Doc #109 — Aluminium Smelting and Recycling

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RECOMMENDED ACTIONS

First week (Phase 1)

1. Verify alumina inventory at Tiwai Point — exact tonnage, grade, and storage condition. This number determines how long the smelter can operate and is a top-10 national strategic information priority. (Doc #1)
2. Verify operational status of all three potlines — how many pots are operating, their condition, and current production rate.
3. Classify NZAS operational workforce as essential personnel — prevent redeployment. Ensure families are supported to maintain workforce retention. (Doc #145)
4. Secure the Tiwai Point site — prevent unauthorised removal of any materials, particularly finished aluminium ingots and alumina stocks.
5. Contact Meridian Energy — confirm Manapouri power supply status and agree interim power allocation pending the government’s smelter decision. (Doc #65, Doc #67)
6. Inventory finished aluminium on site — ingots, billets, any semi-finished product.
7. Assess the HVDC link and Transpower southern grid — Tiwai Point’s power supply depends on the grid path from Manapouri. Confirm operational status. (Doc #67)

First month (Phase 1)

8. Make the smelter operating decision — this is a Cabinet-level decision that must be made within the first month, informed by alumina stock data, grid demand assessment, and aluminium demand projections. See Section 3 for the decision framework.
9. If continuing operation: Implement reduced potline operation to extend alumina supply and reduce grid demand. Target approximately one-third to one-half of normal production.
10. Begin planning for smelter shutdown — even if operation continues, plan the controlled shutdown sequence to maximise the residual value of the plant and materials.
11. Establish aluminium allocation framework — prioritise allocation to applications where aluminium’s properties (lightweight, corrosion-resistant) are essential and cannot be substituted by steel, timber, or other NZ-producible materials.

Months 2–3

The smelter go/no-go decision and immediate operational adjustments are genuinely time-sensitive and belong in Month 1. The knowledge capture and national inventory work below is important but does not compete for the same narrow decision window — it can proceed once the smelter’s operating posture is settled and the government has bandwidth.

12. Begin knowledge capture from NZAS smelter specialists — the electrolytic reduction process, pot management, anode production, and cast house operations. This knowledge is not needed for recycling but is irreplaceable industrial heritage and may have long-term value if alumina trade resumes.
13. Inventory all aluminium stocks nationally — at NZAS, at NZ distributors (Ullrich Aluminium, Capral, others), at fabricators, and in wholesale channels. This is the “bridge” stock between smelter shutdown and recycling.
14. Identify and assess all aluminium scrap sources nationally — vehicles, window frames, roofing, cladding, cookware, industrial equipment. Categorise by alloy family where possible.

First 3 months (Phase 1–2)

15. If alumina stocks are running low: Execute the controlled shutdown sequence (Section 10).
16. Establish at least one operational aluminium recycling facility — either adapt an existing NZ foundry (Doc #93) or use NZAS’s own cast house equipment for remelting scrap after smelting ceases.
17. Begin scrap collection and sorting program — aluminium scrap must be separated from other metals and sorted by alloy family for useful recycling (Section 8.2).
18. Cross-train smelter workforce in recycling operations, foundry work, and other essential recovery skills — the workforce transition must begin before shutdown, not after.
19. Assess Tiwai Point site for post-smelter uses — the deep-water port access at Bluff, the electrical infrastructure, and the industrial buildings are significant assets regardless of whether smelting continues.

Phase 2–3 (Years 1–7)

20. Scale up aluminium recycling to meet national demand from regional foundries and the Tiwai Point cast house (if retained as a recycling facility).
21. Develop NZ capability to produce aluminium casting alloys from mixed scrap — alloying control using available silicon, copper, and other elements.
22. Establish aluminium extrusion capability if existing NZ extrusion presses can be maintained — extending the product range beyond castings to profiles (structural shapes, tubing).
23. If maritime trade with Australia develops, negotiate for alumina supply as a high-priority import — even modest quantities of alumina enable periodic smelter-scale production runs if the potlines can be kept alive (uncertain — see Section 4.3).

Phase 4+ (Years 7+)

24. Mature recycling economy — NZ’s aluminium supply is entirely recycled stock, supplemented by any trade imports.
25. Long-term: If trade routes stabilise and Australian alumina is reliably available, reassess whether any smelting capacity can be restored or whether a smaller-scale electrolytic cell is feasible using Manapouri power.

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ECONOMIC JUSTIFICATION

3.1 The energy trade-off and opportunity cost

The core economic question is whether the aluminium produced by running the smelter is worth the electricity consumed. The opportunity cost of continued smelting is large and must be stated plainly: NZAS consumes approximately 12–13% of NZ’s total electricity generation. Every megawatt-hour directed to the potlines is a megawatt-hour unavailable for hospitals, heating, water treatment, communications, and machine shops. This is the most significant single energy trade-off in the recovery’s first weeks.

Energy cost of smelting: NZAS consumes approximately 14–15 MWh of electricity per tonne of aluminium produced.⁷ At reduced production (say 150,000 tonnes/year), that is approximately 2,100–2,250 GWh/year — still roughly 5% of NZ’s total generation.

Energy cost of recycling: Remelting aluminium scrap in an electric furnace consumes approximately 0.7–1.0 MWh per tonne⁸ — roughly 5% of the smelting energy. The energy saving is enormous. Once the smelter closes, the freed Manapouri capacity (~5,000 GWh/year) becomes available to the national grid at zero marginal cost.

Value of aluminium: Under recovery conditions, aluminium’s value is measured not in dollars but in what it enables. Aluminium is essential for:

• Electrical transmission: NZ’s grid uses aluminium conductors (ACSR — aluminium conductor, steel reinforced). Replacement conductor requires aluminium. (Doc #67)
• Lightweight transport: Aluminium boat fittings, bicycle components, vehicle body repairs.
• Corrosion resistance: Marine hardware, food-contact equipment, roofing in coastal areas.
• Casting: Aluminium is the easiest metal to cast in a small foundry due to its low melting point (~660°C). This makes it the entry-level material for new foundry operations. (Doc #93)
• Heat exchange: Radiators, heat exchangers, solar thermal components.

The calculation: If the smelter has 4 weeks of alumina stock and operates at half capacity, it produces approximately 6,000–7,000 tonnes of aluminium in that period, consuming approximately 90,000–100,000 MWh of electricity. That same electricity, redirected to the grid, could power approximately 15,000–20,000 average NZ households for 4 weeks.⁹

The 6,000–7,000 tonnes of aluminium, however, represents years of NZ’s essential aluminium needs — perhaps a decade or more of carefully managed supply for the applications listed above. The trade-off favours continuing smelting until alumina runs out, provided grid demand can be managed by load shedding non-essential loads during the smelting period.

3.2 Person-years and workforce breakdown

Tiwai Point is NZ’s only source of primary aluminium. It cannot be replicated from local materials: no domestic bauxite, no refining capability, no alternative electrolytic pathway. Every person-year of labour invested in operating the smelter during its final weeks produces aluminium that NZ has no other means of obtaining. The workforce investment is therefore among the highest-value labour allocations in Phase 1.

Smelter operations workforce (~600–700 workers during run-down):

• Potroom operators: responsible for monitoring and managing individual electrolytic pots — adding alumina, adjusting current, managing anode effects. Highly process-specific; this knowledge is not transferable to recycling operations.
• Carbon plant workers: producing prebaked anodes from petroleum coke and pitch. These workers have furnace operations skills applicable to other high-temperature industrial work after shutdown.
• Cast house operators: tapping metal from the pots, casting ingots and billets. This skill set translates directly to aluminium recycling foundry work.

Electrical engineering workforce (~100–150 workers during run-down):

• High-voltage electrical engineers and technicians: managing the 572 MW Manapouri supply, the rectifier plant (which converts AC to the high-current DC used by the pots), and the site’s internal HV distribution. The rectifier plant is one of the largest DC power systems in the Southern Hemisphere and requires specialist expertise.
• Instrument and control technicians: the potline control systems manage current, temperature, alumina feed rates, and anode effect response automatically. Keeping these systems functional during the run-down period maximises production efficiency and safety.
• These workers are among the highest-value skilled personnel in the national recovery — electrical engineers with high-current DC, industrial controls, and high-voltage AC experience are needed across the recovery for grid maintenance, hydroelectric station operation, and industrial motor systems. Their allocation to smelter operations during the run-down period is warranted but temporary.

