ISASMELT™ Technology for Sulfide Smelting

Abstract

Since the development of the top-submerged lance (TSL ) technology for copper and lead smelting by the cooperation of Mount Isa Mines (MIM), now owned by Glencore, and the Commonwealth Scientific Industrial Research Organisation (CSIRO) the core of the ISASMELT™ technology has always resided in the lance system. Through continuous innovation and operation of our own smelters, first at MIM, subsequently at Mopani, and also at both the Kazzinc Copper and Kazzinc Lead smelters, Glencore Technology have expanded the core equipment supply to enhance the plant operability. The success of Glencore Technology’s expertise can be directly measured by the success of the Kansanshi Copper Smelter plant, which achieved 100% nameplate capacity within three months of start-up. This paper describes the ISASMELT™ core equipment and how it is applied to smelt sulfide materials. It highlights the strength of the ISASMELT™: continuous innovation to facilitate the versatility and continued increased capacity with every plant implementation.

Introduction

During the 1970s Mount Isa Mines Limited (MIM), now owned by Glencore, was searching for new technologies that could be applied to its lead and copper smelter operations . At the time the Commonwealth Scientific Industrial Research Organisation (CSIRO) in Australia was developing the Top Submerged Lance (TSL ) technology, a new concept for smelting using the Sirosmelt lance. The two organisations joined forces to apply these developments to the smelters in Mount Isa to reduce operating costs whilst improving the environmental performance.

The concepts of the Lead ISASMELT™ and Copper ISASMELT™ processes were jointly developed and then pilot tested on a 250 kg/h test rig in Mount Isa in the early 1980s [1]. Since then ISASMELT™ has progressed from the pilot plant scale to industrial facilities that have in excess of 200 t/h of dry concentrate feed and treat a variety of materials including nickel [2], lead [3] and copper [4, 5] concentrates and secondary materials. Since the first plant was built at Mount Isa, twenty-one ISASMELT™ plants have either been constructed or are under construction. Figure 1 shows the location of the commercial plants that have been licensed to date.

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Location of ISASMELT™ plants licensed to date

The important milestones in the market consolidation of the technology were when MIM became part of Xstrata plc in 2003 and part of Glencore plc in 2013. At that time MIM Process Technologies, the division that was responsible for the commercialization of the technology, became first Xstrata and then Glencore Technology. Glencore Technology’s mission is to market the core technologies developed in Glencore’s operating sites: IsaMill™ and Jameson Cell technologies in mineral processing , ISAKIDD™ for the electrorefining and electrowinning of copper , the Albion Process ™ in atmospheric leaching , and the ISASMELT™ and ISACONVERT™ technologies for the smelting and converting of non-ferrous materials.

The ISASMELT™ Principles

ISASMELT™ Concept

ISASMELT™ technology is based on vertical submerged lance injection technology to provide highly efficient mixing and reaction of feed materials in the molten slag bath. The lance contains a device to maximize heat-transfer and cooling of the lance wall by the passing process/blast air. This cools the lance and allows the formation of a protective layer of frozen slag to form on the outer wall of the lance, thus protecting it from the rigours of the environment inside the furnace . The process concept of the ISASMELT™ furnace is summarized in Fig. 2.

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The ISASMELT™ furnace concept

The result of the injection of the air directly into the slag is an intense smelting process in a highly turbulent bath, allowing the construction of plants with relatively low capital costs and smaller footprints than other base-metal sulfide smelting approaches. These plants are highly energy efficient, using the chemical energy contained in the sulfide concentrates as the major source of energy for the smelting process, and lower cost than alternative approaches. In typical base metal sulfide smelting applications, the technology also avoids the necessity for drying of raw materials by permitting filtered concentrate and residues to be mixed with fluxes and dropped directly into the furnace rather than requiring homogeneous, bone dry feed with a narrow specification for injection through complicated burners, lances, tuyeres or injectors.

