Palladium Refining Process

— Palladium Refining Process: From Feed to 99.95% Pd Sponge

The palladium refining process is a hydrometallurgical sequence that dissolves palladium-bearing feed in a chloride medium, separates palladium from platinum group and base metals by selective precipitation, re-refines the intermediate salt, and reduces it to metallic palladium sponge of 99.95% (3N5) purity or higher. YuSai Machinery engineers the full line — reactor train, filtration, reductant dosing, resin scavenging and off-gas control — around your actual feed assay. Final purity: Pd ≥ 99.95% (3N5) as standard; 99.99% (4N) achievable on a repeat refining cycle. Palladium recovery: ≥ 98% overall, supported by ion-exchange and cementation scavenging of the barren liquor. Accepted feed: spent Pd/C and Pd/Al₂O₃ catalysts, catalytic converter concentrates, anode slimes, PGM black powder, Pd–Ag and Pd–Cu alloy scrap, plating baths and sludges. Product forms: palladium sponge or powder, ammonium chloropalladate crystals, palladium(II) diammine chloride, tetraammine palladium chloride and palladium nitrate solution.

Product Overview

Palladium is rarely refined in isolation. It arrives bonded to platinum, rhodium, iridium, gold and silver in the same chloride solution, and its chemistry is close enough to its sister platinum group metals that a single pass almost never delivers commercial purity. A workable palladium refining process therefore has to do three things in sequence: put the metal into a clean, concentrated chloride solution; drive it out of that solution as a salt that the other metals cannot follow; and repeat the cycle often enough that the accumulated impurities fall away.

The YuSai process starts from a palladium-bearing feed — spent supported catalyst, converter concentrate, anode slime, PGM black powder or alloy scrap — and opens with assay and classification, because the appropriate upstream pretreatment differs sharply between a carbon-supported catalyst that must be incinerated first and an alloy that can be dissolved directly. The selected feed is dissolved in hydrochloric acid with a controlled oxidant, then evaporated with repeated acid additions until no further brown fumes evolve. That denitration step is not cosmetic: residual nitrate and free nitric acid are the most common reason separations in the following stages become irreproducible.

Once the solution is a clean, concentrated chloropalladate liquor, ammonium chloride is introduced. Platinum, and any rhodium or iridium present, precipitate immediately as sparingly soluble ammonium hexachlorometallate salts and are filtered off. Palladium stays in the liquid phase as (NH₄)₂PdCl₄. A further oxidation step — chlorine gas, hydrogen peroxide, sodium chlorate or hypochlorite, dosed under control — pushes palladium to the tetravalent state so that it precipitates as brick-red ammonium hexachloropalladate. Excess ammonium chloride of 10–15% over the stoichiometric requirement is added to drive the precipitation to completion, and the filtered salt is washed with dilute ammonium chloride solution rather than water, since these salts are partly water-soluble.

Because the first salt is not yet pure, the line then runs a re-refining loop. The salt is slurried in pure water and boiled until it dissolves, which reduces the chloropalladate back to soluble (NH₄)₂PdCl₄; the solution is cooled, re-oxidised and re-precipitated. Two to three passes separate base metals effectively. A second and independent branch is available where the end product is wanted as a palladium ammine salt, or where the impurity still to be removed is a sister platinum group metal rather than a base metal: the palladium solution is complexed with ammonia at 80 °C and pH 8–9 to form soluble [Pd(NH₃)₄]Cl₂, insoluble material is filtered off, and acidification to pH 1.0–1.5 precipitates bright-yellow dichlorodiammine palladium(II). Copper and nickel follow palladium into the ammine complex rather than precipitating, so this branch is never relied on for base metal rejection — that duty stays with the chloropalladate route — but repeated ammine passes separate residual platinum, rhodium and iridium effectively, and the yellow salt they produce converts to metal at a far lower temperature.

The purified salt is finally reduced to metal with hydrazine hydrate, formic acid or hydrogen, or converted by calcination, yielding palladium sponge that assays 99.95% or better. The barren liquors and wash waters are not discarded: residual palladium is recovered by ion-exchange resin and cementation and returned to the dissolution stage, while the spent solutions move to neutralisation. All stages that evolve NOx, chlorine or acid mist are enclosed and vented to the scrubber train, so the process meets emission limits without shifting the problem to the wastewater plant.

Product Core Selling Points

One continuous route from feed to sponge. Dissolution, separation, re-refining, reduction, scavenging and finishing are delivered as a single engineered line, not as isolated vessels to be integrated on site.
Selective ammonium chloropalladate precipitation. Controlled chlorine-side oxidation plus a 10–15% stoichiometric excess of ammonium chloride drops palladium as brick-red (NH₄)₂PdCl₆ while platinum, rhodium and iridium leave the circuit as their own salts.
Nitric-free dissolution option. HCl–H₂O₂ and HCl–NaClO₃ media replace aqua regia where the feed allows, reducing NOx generation at the source instead of diluting it in a larger scrubber.
Two independent purification branches. The ammonium chloropalladate route carries the base-metal rejection duty, while the ammonia complexation route removes residual sister platinum group metals and yields a salt that converts to metal at a far lower temperature. Run in sequence, they clear feed compositions that neither branch handles alone.
Low residual losses. Barren-liquor scavenging by three-stage ion-exchange resin and iron or zinc cementation keeps palladium in the discard stream below 1 ppm.
Purpose-built for small batches. Reaction in vessels inside a fume hood, filtration in dedicated filter units and vacuum liquid transfer match the low single-batch tonnages typical of PGM refining.