Recycling operations workforce (~50–100 workers, ongoing from Phase 2):

• Furnace operators: remelting aluminium scrap in reverberatory or induction furnaces. Less technically complex than potroom operations but still requires consistent temperature management (avoiding overheating that accelerates oxidation loss), flux practice, and degassing discipline.
• Scrap sorters and collectors: identifying and separating aluminium from mixed scrap. Can be trained quickly; requires basic metallurgical knowledge rather than specialist skills.
• Casters and moulders: producing ingots and castings from recycled metal. Foundry skills (Doc #93) directly applicable.
• Alloy technicians: managing alloy composition in recycled metal streams. Laboratory analysis capability needed for higher-specification products.

Total person-years (Phase 1 run-down): Approximately 800–1,000 workers for 1–3 months = roughly 70–250 person-years of skilled labour during the run-down period. After shutdown, 900+ workers become available for other recovery priorities — a significant labour release.

Breakeven: The smelter is NZ’s only source of primary aluminium. There is no breakeven threshold to calculate — once the smelter shuts down and the alumina runs out, NZ’s primary aluminium supply ends permanently. Every tonne produced before shutdown is aluminium NZ could not otherwise have. Recycling extends NZ’s aluminium supply by drawing down the existing stock of ~500,000–1,000,000 tonnes of aluminium in the national economy, but it does not replace primary production. The combination — smelt to alumina exhaustion, then recycle — is the only strategy that maximises total aluminium available to the recovery.

3.3 Comparison: maintaining production vs. losing access

The relevant comparison is not “smelting vs. recycling” as competing strategies — both are necessary, in sequence. The relevant comparison is between the combined strategy (smelt to exhaustion + recycling) versus losing access to aluminium entirely.

If aluminium becomes unavailable:

• Grid maintenance (conductor replacement, transformer windings) requires copper as a substitute — NZ has limited copper and limited copper recycling throughput. Grid extension and repair capacity is severely constrained.
• Aluminium casting for engine components, pump housings, and marine fittings requires substitution to grey iron or bronze. Grey iron foundry capability exists in NZ (Doc #93) but produces heavier components. Marine vessels cannot be built at aluminium weights.
• Aluminium extrusion (window frames, structural profiles, tubing) is replaced by timber or steel where possible — structurally feasible but with significant weight and corrosion penalties in coastal applications.
• No workaround exists for aluminium conductor in high-voltage transmission lines at scale. Copper conductor is theoretically possible but requires copper wire drawing capability and copper supply that NZ does not have in sufficient quantity.

If aluminium is maintained through the combined strategy:

• 6,000–15,000 tonnes of primary aluminium produced before smelter shutdown (depending on alumina stock)
• Indefinite recycling supply at lower throughput, drawing on ~500,000–1,000,000 tonnes of national aluminium stock
• Grid maintenance capability maintained for conductor replacement
• Casting and extrusion capability maintained for the life of existing equipment

The economic argument: The cost of the combined strategy is the electricity consumed during the run-down (offset by the value of the aluminium produced) and the short-term deployment of ~1,000 skilled workers in smelter operations. Both costs are bounded and temporary. The benefit is permanent: NZ retains access to a light metal with no general-purpose substitute for the applications listed above. Losing that access permanently — which is the consequence of shutting down immediately and allowing the smelter to freeze — is the scenario this document recommends against.

Strategy	Aluminium produced	Energy cost	Workforce	Duration
Continue smelting until alumina runs out	~6,000–15,000 tonnes (depending on stock)	2,000–5,000 GWh per year at full rate	~1,000	Weeks to months
Recycling from existing NZ stock	Depends on scrap collection — potentially 5,000–10,000 tonnes/year	~50–100 GWh/year	50–100	Indefinite
Do nothing (abandon smelter immediately)	0 additional primary aluminium	0 — electricity freed for grid	0 — workers redeployed	—

Recommendation: Continue smelting at reduced capacity until alumina is exhausted. The aluminium produced is irreplaceable. Then transition to recycling. Shutting down immediately saves electricity and frees workers, but permanently forgoes aluminium that NZ has no other means of obtaining.

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4. THE SMELTER: WHAT IT IS AND HOW IT WORKS

4.1 Location and physical plant

NZAS is located at Tiwai Point, a peninsula at the eastern entrance to Bluff Harbour, approximately 25 km south of Invercargill. The site covers approximately 250 hectares and includes three potlines (potrooms), a carbon plant (for anode production), a cast house, alumina storage facilities, port facilities for alumina receival, and supporting infrastructure.¹⁰

The location was chosen in the 1960s for its proximity to both the Manapouri hydroelectric scheme and the deep-water port at Bluff, through which alumina is imported. Construction began in 1968 and the first aluminium was produced in 1971.¹¹

4.2 The Hall-Heroult process

Aluminium smelting uses the Hall-Heroult process, which has been the sole industrial method for producing aluminium since its independent invention by Charles Martin Hall and Paul Heroult in 1886.¹² The process is electrolytic: alumina (Al₂O₃, aluminium oxide) is dissolved in a molten cryolite (Na₃AlF₆) bath at approximately 950–970°C, and a powerful direct current is passed through the bath. The electric current reduces the alumina to metallic aluminium, which sinks to the bottom of the pot and is periodically siphoned off, while oxygen reacts with the carbon anodes, consuming them.

Key features:

• Temperature: The electrolyte bath operates at approximately 950–970°C. This temperature is maintained by the resistive heating of the electric current flowing through the bath — the process is self-heating.
• Current: Each pot draws approximately 170,000–320,000 amperes of direct current at very low voltage (approximately 4–5 volts per pot).¹³ The pots in a potline are connected in series, so the total potline voltage is the sum of all pot voltages — typically 700–1,200 volts for a full potline.
• Anodes: Carbon anodes, manufactured on-site from petroleum coke and coal tar pitch, are consumed in the process. Anode consumption is approximately 0.4–0.5 kg of carbon per kg of aluminium produced.¹⁴
• Cathode: The pot floor is lined with carbon cathode blocks, which serve as the negative electrode and the container for the molten aluminium. Cathode life is typically 5–8 years before relining is required.¹⁵
• Alumina feed: Alumina is added to the bath periodically (automatically in modern smelters) to maintain the dissolved alumina concentration within the correct range. Too little alumina causes “anode effects” — voltage spikes that waste energy and damage the pot. Too much causes sludge formation on the pot floor.

4.3 The potline freeze problem

This is the critical constraint on smelter restartability. When a potline is shut down and the pots cool, the electrolyte bath and the molten aluminium in each pot solidify. The frozen bath material contracts and adheres to the pot lining, creating a solid mass that is extremely difficult to remove without damaging the carbon cathode lining.

Restarting frozen pots is possible but costly and slow. It requires:

• Removing the frozen bath material (typically by mechanical breaking and manual removal — a labour-intensive process taking days to weeks per pot)
• Inspecting and potentially replacing damaged cathode linings
• Preheating the pots before re-establishing the electrolytic process
• A controlled startup sequence that gradually increases current and temperature

NZAS has over 600 electrolytic pots across its three potlines.¹⁶ Restarting even a fraction of these after a prolonged cold shutdown would be a major engineering project taking months and requiring alumina — the very material whose absence caused the shutdown. A short shutdown (days) is recoverable. A shutdown of weeks to months causes progressive pot damage. A shutdown of more than several months likely makes potline restart impractical without full reline of many pots — a project measured in years and requiring imported cathode carbon, refractory materials, and significant capital.

Implication: The smelter decision is effectively irreversible. Once it shuts down, NZ should plan on the basis that primary aluminium smelting will not resume for years at minimum, and possibly never without restored trade links for alumina and pot-lining materials.

