Extractive Metallurgy of Copper Part 6 pot

The first Ausmelt furnace specifically dedicated to matte converting recently came on-line in the Houma copper smelter in China Mounsey et al., 1999.. CHAPTER 9 Batch Converting of Cu M

A usnwlt/lsasndt Matte Smelting 127

(c) Sterlite smelter, Tuticorin, India (1995)

(d) Union Miniere secondary copper smelter, Chapter 22, Hoboken, Belgium ( I 997)

(e) Yunnan Copper smelter under construction at Kunming, China (startup

200 1 )

8.7 Other Coppermaking Uses of Ausmelt/Isasmelt Technology

AusmeltiIsasmelt smelting is the outgrowth of technology originally designed for use in tin smelting (Robilliard, 1994) Ausmelt in particular have been active since then in developing uses for their furnace beyond sulfide matte smelting (Hughes, 2000)

One of these is matte converting, which has been demonstrated on a small scale The Ausmelt furnace for converting is similar to that used for smelting

(Mounsey et al., 1999) In fact, in small smelters, smelting and converting can

be performed in the same furnace (Mounsey et al., 1998)

The matteislag mixture produced by smelting is allowed to settle, the slag is tapped, and the lance is reinserted into the matte for converting A two-step process is used It begins by converting the matte to molten Cu,S (white metal) followed by tapping slag It is finished by oxidizing the Cu,S to copper and SO, As in the case of smelting, magnetite in the slag appears to act as a catalyst for the converting reactions

The process is autothermal, although some coal is added to reduce the copper oxide content of the slag to about 15% Cu The first Ausmelt furnace specifically dedicated to matte converting recently came on-line in the Houma copper smelter in China (Mounsey et al., 1999)

Unfortunately, discontinuous two-step smelting/converting sends an intermittent stream of SO, to acidmaking For this reason, it is unlikely to become prominent

Ausmelt technology is also u s e h l for recovering copper from non-sulfide materials, particularly slags and sludges (Hughes, 2000) Its ability to control air and fucl inputs means that conditions can be changed from oxidizing to reducing without transferring material to a second furnace This is particularly effective for smelting Cu/Ni hydrometallurgical residues

8.8 Summary

Ausrnelt and Isasmelt smelting is done in vertically aligned cylindrical furnaces

128 Extractive Metallurgy of Copper

-3.5 m diameter and 12 m high The smelting entails:

(a) dropping moist concentrate, flux and recycle materials into a molten matteklag bath in a hot furnace

(b) blowing oxygen-enriched air through a vertical lance into the matte/slag bath

Most of the energy for smelting is obtained from oxidizing the concentrate's Fe and S

The vertical lance consists of two pipes - the inner for supplying supplementary hydrocarbon fuel, the annulus for supplying oxygen-enriched air The outer pipe penetrates -0.3 m into the bath The inner pipe ends -1 m above the bath The oxygen-enriched blast is swirled down the lower part of the lance by helical swirl vanes This causes rapid heat extraction from the lance into the cool blast and solidification of a protective slag coating on the lance's outer surface This

is a unique feature of the process

The principal product of the furnace is a matteislag mixture It is tapped into a hydrocarbon fired or electric settling furnace The products after settling are 60% Cu matte and 0.7% Cu slag

The main advantages of the process are:

(a) its small 'footprint', which makes it easy to retrofit into existing smelters (b) its small evolution of dust

The 1990's and early 2000's saw Ausmelt and Isasmelt smelting adopted around the world It should soon account for 5% of world copper smelting

The future may see dry concentrate injection through the lance

improve the thermal efficiency of the process

Mounsey, E.N., Li, H., and Floyd, J.W (1999) The design of the Ausmelt technology

smelter at Zhong Tiao Shan's Houma smelter, People's Republic of China, 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, 357 370

Ausmelt/lsasmelt Matte Smelting I29

Player, R.L., Fountain, C.R., Nguyen, T.V., and Jorgensen, F.R (1992) Top-entry

submerged injection and the Isasmelt technology In SavardILee International Symposium

on Bath Smelting, ed Brimacombe, J.K., Mackey, P.J., Kor, G.J.W., Bickert, C., and

Ranade, M.G., TMS, Warrendale, PA, 215 229

References

Ausmelt Commercial Operations (2002) http://www.ausmelt.com.au/comops.html

Binegar, A.H (1995) Cyprus Isasmelt start-up and operating experience In Copper95- Cobre 95 Proceedings o f t h e Third International Conference, Vol IV Pyrometallurgy of