Application Scenarios

Secondary precious metal refineries. Stand-alone PGM refineries that buy mixed palladium-bearing residues and need a repeatable route from assay to sellable sponge or salt.
Spent catalyst recyclers. Plants handling hydrogenation, hydrogenation–oxidation and fine-chemical catalysts on carbon, alumina or metal honeycomb supports, where palladium is the dominant value metal.
Automotive catalytic converter recyclers. Operations that already produce a PGM concentrate or smelter bullion and now want to separate palladium in-house instead of selling a mixed PGM intermediate.
Copper and nickel electrorefining plants. Anode slime circuits where palladium reports with platinum, gold and silver and is currently exported as a slime for toll refining.
Electronics and PCB recyclers. Recovery of palladium from colloidal palladium activation baths, electroless plating sludges, MLCC scrap and plating rinse waters.
Catalyst manufacturers and chemical plants. In-house refineries that regenerate or recover their own spent catalyst and want the recovered palladium returned as a salt suitable for catalyst re-manufacture.
Dental, jewellery and alloy fabricators. Pd–Ag, Pd–Cu and Pd–Ru alloy scrap, including high-palladium dental alloys and white-gold alloy residues.
Fuel cell and electrolyser recycling. Membrane electrode assembly scrap and stack residues, processed after incineration to a palladium-bearing ash or concentrate.
Assay and research laboratories. Pilot-scale lines that validate a flowsheet on a few kilograms before it is scaled to a production refinery.

Applicable Raw Materials

Each feed below enters the line at the point its composition requires. Feeds that carry carbon, organics or a refractory support are first incinerated, mechanically liberated or smelted to a concentrate, which is why the route sheets differ even though the dissolution-to-sponge core is common. Output is stated for each feed.

Spent palladium on carbon catalyst (Pd/C). The most common secondary palladium feed, used in hydrogenation and fine-chemical synthesis; incinerated or leached directly, with the carbon removed before the separation stage. Output: palladium sponge 99.95%; separated activated carbon residue.
Spent Pd/Al₂O₃ and Pd/silica catalysts. Alumina- or silica-supported catalysts from petrochemical and refining service, processed by support dissolution or full dissolution depending on grade. Output: palladium sponge 99.95%; aluminium-bearing residue.
Spent metal honeycomb and gauze catalysts. Ferritic or stainless-steel supported catalysts used in ammonia oxidation and off-gas service, containing palladium together with platinum and rhodium. Output: palladium sponge; platinum and rhodium salts routed to their own refining lines.
Automotive catalytic converter concentrate. PGM-bearing washcoat concentrate or smelter bullion, typically palladium-dominant with platinum and rhodium. Output: palladium sponge 99.95%; platinum and rhodium intermediates.
PGM black powder. Mixed platinum group metal powder recovered from converters, monolithic ceramic capacitors or dental scrap, with little or no base metal content. Output: palladium sponge; separated PGM salts.
Palladium-bearing anode slime. Slime from copper and nickel electrorefining, where palladium reports alongside gold, silver, platinum and selenium. Output: palladium sponge; gold and silver recovered on separate circuits.
Palladium–silver and palladium–copper alloy scrap. Electrical contacts, brazing alloys and coinage scrap, dissolved directly after silver removal as silver chloride. Output: palladium sponge; silver chloride to the silver circuit.
High-palladium dental and jewellery alloys. Pd–Ag, Pd–Cu–Ga and Pd–Ru dental alloys and white-gold residues requiring base metal removal before palladium recovery. Output: palladium sponge; gold and silver by-products.
Electroless plating and colloidal palladium baths. Spent activation baths and plating electrolytes where palladium is wrapped in a tin colloid or present as free ions. Output: palladium concentrate; polished effluent under 1 ppm Pd.
Plating sludges and rinse waters. Low-concentration liquid and solid streams requiring concentration by resin adsorption, precipitation or electrowinning before refining. Output: palladium-bearing concentrate returned to dissolution.
Palladium process residues and nitrite–nitrate liquors. Catalyst manufacturing residues, palladium nitrate and nitrite mother liquors and spent precipitation filtrates. Output: palladium sponge; reclaimed process solution.
Fuel cell and electrolyser catalyst scrap. Membrane electrode assemblies and stack catalyst layers, incinerated to ash before leaching. Output: palladium sponge; platinum where co-present.

Finished Products

The line is configured to deliver the product form the buyer or the downstream catalyst plant requires, from a saleable intermediate salt to certified metal.

Palladium sponge and powder. The primary output, assaying Pd ≥ 99.95% (3N5) with 99.99% (4N) achievable through an additional re-refining cycle; supplied as free-flowing sponge or powder, or melted and cast to bar or shot on request. Output: certified palladium sponge with certificate of analysis.
Ammonium hexachloropalladate (NH₄)₂PdCl₆. The brick-red intermediate salt, available as a saleable product for buyers who prefer to run their own reduction. Output: washed, dried crystalline salt.
Dichlorodiammine palladium(II) Pd(NH₃)₂Cl₂. The bright-yellow palladium salt widely used as a catalyst precursor and plating intermediate, produced on the ammonia complexation branch. Output: high-purity yellow crystalline powder.
Tetraammine palladium(II) chloride [Pd(NH₃)₄]Cl₂. A soluble palladium complex for electroless plating and catalyst preparation. Output: solution or crystallised salt.
Palladium nitrate solution. Produced where the downstream application calls for a nitrate medium rather than a chloride one. Output: filtered, concentration-adjusted Pd(NO₃)₂ solution.
Silver by-product (AgCl). Silver removed at the start of the process is recovered as silver chloride and transferred to the silver refining circuit. Output: silver chloride to silver electrolysis.
Platinum, rhodium and iridium salts. Sister PGMs precipitated during the platinum group separation stage leave as ammonium salts for their own purification lines. Output: (NH₄)₂PtCl₆ and associated PGM salts.