4.4 Anode production

NZAS manufactures its own carbon anodes on-site. The carbon plant mixes calcined petroleum coke with coal tar pitch binder, forms the mixture into anode blocks, and bakes them at approximately 1,100–1,200°C in large ring furnaces.¹⁷

Dependencies:

• Petroleum coke: Imported. NZ does not produce petroleum coke (Marsden Point refinery, NZ’s only refinery, ceased refining operations in 2022).¹⁸ Without imports, anode production stops when petroleum coke stocks are exhausted — typically weeks to a few months of supply on site.
• Coal tar pitch: Imported. Could potentially be produced from NZ coal through high-temperature pyrolysis (destructive distillation of coal yields coal tar, from which pitch is separated by distillation), but this is not current practice in NZ and would require development of coal carbonisation capability — a significant project with its own dependency chain including NZ coal supply, refractory-lined retort construction, and tar distillation equipment. (See Doc #106 for related electrode carbon discussions.)

Assessment: Even if alumina were somehow available beyond existing stocks, anode production would cease independently when petroleum coke runs out. This reinforces the conclusion that the smelter has a finite operational window measured in weeks to months, not years.

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5. THE ALUMINA SUPPLY CHAIN

5.1 Where alumina comes from

Alumina (aluminium oxide, Al₂O₃) is produced by refining bauxite ore using the Bayer process — dissolution in hot sodium hydroxide, separation of the aluminium-bearing solution from the insoluble residue (“red mud”), and precipitation and calcination of alumina. This is a large-scale chemical process requiring significant energy and caustic soda.¹⁹

NZAS’s alumina is supplied primarily from Queensland Alumina Limited (QAL) at Gladstone, Queensland, Australia, and possibly other Australian sources. The alumina is shipped in bulk carriers across the Tasman Sea to Bluff, where it is unloaded at the Tiwai Point wharf and stored in large silos before being conveyed to the potrooms.²⁰

5.2 NZ’s complete absence of the alumina supply chain

NZ has:

• No bauxite deposits. NZ’s geology does not include the laterite weathering profiles that produce bauxite.²¹
• No alumina refining capability. The Bayer process requires a purpose-built refinery — a multi-billion-dollar facility even at modest scale.
• No alternative aluminium ores. Aluminium is the most abundant metal in the Earth’s crust, present in many NZ minerals (clays, feldspars), but extracting it from anything other than bauxite/alumina using electrolytic methods is not commercially practised anywhere. Alternative processes (e.g., carbothermic reduction of alumina, direct reduction of clays) have been researched for decades but none has achieved commercial viability.²²

This is a hard constraint. NZ cannot produce alumina domestically. When existing alumina stocks at Tiwai Point are consumed, primary aluminium production ends. There is no workaround, no substitution, and no alternative pathway — only trade.

5.3 Australian trade potential

If maritime trade with Australia develops (Doc #151), alumina is a high-priority import. Australia is the world’s largest bauxite miner and a major alumina producer, with multiple refineries in Western Australia and Queensland.²³ From Australia’s perspective, alumina is abundant, its production infrastructure existed pre-event, and NZ-bound alumina represents a small fraction of Australian production. What NZ could offer in return is an open question (see Doc #151 for trans-Tasman trade analysis).

However, this document does not assume trade will materialise on any specific timeline. The base case is that NZ’s aluminium supply transitions to recycling.

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6. THE ENERGY RELATIONSHIP: MANAPOURI AND TIWAI POINT

6.1 Manapouri Power Station

The Manapouri Power Station, located underground on the western arm of Lake Manapouri in Fiordland, is NZ’s largest single power station with a capacity of approximately 800 MW from seven generating units. The station was constructed specifically to power the Tiwai Point smelter, with the first units commissioned in 1969 and the second tailrace tunnel expansion completed in 2002.²⁴

Meridian Energy owns and operates Manapouri. Under the long-term electricity supply contract, approximately 572 MW (roughly 70% of station capacity) has been contracted to NZAS.²⁵ The remainder is available to the national grid.

6.2 What happens to Manapouri’s power after the smelter closes

This is the single largest positive consequence of smelter shutdown. When NZAS ceases operations, approximately 5,000–5,200 GWh per year — 12–13% of NZ’s total generation — becomes available for other uses.²⁶ This is a major increase in available electricity for the rest of the recovery economy.

Potential uses for freed Manapouri capacity:

• Southland and Otago electrification: Direct heating, industrial power for Invercargill and Dunedin, agricultural processing.
• National grid reinforcement: Additional base-load generation strengthens grid stability and provides reserve margin for equipment failures at other stations.
• Industrial development: The energy-intensive industries that recovery requires — steel production at Glenbrook (Doc #89), glass production (Doc #98), cement production (Doc #97), electric arc furnace scrap recycling (Doc #106), lime production (Doc #112) — all benefit from abundant electricity.
• Hydrogen production: Electrolytic hydrogen for industrial chemistry and (speculatively) fuel applications (Doc #63, Doc #64).
• Southland as industrial hub: The combination of freed Manapouri power, the Bluff port, and the industrial infrastructure at Tiwai Point makes Southland a candidate for new industrial development. The smelter buildings, cranes, and electrical infrastructure have value even if the potlines are decommissioned.

Grid constraint: The freed power must travel from Southland to where it is needed. The existing Transpower grid (Doc #67) includes the HVDC link between the South Island and North Island (rated at approximately 1,200 MW), which can carry Manapouri’s output northward. However, the HVDC link is itself a complex piece of equipment with imported components and finite life. Its continued operation is not guaranteed indefinitely (Doc #67, Section on HVDC).

6.3 The Manapouri operating decision

Manapouri itself continues to operate regardless of the smelter decision — the station is a national asset. The question is only whether its output goes to the smelter or to the grid. From the grid’s perspective, smelter closure is unambiguously positive: it frees approximately 5,000–5,200 GWh per year at zero marginal cost (Manapouri is hydroelectric, with no fuel inputs).²⁷

From a lake management perspective, reduced generation might allow Lake Manapouri levels to be managed more conservatively, building storage for dry periods — though Manapouri’s operating consents historically imposed strict lake level controls to protect the lake’s natural character.²⁸ Under emergency conditions, these consents may be modified to optimise energy production.

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7. ALUMINIUM STOCKS IN NZ

7.1 Primary aluminium stocks

At any given time, NZAS holds stocks of finished aluminium at Tiwai Point — ingots, billets (logs), and some specialty products awaiting shipment. Under normal conditions, NZ exports over 90% of Tiwai Point’s production, with only a small proportion consumed domestically.²⁹

Estimate: Finished aluminium inventory at Tiwai Point at the time of the event could range from 5,000 to 30,000 tonnes, depending on production schedules, shipping schedules, and market conditions. This is highly uncertain and must be verified directly. This stockpile — plus whatever is produced during the smelter run-down period — constitutes NZ’s “new” aluminium supply, potentially for decades.

7.2 Distributor and fabricator stocks

NZ’s aluminium distribution and fabrication industry holds additional stocks:

• Ullrich Aluminium: NZ’s largest aluminium extruder and distributor, with facilities in Auckland and other locations. Holds stocks of extrusion billets, extruded profiles, and flat products.³⁰
• Capral Limited (NZ operations): Aluminium extrusion and distribution.
• Fletcher Aluminium: Extrusion and fabrication.
• Numerous smaller fabricators and distributors across NZ.

Estimate: Total distributor and fabricator stocks are probably 5,000–15,000 tonnes nationally, though this requires verification through the national census (Doc #8). These stocks are immediately available for allocation.

7.3 Aluminium in the existing economy (the recycling stock)

NZ has a large accumulated stock of aluminium in use:

• Building and construction: Window and door frames (a major aluminium application in NZ residential construction), cladding, roofing (in some applications), structural glazing systems. NZ’s building stock contains an estimated several hundred thousand tonnes of aluminium in window frames alone.³¹
• Vehicles: Engine blocks, cylinder heads, transmission cases, wheels, body panels (especially in modern vehicles), radiators. The NZ vehicle fleet of approximately 4.4 million registered vehicles contains substantial aluminium.³²
• Marine: Aluminium hulls (NZ’s commercial and recreational boat fleet includes many aluminium vessels), masts, fittings.
• Industrial equipment: Heat exchangers, process vessels, piping, electrical bus bars.
• Consumer goods: Cookware, furniture, packaging (aluminium cans — NZ consumes millions annually, with large stocks in recycling streams and landfill).
• Electrical: Aluminium conductors in the transmission and distribution network (Doc #67). NZ’s transmission and distribution network comprises tens of thousands of kilometres of ACSR conductor — each kilometre of 100mm² ACSR contains roughly 100–150 kg of aluminium — making the electrical network one of the largest single concentrations of aluminium in NZ infrastructure, though exact quantification requires Transpower and EDB inventory data.³³

Total estimate: NZ’s total accumulated aluminium stock is probably in the range of 500,000–1,000,000 tonnes, though this is a rough estimate based on per-capita aluminium-in-use figures from comparable economies.³⁴ The accessible portion (scrap that can be economically collected and recycled) is a fraction of this — perhaps 200,000–500,000 tonnes over time, as buildings are demolished, vehicles are scrapped, and products reach end of life.

