Copper Loss in Slag 177 Others accept converter slag in addition to smelter slag, requiring more emphasis on reduction. Most commonly, these furnaces are fed only smelting-furnace slag and are used primarily as a 'final settling' furnace. Fig. 1 1.1 illustrates a typical electric slag-cleaning furnace (Barnett, 1979; Higashi et al., 1993; Kucharski, 1987). Heat is generated by passing electric current through the slag layer. AC power is used, supplied through three carbon electrodes. This method of supplying heat generates the least amount of turbulence, which improves settling rates. The furnace sidewalls are cooled by external water jackets to minimize refractory erosion. Table 1 1.2 compares the operating characteristics of seven electric furnaces. Required capacities are set by the size of the smelting operation and the choice of input slags. Settling times are usually on the order of one to five hours. Typical energy use is 15-70 kWh per tonne of slag, depending upon furnace inputs, target YO Cu, temperature and residence time. While some electric slag-cleaning furnaces process only smelting furnace slag, others are fed a variety of materials. Several furnace operators input converter slag or solid reverts in addition to smelting slag. When this is done, a reducing agent is often required to reduce Cu oxide in the slag to Cu metal or Cu sulfide. Coal or coke is often added for this reduction. Pyrite may also be added if additional sulfur is needed to form matte (Ponce and SBnchez, 1999): c + Cu2O -+ co + 2CU" (11.4) C + CuzO + FeS2 -+ Cu2S + FeS + CO (1 1.5). Carbon additions also reduce solid magnetite in the slag to liquid FeO: C + Fe304(s) -+ CO + 3Fe0 (1 1.6). This decreases slag viscosity and improves settling rates. Ferrosilicon is occasionally used as a reducing agent (Shimpo and Toguri, 2000), especially in the Mitsubishi slag-cleaning furnace, Chapter 13. Recent initiatives in slag-cleaning furnace practice have involved lance injection of solid reductants or gaseous reducing agents such as methane, to improve reduction kinetics (Addemir, et al., 1986; An, et al., 1998; Sallee and Ushakov, 1999). Fuel-fired slag cleaning furnaces are also used in a few smelters, Table 1 1.3. The foremost is the Teniente slag-cleaning furnace, which is similar in design to a rotary fire-refining furnace (Chapter 15, Campos and Torres, 1993; Demetrio et al., 2000). 178 Extractive Metallurgy ofcopper Self-baking carbon - electrode Electrode holding clamps I Contact clamp Port -Solid feed Converter slag return launder \ Matte tapping launder Fig. 11.1. Electric slag cleaning furnace. A furnace of this size 'cleans' 1000 to 1500 tomes of slag per day. Table 11.2. Details of electric slag cleaning furnaces, 2001 Caraiba Metais Norddeutsche Nippon Sumitomo LG Nikko Mexicana de Mexicana de Smelter Dias d'Avila Affinerie Mining Toyo Onsan Cobre Cobre Brazil Hamburg Saganoseki Japan Korea Mexico Mexico Japan Furnace 1 Furnace 2 Slag details, tonnedday smelting furnace slag % cu converter slag % cu slag, % Cu matte, % Cu Furnace details shape diameter, m power rating, MW electrodes mat e ri a I diameter. m Products Operating details slag residence time, hours energy use, kwihltonne of slag reductant, kgitonne of slag slag layer thickness, m 880 OK flash furnace 1.7 0.7 65-70 circular 11 2-4 3 self baking 1 2-3 70 coke, 8.3 0.97- 1.4 1600 OK flash furnace 1-1.5 0 0.6-0.8 65-70 circular 10.2 2-3 3 self baking 1 5 40-50 coke, 4-5 1.5-1.8 1386 OK flash furnace 1-1.2 0.8 65.5 circular 9 0.7-1.1 3 self baking 0.68 1.5-3.0 15 coke, 15 0.5-0.9 1212 OK flash furnace 1.3 0.7 63 ellipse 5.1 x 13 1.85 5 self baking 3x 0.72; 2x 0.55 2 16 coal, 2 0.6 609 OK flash furnace 2 260 5 0.8 68-72 circular 8.1 2-3 3 self baking 0.8 2-5 50 12.5 coke 1-1.3 900 OK flash furnace 1.5 to 2.5 113 8 1.26 70.3 circular IO 1.5-4.5 3 self baking 0.9 0.25-1 57 7. I7 coke 0.8-1.5 740 Teniente furnace 5 184 8 1.3 70.5 circular 10 1.5-4.5 3 ? self baking 0.9 3 5 ts 2 G 0.25-1 3 69 h 7.32 coke 0.8-1.5 - 4 W matte layer thickness, m 0-0.45 0-0.4 0.4-0.8 0.8 0-0.3 0-0.2 0-0.2 180 