Extractive Metallurgy of Copper Part 8 doc

The chapter indicates that the principal problems with the process are that: a about 25% of the Cu entering a direct-to-copper smelting furnace ends up dissolved in its slag b the cost o

CHAPTER 12

Direct-To-Copper Flash Smelting

Previous chapters show that coppermaking from sulfide concentrates entails two major steps: smelting and converting They also show that smelting and converting are part of the same chemical process, Le.:

oxidation of Fe and S from a Cu-Fe-S phase

It has long been the goal of metallurgical and chemical engineers to combine these two steps into one continuous direct-to-copper smelting process

The principal advantages of this combining would be:

(a) isolation of SOz emission to a single, continuous gas stream

(b) minimization of energy consumption

(c) minimization of capital and operating costs

This chapter (i) describes direct-to-copper smelting in 2002 and (ii) examines the degree to which its potential advantages have been realized The chapter indicates that the principal problems with the process are that:

(a) about 25% of the Cu entering a direct-to-copper smelting furnace ends up dissolved in its slag

(b) the cost of recovcring this Cu will probably restrict future expansion of direct-to-copper smelting to low-Fe concentrates (e.g chalcocite (Cu2S) and bornite (Cu5FeS4) concentrates) rather than high-Fe chalcopyrite concentrates

12.1 The Ideal Direct-to-Copper Process

Fig 12.1 is a sketch of the ideal direct-to-copper process The principal inputs to the process are:

187

188 Extractive Metallurgy of Copper

concentrate, oxygen, air, flux and recycles

The principal outputs are:

molten copper, low-Cu slag, high-SO2 offgas

The process is autothennal With highly oxygen-enriched blast, there is enough

excess reaction heat to melt all the Cu-bearing recycle materials from the smelter and adjacent refinery, including scrap anodes The process is continuous The remainder of this chapter indicates how close we have come to this ideality

Concentrates Flux and reverts Scrap copper Oxygen and air

SO2 - rich offgas

Liquid copper

low enough in

Cu for direct discard

Fig 12.1 Ideal single-furnace coppermaking process Ideally the copper is low in

impurities, the slag is discardable without Cu-recovery treatment and the offgas is strong enough in SO1 for sulfuric acid manufacture

12.2 Industrial Single Furnace Direct-to-Copper Smelting

In 2002, single furnace direct-to-copper smelting is done by only one process - Outokumpu flash smelting, Fig 1.4 It is done in two locations; Glogow, Poland (Czernecki et al., 1998, 1999a,b,c) and Olympic Dam Australia (Hunt et al.,

1999a,b) Both furnaces treat chalcocite-bornite concentrates

For several years the Noranda submerged-tuyere process (Fig 1.5) also produced copper directly (Mills et al., 1976) It now produces high-grade matte,

72-75% Cu The change was made to increase smelting rate and improve impurity elimination

The products of direct-to-copper flash smelting (Table 12.1) are:

Direct-To-Copper Flash Smelting 189

(a) the degree of oxygen enrichment of the blast, i.e the amount of N2

'coolant' entering the furnace

(b) the rate at which fossil fuel is burnt in the furnace

The O2 content of industrial direct-to-copper flash furnace blast is 50 to 90 volume% 02, depending on the furnace's solid feed mixture Considerable fossil fuel is burnt in the reaction shaft and in settler burners, Table 12.1

12.3 Chemistry

Direct-to-copper smelting takes place by the schematic (unbalanced) reaction:

Cu2S,CugFeS4 + O2 + S i 0 2 + Cu; + Fe0,Fe3O4,SiO2 + SO2

enriched blast

(12.1)

Just enough O2 is supplied to produce metallic copper rather than Cu2S or Cu20

In practice, the flash furnace reaction shaft product is a mixture of overoxidized (oxide) and underoxidized (sulfide) materials Individual particles may be overoxidized on the outside and underoxidized on the inside The overoxidized and underoxidized portions react like:

2 C ~ 2 0 + C U ~ S -+ ~ C U ; + SO, (1 2.2)

2Fe304 + Cu2S + 2Cui + 6 F e 0 + SO2

to produce molten copper, molten slag and SO2

Industrially, the overall extent of Reaction 12.1 is controlled by:

(12.3)

(a) monitoring the Cu content of the product slag and the S content of the product copper

(b) adjusting the:

190 Extractive Metallurgy ofCopper

0, -in - blast i n w t rate concentrate input rate ratio based on these measured Cu-in-slag and S-in-copper values