This stock, managed carefully, represents decades of aluminium supply for essential applications through recycling.

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8. ALUMINIUM RECYCLING

8.1 Why recycling is the long-term answer

Aluminium recycling is one of the most energy-efficient metal recycling processes:

• Energy: Remelting aluminium scrap requires approximately 5% of the energy needed for primary smelting — roughly 0.7–1.0 MWh per tonne compared to 14–15 MWh per tonne.³⁵ This is because the electrolytic reduction step (breaking the aluminium-oxygen bond, which consumes the vast majority of smelting energy) has already been done. Recycling only requires melting the metal — heating aluminium to approximately 660°C, which is modest by metallurgical standards.
• Quality: Aluminium can be recycled repeatedly with minimal loss of material properties, provided alloy contamination is managed. Each recycling cycle loses approximately 1–3% of the aluminium to oxidation (dross), which can be partially recovered.³⁶
• Equipment: Aluminium can be melted in reverberatory furnaces, electric resistance furnaces, or induction furnaces, all of which NZ can build or maintain from existing infrastructure. The low melting point (660°C) means even a charcoal-fired crucible furnace can melt aluminium, making it accessible to small-scale and distributed operations — though a functional crucible furnace requires refractory-lined construction, a reliable charcoal or gas supply, and appropriate crucible materials (silicon carbide or cast iron), none of which are trivial to source or fabricate. (Doc #102, Doc #93)
• Existing precedent: Aluminium recycling is a mature global industry. NZ already recycles aluminium (primarily beverage cans and industrial scrap) through several commercial operators.

8.2 The alloy contamination problem

This is the primary technical challenge in aluminium recycling, and it must be addressed honestly.

Aluminium alloys contain deliberate additions of silicon, copper, magnesium, manganese, zinc, and other elements to achieve specific properties. Different applications use different alloys:

• Casting alloys (3xx.x series): High silicon (5–12%) for fluidity. Used in engine blocks, housings, and general castings.
• Wrought alloys (1xxx–7xxx series): Various compositions optimised for different forming processes and applications. Window frames are typically 6063 alloy (Al-Mg-Si). Aircraft and marine applications use 2xxx (Al-Cu) or 7xxx (Al-Zn) series.
• Electrical conductor grade (1350): High-purity aluminium (99.5%+) with minimal alloying for maximum electrical conductivity.

The problem: When scrap from different alloys is melted together, the alloying elements mix and cannot be economically separated. Copper, zinc, and iron are particularly problematic — once present, they cannot be removed by conventional remelting. The result is a “mixed” alloy that may not meet any specific alloy specification.³⁷

The consequence: Mixed-alloy scrap is usable for casting alloys (which are tolerant of varied composition) but not for wrought products requiring specific alloy properties (extrusions, sheet, conductor grade). This means:

• Careful sorting is essential. Scrap should be sorted by alloy family before melting — casting alloys together, wrought alloys by series, conductor grade separately. Visual identification is unreliable. Spark testing, chemical analysis (if laboratory capability exists), or — for known-source scrap — documentation of the original material provides better results.
• Most recycled aluminium will become casting alloy. This is the practical reality. The tolerance of casting alloys for varied composition means mixed scrap can be used for castings (pipe fittings, housings, gear blanks, hardware) even when the exact composition is uncertain. This is acceptable for most recovery applications.
• Electrical conductor grade requires dedicated scrap streams. NZ’s grid conductor replacement needs (Doc #97) require high-purity aluminium with minimal alloying. This should be recycled from identified conductor scrap only — never mixed with general aluminium scrap.

8.3 Recycling process

Collection: Scrap aluminium from all sources — end-of-life vehicles (engine blocks, transmission cases, wheels are the highest-yield vehicle components), building demolition (window frames, cladding), industrial equipment, consumer goods.

Sorting: Separate aluminium from other metals. Aluminium is non-magnetic (unlike steel), light, and has a distinctive appearance. Sorting methods:

• Magnet test (removes steel contamination)
• Weight/density (aluminium is approximately 2.7 g/cm³ — noticeably lighter than steel, copper, or zinc)
• Spark test on a grinding wheel (aluminium produces no sparks, unlike steel)
• Visual identification of known aluminium products (window frames, drink cans, engine blocks)
• Where laboratory analysis is available, spectrographic or XRF analysis for alloy identification

Preparation: Remove non-aluminium attachments (steel bolts, rubber seals, plastic inserts, paint coatings). Shred or cut to sizes that fit the furnace. Remove excessive dirt and oil.

Melting: In a suitable furnace:

• Reverberatory furnace: A box-shaped furnace where the flame or heat reflects off the roof onto the charge below. Suitable for large volumes. Can be gas-fired, oil-fired, or charcoal-fired. This is the standard industrial aluminium recycling furnace.
• Electric induction furnace: Clean, precise, and powered by NZ’s grid. The preferred option where existing induction furnaces are available. Induction furnaces are used in NZ foundries (Doc #93) and may already be in place at metal recycling operations.
• Crucible furnace: For small batches. A refractory-lined crucible furnace capable of reaching 750°C. The Gingery-type charcoal-fired approach (Doc #93) is entirely suitable for aluminium melting, provided appropriate crucibles and refractory lining materials are available.

Fluxing and degassing: Molten aluminium absorbs hydrogen from moisture in the atmosphere, which causes porosity in castings. Degassing (bubbling an inert gas — nitrogen or argon — through the melt) removes dissolved hydrogen. Fluxing salts (typically a mixture of sodium chloride and potassium chloride, both available from NZ salt production, Doc #103) are used to separate oxides and contaminants from the melt.³⁸

Casting: The molten aluminium is cast into ingots for storage and later use, or directly into sand moulds for finished castings (Doc #93). Typical casting temperature for aluminium alloys: 680–750°C.³⁹

8.4 Dross recovery

When aluminium is melted, a layer of dross (a mixture of aluminium oxide and entrapped metal) forms on the surface. Dross typically contains 15–70% recoverable aluminium.⁴⁰ In a well-managed recycling operation, dross is skimmed off, cooled, and processed to recover the metallic aluminium — either by mechanical separation (crushing and screening) or by remelting. Discarding dross without recovery wastes a significant fraction of the aluminium.

8.5 Recycling infrastructure in NZ

NZ has existing aluminium recycling infrastructure, though at modest scale:

• Metalman (Sims Metal Management operations in NZ): Scrap metal collection and processing, including aluminium.
• NZ Aluminium Smelters’ own recycling: NZAS has historically purchased some domestic scrap for remelting.
• Smaller operators: Various scrap dealers and recyclers across NZ.

Under recovery conditions, this infrastructure needs to be expanded and formalised. The national census (Doc #8) should identify all existing aluminium recycling capability and scrap stocks.

