Why mineral processing HVAC is its own engineering problem
Mineral processing plants are not commercial buildings with bigger fans. They are 24-hour heavy-industrial sites where the air carries silica, sulphide dust, cyanide vapour, caustic mist, sulphur dioxide and chloride salt — often all on the same site — and where a single failure of the ventilation system can stop a circuit worth tens of millions of dollars a day. Specifying the HVAC ductwork to a commercial standard, fabricating it from galvanised steel and hoping it lasts the campaign is the most expensive mistake a process designer can make.
This guide is written for the engineers, fabricators and procurement leads who design and build that ductwork in the Australian mining heartland — Pilbara, Kalgoorlie, Mount Isa, Olympic Dam, Boddington, Cadia, Telfer, Worsley, Pinjarra, Boyne Island and the rapidly expanding lithium corridor through Wodgina, Pilgangoora, Mt Marion and Kathleen Valley. It complements our earlier articles on underground mine ventilation, steel-mill and ferrous smelter ductwork, and cement plant HVAC. The objective here is to draw the boundary between mineral processing surface plant and those adjacent disciplines, and to be specific about where materials, joints, hazardous area certifications and fabrication machinery differ.
The Australian standards framework
Four documents form the spine of the design package. None of them on their own is sufficient — the engineer needs all four open on the desk during specification.
AS 1668.2 — Mechanical ventilation in buildings
AS 1668.2 is the umbrella standard for mechanical industrial ventilation in Australia. For a mineral processing plant it sets the minimum outside air rates, the calculation method for local exhaust ventilation at dust and fume sources, the supply air temperature and humidity ranges for occupied process areas, and the smoke management requirements where the building falls under the National Construction Code as well. Mineral processing plants are not buildings in the commercial sense, but enclosed crusher houses, mill rooms, flotation buildings and pulpit control rooms are all governed by AS 1668.2 where workers occupy them.
The practical numbers to remember are eight to twelve air changes per hour as the floor across process plant areas, increasing to fifteen to twenty air changes per hour where dust generation is heavy. These are starting points, not endpoints. The real design number comes from the local exhaust ventilation calculation at every source.
AS/NZS 1668.4 — The use of ventilation and air-conditioning in buildings
AS/NZS 1668.4 sits alongside AS 1668.2 and covers natural ventilation. For a mineral processing plant it is most relevant on the upper levels of crusher houses and flotation buildings where deliberately designed wall louvres and roof ventilators do most of the air movement work and the mechanical system serves only the occupied lower decks and pulpit. The combination of high-level natural ventilation and low-level mechanical capture is the dominant pattern across the larger Pilbara processing plants — a design choice driven as much by the cost of conditioning Pilbara summer air as by ventilation effectiveness.
AS/NZS 60079 — Hazardous area classification
AS/NZS 60079 is the family of standards governing electrical equipment selection and installation in explosive atmospheres. Part 10.1 covers gas atmospheres and Part 10.2 covers dust atmospheres. For a mineral processing operation both apply. Coarse ore conveyors and crusher houses generate combustible sulphide dust where Zone 22 dust classification is the typical outcome. Solvent extraction circuits on copper, uranium and rare earth plants generate flammable kerosene vapour and are classified Zone 1 or Zone 2 gas. Lithium spodumene decrepitation produces small quantities of finely divided lithium-bearing dust where Zone 22 again applies. Gold cyanidation circuits generate hydrogen cyanide which is flammable above its lower explosive limit although the dilution at room scale rarely puts the area above LEL.
The implication for ductwork is that fans, motors, switchgear, lighting and instrumentation inside the duct routing must carry an Ex rating matched to the zone. The ductwork itself does not require Ex certification — it is passive — but the bonding and earthing to bleed off static, the choice of conductive gasket material on flanges, and the construction of fire dampers all change in Ex zones.
AS 4024 — Machinery safety
AS 4024 is the Australian implementation of the international machinery safety framework that aligns with ISO 12100. For HVAC ductwork it governs the fan and damper actuator installations, the lifting and rigging of large duct sections during installation, the access platforms and walkways alongside the duct run, and the lockout-tagout procedures during maintenance. It is the standard that the EPC contractor will use during construction safety design and that the operator's maintenance team will use during the campaign.
State mine safety overlay
The federal AS framework is enforced by state mine safety legislation, and the three jurisdictions where most Australian mineral processing happens have separate Acts.
Western Australia — Mine Safety and Inspection Act
The Mine Safety and Inspection Act and its regulations are administered by the Department of Mines, Industry Regulation and Safety. The WA regime covers the entire mine, from the pit through the processing plant to the rail loadout. For HVAC ductwork on a processing plant in WA the relevant clauses cover the duty of the principal employer to maintain ventilation adequate to dilute airborne contaminants to the WA workplace exposure standards, and the requirement that ventilation systems on the plant are subject to scheduled inspection by the mine site senior on a documented programme. Operators including BHP Nickel West, BHP Mt Whaleback, Rio Tinto Pilbara iron, Fortescue Pilbara iron, South32 Worsley alumina, Newmont Boddington, Mineral Resources Wodgina, Pilbara Minerals Pilgangoora and Liontown Resources Kathleen Valley all operate under this Act.
