Battery Recycling Hydrometallurgy: Process Flows Guide

Last updated: 2026-10-23

Battery recycling hydrometallurgy typically recovers 95–98% of the nickel and cobalt in end-of-life lithium-ion cells as battery-grade sulfate salts, based on recovery ranges reported in the peer-reviewed literature. The logic is straightforward: shredded cells become black mass, sulfuric acid leaching dissolves the nickel, cobalt, manganese and lithium, solvent extraction purifies and separates the metals, and crystallization delivers saleable products. This guide walks through each stage and its equipment implications for plant investors and process engineers.

Key Takeaways

• Hydrometallurgical recycling converts shredded end-of-life cells into battery-grade nickel, cobalt and lithium salts.
• Black mass assay drives every downstream decision: reagent dose, pH setpoints and equipment sizing.
• D2EHPA removes Cu, Fe, Al and Mn; Cyanex 272 splits cobalt from nickel at pH 5–5.5.
• Lithium is recovered as Li2CO3 by hot sodium carbonate precipitation, with mother liquor managed for zero liquid discharge.
• EU Regulation 2023/1542 recycled-content mandates create durable structural demand for recycled battery metals.

What Is Battery Recycling Hydrometallurgy?

Hydrometallurgy is a branch of extractive metallurgy that recovers metals by dissolving them into aqueous solution, then purifying, separating and crystallizing them; for the fundamentals, see our primer on what is hydrometallurgy. Applied to spent lithium-ion cells, battery recycling hydrometallurgy takes the output of mechanical processing and converts it into refined, battery-grade products at moderate temperature, with selective chemistry that pyrometallurgy cannot match. Three definitions anchor the rest of this guide.

Black mass is a dark, granular powder that remains after steel casings, plastics and metal foils are stripped from shredded cells; it concentrates the cathode values — nickel, cobalt, manganese and lithium — together with graphite and residual fluoride species. Solvent extraction (SX) is a separation process that partitions metal ions between an aqueous phase and an organic phase carrying selective extractants, and it is the workhorse of Ni/Co purification. Pregnant leach solution (PLS) is a metal-bearing liquor that leaves the leach circuit and feeds the purification train. Finally, zero liquid discharge (ZLD) is a design philosophy that recycles all process water within the plant boundary, leaving only solid by-products to handle.

Cathode chemistry determines the economics. Nickel manganese cobalt oxide (NMC) cathodes dominate electric-vehicle packs and carry most of the contained metal value; lithium iron phosphate (LFP) cathodes contain iron and phosphate, so lithium is essentially the only recoverable value and the business case shifts toward tolling or gate-fee models. Hydrometallurgical treatment suits both, but flowsheet details differ: an NMC plant justifies a full SX purification train, while an LFP-focused operation may stop at crude lithium carbonate.

Why choose hydrometallurgy over pyrometallurgy at all? Smelting is robust against mixed feed but typically reports lithium and aluminum to slag, consumes graphite as reductant, and delivers an alloy that still requires downstream hydrometallurgy. A direct hydrometallurgical route skips the furnace, recovers lithium in the same flowsheet, and operates at under 100 °C — but it demands tight control of impurities, pH and organic entrainment. Those demands shape every equipment choice in the sections below.

Battery Recycling Hydrometallurgy Flowsheet: Stage by Stage

The lithium battery recycling process from pack intake to crystallized salts follows a consistent sequence, whatever the vendor diagram looks like: make the pack safe, liberate the active material, dissolve it, purify it, and crystallize it. In battery recycling hydrometallurgy, each stage’s conditions and recoveries depend heavily on feed assay, so treat the numbers in Table 1 as illustrative starting points for NMC-dominated feed, stated on a dry basis for one tonne of black mass — not as guarantees.

1. Discharge and deactivation. Packs are resistively or brine-discharged to a low state of charge before any cutting, so residual electrical energy cannot ignite the electrolyte during shredding. Remaining electrolyte — lithium hexafluorophosphate (LiPF6) dissolved in organic carbonates — still off-gases HF when wet, which dictates materials of construction later.

2. Shredding and mechanical separation. Rotary shears and hammer mills operate under nitrogen or CO2 inerting to suppress thermal events. Sieving, air classification and eddy-current separation then reject steel casings, aluminum and copper foils, and plastics, leaving the fine active-material fraction.

3. Black mass production. The sub-millimetre fraction is black mass. Illustrative dry-basis assays for NMC feed run 25–35% Ni, 10–20% Co, 8–12% Mn and 3–5% Li; graphite typically accounts for a further 15–30%. Send samples to an accredited laboratory before committing to any design number.

4. Acid leaching. H2SO4 with H2O2 as reductant is the industry-standard black mass leaching recipe: hydrogen peroxide reduces insoluble Co(III) to soluble Co(II), which is the key to high recoveries. Typical conditions are 60–80 °C, 1–3 hours residence, pH 1.5–2.0, and roughly stoichiometric acid plus excess peroxide. Literature leach extractions of 95–98% for Ni and Co and 90–95% for Li are typical reported ranges, not promises — our guide to leaching recovery calculation shows how to convert assays into recoveries you can defend, and the leaching pillar article covers reactor selection.

5. Impurity removal. Iron and aluminum precipitate as hydroxides at pH 3.5–4.5; copper and residual calcium follow in the SX train.

6. SX purification and Ni/Co/Mn separation. Detailed in the next section.

7. Crystallization. Purified sulfate liquors are concentrated and crystallized to battery-grade products — covered in the lithium recovery section, though nickel and cobalt sulfate crystallization follows the same logic.

Basis: one tonne of NMC-dominated black mass, dry basis; ranges are illustrative design starting points compiled from published literature, to be confirmed by pilot testing on your actual feed.

Impurity Removal and Ni Co Mn Solvent Extraction

Once the PLS is clarified, solvent extraction does the heavy lifting of purification and separation. Two extractants dominate commercial flowsheets, and understanding their selectivity orders is the fastest way to read any Ni Co Mn solvent extraction diagram.

Di-2-ethylhexylphosphoric acid (D2EHPA) extracts trivalent and divalent impurity metals ahead of nickel: its selectivity sequence runs Fe(III) > Al(III) > Cu(II) > Mn(II) > Co(II) > Ni(II). That ordering defines its role — at controlled pH 3.0–4.0, D2EHPA scavenges copper, residual iron, aluminum and, critically, manganese, while leaving nickel and cobalt largely in the aqueous phase. Stripping with strong sulfuric acid (typically 150–200 g/L, illustrative) regenerates the organic and produces a small impurity-rich bleed. A detailed extractant comparison is in D2EHPA vs Cyanex 272.

Bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272) then performs the cobalt–nickel split. Cyanex 272 extracts cobalt strongly at pH 5.0–5.8 while nickel extraction only becomes significant above pH 6.5–7, so a staged extraction at tightly controlled pH 5.5 transfers cobalt into the organic and leaves a nickel-rich raffinate with Co typically below 10 mg/L (illustrative single-stage-difference; multi-stage performance is better). Cobalt is stripped with dilute H2SO4 (20–50 g/L, illustrative) to yield a purified CoSO4 solution bound for crystallization. The general theory behind these circuits is covered in our solvent extraction guide.

pH control is the make-or-break variable. Extraction liberates hydrogen ions, so each stage needs live neutralization — usually dilute NaOH rather than lime, because calcium carried by lime slurry meets sulfate downstream and precipitates as gypsum scale (a failure mode detailed in the troubleshooting section). Full-name equipment matters too: mixer-settler boxes with properly sized Residence time, settling area and organic recycle are specified in our mixer-settler design guide.

The organic-to-aqueous (O/A) ratio sets stage efficiency and entrainment behaviour. Too high an O/A ratio wastes extractant and increases organic losses to the raffinate; too low starves the stages. Worked guidance is in the O/A ratio article. Wash and strip stages complete the picture: a dilute-acid scrub washes entrained impurities from loaded organic, and polishing coalescers or flotation cells strip physically entrained organics from the raffinate before it moves on — entrained D2EHPA in the nickel liquor will poison later lithium crystallization.

All values illustrative and typical of published practice; confirm on your own PLS chemistry.

How Is Lithium Recovered and Crystallized to Battery-Grade Salts?

After manganese and the cobalt–nickel split, lithium remains in the SX raffinate as dilute Li2SO4 — commonly 5–15 g/L Li, depending on upstream recovery choices. Two product routes exist, and the choice is a commercial decision as much as a technical one.

The dominant route is sodium carbonate precipitation of lithium carbonate. Sodium carbonate is dosed into the heated liquor at 85–95 °C, holding pH near 9–10 and pushing the reaction toward Li2CO3. Lithium carbonate has inverse solubility — it is less soluble hot than cold — which is why precipitation, filtration and washing all happen hot: yield improves and sodium co-precipitation falls. Washed, dried cake at ≥99.5% Li2CO3 (a commonly quoted commercial grade; verify against your offtaker’s specification) is the product. Spent mother liquor carries Na2SO4 and unprecipitated lithium.

The second route produces lithium hydroxide monohydrate, increasingly demanded by high-nickel cathode makers. From a sulfate medium this requires an extra conversion step — causticization with lime, ion exchange, or electrodialysis — followed by crystallization of LiOH·H2O. Each step adds capital and sodium or calcium management burden, so most new plants start with Li2CO3 and add LiOH capability later.

Impurity control at this stage is unforgiving. Calcium, magnesium, sodium and boron are the usual suspects; battery-grade salt specifications commonly quote limits in the single-digit mg/kg range for elements like Cu, Fe and Ca — confirm the actual limits with your offtaker rather than designing to a generic number. Every upstream unit feeds this endgame: entrained organics from SX, calcium from careless neutralization, or manganese breakthrough will each find their way into the crystallizer.

Mother liquor management decides plant economics and environmental performance. Each precipitation–wash cycle leaves sodium and sulfate behind; endless recycle concentrates them until they contaminate product. The standard answer is a purge through an evaporative crystallization circuit — mechanical vapour recompression (MVR) evaporators concentrate the purge, recover residual lithium as a lower-grade carbonate or as feed back to precipitation, and crystallize sodium sulfate as a saleable or landfillable by-product. Our evaporation and crystallization pillar article details evaporator selection, boiling-point rise and crystallizer types. True zero liquid discharge (ZLD) closes the loop: condensate returns as wash water, purge solids leave as by-products, and nothing liquid crosses the fence.

What Goes Wrong in Recycling Plants? Troubleshooting Patterns from the Field

Every flowsheet failure we have audited in battery recycling plants falls into a handful of recurring patterns. Here they are in symptom → cause → remedy form, with the remedies ranked by how often they actually work.

ASME VIII Div 1 vs Div 2 in practice

1. Fluoride attack on standard acid equipment. Symptom: unexplained pitting and liner blistering in vessels that passed generic H2SO4 service review. Cause: residual LiPF6 electrolyte and PVDF binder hydrolyze to hydrofluoric acid (HF), which attacks glass linings and silica-bearing alloys that sulfuric acid alone never touches. Remedy: specify PTFE or PVDF linings and HF-resistant alloys wherever wet black mass exists, and monitor fluoride in process streams routinely. From field experience, this is the single most underestimated design input in battery recycling hydrometallurgy — fluorine shows up in every lot of black mass we have assayed, and generic acid-service equipment specifications have failed within months at more than one site.

2. Manganese co-extraction into the cobalt strip. Symptom: cobalt sulfate purity drifts downward over weeks. Cause: manganese(II) extracts more strongly than cobalt on Cyanex 272, so any Mn not removed upstream rides the same path into the cobalt circuit. Remedy: a dedicated D2EHPA manganese-removal stage at pH 3.0–3.5 before the Co/Ni split, plus a pH-controlled scrub on loaded organic.

3. Gypsum scaling in pipes and heat exchangers. Symptom: rising pump pressure and falling heat-transfer coefficients. Cause: calcium introduced with lime slurry meets sulfate and precipitates as CaSO4 on every warm surface. Remedy: switch neutralization to NaOH or MgO where chemistry allows, run a calcium-removal step ahead of crystallization, and design circuits for periodic descaling access.

4. Graphite blinding filters and thickeners. Symptom: filter press cycle times collapse and clarifier rakes overload. Cause: fine, hydrophobic graphite from black mass leaching is poorly flocculated by standard reagent programs. Remedy: select coagulant/flocculant packages on real leach residue — not on alumina-plant experience — and consider graphite recovery as a saleable by-product rather than a waste cost.

5. pH control oscillation in SX stages. Symptom: extraction efficiency swings between shifts with no feed change. Cause: lagged pH loops combined with lime-slurry dosing dead time push stages across their selectivity windows. Remedy: inline NaOH dosing with fast loop tuning, and where budgets allow, online metal analyzers closing the loop on actual stage performance.

6. O/A ratio drift and organic entrainment. Symptom: organic carryover into raffinate and rising extractant make-up costs. Cause: flow imbalance between organic and aqueous circuits after upstream tonnage changes. Remedy: instrument both circuits, alarm on ratio deviation, and revisit the design guidance in our O/A ratio article before blaming the extractant.

Economics and Market Drivers: What Justifies the Capex?

Metal value does almost all the economic work. In an NMC-based battery recycling hydrometallurgy business, cobalt and nickel typically contribute 80–90% of gross revenue, with lithium and manganese making up the remainder — the exact split moves with prices and feed assay. Table 3 shows an illustrative netback calculation; every input is an assumption for demonstration, not a quote.

Working the calculation: 300 kg Ni at 15,000 USD/t gives 4,500 USD; 150 kg Co at 30,000 USD/t gives 4,500 USD; 40 kg Li at 12,000 USD/t gives 480 USD; total 9,480 USD contained value. Applying 96% recovery to the Ni/Co value yields roughly 9,100 USD of realized revenue per tonne. Subtract the processing range and the netback lands between roughly 5,600 and 7,600 USD per tonne of black mass — a number that must then carry capital amortization, feedstock purchase or gate-fee pricing, and working capital. Sensitivity to feed assay is brutal: an LFP-dominated black mass can contain a tenth of the metal value of NMC feed, which is why offtake contracts and gate fees, not spot metal prices alone, anchor bankable projects.

On the demand side, regulation does what price signals alone cannot. Regulation (EU) 2023/1542 obliges batteries placed on the EU market to include minimum shares of recycled cobalt, lithium and nickel from the early 2030s, documented through battery passports and due-diligence requirements. The regulation does not set prices, but it converts recycled battery metals from an optional feedstock into a compliance input for every cell maker selling into Europe — the structural driver behind most current project financing decisions, alongside raw-material security concerns and EV fleet growth.

What Recovery Does an Actual Plant Achieve? An Illustrative Pilot Campaign

Published literature ranges say little about your feed, your water chemistry or your operator training. The numbers below come from an illustrative pilot-scale campaign we use in feasibility workshops — a single 2 m³ agitated-leach campaign on NMC black mass, reported on a dry-basis assay with ICP-OES solution analysis. Treat them as a worked example of what pilot data should look like, not as a performance guarantee.

The leach ran at 70 °C, pH 1.8, two hours residence, with H2O2 at 1.1× stoichiometric relative to the divalent-metal demand and H2SO4 at 1.4× stoichiometric. End-of-campaign extractions were 97.1% Ni, 96.8% Co, 95.5% Mn and 93.4% Li — inside the literature ranges quoted earlier, and confirming that peroxide availability, not acid strength, was the limiting variable (extractions plateaued whenever peroxide dosing lagged).

Downstream, the illustrative D2EHPA circuit took manganese from 6.2 g/L in the PLS to below 10 mg/L in three extraction stages at pH 3.2 with an O/A ratio of 1.2, while carrying less than 1% of the cobalt inventory. The Cyanex 272 split at pH 5.5 left the nickel raffinate below 20 mg/L Co across four stages; cobalt strip liquor crystallized to CoSO4·7H2O at 99.9% purity on the elements analyzed. Hot sodium carbonate precipitation at 90 °C recovered 88% of raffinate lithium as Li2CO3 assaying 99.6% after a single hot wash, with the balance retained in mother liquor and recycled through the purge circuit.

Three lessons transfer. First, lithium recovery is set by the precipitation–recycle strategy, not by a single precipitation yield — the 88% stage figure becomes 96%+ cumulative with disciplined mother-liquor purge design. Second, every impurity breakthrough you tolerate upstream reappears as a specification problem in the crystallizer. Third, use our leaching recovery calculation method to reconcile solution and solid assays before believing any single number — mass-balance closure better than 97% is the minimum credibility bar for bankable pilot data.

Frequently Asked Questions

What is black mass and why does its assay matter so much?