Palladium Refining Process Flow

The nine stages below form the standard palladium refining flowsheet. Pretreatment, such as incineration of a carbon-supported catalyst or smelting enrichment of converter material, is added upstream only where the feed demands it. Engineering setpoints — temperature, acidity, pH, oxidant dose and excess reagent ratio — are fixed during process design against your own assay.

Palladium refining process flow — feed to certified Pd sponge of 99.95% (3N5) and above.

Steps 1 — Feed Preparation and Assay. Incoming material is weighed, sampled by riffling and split for analysis by XRF and ICP-OES, supported by potentiometric titration where chloride matrices interfere. The assay fixes the palladium head grade, the base metal load, the silver and platinum content and the presence of refractory phases, and it determines whether the feed goes directly to dissolution or first to incineration, mechanical liberation or smelting enrichment. Carbon-supported catalysts are incinerated to burn off the support; alloy scrap is granulated; slimes and residues are dried and ground. Each batch is assigned a route sheet and an internal lot number so that the mass balance can be closed at the end of the campaign. Reagent and utility input: sample splitting equipment, XRF and ICP-OES analysis. Output: refining route sheet and batch record.

Steps 2 — Oxidative Dissolution. The prepared feed is charged to a titanium or glass-lined reactor and covered with hydrochloric acid, then heated to a controlled 60–90 °C. The oxidant is added in small increments — nitric acid in the aqua regia route, or hydrogen peroxide, sodium chlorate or hypochlorite where a nitric-free medium is preferred — until no further reaction occurs. The objective is a complete dissolution of everything that will dissolve while using the minimum quantity of oxidant, because surplus oxidant has to be destroyed later and consumes reagents in the separation stage. Insoluble material such as silver chloride, lead chloride and unreacted refractory PGM phases is retained for separate treatment. Reagent and utility input: HCl, HNO₃ or H₂O₂, controlled dosing, heating. Output: palladium chloropalladate liquor; NOx off-gas to scrubber.

Steps 3 — Nitric Destruction and Concentration. The loaded solution is evaporated gently — never boiled — with repeated additions of hydrochloric acid until no brown fumes appear when fresh acid is added. This destroys residual nitrate and free nitric acid and drives the metal complexes into a pure chloride form. The solution is then concentrated to a palladium concentration of roughly 40–50 g/L, because separation performance in the following stages depends on working with concentrated rather than dilute liquors. Condensate from the evaporator is routed to acid recovery and returned to the process. Reagent and utility input: repeated HCl additions, low-heat evaporation. Output: concentrated, nitrate-free chloropalladate liquor; recovered acid condensate.

Steps 4 — Base Metal and Silver Removal. The concentrated liquor is cooled and held so that silver chloride and lead chloride crystallise and settle, then filtered. Filtration is carried out on a vacuum filter plate or candle filter so that the cake can be washed with minimal dilution of the mother liquor. The silver chloride cake is washed free of entrained palladium and transferred to the silver circuit for reduction. Base metals that remain in solution — copper, nickel, iron and zinc — are left for the precipitation stages to reject, since they do not form insoluble ammonium salts under the same conditions as palladium. Reagent and utility input: chilled settling, vacuum filtration. Output: AgCl and PbCl₂ cake; clarified palladium liquor.

Steps 5 — Platinum Group Separation. A saturated ammonium chloride solution is added to the clarified liquor. Platinum precipitates at once as bright-yellow ammonium hexachloroplatinate, (NH₄)₂PtCl₆; rhodium comes down with the platinum where present, and iridium follows more slowly, so the batch is held for one to two hours before filtration when iridium is suspected. The precipitate is filtered and washed several times with cold dilute ammonium chloride solution until the washings run colourless, and the wash liquor is returned to the process rather than discarded. Palladium remains in the filtrate as soluble (NH₄)₂PdCl₄. Reagent and utility input: saturated NH₄Cl solution, cold dilute NH₄Cl wash. Output: platinum, rhodium and iridium salt cake routed to PGM refining lines; palladium-bearing filtrate.

Steps 6 — Palladium Precipitation as Ammonium Chloropalladate. Palladium in the filtrate is already bound to ammonium as (NH₄)₂PdCl₄. To bring it out of solution it is oxidised to the tetravalent state with chlorine gas, hydrogen peroxide, hydrogen peroxide plus hydrochloric acid, sodium chlorate or hypochlorite, added in small portions and allowed to react completely before the next addition. Additional solid ammonium chloride is then introduced at 10–15% above the stoichiometric requirement. Palladium precipitates as brick-red crystalline ammonium hexachloropalladate, and the reaction is driven to completion until no further red salt forms. The precipitate is filtered on a vacuum system and washed with cold dilute ammonium chloride until the washings are colourless, keeping dilution of the main liquor to a minimum. The spent liquor is sampled for residual palladium before it leaves the stage.

H₂PdCl₄ + 2NH₄Cl + Cl₂ → (NH₄)₂PdCl₆ + 2HCl

Reagent and utility input: chlorine-side oxidant, NH₄Cl at 10–15% excess. Output: brick-red (NH₄)₂PdCl₆; palladium-depleted filtrate.

