Spent tantalum capacitors secondary resource
Discarded tantalum capacitor components separated from electronic equipment, distinct from tantalum element, whole printed circuit boards, other capacitor technologies and a recovered tantalum product. The accepted laboratory feed comprised visually identified surface-mounted capacitors manually removed from spent mobile phones and milled. One primary study supports qualified base-metal mobilization by acidophile cultures and a fungal-culture filtrate, while tantalum was not detected in the reported leachates. It does not establish industrial deployment, pure feed phases or isolated-metal recovery.
Microbial & Biochemical Mechanisms (2)
Acidophile-associated base-metal mobilization from capacitor scrap
bioleaching
Microbial
An actively growing mixed iron- and sulfur-oxidizing culture was associated with mobilization of several base metals from milled capacitor scrap into sampled liquor. Biogenic ferric iron and acid generation are proposed contributors, alongside externally maintained acidity. The experiment does not isolate each consortium member, establish a unique molecular pathway or demonstrate recovery of purified metals. Tantalum nondetection is a condition-specific limitation, not proof that every microbial route fails or that a purified tantalum residue was produced.
Experimental Context & Analytical Limits:
The source names Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans and Acidithiobacillus thiooxidans without strain accessions, relative abundance or member-specific tests; no taxon identifiers are assigned to this unresolved experimental mixture. Visually identified capacitors were removed manually and ground to 0.5 and 0.75 mm fractions. Table 1 reports bulk elemental analysis after an HF-containing microwave digestion, not mineralogical phase identity or proof of device purity. Laboratory assays used 250 mL flasks, 100 mL active modified 9K culture, 2% w/v scrap, 30 degrees C and 150 rpm for ten days. Activation medium included sulfur and ferrous sulfate; the final iron concentration for the capacitor arm is not unambiguously specified by the separate PCB iron-series design. Added iron prevents attributing all liquor iron to the scrap. Sulfuric acid maintained pH 1.8 as required. Trials were described as triplicate with uninoculated medium controls. Every second day, 1 mL of 0.45 micrometre filtered liquor was taken for analysis; sterile water replaced sampling and evaporation losses. The sentence describing sample sterilization is ambiguous. Bulk digestion and leachate analysis used ICP-OES; no numeric tantalum detection limit or complete metal mass balance is supplied.
The source names Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans and Acidithiobacillus thiooxidans without strain accessions, relative abundance or member-specific tests; no taxon identifiers are assigned to this unresolved experimental mixture. Visually identified capacitors were removed manually and ground to 0.5 and 0.75 mm fractions. Table 1 reports bulk elemental analysis after an HF-containing microwave digestion, not mineralogical phase identity or proof of device purity. Laboratory assays used 250 mL flasks, 100 mL active modified 9K culture, 2% w/v scrap, 30 degrees C and 150 rpm for ten days. Activation medium included sulfur and ferrous sulfate; the final iron concentration for the capacitor arm is not unambiguously specified by the separate PCB iron-series design. Added iron prevents attributing all liquor iron to the scrap. Sulfuric acid maintained pH 1.8 as required. Trials were described as triplicate with uninoculated medium controls. Every second day, 1 mL of 0.45 micrometre filtered liquor was taken for analysis; sterile water replaced sampling and evaporation losses. The sentence describing sample sterilization is ambiguous. Bulk digestion and leachate analysis used ICP-OES; no numeric tantalum detection limit or complete metal mass balance is supplied.
Curated Evidence Points:
Support
Source:
sikander_2022
Sections 2.1-2.3.2 and 3.2.3, with Figures 6, 8 and 12, support the capacitor-feed experiment and base-metal mobilization. Figure 12 separately compares the two capacitor particle fractions; PCB optimization arms and their controls are not substituted for those experiments. Section 4.3 reports tantalum nondetection. Its narrative control values for copper and iron are not clearly assigned to a specific feed, so they are not imported as capacitor-specific controls.
Partial
Source:
sikander_2022_si
Table S6 supplies separate Ta.Cap rows, but its percentages do not consistently match the main text's summary; for example, the 0.5 mm row lists copper at 88.04%, whereas the main summary says 92%. Table 1 lists capacitor iron at 4.7 g/kg for the 0.75 mm fraction, while Table 2 lists 28.7 g/kg, leaving the iron normalization unresolved. Table S6 also has nonzero lead entries despite the main discussion's lead-nondetection statement. These conflicts preclude adopting the reported percentages as reconciled extraction yields. Both Ta.Cap rows encode tantalum concentration as u and percent as 0, without defining u or providing a detection limit; these are not measured zero concentrations. Table S1 describes non-HF composition, despite the Methods calling it analytical validation, and does not resolve calibration or detection limits. This is the same experiment already used for a scoped Ta nondetection in the element record.
Fungal-culture filtrate-associated mobilization compared with spores
bioleaching
Microbial
A separately grown fungal-culture filtrate produced greater reported base-metal mobilization from capacitor scrap than the source's spore treatment under the tested conditions. The low spore response and tantalum nondetection are retained. The filtrate was not demonstrated sterile or chemically characterized sufficiently to assign the effect to a particular acid, enzyme or metabolite. Lower metal release with spores does not by itself establish absence of growth or universal fungal intolerance to electronic waste.
