Crystallization
Rhodium is the most expensive metal on the market (~$8,100/oz ≈ ~$260,000/kg, July 2026, +47 % y/y; 2021 peak ~$30,000/oz).
Technology brief
Rhodium is the most expensive metal on the market (~$8,100/oz ≈ ~$260,000/kg, July 2026, +47 % y/y; 2021 peak ~$30,000/oz).
The challenge
Primary use cases: rhodium (+ Pt, Pd, Ru, Ir) recovery from PGM refinery raffinates and bleed streams, autocatalyst recycler leach effluents, electroplating rinse waters, PGM-mine tailings return water.
Outputs/uses: rhodium and sister PGMs to refining/offtake; clean water; dry ballast salts.
Industries and users: PGM refiners, autocatalyst recyclers, electroplaters, PGM miners.
Scale: container-class; single unit to cascades on refinery/recycler effluent circuits.
ARBOK solution
Rhodium is the most expensive metal on the market (~$8,100/oz ≈ ~$260,000/kg, July 2026, +47 % y/y; 2021 peak ~$30,000/oz). It has no ore or mine of its own — recovered only as a byproduct of platinum and nickel mining. World production ~25 t/year; >80 % of primary supply from South Africa, Russia second, US near zero; autocatalyst recycling adds ~1/3 of supply. ~85 % of demand is three-way autocatalysts (the only qualified NOₓ metal). The structural loss: all PGM refining and autocatalyst recycling run through chloride hydrometallurgy, and rhodium's chloro-/aqua-complexes are exceptionally stable and kinetically inert — in ion-exchange polishing Rh breaks through 5–20× earlier than Pd and 3–8× earlier than Pt, with resin capacity an order of magnitude lower. Dissolved rhodium escapes in refinery raffinates, bleed streams, recycler leach effluents, electroplating rinse waters, and tailings return water — precipitated into mixed sludges or discharged. ARBOK recovers it from the whole aqueous stream.
> Core technology and architecture: see ARBOK-VC (Vacuum Cracking). This entry covers the rhodium feedstock, market, and economics.
Per the platform: the whole effluent stream is concentrated by deep vacuum at ambient temperature; only water evaporates and condenses as clean product (no membranes, electrodes, or reagents in the core; zero liquid tails). Ballast load (chlorides, sulfates, base metals) exits as dry product; noble ions, rhodium included, concentrate in the residual liquor by a factor of hundreds. A compact selective ion-exchange / solvent-extraction finishing stage then takes Rh (and co-present PGMs) at high yield — the classical chemistry that fails on dilute effluent works on the concentrate. ARBOK does not replace the refiner's chemistry; it removes the volume problem that made it uneconomic.
(Full mechanism: see platform entry.)
Market and application
Rhodium is the most expensive and among the most supply-concentrated metals: ~25 t/year, >80 % from South Africa, ~85 % of demand locked in autocatalysts with no qualified substitute for NOₓ, and every emissions tightening (Euro 6d, US Tier 3, China VI) narrows the market further. Recovering the dissolved fraction lost in refining/recycling effluents is the cheapest incremental supply available — the metal is already mined, milled, and dissolved.
Reference: 50 m³/h effluent stream (~440,000 m³/year, 6 container modules of 200 m³/day); at 0.1–1 mg/L dissolved Rh → 44–440 kg/year → $11–114 million/year at ~$260,000/kg (mid grade 0.5 mg/L ≈ 220 kg ≈ $57 million). Per single module that is $1.9–19 million/year.
Plant-scale frame: a typical South African platinum complex withdraws ~9,700,000 m³ water/year; the Rh-bearing refining/recycling circuit is ~440,000 m³/year, some 4–5% of intake. Tailings return water — the remaining ~9 million m³ — is a second tier: at an assumed 1–10 µg/L it carries 9–90 kg Rh/year, $2–23 million (concentration assumed, assay required). Co-recovered Pt/Pd/Ru/Ir add less than their reef ratio implies, because Rh is enriched in the effluent by the breakthrough mechanism; conservatively 30–100% of the Rh line, $17–57 million at mid grade. Aggregate mid-grade case: ~$76–137 million/year from one plant.