New South Wales — Work Health and Safety (Mines and Petroleum Sites) Act
The NSW Act layers an additional mine-specific regime on top of the general WHS Act. It includes a mine operator's principal hazard management plan obligation that covers airborne contaminants explicitly, and it places the operator under a duty to consult with the regulator on significant ventilation changes. Newcrest Cadia, Evolution Mining Cowal, BHP Mt Arthur coal and Glencore underground operations all sit under the NSW regime.
Queensland — Mining and Quarrying Safety and Health Act
The Queensland Act applies a Safety and Health Management System obligation on mineral processing operations, with mandatory site senior executive accountability for any failure of the ventilation system that contributes to a notifiable incident. Glencore Mt Isa copper-zinc-lead, South32 Cannington silver-lead-zinc, Evolution Mining Ernest Henry and Rio Tinto Boyne Aluminium at Boyne Island all operate under this Act.
The practical engineering implication is that the design package needs to satisfy AS 1668.2 plus the relevant state Act, and the operator will not sign off on commissioning until the documentation is complete to both. The fabricator who supplies ductwork without traceable mill certificates for the 316L coil, without weld procedure specifications for the welded-seam circuits, and without a positive pressure test record for the pulpit supply ducts will be sent back to redo the paperwork before the first kilogram of ore goes through the plant.
The five unit operations and their HVAC duties
A mineral processing plant is not a single ventilation problem. It is five or six unit operations stacked together, each with a distinct chemistry, distinct dust generation profile and distinct duct material requirement. This section walks each one.
Crusher and screening exhaust
The primary, secondary and tertiary crushers are the largest dust generators on the surface plant. A 60-inch primary gyratory crusher feeding the SAG mill on a major Pilbara iron operation generates several tonnes of dust per hour from the impact of haul truck tipping and rock fragmentation. The local exhaust ventilation system pulls air through hoods over the dump pocket, the discharge chute and the conveyor transfer points, and routes it to a baghouse where the dust is captured and the cleaned air is discharged through a stack.
The ductwork between hood and baghouse is exposed to the abrasive ore dust and the operating temperature is close to ambient — there is no chemistry challenge here, only abrasion. Painted carbon steel duct with abrasion-resistant liners at elbows is the typical specification. Where the ore is sulphide and the dust contains pyrite or pyrrhotite, low-level sulphuric acid forms in damp duct sections and 316L stainless is preferred. For an iron ore haematite operation the duct chemistry is benign and carbon steel is acceptable for the entire campaign.
The NIOSH lookout on respirable crystalline silica is the dominant health hazard. The Safe Work Australia workplace exposure standard for respirable crystalline silica was reduced to 0.05 mg/m³ in 2020 and operators are designing to the 0.025 mg/m³ action level. This drives larger ducts, lower face velocities at hoods, more redundant baghouse cells, and tighter pressure monitoring on the duct system than would have been specified a decade ago.
Ball mill and SAG mill rooms
The grinding circuit room generates a different ventilation challenge. The mill discharge is wet, the dust generation is low, but the lubricant aerosol from the trunnion bearings and the gearbox oil mist forms a fine mist that needs to be captured. The aerosol load is small in absolute terms but the residual mist on building structure becomes a slip hazard and a fire hazard over the campaign.
Local exhaust ventilation at the trunnion bearing housings and at the gearbox vent ports, ducted to a mist eliminator with a coalescing media, is the standard design. The duct material is typically galvanised or painted carbon steel because the mist chemistry is hydrocarbon oil rather than mineral acid or caustic. The exception is where the mill is grinding a sulphide concentrate slurry that is splashing into the mill room atmosphere — in that case 316L stainless is the safer specification because the splashed liquor will be mildly acidic.
Ventilation rates in the SAG mill room are driven by the heat load from the gearbox cooling, the lighting and the workers, not by the contaminant capture. Twelve to fifteen air changes per hour with relief through wall louvres and forced supply at the lower level is the typical design.
Flotation cell rooms
The flotation cell room has the most complex air chemistry on the plant. The frother chemistry — methyl isobutyl carbinol or polyglycol — generates a vapour that is recognisable by its distinctive smell at trace levels. The collector chemistry — xanthate on copper and lead-zinc plants, or fatty acid on iron ore reverse flotation — adds its own vapour signature. The pH regulator chemistry — lime slurry, sulphuric acid, sodium carbonate — generates fine mist when the slurry is splashed by the impellers.
The ventilation design priority is to capture the froth phase vapours and the splash mist before they accumulate in the building atmosphere. Direct extract from above each row of cells, with the duct rising vertically to a roof discharge, is the cleanest layout. The duct material is 316L stainless because the captured air carries acid mist, sulphide dust and frother condensate that will pit galvanised steel over the campaign.
Pulpit access to the flotation cells is at the operating floor level, and the pulpit needs positive pressure of plus 25 Pa relative to the cell room atmosphere to prevent vapour ingress. HEPA filtration on the pulpit supply air and a separately ducted return that exhausts through a charcoal scrubber are standard on a modern flotation plant.
Tailings handling and storage
Tailings handling is the quiet hazard. The thickened tailings stream from the flotation circuit is pumped to the tailings storage facility through pipework that vents to atmosphere at the discharge spigot. On a copper or lead-zinc concentrator the tailings carry residual collector chemistry, sulphate ions and trace metals. On a gold cyanidation plant the tailings carry residual cyanide and require detoxification before discharge.
