Reducing energy intensity in modern copper smelting plants

Brisbane, Australia

For immediate release

The economics of copper smelting have always been tied to energy. As concentrate grades decline, regulatory pressure on emissions intensifies and energy costs stay volatile, the conversation has shifted from managing energy as a line item to redesigning the furnace system entirely. The smelters winning on cost today are not just running leaner. They are built differently from the ground up with that outcome in mind.

Why Furnace Design Is the Starting Point for Copper Plants

Energy intensity in a copper smelting plant is not primarily a function of how well you operate a furnace. It is a function of which furnace you chose. The foundational design decision, the geometry of the vessel, the mechanism of gas and feed injection, and the degree of oxygen enrichment, set the ceiling on what operational optimisation can be achieved.

Conventional reverberatory and blast-furnace smelting operations depend on the combustion of fossil fuels to generate heat for smelting. This method of processing is inherently inefficient. A large proportion of the heat generated is carried away with the off-gas, and the relatively low SO2 concentrations in that gas complicate any attempt at acid plant integration. Sulphur capture rates are lower, emissions compliance is harder to maintain, and the energy cost per tonne of copper produced remains structurally high. Reverberatory furnace smelting played a pivotal role in the historical development of the copper industry, especially in processing sulphide copper ores and forming copper matte. However, its energy inefficiency and difficulty in capturing sulphur dioxide led to its gradual replacement by more efficient methods. The introduction of the reverberatory furnace to Chile around 1830 revolutionised copper concentrate processing in the region and significantly increased production capacity.

ISASMELT™ top submerged lance (TSL) bath smelting furnace works differently. The lance injects a controlled stream of oxygen-enriched air directly into the molten slag bath, where the chemical reactions actually occur. The high turbulence of the bath accelerates heat and mass transfer, concentrates reaction energy at the point of gas entry, and dramatically reduces the volume of off-gas generated per tonne of material processed. Less off-gas means less energy lost to the exhaust stream, and a higher SO2 concentration that is amenable to acid plant treatment and sulphur capture.

This is change not incremental optimisation. It is a different operating principle altogether. Smelting is essential because it bridges the gap between raw mining product and final, usable cathode-grade copper - vital for renewable energy transition, providing materials for solar panels, electric vehicles, and national defence systems.

Oxygen Enrichment and Specific Copper Concentrate Smelting Rates

The core energy lever in a  ISASMELT™ copper smelting furnace is oxygen enrichment of the lance air. Increasing the oxygen proportion in the lance stream allows operators to sustain smelting reactions with less total gas volume, reduce the energy required to heat the inert nitrogen from air, and increase the specific smelting rate: the tonnes of concentrate treated per unit of molten bath volume per unit of time.

In primary copper smelting, the ISASMELT™ furnace typically operates with oxygen concentrations in the lance air ranging from 60 to 90% O2. This enrichment value is typically selected during design so that the process can approach autogenous operation, where the sulphur and iron in the concentrate provide sufficient energy for smelting with minimal external fuel input.

At Kazzinc's copper ISASMELT™ furnace in Ust-Kamenogorsk, operation was often autogenous in practice. The waste heat boiler received around 30% less gas than its design volume because so little supplementary fuel was required. That is a direct energy saving built into the process chemistry, not achieved through operator effort.

This specific smelting rate advantage translates directly into capital and operating savings. A single ISASMELT™ furnace has demonstrated production capacities exceeding 330,000 tonnes per year of copper, with instantaneous concentrate feed rates reaching over 200 tonnes per hour. The Southern Peru Copper Corporation (SPCC) plant in Ilo processed 1,200,000 tonnes of copper concentrate per year through a single furnace. SPCC selected the ISASMELT™ technology based on proven capacity at that scale and lower capital and operating costs compared with all other competing technologies. By June 2009, the plant was operating at up to 183 t/h with an average oxygen enrichment of 66.7% in the lance air.

A compact furnace processing high volumes offered at high oxygen enrichment requires less building footprint, fewer ancillary systems, and lower capital spend per tonne of annual capacity. These are structural cost advantages, not soft marketing or sales claims.

ISASMELT™ Operating Parameters Across Smelting Applications

The table below draws on operational data from the numerous ISASMELT™ installations to show how process air oxygen enrichment, lance flow, and furnace size scale across different smelting applications. The contrast between secondary lead smelting and primary copper smelting illustrates how the design flexes to meet specific thermal and chemical demands.

Source: ISASMELT™ 2020 Compendium of Technical Papers, Glencore Technology

What stands out is that even the largest primary copper furnaces, treating up to 1,400,000 tpa of feed, do so within a vessel of 4.5 metres internal diameter. The throughput-to-footprint ratio is exceptional and has direct implications for both capital efficiency and the feasibility of retrofitting into existing smelter infrastructure.