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9. APPLICATIONS AND ALLOCATION PRIORITIES

9.1 Where aluminium is essential (no practical substitute)

• Electrical conductors: Grid and distribution network conductor is aluminium (ACSR). Copper conductor is an alternative but NZ has limited copper. Aluminium conductor production requires drawing aluminium rod — a capability that exists at NZAS and possibly at Ullrich Aluminium. This is the highest-priority aluminium application. (Doc #67, Doc #97)
• Lightweight marine applications: Aluminium hull vessels for coastal and inter-island service. Steel is an alternative but a comparable vessel will be 30–50% heavier, reducing payload and degrading sailing performance measurably — a significant penalty for sail-powered trade vessels where windward efficiency and load capacity are operational requirements. (Doc #143, Doc #138)
• Heat exchangers: Aluminium’s thermal conductivity (approximately 205 W/m·K) and corrosion resistance make it the preferred material for radiators, solar thermal panels, and industrial heat exchangers. Copper (approximately 385 W/m·K) has higher thermal conductivity but is scarcer in NZ; for most heat exchanger applications the conductivity advantage of copper is secondary to surface area design, so aluminium is a workable substitute in new-build exchangers — provided alloy purity is sufficient to resist corrosion in the specific service environment.⁴¹

9.2 Where aluminium is preferred but steel can substitute

• General casting: Aluminium castings (pump housings, valve bodies, machine components) can often be substituted with grey iron or bronze castings. Iron is heavier but NZ has an abundant scrap supply and proven casting capability (Doc #93). Aluminium casting should be reserved for applications where weight matters.
• Structural profiles: Aluminium extrusions in buildings (window frames, curtain walling) can be substituted with timber or steel. Timber windows require more maintenance and are less airtight than aluminium joinery without careful detailing; steel windows are heavy and prone to condensation-driven corrosion in NZ’s coastal climate without galvanising. These are real performance gaps, but manageable ones in the recovery context.
• Cookware: Aluminium pots and pans can be substituted with cast iron or stainless steel. NZ’s existing stock of aluminium cookware is large and will serve for many years regardless.
• Vehicle body panels: Steel is heavier but entirely functional. Under recovery conditions, vehicle weight efficiency is not a priority.

9.3 Allocation framework

Aluminium should be allocated based on the following priority order:

1. Grid and electrical infrastructure (conductor, bus bar, electrical hardware)
2. Maritime (hull plate, masts, fittings for essential vessels)
3. Heat exchange (radiators, industrial heat exchangers, solar thermal)
4. Foundry stock (casting ingots for regional foundries producing essential components)
5. General fabrication (roofing, cladding, structural applications where alternatives are impractical)

All other applications should use substitute materials (steel, timber, copper where available). This allocation framework should be enforced through the same centralized distribution system used for other strategic materials (Doc #1).

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10. THE SMELTER SHUTDOWN SEQUENCE

10.1 Controlled shutdown

A controlled shutdown — planned and executed methodically — preserves maximum value from the smelter and minimises environmental and safety risks. The sequence:

1. Reduce potline load progressively. Shut down individual pots one at a time, starting with the poorest-performing pots. This reduces alumina consumption and extends the period of reduced-rate production.
2. Tap all remaining aluminium from each pot as it is shut down. Siphon or ladle the molten aluminium from the cathode cavity. This recovers the “metal pad” — the pool of liquid aluminium sitting on the pot floor during normal operation, typically several tonnes per pot.
3. Allow pots to cool. Once tapped, pots are de-energised and allowed to cool naturally. The remaining bath material and cathode lining are left in place.
4. Continue anode production to service the remaining operating pots until the last potline is shut down.
5. Final shutdown of the last potline. Tap all remaining metal. De-energise.
6. Cast house operations continue after potline shutdown — casting the accumulated molten and tapped aluminium into ingots for stockpiling. The cast house should then be assessed for conversion to a recycling facility.

10.2 Environmental considerations

The smelter site has significant environmental management requirements:

• Spent pot lining (SPL): The used carbon cathode linings are classified as hazardous waste. They contain cyanide compounds, fluorides, and other contaminants that leach if exposed to water.⁴² Under normal operations, SPL is processed or exported for treatment. Under recovery conditions, SPL must be stored safely — in lined, covered containment — to prevent groundwater contamination. The Tiwai Point site’s low-lying, coastal location makes this a genuine concern.
• Fluoride emissions: During normal operation, the smelter emits fluoride compounds (primarily gaseous HF and particulate fluorides), which are captured by fume treatment systems (dry scrubbers using alumina). After shutdown, fugitive emissions cease, but stored materials (anode butts, bath material, SPL) continue to pose a fluoride contamination risk if not managed.
• Alumina dust: Stored alumina is a fine powder that becomes airborne in wind. Existing storage silos should be sealed after final use. Any loose alumina should be swept up and stored under cover.

10.3 Site value after shutdown

Even without smelting, the Tiwai Point site has significant recovery value:

• Port access: The deep-water wharf at Tiwai Point can handle large vessels — useful for any Bluff-based maritime trade operations.
• Industrial buildings: Large, roofed industrial structures suitable for workshops, storage, or alternative manufacturing.
• Electrical infrastructure: The high-voltage supply infrastructure (220 kV from Manapouri) and on-site electrical distribution could power alternative industrial operations.
• Cranes and heavy-lift equipment: The site’s overhead cranes and material-handling equipment are useful for any heavy industrial application.
• Cast house: The remelting and casting equipment in the cast house is directly applicable to aluminium recycling operations.
• Laboratory: The smelter’s analytical laboratory can support metallurgical testing for any NZ industrial operation in the Southland region.

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11. ALUMINIUM FABRICATION AFTER SMELTING ENDS

11.1 Casting

Aluminium casting is covered in detail in Doc #93. In summary: aluminium’s low melting point makes it the most accessible casting metal. Small foundry operations using crucible furnaces can produce aluminium castings with minimal infrastructure. The limiting factor is alloy control (Section 8.2), not the casting process itself.

Priority castings from recycled aluminium:

• Replacement engine components (cylinder heads, transmission cases, intake manifolds)
• Pump housings and impellers
• Marine fittings
• Electrical hardware (terminal connectors, bus bar joints)
• Micro-hydro turbine components (Doc #72)

11.2 Extrusion

Aluminium extrusion — forcing heated aluminium through a shaped die to produce profiles (tubes, channels, angles, custom cross-sections) — is a valuable fabrication process that NZ currently possesses. Ullrich Aluminium and Fletcher Aluminium operate extrusion presses in NZ.⁴³

Dependencies for continued extrusion:

• Extrusion press: The hydraulic press itself is a major piece of equipment that cannot be manufactured in NZ. Maintenance of existing presses depends on hydraulic components, seals, and control systems — all imported with finite life.
• Dies: Extrusion dies are precision-machined tool steel items. NZ’s machine shops (Doc #91) can produce simple dies; complex profiles require EDM (electrical discharge machining) or precision milling capability.
• Billet stock: Extrusion feedstock is cast aluminium billets (cylindrical logs). These can be cast from recycled aluminium using the Tiwai Point cast house or regional foundries.
• Heat: Billets must be heated to approximately 450–500°C for extrusion. Gas-fired or electric resistance furnaces of this temperature range are within NZ’s fabrication capability, though accurate temperature control (±10°C) matters for extrusion quality and requires functioning thermocouples and instrumentation.

Assessment: NZ can continue aluminium extrusion for as long as the presses and their hydraulic systems remain functional. The limiting factor is likely hydraulic seals, cylinder bores, and control electronics rather than the press frame itself — typical heavy hydraulic equipment in industrial service has a service life measured in decades with maintenance, but without imported spare parts (seals, hydraulic valves, control components), failure of a critical component could halt a press permanently. A realistic estimate, contingent on the condition of the presses and the availability of hydraulic consumables at the time of the event, is 5–15 years of continued operation under careful use and maintenance.⁴⁴ This is a valuable but time-limited capability. The extrusion presses should be classified as critical national industrial equipment and maintained as a priority, with spare parts inventoried and rationed from the start.

11.3 Sheet and plate

NZ does not currently roll aluminium sheet or plate. Under normal conditions, flat aluminium products are imported. Without imports, NZ’s options for flat aluminium products are limited:

• Hammering and hand-forming from cast plate: Functional for small items but labour-intensive and impractical for sheet metal at scale.
• Trade with Australia: If Australian aluminium rolling mills remain operational, sheet and plate could be imported.
• Casting to near-net shape: For some applications, cast aluminium slabs can substitute for rolled plate, with surface machining where needed.

This is a genuine capability gap. NZ’s aluminium product range after trade cessation will be limited to castings and (for as long as presses last) extrusions. Rolled flat products will not be available unless trade develops.