Copper, ed Chen, W.J Diaz, C., Luraschi, A., and Mackey, P.J., The Metallurgical Society of CIM, Montreal, 117 132

Hughes, S (2000) Applying Ausmelt technology to recover Cu, Ni, and Co from slags,

JOM, 52 (8), 30 33

Isasmelt Installations (2002) http://www.mimpt.com.au/isasmelt-installations.html

Isasmelt Technology (2002) http://www.mimpt.com.au/isasmeIt-technology.htm1

Mounsey, E.N., Floyd J.M., and Baldock, B.R (1998) Copper converting at Bindura

Nickel Corporation using Ausmelt technology In Sulfide Smelting ’98, ed Asteljoki,

J.A., and Stephens, R.L., TMS, Warrendale, PA, 287 301

Mounsey, E.N., Li, H., and Floyd, J.W (1999) The design of the Ausmelt technology smelter at Zhong Tiao Shan’s Houma smelter, People’s Republic of China 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, 357 370

Mounsey, E.N., and Robilliard, K.R (1 994) Sulfide smelting using Ausmelt technology

JOM, 46 (8), 58 60

Player, R.L (1996) Copper Isasmelt - Process investigations In Howard Worner International Symposium on Injection in Pyrometallurgy ed Nilmani, M and Lehner, T., TMS, Warrendale, PA, 439 446

Pritchard, J.P and Hollis R (1994) The Isasmelt copper-smelting process Int Miner Met Technol 1, 125 128

Robilliard, K (1994) The development of Sirosmelt, Ausmelt and Isasmelt Int Miner Met Technol., 1, 129 134

Solnordal, C.B and Gray, N.B (1996) Heat transfer and pressure drop considerations in

the design of Sirosmelt lances Met and Mater Trans E , 27B (4), 221 230

CHAPTER 9

Batch Converting of Cu Matte

Converting is oxidation of molten Cu-Fe-S matte to form molten 'blister' copper (99% Cu) It entails oxidizing Fe and S from the matte with oxygen-enriched air

or air 'blast' It is mostly done in the Peirce-Smith converter, which blows the blast into molten matte through submerged tuyeres, Figs 1.6 and 9.1 Several other processes are also used or are under development, Section 9.6 and Chapter

10

The main raw material for converting is molten Cu-Fe-S matte from smelting Other raw materials include silica flux, air and industrial oxygen Several Cu- bearing materials are recycled to the converter - mainly solidified Cu-bearing reverts and copper scrap

The products of converting are:

(a) molten blister copper which is sent to fire- and electrorefining

(b) molten iron-silicate slag which is sent to Cu recovery, then discard

( c ) SOz-bearing offgas which is sent to cooling, dust removal and &So4

manufacture

The heat for converting is supplied entirely by Fe and S oxidation, Le the process is autothermal

9.1 Chemistry

The overall converting process may be described by the schematic reaction:

Cu-Fe-S + 0, + Si02 + Cu; +

Batch Converting ofCu h4atte 133

Fig 9.lb Details of Peirce-Smith converter tuyere (from Vogt et a/., 1979) The tuyeres are nearly horizontal during blowing ‘Blast’ pressure is typically 1.2 atmospheres (gage)

at the tuyere entrance Reprinted by permission of TMS

Converting takes place in two stages:

(a) the Slag-forming stage when Fe and S are oxidized to FeO, Fe304 and SO2

by reactions like:

FeS + $ 0 2 -+ FeO + SO, (9.2)

The melting points of FeO and Fe304 are 1385°C and 1597°C so silica

flux is added to form a liquid slag with FeO and Fe304 The slag-forming

134 Extractive Metallzrrgy of Copper

stage is finished when the Fe in the matte has been lowered to about 1% The principal product of the slag-forming stage is impure molten C U ~ S ,

‘white metal’, -1200°C

(b) the comermaking stage when the sulfur in Cu2S is oxidized to SO2

Copper is not appreciably oxidized until it is almost devoid of S Thus, the blister copper product of converting is low in both S and 0 (0.001- 0.03% S, 0.1-0.8% 0) Nevertheless, if this copper were cast, the S and 0 would form SO2 bubbles or blisters which give blister copper its name Industrially, matte is charged to the converter in several steps with each step followed by oxidation of FeS from the charge Slag is poured from the converter after each oxidation step and a new matte addition is made In this way, the amount of Cu in the converter gradually increases until there is sufficient (100-