An increasing % Cu-in-slag is reversed by decreasing the Oz/concentrate ratio and vice versa The % Cu-in-slag is kept between 14 and 24%

12.4 Industrial Details

Operating details of the two direct-to-copper flash furnaces are given in Table 12.1 The furnaces are similar to conventional flash furnaces Differences are: (a) the hearths are deeply 'bowl' shaped to prevent molten copper from contacting the furnace sidewalls

(b) the hearths are more radically arched and compressed to prevent their refractory from being floated by the dense (7.8 tonnes/m3) molten copper layer (Hunt, 1999)

(c) the furnace walls are extensively water cooled and the hearth extensively air cooled to prevent metallic copper from seeping too far into the refractories

(d) the refractories are monolithic to prevent molten copper from seeping under the bricks, solidifying and lifting them

Also, the copper tapholes are designed to prevent the out-flowing molten copper from enlarging the taphole to the point where molten copper contacts cooling water

Olympic Dam's molten copper passes through magnesite-chrome brick (inside),

a silicon carbide insert and a graphite insert (outside) (Hunt et a l , 1999b) The graphite insert is replaced after -1200 tonnes of tapped copper and the silicon carbide insert is replaced after -2400 tonnes Excessive copper flow (i.e an excessive taphole diameter) initiates earlier replacement

Direct-To-Copper Flash Smelting 191

Table 12.1 Details of Olympic Dam and Glogow direct-to-copper Outokumpu flash

furnaces Note the high product temperatures as compared to matte smelting, Table 5.1

Dam, Australia Glogow Poland

slag layer thickness, m

copper layer thickness, m

active slag tapholes

active copper tapholes

concentrate burners

settler burners

Feed details, tonnedday

new concentrate (dry)

Cu-from-slag recovery method

offgas, thousand Nm'/hour

volume% SO2, leaving furnace

temperature, "C

dust production, tonnedday

burnt in reaction shaft

Hydrocarbon fuel inputs, kg/hour

6.3 x 19.2 x 1.9 4.8 5.8 3.7 7.5 0-0.65 0.5-0.85

2

8

1

2 1200-1600: 41-56% CU 90-450 12-120 (95% S i 0 2 ) 0-144

ambient SO-90

22 390-680 99% Cu, 0.7 to 0.85% S, 0.4% 0

1280

24 0.5

1320 electric furnace

25

19 1320-1400 boiler 65, ESP 55 oil, 0-200 620-883

1978 9.2 x 26.4 x 3.0 7.4 8.3 6.7 12.3 0.5 0.7

6

10

4 normally none

2000 (28% Cu) self- fluxing

270 IO0 desulfurizing dust

140

75

32

392 0.007% Fe, 0.25% Pb

35

15 I320

260 0.04% S, 0.45?'00,

oil, 300

192 Extractive Metallurgy of Copper

flux input rate concentrate input rate

The temperatures of the products are controlled by adjusting the oxygen- enrichment level of the blast (as represented by the N2/02 ratio) and the rate at which fossil fuel is burnt in the furnace

12.5.1 Target: No Matte Layer to Avoid Foaming

The Glogow and Olympic Dam furnaces are operated with 02/concentrate ratios which are high enough to avoid forming a Cu2S layer This is done to avoid the possibility of foaming slag out the top of the furnace (Smieszek et al., 1985;

Asteljoki and Muller, 1987; Day, 1989; Hunt et al., 1999a)

A molten Cu2S layer, once built up between the molten copper and molten slag layers, has the potential to react with slag by reactions like:

all of which can produce SO2 beneath the slag layer

Foaming is particularly favored if the input 02/concentrate ratio is subsequently increased to shrink or remove an existing Cu2S layer This results in a highly oxidized slag, fill of Fe304, CuO and Cu20, which has great potential for producing SO2 beneath the slag layer

The foaming problem is avoided by ensuring that the 02/concentrate ratio is always at or above its set point, never below This may lead to high copper oxide-in-slag levels but it avoids the potentially serious operational problems caused by foaming (Hunt et al., 1999a) S-in-copper below -1% S guarantee that a Cu2S layer does not form (Fig 9.2a)*

*Glogow copper contains 0.04% S, Le much less than is necessary to prevent matte layer formation This extra oxidation is done to oxidize Pb (from concentrate) to PbO, keeping Pb-in-copper below 0.3%