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CRITICAL UNCERTAINTIES

Uncertainty	Impact if Wrong	Resolution Method
Alumina inventory at Tiwai Point	Determines remaining smelter life. Could be weeks or months.	Direct verification with NZAS management — first week priority
Petroleum coke and coal tar pitch stocks	Determines anode production capability independent of alumina.	Direct verification with NZAS carbon plant management
Finished aluminium inventory at Tiwai Point	Determines size of primary aluminium stockpile for recovery.	Physical inventory — first week
Number and condition of operating pots	Determines production rate during run-down.	NZAS operations verification — first week
Manapouri power supply stability	If Manapouri has issues, smelter loses power regardless.	Coordination with Meridian Energy (Doc #65)
HVDC link reliability	If the HVDC link fails, freed Manapouri power cannot reach the North Island.	Transpower assessment (Doc #67)
NZ aluminium scrap stock	If lower than estimated, recycling supply is tighter and allocation must be stricter.	National census (Doc #8) — aluminium as specific category
Extrusion press remaining service life	Determines how long NZ can produce extruded profiles.	Condition assessment of Ullrich and Fletcher presses
Aluminium conductor stock for grid maintenance	If grid conductor demand exceeds available aluminium, grid maintenance is compromised.	Transpower and EDB inventory (Doc #67)
Alloy contamination in recycled aluminium	If scrap sorting is poor, recycled aluminium is only usable for castings — wrought and conductor grades cannot be produced.	Establish sorting protocols and analytical testing early
Smelter restartability after shutdown	If pots are damaged beyond economical repair, smelting is permanently lost even if alumina trade resumes.	Engineering assessment during shutdown — pot-by-pot condition reporting

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CROSS-REFERENCES

• Doc #1 — National Emergency Stockpile Strategy (aluminium allocation, alumina as strategic material, smelter workforce as critical personnel)
• Doc #8 — National Skills and Asset Census (aluminium scrap inventory, smelter workforce skills, extrusion press inventory)
• Doc #65 — Hydroelectric Station Maintenance (Manapouri operations, power supply to Tiwai Point)
• Doc #67 — Transpower Grid Operations (HVDC link, freed Manapouri capacity distribution, aluminium conductor supply for grid maintenance)
• Doc #69 — Transformer Maintenance and Rewinding (aluminium conductor for transformer windings)
• Doc #89 — NZ Steel Glenbrook (coordination on aluminium supply for ZINCALUME coatings; complementary smelter decision)
• Doc #93 — Foundry Work and Metal Casting (aluminium casting processes, alloy management, regional foundry network)
• Doc #97 — Cement and Concrete (refractory materials for furnace linings)
• Doc #98 — Glass Production (aluminium for furnace components)
• Doc #102 — Charcoal Production (charcoal fuel for crucible furnaces melting aluminium scrap)
• Doc #103 — Salt Production (fluxing salts for aluminium recycling)
• Doc #138 — Sailing Vessel Design (aluminium masts and fittings, lightweight hull construction)
• Doc #141 — Boatbuilding Techniques (aluminium hull fabrication)
• Doc #145 — Workforce Reallocation (smelter workforce transition planning)
• Doc #150 — Treaty of Waitangi and Māori Governance (Ngai Tahu partnership on Tiwai Point decisions)
• Doc #151 — NZ–Australia Relations (alumina as trade priority, Australian aluminium supply)
• Doc #157 — Accelerated Trade Training (foundry and metalworking training for aluminium recycling)

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ECONOMIC JUSTIFICATION SUMMARY

The economic case reduces to a simple comparison:

Continuing to smelt (until alumina exhaustion):

• Produces 6,000–15,000 tonnes of irreplaceable primary aluminium (the exact figure depends on alumina stock)
• Consumes 12–13% of NZ’s electricity for weeks to months
• Occupies ~1,000 skilled workers for the same period
• The aluminium produced represents years to decades of essential supply
• Recommended — the value of the aluminium exceeds the opportunity cost of the electricity and labour over the short run-down period

Transition to recycling:

• Provides indefinite aluminium supply from NZ’s existing stock of ~500,000–1,000,000 tonnes
• Requires only 5% of smelting energy per tonne
• Employs 50–100 workers on an ongoing basis (the other 900+ smelter workers are freed for other recovery priorities)
• Product range is limited to castings and (while presses last) extrusions — no wrought flat products
• This is the long-term strategy regardless — the smelter cannot operate without alumina

The combined strategy — smelt to exhaustion, then recycle — maximises NZ’s total aluminium supply while freeing both energy and workforce for broader recovery at the earliest feasible point. There is no scenario in which both strategies do not apply sequentially. The only decision variable is whether to continue smelting for the remaining alumina supply period or to shut down immediately and redirect the energy. The analysis in Section 3 supports continued smelting at reduced capacity.

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1. NZAS electricity consumption: Approximately 5,000–5,200 GWh per year, making it NZ’s single largest electricity consumer — approximately 12–13% of total NZ generation (~42,000–44,000 GWh). The smelter’s contract with Meridian Energy is for approximately 572 MW of supply from Manapouri. See: Electricity Authority market data. https://www.emi.ea.govt.nz/ — MBIE energy statistics. The exact percentage varies by year with total NZ generation.↩︎

2. Alumina inventory at NZAS: The smelter typically maintains buffer stocks of alumina in storage silos at Tiwai Point. The size of this inventory varies with shipping schedules and is commercially sensitive. Industry practice for smelters dependent on shipped alumina is to maintain 2–8 weeks of supply as buffer stock, though this can be higher or lower. The actual figure at the time of the event is one of the most important numbers for the smelter operating decision and must be verified directly with NZAS management.↩︎

3. New Zealand Aluminium Smelters (NZAS): Joint venture between Pacific Aluminium (Rio Tinto subsidiary, 79.36%) and Sumitomo Chemical (20.64%). Production capacity approximately 330,000–345,000 tonnes per year of primary aluminium. See: Rio Tinto NZAS information. https://www.riotinto.com/ — NZ Ministry of Business, Innovation and Employment (MBIE), NZ Energy Data Tables.↩︎

4. Alumina inventory at NZAS: The smelter typically maintains buffer stocks of alumina in storage silos at Tiwai Point. The size of this inventory varies with shipping schedules and is commercially sensitive. Industry practice for smelters dependent on shipped alumina is to maintain 2–8 weeks of supply as buffer stock, though this can be higher or lower. The actual figure at the time of the event is one of the most important numbers for the smelter operating decision and must be verified directly with NZAS management.↩︎

5. NZAS workforce: Approximately 1,000 people including direct employees and regular contractors, encompassing potroom operators, carbon plant workers, cast house operators, electricians, mechanical fitters, process engineers, metallurgists, laboratory technicians, and administrative staff. Exact current staffing should be verified with NZAS management. See: Rio Tinto employment reports; NZAS community publications.↩︎

6. Aluminium recycling energy: Recycling aluminium from scrap requires approximately 5% of the energy needed for primary smelting from alumina. Primary smelting requires approximately 14–15 MWh per tonne; remelting scrap requires approximately 0.7–1.0 MWh per tonne. This enormous energy saving is because the energy-intensive electrolytic reduction step (breaking the Al-O bond) has already been done. See: International Aluminium Institute, “Aluminium Recycling.” https://www.international-aluminium.org/ — European Aluminium Association publications.↩︎

7. Energy intensity of aluminium smelting: The global average is approximately 14–15 MWh per tonne of aluminium produced, with modern high-amperage smelters at the lower end and older or inefficient facilities at the higher end. NZAS’s specific energy consumption may vary somewhat from this range depending on pot technology, amperage, and operational efficiency. See: International Aluminium Institute statistics; NZAS environmental reporting.↩︎

8. Aluminium recycling energy: Recycling aluminium from scrap requires approximately 5% of the energy needed for primary smelting from alumina. Primary smelting requires approximately 14–15 MWh per tonne; remelting scrap requires approximately 0.7–1.0 MWh per tonne. This enormous energy saving is because the energy-intensive electrolytic reduction step (breaking the Al-O bond) has already been done. See: International Aluminium Institute, “Aluminium Recycling.” https://www.international-aluminium.org/ — European Aluminium Association publications.↩︎

9. NZ household electricity consumption: Average NZ household consumption is approximately 7,000–8,000 kWh per year (~600–670 kWh per month). 100,000 MWh divided by ~600 kWh per household per month ≈ 170,000 household-months, or approximately 15,000–20,000 households for 4 weeks (depending on seasonal variation). See: MBIE, Electricity Authority household consumption data.↩︎

10. NZAS Tiwai Point site: Located on the Tiwai Peninsula, approximately 25 km south of Invercargill. The site includes three potlines (historically — operational configuration may have changed), a carbon plant, cast house, alumina receival and storage, wharf facilities, and supporting infrastructure. See: NZAS site information; Invercargill City Council planning documents.↩︎