The ventilation duty on the tailings thickener building, the cyanide destruction circuit and the tailings pump house is to capture vapour at source and to ensure the building atmosphere stays below the relevant workplace exposure standard. On a gold plant this means hydrogen cyanide detection at every entry to the cyanide circuit, with continuous monitoring set to alarm at 4 ppm and to evacuate at 10 ppm. The Safe Work Australia time-weighted average exposure standard for hydrogen cyanide is 5 ppm as a ceiling — there is no eight-hour TWA because the gas is too acutely toxic.
The ductwork on the cyanide circuit is 316L stainless throughout, with welded seams. Mechanical joints are not acceptable. The exhaust point is a tall stack with a wind-direction sensor that triggers a downwind dispersion model and an alarm at the gatehouse if the predicted ground-level concentration exceeds the off-site limit.
Reagent storage and mixing
Reagent storage and mixing is a small footprint with disproportionate hazardous area implications. The flotation reagent shed holds drums of xanthate, frother, collector and pH regulator. The cyanide reagent storage on a gold plant holds drums or a silo of sodium cyanide briquettes. The solvent extraction reagent storage on a copper or rare earth plant holds bulk diluent — typically a kerosene cut — and the proprietary extractant. The ventilation duty is to dilute any leak below the relevant exposure standard, prevent build-up of flammable vapour above 25 percent of the lower explosive limit, and provide a path for fire-fighting smoke to clear. Duct material is 316L stainless on the cyanide reagent room because the storage atmosphere generates trace hydrogen cyanide. On the SX diluent storage the duct material is painted carbon steel but the entire room is classified Zone 2 and all electrical equipment in the duct routing must be Ex e or Ex d rated.
The four major refinery and smelter chemistries
The mineral processing plant is upstream of the refinery or smelter, and the four major chemistries downstream each have their own duct specifications.
Alumina refinery — the Bayer process
The Bayer process digests bauxite ore in hot caustic soda solution to produce sodium aluminate, from which alumina is precipitated. Australian Bayer process refineries — South32 Worsley in WA, the Rio Tinto refineries through the Boyne and Yarwun complex in Queensland, and Alcoa Wagerup, Pinjarra and Kwinana in WA — operate at digestion temperatures up to 270 °C and caustic concentrations up to 270 grams per litre as NaOH.
The digestion vessel atmosphere is saturated with caustic vapour and water vapour. The vent ducting from the digesters to the condensate recovery and the atmospheric vent stack carries this vapour at temperatures between 100 and 150 °C. The duct material is 316L stainless throughout — 304 stainless is not adequate because of stress corrosion cracking under hot caustic — and the welded seams are post-weld pickle-and-passivated to remove the heat-affected zone chromium depletion.
The red mud handling area, where the iron oxide tailings are pumped to the residue storage, carries dust from the dryer overheads and vapour from the spent liquor flash tanks. The duct material is again 316L stainless and the welded seams are the rule, not the exception. Mechanical joints with EPDM gaskets are used only on isolation flanges at maintenance break points.
The calciner exhaust at the precipitation back end of the refinery operates at gas temperatures up to 1,100 °C in the kiln and 250 °C at the stack inlet. The exhaust ducting is refractory-lined carbon steel — the temperature exceeds the service limit of stainless. Refractory monolithic castable backed by ceramic fibre blanket inside a carbon steel duct shell is the standard construction.
Copper smelter — the sulphur dioxide problem
Copper smelters convert sulphide copper concentrate into anode copper through a flash furnace and converter sequence. The off-gas from the flash furnace is a hot, dust-laden gas with 15 to 25 volume percent sulphur dioxide. The off-gas from the converters is a smaller volume but higher SO2 concentration. Both streams are routed to a gas cleaning train — waste heat boiler, electrostatic precipitator, gas conditioning — and then to a sulphuric acid plant where the SO2 is converted to sulphur trioxide and absorbed in concentrated sulphuric acid to make 98 percent acid.
The duct from the smelter primary exhaust to the gas cleaning is refractory-lined carbon steel at the front end where the gas is above 700 °C, transitioning to bare carbon steel after the waste heat boiler where the gas drops to 350 °C. The acid plant inlet duct from the gas cleaning to the contact tower is bare carbon steel with weep drains at the low points to remove condensed acid.
The acid plant tail gas, after the SO2 has been converted, carries residual SO2 at typically 250 to 500 ppm depending on the conversion efficiency. The workplace exposure standard for SO2 in Australia is 2 ppm as an eight-hour TWA and 5 ppm as a short-term exposure limit. The tail gas stack and any vent ductwork from the acid plant must be designed to keep ground-level concentrations well below these limits, and the off-site air quality criterion under the state EPA licence is typically tighter again.
Inside the smelter building, the secondary capture ducting that pulls fugitive emissions from the converter aisle, the matte tapping and the slag granulation is 316L stainless because the gas carries condensed sulphuric acid mist. Carbon steel duct in this service rusts through within months.
Australian copper smelters at BHP Olympic Dam in South Australia and Glencore Mt Isa in Queensland are the two operating examples. Both run the same general chemistry and both have the same duct specification logic, although Olympic Dam's autoclave leaching front end is a hydrometallurgical operation rather than a pyrometallurgical smelter and has its own duct chemistry — see the autoclave section below.
Gold processing — the cyanide circuit
Gold extraction from sulphide and oxide ores uses cyanide leaching followed by carbon-in-pulp or carbon-in-leach adsorption. The reagent is sodium cyanide added as briquettes or as a solution at concentrations of 100 to 500 ppm in the leach tank. The risk is that cyanide ion in water in equilibrium with hydrogen cyanide gas — the gas concentration above the leach tank can reach the 5 ppm ceiling under stagnant air conditions, and personnel exposure must be controlled by extract ventilation, gas detection and respiratory protection.