Experimental Context & Analytical Limits:
The paper identifies the fungus as Aspergillus niger DSM-2182, while the current DSMZ catalogue assigns DSM 2182 to Aspergillus tubingensis. The experimental culture was not sequence-verified in the paper, so the historical label and present authority are kept distinct and no unqualified species identifier is assigned. Cultivation was described in a sucrose-containing mineral medium at initial pH 5.6 plus or minus 0.1, 30 degrees C and 150 rpm for 48 hours, followed by filtration. The paper does not give the culture-filtration pore size or prove removal of viable cells. Separate filtrate and spore treatments used 0.75 mm capacitor scrap at 2% w/v in 250 mL flasks, 30 degrees C and 150 rpm over twenty days; a separate fungal working volume and inoculum quantity are not explicitly specified. A comparator was adjusted to the same initial pH with HCl; its composition and arm-specific quantitative metal results are incompletely documented. pH was measured every five days, and endpoint liquor was analyzed. No isolated-product yield, residual Ta purity, matched final-pH comparison or industrial operation is shown.
The paper identifies the fungus as Aspergillus niger DSM-2182, while the current DSMZ catalogue assigns DSM 2182 to Aspergillus tubingensis. The experimental culture was not sequence-verified in the paper, so the historical label and present authority are kept distinct and no unqualified species identifier is assigned. Cultivation was described in a sucrose-containing mineral medium at initial pH 5.6 plus or minus 0.1, 30 degrees C and 150 rpm for 48 hours, followed by filtration. The paper does not give the culture-filtration pore size or prove removal of viable cells. Separate filtrate and spore treatments used 0.75 mm capacitor scrap at 2% w/v in 250 mL flasks, 30 degrees C and 150 rpm over twenty days; a separate fungal working volume and inoculum quantity are not explicitly specified. A comparator was adjusted to the same initial pH with HCl; its composition and arm-specific quantitative metal results are incompletely documented. pH was measured every five days, and endpoint liquor was analyzed. No isolated-product yield, residual Ta purity, matched final-pH comparison or industrial operation is shown.
Curated Evidence Points:
Support
Source:
sikander_2022
Sections 2.2-2.3.2 and 3.2.3 and Figure 14 distinguish the capacitor filtrate and spore arms and support the narrower comparative observation. The Results describe negligible control release but provide no complete capacitor-specific control table. The proposed organic-acid and manganese-enzyme explanations in Section 4.4 were not directly established by metabolite or enzyme assays here.
Partial
Source:
sikander_2022_si
Table S7 separates capacitor spore and filtrate rows, preserving lower but nonzero spore mobilization. Its filtrate copper entry is 60.91%, consistent with the Results' rounded 61% but not the Discussion's 65%; percentages are therefore not promoted to reconciled recovery yields. Both capacitor rows mark tantalum as u with percent 0, with no definition or detection limit. Main Figure 16 has a capacitor caption but a PCB legend, so its curve is not treated as an unambiguous capacitor-specific pH trajectory. Main Table 3 is explicitly a PCB summary and even lists ten days for fungal arms that the Methods describe as twenty; it is not transferred to the capacitor experiments.
Partial
Source:
dsmz_2182
The live authority resolves DSM 2182 to Aspergillus tubingensis, in conflict with the publication's Aspergillus niger label. This documents present nomenclatural context without proving experimental strain identity or transferring the assay to every member of either species. The fungal and acidophile arms share one publication and feed preparation, not two independent replications of one mechanism.
Sources & References
-
sikander_2022: Sikander A, Kelly S, Kuchta K, Sievers A, Willner T, Hursthouse AS (2022). Chemical and Microbial Leaching of Valuable Metals from PCBs and Tantalum Capacitors of Spent Mobile Phones. International Journal of Environmental Research and Public Health 19:10006. DOI 10.3390/ijerph191610006; PMC9408593. Complete original, especially Sections 2.1-2.3.2, 3.2.3, 4.3-4.4; Tables 1-3 and Figures 6, 8, 12, 14 and 16.
https://doi.org/10.3390/ijerph191610006 (accessed 2026-10-14) -
sikander_2022_si: Sikander et al. (2022), supporting document ijerph-1818908-supplementary.pdf, five pages; Tables S1-S7, especially S6 capacitor particle-size arms and S7 separate fungal-spore and filtrate arms. Same original study, not independent replication.
https://www.mdpi.com/article/10.3390/ijerph191610006/s1 (accessed 2026-10-14) -
dsmz_2182: DSMZ culture catalogue, DSM 2182: current name Aspergillus tubingensis Mosseray; other collection numbers include ATCC 10581 and CBS 121.49. Current strain-authority context differs from the original paper's Aspergillus niger label; it does not retrospectively identify the material actually used in that experiment.
https://www.dsmz.de/collection/catalogue/details/culture/DSM-2182 (accessed 2026-10-14)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-14T17:16:21.758685+00:00 |
Codex (GPT-6; Codex) | CREATE | Created a distinct capacitor-scrap owner with qualified acidophile and fungal-filtrate evidence from a shared primary study; preserved tantalum nondetection, analytical and control conflicts, present DSM2182 nomenclature and laboratory scope. |
Record source: data/records/spent-tantalum-capacitors.yaml