Recovery of germanium and indium from leaching solution of germanium dross using solvent extraction with TOA, TBP and D2EHPA
Graphical abstract
Introduction
Germanium and indium are quite rare elements considered by many economies, e.g. European Union (European Comission, 2017) or USA (Shanks III et al., 2017) as critical raw materials. Both elements find many important applications, especially in telecommunication. Germanium is an important component of optical fibres, used in cables for fast telecommunication systems, e.g. for backhaul networks in 5G systems. Due to transparency to infrared it is also widely used in night vision systems, e.g. lenses. Its other application areas include polymerisation catalysts (mostly PET production for plastic bottles), electronics, semiconductors, solar cells (Buchholz, 2014). Indium phosphide lasers and receivers may be found in fibre-optic networks. Indium‑tin oxide films are mainly used to produce flat panel displays. Applications of indium include also low-temperature solders, photovoltaic cells, thermal interface materials and alkaline batteries (European Comission, 2017).
Different methods may be applied for germanium recovery depending on the origin of the initial material, its composition and germanium concentration. Precipitation with tannic acid is most often used in the case of Ge-bearing sulphate solution (Liang et al., 2008a; Liu et al., 2020). However, this method requires huge consumption of tannins. Other methods, which may be considered for preparation of germanium concentrates include sulphide or catechol-cetyltrimethylammonium precipitation (Arroyo et al., 2009a), co-precipitation with ferric hydroxide (Liang et al., 2008b) as well as cementation with zinc (Drzazga et al., 2020) or iron (Zhou et al., 2013). Moreover, germanium may be also recovered by ion exchange (Arroyo Torralvo et al., 2018; Chen et al., 2018; Cruz et al., 2018), nanofiltration (Werner et al., 2019) as well as ion-exchange membranes (Takemura et al., 2013; Kawakita et al., 2014; Kuroiwa et al., 2014). Hydrometallurgical routes for indium recovery from aqueous solutions generally include solvent extraction, cementation with aluminium and electrorefining (Alfantazi and Moskalyk, 2003). Indium may be extracted from solutions using ion exchange resins (Ferella et al., 2017; Adhikari et al., 2012; Liu et al., 2006), cementation (Koleini et al., 2010; Gu et al., 2018), electrolysis or membrane techniques (Zimmermann et al., 2014).
Important method successfully applied for recovery of both germanium and indium is solvent extraction. High extraction yields of germanium (>90%) were achieved for chloride and sulphate solutions as well as for leachates obtained by treatment with organic acids. Examples of promising extractants are Cyanex 301, Cyanex 923 (Gupta and Mudhar, 2006) and N-n-octylaniline (Sargar and Anuse, 2005) for HCl solution, LIX 63 (de Schepper, 1976), hydroxamic acid+D2EHPA (di-(2-ethylhexyl) phosphoric acid) (Tang et al., 2000), D2EHPA + TBP (tributyl phosphate) (Ma et al., 2013) for H2SO4 solutions. For solutions containing organic acids like oxalic acid, tartaric acid and catechol Cyanex 923, Alamine 336, Aliquat 336 (Haghighi et al., 2018a) and trioctylamine (Arroyo and Fernandez-Pereira, 2008; Liu et al., 2017) allowed high germanium extraction yields. Overview of extractants and respective stripping agents used for germanium recovery is presented in Table 1. Combination of membrane and solvent extraction techniques, i.e. supported liquid membranes (SLE) were also successfully applied for germanium recovery – e.g. SLE composed of polytetrafluoroethylene (PTFE) membrane with trioctylamine (Haghighi et al., 2018b), Cyanex 301 (Haghighi et al., 2019a) or Aliquat 336 (Haghighi et al., 2019b) mobile carriers dissolved in kerosene. Interesting approach is the application of tertiary amines (trioctylamine or N235) for solvent extraction of germanium from sulphate solutions doped with organic acid (Liang et al., 2012; Chen et al., 2017a; Zhang et al., 2019). In acidic solutions (at pH < 5) germanium is predominantly present in the form of germanic acid, which formula is shown as H4GeO4 or Ge(OH)4 (Virolainen et al., 2013; Tao et al., 2021). Addition of organic acid lead to formation of anionic germanium complex, which may be extracted from aqueous phase by the amine. Suitable complexants for this system include tartaric acid (Haghighi et al., 2018a; Liang et al., 2012; Chen et al., 2017a; Zhang et al., 2019; Zhang et al., 2021), catechol (Arroyo and Fernandez-Pereira, 2008; Arroyo et al., 2009b), oxalic acid (Haghighi et al., 2018a; Zhang et al., 2021), citric acid (Zhang et al., 2021) or gallic acid (Zhang et al., 2021). Among them, the best germanium extraction yields were achieved for tartaric acid (Zhang et al., 2021) in acidic solutions and catechol for neutral and basic ones (Pokrovski and Schott, 1998). Addition of e.g. tartaric acid (H4Tart) allows formation of complex anion, which may be extracted by an amine (e.g. trioctylamine – tertiary amine represented as R3N). The reactions during extraction stage are presented below (Haghighi et al., 2019b; Pokrovski and Schott, 1998):