Plus ~440,000 m³/year clean water and removal of discharge-compliance and sludge-disposal costs. Rhodium rides on water and base-product credits at near-zero marginal cost. Payback 5–8 years (purchase) or zero capital via BOOM. Exact figures per stream assay.
Use cases
Primary use cases: rhodium (+ Pt, Pd, Ru, Ir) recovery from PGM refinery raffinates and bleed streams, autocatalyst recycler leach effluents, electroplating rinse waters, PGM-mine tailings return water.
Outputs/uses: rhodium and sister PGMs to refining/offtake; clean water; dry ballast salts.
Industries and users: PGM refiners, autocatalyst recyclers, electroplaters, PGM miners.
Scale: container-class; single unit to cascades on refinery/recycler effluent circuits.
Steps: effluent assay → recovery + finishing configuration → install on the effluent circuit → commissioning. Container-class, automated; purchase (payback 5–8 years) or BOOM (Build, Own, Operate, Maintain; PAY&GO + off-take at a discount to the exchange price).
Co-locates with PGM refinery and autocatalyst-recycling effluent circuits, electroplating shops, and PGM-mine tailings water; cascades on the platform with other metal recovery; recovered water returns to the process.
Rhodium is the most expensive metal on the market (~$8,100/oz ≈ ~$260,000/kg, July 2026, +47 % y/y; 2021 peak ~$30,000/oz). It has no ore or mine of its own — recovered only as a byproduct of platinum and nickel mining. World production ~25 t/year; >80 % of primary supply from South Africa, Russia second, US near zero; autocatalyst recycling adds ~1/3 of supply. ~85 % of demand is three-way autocatalysts (the only qualified NOₓ metal). The structural loss: all PGM refining and autocatalyst recycling run through chloride hydrometallurgy, and rhodium's chloro-/aqua-complexes are exceptionally stable and kinetically inert — in ion-exchange polishing Rh breaks through 5–20× earlier than Pd and 3–8× earlier than Pt, with resin capacity an order of magnitude lower. Dissolved rhodium escapes in refinery raffinates, bleed streams, recycler leach effluents, electroplating rinse waters, and tailings return water — precipitated into mixed sludges or discharged. ARBOK recovers it from the whole aqueous stream.
> Core technology and architecture: see ARBOK-VC (Vacuum Cracking). This entry covers the rhodium feedstock, market, and economics.
Primary use cases: rhodium (+ Pt, Pd, Ru, Ir) recovery from PGM refinery raffinates and bleed streams, autocatalyst recycler leach effluents, electroplating rinse waters, PGM-mine tailings return water.
Outputs/uses: rhodium and sister PGMs to refining/offtake; clean water; dry ballast salts.
Industries and users: PGM refiners, autocatalyst recyclers, electroplaters, PGM miners.
Scale: container-class; single unit to cascades on refinery/recycler effluent circuits.
Per the platform: the whole effluent stream is concentrated by deep vacuum at ambient temperature; only water evaporates and condenses as clean product (no membranes, electrodes, or reagents in the core; zero liquid tails). Ballast load (chlorides, sulfates, base metals) exits as dry product; noble ions, rhodium included, concentrate in the residual liquor by a factor of hundreds. A compact selective ion-exchange / solvent-extraction finishing stage then takes Rh (and co-present PGMs) at high yield — the classical chemistry that fails on dilute effluent works on the concentrate. ARBOK does not replace the refiner's chemistry; it removes the volume problem that made it uneconomic.
(Full mechanism: see platform entry.)
Platform base: deep vacuum, ambient temperature; water return up to 99.98 %; extraction of >90 % of dissolved substances; energy ~0.72 kWh/m³ (net, condensation-heat recuperation up to 98 %); container module ~200 m³/day; service life 15–20 years.
