**2. Germanium-bearing minerals and residues**

Nearly 30 minerals are known to contain Ge, mostly sulfides (**Table 1**). Germanium is a substituting element in Zn-sulfide structures (up to 3000 ppm in sphalerite and wurtzite ((Zn,Fe)S) and Cu sulfides (up to 5000 ppm in enargite, tennantite, bornite, and chalcopyrite) [3]. Germanium is also present as a substituting element in oxides (e.g., up to 7000 ppm in hematite (Fe<sup>2</sup> O3 )), hydroxides (up to 5310 ppm in goethite (FeOOH)), phosphates, arsenates, vanadates, tungstates, and sulfates [3, 11].

Germanium can also occur in rare minerals such as argyrodite (Ag8 GeS6 ), germanite (Cu13Fe<sup>2</sup> Ge2 S16), renierite ((Cu,Zn)11(Ge,As)<sup>2</sup> Fe<sup>4</sup> S16), or briartite (Cu<sup>2</sup> (Fe,Zn)GeS<sup>4</sup> ). Germaniumbearing ores are hosted in a variety of deposit that contains Au, Pb, and Ag, apart from those of Cu and Zn. Deposit types that contain significant amounts of Ge include volcanogenichosted massive sulfide (VMS), sedimentary exhalative (SEDEX), Mississippi Valley-type (MVT), Pb-Zn (including Irish-type Zn-Pb deposits), Kipushi-type Zn-Pb-Cu replacement bodies in carbonate rocks, polymetallic Zn-Sn vein, and coal deposits [9].

The VMS deposits are major sources of Zn, Cu, Pb, Ag, and Au and significant sources for Ge. They typically occur as lenses of polymetallic massive sulfides that form at or near the seafloor in submarine volcanic environments and are classified according to base metal content, Au content, or host-rock lithology [12]. There are close to 350 known VMS deposits in Canada and over 800 known worldwide. The most common feature among all types of VMS deposits is that they are formed in extensional tectonic settings, including both oceanic seafloor spreading and arc environments. Sedimentary-exhalative (SEDEX) deposits, on the other


Adapted from [13].

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

Germanium is a scarce element in the Earth's crust (about 1.6 ppm Ge crustal average) that

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.

Nearly 30 minerals are known to contain Ge, mostly sulfides (**Table 1**). Germanium is a substituting element in Zn-sulfide structures (up to 3000 ppm in sphalerite and wurtzite ((Zn,Fe)S) and Cu sulfides (up to 5000 ppm in enargite, tennantite, bornite, and chalcopyrite) [3]. Germanium is also present as a substituting element in oxides (e.g., up to 7000 ppm in hema-

Fe<sup>4</sup>

bearing ores are hosted in a variety of deposit that contains Au, Pb, and Ag, apart from those of Cu and Zn. Deposit types that contain significant amounts of Ge include volcanogenichosted massive sulfide (VMS), sedimentary exhalative (SEDEX), Mississippi Valley-type (MVT), Pb-Zn (including Irish-type Zn-Pb deposits), Kipushi-type Zn-Pb-Cu replacement

The VMS deposits are major sources of Zn, Cu, Pb, Ag, and Au and significant sources for Ge. They typically occur as lenses of polymetallic massive sulfides that form at or near the seafloor in submarine volcanic environments and are classified according to base metal content, Au content, or host-rock lithology [12]. There are close to 350 known VMS deposits in Canada and over 800 known worldwide. The most common feature among all types of VMS deposits is that they are formed in extensional tectonic settings, including both oceanic seafloor spreading and arc environments. Sedimentary-exhalative (SEDEX) deposits, on the other

Germanium can also occur in rare minerals such as argyrodite (Ag8

bodies in carbonate rocks, polymetallic Zn-Sn vein, and coal deposits [9].

)), hydroxides (up to 5310 ppm in goethite (FeOOH)), phosphates, arsenates, vana-

S16), or briartite (Cu<sup>2</sup>

) and in solution as germanic acid [7, 8]. However, most Ge is dispersed through

) or the

GeS6

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

), germanite

). Germanium-

rarely forms its own minerals [6]. It often appears in the form of the oxide (GeO<sup>2</sup>

a natural abundance of approximately 36% [3].

10 Advanced Material and Device Applications with Germanium

**2. Germanium-bearing minerals and residues**

S16), renierite ((Cu,Zn)11(Ge,As)<sup>2</sup>

sulfide (GeS<sup>2</sup>

tite (Fe<sup>2</sup>

(Cu13Fe<sup>2</sup>

O3

Ge2

dates, tungstates, and sulfates [3, 11].

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

hand, occur as tabular Zn-Pb-Ag deposits that contain laminated, stratiform mineralization and may be hosted in shale, carbonate, or carbonate- or organic-rich clastic rocks (siltstone and less commonly sandstone and conglomerate rich).

