Extractive Metallurgy of Copper 4th ed. - W. Davenport_ et. al. (2002) WW Part 12 pdf

CHAPTER 18 Solvent Extraction Transfer of Cu from Leach Solution to Electrolyte (Written with Jackson Jenkins, Phelps Dodge, Morenci, AZ) The pregnant leach solutions produced by most leaching operations are: (a) too dilute in Cu (1-6 kg Cu/m3) and: (b) too impure (1 - 10 kg Fe/m3) for direct electrodeposition of high purity cathode copper. Electrowinning from these solutions would give soft, impure copper deposits. Industrial electrowinning requires pure, Cu-rich electrolytes with >35 kg Cu/m3. This high concentration of Cu: (a) ensures that CU++ ions are always available for plating at the cathode surface (b) gives smooth, dense, high purity, readily marketable cathode copper. Solvent e,xtraction provides the means for producing pure, high Cu" electrolytes from dilute, impure pregnant leach solutions. It is a crucial step in the production of -2.5 million tonnes of metallic copper per year. It continues to grow in importance as more and more Cu ore is leached. 18.1 The Solvent Extraction Process Copper solvent extraction (Fig. 18.1) entails: 307 308 Extractive Metallurgy of Copper Mixer EXTRACT Raffinate return to leach f- Settler < Settler + to electrowinning -1.5 kg Culm3 45 kg Culm3 STRIP Loaded organic Mixer Fig. 18.1. Schematic plan view of copper solvent extraction circuit. The inputs are pregnant leach solution and Cu-depleted electrolyte. The products are Cu-enriched electrolyte and low-Cu raffinate. Fig. 18.3 shows an industrial mixer-settler. Fig. 18.4 shows the most common industrial circuit. (a) contacting pregnant aqueous leach solution (1-6 kg Cu++/m3, 0.5 to 5 kg H2S04/m3) with a Cu-specific liquid organic extractant - causing extraction of Cu++fyom the aqueous solution into the organic extractant (raffinate) from the now-Cu-loaded organic extractant (c) sending the low-Cu raffinate back to leach (d) sending the Cu-loaded organic extractant to contact with strong-H2S04 electrowinning electrolyte (170-200 kg H2SO4/m3) - causing Cu to be stripped from the organic into the electrolyte (e) separating by gravity the now-Cu-stripped organic extractant from the now-Cu”-enriched aqueous electrolyte (f) returning the stripped organic extractant to renewed contact with pregnant leach solution (8) sending the Cu++-enriched electrolyte to electrowinning where its Cu* is (b) separating by gravity the now-Cu-depleted aqueous leach solution electrodeposited as pure metallic ccpper. The process is continuous. It typically takes place in ‘trains’ of 2 extraction mixer-settlers for steps (a) and (b) and 1 strip mixer-settler for steps (e) and (0. An extraction system typically consists of 1 to 4 ‘trains’ (Jenkins et a/., 1999). Solvent Extraction Transfer of Copper 309 The organic extractants are aldoximes and ketoximes (Kordosky et al., 1999). They are dissolved 5 to 20 volume% in purijied kerosene. 18.2 Chemistry The organic extractant removes Cu++ from pregnant leach solution by the reaction: 2RH + Cu" + SO4 -+ R2Cu + 2H+ + SO4 (18.1) organic aqueous pregnant loaded raffinate extractant leach solution organic (0.3 kg Cu/m3) (1 to 6 kg Cu/m3 ) where RH is the aldoxime or ketoxime extractant. Loading of organic extractant with Cu is seen to be favored by a low concentration of sulfuric acid (H') in the aqueous phase. So contact of dilute HzS04 aqueous pregnant leach solution with organic gives extraction of Cu from the aqueous phase into the organic phase. After this organic loading step, the organic and aqueous phases are separated. The Cu++-depleted raffinate is sent back to leach to pick up more Cut+. The Cu- loaded organic phase is sent forward to a 'strip' mixer-settler where its Cu is stripped into Cu*-depleted aqueous electrolyte. The strip reaction is the reverse of Reaction 18. I, Le.: 2H' + SO4 + R2Cu + 2RH + Cu'+ + SO4 (18.2). high acid, Cu- loaded depleted Cu-replenished depleted electrolyte organic organic electrolyte (-185 kg H2S04/m', extractant extractant (-165 kg H2S04im3, -35 kg Cu/m') -45 kg Cuim') It is pushed to the right by the high sulfuric acid concentration of the