Nkrumah et al. 2022 — Farming for battery metals

Nkrumah, Echevarria, Erskine and van der Ent set out the case for agromining (also called phytomining) as a route to battery-grade metals. Hyperaccumulator plants, grown on naturally metal-rich ultramafic soils or on mine wastes and tailings, take metals up into their biomass; the biomass is harvested, dried and incinerated to a metal-rich “bio-ore”, and the bio-ore is processed into high-purity metal salts suited to lithium-ion battery manufacture. The article is a perspective by the principal agromining research group rather than a primary measurement study, and it reports no measurement of metals in food, ingredients, or consumer products. For Heavy Metal Index purposes it is context-only: its value is mechanistic. Nickel hyperaccumulation on ultramafic and serpentine soils is the extreme end of the same soil-to-plant transfer continuum that governs food-side metal uptake, and the same plant physiology that lets a “metal crop” concentrate nickel is what drives cadmium, arsenic and nickel into edible crops grown on contaminated ground.

Key numbers

All values are reported as printed in the source and carry the source’s own framing.

Demand driving the field

• Battery-metal demand is described as rising at escalating rates, increasing by factors of 18–20 for lithium, 17–19 for cobalt, and 28–31 for nickel over the coming decades; the abstract frames the required increase for the critical battery metals as factors greater than 20.
• The two most common electric-vehicle battery chemistries, NCA (nickel cobalt aluminium) and NMC (nickel manganese cobalt), use roughly 80% and 50% nickel respectively.
• Nickel demand for batteries is cited (Xu et al. 2020) as rising from 115,000 t in 2020 to 580,000 t in 2025.
• Nickel sulfate is valued at roughly $25,000/t expressed on a nickel basis (LME 2022).

Nickel agromining (the most mature case)

• Ultramafic soils naturally enriched in nickel occur in tropical South-East Asia (Indonesia, Philippines, Malaysia) and Central-South America (Guatemala, Brazil); the Indonesian island of Sulawesi alone has over 15,000 km² of ultramafic land.
• More than 500 nickel hyperaccumulator species are known, of which roughly 50 are suitable for use as agromining “metal crops”.
• Temperate / Mediterranean metal crops include Odontarrhena chalcidica (Alyssum murale) and Berkheya coddii; tropical candidates include Phyllanthus rufuschaneyi and Blepharidium guatemalense. Odontarrhena is biannual and must be re-sown; Berkheya is perennial and is harvested leaving the rootstock to resprout. The best tropical candidate, the woody Phyllanthus rufuschaneyi, yields biomass from regular pruning.
• Sustained yields of 200–400 kg nickel per hectare per year over a 20–30 year horizon have been modelled from field and glasshouse results. At a base nickel value of $25/kg(early2022),thisisworth$5,000–10,000 per hectare per year, excluding extraction and processing costs.

Cobalt, manganese, lithium

• Cobalt: the Democratic Republic of the Congo supplied about 70% of world cobalt production in 2021, with attendant supply-chain and social/environmental risk. The herb Haumaniastrum robertii is projected to yield 25 kg cobalt per hectare per year, worth about $1,825/ha/year on early-2022 prices. Around 12,000 ha of mine-waste-impacted land in Zambia carries high residual cobalt and is flagged as a target resource.
• Manganese: geologically abundant with no immediate supply threat, but a premium may exist for “green manganese”. Gossia bidwillii accumulates >40,000 mg/kg in its leaves but is a slow-growing rainforest tree unsuited to agromining; the fast-growing Phytolacca americana (>30,000 mg/kg) is a better candidate and a pioneer on mine wastes that could serve as a temporary cover crop on tailings dams.
• Lithium: no lithium hyperaccumulator plants are known. Systematic screening for suitable species is the prerequisite for any lithium agromining, following the path developed for nickel.