The duct from the leach tank overheads to the cyanide destruction circuit is 316L stainless with welded seams. Pittsburgh lock joints are not acceptable because the joint cannot be reliably sealed against trace HCN leakage. Hydrogen cyanide detection is mandatory at every workstation around the leach circuit, with the alarm set to evacuate at 10 ppm. The detection sensor type is electrochemical with a service life of two years — the maintenance management system tracks the replacement programme.
Australian gold operations using this circuit include Newmont Boddington in WA, Newmont Tanami in NT, Newmont Cadia East in NSW, Northern Star Resources at the Kalgoorlie Super Pit, Evolution Mining Cowal in NSW, Newcrest Telfer in WA and the multiple smaller operations through the Kalgoorlie Goldfields. Every one of these sites runs ductwork on the cyanide circuit that is 316L stainless throughout. The fabricator that quotes carbon steel or galvanised duct on a gold cyanide circuit will lose the bid before the design review.
Lithium concentrator — spodumene to lithium hydroxide
The lithium concentrators serving the Pilbara hard-rock lithium operations are a newer class of mineral processing plant in Australia. Mineral Resources Wodgina, Pilbara Minerals Pilgangoora, Mineral Resources Mt Marion, Liontown Resources Kathleen Valley, and the legacy Galaxy Resources Mt Cattlin operation (now under the Allkem and then Arcadium banner) are all hard-rock spodumene operations producing a 6 percent lithium oxide concentrate by gravity, flotation and magnetic separation. The concentrator itself is a relatively conventional flotation circuit with duct specifications similar to a copper or lead-zinc concentrator — 316L stainless on the flotation cell extract because of collector chemistry, painted carbon steel on the dry comminution circuits with abrasion-resistant liners.
The difference is at the back end. Hard-rock spodumene must be decrepitated — heat-treated at around 1,050 °C in a rotary kiln — to convert alpha-spodumene to the more soluble beta-spodumene. The decrepitation furnace exhaust is the highest-temperature duct work on the plant; refractory-lined carbon steel is the only acceptable material at the kiln exit, transitioning to 316L stainless as the gas cools through waste heat recovery to around 200 °C because it carries trace fluoride and chloride from the ore. The decrepitation circuit is where the Australian hard-rock route diverges from the South American brine operations — Allkem Olaroz in Argentina and the Salar de Atacama operations in Chile evaporate brine in solar ponds and avoid the decrepitation step entirely. All the Australian operations are hard-rock and the decrepitation furnace is part of the standard scope.
Beyond decrepitation, the lithium hydroxide refinery converts the beta-spodumene concentrate to lithium hydroxide via sulphation, water leaching and conversion. Duct specification in the refinery is 316L stainless throughout because of the sulphuric acid roast off-gas, caustic conversion circuit and residual fluoride chemistry. Australian refinery developments at Kwinana and Kemerton sit in this category.
Rare earth processing — the Lynas chain
Rare earth processing in Australia is dominated by Lynas Rare Earths, which mines monazite-rich ore at Mt Weld in WA, runs initial concentration at the Mt Weld concentrator, and ships the concentrate to the Lynas Advanced Materials Plant for cracking, leaching and individual rare earth separation. Lynas is also developing a Kalgoorlie processing facility to add Australian sovereign capacity. Duct chemistry on a rare earth cracking and leaching plant is sulphuric acid bake off-gas at the front end — refractory-lined carbon steel transitioning to 316L stainless — followed by hydrochloric acid leach extract and solvent extraction off-gas at the back end. The HCl service is the harder duct duty; even 316L is marginal under hot HCl conditions, and FRP or polypropylene-lined steel is the alternative for leach tank vent ducting where temperature is below 80 °C. Above that temperature the duct returns to 316L stainless and the operator accepts a shorter campaign life with planned-shutdown replacement. The Iluka Resources Eneabba refining facility in WA will operate similar chemistry on the heavy rare earth side and will face the same trade-offs.
Other Australian operators and their processing footprints
The major Australian operators each run distinct mineral processing operations with distinct HVAC duct duties. Rather than catalogue every plant, the following grouping summarises the operators by chemistry and points to the corresponding duct specification.
Diversified iron, copper and base metal majors
BHP operates a diversified portfolio: Olympic Dam in South Australia for copper, uranium, gold and silver through autoclave leaching and copper smelting; Nickel West in WA for nickel through flash smelting and refining; Mt Whaleback and the WAIO Pilbara operations for haematite iron ore with conventional dry processing; and Mt Arthur Coal in NSW for thermal coal washing. The duct duty varies from high-acid service at Olympic Dam, through sulphide flash smelting duct service at Nickel West Kalgoorlie, to dry abrasion-only duct service at the Pilbara iron operations. Rio Tinto similarly operates iron ore through the Pilbara at high tonnage with dry processing, aluminium through Boyne Aluminium and the Yarwun and Queensland Alumina Limited refineries, copper through Kennecott Utah and Bingham Canyon overseas, and the Resolution Copper project in Arizona. The Australian duct duty is dominated by Pilbara iron — low-chemistry, low-temperature, carbon steel duct with abrasion lining — and by Boyne aluminium and Queensland alumina refinery duty where 316L stainless and refractory lining come into play. Fortescue Metals Group operates the Pilbara iron portfolio with Cloudbreak, Christmas Creek, Solomon and Iron Bridge; Iron Bridge in particular is a magnetite operation with a wet beneficiation circuit and ducted air on the dryers, where the duty is intermediate between dry haematite and sulphide flotation.