250 tonnes Cu as molten Cu2S) for a final coppermaking ‘blow’ At this point, the Fe in the matte is oxidized to about I%, a final slag is removed, and the resulting Cu2S ‘white metal’ is oxidized to molten blister copper The converting process is terminated the instant copper oxide begins to appear in samples of the molten copper

The copper is poured from the converter into ladles and craned molten to a fire- refining furnace for S and 0 removal and casting of anodes A start-to-finish converting cycle is 6 to 12 hours, Table 9.2

9 I I Coppermaking reactions

Blowing air and oxygen into molten ‘white metal’ creates a turbulent Cu2S- copper mixture The products of oxidation in this mixture are SOz, molten copper and copper oxide The molten copper is dense and fluid It quickly sinks below the tuyeres

The most probable coppermaking reactions are:

3

c u 2 s + ?02 + c u 2 0 + so2 (9.4)

C U ~ S + 2 C ~ 2 0 + ~ C U ; + SO2 (9.5) though some copper may be made directly by:

c u 2 s + 0 2 + 2cu; + so2 (9.6)

In principle, there are three sequential steps in coppermaking as indicated on the Cu-S phase diagram, Fig 9.2a

Batch Converting of Cu Matte I35

d, 1200OC) (Sharma and Chang, 1980)

'enriched air

Fig 9.2b Sketch of Peirce-Smith converter and its two immiscible liquids during the

coppermaking stage of converting (after Peretti, 1948) In practice, the liquid 'b' region is

a Cu2S-Cu-Cu20-gas foademulsion from which metallic copper 'c' descends and SO2

and N2 ascend The immiscibility of copper and Cu2S is due to their different structures - copper is metallic while Cu2S is a semiconductor

136 Extractive Metallurgy of Copper

(a) The first blowing of air and oxygen into the Cu2S removes S as SO2 to give S-deficient ‘white metal’, but no metallic copper The reaction for this step is:

It takes place until the S is lowered to 19.6% (point b, 1200°C, Fig 9.2a)

(b) Subsequent blowing of air and oxygen causes a second liquid phase, metallic copper (1% S, point c), to appear It appears because the average composition of the liquids is now in the liquid-liquid immiscibility region The molten copper phase is dense and sinks to the bottom of the converter, Fig 9.2b Further blowing oxidizes additional S from the CuzS and the amount of molten copper increases at the expense of the ‘white metal’ according to overall Reaction (9.6) As long as the combined average composition of the system is in the immiscibility range, the converter contains both ‘white metal’ (19.6% S) and molten copper (1% S) Only the proportions change

(c) Eventually the ‘white metal’ becomes so S deficient that the sulfide phase disappears and only molten copper (1% S) remains Further blowing removes most of the remaining S (point d) Great care is taken during this period to ensure that the copper is not overoxidized to Cu20 This care is necessary because CuzS is no longer available to reduce CuzO back to Cu

by Reaction (9.5)

Step (a) is very brief, Le very little S oxidation is required Step (c) is also brief Its beginning is marked by a change in the converter flame color from clear to green when metallic copper begins to be oxidized in front of the tuyeres This tells the converter operator that the copper blow is nearly finished

9 I.2 Elimination of impurities during converting

The principal elements removed from matte during converting are Fe and S However, many other impurities are partially removed as vapor or in slag Table 9.1 shows some distributions The outstanding feature of the data is that impurity retention in the product blister copper increases significantly with increasing matte grade (%Cu in matte) This is because high-Cu mattes have less ‘blast’ blown through them and they form less slag

