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The Elements in the Second Rank

10 Platinum

10.1 Identity

Table 10.1
CAS No., EINECS No. and molecular weight for platinum. Data from [3]

10.2 Physico-chemical properties

Platinum is a heavy metal belonging to group VIII in the periodic table (the platinum group). The valences +2 (Pt(II)), and +4 (Pt(IV)) are most common, but +3 and +6 are also possible [1, 2].

In its pure form platinum is silver-white. It is not oxidised even at high temperatures. Platinum cannot be dissolved in concentrated hydrochloric acid or nitric acid, but dissolves as gold in aqua regia, forming H₂PtCl₆ [1]. Furthermore it is attacked by hot, concentrated sulphuric acid or phosphoric acid, and can be dissolved in molten alkali salts. Platinum binds to organic matter as Pt²⁺ or as Pt(OH)₂⁰ in the aqueous environment.

Table 10.2 shows selected physico-chemical data for platinum.

Table 10.2
Physico-chemical data for metallic platinum. Data from [1, 9]

10.3 Uses and consumption

10.3.1 Uses

The use of platinum to catalytically convert nitrous gasses from e.g. car engines (both gasoline and diesel) is regarded as the quantitatively most important. The content of platinum in a catalytic converter of an automobile is on average about 1.5 g [7].

The catalytic properties of platinum are also used in the chemical and especially in the petrochemical industry [7]. The amount of platinum used in jewellery is similar to what is used for catalytic conversion purposes [7].

In the electronics industry platinum is used for especially in the production of printed circuit boards. Platinum used in printed circuit board shall be recycled according to a Danish government order [4].

Other uses in the electronics industry are high temperature thermometers, thermo elements, crucibles and other laboratory equipment [11].

Platinum is used in displays for computers and televisions [7].

Some medicals contain platinum, e.g. cis-platinum, Pt(NH₃)Cl₂, used in cancer treatment [7].

Platinum is used for special equipment in e.g. airplanes, automobiles, electronics and the pharmaceutical industry [8].

10.3.2 Consumption

The global production was 150 tons in 1995, and the consumption in USA was approximately 60 tons [7]. From the per capita consumption in USA, the Danish consumption is assumed to be 1.1-1.3 tons per year (1995 numbers).

The Danish consumption is probably higher today, even though platinum in recent years has been replaced with the cheaper palladium. The development of fuel cells for use in the automobile industry possibly equalizes the decreasing consumption for catalytic converters.

In Table 10.3, the yearly consumption of 1.1-1.3 tons in Denmark is divided into consumption areas.

Table 10.3
The relative distribution of global consumption and the Danish use of platinum in 1996 based on [7]

Due to the high market price on platinum its recycling has economical interest. In USA, the recycling is estimated to account for 30-40 % of the consumption. If this recycling percentage is also valid in Denmark, the yearly loss to the Danish environment is 560-900 kg.

10.4 Emissions to and occurrence in the environment

The concentration of platinum in the aquatic and terrestrial environment is very low, see Table 10.4.

Table 10.4
Typical background concentration of platinum in the environment. Data from [6, 7, 10]

From the literature search no data on the platinum level in Danish waste was found. Hence, the measurements conducted as part of this study, are the only available data on emissions and waste streams, see Table 10.5. A Swedish study confirmed that the platinum concentration in general was lower than the concentration of palladium [7]. I cinder, fly ash, sludge and sediment 30, 87, 34 and 4.2 µg/kg dw was found, respectively [7].

Table 10.5
Levels of platinum in selected emissions and waste products from measurements conducted as part of this study in the autumn of 2001.

Due to the commercial interest in platinum recycling, the emissions from waste are assumed to be lower than emissions related to the use of platinum containing products. This is confirmed by the low concentrations found in waste from Swedish incineration plants.

Emission of platinum is a result of its use in catalytic converters, and the concentration of platinum is high close to roads with a heavy traffic load [7]. Despite this, the concentration of platinum is low in sediment from road runoff retention basins compared to palladium, see Table 10.5. Since platinum has been detected in sediments of lakes close to urban areas it seems probable that emission of platinum from motor vehicle catalysts can be spread over medium to long distances [7]. Coal contains platinum in a concentration of 0.001 to 1.7 mg/kg [7], and it is expected that a minor amount of platinum will be emitted from coal-fired power plants.

The concentration of platinum in different environmental matrices is given in Table 10.4. Compared to e.g. palladium, soil and earth crust has a relatively high concentration of platinum.

10.5 Danger classification

Several platinum compounds such as chloro platinates are toxic by ingestion, sensitizing and irritating to skin and/or can result in serious eye damage [8]. Platinum compounds found on the Danish list of dangerous compounds are not classified as dangerous to the aquatic environment. According to [7], platinum should be classified as dangerous to the environment with risk sentence R50 (very toxic to aquatic organisms).

Table 10.6
Classification of and risk phrases for platinum compounds

10.6 Toxicology

Platinum it its metallic form is relatively harmless, but allergic dermatitis from especially complex salts is known [9, 13]. Platinum is as the other noble metals relatively toxic on ionic form or soluble form. This type of exposure is, however, rare due the high price of the metal. Chloroplatinates are toxic by ingestion and irritating to skin.

10.7 Environmental properties

10.7.1 Environmental chemistry

Platinum is found as Pt(OH)₂⁰ in fresh water or bound to organic matter as Pt(II). In seawater PtCl₄^2- is also seen. Platinum can be assimilated by algae and plankton in the aquatic environment, and is released once the organic material degrades. It is not strongly bound to particles. No volatile Pt-compounds exist, and platinum is predominantly found in soil, sediment and the aquatic environment [7]. Platinum emitted from catalytic converters can be distributed over significant distances and will accumulate in e.g. sediment. It has been shown that platinum emitted from catalytic converters is biologically available.

10.7.2 Environmental toxicology

Hexachloro platinum acid has an acute toxicity on Tubifex tubifex of 61 µg/L determined in a 96-hour test, see Table 10.7. According to this result, hexachloro platinum acid is very toxic to aquatic organisms.

Table 10.7
Test results for environmental toxicity. Data from Aquire [5]

10.7.3 Bioaccumulation

Platinum is not an essential micro nutrient, and the available information does not give any reason to regard platinum as bioaccumulating.

10.8 Conclusions

The catalytic properties of platinum are widely used in the chemical and the petrochemical industry. Platinum-containing waste is collected for recycling, and emission is related mainly from use of products with platinum. The concentration of platinum in areas with much traffic is high, and platinum can be distributed over relatively long distances according to the wind conditions. The concentration of platinum in sludge and fly ash is low. Several platinum compounds are toxic, and hexachloro platinum acid is toxic to aquatic organisms.

10.9 References

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