The design of smelting furnaces must account for the mineral composition and copper content of the concentrates being processed, as these factors influence extraction efficiency, slag formation, and overall copper recovery. Smelting helps reduce enormous amounts of mined rock from ore bodies into a concentrated, dense, high-value product, which is a key factor in the economics of copper production.

Waste Heat Recovery

Every smelting furnace generates hot off-gas. The difference between a highly-efficient operation and a wasteful one often comes down to how that heat is captured and used.

ISASMELT™ furnaces are integrated with waste heat boilers (WHB) that cool the off-gas stream and simultaneously generate steam for plant use or energy generation. That steam offsets purchased energy for heating, process requirements, and facility services. At Kazzinc, the WHB was sized and designed with careful attention to the gas flow profile and proved robust in practice, with dust accretions from the lead-bearing concentrate not adversely affecting heat transfer as had initially been a concern during project planning.

The performance outcomes at the Aurubis-owned Kayser Recycling System (KRS) plant in Lünen, Germany put numbers to what this technology substitution can deliver. A single ISASMELT™ furnace replaced three blast furnaces and one Peirce-Smith converter. The reported results were:

• Energy consumption reduced by more than 50%
• CO2 emissions reduced by more than 64%
• Overall emissions across the operation reduced by 90%
• Production capacity exceeded the original design by 40%

These outcomes came from a technology substitution, not an incremental operational improvement programme.

The off-gas from a high-oxygen-enrichment ISASMELT™ furnace has a higher SO2 concentration than that produced by legacy technologies. SO2-rich gas is the necessary feed for sulphuric acid plant production, making sulphur capture both an environmental compliance outcome and a revenue stream. Smelters that previously released low-grade SO2 to the atmosphere, or could not route the gas through contact acid plants because concentrations were too low, can close that loop with ISASMELT™ technology.

Furnace Flexibility and Feed Handling

One of the underappreciated energy-efficient advantages of the ISASMELT™ design is its tolerance of variable feed quality. In conventional smelting, feed preparation - particularly grinding and drying - is capital and energy-intensive. Any deviation from design feed properties can result in significant downtime or reduced throughput.

The ISASMELT™ bath smelting process is inherently tolerant of feed variations and can process a wide range of feed rates, compositions, impurity levels, moisture levels, and sizes/shapes. As such, the feed preparation requirements are minimal: an agglomeration drum, bins, conveyors, and feeders are sufficient for most concentrate types. The feed drops into the lance-agitated bath, where automated process control parameters keep the furnace products within a tight range regardless of changes in the feed properties.

At Kazzinc, the copper ISASMELT™ furnace handled concentrates that were significantly different from the original design specification, including proportional increases of lead and antimony exceeding 50% and a proportional decrease in silica content of more than 50%. The operational response was limited to adjusting silica flux addition rates and minor tuning of the furnace operation. The furnace continued to operate within acceptable parameters throughout.

Feed flexibility reduces the energy and cost burden of feed preparation and minimises operational disruption that leads to suboptimal smelting conditions and elevated energy use per tonne.

The ISASMELT™ design also supports rapid start-up and shutdown. Unlike reverberatory furnaces, which require extended heat-up and cool-down periods, the compact refractory-lined vessel reaches operating temperature more quickly and can be restarted without lengthy bath reheating campaigns. This advantage reduces the energy expended during non-productive furnace time, a real and measurable cost for operations that experience planned or unplanned interruptions.

Impurity Removal and Flowsheet Simplification

Impurity elements in copper concentrates, including arsenic, lead, bismuth, antimony, and zinc, must be removed to produce acceptable copper quality and to protect downstream refinery equipment. In conventional smelting flowsheets, impurity management often requires additional process steps, dedicated slag treatment, or recycling of impurity-laden streams back through the main furnace at extra energy cost.

The ISASMELT™ process leverages strong bath agitation and high operating temperatures to volatilise impurity elements to the gas phase at rates conventional smelting cannot match. Elements such as arsenic, lead, and zinc preferentially report to the off-gas stream, where they are captured in the gas-cleaning circuit. These high-volatilisation rates reduce the need for additional downstream impurity-removal steps and simplify the overall process flowsheet.

At the Yunnan Copper Corporation (YCC) ISASMELT™ plant in China, commercial-scale data confirmed the furnace's capacity to efficiently eliminate volatile impurity elements, consistent with Mount Isa Mines operating experience. At Kazzinc, the ISASMELT™ furnace’s ability to tolerate and eliminate volatile impurity elements, including lead, arsenic, zinc, bismuth, and antimony, was identified as a specific process benefit and selection criterion for handling polymetallic concentrates.

