Engineered evaporation, concentration and crystallization for rare earth extraction (bastnäsite / monazite leachate, (NH₄)₂SO₄ recovery, RECl₃ concentration), non-ferrous smelting wastewater (Cu / Zn / Ni / Co, trace As / Sb) and heavy-metal-bearing streams — with material selection that survives 5,000–30,000 mg/L chloride and acidic service.
High-value metal recovery, aggressive corrosion profiles and complex impurity systems combine to make these streams among the most engineering-intensive in the industry.
Cu ($6–9/kg), Ni ($15–22/kg), Co ($30–50/kg), rare earth oxides (Nd₂O₃ $50–150/kg, Dy₂O₃ $200–600/kg) carry significant unit value.
Chloride-rich RECl₃ leach solutions (Cl⁻ 5,000–30,000 mg/L), sulfate pickling streams (pH 1–2) and acidified extraction circuits (pH <1) drive corrosion rates that defeat 316L within weeks.
Rare earth streams carry co-extracted Fe³⁺ (1–10 g/L), Al³⁺ (0.5–5 g/L), Ca²⁺ / Mg²⁺ (0.5–3 g/L), residual extractants (P204 / P507 / P350 at 50–500 mg/L) and buffered sulfate / chloride backgrounds.
Non-ferrous smelters run campaign-mode operation: feed ore changes, copper concentrate grade swings, and rare earth batches shift composition.
For rare earth mines whose water problem is hardness, silica and moderate dissolved salts at large flow, the workable route before any thermal ZLD is membrane concentration with engineered softening:
MVR evaporation and crystallization system for rare earth metallurgy RO reject: ammonium sulfate and chloride salt recovery, condensate ammonia polishing and ZLD compliance.
For rare earth separation plants, ammonia nitrogen treatment is not one process but three, selected by concentration: high-strength streams (tens of grams per liter as NH4Cl) go to vacuum evaporation-crystallization
For rare earth operations working ores that carry uranium and thorium, water closure is a radiological design problem before it is a salinity problem: beneficiation and transport waters are mildly
For rare earth smelting and separation wastewater – the streams that carry salt above 10%, pH below 1, COD in the tens of thousands and ammonia nitrogen in the thousands,
Four application families — from extraction liquor concentration to smelting wastewater ZLD and battery-precursor salt crystallization.
Stream characteristics after SX (solvent extraction) raffinate — concentration before precipitation / crystallization.
Acid mine drainage and smelter scrubber blowdown — heavy-metal-bearing brine management.
Battery-precursor grade CoSO₄·7H₂O — morphology and purity control for cathode use.
Rare earth precipitation with (NH₄)₂SO₄ / NH₄HCO₃ — linkage to S2 ammonium sulfate crystallization know-how.
Common feed streams in rare earth and non-ferrous metallurgy, with the technology route typically considered for first-pass screening.
| Chemical / Stream | Source & Context | Key Behavior | Typical Route | Material Focus |
|---|---|---|---|---|
| Copper smelting wastewater | Cu concentrate smelting, electrorefining bleed | Cu²⁺ 1–20 g/L; H₂SO₄ 5–50 g/L; As 10–500 mg/L; Sb 5–100 mg/L | MVR + FC | Duplex 2205 |
| Zinc / Cadmium sulfate | Hydrometallurgical Zn refining (roast-leach-electrowin), Cd recovery | Zn²⁺ 30–150 g/L; Cd²⁺ 0.1–5 g/L; Cl⁻ <500 mg/L | DTB / Cooling | 316L / Duplex |
| Nickel / Cobalt sulfate / chloride | Laterite HPAL leach, battery precursor streams — see Battery Materials & Hydrometallurgy | Ni²⁺ 20–90 g/L; Co²⁺ 1–10 g/L; Mg²⁺ 5–30 g/L | MVR + Crystallization | Hastelloy / Ti |
| Rare earth chloride solution | Bastnäsite / monazite HCl leach, extraction raffinate | RECl₃ 100–400 g/L; Cl⁻ 50–150 g/L; Fe³⁺ / Al³⁺ trace | Vacuum + FC | Titanium / Hastelloy |
| Rare earth sulfate solution | Sulfuric acid bake leach (monazite), separation circuits | RE₂(SO₄)₃ 30–150 g/L; pH 1–3; Fe³⁺ 1–10 g/L | MVR + Cooling | Duplex 2205 |
| Ammonium salt by-product | Rare earth precipitation with (NH₄)₂SO₄ / NH₄HCO₃ | (NH₄)₂SO₄ 20–40%; NH₄Cl 10–20%; recoverable | DTB / FC | 316L / Duplex |
Routes shown are for preliminary screening only. Final selection requires solubility data, trace metal profile, extractant residual analysis and project-specific engineering evaluation.
Indicative process flow for smelting wastewater with mixed heavy metals, residual acidity and ZLD requirement.
The canonical sequence for non-ferrous smelting wastewater: heavy-metal pre-treatment (sulfide at pH 8–9, hydroxide at pH 9–10) → As / Sb co-precipitation with ferric iron → pH adjustment → MVR (15–25 kWh per tonne water) or multi-effect (0.25–0.40 t steam per tonne water) concentration → forced-circulation (tube velocity 2–3 m/s) or cooling crystallization for metal-salt recovery → condensate reuse.
Simplified PFD for indicative routing only. Actual configuration depends on metal speciation, chloride/sulfate ratio, extractant residual, scaling tendency and target product purity. Heavy metal precipitation feasibility requires laboratory verification.
Evaporation and crystallization sit inside the hydromet circuit — not beside it. Four integration points decide the plant water and salt balance.
Concentrate leach liquor ahead of downstream separation — acid values returned to the leach circuit.
