**4.3. Germanium recovery from copper smelting flue dust**

In 1998, a hydrometallurgical procedure for extracting Ge from coal FAs based on the leach-

A recovery of 100 g of Ge per ton of coal FA was achieved between 70 and 200°C [71]. Other

pyridiniumchloride as a surfactant [72]. The authors obtained 95–100% yield of Ge after 3–5 min of flotation. A research about tannin (poly-hydroxy polyphenols) precipitation to extract Ge was proposed in 2008 [73]. The tannins were capable of forming chelates with Ge ions, resulting in low grade of precipitated tannin-germanium complex. Currently, research is aimed at developing methods for increasing FA utilization focused on reducing the concentrations of heavy metals and at the same time obtaining higher added value products.

FAs generated in an IGCC power plant, prompted the study of Ge recovery from coal FAs using pure water in an attempt to develop an extraction process of a low cost and environmentally able to culminate in a commercial Ge end-product [26]. Results revealed high recovery efficiency (up to 86%) at 90°C, indicating that the extraction temperature was the most important parameter in the process. These results led authors to conduct research toward the study of enrichment and precipitation methods for Ge recovery such as ion flotation, adsorption on activated carbon, and/or SX. Adsorption and SX were the methods that allowed

In 2006, a study evaluated the selectivity of the process developed by [26] for the recovery and purity of Ge by ion flotation tests on the leachates arising from the water extraction of Ge, using pyrogallol, catechol, hydroquinone, and resorb in complexing agents at a pH range of 4–7. Pyrogallol or catechol as complexing agents and dodecylamine as a surfactant showed

A complex water leaching process consisting of Ge complexation with catechol followed by SX system, reaching an extraction yield of 95%, was published [77]. In 2014, same authors

studies implemented the ion flotation method using a mixed HCl/HNO3

achieving Ge-bearing solutions with 256 and 1623 mg/L, respectively [74, 75].

the isolation of the Ge complex recovering 100% of Ge in 30 min [76].

The occurrence of Ge as water-soluble species such as GeS<sup>2</sup>

**Figure 5.** Scanning electron microscope photomicrographs of IGCC FAs [69].

and NaOH followed by ion flotation separation of Ge was prompted.

solution and cetyl-

, in the

, GeS, and hexagonal-GeO<sup>2</sup>

ing of FA with H<sup>2</sup>

SO<sup>4</sup>

20 Advanced Material and Device Applications with Germanium

Flue dust from Cu smelting has also been suggested as a potential source of Ge, since relatively high contents of this element may be present in Cu-sulfide ores [27]. Copper is extracted from the ore through hydrometallurgical and/or pyrometallurgical processes. The selection of the process is determined by the Cu minerals bound to ores, being Cu sulfides predominantly treated by pyrometallurgical process and Cu oxides by hydrometallurgical process. However, the pyrometallurgical process is the most commonly employed technology for Cu [79].

The processing of Cu minerals, associated to sulfides by high temperatures, produces several residues [80]. Among the residues, dust generated from physical process, flue dust and slags from smelting process, and sludge from electrowinning process are those with potential for the Ge recovering.

Although the qualitative and quantitative phase determination of dust from Cu smelting depends on the compositional characteristics of the fed into smelting furnaces, temperature and oxidative conditions inside the furnace, and equipment, the recovery of rare and precious metals such as Ge from flue dusts has not been a widely studied subject in the literature. Most of the research on flue dust composition from Cu smelting have been focused on As, Zn, and Pb since the main Cu-ores present elevated amounts of As, Zn, Cd, and Pb which are potentially hazardous to human health or the environment [27].

Font et al. (2011) evaluated for the first time the potential of Cu smelting flue dust (Cu-SFD) as a source of Ge and the possibilities to apply extraction and recovery methods similar to those patented for coal gasification FA [81]. These authors reported Ge concentrations ranging from 417 to 1375 ppm in flue dust samples with Ge extraction yields from 73 to 99%. In 2017, Chilean Cu-SFD was characterized and evaluated for the potential extraction of Li, Rb, and Ge with different chemical leaching agents [27]. The authors found high extraction yields for Ge, Li, and Rb using pure water as extractant at 25°C. Both studies suggest that Ge may occur in the form of highly soluble minerals and that Cu-SFD can be regarded as a promising source of elements with high added value such as Ge.