Steps 7 — Salt Re-Refining Cycle. The first precipitate still carries base metal and traces of sister PGMs, so it is re-refined rather than converted directly. The salt is slurried in pure water and boiled until it dissolves, which reduces the chloropalladate back to soluble black-red (NH₄)₂PdCl₄; the solution is then cooled, re-oxidised and re-precipitated with ammonium chloride, and the wash-and-filter sequence is repeated. Two to three complete passes remove base metals effectively — typically to the point where one pass yields about 99% purity and the re-refined salt supports 99.9% and above. On this branch the base metals do not follow palladium, because they cannot form an insoluble ammonium salt under these conditions and remain in the filtrate. The ammonia complexation branch is used where the yellow salt or the tetraammine complex is the required product and where the impurity still to be removed is a sister platinum group metal: the palladium solution is heated to 80 °C and complexed with ammonia at pH 8–9 to form soluble [Pd(NH₃)₄]Cl₂, insoluble material is filtered off, and the filtrate is acidified with hydrochloric acid to pH 1.0–1.5 to precipitate bright-yellow Pd(NH₃)₂Cl₂. Copper and nickel form soluble ammine complexes of their own under those conditions and are not rejected by this branch, so they are managed on the chloropalladate branch instead; repeated ammine passes do remove residual platinum, rhodium and iridium effectively. The two branches can be run alternately, and the choice of branch for each pass is set in the flowsheet.

(NH₄)₂PdCl₆ + H₂O → (NH₄)₂PdCl₄ + HCl + HClO

H₂PdCl₄ + 4NH₃·H₂O → [Pd(NH₃)₄]Cl₂ + 4H₂O + 2HCl

Pd(NH₃)₄Cl₂ + 2HCl → Pd(NH₃)₂Cl₂↓ + 2NH₄Cl

Reagent and utility input: pure water, boiling, re-oxidation; ammonia complexation at pH 8–9 and acidification at pH 1.0–1.5 on the alternative branch. Output: re-refined palladium salt or yellow Pd(NH₃)₂Cl₂; base-metal wash to effluent treatment.

Steps 8 — Reduction to Palladium Sponge. The purified salt is converted to metal. On the hydrazine route the salt is charged to a glass-lined reactor, hydrazine hydrate is added, and the mixture is heated with vigorous agitation until the liquor is fully reduced and no colour remains; the sponge is then filtered, washed and dried. Formic acid reduction is used where hydrazine handling is restricted, and hydrogen reduction in a tube furnace is used where a very low residual chloride content is required. Calcination is retained as a route for the red salt: the dried salt is heated gradually in a fused-silica or borosilicate dish with sand bedding to spread the heat, and the temperature is stepped up slowly to above 400 °C while the evolved ammonium chloride is carried away by the exhaust system. The yellow palladosammine salt converts at a much lower temperature, around 150 °C, which is one practical reason for introducing the ammonia branch. Gradual heating matters in both routes: a temperature spike causes values to leave with the smoke.

Pd(NH₃)₂Cl₂ + 2N₂H₄·H₂O → Pd↓ + 2NH₄Cl + N₂↑ + 2NH₃·H₂O

Reagent and utility input: hydrazine hydrate, formic acid or hydrogen; 60–90 °C in a glass-lined reactor. Output: palladium sponge; barren liquor to scavenging.

Steps 9 — Assay Verification and Emission Control. Every filtrate, wash water and final product is assayed. Barren liquors still contain palladium in the parts-per-million range, so they pass through a three-stage ion-exchange resin train that lifts overall recovery above 95%, followed by iron or zinc cementation of the polish filtrate; the cementation residue is returned to dissolution and the depleted solution goes to neutralisation. The sponge is sampled and analysed by ICP-OES against a certified reference material, and the batch is released only when the certificate of analysis confirms 99.95% or better. Off-gas from dissolution, precipitation and calcination passes through the NOx absorption tower and alkali washing circuit, with HCl recovery upstream, and the emission log is retained with the batch record. Finished sponge is packed in airtight containers, because palladium catalyses the formation of surface carbonates on contact with airborne carbon monoxide, which can affect the purity reading at a later melt.

Reagent and utility input: ICP-OES and potentiometric titration; resin and cementation reagents. Output: certificate of analysis; compliance and emission record; polished effluent under 1 ppm Pd.

Product Structure (Main Equipment)

The line is assembled from the following equipment groups. Materials of construction are selected per stream — titanium for the hot chloride dissolution duty, glass-lined steel where oxidant and ammonia are combined, polypropylene and PVDF for atmospheric acid service, and borosilicate glass where the reaction must be observed directly.

Feed preparation and pretreatment

Weighing, sampling and splitting station. Riffling and sample division equipment that produces a representative assay sample from each incoming lot before any material enters the process.
Incineration and roasting unit. A controlled-temperature furnace that burns off carbon and organic content from Pd/C catalysts and membrane scrap and converts the residue to a leachable ash. Output: palladium-bearing ash for dissolution.
Crushing, granulation and grinding set. Size reduction for alloy scrap, slimes and agglomerated residues so that dissolution proceeds at a predictable rate.

Dissolution and reaction train

Titanium dissolution reactor. Heated reactor for HCl and HCl–HNO₃ dissolution duty, fitted with a condenser, controlled reagent dosing and vapour take-off to the scrubber.
Glass-lined and enamelled reaction vessels. Used for ammonia complexation, acidification and hydrazine reduction, where both oxidising and alkaline conditions occur in the same vessel.
Reagent dosing system. Metered pumps with interlocks that add oxidant in small increments and stop on the reaction endpoint rather than on a fixed volume.
Condenser and acid recovery unit. Recovers hydrochloric acid from evaporator condensate and returns it to the process, reducing reagent make-up and load on the effluent plant.

