Electrochemical recovery of tellurium from metallurgical industrial waste
- 30 Downloads
The current study outlines the electrochemical recovery of tellurium from a metallurgical plant waste fraction, namely Doré slag. In the precious metals plant, tellurium is enriched to the TROF (Tilting, Rotating Oxy Fuel) furnace slag and is therefore considered to be a lost resource—although the slag itself still contains a recoverable amount of tellurium. To recover Te, the slag is first leached in aqua regia, to produce multimetal pregnant leach solution (PLS) with 421 ppm of Te and dominating dissolved elements Na, Ba, Bi, Cu, As, B, Fe and Pb (in the range of 1.4–6.4 g dm−3), as well as trace elements at the ppb to ppm scale. The exposure of slag to chloride-rich solution enables the formation of cuprous chloride complex and consequently, a decrease in the reduction potential of elemental copper. This allows improved selectivity in electrochemical recovery of Te. The results suggest that electrowinning (EW) is a preferred Te recovery method at concentrations above 300 ppm, whereas at lower concentrations EDRR is favoured. The purity of recovered tellurium is investigated with SEM–EDS (scanning electron microscope–energy dispersion spectroscopy). Based on the study, a new, combined two-stage electrochemical recovery process of tellurium from Doré slag PLS is proposed: EW followed by EDRR.
KeywordsEDRR EW Circular economy of metals Doré slag
Tellurium is a metalloid element , which is currently produced primarily as a by-product of copper electrorefining via anode slime treatment [2, 3]. It is commonly used in solar panels [4, 5, 6], production of thermoelectric materials [6, 7, 8], semiconductors [9, 10] and as an alloying element in metals like steel to improve the machinability [6, 11]. Although tellurium is mainly produced as a side product of a base metal industry [2, 3], the growth of large-scale renewable energy generation, particularly use of solar panels, has resulted in an increased demand for Te [12, 13]. The conventional way to recover tellurium metal is to treat the anode slime via a number of combined hydro- and pyrometallurgical stages, e.g. pressure leaching in an acidic and/or alkaline environment [3, 14, 15, 16, 17]. Nevertheless, as the Doré process—normally carried out in a TROF (Tilting, Rotating Oxy Fuel) furnace—uses treated anode slime as a raw material, any tellurium remaining in the slime distributes to the slag and is considered to be an irretrievable resource [18, 19]. Due to the increased pressure on the world’s natural resources, it is essential that the loss of even minor amounts of critical and valuable elements is avoided in order to promote more sustainable behaviour. Therefore, the ability to recover even minor concentrations of economically significant or critical elements, like tellurium, is essential according to the principles of the materials circular economy.
The slag produced in the Doré process typically includes B, Fe, Ba, Pb, Na and Si, which originates from the added slag formers, whereas Bi, Cu, Se, Te, PM (precious metals) and PGM (platinum group metals) that result from anode slimes are also often found at minor concentrations. Consequently, any methodology that leads to improved recovery from copper anode slimes could have a significant impact on the overall environmental and economic sustainability of a base metal smelter process. The current study addresses this challenge by focusing on the recovery of Te via the application of electrodeposition-redox replacement (EDRR) and electrowinning (EW). These methods—when combined—offer the opportunity to decrease Te wastage whilst enhancing the overall sustainability of tellurium production.
During the ED step of the EDRR process, only a very thin (porous) layer of a sacrificial metal is deposited and this formed metal layer is then spontaneously replaced by a more noble metal during the redox replacement (RR) step, without the use of any externally applied potential or current, i.e. energy. The impetuous for the redox replacement reactions between two or more reactive metals is driven by the difference between their standard potentials [20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30]. This is not only the basic principle of EDRR (electrodeposition-redox replacement) but also of similar methods like surface-limited redox replacement (SLRR) [29, 30, 31, 32] and electrochemical atomic layer deposition (e-ALD) [33, 34, 35, 36]; the main difference is that in SLRR and e-ALD thin, defect free monolayers are formed via underpotential deposition, whereas in EDRR more porous films grow on the surface. In contrast, electrowinning (EW) relies on the direct electroplating of the desired metal element on the electrode surface—by the application of the appropriate potential or current—to produce a surface layer. To date, the EDRR method has been employed for metal reclamation, including Ag recovery from synthetic Zn process solutions [37, 38, 39], Au recovery from synthetic cyanide-free cupric chloride leaching solutions [39, 40] and Pt recovery from synthetic and real industrial nickel solutions [41, 42]. Nevertheless, there are no previous reports related to the recovery of Te by EDRR, or even more, combining the electrowinning (EW) and EDRR sequentially to maximise the recovery. This paper demonstrates how both EDRR and EW are employed as part of a comprehensive investigation into the recovery of Te from a Doré slag pregnant leach solution (PLS).