aqueous electrolyte. It strips Cu from the organic extractant and enriches the electrolyte to its desired high-Cu++ concentration. In summary, the organic extractant phase is: (a) loaded with Cu from weak H2S04 pregnant leach solution (b) separated from the pregnant leach solution (c) contacted with strong H2S04 electrolyte and stripped of its Cu. It is the different H2S04 strengths of pregnant leach solution and electrolyte which make the process work. 3 10 Extractive Metallurgy of Copper 18.3 Extractants The organic extractants used for Cu are oximes, Fig. 18.2. Two classes are used: aldoximes and ketoximes, Table 18.1. They are dissolved in petroleum distillate to produce an organic phase, 8 to 20 volume% extractant. This organic is (i) immiscible with CuSO4-H2SO4-H*0 solutions and (ii) fluid enough (viscosity = 0.01 to 0.02 kg/m.s) for continuous mixing, gravity separation and pumping around the solvent extraction circuit. A successful Cu-extractant for any leach project must (Kordosky, 1992; Kordosky et al., 1999): (a) efficiently extract Cu from the project’s pregnant leach solution (b) efficiently strip Cu into the project’s electrowinning electrolyte (c) have economically rapid extraction and strip kinetics (d) disengage quickly and completely from leach solution and electrolyte, i.e. not form a stable emulsion R /bH/O OH R I A\ c I/ Q Fig. 18.2. Oxime molecules and copper complex. The copper complex is formed from two oxime molecules, Eqn. 18.1. Alodoximes: R = C9HtY or C,ZH2S, A = H. Ketoxime: R = CyH19, A = CH3 (Dalton et al., 1986; Kordosky et al 1999). Solvent Extraction Transfer of Copper 3 1 1 (e) be insoluble in the project’s aqueous solutions (f) be stable under extraction and strip conditions so that it can be recycled many times (g) not absorb sulfuric acid (h) extract Cu preferentially over other metals in the pregnant leach solution, particularly Fe and Mn (i) not transfer deleterious species from pregnant leach solution to electrolyte, particularly C1 (i) be soluble in an inexpensive petroleum distillate diluent (k) be nonflammable, nontoxic and non-carcinogenic. Ketoxime and aldoxime extractants satisfy these requirements. 18.3. I Ketoximes vs aldoximes Ketoximes have a methyl (CH3) group for A in Fig. 18.2. Aldoximes have hydrogen. Ketoximes are relatively weak extractants with excellent physical properties, Table 18.1. Table 18.1. Properties of Cu solvent extraction extractants (Kordosky et ul., 1999) Aldoxime-ketoxime extractants are customized by adjusting their relative quantities. Aldoxime- Property Ketoxime Aldoxime with modifier ketoxime mixtures, no modifiers Extractive strength Stripping ability CuiFe selectivity Cu extraction and stripping speed Phase separation speed Stability Crud generation** Examples moderate very good excellent fast very fast very good low LIX 84-1 strong good excellent very fast very fast very good* variable LIX 622 (tridecunol modified) Acorga M5640 (ester modified) customized customized excellent fast very fast very good low LIX 984N ~ * Depends on modifier. **Depends on pregnant leach solution and modifier 3 12 Extractive Metallurgy of Copper Aldoximes are strong extractants. However, their Cu can only be stripped by contact with 225+ kg H2S04/m3 electrolyte. This level of acid is too corrosive for industrial electrowinning. It also tends to degrade the extractant. For these reasons, aldoximes are only used when mixed with ketoximes or modifiers, e.g. highly branched alcohols or esters. The most common extractants in 2002 are ketoxime-aldoxime and ester- modified aldoxime solutions. 18.3.2 Diluents Undiluted ketoxime and aldoxime extractants are thick, viscous liquids. They are totally unsuitable for pumping, mixing and phase separations. They are, for this reason, dissolved 8 to 20 mass% in moderately refined high flash point petroleum distillate (purified kerosene), hydrogenated to avoid reactive double bonds (Bishop et a/., 1999). Commercial diluents typically contain -20 volume% alkyl aromatics, -40% naphthenes and -40% paraffins (Chevron Phillips, 2002). 18.3.3 Rejection of Fe and other impurities An efficient extractant must carry Cu forward from pregnant leach solution to electrolyte while not forwarding impurities, particularly Fe, Mn and CI. This is a critical aspect of efficient electrowinning of high purity copper. Fortunately, ketoxime and aldoxime extractants have small solubilities for these impurities. Ester-modified aldoximes are especially good in this respect (Cupertino et al., 1999, Kordosky et al., 1999). Impurities may, however, be carried forward to electrolyte in droplets of pregnant leach solution in the Cu-loaded organic. This carryover can be minimized by (i) coalescing the pregnant solution droplets on polymer scrap; (ii) filtering and (iii) washing the loaded organic (Jenkins et al., 1999). 18.4 Industrial Solvent Extraction Plants Solvent extraction plants are designed to match the rate at which Cu is leached in the preceding leach operation. They vary in capacity from 20 to 600 tonnes of Cu per day. Table 18.2 gives operational details of five solvent extraction plants. Additional details are given in Jenkins et a/., 1999. The key piece of equipment in a solvent extraction plant is the mixer-settler, Fig. 18.3 (Lightnin, 2002). Mixer-settler operation consists of (a) pumping aqueous and organic phases into a mixer at predetermined rates Organic overflow Barren Settler organic extracta u - enriched Cu - depleted aqueous Pregnant leach solution Fig. 18.3. Copper solvent extraction mixer-setter. The two mixing compartments, the large settler and the organic overflow/aqueous underflow system are notable. Flow is distributed evenly in the settler by picket fences (not shown), Table 18.2. 3 14 Extractive Metallurgy of Copper Table 18.2. Details of five Cu solvent extraction plants, 2001. Details of the Operation Cerro Colorado El Ahra Startuo date 1994 1996 Cathode production, tonnesiyear Total pregnant solution input rate, m'lhour SX plant detals plant type number of SX 'trains' extraction mixer-settlers per train strip mixer-settlers per train Mixer-settler details Mixers round or square number of mixing compartments compartment size: depth x width x length, m mixer system construction materials liquids residence time, minutes length x width x depth, m flow distributor system construction materials organic depth, m aqueous depth, m estimated residence time, minutes estimated phase separation time, minutes Organic details extractant volume% in organic diluent diluent organic washing? aqueous removal from organic crud removal system crud treatment system organic cleaning system organic removal from raffinate Settler Flowrates per train, m31hour pregnant solution input rate organic flowrate, extraction to strip depleted electrolyte input rate % of electrolyte flow sent to SX Solution details, kg/m3 pregnant solution raffinalc barren organic loaded organic depleted electrolyte enriched electrolyte organic removal from electrolyte electrolyte treatment before tankhouse 130 000 4000 series 5 2 1 square 3 Lightnin pump mixer 77030 316 stainless steel 3 22 x 22 xo.9 2 picket fences HDPE-lined concrete 0.28-0.3 0.45 4 3 LIX 860-NIC/LIX 84-IC 13 Orfom SX-12 no wash none pneumatic pump Chuquicamata mechanical breakage clay treatment with Sparkle filter skimmer 750 1040 I80 18 cu H2S04 4.8 5 0.4 II 3 5.6 37 180 52 159 none garnevanthracite filtration 218 000 5000-7500 2 series 2 series-parallel 4 series 2; series-parallel 3 series 2; series-parallel 1 square 3 3.1 x 3.7 x 12.7 suction mixer polymer concrete 2.4 28 x 29 x 1.1 2 picket fences HDPE-lined concrete 0.27 0.63 3 PT5050-LIX 984NC 2 I .4%Ll, 15.8% L2 Conosol 170ES water wash to pH I. I Wemco coalescers pneumatic pump centrifuge and pressure filter zeolite treatment Wemco coalescers 1400 series 2400 series-parallel 1500-l650 450-500 25 cu His04 4.94 6.44 0.70 12.10 3.33 7.40 36.33 171.41 40.29 170.9 Wemco pacesetter coalescence sand/garnet/anthracite filtration Solvent Extraction Transfer of Copper 3 15 equivalent leach and electrowinning plants are given in Chapters 17 and 19. Zaldivar Hellenic Copper Morenci (Stargo) 1995 1996 1998 I45 000 4800 series 4 2 1 round 2 Outokumpu VSF mixers Ti & 3 16L stainless