Solid–liquid separation

Vacuum filter plate and filter trolley. Mobile filtration units with diaphragm vacuum pumps that separate salts and cakes while keeping wash volumes low, so the mother liquor is not diluted.
Candle filter. Pressure filtration with reverse gas pulse for the cake release duty, used where high solids loading makes plate filtration slow and labour-intensive.
Crystallising and settling tanks. Chilled vessels that allow silver chloride and lead chloride to crystallise and settle ahead of filtration.
Vacuum generator and liquid-ring pump set. Provides the vacuum for filtration and for liquid transfer by vacuum lift, which avoids pumping hot chloride liquors through mechanical seals.

Purification, reduction and recovery

Precipitation and complexation reactors. Vessels for ammonium chloride precipitation, ammonia complexation and acidification, arranged inside the fume hood so that reactions of a few kilograms can be run and observed batch by batch.
Reduction reactor. Glass-lined reactor with heating, agitation and reagent dosing for hydrazine hydrate or formic acid reduction of the purified salt to palladium sponge.
Calcination furnace and tube furnace. Programmable furnaces with forced exhaust for converting palladium salt by thermal decomposition, and hydrogen reduction furnaces where a low chloride residue is specified.
Ion-exchange resin columns. A three-stage resin train that scavenges residual palladium from barren liquors and wash waters before they reach neutralisation.
Cementation tank. Iron or zinc cementation vessel for the final polish of the resin effluent; the cementation residue is returned to dissolution.
Swirl electrowinning unit. Optional module for recovering palladium and companion metals from very dilute solutions where resin capacity is better reserved for other streams.

Melting, control and environmental systems

Induction melting furnace and casting set. Melts palladium sponge under protective atmosphere into bars, buttons or shot where the buyer requires metallic form rather than powder.
PLC control and HMI panel. Supervises dosing, temperature, pH and redox potential, logs every batch, and holds the interlocks that prevent reagent addition out of sequence.
NOx absorption tower and alkali washing circuit. Two-stage scrubbing for nitrogen oxides plus an alkali wash and acid-mist eliminator for the chloride stages. Output: compliant stack emission and recovered scrubber liquor.
Effluent neutralisation and settling unit. Neutralises spent acid streams and settles the metal hydroxide sludge before discharge or further treatment.
Assay laboratory equipment. XRF, ICP-OES, potentiometric titration and a dedicated fume hood for sample preparation, so that feed, intermediate and product assays are generated in-house on the same day as production.

Product Features

Single-supplier turnkey scope. Assay, flowsheet design, equipment manufacture, installation, commissioning, operator training and handover are delivered as one contract, so the interfaces between reaction, filtration, reduction and scrubbing are no one else’s problem.
Two purification routes in one plant. The ammonium chloropalladate precipitation route and the ammonia complexation route are both built into the same line, and the flowsheet specifies which pass uses which branch for your feed.
Selective chemistry, not a generic leach. The precipitation stage is designed around the specific behaviour of palladium(IV) chloro-complexes, which is why platinum, rhodium and iridium can be taken out of the circuit before palladium is dropped.
Nitric-free dissolution available. HCl–H₂O₂ and HCl–NaClO₃ media are offered as standard alternatives to aqua regia, cutting NOx formation at the reactor rather than relying on end-of-pipe treatment alone.
Small-batch architecture. Reactions run in vessels inside a fume hood, with filtration in dedicated filter units and vacuum liquid transfer — a layout that suits the low single-batch tonnages of PGM refining and keeps the working inventory of metal small.
Visible process control. Where the reaction must be watched, glass and transparent polymer vessels are used so that operators can judge the endpoint by colour and behaviour, which is more reliable than a timer on this chemistry.
Recovery designed to the last part per million. Resin scavenging and cementation are part of the standard scope, not an optional extra, so barren liquors are polished below 1 ppm palladium before neutralisation.
Closed-loop reagent and water management. Evaporator condensate returns as recovered acid, ammonium chloride wash liquors return to precipitation, and final-stage rinse waters return to the resin train.
Assay-linked traceability. Every lot carries a route sheet, a mass balance and the assay results of feed, intermediate and product, which is what makes a refining guarantee defensible.
Configuration to feed, not to a catalogue. Capacity, footprint, power demand and utility consumption are engineered from your assay and target throughput, so the plant is sized to the metal actually available rather than to a standard model number.

Technical Parameters & Specifications

Engineering setpoints below are the standard design basis and are confirmed or adjusted during process design once the feed assay is known. Capacity, footprint, installed power and utility consumption are engineered to your throughput and site conditions.

Palladium refining process — technical parameters and specifications.