Operations and bio-ore quality

• Nickel-metal farms are projected to produce 150–300 kg nickel per hectare per year over a 15–25 year lifetime. A farm producing 150 kg Ni/ha/year over a 265-ha cropping area is estimated to generate $1Mintotalsales(at$25/kg), excluding production costs, returning about $3,750/ha/year to the farmer — on par with the best-performing agricultural crops such as oil palm on fertile soils.
• Setup cost is dominated by establishing a large commercial nursery; Phyllanthus is planted at 20,000 plantlets/ha, so a 265-ha farm needs about 5.3 million plants, planted once per metal-farm lifetime.
• The bio-ore is high purity and essentially free of iron, chromium and titanium impurities; nickel sulfate of 99.995% purity is reported. The process route is drying and incineration of biomass (1–3 wt% nickel) to ashes (15–30 wt% nickel), with the heat used to generate electricity. The authors note room for a lower-tech variant that omits the ashing step in favour of on-site composting and leaching to make a concentrate, keeping the system scalable and suited to rural areas with little infrastructure.

Framing

The authors position agromining as recovering “treasure from trash” — mining critical metals from wastes, tailings and unconventional sources (van der Ent et al. 2021) — and as producing “green technologies from green sources”. They emphasise the low-tech, ethical and ESG character of the approach, its potential to support smallholder livelihoods in developing countries, and a phytoremediation co-benefit when metal farming is conducted with affected communities.

Methods (brief)

Perspective / short review article. No primary sampling, no analytical chemistry, no statistical analysis. The piece synthesises the authors’ own prior agromining field and modelling work and the wider literature; yields, prices and purities are quoted from cited sources and from early-2022 metal prices. It does not follow a systematic-review protocol.

Implications

Certification: This source contributes nothing to HMT&C threshold-setting evidence pools. It reports no occurrence of metals in food, supplements, or personal-care products, and agromining is metal recovery as a product, not removal of a contaminant from a food crop. Its certification-adjacent value is mechanistic and educational: it is the canonical entry point into the hyperaccumulation literature that explains why certain crops grown on ultramafic, serpentine, or mine-affected soils carry the nickel (and, by the same physiology, cadmium and arsenic) burdens recorded on ingredient pages. Route as exposure / mechanism context to Soil-to-plant transfer of heavy metals and Nickel; do not route as food-occurrence or food-remediation evidence.

Courses: A strong case study in how soil geochemistry (ultramafic and serpentine parent material) and plant physiology together govern metal uptake, and a vivid circular-economy / ESG framing that connects the contamination story to a recovery-and-remediation story. Useful educator material on the soil-to-plant pathway and on why origin and growing-site geology drive ingredient-side risk.

App: No contamination_profile blocks are touched. No food, ingredient, or product values are reported.

Microbiome: Rhizosphere microbes and arbuscular mycorrhizal fungi modulate metal hyperaccumulation; this is a signpost for WikiBiome federation review of soil-microbiome-metal interactions, though the paper does not develop the microbial angle itself.

Wiki pages this source may touch

• Nickel
• Cobalt
• Manganese
• Lithium
• Soil-to-plant transfer of heavy metals
• Agronomic mitigation

Verification notes

• Evidence tier set to C, not B. The journal (Science of the Total Environment) is a strong peer-reviewed venue and the authors (van der Ent, Echevarria and colleagues) are the leading agromining group, but the article is a perspective with no primary measurements and no systematic methodology. It is treated as context / lead-level for the agromining-mechanism story, not as measurement evidence. Tier reflects study design, not venue.
• Not open access. The PDF is © 2022 Elsevier B.V., all rights reserved. Only the quantitative claims and the authors’ framing are summarised here; the full text is not reproduced. Numeric values are preserved as printed in the source.
• metals: includes Co, Mn and Li, which are not HMT&C analytes, because the paper addresses all four metals. Only nickel is both an HMT&C analyte and a food-contamination-relevant element; Co, Mn and Li are carried for completeness and to route to their respective metal pages.
• ingredients: [] and products: [] are correct and are not a Part 5 missing-products defect. This is a supply-chain / mechanism source that reports no food, ingredient, or product occurrence, mirroring the handling of Phytoremediation of Heavy Metals in Tropical Soils an Overview.
• No brand names appear in the source.
• Part 2 direction-of-edit check: this ingest adds upstream mechanism literature and neither softens nor strengthens any HMT&C threshold claim. The edit moves toward the literature (it deepens the mechanistic basis for why food crops carry the metals they do); it does not move toward HMT&C convenience.

Page history

The five most recent substantive edits to this page. The full version history lives in git; when DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.