33
Platinum [Pt, 78]
33.1 INTRODUCTION
Platinum (Pt) is a dense, malleable, precious, transition metal of group 10 in the
periodic table of elements. It is one of the rarest in the Earth’s crust, at an average
abundance of approximately 5 μg/kg. It is considered a noble metal and exhibits a
remarkable resistance to corrosion in various conditions. Its highest contents, up to
3 μg/kg, are in ultramafic rocks and the lowest, 0.05 μg/kg, in limestones. Its mean
content of coal in the United States is <1 μg/kg (Finkelman 1999). However, there
are reported much higher Pt concentrations in coal, up to 230 μg/kg (Li vide KabataPendias 2011). It exists in higher abundances on the moon and in meteorites.
As a very nonreactive metal, Pt occurs mainly in alloys with other platinum
group metals (PGMs). Its more common minerals are as follows: sperryllite, PtAs 2 ;
cooperite, (Pt,Pd)S; braggite, (Pt,Pd,Ni)S; telluride, PtBiTe; arsenite, PtAs 2 ; and nigglite, PtSn. Several sulfide minerals, and ilmenite, zircon, and gadoline may be hosts
for Pt, within the range of its concentrations from 0.2 to 2 mg/kg. Platinum may be
combined with other PGMs and deposited in alluvial sediments, from which it was
mined.
Platinum has various oxidation states, from +2 to +5, and the most common is +4
state. It occurs in some Ni and Cu ores, as well as in some native deposits, mostly
in South Africa, which account for about 80% of the world Pt production. Platinum,
as well as other PGMs, is obtained commercially as a by-product from Ni and Cu
mining and processing.
The global Pt production (rounded) in 2010 was estimated to be 183 t, of which
138 t was produced in South Africa, 24 t in Russia, and 8 t in Zimbabwe (USGS
2011). Platinum is still used, in great quantities, for catalytic converters, laboratory
equipment, electrical contacts, electrodes, thermometers, medical equipments (especially in some implantations), and jewelry. The common use of Pt is as a catalyst
in some chemical reactions. Pt compounds, mainly cisplatin, cis-[Pt(NH 3 ) 2 Cl 2 ], are
applied in the chemotherapy against certain types of cancer. Effluents of some hospitals are considered as a main Pt source in sewage sludge. Its contents in sewage
sludge of some cities in Germany varied (in the last century) from 86 to 266 μg/kg.
Platinum concentrations in ash from sewage sludge is about 300 μg/kg (Pyrzyńska
vide Kabata-Pendias 2011).
33.2 SOILS
The common Pt contents in surface soils vary from 2 to about 40 μg/kg. Its contents in uncontaminated soils are highly dependent on its concentrations in mother
rocks, and relatively high Pt contents, up to 75 μg/kg, are in soils over weathered
norite. The magnetic fraction of these soils contain Pt within the range of 860 to
243