Parameter	Specification
Feed palladium grade	Pd ≥ 20% for direct refining; lower-grade material accepted after pretreatment and enrichment
Feed forms accepted	Spent supported catalyst, converter concentrate or bullion, PGM black powder, anode slime, alloy scrap, plating sludges and liquors, process residues
Feed pretreatment	Incineration, granulation, grinding or smelting enrichment, selected per feed type
Dissolution medium	HCl + HNO₃ (aqua regia route); HCl + H₂O₂ or HCl + NaClO₃ (nitric-free route)
Dissolution temperature	60–90 °C, controlled with incremental oxidant addition to the reaction endpoint
Denitration	Low-heat evaporation with repeated HCl additions until no brown fumes evolve
Working Pd concentration at separation	40–50 g/L in the chloropalladate liquor
Silver removal	Chilled crystallisation and filtration of AgCl and PbCl₂ ahead of the separation stage
Platinum group separation reagent	Saturated ammonium chloride solution; cold dilute NH₄Cl for cake washing
Ir addition reaction hold	1–2 hours where iridium is present, before the Pt/Rh/Ir salt is filtered off
Palladium oxidation	Cl₂ gas, H₂O₂, NaClO₃ or hypochlorite, added in portions to complete reaction
NH₄Cl dose	10–15% above the stoichiometric requirement, added dry or as saturated solution
Precipitated palladium salt	Brick-red crystalline ammonium hexachloropalladate (NH₄)₂PdCl₆
Ammonia complexation pH	pH 8–9 at 80 °C, forming soluble [Pd(NH₃)₄]Cl₂
Acidification pH (yellow salt)	pH 1.0–1.5, precipitating Pd(NH₃)₂Cl₂
Re-refining passes	2–3 complete dissolution, re-oxidation and re-precipitation cycles
Reductant	Hydrazine hydrate (N₂H₄·H₂O), formic acid, or hydrogen in a reduction furnace
Reduction temperature	60–90 °C with agitation for the hydrazine and formic acid routes
Calcination temperature	≥ 400 °C for (NH₄)₂PdCl₆; approximately 150 °C for Pd(NH₃)₂Cl₂
Final palladium purity	Pd ≥ 99.95% (3N5) as standard; up to 99.99% (4N) with an additional re-refining cycle
Palladium recovery	≥ 95% direct recovery from solution; ≥ 98% overall with resin and cementation scavenging
Residual palladium in effluent	Below 1 ppm after three-stage resin polishing
Product forms	Palladium sponge or powder; optional fused bar, button or shot; intermediate salts on request
Product packaging	Airtight containers, because palladium powder catalyses carbonate formation on contact with airborne carbon monoxide
Materials of construction	Titanium, glass-lined or enamelled steel, polypropylene, PVDF, borosilicate glass
Filtration equipment	Vacuum filter plate, filter trolley with diaphragm pump, candle filter with reverse gas pulse
Barren liquor recovery	Three-stage ion-exchange resin train followed by iron or zinc cementation
Off-gas treatment	NOx absorption tower, alkali washing tower, acid-mist eliminator, HCl recovery from condensate
Instrumentation and control	PLC with HMI supervision of temperature, pH, redox potential, dosing and batch logging
Quality verification	XRF, ICP-OES and potentiometric titration; certificate of analysis issued per batch
Capacity, footprint, power, utilities	Engineered to feed assay, target throughput and site conditions

Technical Advantages

Separation before reduction, not after. By taking platinum, rhodium and iridium out of the liquor as their own salts before palladium is precipitated, the process protects palladium purity at the point where it is easiest to control. Correcting purity afterwards is far more expensive than preventing the contamination in the first place. Result: a first-pass salt that already approaches 99% purity.
A re-refining loop instead of a single pass. The process is designed around the fact that a single cycle cannot fully separate palladium from its sister metals. Two to three dissolution and re-precipitation passes move the product from about 99% to 99.9% and above, with the number of passes set by the actual impurity profile of your feed rather than by assumption. Result: 99.95% (3N5) as standard, 99.99% (4N) available.
Choice of purification chemistry, with the duties correctly divided. The chloropalladate branch is the base-metal rejection step, because copper, nickel and iron cannot form an insoluble ammonium salt under those conditions and leave in the filtrate. The ammonia complexation branch works on a different basis — a soluble ammine complex at pH 8–9, filtration of insoluble material, then precipitation of the yellow palladosammine salt by acidification — which makes it effective against residual platinum, rhodium and iridium and gives a salt that converts to metal at around 150 °C. Because copper and nickel also form soluble ammine complexes, base-metal duty is assigned to the chloropalladate branch rather than the ammine branch in the flowsheet. Result: applicability across catalyst, slime and alloy feeds with one equipment set.
Nitric-free dissolution where the feed permits. Substituting HCl–H₂O₂ or HCl–NaClO₃ media for aqua regia reduces NOx generation at the reactor. Fewer nitrogen oxides means a smaller scrubber duty, lower alkali consumption and less nitrate load on the effluent plant. Result: lower reagent and abatement cost per kilogram of palladium.
Concentrated liquors by design. Separation performance in this chemistry degrades as the liquor is diluted, so the flowsheet deliberately keeps working solutions concentrated and minimises rinse water at every filtration step, using cold dilute ammonium chloride rather than water for cake washing. Result: higher precipitation efficiency and smaller vessel volumes per kilogram of palladium.
Loss recovery engineered into the flowsheet. Barren liquors and wash waters are treated with a three-stage resin train and then cemented, so the palladium that does not precipitate is captured rather than written off. Result: overall recovery of 98% and above, with effluent palladium below 1 ppm.
Low working inventory of metal. Because the process is built around small batch sizes with vacuum transfer and rapid filtration, the amount of palladium held inside the circuit at any moment is small. Result: less capital tied up in in-process metal and faster campaigns.
Hydrometallurgical energy profile. The line operates well below pyrometallurgical smelting temperatures, with heating limited to dissolution, evaporation and reduction duties. Result: lower thermal energy demand and no high-temperature furnace duty in the main separation circuit.
Emissions managed at the source and at the stack. NOx, chlorine and acid mist are captured where they are generated and routed through a two-stage scrubber with acid recovery upstream. Result: compliance that does not depend on diluting the problem downstream.
Verifiable numbers. Assay-linked mass balance, per-batch logging and certificate of analysis mean purity and recovery claims can be checked against your own analysis on the same lot. Result: a refining specification that can be audited by the buyer or by a toll-refining counterparty.
Designed to scale with the market. The layout is modular, so a pilot line that validates the flowsheet on a few kilograms can be extended with additional reaction, filtration and resin capacity rather than replaced. Result: an entry point that does not become stranded capital.
Integration with the wider plant. Feed from an anode slime circuit, converter smelter or catalyst recycling line can be routed into this process, and the silver, platinum, rhodium and iridium by-products are delivered as intermediates that downstream refining lines accept. Result: one circuit that closes the palladium loop without breaking the others.

