statistics Denmark on import, export and production of alloyed steel does not provide any details about the types of alloyed steel found within the individual product groups, we have chosen to apply an average chromium content of 0.5–0.8% in alloyed steel.

The group of iron and unalloyed steel which is chromium-plated comprises products which are coated with a layer of chromium.

Iron and unalloyed steel contains chromium as an impurity. It is estimated that the chromium content due to such impurities is in the region of 0.05%. (Det Danske Stålvalseværk, 2002a/b).

Table 2.1
Import, export and Danish production of goods, raw materials and semi-finished goods

Stainless steel is not produced in Denmark. Scrap stainless steel is exported in order to be used as a raw material once again. According to Avesta Polarit (2002), the total production of new stainless steel is made up of 95% recycled steel and 5 % new raw iron.

Det Danske Stålvalseværk was the only manufacturer of steel in Denmark. Approximately 75% of the total quantities produced there were used for export (Det Danske Stålvalseværk, 2001). This steel was made from 90% scrap steel and 10% new raw iron (Det Danske Stålvalseværk, 2002a). The scrap steel primarily comes from Danish scrap merchants, whereas the raw iron comes from Russia and Poland. A total of 20% of the steel used in Denmark comes from the Stålvalseværk, while the rest is imported (Det Danske Stålvalseværk, 2002a; Stålforeningen, 2002).

Scrap metal and iron ore only contains small quantities of chromium – around 0.01% (Kjeldgaard, 1991). Naturally, this chromium will reappear in the steel materials made. Suppliers of scrap steel are good at sorting out scrap made from alloyed steel and cast steel, as these types of steel attract higher prices. This means that the chromium content in the steel produced remains low. As the steel is manufactured, it is monitored for levels of chromium and other substances. If the chromium levels are too high, the steel is diluted by means of additional raw iron (Det Danske Stålvalseværk, 2002a). During the production process, ferrous chromium is added to harden the steel. In 2001, for example, ferrous chromium was added in quantities corresponding to approximately 580 tonnes of pure chromium. Chromium sand is also used to transport the finished steel out of the furnaces. In 2001, a total of 170 tonnes of chromium sand was used, corresponding to approximately 16 tonnes of pure chromium (Det Danske Stålvalseværk, 2002b).

In 2001, Det Danske Stålvalseværk produced approximately 750,000 tones of raw steel. Approximately 665,000 tonnes were used for steel products (Det Danske Stålvalseværk, 2002b). Table 2.2 presents the mass balance for heavy metals in general and specifically for chromium per tonne of raw steel in connection with steel production.

Table 2.2
Mass balance for chromium and heavy metals in general in connection with production of 1 tonne of raw steel (calculated on the basis of Det Danske Stålvalseværk, 2001; 2002b)

This means that production of 750,000 tonnes of raw steel entails disposal / deposit of 2.25 tonnes of chromium. Table 2.3 shows the discharges of chromium into water associated with production of sheets and bars, respectively, at Det Danske Stålvalseværk.

Table 2.3
Discharges of heavy metals into water associated with production of steel at Det Danske Stålvalseværk (Det Danske Stålvalseværk, 2001)

In 2000, a total of 326,000 tonnes of steel sheets and 223,000 tonnes of bar steel was produced. This corresponds to discharges of heavy metals into water in the region of 0.34 tonnes per year. We do not know the exact quantities of chromium involved, but on the basis of the information in Table 2.2 it is estimated that chromium accounts for between 5 and 10% of all the heavy metals. This corresponds to discharges of between 0.017 and 0.034 tonnes chromium each year. The chromium content of the landfill at Det Danske Stålvalseværk has not been assessed.

If the same assumption is applied to a calculation of chromium emissions to air, we arrive at the following figure: emissions of 0.12–0.24 g per tonne raw steel or 0.09–0.18 tonnes chromium per year from production at Det Danske Stålvalseværk.

2.2 Aluminium

Metallic aluminium may contain small amounts of chromium, mainly in the form of impurities. In the Combined Nomenclature (CN), metallic aluminium is divided into unalloyed and alloyed aluminium, and these categories are divided into five product groups: bars, profiles, wire, sheets/strip/foil and pipes. In the CN, one of the characteristics of unalloyed aluminium is that is has a limit value of 0.1 per cent (by weight) for ingredients other than aluminium. Naturally, this includes chromium. Alloys of aluminium are defined by having greater contents of other ingredients than unalloyed aluminium.

A life cycle analysis of chromium carried out on behalf of US authorities included calculations of the chromium contents in aluminium (US Bureau of Mines, 1994). The study used two methods to calculate the average chromium content of aluminium in general. One of these methods used an average of the chromium contents in aluminium alloys, categorised by alloy class, and this yielded a result of 0.02–0.06% chromium. The other method was based on the average chromium content in the aluminium alloys actually used. The result of this method was 0.13–0.21% chromium. It is, however, believed that the latter method results in too high a chromium content, as it only includes types of aluminium for which the chromium contents have been specified.