Direct-To-Copper Flash Smelting I93

12.5.2 High %Cu-in-slag from no-matte-layer strategy

An unfortunate side effect of the above no-matte-layer strategy is high %Cu-in- slag, mainly as dissolved Cu20 It arises because there is no permanent layer of CuzS in the furnace to reduce Cu20 to metallic copper, Reaction ( 1 2.2)

Simply stated, direct-to-copper smelting is operated in a slightly over-oxidizing mode to prevent the foaming described in Section 12.5.1 The downside of operating this way is 14 to 24% Cu in slag, Table 12.1

12.6 Cu-in-Slag: Comparison with

Conventional Matte Smelting/Converting

A significant difference between direct-to-copper flash smelting and flash smelting/Peirce-Smith converting is the large amount of Cu in direct-to-copper slag This extra Cu-in-slag arises because:

(a) % Cu in direct-to-copper slags (14-24%, Table 12.1) is much greater than

% Cu in conventional smelting slags (1-2% Cu) and converting slags (b) the amounts of slag produced by direct-to-copper smelting and

(-6% CU)

conventional smelting/converting are about the same

Also, direct-to-copper slags contain most of their Cu in oxidized form (Le copper oxide dissolved in the molten slag) - so they must be reduced with carbon to recover their Cu

12.6.1 Electric furnace Cu recovery

Both direct-to-copper smelters reduce their flash furnace slag in an electric slag cleaning furnace The slag flows from the flash furnace directly into an electric furnace where it is settled for about 10 hours under a 0.25 m blanket of metallurgical coke (Czernecki et al., 1999b) This coke reduces the oxidized Cu

from the slag by reactions like:

194 Extractive Metallurgy ofcopper

15-25% Pb (from Pb in the concentrate)

This product is too impure to be sent directly to anode-making It is oxidized in

a Hoboken converter (Section 9.6.1) to remove its Fe and Pb, then sent to anode- making

Olympic Dam results

Olympic Dam lowers its direct-to-copper slag from 24% to -4% in its 15 000 kVA electric furnace (Hunt et al., 1999a) It could lower it more by using more

coke and a longer residence time, but the copper product would contain excessive radioactive '"Pb and '"Po, from the original concentrate

Instead, the Cu-in-slag is lowered further by solidificationicommunitiodflotation

in its mine flotation circuit, Section 11.5

12.7 Cu-in-Slag Limitation of Direct-to-Copper Smelting

The principal advantage of direct-to-copper smelting is isolation of SO2

evolution to one furnace The principal disadvantage of the process is its large amount of Cu-in-slag

Balancing these factors, it appears that direct-to-copper smelting is best suited to Cu2S, Cu5FeS4 concentrates These concentrates produce little slag so that Cu recovery from slag is not too costly

Direct-to-copper smelting will probably not, however, be suitable for most chalcopyrite concentrates, -30% Cu These concentrates produce about 2 tonnes

of slag per tonne of Cu so that the energy and cost of recovering Cu from their slag is considerable Only about 60% of new Cu in concentrate would report directly to copper, 40% being recovered from slag

Flash Smelting 195

Davenport et ai (2001) confirm this view but Hanniala et al (1999) suggest that

direct-to-copper smelting may be economic even for chalcopyrite concentrates

12.8 Direct-to-Copper Impurities

The compositions of the anode copper produced by the direct-to-copper smelters are given in Table 12.2 The impurity levels of the copper are within the normal range of electrorefining anodes, Chapter 15 The impurity levels could be reduced further by avoiding recycle of the flash hrnace dust

Impurities do not seem therefore, to be a problem in the two existing direct-to- copper smelters However, metallic copper is always present in the direct-to- copper furnace, ready to absorb impurities For this reason, concentrates destined for direct-to-copper smelting should always be carefully tested in a pilot furnace before being accepted by the smelter

Table 12.2 Anode compositions from direct to copper smelters

Olympic Dam Glogow I1

The main advantage of the process is its restriction of SOz evolution to a single continuous source of high S02-strength gas In principal, the energy, operating and capital costs of producing metallic copper are also minimized by the single- furnace process

196 Extractive Metallurgy of Copper

Metallic copper is obtained in a flash furnace by setting the ratio:

0, -in -blast input rate concentrate input rate

at the point where all the Fe and S in the input concentrate are oxidized The ratio must be controlled precisely, otherwise Cu2S or Cu20 will also be produced Avoidance of forming a molten Cu2S layer in the furnace is

particularly important Reactions between Cu2S layers and oxidizing slag have caused rapid SOz evolution and slag foaming