Gold specialists
Newcrest Mining and Newmont — combined under the Newmont banner — operate Cadia in NSW, Boddington in WA, Telfer in WA and Tanami in the Northern Territory among others. All four are cyanide circuit operations with the corresponding 316L stainless welded-seam duct specification. Northern Star Resources operates the Kalgoorlie Super Pit and the Pogo operation in Alaska, with similar circuit chemistry. Evolution Mining operates Cowal in NSW and Ernest Henry in QLD, again on the cyanide circuit specification.
Diversified mid-cap miners
South32 operates Worsley alumina in WA, GEMCO manganese in the Northern Territory, Cannington silver-lead-zinc in QLD, and the Illawarra metallurgical coal operations in NSW. Worsley sits in the alumina refinery duct duty category. GEMCO is a manganese open-pit and dense media plant with conventional duct chemistry. Cannington is a silver-lead-zinc concentrator with the corresponding sulphide flotation duct duty. The diversity in South32's portfolio is unusual — most miners specialise in one or two commodities — and the corresponding duct specification scope on a South32 site visit is similarly broad.
Glencore in Australia operates Mt Isa copper-zinc-lead in QLD with smelting and refining on site, alongside the various coal operations through NSW and QLD. The Mt Isa complex includes a copper smelter and lead smelter, both of which have the corresponding pyrometallurgical duct duty.
Lithium specialists
Mineral Resources operates Wodgina and Mt Marion lithium concentrators in WA. Pilbara Minerals operates Pilgangoora. Liontown Resources is bringing Kathleen Valley into production. The legacy Galaxy Resources operations at Mt Cattlin in WA and Olaroz in Argentina merged into Allkem and subsequently into the Arcadium banner. All the Australian operations are hard-rock spodumene concentrators with the corresponding lithium decrepitation duty if the operator also runs the refinery domestically, or with the simpler concentrator-only duct duty if the concentrate is shipped to an overseas refinery.
Specialty mineral operators
Iluka Resources operates the zircon and titanium mineral sands business out of South Australia and WA, plus the rare earth refining development at Eneabba. The mineral sands plants run dry electrostatic and magnetic separation with relatively low-chemistry duct duty — carbon steel duct with abrasion lining on the dryer overheads is the typical specification. Lynas Rare Earths runs the Mt Weld mine and concentrator in WA, the Kalgoorlie processing development, and the Lynas Advanced Materials Plant for separation. The duct duty is in the rare earth cracking and leaching category — refractory-lined at the bake furnace, 316L stainless through the leach circuit, FRP or polypropylene-lined for low-temperature HCl service.
EPC contractors and the duct supply chain
The mineral processing duct supply chain in Australia is intermediated by a handful of EPC and EPCM contractors. The duct fabricator's customer is usually the EPC contractor's mechanical subcontractor, not the operator directly.
Worley is the dominant Australian engineering contractor on large-scale mineral processing and has been the engineering partner on Pilbara iron ore expansions, lithium concentrator builds and alumina refinery upgrades. Their duct specifications follow the AS standards framework strictly and require traceable mill certificates on stainless coil and weld procedure specifications on the welded-seam circuits. Fluor operates through Fluor Australia and is a major presence in copper, alumina and lithium project delivery; their specification template tends to align closely with the US AISC and ASME standards alongside the AS framework, with welding qualification documentation referenced to ASME Section IX as well as AS/NZS 1554.
GR Engineering Services and Lycopodium Limited have strong mid-market presences on gold and lithium concentrator delivery, with conservative duct specifications — 316L stainless where chemistry justifies it, painted carbon steel elsewhere, and welded seams as default on any chemistry-exposed circuit. Primero Group works at the smaller end of the lithium and gold market. NRW Holdings and Civmec operate at the construction and fabrication delivery end of the chain; Civmec in particular runs a large Henderson WA fabrication facility and is a major buyer of duct fabrication machinery.
The implication for a duct fabricator entering this market is that the qualification scope needs to include the EPC contractor's vendor approval and audit programme, requiring evidence of ISO 9001, AS/NZS 1554 welder qualifications, traceable material supply, and historical project references in similar mineral processing service.
Hot-climate ambient design
The Australian mineral processing heartland sees summer ambient temperatures above 45 °C across the Pilbara, the Kalgoorlie Goldfields, the Mt Isa region and the South Australian copper belt. The pulpit and central control room conditioning load is dominated by solar gain through the walls and roof and by the operator population — typically 4 to 8 people per pulpit, plus heat from the SCADA workstations. Supply air design temperature is 14 to 16 °C off the cooling coil to give the 18 to 22 °C dry bulb room condition with 50 plus or minus 5 percent relative humidity, after picking up the room load.