Because Ge occurs in coal deposits, by-products and residues from coal combustion and/or gasification should also be considered as Ge sources. Fly ashes (FAs) generated by combustion and gasification processes of certain coals may contain important amounts of Ge (**Table 2**). In the same way, Ge is retrieved as a by-product of sulfides ores (e.g., Zn and Cu-Zn-Pb ores); therefore, residues obtained from the ore processing, e.g., smelting flue dust, should also be considered as a potential source of Ge. By including these sources, the potential supply of Ge

**Ge-bearing residues/by-products. Ge mineral phases\* Ge content (mg/kg) Reference** Zn refinery residue n.d. 3620 [23] Cu-cake n.d. 700 [24] coal fly ash GeO<sup>2</sup> 4986 [25]

, GeSnS<sup>3</sup> <500 [26]

Germanium: Current and Novel Recovery Processes http://dx.doi.org/10.5772/intechopen.77997 13

, GeS2

Cu smelting flue dust n.d. 417 [27] Waste optical fibers n.r 1100 [28]

Germanium was initially used industrially in transistors due to its semiconductor properties. However, it was later replaced by silicon, which has better behavior with respect to temperature [9]. In 2016, Ge applications in solar cells, fiber optics, metallurgy, and chemotherapy and as catalyst for polymerization of polyethylene terephthalate (PET) comprised in 2016 almost

Fiber optics are the major use of Ge worldwide since it is used as a doping element in optical

increases the refractive index of the optical fiber which helps to contain the light within the fiber and enables the transmission of the digital signal. Germanium can also be used to make lenses and window panes for infrared detectors, infrared devices mainly destined to military guidance, and weapon-sighting applications and cameras because of its transparency to infrared radiation. It can, therefore, be used in numerous applications such as surveillance, night vision, and satellite systems [29–31]. With regard solar cell applications, Ge is used in high-performance multi-junction cells (typically III–V cells) in the domain of photovoltaics (PV) and in the bottom-cell part of triple junction PV, for the substrate, base, and emitter layers, because of its lattice constant, robustness, low cost, abundance, and ease of production.

Other diverse uses of Ge could be as an alloying element (0.35%) for Sn, or Al-Mg alloys, to increase their hardness; soldering material (12%Ge/88%Au) for gold-based dental prosthesis;

; bismuth germanate oxide crystals (BGO- Bi<sup>4</sup>

). Germanium

O/TiO<sup>2</sup>

Ge<sup>3</sup>

 or K<sup>2</sup> O/

O12) for

fibers, which contain approximately 4% Ge, the rest being silicon oxide (SiO<sup>2</sup>

luminescent material; photographic and wide-angle lenses; ceramics, with Na<sup>2</sup>

(GeO3 )3

could exceed its current primary production [22].

Gasification fly ash GeO<sup>2</sup>

**3. Germanium production and its main applications**

**Table 2.** Selection of residues and by-products with a high potential for Ge recovery.

\*Mineral phases obtained through X-ray diffraction; n.d., not detected; n.r, not reported.

80% of the global consumption of Ge [20, 28–30].

Ta2 O5

; gamma-ray detector Bi<sup>2</sup>

Most SEDEX deposits are hosted either by bimodal volcanic and clastic sedimentary sequence that is commonly metamorphosed to amphibolite-granulite facies, as at Broken Hill, Australia, or by basinal marine, fine-grained sedimentary rocks comprised mostly of carbonaceous chert, shales, and siltstones, less commonly by sandstones and conglomerates [14]. Mineralogy of the SEDEX deposits includes sulfides, carbonates, barite, and quartz. The most common sulfide mineral is pyrite, but the main ore minerals are invariably sphalerite and galena. SEDEX deposits account for 50% of the Pb and Zn reserves and about 25% of the global production of these metals [14]. There are more than 120 SEDEX deposits worldwide with known grade and tonnage figures, and of these 45 have geological resources greater than 20 million tons of Pb + Zn [15].

The Mississippi Valley-type (MVT) deposits can be found in the Gordonsville-Elmwood Zn-Pb district in Tennessee. These deposits, on average, have grades of 400 ppm Ge in Zn ore concentrate, while other MVT deposits in the USA may contain 50 ppm Ge in sphalerite. The Huize MVT deposit, which is located in China (Yunnan Province), is one of the largest MVT deposits in China and produces zinc-lead and Ag, Ge, and Cd by-products [16].

The most significant carbonate-hosted Zn-Pb-Cu deposits that contain notable amounts of Ge are the Kipushi deposit in the Democratic Republic of the Congo and the Kabwe deposits in Zambia [9]. Germanium averages 68 ppm in bulk samples in the Kipushi deposit and occurs substituted in sulfide minerals, although it sometimes occurs in separate Cu-Fe-Ge sulfide minerals [17].

Coal and lignite deposits are also a significant source of Ge. The Lincang lignite mine (Yunnan Province) produces 16 metric tons of high-grade GeO<sup>2</sup> annually, of which 90% is exported [11]. Germanium-rich coal seams are interblended with siliceous rocks that have oxygen and carbon isotope characteristics which suggested a hydrothermal origin. However, it has also been proposed that hydrothermal fluids were then discharged first as hot springs along fault zones into Miocene basins where the Ge was concentrated in lignite seams within stratiform siliceous and siliceous-limestone deposits [18].