Extractive Metallurgv of Copper Table 11.3. Details of Teniente rotary hydrocarbon-fired slag settling furnace at Caletones, Chile, 2001. Smelter Caletones, Chile Slag details smelting furnace slag, tonnes/day 3000 % cu 6 to 8 % cu converting furnace slag, tonnedday 0 Products slag, % Cu matte, % Cu matte destination % Cu recovery 1 72 Peirce-Smith converters Teniente smelting furnace 85% Furnace details number of slag cleaning hrnaces 4 shape horizontal cylinder diameter inside refractory, m 4.6 length inside refractory, m 3 x 10.7; 1 x 12.7 tuyere diameter, cm 6.35 number of reducing tuyeres 4 Operating details slag residence time, hours 2 reductant slag layer thickness, rn 1.4 matte layer thickness, m 0.4 fuel bunker C fuel oil 8.8 coal, oil or natural gas 6 kg per tonne of slag kg per tonne of slag It features injection of powdered coal and air into molten slag. It operates on a batch basis, generating slag with 0.643% Cu (Achurra, et al., 1999). Ausmelt has also developed a fuel-fired furnace (like Fig. 8.1) for cleaning slags and residues. % Cu-in-slag after pyrometallurgical settling is 0.7 to 1.0% Cu, which is lost when the slag is discarded. Some effort has been made to recover this Cu by leaching (Das, et al., 1987). The leaching was successful, but is likely to be too expensive on an industrial scale. Copper Loss in Slag 18 1 11.5 Decreasing Copper in Slag IV: Slag Minerals Processing Several options are available for recovering Cu from converter slags. Pyrometallurgical 'cleaning' in electric furnaces is quite common. Molten converter slag is also recycled to reverberatory smelting furnaces and Inco flash furnaces. Outokumpu and Teniente smelting furnaces occasionally accept some molten converter slag (Warczok et al., 2001). Cu is also removed from converter slags by slow solidification, crushindgrinding and froth flotation. It relies on the fact that, as converter slags cool, much of their dissolved Cu exsolves from solution by the reaction (Victorovich, 1980): CuzO + 3Fe0 + 2Cu0(4 + Fe304 (11.7). Reaction (1 1.7) is increasingly favored at low temperatures and can decrease the dissolved Cu content of converter slag to well below 0.5% (Berube et af., 1987; ImriS et al., 2000). After the slag has solidified, the exsolved copper and suspended matte particles respond well to froth flotation. As a result, converter slags have long been crushed, ground and concentrated in the same manner as sulfide ores (Subramanian and Themelis, 1972). The key to successful minerals processing of converter slags is ensuring that the precipitated grains of matte and metallic Cu are large enough to be liberated by crushing and grinding. This is accomplished by cooling the slag slowly to about 1000°C (Subramanian and Themelis, 1972), then naturally to ambient temperature. Once this is done, the same minerals processing equipment and reagents that are used to recover Cu from ore can be used to recover Cu from slag, Table 1 1.4. Some smelting slags are also treated this way, Table 11.4 and Davenport et al., (2001). 11.6 Summary Cu smelters produce two slags: smelting furnace slag with one to two percent Cu and converter slag with four to eight percent Cu. Discard of these slags would waste considerable Cu, so they are almost always treated for Cu recovery. Cu is present in molten slags as (i) entrained droplets of matte or metal and (ii) dissolved Cu'. The entrained droplets are recovered by settling in a slag- cleaning furnace, usually electric. The dissolved Cu' is recovered by hydrocarbon reduction and settling of matte. Table 11.4. Details of four slag flotation plants, 2001. The 0.4 to 0.65 % Cu in slag tailings is notable. Uomnda, Quebec Saganoseki, Japan Toyo, Japan PASAR, Philippines Smelter Slag inputs, tonnedday smelting furnace slag converter slag %Cu %Cu Products slag concentrate, %Cu slag tailings, %Cu Cu recovery, % Operating details solidification method cooling description equipment Crushing/grinding particle size after grinding machinery flotation residence time promoter collector Flotation Flotation reagents frother