2 Experimental procedure
2.1 Raw material
Composition of investigated Doré slag PLS as determined by ICP-OES (g/L and ppm) and ICP-MS (ppb)
As (g dm−3)
B (g dm−3)
Ba (g dm−3)
Bi (g dm−3)
Cu (g dm−3)
Fe (g dm−3)
Na (g dm−3)
Pb (g dm−3)
2.2 Cell set-up
Electrochemical measurements were conducted with a standard three-electrode cell set-up comprised of a reference saturated calomel electrode (SCE, B521, SI Analytics, Germany), 0.1-mm-thick (A = 24 cm2) Pt plate as a counter electrode (CE) and 0.1-mm-thick (A = 0.24–0.4 cm2) Pt plate as a working electrode (WE, both Kultakeskus, Finland). The cell set-up was controlled using an IviumStat 24-bit CompactStat potentiostat (Ivium Technologies, The Netherlands) and is described in more detail elsewhere [37, 38, 39, 40, 41]. N.B. All subsequent potentials detailed are versus SCE unless otherwise stated.
2.3 EDRR measurements
EDRR parameters investigated, E1 = deposition potential, E2 = cut-off potential, t1 = deposition time, t2 = cut-off time and n = amount of cycles
E1 [mV vs. SCE]
− 500, − 300, − 100, +100
E2 [mV vs. SCE]
− 50, +50, +150
2.4 EW experiments
EW parameters investigated, E = deposition potential and t = deposition time
Te in solution [ppm]
400, 300, 200, 100, 50, 25, 20, 15, 10, 1
E [mV vs. SCE]
− 600, − 500, − 360, − 245, +75, +150, +250
3 Results and discussion
3.1 Determination of the EDRR and EW parameters
As can be seen in Fig. 1a, the deposition of Te commences at approximately + 250 mV versus SCE and has a peak centred at + 75 mV versus SCE. These values are in good correlation with the literature [44, 45]. The reduction and oxidation peaks of Ag (Fig. 1b) in 30% aqua regia are around − 110 and − 25 mV versus SCE, respectively. For As, the reduction showed a peak around − 50 mV, Fig. 1c. Iron showed a reduction peak around − 100 mV, whereas another reduction peak was found approximately at + 400 mV, which relate to Fe0/Fe2+ and Fe2+/Fe3+, respectively (Fig. 1d). For Cu, two reduction peaks around − 150 mV and + 200 mV (Fig. 1e) correspond to Cu0/Cu+ and Cu+/Cu2+. However, as the aqua regia media includes also chlorides, the dissolved copper is most likely complexed with chlorides, e.g. as CuCl+ and CuCl2−, rather than ions . The reduction peak for Pb was determined to be around − 150 mV (Fig. 1f), whereas the CV of Bi—shown in Fig. 1g—highlights that although the Bi reduction potential is similar to that of Pb, the oxidation is at around + 75 mV. In addition, a CV was measured using the Doré slag PLS as the electrolyte (Fig. 1h) and this shows a wide number of peaks as a result of the complex combination of elements within the solution. For example, depending on pH, Te has a number of oxidation stages [47, 48] and can form complexes with other metals like bismuth, silver and/or copper [7, 8, 49, 50, 51, 52, 53, 54]. Based on the results from the CV investigations, the E1 (deposition) potentials and E2 (cut-off) potentials—outlined in Table 2—were selected as the EDRR parameters in the multimetal PLS electrolyte.
As tellurium electrowinning has been previously investigated under different pH conditions [55, 56, 57, 58, 59], this information, along with the findings from the PLS CV measurements (Fig. 1h), was used to select the EW experimental potentials shown in Table 3. Previous research [55, 56, 57, 58, 59] has demonstrated that along with pH, the choice of electrolyte and presence of other elements all affect the deposition potentials of tellurium.
Cyclic voltammograms (Fig. 1a–h) together with existing literature [41, 42, 43, 44, 45, 46, 47, 48] highlight that copper would be the most beneficial candidate to act as a sacrificial element in EDRR, especially as chloride-based solutions decrease Cu reduction potential (− 150 mV vs. SCE, Fig. 1e) due to the formation of monovalent (Cu+) copper chloride complexes. This provides a unique advantage in selective Te recovery; for example, the reduction potential in the current study is ca. 243 mV lower compared to non-chloride solution (+ 93 mV vs. SCE, standard electrode potential). Such values are of a similar magnitude to the calculations previously outlined by Lundström et al.  (220 mV decrease with [Cl−] ~ 2.9 mol dm−3). This theoretical background highly supports the development of electrochemical Te recovery in chloride media, as the reduction potentials of Te and Cu are not overlapping, but the nobility difference supports both direct recovery (EW) as well as the recovery through electrodeposition followed by spontaneous redox replacement (EDRR).
3.2 Tellurium recovery by EDRR from PLS
Investigation of the EDRR method to recover Te from Doré PLS initially involved the optimisation of the EDRR parameters, i.e. deposition potential (E1), cut-off potential (E2), deposition time (t1), cut-off time (t2) and number of cycles (n). More information about the definition of these parameters has been published earlier [37, 38, 39, 40, 41]. Five deposition times, t1, were studied in the range of 2–10 s, along with the four deposition potentials, E1 and three cut-off potentials, E2, presented in Table 2. Cut-off time, t2, and the number of cycles, n, were kept constant at 1000 s and 100, respectively.
Quantitative SEM–EDS results of the electrode surface metal deposits after EDRR experiments at E1 = − 500 mV and E2 = + 75 mV or +150 mV, t1 = 2 s and n = 100
E2 [mV vs SCE]
Te (wt %)
Bi (wt %)
Cu (wt %)
Ag (wt %)
As (wt %)
Figure 3 also highlights that both Ag and Bi behave in a similar way to Te, although Ag and Bi are detected in lower amounts at the electrode surface. The ratio between Ag and Te found on the electrode is similar to that found in the original solution, where the Te concentration is ca. 8 times higher, which suggests comparable electrochemical behaviour. The presence of Ag, As, Bi and Cu on the surface is probably due to tellurium’s ability to form several different alloys with other elements [7, 8, 49, 50, 51, 52, 53, 54]. If tellurium is deposited as an alloy, the alloying element can be replaced with another tellurium ion which promotes tellurium recovery as Te is the most noble element in the solution (with the exception of silver) . Consequently, there exist two pathways for Te deposition, which occur simultaneously, leading to increased levels of Te at the surface: the redox replacement reaction of alloying elements resulting in Te alloys and redox replacement of metallic sacrificial element, resulting in metallic Te recovery. Therefore, the content of tellurium detected on the surface is the combination of a pure tellurium and telluride alloying, and the possible tellurides could include for example, Ag2Te  and Bi2Te3 .
In the case of Bi, on the other hand, a different behaviour is observed: even though Bi concentration in the PLS solution is significantly higher (4.6 g dm−3), the level detected after EDRR is considerably lower relative to Te. During the RR phase, one limiting factor is mass-transport of electrolyte to the surface of the electrode, whereas at the electrode surface, the reaction rate is dictated by the metal reduction potential differences—the higher the reduction potential difference, the more likely the redox replacement. Consequently as both Te and Ag have similar reduction potentials, it is possible that during the RR step, both these elements replace the sacrificial Cu and to a lesser extent Bi (see Fig. 3 and Table 4).
3.3 Tellurium recovery by EW from PLS
Quantitative SEM–EDS results of the metals deposits on the surface of the employed electrode after EW experiments at different potentials and duration = 1200 s
Potential (mV vs. SCE)
Te (wt %)
Bi (wt %)
Cu (wt %)
Ag (wt %)
As (wt %)
The results in Table 5 demonstrate that although notable Te enrichment is achievable by optimised EW operation with 1200 s duration, the comparative active deposition time for EDRR is only 200 s (n = 100, t1 = 2 s) and provides a higher level of Te enrichment (Fig. 2). Overall, these findings clearly indicate that relatively selective Te recovery from Doré slag PLS can be achieved with both optimised EDRR and EW methodologies.
3.4 Morphology of tellurium deposits achieved by EDRR and EW
3.5 Combining EW and EDRR for tellurium recovery from Doré slag
Results in Fig. 6 show that when the synthetic solution has approximately the same Te content as the original PLS (400 ppm cf. 421 ppm) the level of Te deposition on the Pt electrode surface is relatively high after only 200 s. However, as concentration is reduced to ≤ 300 ppm Te, the amount recovered drops dramatically. As a result, the energy efficiency of EW becomes critical when compared to the level of tellurium recovered, due to the mass-transport limited reactions that comprise the EW process, as with more dilute solutions longer time is required for a critical mass of ions to reach the electrode surface.