The use of a single, centrally positioned lance also means that the process air/oxygen gases are injected remote from the refractory lining. In a typical ISASMELT™ furnace , with an internal diameter of 4–5 m, the lance tip is more than one metre from the refractory walls. As a result, the refractory lining is protected from the abrasive and corrosive action caused by adjacent gas motion that is common with tuyere-based processes. The typical ISASMELT™ lance is 250–500 mm in diameter and may inject up to 50,000 Nm³/h of oxygen enriched air. The lance can be easily removed from and reinserted into the furnace using its purpose-built proprietary hoisting system.

Unlike in tuyere-based processes the ISASMELT™ lance does not block easily. Even if the supply pressure to the lance is lost through a malfunction of plant equipment or the inadvertent closure of supply valves, the lance can be removed from the bath and cleaned easily within a matter of minutes. This is compared with a barrel tuyere injection type furnace , which is a bottom blown vessel, in which loss of pressure to the tuyeres will result in run back of molten metal into the tuyere interior necessitating an extended stoppage of the process. Replacement of the tuyere will be required in most cases, which is a difficult and time consuming exercise.

ISASMELT™ Reaction Mechanisms

The ISASMELT™ process is a slag reaction process, where fresh feed is digested into the molten slag phase. The slag phase itself is both continuously produced and continually provided with fresh oxidant or reductant , depending on the process reactions taking place, by the feed materials and the inlet air/oxygen/reductant being added down the lance. Unlike other processes, which either over and under oxidise the feed through a burner or pass the oxygen through a matte layer, necessitating thermal control , slag phase reaction allows for near thermal and chemical equilibrium to be achieved. The reaction mechanisms for the copper ISASMELT™ reactions are shown in Fig. 3.

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The ISASMELT™ reaction mechanisms for copper sulfides

ISASMELT™ Industrially Proven Development

Mount Isa Mines Copper Plant

Mount Isa Mines was founded in 1924 to mine the lead -zinc-silver orebody that had been discovered the preceding year by John Campbell Miles. Mining the lead -zinc-silver orebody was the mainstay of the operations for the next 20 years and continues to be integral to metal production from the site. Copper production commenced in Mount Isa in 1943 to provide copper for the war effort and was ceased in 1946. Both lead and copper production began in parallel in 1953 after construction of a copper smelter on the Mount Isa lease.

The first copper smelter made use of three multi-hearth roasters to feed a single reverberatory furnace . In 1962, a second larger reverberatory furnace was commissioned and the first reverberatory furnace was shut down. The first reverberatory furnace was recommissioned in 1973 to provide additional smelting capacity when a Fluo-Solids Roaster (FSR) was installed to replace the multi-hearth roasters. Operation of the FSR with two reverberatory furnaces continued until 1987 when a demonstration copper ISASMELT™ furnace was added. The demonstration copper ISASMELT™ furnace operated for five years to gain the knowhow needed to design a commercial scale ISASMELT™ furnace .

Before the demonstration plant was shut-down, high rate trials were performed to reduce the scaling factor from the demonstration ISASMELT™ furnace to the commercial ISASMELT™ furnace down to a factor of just two (2). The commercial scale copper ISASMELT™ furnace has now been in operation in Mount Isa for 26 years. The plant has been through two major upgrades during this time to increase the instantaneous feed rate of copper bearing material from 104 to 184 t/h. This was achieved without change to the ISASMELT™ vessel or lance system. The flowsheet for the Mount Isa plant, refer to Fig. 4, has now become one of the generic flowsheets for the ISASMELT™ technology implementation that has been applied to smelters across the world.

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Generic ISASMELT™ flowsheet as used at Mount Isa, Ilo and Tuticorin

Mopani Copper Mines Plant

Mopani Copper Mines Plc (MCM) decided, at the end of 2003, to replace its primary electric smelting furnace and to upgrade its smelting facility in Mufulira with the installation of an ISASMELT™ furnace and a matte settling electric furnace (MSEF). The new facility was designed with a view to toll treat concentrate in addition to those produced from MCM mines [6]. The ISASMELT™ furnace was designed, constructed and commissioned within 30 months, and production has been steadily increasing in the years since.