The table also shows that significant amounts of impurities report to the offgas They are eventually collected during gas cleaning They contain sufficient Cu to

be recycled to the smelting furnace However, such recycle returns all impurities

to the circuit

Batch Converting of Cu Matte 137

Table 9.1 Distribution of impurity elements during Peirce-Smith converting of low and high grade mattes (Vogt et al., 1979, Mendoza and Luraschi, 1993) Ag, Au and the Pt metals report mainly to blister copper Tenmaya et al., 1993 report that extra blowing of air at the end of the coppermaking stage lowers As, Pb and Sb in the converter’s product copper

blister converter converter

blister converter converter

9.2 Industrial Peirce-Smith Converting Operations (Tables 9.2,9.3)

Industrial Peirce-Smith converters are typically 4 m diameter by 11 m long, Table 9.2 They consist of a 5 cm steel shell lined with -0.5 m of magnesite- chrome refractory brick Converters of these dimensions treat 300-700 tonnes of matte per day to produce 200-600 tonnes of copper per day A smelter has two

to five converters depending on its ovcrall smclting capacity

Oxygen-enriched air or air is blown into a converter at -600 Nm3/minute and 1.2 atmospheres gage It is blown through a single line of 5 cm diameter tuyeres, 40

to 60 per converter It enters the matte 0.5 to 1 m below its surface, nearly

horizontal (Lehner et al., 1993)

The flowrate per tuyere is about 12 Nm3/minute at a velocity of 80 to 120 meters per second Blowing rates above about 17 Nm’/minute/tuyere cause slopping of matte and slag from the converter (Johnson et al., 1979) High blowing rates without slopping are favored by deep tuyere submergence in the matte (Richards, 1986)

About half of the world’s Peirce-Smith converters enrich their air blast with industrial oxygen, up to -29 volume% 02-in-blast, Table 9.2

138 Extractive Metallurgy of Copper

Table 9.2 Production details of industrial

Affinerie Smelting and Refining

Smelter Hamburg, Germany Onahama, Japan

Converter type Peirce-Smith Peirce-Smith

usual blast rate per converter

slag blow, Nm’lminute

copper blow, Nm3/minute

slag blow

copper blow

usual volume% 0 2 in blast

SO2 in offgas, volume%

usual converter cycle time, hours

slag blow, hours

copper blow, hours

15t ladle skulls 90t concentrate

50t Cu scrap etc

+ 10t secondaries + 2St reverts 75t Cu scrap

9

2 4.5

120

I50

5 0.63

13

5

3 Campaign details

copper produced between tuyere line

time between complete converter re-

refractory consumption, kg/tonne of Cu 1.93

Batch Converting ofCu Matte 139

Peirce-Smith and Hoboken converters

25

25

12

180 (62% Cu) Outokumpu flash furnace 5.8 tonnes of reverts

60 tonnes anodes, cathodes, molds, reverts, etc

180

56

3 0.5 1 8.6 1.75 3.91

125 tuyere & body

54 000 2.5

48

46 6.35 only copper blow

600 none

21 15

200 (74.3% CU) Teniente & slag cleaning furnaces none

5

30 tuyere line (I80 tuyere line &body)

1 I200 2.0

195

63 6.5

P

0

k'

3

Table 9.3 Representative analyses of converter raw materials and products, mass% The data are from recent industrial surveys and Johnson et

Butch Converting of Cu Matte 141

9.2 I Tuyeres and offgas collection

Peirce-Smith tuyeres are carbon steel or stainless steel pipes embedded in the converter refractory (Figs 1.6 and 9.lb) They are joined to a distribution

‘bustle’ pipe which is affixed the length of the converter and connected through

a rotatable seal to a blast supply flue The blast air is pressurized by electric or steam driven blowers Industrial oxygen is added to the supply flue just before it connects to the converter

Steady flow of blast requires periodic clearing (‘punching’) of the tuyeres to remove matte accretions which build up at their tips - especially during the slag

blow (Fig 9.3, Bustos et al., 1984, 1988) Punching is done by ramming a steel bar completely through the tuyere It is usually done with a Gasp6 mobile carriage puncher (Fig 1.6) which runs on rails behind the converter The puncher is sometimes automatically positioned and operated (Dutton and Simms,

1988; Fukushima et al., 1988)

Peirce-Smith converter offgas is collected by a steel hood (usually water cooled)

which fits as snugly as possible over the converter mouth (Fig 1.6, Sharma et al., 1979, Pasca, et al., 1999) The gas then passes through a waste heat boiler or

water-spray cooler, electrostatic precipitators and a sulfuric acid plant Peirce- Smith converter offgases contain -8 volume% SO2 (slag blow) to -10 volume%

SO2 (copper blow) after cooling and dust removal, Table 9.2

(a) raising or lowering O2 enrichment level, which raises or lowers the rate at

which N2 ‘coolant’ enters the converter

(b) adjusting revert and scrap copper ‘coolant’ addition rates

9.2.3 Choice of temperature

Representative liquid temperatures during converting are: