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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 completed. This survey updates the previous mass flow analysis of chromium and chromium compounds (Tørsløv & Hansen, 1985). The analysis was carried out on the basis of information from Statistics Denmark, the Danish Product Register, previously completed mass flow analyses, information from importers and manufacturers. Priorities in this survey were based on a general knowledge about the use and occurrence, hazardousness and potential exposure of chromium, as well as a preliminary analysis of statistical information about the chromium content in products.

Thus, a detailed survey of the use of chromium for surface treatment, wood preservative, pigment, leather tanning, laboratory chemicals, accelerators/catalysts/hardeners, corrosion inhibitors and textiles was completed. Furthermore, a survey of the use of chromium as an alloy metal in connection with iron, aluminium, and copper as well as in the electronic storage industry was carried out at a general level. It has been of special importance to ascertain the use and diffusion of chromium(VI) compounds (hexavalent chromium).

The analysis 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 has been included in the calculation.

Occurrence, production of chromium and chromium compounds

Chromium is found in nature as red lead ore (PbCrO₄, crocoite) and as chromium ironstone (FeO,Cr₂O₃). Metallic chromium is produced by reducing chromium oxide (Cr₂O₃) with aluminium. Chromium occurrences are found in, for example, South Africa, Kazakhstan, India, Brasilia, Finland, Turkey, and Zimbabwe. These countries represent more than 90% of the production. Metallic chromium is used as an alloy metal in iron, aluminium and copper, as well as surface coating. In the Danish Product Register, about 130 chromium compounds are registered, of which chromium(III) oxide, chromium (VI) oxide, metallic chromium and lead(II) chromate make up more than 95% of the registered consumption. No production of chromium compounds takes place in Denmark.

Chromium balance for Denmark

In Figure 1, a simplified chromium balance for Denmark is shown. The balance is described and discussed in part 6.3 "Chromium balance for Denmark 1998-2000".

Figure 1
Chromium balance for Denmark 1999.

Chromium is imported in metallic form with iron, aluminium, and copper, as well as with their respective alloys. Furthermore, chromium is found as an impurity in these metals. The export of chromium is as metal scrap, which is exported for recycling.

Chromium compounds are imported for production of finished goods in Denmark or as an ingredient in finished goods. In most products, the chromium content gives no reason for labelling or any other focus, and therefore knowledge of the actual content of chromium compounds as well as emissions to the environment is scanty.

Use of finished goods containing chromium as well as emissions to the environment are summarised below.

Consumption

The consumption of chromium in alloys, chemical compounds, and as a trace constituent has been analysed for Denmark for the year 1999 (the average of the years 1998, 1999 and 2000).

The consumption of chromium and chromium compounds in Denmark divided among fields of application is summarized in Table 1. The survey of different fields of application was carried out at different detailed levels as described in part 1.4 "Prioritisation of the survey" on the basis of information from Statistics Denmark, the Danish Product Register, previous mass flow analyses for other materials, and contact to selected trade associations, importers and manufacturers.

Table 1
Consumption of chromium, chromium compounds and chromium as a trace constituent in Denmark in 1999 (average of the years 1998, 1999 and 2000) divided among fields of application. The consumption of Cr(VI) is also included for the relevant applications.

In the survey of the consumption of chromium compounds, it has been important to ascertain the consumption and emission of chromium(VI) compounds, as they form a considerably larger environmental and health risk than other chromium compounds. Use of chromium(VI) compounds is subject to a number of restrictions and this is why the consumption within some fields of application is decreasing.

Chromium, metallic

Metallic chromium is primarily found as an impurity and alloy metal in iron, aluminium, and copper. The survey of this is also primarily based on updating previous mass flow analyses of these substances. This application represents more than 97% of the total consumption of chromium in Denmark. Metallic chromium is also found as a coating, for instance on metals and plastic as chromium plating. The actual process is described under chromium compounds. Recycling of metallic chromium is done with iron, aluminium, and copper, and a substantial part of this is exported as alloy steel for recycling.

Chromium compounds

Chromium compounds are used in a number of different products as surface treatment, colour pigments, in leather tanning, as wood impregnation, in textiles etc. The use of chromium compounds in wood preservatives has been terminated, but because of a long lifetime, disposal of impregnated wood will be a source for chromium in waste flows in future. No real recycling of chromium compounds takes place.

Chromium as a trace constituent

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

Emissions to the environment

The available information about disposal and dispersal of chromium to the environment in Denmark in 1999 is summarised in Table 2. The emissions to the different recipients are discussed below.

Emissions to air

Chromium and chromium compounds are constant compounds with a high melting point/boiling point. This means that emissions to air are primarily connected to thermal processes. Thermal processes occur in waste incineration, energy conversion, and in production and processing of iron, aluminium and copper, as well as alloys of these metals. Primary production of these metals or alloys does not occur in Denmark, but processing might occur just as recycling of metals occurs in Denmark. The most important general source to emission of chromium to air is considered to be energy conversion.

Emissions to water

Emissions of chromium and chromium compounds to the aquatic environment occur, for instance through the discharge of process chemicals from surface treatment or wastewater from the paint/lacquer industry. In the use phase, emissions to water will primarily occur through corrosion of iron, steel, aluminium, and copper, through use of paints containing chromium pigments, through leaching from impregnated wood, and through disposal of laboratory chemicals. The largest secondary source of chromium in water is via atmospheric deposition or discharge from municipal wastewater treatment plants.

Emissions to soil

Emissions of chromium and chromium compounds in the use phase will primarily be found through corrosion of iron, steel, aluminium, and copper, leaching from impregnated wood and painted surfaces, as well as peeling from chromium-plated products. The largest secondary source of chromium to soil is via atmospheric deposition or from sludge from municipal wastewater treatment plants.

Landfill

Chromium and chromium compounds are supplied to landfills in products containing the substances. The most substantial sources are estimated to be disposal of iron and stainless steel, as well as residual products from waste incineration. Furthermore, smaller amounts will be supplied to landfills with construction waste, leather, and textiles.

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

Summarizing evaluation

The total consumption of chromium is calculated at 25,000-30,000 tonnes/year, more than 97% being metallic chromium and the rest being chromium compounds and a trace constituent. Of this chromium(VI) compounds are estimated to be 50-53 per/year. The consumption of chromium(VI) compounds is estimated to be falling as a result of the use restrictions. Metallic chromium in waste is recycled to a large degree together with iron, aluminium, and copper, while there is no recycling of chromium compounds.

The most substantial emission to air is from energy conversion processes, while the most substantial contribution to the aquatic environment is atmospheric deposition. The most substantial emissions to soil are atmospheric deposition and processing, use and disposal of iron and steel.

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