At the time of initiating the Mufulira smelter upgrade project, MCM’s production forecasts anticipated relatively consistent production of approximately 400,000 tpa concentrate from MCM’s mines (Nkana and Mufulira) and concentrators [6], with these providing much of the feed to the ISASMELT™ furnace . Typically, Nkana produced 55–60% of Mopani’s mined production, with Mufulira producing the remainder [7]; both of which produced bornite rich concentrates.

During the past few years toll-treated based concentrates have gradually become more prevalent due to increased smelter throughput. The effect of treating more third party concentrate has been a decline in the average copper grade of the smelter feed. Whereas Mufulira concentrate contains a significant amount of bornite and chalcocite , the toll-treated concentrates overwhelmingly contain only chalcopyrite . Although this would have been detrimental to smelter production using the original primary smelting flowsheet , which involved a rotary drier and an electric furnace , MCM have been able to smelt productively using the current flowsheet including the ISASMELT™ furnace and MSEF [8]. In fact, it has been an excellent fit; Mufulira smelter now produces, per unit of copper production, much more sulphuric acid than would otherwise have been the case. The acid can be used for leaching operations or sold to other operations in the region.

Kazzinc Copper Plant

Kazzinc Ltd is a major, fully integrated, zinc producer established in 1997 through the merger of Eastern Kazakhstan ‘s three main non-ferrous metals companies. In addition to zinc, the concentrates from Kazzinc’s mines contain significant amounts of lead , copper and precious metals . Since 1943, Ust-Kamenogorsk has been home to a multi-smelter metallurgical complex specialising in the production of zinc, lead , silver , gold , antimony , bismuth and various other by-products. The Ust-Kamenogorsk Metallurgical Complex (UKMC) is one of Kazzinc’s assets, and in 2005 when Kazzinc wished to add a copper smelter and refinery to UKMC it approached Glencore Technology to provide the ISASMELT™ and ISAPROCESS™ technologies for the new copper plant [9].

The concept of the new copper plant was that it should have a nominal production capacity of 70,000 tpa of cathode copper , be able to treat polymetallic copper concentrates and a range of by-products from zinc and lead refining , be tolerant of minor element fluctuations, and be readily expandable in the future. For the primary copper smelting furnace , an ISASMELT™ was a logical choice to meet these objectives. The copper smelter at UKMC has a conventional flowsheet . Concentrate smelting is performed in the copper ISASMELT™ furnace , matte is converted in one of two Peirce-Smith converters, and fire refining occurs in two anode furnaces, prior to anode casting . The sulphuric acid plant is able to accept gas from the ISASMELT™ furnace and one blowing P-S Converter.

One of the main advantages identified by Kazzinc in employing the ISASMELT™ process was its ability to treat a wide range of copper concentrate compositions. In fact, the composition of the feed available at the start of smelter operation (refer to Table 1) deviated significantly from the design basis for certain elements. The differences included a proportional increase of lead and antimony in the actual concentrate by more than 50%, and a proportional decrease of silica in the actual concentrate by more than 50%, compared with the design concentrate.

Table 1

Comparison of actual Kazzinc copper smelter feed at start-up with design

	Cu	Pb	Zn	Fe	S	SiO2	Sb	As
Design (wt%)	25.0	2.68	3.14	24.85	31.74	5.11	0.16	0.55
Actual (wt%)	25.68	4.35	3.53	26.65	32.92	2.39	0.25	0.49
Relative deviation (%)	+3	+59	+12	+7	+4	−53	+56	−10

The lower level of silica in the copper concentrate required the simple action of greater addition of silica -based fluxes. The increased level of antimony in the concentrate made the task of producing MOOK grade cathode more challenging. The increase in the level of lead in the concentrate, which was reasonably high to begin with, required modification to the flowsheet and the development of management strategies after the commissioning process was complete. The main strategy for coping with the higher loads of lead was to install a bleed by milling and flotation of the slag from the end of each P-S converter copper blow. This approach avoided the build-up of recirculating lead that occurred when the slag was charged to the electric settling furnace for electro-thermal reduction . In combination, these measures have been sufficient to prevent problems, such as inadvertent generation of lead bullion by chemical reduction of the slag in the electric settling furnace , and the smelter has settled into its role of treating lead -laden copper concentrate without great difficulty.

The ISASMELT™ Technology Package

The success behind the implementation of ISASMELT™ projects within the copper smelting industry is the concept of delivering a technology package where all the components need to work in cohesion—the furnace , the lance system, the refractories, feed preparation, product tapping systems, control system, off-gas cooling /cleaning systems, impurity management through dust treatment, together with training and procedures for operations and maintenance personnel. The ISASMELT™ technology package is an integrated assortment of technological research and development, specialist process and mechanical design, proprietary equipment, know-how, training programs, commissioning assistance and on-going technical support and collaboration that combine to ensure successful smelter projects for all of Glencore Technology’s ISASMELT™ licensees.

The technology transfer includes a unique arrangement for training operators for new licence holders—they learn by operating the full-scale production smelter at Mount Isa. Clients from the USA, Belgium, Germany, China, Peru, India, Zambia and Kazakhstan have been trained at the MIM smelter over the years. During the training period, client operators and maintenance personnel are given the opportunity to operate and maintain the Mount Isa plant. This “real life” training is a great advantage for the trainees when it comes to operating their own plants. By applying accumulated operating and maintenance know-how along with the full technology package, new users can very quickly achieve high production levels and long furnace campaigns, avoiding the pitfalls that often plague new smelter projects and reduce their profitability.

Kansanshi Mining PLC—Copper Smelting Plant

A recent addition to the list of successful operating plants has been the Kansanshi Mining PLC Copper ISASMELT™ plant located in the town of Solwezi, Zambia. The Kansanshi Copper Smelter was designed for a nominal treatment rate of 1.2 million tonnes of copper concentrates per annum. Kansanshi’s trainees completed in-plant training in Mount Isa, prior to Kansanshi’s own smelter commissioning. This allowed the operators to learn the control philosophy of a real ISASMELT™ plant. Hot commissioning was commenced during the first quarter of 2015 and the plant was able to achieve 100% nameplate capacity within three months of start-up [10]. However when considering the plant performance from a monthly production basis, Fig. 5, it appears that the plant was not able to achieve the design treatment until more than one year after commissioning. However, from when the plant achieved nameplate capacity it was constrained for the last four months of 2015 by a lack of concentrate supply. The Smelter’s faster than budgeted ramp up, coupled with power restrictions at First Quantum Minerals Limited’s Sentinel mine, resulted in the shortage of concentrate [11, 12]. By the first quarter of 2016 sufficient concentrate was available however the plant was shut-down for 11 days in February to complete modifications in the Acid Plant. Following this period the plant was able to meet or achieve the plant design concentrate treatment rate of 1.2 Mt/a equivalent.

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The copper ISASMELT™ concentrate treatment rates at Kansanshi copper smelter

Even whilst completing the plant’s first full rebrick, in the third quarter of 2017, Kansanshi was still able to smelt above the design rate for the 2017 calendar year. Monthly concentrate smelting rate in 2017 matched or exceeded the design maximum plant production rates. The flexibility of the ISASMELT™ process has been a key part of the success that Kansanshi have been able to achieve.

Conclusions

The application of the Copper ISASMELT™ technology to process primary and secondary materials has steadily grown over the past 20 years, transforming the non-ferrous smelting industry. The basis for the success of the technology is a combination of the elegance of the process concept with the diverse plant experience gained over more than 25 years of operation of ISASMELT™ plants at Mount Isa, and a technology package that allows Glencore Technology to provide its clients with process and engineering designs, equipment supply and strong technical assistance through all the stages of the project from initial conceptual studies at feasibility level through to construction and the hot commissioning of the plant, and into the initial years of plant operation until the process is optimised for the specific feed materials being treated. The Kansanshi smelter project constitutes an example of how the success of Glencore Technology’s expertise and ISASMELT™ technology can be directly measured, with the plant achieving 100% nameplate capacity within three months of start-up and being able to consistently operate above design capacity.

Acknowledgements

The authors would like to thank Glencore Technology for permission to publish this work and the ISASMELT™ licensees, who are part of the continuous evolution and development of the technology.

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