11. NZAS history: The smelter was developed by the Consolidated Zinc Corporation (later CRA, then Rio Tinto) and Sumitomo Chemical, with construction beginning in 1968. First aluminium was produced in September 1971. A third potline was added in 1996. See: Rio Tinto corporate history; NZ Ministry for Culture and Heritage. https://nzhistory.govt.nz/↩︎

12. Hall-Heroult process: Independently invented in 1886 by American Charles Martin Hall and Frenchman Paul Heroult. It remains the only commercial process for aluminium smelting over 135 years later. No alternative process has achieved commercial viability despite extensive research. See: any standard metallurgy text; Grjotheim, K. and Kvande, H., “Introduction to Aluminium Electrolysis,” Aluminium-Verlag.↩︎

13. Pot current and voltage: Modern aluminium smelting pots operate at high current (150,000–600,000 amperes for the newest designs) and low voltage (3.5–5.0 volts per pot). NZAS pots operate at approximately 170,000–320,000 amperes depending on the potline. Pots are connected in series within a potline, so total line voltage is the sum of individual pot voltages. See: International Aluminium Institute technical documentation; general aluminium smelting engineering references.↩︎

14. Anode consumption: The theoretical carbon consumption for aluminium reduction is 0.33 kg C per kg Al (stoichiometric). Actual consumption is approximately 0.4–0.5 kg per kg Al due to air oxidation of the anode, CO₂ re-oxidation, and mechanical losses. For NZAS’s annual production, this represents approximately 130,000–170,000 tonnes of anode carbon consumed per year. See: Grjotheim and Kvande (note 10); general aluminium smelting references.↩︎

15. Cathode life: The carbon cathode lining of an electrolytic pot has a service life of typically 5–8 years, after which the pot must be taken offline and relined. Cathode failure modes include sodium penetration (which causes swelling and cracking), erosion, and electrical degradation. Relining requires replacement cathode carbon blocks and seam paste — both imported materials. See: International Aluminium Institute; smelter engineering references.↩︎

16. NZAS pot count: The smelter has three potlines. The total number of pots has varied with configuration changes but is in the range of 600–672 pots. The exact current configuration should be verified with NZAS. See: NZAS operational documentation; Rio Tinto annual reports.↩︎

17. Anode production: NZAS operates an on-site carbon plant that produces prebaked anodes. The process involves mixing calcined petroleum coke aggregate with coal tar pitch binder, forming (pressing or vibration-compacting) the green anodes, and baking them in ring furnaces at approximately 1,100–1,200°C for 2–3 weeks. The baking process converts the pitch binder to solid carbon, bonding the aggregate into a strong, electrically conductive block. See: general aluminium smelting engineering references; NZAS environmental assessments.↩︎

18. Marsden Point refinery: New Zealand Refining Company (now Channel Infrastructure NZ) operated NZ’s only petroleum refinery at Marsden Point near Whangarei. The refinery ceased refining operations in 2022, converting to an import-only fuel terminal. Without refining, NZ cannot produce petroleum coke domestically. See: Channel Infrastructure NZ. https://www.channelnz.com/↩︎

19. Bayer process: Developed by Karl Josef Bayer in 1888, this is the standard industrial process for producing alumina from bauxite. Bauxite is digested in hot (150–250°C) sodium hydroxide solution under pressure, dissolving the aluminium as sodium aluminate while iron, silica, and titanium compounds remain as insoluble “red mud.” The aluminate solution is clarified, aluminium hydroxide is precipitated by cooling and seeding, and the hydroxide is calcined at approximately 1,000°C to produce alumina. See: any standard extractive metallurgy text.↩︎

20. NZAS alumina supply: Primarily from Queensland Alumina Limited (QAL) at Gladstone, Queensland — a joint venture including Rio Tinto. Alumina is shipped in bulk carriers to Bluff and unloaded at Tiwai Point’s dedicated wharf. The Tasman Sea crossing is approximately 2,000 km. See: Rio Tinto supply chain documentation; QAL company information.↩︎

21. NZ bauxite: NZ has no known bauxite deposits. Bauxite forms through intense tropical weathering (lateritisation) of aluminium-bearing rocks — a geological process that requires prolonged tropical or subtropical conditions that NZ’s geology has not experienced in the relevant timeframes. See: GNS Science (Institute of Geological and Nuclear Sciences) mineral resource databases. https://www.gns.cri.nz/↩︎

22. Alternative aluminium production: Carbothermic reduction of alumina (using carbon to reduce alumina directly, without electrolysis) has been researched extensively but has not achieved commercial viability due to the extreme temperatures required (>2,000°C) and the difficulty of separating aluminium from aluminium carbide by-products. Direct electrolytic reduction of clays and other non-bauxite aluminium minerals has also been researched without commercial success. See: Grjotheim and Kvande (note 10); various metallurgical research publications.↩︎

23. Australia’s bauxite and alumina industry: Australia is the world’s largest bauxite producer (approximately 100 million tonnes per year) and a major alumina producer, with refineries at Gladstone (QAL, Yarwun), Kwinana, Pinjarra, Wagerup, and Gove. See: Australian Government Department of Industry; Geoscience Australia mineral resource reports.↩︎

24. Manapouri Power Station: Underground powerhouse on the western arm of Lake Manapouri, Fiordland. Seven generating units with a combined capacity of approximately 800 MW. First units commissioned 1969; second tailrace tunnel (to Deep Cove, Doubtful Sound) completed 2002, significantly increasing capacity. Owned and operated by Meridian Energy. See: Meridian Energy. https://www.meridianenergy.co.nz/ — MBIE generation data.↩︎

25. Meridian-NZAS power contract: The specific terms of the electricity supply contract between Meridian Energy and NZAS have been the subject of extensive commercial negotiation and public discussion. The contracted supply is approximately 572 MW, with pricing arrangements that have been commercially contentious. See: Meridian Energy annual reports; Electricity Authority; NZ media coverage of the Tiwai Point power contract negotiations.↩︎

26. NZAS electricity consumption: Approximately 5,000–5,200 GWh per year, making it NZ’s single largest electricity consumer — approximately 12–13% of total NZ generation (~42,000–44,000 GWh). The smelter’s contract with Meridian Energy is for approximately 572 MW of supply from Manapouri. See: Electricity Authority market data. https://www.emi.ea.govt.nz/ — MBIE energy statistics. The exact percentage varies by year with total NZ generation.↩︎

27. NZAS electricity consumption: Approximately 5,000–5,200 GWh per year, making it NZ’s single largest electricity consumer — approximately 12–13% of total NZ generation (~42,000–44,000 GWh). The smelter’s contract with Meridian Energy is for approximately 572 MW of supply from Manapouri. See: Electricity Authority market data. https://www.emi.ea.govt.nz/ — MBIE energy statistics. The exact percentage varies by year with total NZ generation.↩︎

28. Lake Manapouri operating consents: The “Save Manapouri” campaign of the late 1960s and early 1970s — one of NZ’s first major environmental campaigns — resulted in legal restrictions on Lake Manapouri levels. The Manapouri-Te Anau Development Act 1963 and subsequent resource consents set operating guidelines for lake levels. Under emergency conditions, these consents could be modified by Order in Council under the CDEM Act, but this would be a politically sensitive decision given the history. See: Ministry for the Environment; NZ Heritage.↩︎

29. NZAS production and exports: Over 90% of NZAS’s aluminium production has historically been exported, primarily to Japan, South Korea, and other Asian markets. NZ’s domestic aluminium consumption is relatively small. See: Statistics NZ trade data; NZAS/Rio Tinto production reports.↩︎

30. Ullrich Aluminium: NZ’s largest aluminium extruder and distributor, operating extrusion presses and distribution facilities. Produces a wide range of extruded aluminium profiles for building, industrial, and transport applications. See: Ullrich Aluminium company information. https://www.ullrich.co.nz/ — Note: company status and inventory should be verified through the national census.↩︎

31. Aluminium in NZ buildings: NZ residential construction has used aluminium window and door frames extensively since the 1970s, replacing earlier timber joinery. The quantity of aluminium in NZ’s building stock is not precisely known but is substantial given the widespread adoption. Estimate based on typical aluminium content per dwelling and NZ’s housing stock of approximately 1.9 million dwellings. See: BRANZ (Building Research Association of NZ) building stock data. https://www.branz.co.nz/↩︎