Direct-to-copper flash smelting has proven effective for SO2 capture However, 15-35% of the Cu-in-concentrate is oxidized, ending up as copper oxide dissolved in slag This copper oxide must be reduced back to metallic copper, usually with coke

The expense of this Cu-from-slag recovery treatment will probably restrict future direct-to-copper smelting to concentrates which produce little slag Chalcopyrite concentrates will probably continue to be treated by multi-furnace processes - either by conventional smeltingkonverting or by continuous multi-furnace processing, Chapter 13

Suggested Reading

Czemecki, J., Smieszek, Z., Miczkowski, Z., Dobrzanski, J and Warmuz, M (1999) Copper metallurgy at the KGHM Polska Miedz S.A - present state and perspectives In

Copper 99-Cobre 99 Proceedings of the Fourth International Conference, Vol V

Smelting Operations and Advances, ed George, D.B., Chen, W.J., Mackey P.J and Weddick, A.J., TMS, Warrendale, PA, 189 203

Davenport, W.G., Jones, D.M., King, M.J and Partelpoeg, E.H (2001) Flash Smelting, Analysis, Control and Optimization, TMS, Warrendale, PA (especially Chapters 19-2 1)

Hunt, A.G., Day, S.K., Shaw, R.G and West, R.C (1999) Developments in direct-to- copper smelting at Olympic Dam In Copper 99-Cobre 99 Proceedings o f t h e Fourth

International Conference, Vol V Smelting Operations and Advances, ed George, D.B., Chen, W.J., Mackey, P.J and Weddick, A.J., TMS, Warrendale, PA, 239 253

References

Asteljoki, J.A and Muller, H.B (1987) Direct smelting of blister copper - flash smelting tests of Olympic Dam concentrate In Pyrometallurgy 87, The Institution of Mining and Metallurgy, London, England, 265 283

Direct-To-Copper Flush Smelting 197

Czernecki, J., Smieszek, Z., Gizicki, S., Dobrzanski, J and Warmuz, M (1998) Problems with elimination of the main impurities in the KGHM Polska Miedz S.A copper concentrates from the copper production cycle (shaft furnace process, direct blister smelting in a flash furnace) In Sulfide Smelting ’98, ed Asteljoki, J.A and Stephens,

R.L., TMS, Warrendale, PA, 3 15-343

(a) Czernecki, J., Smieszek, Z., Miczkowski, Z., Bas, W., Wamuz, M and Szwancyber,

G (1999) Changes in the construction of the KGHM flash smelting furnace of Glogow I1 introduced in the years 1996-1998 In Proceedings of gh International Flush Smelting Congress, Australia, June 6-12, 1999

(b) Czerneclu, J., Smieszek, Z., Miczkowski, Z., Dobrzanski, J., Bas, W., Szwancyber,

G , Warmuz, M and Barbacki, J (1999) The process flash sla cleaning in electric

furnace at the Glogow I1 copper smelter In Proceedings of 9’ International Flash Smelting Congress, Australia, June 6- 12, 1999

(c) Czernecki, J., Smieszek, Z., Miczkowski, Z., Dobrzanski, J and Wamuz, M (1999) Copper metallurgy at the KGHM Polska Miedz S.A - present state and perspectives In

Copper 99-Cobre 99 Proceedings of the Fourth International Conference, Vol V Smelting Operations and Advances, ed George, D.B., Chen, W.J., Mackey P.J and

Weddick, A.J., TMS, Warrendale, PA, 189 203

Davenport, W.G., Jones, D.M., King, M.J and Partelpoeg, E.H (2001) Flash Smelting, Analysis, Control and Optimization, TMS, Warrendale, PA (Chapter 19)

Day, B.E (1989) Commissioning of the Olympic Dam smelter Paper presented at the Non-Ferrous Smelting Symposium of the Australasian Institute of Mining and Metallurgy (Parkville, Victoria), held at Port Pirie, South Australia, September 1989, 57 60

Hanniala, P., Helle, L and Kojo, I.V (1999) Competitiveness of the Outokumpu flash smelting technology now and in the Third Millennium In Copper 99-Cobre 99 Proceedings of the Fourth International Conference, Vol V Smelting Operations and Advances, ed George, D.B., Chen, W.J., Mackey P.J and Weddick, A.J., TMS,