Service Process

Step 1 — Enquiry and feed data review. You provide the feed type, an assay or typical analysis, expected monthly metal volume and any site constraints. We confirm whether the material suits this process or needs an upstream pretreatment first. Output: preliminary process route and a clear scope statement.

Step 2 — Laboratory test and small-batch verification. A representative sample is tested at bench scale through dissolution, separation, precipitation, re-refining and reduction. Operating windows and expected recovery are established on real material, not on assumptions. Output: test report and returned product sample for your own assay.

Step 3 — Process design and flowsheet. We issue the process flow diagram, material and reagent balance, mass balance by metal, equipment list, vessel sizing and the utility schedule, with all engineering setpoints stated. Output: process design package and mass balance.

Step 4 — Equipment manufacture and factory testing. Reactors, filtration units, resin columns, scrubbers and the control panel are fabricated, assembled and function-tested before shipment, with material certificates retained. Output: factory acceptance test record.

Step 5 — Layout and site interface design. Equipment layout, civil loading, power supply points, water, compressed air, steam or electric heating and ventilation interfaces are defined against your building. Output: layout and utility interface drawings.

Step 6 — Shipment, installation and commissioning. Equipment ships with the documentation set, and our engineers supervise installation, pressure and leak testing, electrical and control checkout, and water commissioning. Output: mechanically complete line, ready for reagent commissioning.

Step 7 — Operator training and SOP handover. Operating procedures, safe handling of oxidants, hydrazine and ammonia, endpoint judgement, sampling and assay practice, and routine maintenance are taught on site with the actual equipment. Output: trained operators and a signed SOP set.

Step 8 — Production trial and performance acceptance. The line is run on your feed and the agreement is confirmed against measured recovery, product purity and effluent palladium concentration. Output: performance test certificate and first certificate of analysis.

Step 9 — Ongoing technical support. Process troubleshooting, flowsheet refinement as your feed mix changes, spare parts at cost, and reagent or consumable supply on request. Output: continuing production support.

Warranty & After-Sales Service

Warranty period. Twelve months from successful commissioning or eighteen months from shipment, whichever falls earlier, covering design, manufacture and assembly defects of the supplied equipment. Excluded: consumables such as filter cloths, gaskets, membranes and reagents, and damage from misuse or from feed outside the agreed specification.
Performance commitment. Where the feed matches the tested sample, we stand behind the agreed palladium recovery and product purity figures established in the process design package, with the performance test as the reference point. Output: documented performance acceptance.
Spare parts. Wear and critical spares are quoted at the time of order and held available afterwards, with a recommended on-site stock list issued at handover. Output: spare parts list and supply at cost.
Remote support. Telephone, email and messaging support for operating questions, alarm interpretation and process troubleshooting, whenever your line is running. Output: same-day response on operating issues.
On-site service. Engineer attendance for warranty faults, process problems and periodical check-ups, with response and attendance times agreed in the contract according to your location. Output: on-site intervention and a service report.
Operator retraining and refresher visits. Additional training, refresher sessions and process optimisation visits as your feed mix or product requirement changes. Output: updated training and procedure revisions.
Documentation set. Operation and maintenance manuals, process flow diagram, piping and instrumentation diagram, equipment layout, electrical drawings, spare parts catalogue, safety data for reagents and the emergency response plan. Output: complete documentation handover.
Compliance support. Assistance with emission and effluent parameter declarations, scrubber performance verification and the handling, storage and disposal requirements for the reagents used in the process. Output: technical data for your permit applications.
Lifetime technical support. The process design remains yours, and our engineering team remains available for modification and expansion advice for the operating life of the plant. Output: long-term engineering continuity.

Frequently Asked Questions

What feed materials can this palladium refining process handle?

Spent palladium catalysts on carbon, alumina or metal supports; automotive catalytic converter concentrate or bullion; PGM black powder; palladium-bearing anode slime from copper and nickel electrorefining; Pd–Ag, Pd–Cu and Pd–Ru alloy scrap; dental and jewellery alloys; electroless plating baths, colloidal palladium activators and plating sludges; catalyst manufacturing residues and palladium nitrate or nitrite liquors; and fuel cell catalyst scrap. Feeds carrying carbon, organics or refractory supports are incinerated, granulated or smelted to a concentrate first, and that pretreatment step is designed to match the specific feed.

What purity of palladium does the process achieve?

Pd ≥ 99.95% (3N5) is the standard specification, delivered as sponge or powder and released against a certificate of analysis. A simple conversion of the first precipitated salt typically yields above 99% purity, and adding a re-refining cycle — two to three dissolution, re-oxidation and re-precipitation passes — brings the product to 99.9% and above, with 99.99% (4N) achievable where the impurity profile permits. The exact figure for your material is established in the laboratory test before the plant is built.