Consequently, the EDRR methodology is more effective at lower concentrations than conventional EW as the metal redox replacement does not require any external applied energy, but occurs spontaneously due to reduction potential differences. For example, EDRR has already been proved to be capable of recovering Pt from acidic, sulfate-based industrial hydrometallurgical solutions in the ppb range . On the other hand, the energy efficiency of EDRR process is reduced by the capacitive double-layer charging that occurs at the commencement of each ED cycle, i.e. hundreds or thousands of times, depending on the number of cycles applied [83, 84]. In comparison, the EW method only undergoes a short period of capacitive double-layer charging at the start of the process.
A more detailed morphology of the different electrode surfaces is shown in Fig. 9. As can be seen, all show similar types of dendritic-like growth, although when EW only is employed (Fig. 9a, Stage 1) the tellurium deposits are spread across the whole active electrode area, whilst in contrast, EDRR from depleted Te solution (Fig. 9b, Stage 2) shows more compact areas of deposition. Moreover, when compared to the combined method, Fig. 9c, it is evident that tellurium can re-dissolve back to the electrolyte, most likely during the RR (redox replacement) step and such dissolution can be a limiting factor in an EDRR-based process. As seen previously, dendritic-like structures were again observed with these long-term EW, EDRR and EW-EDRR measurements and as stated earlier, they are most likely a direct result of the applied overpotential where either sacrificial elements are deposited on the electrode or, during EW, tellurium is deposited.
Quantitative SEM–EDS results of the metal deposits on the Pt electrode surfaces after the EW only (Stage 1, 96 h), EDRR only (Stage 2, 96 h) and combined EW-EDRR (Stage 1 + 2, 192 h) experiments performed under optimum conditions
Te (wt %)
Bi (wt %)
Cu (wt %)
Ag (wt %)
As (wt %)
Stage 1: EW
Stage 2: EDRR
Combined: EW + EDRR
There are currently only a few studies where tellurium recovery has been performed at similar concentrations to the one utilised here—e.g. recovery from a solution containing < 100 ppm Te by bacterial leaching  or 500 ppm by electrochemical methods . Instead, in most cases clearly higher initial Te concentrations are utilised, e.g. 1.9–3.5 g dm−3 industrial solutions  or anode slimes with ~ 34 wt% Te . Therefore, the combined EW-EDRR route outlined here offers an unparalleled method for the maximisation of Te recovery from the Doré process that enhances the drive towards a more sustainable metal circular economy.
Tellurium recovery from Doré slag PLS via combined EW-EDRR has been demonstrated to be feasible and relatively selective, even though Doré slag PLS contains notable amounts of other elements at high (g dm−3) concentrations. Under the optimised conditions, the recovered metal deposits on the surface contained more tellurium than any other elements combined. The highest tellurium recovery from Doré slag PLS via EW resulted in ~ 55 wt% purity in the deposits, whereas EDRR resulted in ~ 64 wt%. Based on these findings, a new Doré slag treatment circuit for tellurium recovery is proposed.
The working principles and limiting tellurium concentrations were demonstrated with synthetic solutions and the results show that above 300 ppm EW is preferred, whilst below this threshold value, EDRR should be employed. By a combination of EW and EDRR processes, the recovery of pure tellurium from Doré slag can be achieved even from ppm-level solutions.
Since tellurium is still mainly produced as a side product of a copper anode slime treatment, the processing the Doré slag with the proposed combined EW-EDRR could increase the overall profitability of a copper factory. Moreover, in terms of circular economy and sustainable development, the recovery of even a small amount (< 300 ppm) of tellurium metal circulation for use is crucial with the ever-growing demand for metals. Furthermore, the proposed new approach can offer potential for selective tailored recovery of strategically important elements in metallurgical waste and side stream fractions.
Open access funding provided by Aalto University. This work has been financed and supported by the Association of Finnish Steel and Metal Producers (METSEK-project, PH & TH) together with “NoWASTE” project (Grant 297962, KY) and GoldTail (Grant 319691, BW & ML) funded by Academy of Finland. The research also made use of the Academy of Finland funded “RawMatTERS Finland Infrastructure” (RAMI) based at Aalto University.