The cooling source is the design decision. Direct evaporative cooling is the cheapest option and works well in Pilbara dry-heat conditions, but the recirculating water becomes a process dust sink — the dust loading at most mineral processing sites is high enough that the spray nozzles foul within weeks. Indirect evaporative cooling avoids the contamination but requires the heat exchanger surface, which adds cost. Refrigerated DX systems with a glycol secondary loop are the dominant specification on modern Australian processing plants — they avoid the dust contamination, they handle the 45 °C plus ambient if the condenser is correctly sized, and the glycol loop allows the condensing unit to sit on a roof or pad away from the conditioned space. The duct insulation specification is driven by the temperature delta between conditioned space and the plant atmosphere; a 16 °C supply duct running through a 45 °C plant atmosphere needs 50 mm of mineral wool or equivalent thermal resistance, with a vapour barrier on the outside.
The four duct material classes
Four duct material classes cover essentially every duty on an Australian mineral processing plant, smelter or refinery.
Class A — Painted carbon steel
Painted carbon steel is the cheapest and most widely used duct material on the plant. It is suitable for dry dust collection, dry abrasion-only service, mill room ventilation where chemistry is benign, and supply or return air duct in control rooms or office buildings. Wall thickness is typically 1.2 to 2.0 mm depending on duct size and pressure class. A two-pack epoxy primer with polyurethane topcoat at 200 micron dry film thickness is the standard for industrial duty. Hot-dip galvanising is the alternative for ductwork that sees incidental moisture but no aggressive chemistry. Galvanising fails in any acid, caustic or cyanide exposure and is not acceptable on a process duct.
Class B — 316L stainless steel
316L stainless is mandatory for any duct exposed to acid mist, caustic vapour, cyanide vapour or chloride-bearing dust. The 2 to 3 percent molybdenum content provides the chloride pitting resistance that 304 stainless lacks. Wall thickness is typically 1.5 to 3.0 mm depending on duct size and pressure class. Welded-seam construction is the rule on chemistry-exposed duct — Pittsburgh lock and button-punch snap-lock joints leak chemistry over the campaign. TIG welded seam, run on an automated seam welder with documented weld procedure specifications and tracked welder qualifications, is the only acceptable construction method. The post-weld heat-affected zone of a stainless weld is chromium-depleted and corrodes preferentially; pickling with a nitric-hydrofluoric paste followed by passivation with a nitric acid solution restores the protective chromium oxide layer and gives the duct full campaign life.
Class C — Refractory-lined carbon steel
Refractory-lined carbon steel is the specification for furnace exhaust above 250 °C and below the refractory limit of typically 1,400 °C for monolithic alumina-silica castable. Construction is a carbon steel duct shell, anchored to a ceramic fibre blanket insulation layer, with a monolithic castable refractory inner lining. The shell sees the lower temperature on the cold face of the refractory and is engineered to handle thermal expansion through bellows and expansion joints. A copper smelter primary exhaust duct sees a different temperature profile and gas chemistry from a lithium decrepitation furnace exhaust or an alumina calciner exhaust, and the refractory engineer selects castable formulation, anchor pattern and curing schedule to suit. The fabricator's role is the welded carbon steel shell — typically AS 1548 PT430 or equivalent — with structural reinforcement to handle the refractory weight and thermal load.
Class D — FRP or polypropylene-lined carbon steel
FRP and polypropylene-lined carbon steel are alternatives to 316L stainless on duct service exposed to strong acid or chloride at temperatures below 80 °C. Wet HCl scrubber outlet ducting on a rare earth leach plant is a typical application. Construction is either a filament-wound FRP duct or a carbon steel shell with a polypropylene or PVDF lining sheet welded to the inside. The trade-off versus 316L is cost and thermal limit. FRP and PP-lined duct is cheaper than 316L at the same size and pressure class, but the temperature limit is around 80 °C for PP and around 120 °C for FRP with isophthalic resin. Above those temperatures the duct returns to 316L stainless.
Joint methods and the welded-seam mandate
The duct joint method is as important as the duct material itself. There are three joint types in widespread use on Australian mineral processing duct work.
The Pittsburgh lock is a longitudinal mechanical seam used on rectangular duct made from light-gauge carbon steel or galvanised steel. The seam is folded and locked closed by an automatic seamer on the rollforming line. It is acceptable on supply and return air ductwork, on dry dust collection ducts where the gas chemistry is benign, and on control room HVAC ductwork.
The button-punch snap-lock is a similar concept used at the corner of a duct. It is fast to assemble in the workshop and is widely used on commercial HVAC duct. It is not acceptable on chemistry-exposed mineral processing duct because the joint is not leak-tight at the buttons.
The welded seam is the mandatory joint method on any duct exposed to acid, caustic, cyanide, chloride or high temperature. The seam is run as a continuous TIG weld with documented weld procedure specifications referenced to AS/NZS 1554 Part 6 for stainless or AS/NZS 1554 Part 1 for carbon steel. The welder qualifications are documented and traceable, and the welded joints are tested by pressure decay or by die penetrant inspection depending on the duct pressure class.
The implication for fabrication machinery is that a fabricator entering the mineral processing market needs at least one welded-seam capability alongside the rollforming and Pittsburgh seam capability. A standalone TIG seam welder is the right capital investment — it pairs with the existing rollformer to convert dry-duct production capacity into chemistry-exposed duct production capacity.
Acoustic targets
The mineral processing plant is loud. The ball mill and SAG mill generate noise levels in excess of 100 dB(A) at one metre, and the open plant target is a Noise Criterion NC-60 rating — equivalent to around 65 dB(A) at the boundary of a working area. NC-60 in the plant is achieved by the structural shielding of buildings and not by the duct itself. The pulpit and control room targets are tighter: NC-40 in the pulpit (around 45 dB(A), the maximum acceptable level for two-way verbal communication) and NC-35 in the central control room (around 40 dB(A), the level at which long-shift operator comfort is preserved).
