10
Cesium [Cs, 55]
10.1 INTRODUCTION
Cesium (Cs) is an alkali metal of the group 1 in the periodic table of elements. Its
concentration in the Earth’s upper crust is within the (rounded) range 4–6 mg/kg.
In igneous rocks, its average content is 4 mg/kg, and increases up to 5–10 mg/kg in
argillaceous sedimentary rocks. Its content in coal is about 1 mg/kg.
The main oxidation state of Cesium is +1. It reveals lithophilic properties and a great
affinity to aluminosilicates. Its common mineral is pollucite, (Cs,Na) 2 Al 2 Si 4 O 12 ·H 2 O,
which contains 5%–32% Cs 2 O, and is of commercial importance.
Data on resources and mine production of Cs are presently not available. There are
given information on Cs reserves, based on occurrences of pollucite and other pegmatite minerals (mainly lepidolite-Li). Cesium reserves, in Canada (and world), are
estimated at 70 kt. There are information that the next largest Cs source, potentially
economic, is in Zimbabwe. Cesium is used in drilling fluid (petroleum exploration),
chemical production, electric power generation, electronics, and medical applications.
Cesium has several radioactive isotopes, but only 137 Cs has a long half-life of
about 30 years, and is used in medical treatments (cancer). However, it is of a high
health risk if released into the environment. Great amounts of this isotope were
released during the Chernobyl accident in 1986.
10.2 SOILS
Cesium contents in various soils vary from <1 to 30 mg/kg (Table 10.1). Its mean
concentration in soils of Europe is 5.6 mg/kg (FOREGS 2005). Its levels in Bulgarian
soils are 2.2–16.7 mg/kg, being the highest in surface forest soils and chernozems.
This may suggest that soluble organic matter (SOM) has the capability to absorb Cs.
Cesium contents in soils from various countries are reported as follows (in mg/kg):
Japan, 1–11; Switzerland, 0.3–4.5; Bulgaria, 2.2–16.7; and the United States, 0.4–5.1
(Kabata-Pendias 2011).
Cesium and its compounds are easily water soluble, but in soils, they are strongly
adsorbed by clay minerals, especially by illites and apatite. Dust samples from
roadside in the vicinity of metal factories contain Cs within the range from 1.53 to
3.63 mg/kg (ATSDR 2002b).
10.3 WATERS
Cesium concentrations in water are low, usually do not exceed (0.6 μg/L), and are
higher in seas and oceans, than in rivers (Table 10.1). The worldwide mean Cs content in river water is estimated at 0.011 μg/L, and its river flux at 0.4 kt/yr (Gaillardet
et al. 2003).
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