Documents\Palladium-contents. Pdf

Sources of Human and Environmental Exposure
31
Table 6. Distribution of all platinum group metals in the environment
a
Region
Estimated concentration of PGMs 
Earth
~30 mg/kg
Mantle (siliceous lithosphere)
~0.05 mg/kg
Earth’s crust (attainable by mining)
~0.01 mg/kg
Hydrosphere
<10
–6
 mg/litre
Biomass (dry matter)
<10
–7
 mg/kg
a
 
Adapted from Renner & Schmuckler (1991).
Table 7. Palladium output, by country
a
Country
Palladium output (tonnes)
1981
1987
1990
1993
1995
1996
1997
1998
Soviet
Union/
Russia
b
 
44.5
55.7
58.2
71.5
40
37.9
149.4
180.5
South Africa
28.3
33.9
38.2
43.4
44
103.6
56.3
56.3
Canada and
USA
5.0
5.9
11.5
11.5
13
7.5
17.0
20.5
Others
2.2
2.8
2.2
2.2
2.0
3.4
3.0
3.7
Total
(tonnes)
80.0
98.3
110.1
128.6
99.0
152.4
225.7
261.0
a
 
1981–1993 from Kroschwitz (1996); 1995 from Loebenstein (1996); 1996
from MMAJ (1999); 1997–1998 from Cowley (1998, 1999).
b
 
Russian values for 1981–1996: sales to the West.
3.2.1.1
Production processes
Several enrichment steps follow the mining of ores, either under-
ground  or  by  opencast  (strip)  mining  (Renner  &  Tröbs,  1986; Renner,
1992; Kroschwitz, 1996). In the case of PGMs from South Africa, the
crude  ore  is  first  crushed  and  pulverized.  The  metal  sulfide  particles are
then separated from the gangue by froth flotation.
The  PGM   sulfide  pulp   is  melted  in  an  electric  furnace to produce
matte  containing principally copper, nickel and iron  sulfides, together
with  the  PGMs.  Nickel  and  copper  are  separated  by acid leaching to
yield  the  final  PGM   concentrate.  The  concentrate  is  then refined, using
either a selective dissolution and precipitation technique or a solvent
extraction  process, whereby ammonium-chloro-complexes (e.g.,

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EHC 226: Palladium
32
chloropalladosamine)  are  formed.  Thermal  decomposition  (calcination)
of chloropalladosamine gives the impure palladium sponge.
3.2.1.2
Recycling
Processing  of  recycled  material, including both new and old scrap,
resulted  in  the  recovery  of  an  estimated  60  tonnes of PGMs during
1995 in the USA (Loebenstein, 1996).
Scrapped  automobile  catalysts  contributed 5.4 tonnes to the world
palladium  demand of 72 tonnes in the automotive sector in 1998
(Cowley,  1999).  According  to  Cowley (1999), 5.12 tonnes of palladium
were  recovered from old automobile catalysts in North America and
Japan in 1998. The ultimate fate of many automobile catalysts may be
disposal  in  waste  dumps.  Recycling methods comprise pyrometallurgi-
cal  refining techniques that are similar to those described previously
in  section  3.2.1.1 (e.g., Degussa, 1997). The quantities recovered from
s crapped  electrical  components  (electrical  contacts)  are  larger, but
again  no  figures  exist  (Cowley,  1997).  It  is  expected  that  some of the
utilized  palladium  ends  up  in  wastes  or  incineration  ashes.  It  can also
be  expected  that  dental  alloys are completely recycled if dental
prostheses have to be replaced.
Recycling rates for electronic equipment and automobile catalysts
depend  on  both  economic  and political decisions in the different
countries.
3.2.2
Processes for the production of important palladium
compounds
Many   palladium compounds are in use as catalysts, as precursors
of metallic palladium, in preparative chemical production, in photog-
raphy,  in  electroplating and in medicine. The production processes of
some important compounds are described below:
<
Ammine  complexes  of  pallad i u m: Addition of ammonia to
solutions of palladium(II) chloride first causes the formation of a
pink  precipitate  of  the  binuclear complex Pd(NH
3
)
4
PdCl
4
,
Vauquelin’s  salt,  which  is  converted  to  soluble  tetraammine palla-
dium(II) chloride by further addition of ammonia. Acidification of
this solution yields the sparingly soluble light-yellow trans-

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Sources of Human and Environmental Exposure
33
diamminedichloropalladium(II).  Ammonium  hexachloropalladate(IV)  is
an oxidation product of ammonium tetrachloropalladate(II).
<
Palladium(II)  ace tate: This compound is prepared from palladium
sponge (or nitrate) and glacial acetic acid.
<
Palladium(II)   chloride:  Palladium(II)  chloride  is prepared by the
careful  evaporation  of  a  solution  of  hydrogen tetrachloropalla-
date(II) in hydrochloric acid, preferably in a rotary evaporator.
<
Palladium(II) nitrate: This compound is prepared from palladium
and nitric acid (Renner, 1992).
<
Palladium(II)   oxide:  Palladium(II)  oxide is obtained by reaction
of  palladium  black  (powder)  with  oxygen or air at 750 °C.
Decomposition  occurs  at  850  °C.  A  catalytically active palladium
preparation analogous to platinum(IV) oxide (PtO
2
[H
2
O]
x
)  can  be
obtained by evaporating a solution of hydrogen tetrachloropalla-
date(II) and sodium nitrate and fusing the product (Cotton &
Wilkinson, 1982; Neumüller, 1985).
<
Tetrachloropalladic(II) acid: The metal is dissolved in hydro-
chloric  acid/chlorine or hydrochloric acid/nitric acid. If dissolution
occurs  below  about  50  °C,  hexachloropalladic(IV) acid is formed
first.  Commercial  solutions  in  hydrochloric acid contain 20%
palladium (Renner, 1992).
3.2.3
Uses of palladium metal
From  Table 8, it can be seen that demand for palladium, in
particular for use in automobile catalysts, is increasing.
3.2.3.1
Electronics and electrical technology
Palladium  metal  or  silver–palladium  powder  pastes   are  important
products  in  the  production  of  many  electronic  components.  T h e
metallization process is often carried out with silver–palladium thick
film  paste.  The  pastes   are  used  in  active  components such as diodes,
transistors, integrated circuits, hybrid circuits and semiconductor
memories.  They   are  also  needed  for  passive  electronic  components,

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