Extraction raffinate carries residual extractant and acid — evaporated for volume reduction and salt recovery.
Rare earth precipitation liquors recycle or purge — the loop is engineered against impurity accumulation.
Na₂SO₄ / (NH₄)₂SO₄ by-product salts crystallized for sale or managed disposal.
Chloride, acidity and oxidizing metal ions — not TDS — pick the alloy in this industry. Map the stream first; discuss geometry second.
| Stream / Exposure | Typical Service | Material | Selection Logic & Watch-Outs |
|---|---|---|---|
| Cl⁻ above ~5,000 mg/L — RECl₃ leach circuits | Rare earth chloride solution (RECl₃ 100–400 g/L, Cl⁻ 50–150 g/L) | Titanium (TA2) | Workhorse for RECl₃ circuits — Cl⁻ to 30,000 mg/L; 316L is excluded by pitting above ~200 mg/L at evaporation temperature |
| pH <2 acidic + chloride + oxidizing species | Acidified extraction circuits (pH <1), acidic heavy-metal brines | Specialty alloys (Hastelloy C-276, corrosion allowance) | Acidic + chloride service defeats Duplex; confirm by coupon testing at actual T, pH and metal-ion matrix |
| SO₄²⁻-rich · pH 1–3 | Rare earth sulfate solution (RE₂(SO₄)₃ 30–150 g/L), Cu smelting wastewater | Duplex 2205 | Adequate below ~1,000 mg/L Cl⁻ at moderate T; fails under high Cl⁻ combined with low pH |
| Mild ammonium sulfate service | Ammonium salt by-product ((NH₄)₂SO₄ / NH₄HCO₃ precipitation liquors) | 316L | Safe envelope only for Cl⁻ <~200 mg/L at evaporation temperature — verify chloride background before committing |
Final selection must be confirmed by coupon testing at actual operating T, pH and metal-ion matrix — never from a table alone.
Energy reuse and evaporation duty are one decision; crystal growth configuration (FC / DTB / Oslo) is a separate, orthogonal one. Real systems combine them.
Electric-driven concentration ahead of forced-circulation crystallization — the default wastewater ZLD route for smelting streams.
Battery-grade CoSO₄ and metal-salt duty where narrow particle size distribution and easy centrifugation are the product priority.
Large crystals, high purity — for high-purity metal salts where crystal quality outweighs throughput intensity.
FC for scaling, high-TDS smelting brines; multi-effect where smelter LP steam is available and power is dear.
Whether a stream is an asset or a liability depends on its metal value, hazard classification and the local discharge alternative.
Metal value justifies crystallization complexity — CuSO₄·5H₂O (target >99% main content, Fe <100 ppm, free H₂SO₄ <0.2%) and NiSO₄·6H₂O (target >98.5%) are marketable products.
Where metal value does not carry recovery economics, the salt is stabilized for compliant disposal — not forced into a saleable grade.
ZLD is not automatically the answer. The threshold between ZLD and compliant discharge sits where metal recovery revenue plus avoided disposal cost crosses the energy and CapEx cost of the thermal route — a per-project calculation driven by metal prices, discharge limits and utility costs.
EvapCryst organizes its delivery capability around four solution categories. The rare earth & non-ferrous industry most often combines S1 and S2.
Smelting wastewater concentration, metal-bearing brine reduction and condensate recovery.
Copper sulfate, nickel sulfate and ammonium salt crystallization for metal recovery.
Extractant and ammonium salt purge optimization for rare earth separation circuits.
MVR retrofits for existing multi-effect evaporator trains on smelting wastewater duty.
Chloride concentration above ~200 mg/L at evaporation temperature excludes 316L by pitting. Below ~1,000 mg/L at moderate T, Duplex 2205 is usually adequate. Above ~5,000 mg/L or in acidic service (pH <2), Titanium Grade 2 (workhorse for RECl₃ circuits) or Hastelloy C-276 (acidic + oxidizing) is required. Final selection must be confirmed by coupon testing at actual operating T, pH and metal-ion matrix.
Yes, in favorable conditions. Copper sulfate pentahydrate (CuSO₄·5H₂O, target >99% main content, Fe <100 ppm, free H₂SO₄ <0.2%) and nickel sulfate hexahydrate (NiSO₄·6H₂O, target >98.5%) are marketable products. The crystallizer produces the salt; upstream precipitation and solvent-extraction stages define its purity. We will not commit to product-grade salt recovery without a verified impurity profile of your feed (Fe, Ca, Cl⁻, free acid, extractant residual).
MVR (15–25 kWh per tonne water) uses electrical energy to recompress vapor and is favored where electricity is cheap ($0.04–0.08/kWh) or steam is expensive; multi-effect (0.25–0.40 t steam per tonne water) uses motive steam and is favored where low-pressure steam is available from the smelter (at $15–25/t). For high-boiling-point-elevation streams typical of concentrated metal sulfates (BPE 5–15°C), MVR’s effective ΔT advantage narrows — the selection is rarely obvious and requires a per-project energy balance.
Arsenic and antimony must be removed upstream of the evaporator — typically by sulfide precipitation (NaHS or TMT-15 at pH 4–5), co-precipitation with ferric iron (Fe / As molar ratio 4:1–8:1 producing scorodite or ferrihydrite-As), or dedicated As-removal circuits (lime softening + ferric sulfate). Inlet limit to the evaporator is typically <0.5 mg/L As and <0.5 mg/L Sb. EvapCryst does not propose to evaporate As-bearing streams through crystallizer duty without verified upstream As removal.
Send us your feed composition, metal speciation and target output. Within 2 business days you will receive a feasibility assessment, simplified PFD and indicative scope.
Send your feed characterization (TDS, COD, main salts, viscosity), throughput and product targets — we respond with a preliminary process route within two business days.