What is the difference between the ammonium chloropalladate route and the ammonia complexation route?

The ammonium chloropalladate route oxidises palladium in the chloride liquor and precipitates it as brick-red (NH₄)₂PdCl₆. It is the branch that rejects base metals, because copper, nickel and iron cannot form an insoluble ammonium salt under those conditions and remain in the filtrate. The ammonia complexation route works on a different principle: palladium is complexed with ammonia at 80 °C and pH 8–9 to form soluble [Pd(NH₃)₄]Cl₂, insoluble material is filtered off, and acidification to pH 1.0–1.5 precipitates yellow Pd(NH₃)₂Cl₂. That branch is used where the yellow salt or the tetraammine complex is the required product and where the remaining impurity is a sister platinum group metal, which it separates effectively over repeated passes — but it is not relied on for base metal rejection, because copper and nickel also form soluble ammine complexes and follow palladium into solution. The yellow salt brings a further advantage: it converts to metal at around 150 °C rather than the 400 °C needed for the red salt. Both routes are built into the same line, and the flowsheet specifies which pass uses which.

Can the process run without aqua regia?

Yes, where the feed allows it. Hydrochloric acid with hydrogen peroxide, or hydrochloric acid with sodium chlorate, dissolves palladium-bearing material without introducing the nitrate load that aqua regia brings. That removes most of the nitrogen oxides at the reactor instead of relying entirely on scrubbing, and it eliminates the extended denitration evaporation that the aqua regia route requires. The choice is made from the laboratory test, because some feeds — certain alloys and refractory phases — still dissolve more completely in the aqua regia route.

How is platinum separated from palladium?

By selective precipitation with ammonium chloride. Added to a concentrated chloride liquor, it precipitates platinum immediately as bright-yellow ammonium hexachloroplatinate, (NH₄)₂PtCl₆, while palladium stays in solution as (NH₄)₂PdCl₄. Rhodium leaves with the platinum where present, and iridium follows more slowly, which is why the batch is held for one to two hours before filtration when iridium is suspected. The salt is filtered and washed with cold dilute ammonium chloride, since these salts are partly soluble in water. Palladium is then precipitated from the filtrate in a separate, later stage.

How long does one refining cycle take?

It depends on batch size and on how many re-refining passes the feed needs, but the sequence is not the constraint — the endpoints are. Dissolution runs to reaction completion rather than to a fixed time, evaporation runs until brown fumes stop, and precipitation runs until no further salt forms. What can be stated is the structure: silver removal and platinum group separation happen ahead of palladium precipitation, two to three re-refining passes are typical for catalyst and slime feeds, and the reduction and drying stages are short. The campaign length for your material is estimated from the laboratory test.

What is the palladium recovery rate?

Direct recovery from solution is ≥ 95%, rising to ≥ 98% overall once the barren liquors and wash waters are treated. The difference comes from the recovery stage at the end of the line: a three-stage ion-exchange resin train adsorbs residual palladium from the process liquors, and the polish filtrate is then cemented with iron or zinc to capture what remains. The cementation residue returns to dissolution rather than leaving the plant, and the depleted solution leaves with less than 1 ppm palladium after resin polishing.

What capacity can you supply?

Capacity is engineered to your feed assay and your target throughput rather than taken from a catalogue of fixed sizes. What matters in this process is the palladium content of the feed and the number of re-refining passes required, so two plants of the same nominal vessel size can have very different daily metal output depending on grade. We size the reaction vessels, filtration, resin columns and scrubber from your assay and monthly metal volume, and we state the resulting figures in the process design package. The layout is modular, so a pilot line can be extended rather than replaced if throughput grows.

How do you control NOx and acid emissions?

By capturing them where they form and treating them in a dedicated train. Dissolution, precipitation, evaporation and calcination vessels are enclosed and vented through a condenser that recovers hydrochloric acid from the condensate, followed by a NOx absorption tower and an alkali washing tower with an acid-mist eliminator. Choosing the nitric-free dissolution route reduces the nitrogen oxide load before it reaches the scrubber. Emission parameters are logged per batch and retained with the batch record, and scrubber performance data are supplied for your permit applications.

Do you test my material before quoting a plant?

Yes, and it is the step that decides the flowsheet. A representative sample is run through dissolution, separation, precipitation, re-refining and reduction at bench scale, which establishes the operating windows, the number of re-refining passes your feed needs, the expected recovery and the final purity. Part of the recovered product is returned to you so that you can verify it with your own assay. The equipment quotation and the process design package are based on that result, not on a generic assumption about your material.

How do you verify the purity of the finished palladium?

By ICP-OES analysis of a sample taken from the released batch, cross-checked with XRF where applicable and with potentiometric titration for the wet-chemistry stages. The batch is not released until the certificate of analysis confirms the specified purity, and the assay results for feed, intermediates and product are held together with the mass balance for that lot. The same traceability is what allows a buyer or a toll-refining counterparty to audit the results independently.

Why must palladium sponge be stored and packed airtight?

Because palladium is a catalyst. In powder or sponge form it slowly reacts with carbon monoxide in the atmosphere to form carbonates on the metal surface, and that surface layer can affect the purity reading when the metal is later melted. Finished product is therefore packed in airtight containers immediately after drying, and melting is carried out under protective atmosphere in a fused-silica or alumina crucible by induction rather than by a fuel–oxygen torch, which would risk carbon pick-up.