**1. Introduction**

Germanium (Ge) was discovered in Freiberg in 1885. One year later, it was isolated from the uncommon mineral argyrodite (Ag8 GeS6 ) by the chemist Clemens Winkler [1]. Ge is a chemical element with a grayish-white color whose position in the periodic table indicates that it has physicochemical properties similar to silicon (Si) and tin (Sn). Germanium has five

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

naturally occurring isotopes, 70Ge, 72Ge, 73Ge, 74Ge, and 76Ge, the latter being slightly radioactive, with a half-life of 1.58 × 1021 years [2]. However, 74Ge is the most common isotope, having a natural abundance of approximately 36% [3].

**% germanium Mineral name Chemical formula MW** 69.41% Ge Argutite GeO<sup>2</sup> 104.61

31.50% Ge Stottite Fe++Ge(OH)<sup>6</sup> 230.50

Ge++++(SO<sup>4</sup>

Ge4

. 7 Ag3 . 3

[GeO<sup>2</sup> (OH)<sup>2</sup>

Ge(SO<sup>4</sup> )2 (OH)<sup>6</sup> •3(H<sup>2</sup>

Ge<sup>0</sup> . 5

2.90% Ge Tsumgallite GaO(OH) 100.05

(Fe,Cu)Al3

S4

Ge(OH)<sup>6</sup>

) 2 (OH)<sup>6</sup> •3.(H<sup>2</sup>

(SO<sup>4</sup> )(CO3

Mo<sup>2</sup> Ge6

> W<sup>2</sup> Ge6

> > Fe<sup>4</sup>

GeSi12O36•(OH,H<sup>2</sup>

(Ge,C)O<sup>4</sup>

O[(Ge,Si)O<sup>4</sup>

O7

(OH) 401.40

Germanium: Current and Novel Recovery Processes http://dx.doi.org/10.5772/intechopen.77997 11

O<sup>9</sup> 641.63

O8 608.87

(OH)<sup>2</sup> 296.43

(OH)<sup>2</sup> 230.81

O<sup>4</sup> 244.11

(Zn,Fe)GeS<sup>4</sup> 390.97

CdGeS<sup>4</sup> 440.38

) •12H<sup>2</sup>

](OH)<sup>2</sup> 292.20

O) 541.06

O 670.75

S<sup>32</sup> 3296.63

S<sup>32</sup> 3470.24

S<sup>16</sup> 1609.66

(Ge,Fe)1-xS4 470.48

Ge1-xS4 705.33

GeWS8 902.31

GeS6 1127.95

S4 495.06

S<sup>32</sup> 3192.14

)GeS6 925.86

](SO4)<sup>2</sup> 952.35

O) 1006.40

O)<sup>6</sup> 2678.79

S<sup>16</sup> 1673.29

S<sup>16</sup> 1655.51

53.91% Ge Eyselite Fe+++Ge++++3

45.27% Ge Otjisumeite PbGe<sup>4</sup>

35.78% Ge Bartelkeite PbFe++Ge3

24.49% Ge Carboirite-III Fe++Al2GeO5

22.36% Ge Carboirite-VIII Fe++(Al,Ge)<sup>2</sup>

22.31% Ge Brunogeierite (Ge++,Fe++)Fe+++<sup>2</sup>

23.59% Ge Krieselite (Al,Ga)<sup>2</sup>

18.57% Ge Briartite Cu<sup>2</sup>

16.49% Ge Barquillite Cu<sup>2</sup>

13.42% Ge Schaurteite Ca3

10.83% Ge Carraraite Ca3

10.79% Ge Maikainite Cu20(Fe,Cu)<sup>6</sup>

10.15% Ge Germanocolusite Cu13V(Ge,As)3

9.86% Ge Ovamboite Cu20(Fe,Cu,Zn)<sup>6</sup>

6.58% Ge Renierite (Cu,Zn)11(Ge,As)<sup>2</sup>

1.30%Ge Colusite Cu12-13V(As,Sb,Sn,Ge)3

10.03% Ge Polkovicite (Fe,Pb)3

9.78% Ge Morozeviczite (Pb,Fe)3

9.10% Ge Germanite Cu26Fe<sup>4</sup>

7.89% Ge Catamarcaite Cu<sup>6</sup>

7.76% Ge Putzite (Cu<sup>4</sup>

7.62% Ge Itoite Pb3

7.21% Ge Fleischerite Pb3

6.44% Ge Argyrodite Ag8

5.60% Ge Calvertite Cu5

2.71% Ge Mathewrogersite Pb<sup>7</sup>

0.32%Ge Cadmoindite CdIn<sup>2</sup>

**Table 1.** Mineral species sorted by the element Ge.

MW: molecular weight. Adapted from [13].

Germanium is a scarce element in the Earth's crust (about 1.6 ppm Ge crustal average) that rarely forms its own minerals [6]. It often appears in the form of the oxide (GeO<sup>2</sup> ) or the sulfide (GeS<sup>2</sup> ) and in solution as germanic acid [7, 8]. However, most Ge is dispersed through silicate minerals due to the substitution of Ge4+ for the geochemically similar Si4+. Ge is also associated with minerals or ores containing graphite (C), zinc (Zn), copper (Cu), iron (Fe), tin (Sn), and silver (Ag) [8]. Germanium can be classified either as a semimetal or metalloid because it shows both metal and nonmetal properties [4, 5]. As pure element, Ge has a metallic appearance at room temperature and behaves brittle with increasing mechanical deformation. In addition, Ge has a high refractive index and low chromatic dispersion and ability to form extended three-dimensional networks of Ge-O tetrahedra like Si-O [1, 9]. These physical properties determine the high economic importance of Ge and compounds in the industry sector. In this regard, the European Commission included Ge in a list of raw materials of critical concern for members of the European Union (EU) not only because of its high economic importance [10] but also because its industrial production is focalized in a small number of countries (mainly in China), and the world's demand pressure is increasingly growing.