- 13.SolarPower Europe (2018) Global Market Outlook for Solar Power/2018 – 2022, Belgium, Brussels, ISBN: 9789082714319. http://www.solarpowereurope.org. Accessed 12 Aug 2018
- 14.Biswas J, Jana RK, Kumar V, Dasgupta P, Bandyopadhyay M, Anyal SK (1998) Hydrometallurgical processing of anode slime for recovery of valuable metals. In: Bandopadhyay A, Goswani NG, Rao PR (eds) Environmental and Waste Management. National Metallurgical Laboratory, Jamshedpur, pp 2016–2224Google Scholar
- 15.Wang WK, Hoh Y-C, Chuang W-S, Shaw I-S (1981) Hydrometallurgical process for recovering precious metals from anode slime, U.S. Patent, US4293332A, 7 pagesGoogle Scholar
- 16.Robles-Vega A, Sanchez-Corrales VM, Castillon-Barraza F (2009) An improved hydrometallurgical route for tellurium production. Miner Metall Process 26(3):169–173Google Scholar
- 26.Yliniemi K, Wragg D, Wilson BP, McMurray HN, Worsley DA, Schmuki P, Kontturi K (2013) Formation of Pt/Pb nanoparticles by electrodeposition and redox replacement cycles on fluorine doped tin oxide glass. Electrochim Acta 88:278–286. https://doi.org/10.1016/j.electacta.2012.10.089 CrossRefGoogle Scholar
- 32.Ahmadi K, Wu D, Dole N, Monteiro RO, Brankovic SR (2019) Tuning surface chemoresistivity of Au ultrathin films using metal deposition via surface-limited redox replacement of the underpotentially deposited Pb monolayer. ACS Sens. 4(9):2442–2449. https://doi.org/10.1021/acssensors.9b01045 CrossRefPubMedGoogle Scholar
- 34.Ouendi S, Arico C, Blanchard F, Cordon J-L, Wallart X, Taberna PL, Roussel P, Clavier L, Simon P, Lethien C (2019) Synthesis of T-Nb2O5 thin-films deposited by atomic layer deposition for miniaturized electrochemical energy storage devices. Energy Storage Mater 16:581–588. https://doi.org/10.1016/j.ensm.2018.08.022 CrossRefGoogle Scholar
- 41.Halli P, Heikkinen JJ, Elomaa H, Wilson BP, Jokinen V, Yliniemi K, Franssila S, Lundström M (2018) Platinum recovery from industrial process solutions by electrodeposition-redox replacement. ACS Sustain Chem Eng 6(11):14631–14640. https://doi.org/10.1021/acssuschemeng.8b03224 CrossRefPubMedPubMedCentralGoogle Scholar
- 42.Yliniemi K, Nguyen NT, Mohajernia S, Liu N, Wilson BP, Schmuki P, Lundström M (2018) A direct synthesis of platinum/nickel co-catalysts on titanium dioxide nanotube surface from hydrometallurgical-type process streams. J Clean Prod 201:39–48. https://doi.org/10.1016/j.jclepro.2018.08.022 CrossRefGoogle Scholar
- 43.Halli P, Hailemariam T, Latostenmaa P, Lundström M (2018) Leaching behavior of Cu, Bi and Sb from TROF furnace Doré slag during mineral acid leaching, International Mineral Processing Congress, Moscow, Hydro- and Bio-Hydrometallurgy Section, 446–454Google Scholar
- 50.Mori E, Baker CK, Reynolds JR, Rajeshwar K (1988) Aqueous electrochemistry of tellurium at glassy carbon and gold: a combined voltammetry-oscillating quartz crystal microgravimetry study. J Electroanal Chem Interfacial Electrochem 252(2):441–451. https://doi.org/10.1016/0022-0728(88)80228-6 CrossRefGoogle Scholar
- 58.Mezei A, Ashbury M, Canizares M, Molnar R, Given H (2008) Hydrometallurgical recycling of the semiconductor material from photovoltaic materials – Part two; Metal recovery, Hydrometallurgy 2008: Proceedings of the Sixth International Symposium, Phoenix, Arizona, USA, pp 224–237, ISBN: 9780873352666Google Scholar
- 59.Sany S (2009) Optimisation of influential factors in electrowinning of tellurium by means of PLS modelling, Master’s Thesis, Luleå University of Technology, p 47Google Scholar
- 63.Haynes WM, Lide DR, Bruno TJ (2017) CRC handbook of chemistry and physics: a ready-reference book of chemical and physical data, 97th edn. CRC Press, Boca RatonGoogle Scholar
- 67.Mulaudzi N, Kotze MH (2013) Direct cobalt electrowinning as an alternative to intermediate cobalt mixed hydroxide product. In: 7th Base Metals Conference of the Southern African Institute of Mining and Metallurgy, Johannesburg, South Africa, pp 209–222Google Scholar
- 85.Lee CK, Rhee K-I, Sohn H-J (1997) The recovery of tellurium from copper anode slimes by hydrometallurgical processes. J Korean Inst Resour Recycl 6(3):41–45Google Scholar
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.