Resource: world production ~25 t/year; >80 % primary supply from South Africa; ~85 % of demand in autocatalysts; price ~$260,000/kg (July 2026).
Feed concentrations: dissolved Rh in refinery/recycler effluents ~0.1–1 mg/L depending on circuit point (assay per stream); tailings return water leaner but high-volume.
Finishing: compact selective ion-exchange / solvent-extraction for Rh and sister PGMs.
Platform vacuum separation + dry ballast-salt extraction + Rh/PGM selective ion-exchange/solvent-extraction finishing. Container-class: standard module 200 m³/day (73,000 m³/year), so a 50 m³/h stream (1,200 m³/day) needs 6 modules. (See platform entry.)
Technical: captures the dissolved Rh fraction that IX polishing structurally loses (earliest-breakthrough PGM); co-recovers Pt, Pd, Ru, Ir on the same concentration step.
Economic: reference stream 50 m³/h (~440,000 m³/year, 6 modules) at 0.1–1 mg/L Rh → ~44–440 kg/year → $11–114 million/year at ~$260,000/kg; OPEX covered by water and base products, so rhodium comes at near-zero marginal cost; payback 5–8 years (purchase) or zero operator capital (BOOM).
Environmental: ZWD; removes discharge-compliance costs and metal-bearing sludges; returns ~440,000 m³/year clean water per reference stream.
Strategic: supply concentrated in one country (>80 % South Africa); onsite recovery de-risks refiners/recyclers and adds secondary supply to a 25 t/year market.
Co-locates with PGM refinery and autocatalyst-recycling effluent circuits, electroplating shops, and PGM-mine tailings water; cascades on the platform with other metal recovery; recovered water returns to the process.
Steps: effluent assay → recovery + finishing configuration → install on the effluent circuit → commissioning. Container-class, automated; purchase (payback 5–8 years) or BOOM (Build, Own, Operate, Maintain; PAY&GO + off-take at a discount to the exchange price).
Platform TRL 9 — the vacuum phase-separation platform is industrially validated in commercial ARBOK applications. Rhodium selective finishing uses proven classical IX/SX chemistry on the concentrate; per-site configuration and field reference pending.
Rhodium is the most expensive and among the most supply-concentrated metals: ~25 t/year, >80 % from South Africa, ~85 % of demand locked in autocatalysts with no qualified substitute for NOₓ, and every emissions tightening (Euro 6d, US Tier 3, China VI) narrows the market further. Recovering the dissolved fraction lost in refining/recycling effluents is the cheapest incremental supply available — the metal is already mined, milled, and dissolved.
Reference: 50 m³/h effluent stream (~440,000 m³/year, 6 container modules of 200 m³/day); at 0.1–1 mg/L dissolved Rh → 44–440 kg/year → $11–114 million/year at ~$260,000/kg (mid grade 0.5 mg/L ≈ 220 kg ≈ $57 million). Per single module that is $1.9–19 million/year.
Plant-scale frame: a typical South African platinum complex withdraws ~9,700,000 m³ water/year; the Rh-bearing refining/recycling circuit is ~440,000 m³/year, some 4–5% of intake. Tailings return water — the remaining ~9 million m³ — is a second tier: at an assumed 1–10 µg/L it carries 9–90 kg Rh/year, $2–23 million (concentration assumed, assay required). Co-recovered Pt/Pd/Ru/Ir add less than their reef ratio implies, because Rh is enriched in the effluent by the breakthrough mechanism; conservatively 30–100% of the Rh line, $17–57 million at mid grade. Aggregate mid-grade case: ~$76–137 million/year from one plant.
Plus ~440,000 m³/year clean water and removal of discharge-compliance and sludge-disposal costs. Rhodium rides on water and base-product credits at near-zero marginal cost. Payback 5–8 years (purchase) or zero capital via BOOM. Exact figures per stream assay.
Feed-concentration dependence (assay per stream); Rh price volatility (thin 25 t market); finishing-stage configuration per site; offtake/grade qualification; conservative refining incumbents; needs a rhodium field reference.
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