The stripping process may be then performed using aqueous solution of a base, usually sodium hydroxide (Arroyo et al., 2015):
Extractants which were found to be successful in indium recovery include fatty acids (e.g. Versatic 10), D2EHPA and other phosphoric acids (e.g. di-p-octylphenyl, diisostearyl, mono(isooctadecyl)), 2-ethylhexyl-2-ethylhexyl phosphonic acid as well as bis(2,4,4-trimethylpentyl) phosphinic acid (Paiva, 2001; Nguyen and Lee, 2019). Overview of extractants and respective stripping agents used for indium recovery is presented in Table 2. D2EHPA (represented as RH) is one of the most popular due to good indium selectivity and relatively low cost. The reaction taking place during extraction is (Li et al., 2015a):
Indium is usually stripped from organic phase using aqueous solution of hydrochloric acid. The reaction taking place in this case is the reverse of the one presented in Eq. (5).
There are some studies on solvent extraction of germanium using organic acid and trioctylamine as well as indium with D2EHPA. However, the investigations were focused on the solutions containing low concentrations (≤200 mg/dm3) of germanium (Table 1) but also indium (Table 2) (Gu et al., 2018; Li et al., 2015a; Chen et al., 2017b; Pereira et al., 2018; Zhang et al., 2017; Cao et al., 2020). There is also a very limited number of publications dedicated to solvent extraction of solutions containing both germanium and indium. Especially, there are no reports on investigation of germanium extraction by TOA from solutions containing indium. In the present study solvent extraction of the solution containing >5 g/dm3 germanium and > 1.5 g/dm3 indium obtained after leaching of dross from New Jersey zinc distillation process in H2SO4 solution was investigated. The leaching process as well as removal of tin from the solution was described in detail in our previous studies (Drzazga et al., 2018; Drzazga et al., 2019; Kulawik et al., 2019). Moreover, number of theoretical stages required for each operation was determined.
Section snippets
Materials and reagents
The solution investigated in the study was obtained by leaching of germanium-bearing dross in 10% aqueous solution of sulphuric acid at 80 °C, for 2 h, at dross-to-solution ratio 1:10 kg/m3 and by subsequent tin removal from the obtained solution by addition 30% H2O2. The detailed procedure was described in our recent publications (Drzazga et al., 2018; Drzazga et al., 2019). The composition of the selected elements is presented in Table 3. The reagents used in the experiments were
Extraction of germanium
In the first stage extraction of germanium with organic phase composed of TOA and TBP dissolved in Exxsol was investigated. The results are presented in Fig. 1 a-d.
Three complexing agents: tartaric acid, citric acid and ascorbic acid were investigated in the study. It was noticed that highest germanium extraction yield under investigated conditions was achieved for tartaric acid (Fig. 1a). In the case of citric acid, the maximum achieved germanium recovery was ca. 58%, i.e. about 2/3 of the
Conclusions
Solvent extraction process for the real solution obtained after leaching of germanium-bearing dross was investigated. Germanium was extracted using TOA + TBP, while Ge-depleted raffinate was used for indium extraction by D2EHPA. Parameters for individual extraction and stripping operations were determined and flowsheet of the overall process including multistage operations was proposed.
It was found that the highest germanium extraction yield (>99%) was achieved when 12 g/dm3 tartaric acid was
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
The study was funded by the Polish Ministry of Science and Higher Education under the project ST/33/2019/G “Investigation on germanium recovery from post-leaching solutions”. We would like to thank Departments of Analytical Chemistry and Functional Materials for analysis of samples.
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