Based on the chromium contents in aluminium mentioned above, it is assumed that the chromium contents for unalloyed and alloyed aluminium as a whole are between 0.02% and 0.1%.

Table 2.4 shows information from Statistics Denmark about import, export, production and supply of aluminium for the years 1998–2000. This information is listed by CN nos. in Appendix B.

Table 2.4
Import, export and production of raw materials and semi-finished goods made from metallic aluminium (Statistics Denmark, 2001b)

In a mass flow analysis made for aluminium for 1994, the supply of raw materials and semi-finished goods made from metallic aluminium and aluminium alloys is calculated to be 140,095 tonnes (Hansen et al., 1999). Compared to the supply for 1994, the average supply for 1998–2000 is approximately 20% higher. This is consistent with the fact that there has been a general increase in the use of aluminium (the Secretariat for Aluminium and Environment, 2002).

Table 2.5 shows the mass balance for aluminium in Denmark as an average of 1998–2000. The figures have been rounded up. This mass balance was established on the basis of an assumption that the aluminium balance has remained unchanged in 1998–2000 compared to 1994. This assumption is subject to some uncertainty, but is deemed to be acceptable. This is because the contribution from aluminium to the mass flow of chromium in Denmark is of minor significance compared to other sources of chromium, partly due to the amounts involved, and partly because the chromium involved is metallic-bound chromium which will not appear as hexavalent chromium if it enters the environment. In order to counteract the uncertainty associated with extrapolating current values on the basis of 1994 figures, the interval quantities include the 1994 situation and a 20% increase in quantities.

Table 2.5
Mass balance for aluminium in Denmark 1998–2000 (Statistics Denmark, 2001b; Hansen et al., 1999)

2.3 Copper

Like aluminium, metallic copper contains certain amounts of chromium. In the Combined Nomenclature (CN), copper is divided into the following eight product groups: refined copper; copper alloys; master alloys; bars and rods; profiles, wire; plates/sheets/strip/foil; and tubes and pipes. The contents of copper within the product groups vary from approximately 12% for copper foil to 99.9%, for example, for refined copper pipes.

In the Combined Nomenclature, refined copper is characterised by having a limit value for chromium of 1.4% by weight, whereas copper alloys and master alloys may have higher chromium contents. The chromium contents are not described in any more detail for the rest of the product groups.

The chromium content of copper has been calculated in the US authorities' life cycle analysis (US Bureau of Mines, 1994). These calculations are partly based on the average chromium contents of copper alloys based on alloy classes. They are also based on the average chromium content of the actual quantities consumed of copper alloys with specific chromium contents. In both cases, the result of the calculations was chromium contents of 0.024–0.026%.

As it has not been possible to distinguish between different types of copper, it has been assumed that refined copper and copper alloys in general have a chromium content of 0.024–0.026%.

The table below shows statistics on the import, export and production of raw materials and semi-finished goods made from metallic copper. This information is given by CN nos. in Appendix C.

Table 2.6
Import, export and production of raw materials and semi-finished goods made from metallic copper (Statistics Denmark, 2001b)

In a mass flow analysis for copper made for the year 1992, the supply of raw materials and semi-finished goods made from metallic copper is given as being in the region of 39,400–40,100 tonnes (Lassen et al., 1996). Compared to the figures for 1998–2000, this is consistent with the information for 1998 and 1999, whereas a very significant deviation can be seen for the year 2000. This deviation concerns the value of production. As a result, the values for 2000 will not be used. This means that the average value is based solely on the values for 1998 and 1999.

Table 2.7 below shows the mass balance for copper in Denmark. The figures are rounded up and constitute an average of 1998 and 1999 values. The mass balance has been established on the basis of an assumption that the copper balance has remained unchanged in 1998–1999 in relation to 1992. Such an assumption entails a certain level of uncertainty, but is deemed to be acceptable as the supply of copper in society in general has remained unchanged. In addition to this, the contribution made by copper to the mass flow of chromium in Denmark is of minor significance compared to other sources of chromium, partly due to the amounts involved, and partly because the chromium involved is metallic-bound chromium which will not appear as hexavalent chromium if it enters the environment.

Table 2.7
Mass balance for copper in Denmark 1998–1999 (Statistics Denmark, 2001b; Lassen et al., 1996)

2.4 Summary

Chromium occurs as an alloy metal and as an impurity in iron, aluminium and copper. Table 2.8 shows the consumption and dissemination of chromium in connection with use of iron and steel, aluminium and copper in Denmark. This calculation is based on a general calculation of the consumption of iron and steel and an update of previous mass flow analyses made for aluminium (Hansen et al., 1999) and for chromium (Lassen et al., 1996).

Table 2.8

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