The duct system contributes to the noise level inside the control room in two ways. Fan noise transmitted along the ductwork is controlled by silenced fan plenums and lined acoustic plenums in the supply and return ducts. Regenerated noise from air movement at high velocities through grilles and diffusers is controlled by sizing supply diffusers for a face velocity below 2.5 m/s and return grilles for face velocity below 1.5 m/s. Achieving NC-40 and NC-35 on a duct system serving a 45 °C plant ambient requires more insulation than a commercial HVAC system, because the cooling capacity is higher and the supply air velocity tends to creep up to keep the duct sizes manageable.
The 24/7 operation and the 5+5 campaign cycle
Mineral processing plants run 24 hours a day, seven days a week, 50 weeks a year. The two missing weeks each year are taken up by planned maintenance shutdowns where the unit operations are cleaned, inspected and overhauled. The campaign cycle on major equipment — mills, smelter vessels, refinery digesters — is typically five years to a major rebuild and another five years to the next rebuild, giving a ten-year nominal campaign life. The duct system is expected to last the same campaign with planned-shutdown maintenance only — no mid-campaign failure of duct, no unplanned shutdown to replace a leaking joint, no production loss from a duct that wears through before the next shutdown.
The implication for specification is that the design life is ten years of continuous service in the actual chemistry the duct will see, with periodic inspection during planned shutdowns to confirm residual wall thickness and integrity of welded seams. A duct specified to a five-year life because the budget was constrained will fail mid-campaign and the production loss will dwarf the saving. A fabricator that wins the initial contract on a major project will be supplying replacement duct to the same operator for 20 to 30 years — the customer relationship is more valuable than any single transaction.
Where galvanised duct fails
Galvanised steel duct is the default specification for commercial HVAC and for benign industrial applications. On a mineral processing plant it fails in four predictable ways. Acid chemistry exposure — acid plant tail gas, fugitive copper or zinc smelter emissions, and stripped wet scrubber outlet streams — strips the zinc layer within months, and although the corrosion is generally uniform the residual life is too short for a ten-year campaign. Caustic chemistry exposure — Bayer process digester off-gas, caustic scrubber outlet, any vent from a high-pH process stream — dissolves the zinc layer rapidly, and the residual zinc on adjacent areas creates a galvanic cell that drives localised pinhole failure within months.
Cyanide chemistry exposure attacks zinc and copper alloys preferentially; the duct service life on a cyanide circuit with galvanised duct is measured in months, and beyond the duct failure issue the corrosion product creates a leak path for HCN — a personnel safety hazard the regulator will not tolerate. High temperature exposure is the fourth failure mode: hot-dip galvanising has a service temperature limit of around 250 °C continuous, above which the zinc layer alloys with the iron substrate and protective properties are lost. Furnace exhaust ducting above this temperature must be 316L stainless if the temperature is below 600 °C, or refractory-lined carbon steel if the temperature is higher.
Underground mine ventilation versus surface plant HVAC
One area of confusion for buyers new to the mining market is the boundary between underground mine ventilation and surface plant HVAC. The two systems share some terminology — both move air, both have main fans, both deal with dust — but they are designed by different engineering disciplines and the duct specifications are different.
Underground mine ventilation is dominated by the main exhaust fan installation at the top of the shaft or the return airway, with auxiliary ventilation ducting that pushes fresh air to the working face through development drives, stopes and crosscuts. The duct material is typically flexible or rigid plastic — vinyl-on-textile flexible duct for auxiliary ventilation, rigid PVC or HDPE for main airway repairs. Pressure classes are low, temperature is close to ambient, and chemistry is generally benign — diesel particulate, blasting fumes and rock dust are the contaminants. Surface plant HVAC, the topic of this article, uses steel duct — painted carbon, 316L stainless, refractory-lined or FRP — driven by process chemistry. The two engineering disciplines rarely overlap on a project, and for a duct fabricator the practical implication is that a steel duct rollforming and stainless welded-seam capability serves the surface plant market while the underground ventilation duct market is served by flexible duct and rigid plastic specialists with a different supply chain and machinery base.
SBKJ machine configurations for Australian mineral processing fabricators
The duct fabricator serving the Australian mineral processing market needs three core capabilities: rectangular duct production at industrial scale, large-diameter spiral duct production for the major process exhaust circuits, and welded-seam joining for the chemistry-exposed circuits. The following three SBKJ machine configurations cover those capabilities.
SBAL-V auto duct line configured for 316L stainless
The SBAL-V series is SBKJ's modular auto duct production line for rectangular ductwork. The standard configuration handles galvanised and aluminised carbon steel up to 1.2 mm coil thickness. The mineral processing configuration adds the 316L stainless capability — heavier-duty rollformers to handle the higher work hardening of stainless, modified shear blades for the higher tensile strength, and a TDF flange head with stainless-compatible tooling.
The economic case for the SBAL-V on a mineral processing fabricator's shop floor is the throughput. A single-shift output of 1,500 to 2,500 metres per shift on rectangular stainless duct is well above the typical demand on any single project, which means the fabricator can serve multiple projects from one production line and amortise the capital investment across the campaign cycle.
The configuration we supply to Australian fabricators includes Siemens PLC control, full CE marking, an FAT against the buyer's nominated coil specification before shipment, and a one-year wear-parts kit for the rollformer tooling and the shear blades.
