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Mass Flow Analysis of Chromium and Chromium Compounds

Summary and conclusions

Introduction

A mass flow analysis of chromium and chromium compounds has been carried out. This survey updates the previous mass flow analysis of chromium and chromium compounds (Tørsløv & Hansen, 1985). The new analysis has been carried out on the basis of information from Statistics Denmark, the Danish Product Register, previously completed mass flow analyses, and information from importers and manufacturers. The work presented in this survey has been ranked in order of priority on the basis of general knowledge about the use and occurrence, hazardousness and potential exposure of chromium as well as on the basis of a preliminary analysis of statistical information about the chromium supply to the community via goods and products.

Thus, a detailed survey of the use of chromium for surface treatment and in wood preservatives, pigments, leather tanning, laboratory chemicals, accelerators/catalysts/hardeners, corrosion inhibitors and textiles has been carried out. In contrast, the survey of the use of chromium as an alloy metal in connection with iron, aluminium and copper as well as in electronic storage media has been carried out at a general level. Special emphasis has been placed on identifying consumption and diffusion of chromium(VI) compounds (hexavalent chromium).

The balance presented covers imports, production and exports for the year 1999, calculated as an average for the years 1998, 1999 and 2000. In cases where discrepancies between data from the three years were observed, the most probable data were included in the calculations.

Occurrence and production of chromium and chromium compounds

Chromium occurs naturally as red lead ore (PbCrO₄, crocoite) and as chromium ironstone (FeO, Cr₂O₃). Metallic chromium is produced by reducing chromium oxide (Cr₂O₃) with aluminium. Chromium deposits are found in countries such as South Africa, Kazakhstan, India, Brazil, Finland, Turkey and Zimbabwe. These countries account for more than 90% of the total production. Metallic chromium is used as an alloy metal in iron, aluminium and copper and for surface treatment. The Danish Product Register includes records of approximately 130 chromium compounds, and chromium(III) oxide, chromium(VI) oxide, metallic chromium and lead(II) chromates account for more than 95% of the total registered consumption. No production of chromium compounds takes place in Denmark.

Chromium balance for Denmark

Figure 1 shows a simplified chromium balance for Denmark. The balance is described and discussed in section 6.3, "Chromium balance for Denmark 1998–2000".

Figure 1
Chromium balance for Denmark 1999

Chromium is imported in metallic form with iron and iron alloys, aluminium and aluminium alloys as well as copper and copper alloys. Chromium also occurs as an impurity in these metals. Chromium is exported as metal scrap; such export is carried out with a view to recycling.

Chromium compounds are imported with a view to production of finished goods in Denmark, and as ingredients in finished goods. In most products, the chromium content is not sufficiently high to warrant labelling or any other special attention. As a result, we do not have a great deal of knowledge about which products contain chromium compounds, nor about the relevant contents of chromium compounds in those products.

Below is a summary of the consumption of finished goods containing chromium and of emissions into the environment.

Consumption

Consumption of chromium as an alloy metal, chemical compounds and as a trace constituent has been analysed for Denmark for 1999 (average for the years 1998, 1999 and 2000).

Table 1 shows an overview of the consumption of chromium and chromium compounds in Denmark, by field of application. The survey of different fields of application has been carried out at different levels of detail as described in section 1.4, "Prioritisation of the survey". The survey was carried out on the basis of information from Statistics Denmark, the Danish Product Register, previous mass flow analyses, and information provided by selected trade associations, importers and manufacturers.

Table 1
Consumption of chromium, chromium compounds and chromium as a trace constituent in Denmark in 1999 (average for the years 1998, 1999 and 2000), by field of application. Figures on the consumption of Cr(VI) are also provided for relevant applications.

In the survey of the consumption of chromium compounds, emphasis has been placed on identifying consumption and emissions of chromium(VI) compounds, as they represent a significantly greater risk to the environment and health than other chromium compounds. The use of chromium(VI) compounds is subject to a number of restrictions, which explains the drop in consumption within some fields of application.

Chromium, metallic

Metallic chromium mainly occurs as an impurity and alloy metal in iron, aluminium and copper. This is also the reason why the survey of metallic chromium is primarily based on updates of previous mass flow analyses of these substances. This particular field of application accounts for more than 97% of the total consumption of chromium in Denmark. Metallic chromium is also used as a coating/surface treatment, for example, for metals and plastic in the form of chromium plating. The actual process is described under the section on chromium compounds below. Metallic chromium in iron, aluminium and copper is recycled. A substantial part of all recycled metallic chromium is exported in the form of alloy steel sent for recycling.

Chromium compounds

Chromium compounds are used in a wide variety of products, e.g. for surface treatment, colour pigments, leather tanning, wood impregnation, textiles, etc. Chromium compounds are no longer used in wood preservatives, but because of the long lifetime of such products, disposal of impregnated wood will be a source of chromium in waste flows for many years to come. Chromium compounds are not recycled as such.

Chromium as a trace constituent

Chromium occurs as a trace constituent in considerable amounts in cement and fossil fuels (primarily in coal). Recycling of residual products (fly ash) in cement contributes to chromium content in cement, as do other raw materials.

Emissions to the environment

Table 2 contains an overview of the information available about disposal and emissions of chromium into the environment in Denmark in 1999. Emissions to various recipients are discussed below.

Emissions to air

Chromium and chromium compounds are stable compounds with a high melting point/boiling point. This means that emissions to air are mainly associated with thermal processes. Thermal processes occur in connection with waste incineration, energy conversion, and production and reprocessing of iron, aluminium and copper, including alloying of these metals. Primary production of these metals or alloys does not take place in Denmark, but reprocessing might well do so, as might recycling of metals. Energy conversion is regarded as the most important general source of emissions of chromium to air.

Discharges to water

Discharges of chromium and chromium compounds into the aquatic environment occur, for example, through the discharge of process chemicals from surface treatment processes or wastewater from the paint/varnish industry. During the use phase, discharges to water will primarily take place through corrosion of iron, steel, aluminium and copper, through use of paints containing chromium pigments, through leaching from impregnated wood or through disposal of laboratory chemicals. The greatest secondary sources of chromium discharges into water are emissions via atmospheric deposition and/or discharges from municipal wastewater treatment plants.

Emissions to soil

During the use phase, emissions of chromium and chromium compounds will primarily take the form of corrosion of iron, steel, aluminium and copper, leaching from impregnated wood and painted surfaces as well as peelings from chromium-plated products. The largest secondary sources of chromium emissions to soil are via atmospheric deposition and/or sludge from municipal wastewater treatment plants.

Landfill

Chromium and chromium compounds end up in landfill as part of a range of products. It is estimated that the most significant sources are iron and stainless steel, and residual products from waste incineration. Furthermore, smaller amounts are added to landfill with construction waste, leather and textiles.

Table 2
Disposal and dispersal of chromium to the environment in Denmark, 1999

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Summarizing evaluation

The total consumption of chromium is calculated at 25,000–30,000 tonnes/year, of which metallic chromium accounts for more than 97%. Chromium compounds and trace constituents account for the remainder. Chromium(VI) compounds are estimated to account for 50–53 tonnes per year. It is estimated that the consumption of chromium(VI) compounds will fall as a result of the restrictions on their use. Metallic chromium in waste is recycled extensively with iron, aluminium and copper, while there is no recycling of chromium compounds.

The most substantial emissions to air come from energy conversion processes, while the most substantial contributions to the water environment come from atmospheric deposition. The most substantial emissions to soil come from atmospheric deposition and reprocessing as well as use and disposal of iron and steel.