steel 23.5 x 25 x 0.9 I distributor, 1 picket fence HDPE-lined concrete 0.25-0.3 15 LIX 984 NC 14.3 Orfom SX I2 one wash mixer-settler 8 Disep garneuanthracite filters diaphragm pump centrifugc clay treatment + centrifuge + clay filter floating absorption system 1200 I100 350 21 cu H2SO4 3.8 0.55 0.28 6 3 7.2 41.5 165 5s 151 Cominco column flotation Diseu sand/anthracite filters 8000 520 series-parallel I 2 1 square 2 Davy impeller 3 16L stainless steel 2 22x9~1 1 picket fence 3 16L stainless steel 0.3 0.7 15 0.5 Acorga M5640 8 Escaid I 10 no wash aqueous entrainment pumps in loaded organic tank 2.5 cm diaphragm pump bentonite mixing-recovery filter press pumping from pond 520 20 CU H2S04 1.8 1 0.2 4 I .3 3.8 30 180 38 160 sand/anthracite filters and heat exchanging I56 000 4320 series-parallel I 3 I round 3 5 diameter, 3.2 high Outokumpu Spirok and Dop pump mixers stainless steel 3 24 x 26 x 1.25 3 picket fences 3 16L stainless steel 0.425 0.375 12 70 seconds LIX 984 21 Conosol 170 I wash stage mixer-settler drain loaded organic tank interface pumping and settler dumping clay mixing and filter press clay mixing and filter press skimmed from organic recovery tanks 4320 2160 1250 65 cu II2SO4 3.00 3.50 0.30 7.00 3.80 9.80 38.0 200.0 50.0 185.0 organic IS floated from rich booster tank 6 anthracite garnet filters 3 16 Extractive Metallurgy of Copper (b) mixing the aqueous and organic with impellers (c) overflowing the mixture from the mixer through flow distributors into a flat settler where the aqueous and organic phases separate by gravity (organic and aqueous specific gravities, 0.85 and 1.1 respectively [Spence and Soderstrom, 19991) (d) overflowing the organic phase and underflowing the aqueous phase at the far end of the settler. Typical mixer-settler aqueous and organic flowrates are 500-4000 m3 per hour (each). The mixer is designed to create a well-mixed aqueous-organic dispersion. Modem mixers consist of two or three mixing chambers. They create the desired dispersion and smooth forward (plug) flow into the settler. Mixer aqueous/organic contact times are 2 to 3 minutes - which brings the liquids close to equilibrium. Entrainment of very fine droplets is avoided by using low tip- speed (<400 &minute) impellers (Spence and Soderstrom, 1999). The settler is designed to separate the dispersion into separate aqueous and organic layers. It: (a) passes the dispersion through one or two flow distributors (picket fences or screens) to give smooth, uniform forward flow (b) allows separate layers to form as the dispersion flows smoothly across the large settler area. The vertical position of the aqueous-organic interface is controlled by an adjustable weir at the far end of the settler. It avoids accidentally overflowing aqueous or underflowing organic. Modem settlers are square in plan. This shape is the best for smooth flow and an adequate residence time. Liquid residence times in the settlers are 10 to 20 minutes, Table 18.2. This time is sufficient to guarantee complete phase separation (laboratory separations occur in 0.5 to 2 minutes [Spence and Soderstrom, 19991). The aqueous phase is -0.5 m deep. The organic phase is -0.3 m deep. Advance velocities are typically 1 to 5 m per minute. 18.4.1 ‘Trains 2002 solvent extraction plants consist of one to four identical solvent extraction circuits (‘trains’) - each capable of treating 500 to 4000 m3 of pregnant solution per minute. Each train transfers 20-250 tonnes of Cu from pregnant solution to electrolyte per day, depending on the Cu content and flowrate of the pregnant solution. [...]