#### **4.4. PhytoGerm**

Phytomining is an extraction process in which metallic substances in soils or sediments are absorbed by plants [82]. With this in mind, PhytoGerm project emerged in the framework of the r3 -initiative for tech metals and resource efficiency subsidy program of the German Federal Ministry of Education and Research whose goal was to find a plant species that concentrates Ge in aerial plant biomass, which grows well on poor soils and contaminated industrial sites.

**5. Conclusion(s)**

**Acknowledgements**

**Author details**

Aixa González Ruiz1

**References**

2017.03.013

National Research Council (IDÆA-CSIC).

\*Address all correspondence to: agonzalez@uct.cl

\*, Patricia Córdoba Sola<sup>2</sup>

2 Geosciences Department, IDAEA-CSIC, Barcelona, España

2004;**17**:394-402. DOI: 10.1016/j.mineng.2003.11.014

Nowadays, germanium is considered a critical element and also a strategic reserve for hightech industrial applications in several countries. Germanium is used in solar cells, fiber optics, metallurgy, chemotherapy, and polymerization catalysis. Mainly sources of Ge are associated to sulfide ores (e.g., Zn, Pb, and Cu), coal deposits, and also residues from the processing of these ores and coals. Indeed, about one third of global germanium produced come from recycling processes. While the recovery of Ge from sulfide ores presents disadvantages related to the hazardous nature of organic extractants and high acidity of extractant solutions, the occurrence of Ge as water-soluble chemical species in coal gasification and copper smelting fly ashes allows the application of novel extraction methods with water at temperatures <100°C. This approach appears to be a feasible recovery and less harmful novel extraction method for environment, which suggests that both residues are promising sources for Ge. PhytoGerm which is based on absorption of Ge with ribbon grass on soils contaminated with Zn refinery residues results in an energy-efficient and eco-friendly recovery process for Ge.

Germanium: Current and Novel Recovery Processes http://dx.doi.org/10.5772/intechopen.77997 23

The authors thank the support of FONDECYT under grant 11150088. The authors also gratefully acknowledge the Institute of Environmental Assessment and Water Research, Spanish

1 Department of Industrial Processes, Catholic University of Temuco, Temuco, Chile

[1] Moskalyk RR. Review of germanium processing worldwide. Minerals Engineering.

[2] Meija J, Coplen TB, Berglund M, Brand WA, De BP, Gröning M, Holden NE, Irrgeher J, Loss RD, Walczyk T, Prohaska T. Isotopic compositions of the elements 2013 (IUPAC technical report). Pure and Applied Chemistry. 2016;**88**:293-306. DOI: 10.1016/j.chemgeo.

and Natalia Moreno Palmerola<sup>2</sup>

The ribbon grass was selected as suitable for the PhytoGerm project. Ribbon grasses grow well on prolific siliceous soil, and due to the similar chemical properties of Ge and Si, the plant can also absorb Ge [82]. The concept of PhytoGerm project was to make use of elevated Ge levels of tailings from Zn mining sites, thus allowing the plants to accumulate sufficiently high amounts of Ge in order to achieve high yields during the extraction process [83]. The case study developed by the authors assumed that 13,636 tons/year of ribbon grass would be obtained from several cultivation areas, which is the amount needed to utilize an average 500 kW biogas plant. Along the process diagram showed in **Figure 6**, 4112 tons/year of biomass are available for Ge extraction. Once Ge is accumulated in ribbon grass plants, the solid biomass is at first dried and thermally processed in a biomass power plant. The residuals of the combustion process are ashes and FAs, enriched with Ge, with an annual output of approximately 280 tons. The investigated process route ends with producing 3.9 kg of powdery GeO<sup>2</sup> per year.

**Figure 6.** PhytoGerm process diagram. Adapted from [82].