32. NZ vehicle fleet: Approximately 4.4 million registered vehicles as of recent data. Modern vehicles contain increasing amounts of aluminium (engine blocks, transmission cases, wheels, body panels, radiators) — estimated at 100–200 kg per vehicle for the average NZ fleet mix. Total aluminium in the vehicle fleet is therefore very roughly 400,000–800,000 tonnes, though this estimate has wide uncertainty and includes many older vehicles with less aluminium content. See: NZ Transport Agency (Waka Kotahi) vehicle fleet statistics.↩︎

33. Per-capita aluminium-in-use: Studies of aluminium stocks in developed economies typically find 200–500 kg per capita of aluminium in use across all applications (buildings, vehicles, infrastructure, consumer goods). For NZ’s population of approximately 5 million, this suggests 1,000,000–2,500,000 tonnes of total aluminium in the economy. The estimate of 500,000–1,000,000 tonnes in the document text is deliberately conservative, acknowledging that NZ is less industrialised than some comparators and that significant aluminium is in applications (electrical infrastructure, industrial equipment) where it will not become available for recycling for many years. See: International Aluminium Institute, “Global Aluminium Cycle” studies; Cullen, J.M. and Allwood, J.M., various publications on material stock analysis.↩︎

34. Per-capita aluminium-in-use: Studies of aluminium stocks in developed economies typically find 200–500 kg per capita of aluminium in use across all applications (buildings, vehicles, infrastructure, consumer goods). For NZ’s population of approximately 5 million, this suggests 1,000,000–2,500,000 tonnes of total aluminium in the economy. The estimate of 500,000–1,000,000 tonnes in the document text is deliberately conservative, acknowledging that NZ is less industrialised than some comparators and that significant aluminium is in applications (electrical infrastructure, industrial equipment) where it will not become available for recycling for many years. See: International Aluminium Institute, “Global Aluminium Cycle” studies; Cullen, J.M. and Allwood, J.M., various publications on material stock analysis.↩︎

35. Aluminium recycling energy: Recycling aluminium from scrap requires approximately 5% of the energy needed for primary smelting from alumina. Primary smelting requires approximately 14–15 MWh per tonne; remelting scrap requires approximately 0.7–1.0 MWh per tonne. This enormous energy saving is because the energy-intensive electrolytic reduction step (breaking the Al-O bond) has already been done. See: International Aluminium Institute, “Aluminium Recycling.” https://www.international-aluminium.org/ — European Aluminium Association publications.↩︎

36. Aluminium recycling losses: Each remelting cycle loses approximately 1–5% of the aluminium to oxidation (dross formation), with the exact loss depending on scrap quality, furnace type, and operating practice. Well-managed operations with proper fluxing achieve losses at the lower end. Dross contains recoverable aluminium (15–70% metallic content) that can be processed to reduce net losses. See: International Aluminium Institute recycling data; European Aluminium Association, “Aluminium Recycling in Europe.”↩︎

37. Alloy contamination in recycling: This is a well-documented challenge in aluminium recycling. Elements like copper, zinc, iron, and silicon, once dissolved in aluminium, cannot be removed by remelting. Mixed-alloy scrap produces a “generic” alloy that meets no specific wrought alloy specification but is generally suitable for casting alloys (which have wide composition tolerance). See: Gros, A.C., “Aluminium Recycling and Processing for Energy Conservation and Sustainability,” ASM International; various publications on aluminium recycling metallurgy.↩︎

38. Fluxing and degassing: Sodium chloride-potassium chloride flux mixtures (typically 50:50 by weight) are the standard cover and cleaning flux for aluminium melting. The flux forms a molten salt layer on the aluminium surface that absorbs oxides and contaminants. Degassing with nitrogen or argon reduces dissolved hydrogen to prevent porosity. Sodium chloride is available from NZ salt production (Doc #103). Potassium chloride is not produced in NZ as a primary product — NZ has no known economically exploitable potassium mineral deposits. Under recovery conditions, potassium chloride would need to come from stocks of muriate of potash (agricultural fertiliser), which is held in significant quantities by NZ agricultural distributors (Ballance Agri-Nutrients, Ravensdown) and is widely used in NZ farming. These stocks should be inventoried as a potential aluminium flux feedstock. Alternatively, sodium chloride alone can serve as flux for many aluminium recycling applications, with some reduction in flux effectiveness. See: standard aluminium casting references; ASM International casting handbooks; GNS Science NZ mineral resource databases for NZ potassium resource status.↩︎

39. Aluminium casting temperature: Common aluminium-silicon casting alloys (A356, A380, etc.) are poured at approximately 680–750°C. Pure aluminium melts at 660°C; casting alloys have lower melting ranges (typically 570–630°C for eutectic Al-Si alloys). The pouring temperature is above the liquidus to ensure complete filling of the mould. See: ASM Metals Handbook Volume 15: Casting; American Foundry Society aluminium casting guidelines.↩︎

40. Dross recovery: Aluminium dross (skim, slag) contains significant recoverable aluminium — typically 15–70% metallic content depending on how the melt was managed and how quickly the dross was removed. Dedicated dross processing (cooling under inert conditions, mechanical processing, or remelting in a rotary furnace) is standard practice in the aluminium recycling industry. See: International Aluminium Institute; Peterson, R.D., “Aluminium Recycling and Processing for Energy Conservation and Sustainability,” ASM International.↩︎

41. Aluminium and copper thermal conductivity: Pure aluminium thermal conductivity approximately 205 W/m·K; pure copper approximately 385 W/m·K. In practice, heat exchanger alloys differ from these pure-metal values (commercial aluminium alloys typically 150–200 W/m·K depending on composition). However, for most practical heat exchanger designs, thermal conductivity of the wall material is not the primary bottleneck — convective resistance on both fluid sides dominates. Aluminium heat exchangers compensate for lower conductivity with thinner walls and extended surface area (fins). The corrosion behaviour of aluminium in specific service environments (e.g., marine, high-chloride, or acidic process fluids) must be assessed case by case — not all alloys are suitable for all environments. See: Incropera, F.P. and DeWitt, D.P., “Fundamentals of Heat and Mass Transfer,” any edition; ASM Metals Handbook Volume 2 (properties).↩︎

42. Spent pot lining (SPL): Classified as hazardous waste in most jurisdictions including NZ. SPL contains leachable cyanide compounds (formed by reaction of carbon with sodium from the bath), fluoride compounds, and metallic sodium. Direct landfill disposal without treatment risks groundwater contamination. Treatment options include high-temperature incineration (which destroys cyanides and recovers fluoride values) or wet chemical processing. NZAS has historically exported SPL for processing in Australia. Under recovery conditions, on-site secure storage is the practical option. See: International Aluminium Institute, SPL management guidelines; NZ Environmental Protection Authority hazardous waste classifications.↩︎

43. NZ aluminium extrusion: Ullrich Aluminium (NZ-owned) and Fletcher Aluminium operate extrusion presses in NZ. Extrusion presses produce profiles by forcing heated aluminium billets through shaped dies using hydraulic pressure (typically 1,000–5,000+ tonnes of ram force). These are major pieces of equipment that NZ cannot manufacture — their continued operation depends on hydraulic system maintenance and die availability. See: Ullrich Aluminium; Fletcher Building aluminium operations.↩︎

44. Extrusion press service life estimate: Industrial hydraulic extrusion presses are robust equipment with service lives commonly exceeding 30–50 years in normal industrial use with manufacturer-supported maintenance. The binding constraint under recovery conditions is not structural wear but access to consumable hydraulic components (seals, packings, hydraulic valves, instrumentation) and dies (tool steel, heat-treated). The 5–15 year estimate assumes: (a) spare parts inventoried and rationed from event onset; (b) no catastrophic hydraulic failure; (c) controlled production rates to reduce wear. If key hydraulic components are not inventoried, a single seal failure could halt the press within months. If spare parts are well stocked, the high end of the range (or beyond) is plausible. This estimate requires verification against the actual condition and spare parts inventory of Ullrich and Fletcher presses through the national census (Doc #8).↩︎