... Vol IV Hydrometallurgy of Copper, ed Young, S.K., Dreisinger, D.B., Hackl, R.P and Dixon, D.G., TMS, Warrendale, PA, 277 289 Biswas, A.K and Davenport, W.G (1994) Extractive Metallurgy of Copper, 3rd Edition, Elsevier Science Press, New York, NY, 394 395 Chevron Phillips (2002) Orfom SX 12 Solvent Extraction Diluent www.cpchem.co (Mining chemicals, Orfom SX 12) Cognis (1997) The Chemistry of Metals Recovery... Transfer o Copper f 3 1I 18.4.2 Circuit design Most copper solvent extraction is done in series circuits, Fig 18.4 The two extraction mixer-settlers typically transfer -9 0% of Cu-in-pregnant-leachsolution to the extractant (Jenkins et al., 1999) The remaining Cu is not lost It merely circulates around the leach circuit The single strip mixer-settler strips 50% to 65% of the Cu-in-loaded-organic into... is -2 volts as compared to -0 .3 volt for electrorefining It is made up of: theoretical voltage for Reaction (19.2) oxygen deposition overvoltage copper deposition overvoltage electrical resistance @ 300 Aim2 cathode current density -0 .9 -0 .5 -0 .05 -0 .5 V V V V The energy requirement for electrowinning, -2 000 kWh/tonne of copper, is also considerably greater than that for electrorefining, 30 0-4 00 kWWtonne... Production 328 Extractive Metallurgy o Copper f 19.1 Electrowinning Reactions The electrowinning cathode reaction is the same as in electrorefining, Le.: CU+++ 2e- -+ E" Cu" = +0.34V (16.2) The anode reaction is, however, completely different It is formation of oxygen gas at the inert anode: H20 + H+ 1 + OH- -+ -0 2 + 2H' + 2e- 2 E" = -1 .23V (19.1) The overall electrowinning reaction is the sum of Reactions... Tucson, AZ www,cognis.com Cupertino, D.C., Charlton, M.H., Buttar, D., Swart, R.M and Maes, C.J (1999) A study of copperliron separation in modem solvent extraction plants In Copper 99-Cobre 99 Proceedings of the Fourth International Conference, Vol IV Hydrometallurgy of Copper, ed Young, S.K., Dreisinger, D.B., Hackl, R.P and Dixon, D.G., TMS, Warrendale, PA, 263 276 Solvent Extraction Transfer of Copper. .. must be kept below -3 0 ppm More than this causes chlorine gas evolution: 2C 1- + 1 2 -0 2 + H,O -+ C12 + 2(OH )- (19.3) This C12 'pit' corrodes the top of the stainless blade, causing the depositing copper to stick and resist detachment Leach operations with high concentrations of CI- in their pregnant leach solution wash their loaded solvent extraction organic to prevent excessive C 1- transfer to electrolyte... R.P and Dixon, D.G (1999) Copper 99-Cobre 99 Proceedings of the Fourth International Conference, Vol IV Hydrometallurgy of Copper, TMS, Warrendale, PA References Bishop, M.D., Gray, L.A., Greene, M.G., Bauer, K., Young, T.L., May, J., Evans, K.E and Amerson-Treat, I (1999) Investigation of evaporative losses in solvent extraction circuits In Copper 99-Cobre 99 Proceedings of the Fourth International... R.M and Maes, C.J (1999) A study of copperhron separation in modem solvent extraction plants In Copper 99-Cobre 99 Proceedings of the Fourth International Conference, Vol IV Hydrometallurgy of Copper, cd Young, S.K., Dreisinger, D.B., Hackl, R.P and Dixon, D.G., TMS, Warrendale, PA, 263 276 Jenkins, J., Davenport, W.G., Kennedy, B and Robinson, T (1999) Electrolytic copper leach, solvent extraction... aqueous/organic volumetric ratio entering the extraction mixer-settler) Extraction of Cu from a 3 kg Culm’ pregnant leach solution with the Table 18.3prescribed N O volume ratio of 1/1 requires, therefore: volume% LIX 984N in organic = 3 - x 1 0.25 = 12% So each train of the solvent extraction plant requires pumping of 1000 m3/hour of 12 volume% LIX 984N in Orfom SX 12 diluent This calculation is the first step in... in solvent extraction for copper by optimized use of modifiers Paper presented at Mining Latin America, Chile, November 1986 Jenkins, J., Davenport, W.G., Kennedy, B and Robinson, T (1999) Electrolytic copper leach, solvent extraction and electrowinning world operating data In Copper 99-Cobre 99 Proceedings of the Fourth International Conference, Vol IV Hydrometallurgy of Copper, ed Young, S.K., Dreisinger, . easy switching between aqueous-continuous and organic-continuous operation. Industrial O/A ratios are discussed in Biswas and Davenport (1994). 3 18 Extractive Metallurgy of Copper. of Copper, ed. Young, S.K., Dreisinger, D.B., Hackl, R.P. and Dixon, D.G., TMS, Warrendale, PA, 277 289. Biswas, A.K. and Davenport, W. G. (1994) Extractive Metallurgy of Copper, 3rd Edition,. are only used when mixed with ketoximes or modifiers, e.g. highly branched alcohols or esters. The most common extractants in 2002 are ketoxime-aldoxime and ester- modified aldoxime solutions.