CaO? PH 1700 6 (average) 300 42 90-95 ladle cooling with or without water sprays 80% semi autogenous grinding, 20% crushing & ball milling 78% -44 pm mechanically agitated cells 60 minutes thionocarbamate, SPX propylene glycol no 8-9 0 450 8.33 21.8 0.65 95 -I 50 kg ingots on moving slag conveyor cooled on slag conveyor jaw crusher; cone crusher (twice); ball mill (twice) 40-50% -44 pm mechanically agitated cells Na isopropyl xanthate, UZ200 pine oil, MF550 no 7-8 5x 4 0 450 6.5 28 0.4 95 - I50 kg ingots on moving slag conveyor 1 hour in air then immersion in H20 gyratory crusher; cone crusher (twice); ball mill 90% -44 p mechanically agitated cells 30 minutes (roughe*scavenger) thionocarbamate. PAX pine oil 7-8 M 0 370 10-15* 29-33 0.5-0.6 97-98 jaw crusher; cone crusher; ball mills (primary and regrind) 65-75% -45 p mechanical agitator Agilair 48, Jameson cell (Fig. 3.12)" NH, & Na dibutyl dithiophosphate a) Danafloat 245, Penfloat TM3 b) K amyl xanthate pine oil NF 183 Yes 8.5-9.5 All Energy use kWh/tonne slag 32.5 ." "Non-magnetic 'white metal' (Cu,S) pieces are isolated magnetically after crushing. leaving 5 to 6.5% Cu in the ball mill feed slag. ** Switching to all Jameson cells. Copper Loss in Slug 183 A second method of recovering this Cu from slag is slow-cooling/solidification, cmshing/grinding and froth flotation. Slowly-cooledsolidified slag contains the originally entrained matte and Cu droplets plus matte and Cu which precipitate during coolinglsolidification. These Cu-bearing materials are efficiently recovered from the solidified slag by fine grinding and froth flotation. Electric furnace settling has the advantage that it can be used for recovering Cu from reverts and miscellaneous materials around the smelter. Slag flotation has the advantages of more efficient Cu recovery and the possibility of using a company's existing crushinglgrindinglflotation equipment. Suggested Reading Bamett, S.C.C. (1979) The methods and economics of slag cleaning. Min. Mag., 140, 408 417. Demetrio, S., Ahumada, J., Angel, D.M., Mast, E., Rosas, U., Sanhueza, J., Reyes, P. and Morales, E. (2000) Slag cleaning: The Chilean copper smelter experience. JOM, 52 (S), 20 25. ImriS, I., Rebolledo, S., Sanchez, M., Caatro, G., Achurra, G. and Hernandez, F. (2000) The copper losses in the slags from the El Teniente process. Can. Metall. Q., 39,281 290. References Achurra, G., Echeverria, P., Warczok, A,, Riveros, G., Diaz, C. M. and Utigard, T. A. (1999) Development of the El Teniente slag cleaning process. In Copper 99-Cobre 99 Proceedings of the Fourth International Conference. Vol. VI Smelting, Technology Development, Process Modeling and Fundamentals, ed. Diaz, C., Landolt, C. and Utigard, T., TMS, Warrendale, PA, 137 152. Addemir, O., Steinhauser, J. and Wuth, W. (1986) Copper and cobalt recovery from slags by top-injection of different solid reductants. Trans. Ins?. Min. Metall., Sect. C, 95, C149 C 155. Ajima, S., Igarashi, T., Shimizu, T. and Matsutani, T. (1995) The Mitsubishi process ensures lower copper content in slag. In Qualify in Non-ferrous Pyromeiallur~, ed. Kozlowski, M. A,, McBean, R. W. and Argyropoulos, S. A., The Metallurgical Society of CIM, Montreal, Canada, 185 204. An, X., Li, N. and Grimsey, E.J. (1998) Recovery of copper and cobalt from industrial slag by top-submerged injection of gaseous reductants. In EPD Congress 1998, ed. Mishra, B., TMS, Warrendale, PA, 717 732. Bamett, S.C.C. (1979) The methods and economics of slag cleaning. Min. Mug., 140, 408 417. Btrube, M., Choquette, M. and Godbehere, P. W. (1987) Mineralogie des scories cupriferes. CIM Bulletin, 80 (898), 83 90. 