Warrendale, PA, 221 238

(a) Hunt, A.G., Day, S.K., Shaw, R.G., Montgomerie, D and West, R.C (1999) Start up and operation of the #2 direct-to-copper flash furnace at Olympic Dam In Proceedings of 9Ih International Flush Smelting Congress, Australia, June 6-12, 1999

(b) Hunt, A.G., Day, S.K., Shaw, R.G and West, R.C (1999) Developments in direct-to- copper smelting at Olympic Dam In Copper 99-Cobre 99 Proceedings of the Fourth International Conference, Vol V Smelting Operations and Advances, ed George, D.B.,

Chen, W.J., Mackey, P.J and Weddick, A.J., TMS, Warrendale, PA, 239 253

Mills, L.A., Hallett, G.D and Newman, C.J (1976) Design and operation of the Noranda

Process continuous smelter In Extractive Metallurgy of Copper, Vol I Pyrometallurgy and Electrolytic Refining, ed Yannopoulos, J.C and Aganval, J.C., TMS, Warrendale,

CHAPTER 13

Mitsubishi Continuous Smelting/Converting

Chapter 12 indicates that single furnace coppermaking:

(a) successfully restricts SO2 emission to a single continuous source

(b) inadvertently sends -25% of its input Cu to slag as copper oxide

The potential benefits are:

(a) ability to smelt all concentrates, including CuFeS2 concentrates

(b) elimination of Peirce-Smith converting with its SO2 collection and air

infiltration difficulties

(c) continuous production of high S02-strength offgas, albeit from two sources

(d) relatively simple Cu-from-slag recovery

(e) minimal materials handling

The most advanced industrial manifestation of continuous smeltinglconverting is the Mitsubishi process with four systems operating in 2002 (Goto and Hayashi,

1998; Ajima et af., 1999) Other manifestations are Outokumpu flash smeltingkonverting and Noranda submerged tuyere smeltingkonverting, Chapter 10

199

Air, oxygen, dry concentrates, flux,

so2

offgas

Recycle to smelting andlor

Fig 13.1 Mitsubishi process flowsheet and vertical layout at Gresik, Indonesia (Ajima et al., 1999) Note the continuous gravity flow of

liquids between furnaces The smelting furnace is about 15 m higher than the Hazelett caster The smelting and converting furnaces each have 9

or I O rotating lances, Figs 10.1 and 13.2

hlifsuhishi Continuous Snzeliing/Converting 1

13.1 The Mitsubishi Process (Fig 13.1, Tables 13.1 And 13.2)

The Mitsubishi process employs three furnaces connected by continuous gravity flows of molten material They are:

smelting furnace electric slag cleaning furnace converting furnace

The smelting furnace blows oxygen-enriched air, dried concentrates, Si02 flux

and recycles into the furnace liquids via vertical lances, Fig 13.1 It oxidizes the

Fe and S of the concentrate to produce -68% Cu matte and Fe-silicate slag Its matte and slag flow together into the electric slag cleaning furnace

The electric slag-cleaning furnace separates the smelting furnace's matte and

slag Its matte flows continuously to the converting furnace Its slag (0.7-0.9% Cu) flows continuously to water granulation and sale or stockpile

The converting furnace blows oxygen-enriched air, CaCO, flux and granulated

converter slag 'coolant' into the matte via vertical lances It oxidizes the matte's

Fe and S to make molten copper The copper continuously exits the furnace into one of two holding furnaces for subsequent fire- and electrorefining The slag

(14% Cu) flows continuously into a water granulation system The resulting slag granules are recycled to the smelting furnace for Cu recovey and the converting furnace for temperature control

A major advantage of the process is its effectiveness in capturing SO2 It produces two continuous strong SOz streams, which are combined to make excellent feed gas for sulfuric acid or liquid SO2 manufacture Also, the absence

of crane-and-ladle transport of molten material minimizes workplace emissions These environmental advantages plus recent improvements in productivity make the Mitsubishi process well worth examining for new copper smelting projects

13.2 Smelting Furnace Details

Fig 13.2 shows details of the Mitsubishi smelting furnace Solid particulate feed

and oxidizing gas are introduced through 9 vertical lances in two rows across the top of the furnace Each lance consists of two concentric pipes inserted through the furnace roof The diameter of the inside pipe is 5 cm - the diameter of the outside pipe, 10 cm Dried feed is air-blown from bins through the central pipe; oxygen-enriched air (55 volume% 0 2 ) is blown through the annulus between the pipes The outside pipes are continuously rotated (7-8 rpm) to prevent them from sticking to their water-cooled roof collars