A simpler flowsheet is a more energy-efficient flowsheet. Fewer process stages mean fewer in-furnace hours, lower reagent consumption, and less auxiliary equipment to power.

The Retrofit Case: Upgrading Existing Smelters for Electrolytic Refining and Energy Reduction

Not every electrolytic refining and energy reduction project starts with a greenfield build. For many operations, the opportunity is in replacing or augmenting existing furnaces within a working smelter footprint.

The ISASMELT™ vertical furnace has a small footprint relative to its throughput. The cylindrical, refractory-lined vessel is compact, stationary and largely enclosed, which means it can be retrofitted into existing smelter sites to augment or replace existing technology. These factors reduce the civil and infrastructure capital required to upgrade the smelter and allow operations to bring on new capacity without full plant shutdowns.

The Mopani copper smelter upgrade at Mufulira on the Zambian Copperbelt, the Vedanta smelter in India, and Yunnan Copper Corporation's plants in Chuxiong and Chambishi are examples of ISASMELT™ installations representing technology upgrades rather than greenfield builds. Each brought improved energy performance, better emissions control, and higher throughput per unit of installed capital.

The Umicore plant in Hoboken, Belgium, processes up to 300,000 tonnes per year of complex secondary materials, including copper and lead-bearing residues containing precious metals, in a single ISASMELT™ furnace commissioned in 1997. Operating in the demanding secondary smelting conditions, with the furnace cycling between smelting and converting modes at different oxygen partial pressures, the refractory achieved campaign lives of 15 months between full brick replacements. That is sustained commercial performance over decades, not a pilot result.

Emissions Control as Part of the Energy System

Modern emissions standards for SO2, particulates and fugitive gases are not separate from the energy design of a smelting plant. They are part of it.

A copper smelting plant generating high-volume, low-SO2 off-gas faces both higher energy costs to treat that gas and a more difficult compliance challenge. Scrubbing or treating low-grade SO2 streams requires significant reagent and energy inputs, and often still fails to achieve the sulphur capture rates regulators now require.

The ISASMELT™ furnace is stationary and fully enclosed. The geometry of the ISASMELT™ vessel eliminates fugitive emissions that characterise open, rotating, or tipping furnace designs. The concentrated SO2 in the off-gas stream is well suited to contact acid plant processing, achieving high sulphur capture rates without the treatment penalties associated with dilute gas. Meeting modern emissions standards is built into the process architecture, rather than addressed by add-on scrubbing systems that carry their own capital cost and ongoing energy demand.

At Kazzinc's Ust-Kamenogorsk operation, the introduction of the ISASMELT™ copper furnace contributed to a major reduction in air pollution from the metallurgical complex. The new plant met Kazakhstani environmental regulations, with the minor emissions from the new facility contrasting sharply with the performance of the equipment it replaced.

Making the Upgrade Decision

Copper processing is a multi-stage process involving physical, chemical, and electrochemical methods to extract copper from its ores, with methods varying by country depending on ore source and local regulations. For engineers and plant managers evaluating furnace upgrade or replacement options, the energy intensity question cannot be answered by looking at fuel consumption in isolation. The full picture includes:

• Off-gas volume and SO2 concentration, and what that means for acid plant integration and sulphur capture.
• Waste heat recovery potential and the value of steam generation.
• Feed preparation requirements and the energy embedded in those steps.
• The energy cost of impurity management in downstream processes.
• Capital efficiency: what throughput is achievable per unit of installed furnace volume
• Emissions compliance infrastructure: what treatment systems are needed and what they cost to operate.

The ISASMELT™ technology package, developed by Glencore Technology and now installed in copper smelters across six continents with a combined annual treatment capacity exceeding six million tonnes of feed, addresses each of those dimensions as an integrated system. The ISASMELT™ technology has been proven at scales from 70,000 tpa to over 1,200,000 tpa through a single furnace, across primary and secondary feed types, and in operating environments from remote Australia to Kazakhstan, Zambia, Peru, China, and Belgium. 

Reducing energy intensity in a copper smelting plant starts with the furnace technology. Everything downstream is optimised.

Talk to Glencore Technology

If you are evaluating a furnace upgrade, planning a new copper smelting plant, or looking to reduce the energy and emissions intensity of an existing operation, the ISASMELT™ team has the process data, engineering capability and operational track record to support your project from feasibility through to commissioning and beyond.

Get in touch at glencoretechnology@glencore.com.au or visit our contact page to learn more about the ISASMELT™ technology package and what it has delivered for copper smelters globally.