184 Extractive Metallurgy of Copper Campos, R. and Torres, L. (1993) Caletones Smelter: two decades of technological improvements. In Paul E. Queneau International Symposium., Vol. II, ed. Landolt, C. A,, TMS, Warrendale, PA, 1441 1460. Das, R. P., hand, S., Sarveswam Rao, K. and Jena, P. K. (1987) Leaching behaviour of copper converter slag obtained under different cooling conditions. Trans. Inst. Min. Metall., Sect. C, 96, C156 C161. Davenport, W.G., Jones, D.M., King, M.J. and Partelpoeg, E.H. (2001) Flash Smelting, Analysis, Control and Optimization, TMS, Warrendale, PA, 22 25. Demetrio, S., Ahumada, J., hgel, D.M., Mast, E., Rosas, U., Sanhueza, J., Reyes, P. and Morales, E. (2000) Slag cleaning: the Chilean copper smelter experience. JOM, 52 (8), 20 25. Fagerlund, K. 0. and Jalkanen, H. (1999) Some aspects on matte settling in copper smelting. in Copper 99-Cobre 99 Proceedings of the Fourth International Conference, Vol. VI Smelting, Technology Development, Process Modeling and Fundamentals, ed. Diaz, C., Landolt, C. and Utigard, T., TMS, Warrendale, PA, 539 55 1. Higashi, M., Suenaga, C. and Akagi, S. (1993) Process analysis of slag cleaning furnace. in First Int. Con$ Proc. Mater. Prop., ed. Henein, H. and Oki, T., TMS, Warrendale, PA, 369 372. Hughes, S. (2000) Applying Ausmelt technology to recover Cu, Ni and Co from slags. JOM, 52 (8), 30 33. ImriS, I., Rebolledo, S., Sanchez, M., Castro, G., Achurra, G. and Hernandez, F. (2000) The copper losses in the slags from the El Teniente process. Can. Metall. Q., 39,281 290. Ip, S. W. and Toguri, J. M. (2000) Entrainment of matte in smelting and converting operations. In J. M Toguri Symp.: Fund. ofMetall. Proc., ed. Kaiura, G., Pickles, C., Utigard, T. and Vahed, A,, The Metallurgical Society of CIM, Montreal, Canada, 291 302. Kucharski, M. (1987) Effect of thermodynamic and physical properties of flash smelting slags on copper losses during slag cleaning in an electric furnace. Arch. Metall., 32,307 323. Matousek, J. W. (1995) Sulfur in copper smelting slags. In Copper 95-Cobre 95, Vol. IV- Pyrometallurgy of Copper, ed. Chen W. J., Diaz C., Luraschi, A. and Mackey, P. J., The Metallurgical Society of CIM, Montreal, Canada, 532 545. Nagamori, M. (1974) Metal loss to slag. Part I: Sulfidic and oxidic dissolution of copper in fayalite slag from low-grade matte. Metall. Trans., 5,531 538. Poggi, D., Minto, R. and Davenport, W. G. (1969) Mechanisms of metal entrapment in slags, JOM, 21( 1 I), 40 45. Ponce, R. and Sanchez, G. (1999) Teniente Converter slag cleaning in an electric furnace at the Las Ventanas smelter. In Copper 99-Cobre 99 Proceedings ofthe 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, 583 597. Copper Loss in Slag 185 Sake, J. E. and Ushakov, V. (1999) Electric settling furnace operations at the Cyprus Miami Mining Corporation copper smelter. 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, 629 643. Shimpo, R. and Togun, J.M. (2000) Recovery of suspended matte particles from copper smelting slags. In J.M. Toguri Symposium: Fundamentals of Metallurgical Processing, ed. Kaiura, G., Pickles, C., Utigard, T. and Vahed, A., The Metallurgical Society of CIM, Montreal, Canada, 48 1 496. Subramanian, K. N. and Themelis, N. J. (1972) Copper recovery by flotation. JOM, 24 (4), 33 38. Victorovich, G. S. (1980) Precipitation of metallic copper on cooling of iron silicate slags. In Int. Symp. Metall. Slags, ed. Masson, C. R., Pergamon Press, New York, NY, 3 1 36. Warczok, A,, Riveros, G., Mackay, R., Cordero, G. and Alvera, G. (2001) Effect of converting slag recycling into Teniente converter on copper losses. In EPD Congress 2000, ed. Taylor, P. R., TMS, Warrendale, PA, 431 444. [...]... (33.2% Cu) 340 42 240 67 61 5 compressed copper scrap 56 540 500 63 34 560 67 3 86 (82% S O 2 ) 52 96 60 60 14 reverts 90 45 to 55 60 0 450 (99% 0 2 ) 140 30 60 0 to 65 0 60 31 570 60 matte and slag from smelting furnace 1400 68 1300 1018 68 .8 1331 0.8 0.9 500 ( . reduced to Fe by the reaction: 194 Extractive Metallurgy ofcopper FeO + C + Fe + CO (12.8). The Fe joins the newly reduced copper. Glogow results The Cu content of the Glogow. producing metallic copper are also minimized by the single- furnace process. 1 96 Extractive Metallurgy of Copper Metallic copper is obtained in a flash furnace by setting the ratio: 0, -in. injection of solid reductants or gaseous reducing agents such as methane, to improve reduction kinetics (Addemir, et al. , 19 86; An, et al. , 1998; Sallee and Ushakov, 1999). Fuel-fired slag