What Is Ternary Precursor Coprecipitation Wastewater Treatment?
Ternary precursor coprecipitation wastewater treatment is the engineered train that captures nickel, cobalt and manganese from NCM/NMC cathode precursor mother liquor before discharge. A typical 2026 system runs coprecipitation at pH 10.5–11.5 and 50–60°C with NaOH plus NH4HCO3 chelator, then routes the MHP-filtered mother liquor (SO4 15,000–40,000 mg/L; NH3-N 3,000–8,000 mg/L) through pH correction, sulfide polishing, MEE crystallization and ClO2 polishing to meet China GB 30484 limits of Ni ≤ 0.5 mg/L, Co ≤ 0.5 mg/L and NH3-N ≤ 15 mg/L.
The "ternary precursor" in question is the Ni-Co-Mn mixed hydroxide (MHP) intermediate that feeds the NCM811, NCM622 and NCM523 cathode active material lines. Plant molar ratios are tightly specified — 8:1:1, 6:2:2 and 5:2:3 are the production baselines, and the MHP must hit tap density ≥ 2.0 g/cm³ with D50 of 8–12 µm for downstream sintering (Zhongsheng field data, 2026). The chelator in the reactor — almost always NH4HCO3 in Chinese lines, Na2CO3 in some Korean lines — holds the three metals in a common soluble complex so they precipitate as a single phase rather than as three separate hydroxides with different solubilities. The metal-to-ammonia chelator molar ratio is the single most important feed variable; the design baseline most plants operate against is 1:1 to 1:1.2 metal:chelator, with deviations outside ±0.05 producing a soft, poorly filterable MHP.
The wastewater train covers two streams, not one: the reactor mother liquor left over after the MHP filter press, and the wash filtrate from the cake washing step. The treatment goal is dual — produce a reusable MHP filter cake, and a treated effluent that satisfies 2026 GB 30484 and EU IED limits for Ni, Co, Mn, NH3-N and COD. The same train also has to crystallize sodium sulfate from the sulfate-rich bleed so the plant can recycle it as wash water, which is why the full ternary precursor wastewater recycling system design must be read together with this reactor-side reference.
Feed Chemistry and Reactor Operating Window
The coprecipitation reactor runs inside a narrow envelope; the pH must sit at 11.0 ± 0.2, the temperature at 50–60°C, and the dissolved oxygen under 0.5 mg/L or Mn²⁺ oxidizes to MnO₂ and ruins the particle morphology. Main precipitant is NaOH dosed at 4–6 mol/L; chelator is NH4HCO3 (or Na2CO3) fed to maintain a 1:1 to 1:1.2 metal:chelator molar ratio. The mixed sulfate feed carries Ni+Co+Mn at 1.0–2.0 mol/L, free NH3-N at 5–10 g/L, and SO4 at 30,000–80,000 mg/L. Residence time runs 8–20 h depending on target particle size, stirrer speed sits at 400–800 rpm with a 3-pitched-blade impeller, and the headspace is N2-blanketed at 0.3–0.5 m³/h per m³ of reactor to keep DO below 0.5 mg/L (Zhongsheng field data, 2026).
Stoichiometry is straightforward on paper: 2 mol NaOH per mole of M(OH)₂ formed, plus roughly 0.3 mol excess to hold the pH window. The reason Mn²⁺ must stay reduced is the failure mode nobody wants to debug at 02:00 — at DO > 1 mg/L and pH > 8.5, Mn oxidizes to MnO₂, the precipitate darkens from pale green to brown, and the filter press blinding index climbs 3–5× within two hours. The PLC-controlled chemical dosing system for NaOH, Na2S and ClO2 injection is the unit that holds these setpoints within the tolerance band; without closed-loop pH control, pH swings of ±0.5 are routine and MHP tap density drops by 8–12%.
| Parameter | Setpoint | Operating band | Failure mode if violated |
|---|---|---|---|
| pH | 11.0 | 10.5–11.5 | Co-rich segregation; soft cake |
| Temperature | 55°C | 50–60°C | Particle coarsening > 15 µm |
| Residence time | 14 h | 8–20 h | Undersized D50 < 6 µm |
| Stirrer speed | 600 rpm | 400–800 rpm | Aggregation or fines |
| Dissolved O₂ | < 0.3 mg/L | < 0.5 mg/L | MnO₂ formation, brown cake |
| Metal:chelator | 1:1.1 | 1:1.0–1:1.2 | Selective precipitation of Ni |
| NaOH excess | 0.3 mol | 0.2–0.4 mol | Low pH → Co loss to liquor |
Mother-Liquor Composition and Why It Cannot Be Discharged Raw
Mother liquor leaving the MHP filter press is too contaminated to blend with general plant effluent and far too contaminated to send to a municipal biological plant. Typical composition is residual Ni 50–150 mg/L, Co 30–120 mg/L, Mn 80–200 mg/L, SO4 15,000–40,000 mg/L, NH3-N 3,000–8,000 mg/L, and COD 500–1,500 mg/L. Direct discharge would exceed GB 30484 by 100–400× for Ni and 200–500× for NH3-N — there is no dilution ratio that fixes that on a 25,000 t/yr line.
Volume balance makes the problem worse: every 1 t of NCM precursor generates 8–14 m³ of mother liquor and 3–6 m³ of wash filtrate, so a 25,000 t/yr line produces ~280,000 m³/yr of mother liquor plus ~110,000 m³/yr of wash water. Wash filtrate is the easier stream — SO4 5,000–12,000 mg/L, NH3-N 200–800 mg/L, SS 200–800 mg/L from entrained MHP fines — but it cannot be routed to the main plant DAF either, because the metal load spikes kill the biological stage downstream. The 2026 environmental impact assessments filed for new Chinese precursor capacity consistently reject any blending scheme that routes mother liquor through the general biological train; segregated treatment is now the regulatory default (per 2025-11 MEP briefing on battery-sector EIA).
| Species | Mother liquor (mg/L) | Wash filtrate (mg/L) | GB 30484 limit (mg/L) | Overshoot factor |
|---|---|---|---|---|
| Ni | 50–150 | 5–20 | 0.5 | 100–300× |
| Co | 30–120 | 3–15 | 0.5 | 60–240× |
| Mn | 80–200 | 8–25 | 2.0 | 40–100× |
| NH3-N | 3,000–8,000 | 200–800 | 15 | 200–530× |
| SO4 | 15,000–40,000 | 5,000–12,000 | reportable | n/a |
| COD | 500–1,500 | 150–400 | 200 | 2.5–7.5× |
| SS | 50–200 | 200–800 | 70 | 1–11× |
Wastewater Treatment Train: Step-by-Step Process Flow
Step 1 is pH correction. Mother liquor leaves the filter press at pH 10.5–11.5; sulfuric acid (H2SO4, 30–50%) drops it to 8.5–9.0 over 15–20 min in a 30–60 min HRT tank. Lowering pH below 8.5 precipitates the bulk of residual Mn as Mn(OH)₂ and breaks the Ni-ammine complexes that would otherwise hold Ni in solution through the next step. Residual Mn ends up at 5–15 mg/L after this stage; residual Ni and Co are still too high to meet GB 30484.
Step 2 is sulfide polishing. Na2S or NaHS is dosed at 1.2× the stoichiometric requirement for residual Ni²⁺ + Co²⁺, typically 50–200 mg/L as S²⁻. Reactor retention is 30–60 min in a slow-stirred tank to keep sulfide floc dense, and air ingress is prevented — even 0.5 mg/L of DO re-oxidizes S²⁻ and defeats the polish. This stage drives Ni and Co below 0.5 mg/L as NiS/CoS; the sludge is captured in step 3.
Step 3 is coagulation plus dissolved air flotation. PAC at 50–100 mg/L and anionic PAM at 1–2 mg/L flocculate the colloidal metal sulfides, and a ZSQ dissolved air flotation system for sulfide-sludge capture floats the floc to the surface for skimming. Effluent SS drops to <30 mg/L; the floated sludge joins the main metal-sludge stream to the filter press.
Step 4 is ammonia stripping plus ClO2 polishing. The stream is re-raised to pH 11 with NaOH, heated to 60°C, and air-stripped in a packed tower with air-to-liquid ratio 2,000–3,000:1 to drop NH3-N to <50 mg/L. The strip overhead (8–12% NH3) is absorbed in sulfuric acid to make ammonium sulfate fertilizer. Residual NH3-N is then polished to <15 mg/L using a ZS series chlorine dioxide generator for NH3-N polishing at ClO2:NH3-N mass ratio 4–5:1 and 30–60 min contact time; ClO2 also oxidizes any residual S²⁻ to SO4, eliminating sulfide carryover.
Step 5 is MEE plus crystallization. The sulfate-rich brine (SO4 80,000–120,000 mg/L at this point) goes to a mechanical vapor recompression evaporator, concentrates to 250,000–300,000 mg/L, and is fed to a crystallizer at 30–45°C to drop Na2SO4·10H2O. Recovery is 85–92% of the sodium fed, and the crystals are re-dissolved in the MHP wash step — a closed loop that displaces fresh sodium sulfate make-up. MEE condensate (TDS <50 mg/L) returns to the reactor wash step. If the site targets zero liquid discharge, step 6 adds an industrial RO system for final TDS polishing and water reuse on the MEE condensate to bring TDS below the 1,000 mg/L GB 30484 cap.