SBTF-2020 spiral tubeformer configured for stainless coil
The SBTF-2020 is SBKJ's large-diameter spiral tubeformer with a maximum produced diameter of 2,000 mm. The mineral processing configuration handles 316L stainless coil up to 2.0 mm thickness, with the appropriate rollforming station modifications and the slit-coil decoiler sized for the heavier-gauge stainless.
The application is the major process exhaust duct on a flotation plant, an alumina refinery vent system or a copper smelter secondary capture circuit. Large-diameter spiral duct is more economical than the equivalent rectangular cross-section on a long straight run, and the spiral geometry gives a stronger pressure resistance against the negative pressure typical of an exhaust system.
The configuration includes a continuous longitudinal seam closure that is either lock-formed for dry-duct service or TIG-welded for chemistry-exposed service. The fabricator's choice of seam type drives the downstream finishing and inspection sequence.
TIG seam welder for welded-seam duct
The TIG seam welder is the third leg of the configuration. It is the dedicated welding station that closes the longitudinal seam on rectangular duct made from stainless coil that the SBAL-V has produced as a flat-pack blank, and it can also close the longitudinal seam on the SBTF spiral output when the duty calls for a welded rather than mechanical seam.
The TIG seam welder is configured with an automatic wire feed for stainless filler, a documented weld procedure specification matched to the welder qualifications, and a track-mounted welding head that produces a consistent bead across the full length of the seam. The post-weld pickling and passivation is a separate sub-process and is done on a pickling line that the fabricator may share across multiple projects.
The combination of SBAL-V auto duct line, SBTF-2020 spiral tubeformer and TIG seam welder gives the fabricator the capability to serve every duty on the Australian mineral processing market — rectangular and spiral, dry and chemistry-exposed, mechanical seam and welded seam — from one production facility.
What we deliver to Australian mineral processing fabricators
SBKJ Group supplies HVAC duct fabrication machinery to the fabricators serving the Australian mining heartland. Our role is upstream of the fabricator — we provide the production equipment used to make the duct that goes onto the mineral processing plant. The fabricator's customer is the EPC contractor and the operator. We never compete with the fabricator on duct supply.
The standard package we supply on a mineral processing-grade duct line is the machinery, FAT against the buyer's nominated coil, CE marking and ISO 9001 documentation, a one-year wear-parts kit, 5 to 10 days of installation supervision, operator training, written commissioning report and 10-year parts continuity.
The Australian-facing support is run from the SBKJ Group office in Box Hill North, Victoria, with English-language after-sales, local time-zone coverage and a documented spare parts continuity programme. We have configured machines for fabricators serving the major Australian operators — BHP, Rio Tinto, Fortescue, South32, Newmont, Mineral Resources, Pilbara Minerals, Liontown Resources, Iluka Resources, Lynas Rare Earths, Glencore, Northern Star and Evolution Mining — through the major EPC contractors. The configuration changes from project to project, but the spine of the offering is the same three-machine combination described above.
Talk to an SBKJ engineer about a mineral processing duct line configuration →
FAQ
What Australian standards govern HVAC ductwork in mineral processing plants and smelters?
AS 1668.2 for mechanical industrial ventilation, AS/NZS 1668.4 for natural ventilation, AS/NZS 60079 for hazardous area, and AS 4024 for machinery safety. The state mine safety legislation overlays these: the Mine Safety and Inspection Act in WA, the Work Health and Safety (Mines and Petroleum Sites) Act in NSW, and the Mining and Quarrying Safety and Health Act in QLD.
Why does galvanised duct fail in mineral processing service?
Galvanised steel fails in acid, caustic and cyanide chemistry exposure within months, and above 250 °C the zinc layer alloys with the iron substrate. Australian mineral processing duct work is specified in 316L stainless where chemistry is the driver, refractory-lined carbon steel where temperature is the driver, and FRP or polypropylene-lined steel where strong acid at low temperature is the duty.
What is the difference between mining ventilation and mineral processing plant HVAC?
Underground mine ventilation moves air through development drives and stopes to dilute diesel particulate, blasting fumes and rock dust at the working face — flexible or rigid plastic duct, low pressure, ambient temperature. Mineral processing plant HVAC sits on the surface, serves process unit operations and captures process-generated dust and chemical vapour — steel duct, higher pressures, process chemistry exposure. The two are designed by different engineering disciplines.
When is 316L stainless mandatory versus a coated carbon steel duct?
316L stainless is mandatory wherever the duct sees acid plant fume, caustic NaOH vapour, cyanide-containing process air or chloride-bearing concentrate dust. Above 250 °C the answer is refractory-lined carbon steel because stainless loses strength above 600 °C. For dry dust streams without chemical exposure, painted carbon steel or aluminised steel is acceptable and far cheaper.
What SBKJ machine configurations suit Australian mineral processing fabrication?
The SBAL-V auto duct line configured for 316L stainless handles rectangular refinery ductwork at thickness up to 3 mm. The SBTF-2020 spiral tubeformer configured for stainless coil produces large process exhaust spiral duct up to 2000 mm diameter. The TIG seam welder is mandatory for welded-seam duct on acid plant, caustic refinery and cyanide-exposed plants where mechanical joints are not acceptable. All three are offered with FAT supervision, CE certification and 10-year parts continuity from the SBKJ Group office in Box Hill North, Victoria.