Among the deposits containing well-constrained Ge reserves, sulfidic Pb-Zn (> 5000 tons) and high Ge lignite deposits (> 19,000 tons) constitute the two most important types of known Ge deposits [19].

Germanium can exhibit siderophile, lithophile, chalcophile, and/or organophile behavior depending on the geologic environment where it is hosted [11]. Thus, Ge shows a siderophilic behavior due to its relatively high Ge contents (up to 250 ppm) in Fe oxides such as Fe<sup>2</sup> O3 and Fe3 O4 [8]. The lithophile behavior is shown by slight enrichment of Ge in the continental crust relative to the oceanic crust and the upper mantle, while the chalcophilic property of Ge is evident for its economic level in Zn- and Cu-rich sulfide hydrothermal systems. The organophile behavior of Ge, one of the highest affinities for organic matter of all the elements commonly associated with carbonaceous sediments, is marked from its enrichment in organic matter (coal and lignite deposits), which is comparable with some Zn-sulfide ores [2, 8, 11, 20, 21].

Because Ge occurs in coal deposits, by-products and residues from coal combustion and/or gasification should also be considered as Ge sources. Fly ashes (FAs) generated by combustion and gasification processes of certain coals may contain important amounts of Ge (**Table 2**). In the same way, Ge is retrieved as a by-product of sulfides ores (e.g., Zn and Cu-Zn-Pb ores); therefore, residues obtained from the ore processing, e.g., smelting flue dust, should also be considered as a potential source of Ge. By including these sources, the potential supply of Ge could exceed its current primary production [22].


**Table 2.** Selection of residues and by-products with a high potential for Ge recovery.

hand, occur as tabular Zn-Pb-Ag deposits that contain laminated, stratiform mineralization and may be hosted in shale, carbonate, or carbonate- or organic-rich clastic rocks (siltstone

Most SEDEX deposits are hosted either by bimodal volcanic and clastic sedimentary sequence that is commonly metamorphosed to amphibolite-granulite facies, as at Broken Hill, Australia, or by basinal marine, fine-grained sedimentary rocks comprised mostly of carbonaceous chert, shales, and siltstones, less commonly by sandstones and conglomerates [14]. Mineralogy of the SEDEX deposits includes sulfides, carbonates, barite, and quartz. The most common sulfide mineral is pyrite, but the main ore minerals are invariably sphalerite and galena. SEDEX deposits account for 50% of the Pb and Zn reserves and about 25% of the global production of these metals [14]. There are more than 120 SEDEX deposits worldwide with known grade and tonnage figures, and of these 45 have geological resources greater than 20 million tons of

The Mississippi Valley-type (MVT) deposits can be found in the Gordonsville-Elmwood Zn-Pb district in Tennessee. These deposits, on average, have grades of 400 ppm Ge in Zn ore concentrate, while other MVT deposits in the USA may contain 50 ppm Ge in sphalerite. The Huize MVT deposit, which is located in China (Yunnan Province), is one of the largest MVT

The most significant carbonate-hosted Zn-Pb-Cu deposits that contain notable amounts of Ge are the Kipushi deposit in the Democratic Republic of the Congo and the Kabwe deposits in Zambia [9]. Germanium averages 68 ppm in bulk samples in the Kipushi deposit and occurs substituted in sulfide minerals, although it sometimes occurs in separate Cu-Fe-Ge sulfide

Coal and lignite deposits are also a significant source of Ge. The Lincang lignite mine (Yunnan

[11]. Germanium-rich coal seams are interblended with siliceous rocks that have oxygen and carbon isotope characteristics which suggested a hydrothermal origin. However, it has also been proposed that hydrothermal fluids were then discharged first as hot springs along fault zones into Miocene basins where the Ge was concentrated in lignite seams within stratiform

Among the deposits containing well-constrained Ge reserves, sulfidic Pb-Zn (> 5000 tons) and high Ge lignite deposits (> 19,000 tons) constitute the two most important types of known Ge

Germanium can exhibit siderophile, lithophile, chalcophile, and/or organophile behavior depending on the geologic environment where it is hosted [11]. Thus, Ge shows a siderophilic

 [8]. The lithophile behavior is shown by slight enrichment of Ge in the continental crust relative to the oceanic crust and the upper mantle, while the chalcophilic property of Ge is evident for its economic level in Zn- and Cu-rich sulfide hydrothermal systems. The organophile behavior of Ge, one of the highest affinities for organic matter of all the elements commonly associated with carbonaceous sediments, is marked from its enrichment in organic matter (coal and lignite deposits), which is comparable with some Zn-sulfide ores [2, 8, 11, 20, 21].

behavior due to its relatively high Ge contents (up to 250 ppm) in Fe oxides such as Fe<sup>2</sup>

annually, of which 90% is exported

O3 and

deposits in China and produces zinc-lead and Ag, Ge, and Cd by-products [16].

and less commonly sandstone and conglomerate rich).

12 Advanced Material and Device Applications with Germanium

Province) produces 16 metric tons of high-grade GeO<sup>2</sup>

siliceous and siliceous-limestone deposits [18].

Pb + Zn [15].

minerals [17].

deposits [19].

Fe3 O4