Black mass is the fine powder recovered after shredding and separating spent lithium-ion cells; it concentrates the cathode metals — nickel, cobalt, manganese and lithium — plus graphite and fluoride residues. Its assay sets reagent consumption, SX configuration and revenue: a 30% Ni NMC mass and a 2% Ni LFP mass justify entirely different plants, so accredited third-party assay of representative lots is the first step in any project.

Can one plant process both NMC and LFP black mass?

Yes, hydraulically, but not necessarily profitably. The leaching and purification front end is chemistry-flexible, while the value recovery back end is not: LFP feed yields only lithium value, so the SX train idles and unit economics depend on gate fees rather than metal revenue. Many operators run NMC for margin and accept LFP on a tolling basis, flexing which campaign mix keeps the SX train economically loaded.

Why is hydrogen peroxide used in the leaching step?

Cobalt in cathode material arrives as insoluble Co(III). Hydrogen peroxide reduces Co(III) to soluble Co(II), enabling dissolution in dilute sulfuric acid and lifting cobalt extraction into the 95–98% range typical of published flowsheets. Without a reductant, cobalt recovery falls and acid consumption rises. Dosing is stoichiometry-driven: underdosing caps recovery, overdosing wastes reagent and can degrade downstream organics.

What overall recovery can a hydrometallurgical recycling plant achieve?

Peer-reviewed flowsheets typically report 95–98% for nickel and cobalt and 90–95% for lithium at the leach stage, with overall product recovery somewhat lower after SX losses and crystallizer purge. These are typical literature ranges, not guarantees: actual performance depends on feed assay, reagent control and, above all, verified pilot data on your own black mass before design freeze.

How is manganese handled after leaching?

Manganese dissolves with nickel and cobalt in the leach, then is removed preferentially by D2EHPA at pH 3.0–3.5 because manganese extracts more strongly than cobalt and nickel. Removing it before the Cyanex 272 cobalt–nickel split prevents manganese contamination of the cobalt sulfate product. Some flowsheets instead precipitate manganese as a carbonate or dioxide by-product when the contained tonnage justifies recovery as saleable material.

Is graphite in black mass a problem or a product?

Both. During black mass leaching, graphite does not dissolve and reports entirely to the leach residue, where its fineness and hydrophobicity blind filters and overload thickeners if unmanaged. Remedies include flotation before leaching, dedicated dewatering with tailored flocculants, or recovering purified graphite as a battery-anode by-product. Most plants today still treat it as a dewatered waste with a tipping cost; recovery economics are improving.

Conclusion: From Black Mass to Battery-Grade Salts

The chemistry of battery recycling hydrometallurgy is mature; what separates successful projects from stalled ones is disciplined stage-gate development — a verified black mass assay before flowsheet lock, pilot data on your own feed before equipment specification, and crystallizer design built around real mother-liquor chemistry rather than steady-state assumptions. Battery recycling hydrometallurgy rewards investors who treat impurity control, fluoride-resistant materials of construction and lithium mother-liquor management as first-order design decisions rather than detail engineering afterthoughts. Whether you are sizing a greenfield black mass plant or retrofitting an existing SX refinery, validate your flowsheet with Lexin-tech’s pilot testing services, and browse our resource library for the leaching, solvent extraction and crystallization design guides referenced throughout this article.

References

1. USGS. Mineral Commodity Summaries 2025 — Lithium. U.S. Geological Survey, 2025.
2. USGS. Mineral Commodity Summaries 2025 — Cobalt. U.S. Geological Survey, 2025.
3. USGS. Mineral Commodity Summaries 2025 — Nickel. U.S. Geological Survey, 2025.
4. Harper, G., Sommerville, R., Kendrick, E. et al. “Recycling lithium-ion batteries from electric vehicles.” Nature 575, 75–86 (2019).
5. Lu, J., Dreisinger, D., Glück, T. “Cobalt and nickel recovery from lithium ion battery leach solution using Cyanex 272.” Hydrometallurgy 187 (2019) 94–101.
6. Rydberg, J. (ed.). Solvent Extraction Principles and Practice, 2nd ed. CRC Press, 2004.
7. Regulation (EU) 2023/1542 of the European Parliament and of the Council of 12 July 2023 concerning batteries and waste batteries.

Changelog

2026-10-23 — First published.