Step 7 is sludge dewatering. All metal-sludge streams — Mn(OH)₂, NiS/CoS, DAF float, clarifier underflow — combine in a sludge tank and feed a plate-and-frame filter press for MHP cake dewatering at 0.6–0.8 MPa. Cake dry solids reach 55–65%, and the cake is either sent to a secured landfill or sold to a metal recycler that recovers Ni and Co units at 85–90% of LME pricing. Filtrate returns to the front of the train.
2026 Effluent Compliance and Reuse Targets
China GB 30484-2013 sets the discharge ceiling for new precursor capacity at pH 6–9, Ni ≤ 0.5 mg/L, Co ≤ 0.5 mg/L, Mn ≤ 2.0 mg/L, NH3-N ≤ 15 mg/L, COD ≤ 200 mg/L, SS ≤ 70 mg/L; TDS is reportable and is typically capped at 1,000–2,000 mg/L by local environmental authorities, with Inner Mongolia and Qinghai sites enforcing 1,000 mg/L since 2025-08. The EU equivalent — IED 2010/75/EU cross-referenced with the CWW BREF 2023 BAT-AEL — lands tighter on cobalt: Ni 0.3–0.5 mg/L, Co 0.1–0.3 mg/L, Zn 0.3–1.0 mg/L, SS <30 mg/L, total N 10–15 mg/L.
The water-reuse target for 2026 is the figure every new Chinese precursor plant is now designed around: ≥70% process water recycle, with MEE condensate and RO permeate returned to MHP washing and the final RO permeate meeting GB 30484 TDS limits. A 25,000 t/yr NCM811 line that produces ~280,000 m³/yr of mother liquor and runs the train above cuts freshwater intake by 60–75% (Zhongsheng field data, 2026) — about 1.6 million m³/yr of fresh water avoided, which is the number the EPC designer puts in the EIA. For 2026 OPEX benchmarks for wastewater treatment plants, the same train lands at roughly USD 1.8–2.6 per m³ of mother liquor treated, dominated by NaOH, Na2S and steam.
| Parameter | GB 30484-2013 (CN) | EU IED + CWW BREF 2023 | Reuse target 2026 |
|---|---|---|---|
| pH | 6–9 | 6–9 | 6.5–8.5 (wash reuse) |
| Ni | 0.5 mg/L | 0.3–0.5 mg/L | — |
| Co | 0.5 mg/L | 0.1–0.3 mg/L | — |
| Mn | 2.0 mg/L | 0.5–1.0 mg/L (BREF) | — |
| NH3-N / total N | 15 mg/L | 10–15 mg/L | — |
| COD | 200 mg/L | — | — |
| SS | 70 mg/L | < 30 mg/L | — |
| TDS | 1,000–2,000 mg/L (local) | reportable | < 1,000 mg/L (RO permeate) |
| Process water recycle | — | — | ≥ 70% |
Frequently Asked Questions
What pH and temperature are required for ternary precursor coprecipitation? The reactor must hold pH 10.5–11.5 (target 11.0 ± 0.2) and 50–60°C, with N2 blanketing to keep dissolved O₂ below 0.5 mg/L; the PLC-controlled chemical dosing system for NaOH, Na2S and ClO2 injection is what holds those loops in practice.
How is residual nickel and cobalt removed from MHP mother liquor? Sulfide precipitation with Na2S or NaHS at 1.2× stoichiometric dose, 30–60 min retention under air-free conditions, followed by coagulation (PAC 50–100 mg/L + PAM 1–2 mg/L) and DAF capture of the NiS/CoS floc.
Can Na2SO4 from MEE crystallization be reused in the precursor process? Yes — recovery is 85–92% as Na2SO4·10H2O crystallized at 30–45°C from a 250,000–300,000 mg/L brine. The re-dissolved salt is fed back to the MHP wash step and displaces fresh make-up sodium sulfate, which is a meaningful OPEX line on a 25,000 t/yr line.
What is the 2026 Chinese discharge limit for nickel in battery precursor wastewater? 0.5 mg/L per GB 30484-2013. Several local authorities in Inner Mongolia and Qinghai have tightened to 0.2 mg/L since 2025-08, so any 2026 EIA in those provinces should design for 0.2 mg/L at the outlet.
How much mother liquor does a 1 t NCM precursor line generate? 8–14 m³ of mother liquor plus 3–6 m³ of wash filtrate per tonne of MHP, depending on target tap density and wash ratio; a 25,000 t/yr NCM811 line therefore produces ~280,000 m³/yr of mother liquor and ~110,000 m³/yr of wash water.
