A study on copper recovery from the slag of Outokumpu direct-to-copper process

Transcription

1 A study o copper recovery from the slag of Outokumpu direct-to-copper process M. Kucharski (*), T. Sak, P. Madej, M. Wędrychowicz, W. Mróz AGH Uiversity of Sciece ad Techology, Departmet of Metallurgy of No-Ferrous Metals, 30 Mickiewicza Aveue, Kraków, Polad Abstract: The work was aimed at the ivestigatio of the ifluece of the carbo reducer s surface o the rate of the de-copperig of the slag from the flash direct-to-blister process at the Głogów II smelter, Polad. It was foud that, for the experimetal coditios, the copper recovery from the slag icreases as the iterface of the slag/carbo icreases; however this is the case oly to some extet. It is very likely that this limit would deped o the geometry of the ivestigated system. Further icrease of the slag/carbo iterface does ot oticeably chage the fial copper cotet i the slag. The obtaied results do ot follow ay of the reactio rate equatios, so it ca suggest that the trasport pheomea play the key role i the de-copperig process. The ivestigated slag has probably a higher viscosity, which hampers the mass trasfer i this slag. This hypothesis is supported by the fact that the slag layer situated below the peetrator is of a differet colour tha the slag i the viciity of those peetrators where it was agitated by the, ad gases geerated by the reactios of the slag reductios. The slag i the layer uder the peetrator cotaied more copper tha the slag above this layer. Key words: copper recovery, Outokumpu direct-to-copper process 1. Itroductio The Outokumpu direct-to-blister process was commercially implemeted i 1978, i Głogów, Polad. The process requires a high oxyge potetial ad therefore is restricted to those smeltig cocetrates which maily cosist of mierals without iro (e g Cu S, CuS, Cu 9 S 5 ) or with a small iro cotet (Cu 5 FeS 4 ). As a cosequece of the high oxyge potetial i a Outokumpu flash smeltig furace, the produced slag cotais 1-16% Cu i the Głogów case. The copper i the slag is accouted for the approximately 1/3 of the copper cotet i the smeltig cocetrate. Therefore, the recovery of the copper from this slag has a practical importace ad heavily iflueces the operatioal costs. A part of the copper i the slag is i form of fie iclusios suspeded i the slag; however, the majority of the copper is dissolved i it. The slag cleaig process is carried out i a electric furace with coke ad limestoe additios. The limestoe modifies the reduced slag i order to facilitate the process. Slags are ioic liquids [1-3], ad the copper i the slags exists as Cu O ad Cu + associated with the silicate aios, accordig to the reactio: O Si O Si O + Cu O = + O Si O Cu (1) Cu O is a basic oxide ad the oxyge io from it breaks the bridge i the Si-O etwork structure, which leads to the dissociatio of the silicate aio complexes. Durig the reductio process, the situatio becomes reverse. This model [4] suggests that the dissolved copper is almost etirely i the form of (-Si-O-Cu + ), for slags cotaiig about 1 wt-% of

2 copper. This ca be take as a explaatio of the sluggishess of the copper recovery process, whe it is close to completio, as the slag reductio proceeds accordig to the reactios: [ Cu] [ Cu] Cu O + C = + Cu O = + () + (3) The additio of metal oxides (CaO, FeO, ) to the slag causes some of the copper ioic Cu + to be replaced by Ca + ioic ad therefore, the umber of (Cu O) icreases. I this paper, the ifluece of the coal/slag iterface o the rate of the copper recovery from the slag of the direct-to-blister flash smeltig process was ivestigated.. Apparatus A schematic diagram of the apparatus used i this study is show i Figure 1. It cosists of a furace with Superkatal heatig elemets, powered by meas of a trasformer cotrolled by a Eurotherm cotroller, which is also coected to a cotrollig thermocouple Pt-PtRh10. Fig. 1. Experimetal apparatus The furace temperature was maitaied at ± K ad the maximum temperature variatio i the hot zoe was ± 3 K. A alumia reactio tube was sealed at the top ad the bottom by meas of water cooled brass caps ad with the use of rubber O-rigs. The measurig thermocouple Pt-PtRh10 was situated close to the crucible with the ivestigated slag, ad it measured the temperature of the sample with a Keithley s multimeter 000. The graphite peetrators were placed uder the upper cap of the reactio tube. The experimet started whe the graphite peetrator was trasferred ito the

3 slag. I this study four kids of peetrators of differet surfaces were used, as ca be see i Fig.. Fig.. Shape of the graphite peetrators used i this study The dimesio of these peetrators ad their surfaces are eclosed i Table 1. Table 1. Dimesios of the peetrators ad their surfaces Peetrator 1 Peetrator Peetrator 3 Peetrator 3 φ 1, [mm] φ, [mm] h 1, [mm] h, [mm] h 3, [mm] h 4, [mm] S, [cm ] Purified itroge of 5l/h flow rate was admitted to the reactio tube just after the sample was put ito the reactio tube ad durig the experimetal ru. The itroge flow rate was cotrolled with the use of a electroic flow meter maufactured by Brooks. The gas trai was made by meas of steel tubig coected to Hoke s fittigs ad valves. Durig the experimets, a gas composed of itroge, carbo mooxide ad carbo dioxide was formed as a result of the reactios betwee the graphite ad the slag. The ad were determied by a gas aalyzer for ad every 5 secods ad the results were recorded by the computer. 3. Calibratios of the gas aalyzer A ifrared gas aalyzer was used i this study to aalyze the ad i the N -- mixture. To speed up the passage of the reactio gas through the reactio tube, itroge of 5 dm 3 /h flow rate was admitted. For this reaso, the gas aalyzer had to be calibrated. The calibratio was carried out by allowig a passage of a gas mixture cotaiig

4 itroge of 5 dm 3 /h flow rate with additios of predetermied flow rates of,, ad -. The flow rates of these gases were cotrolled by Brooks flow meters ad corrected to 73 K. I cosequece, the gas aalyzer showed some readigs for ad ad the results were recorded by the computer. If the obtaied readig of % ad % did ot chage with time, the these values were take as true values. Figure 3 shows the relatio betwee the gas aalyzer readig for ad the fractio of i the gas mixtures admitted ito the reactio tube. Fig. 3. Correlatio betwee the readig of the gas aalyzer for ad the carbo oxide fractio i the gas mixture N -- passig through the reactio tube of the furace A similar correlatio was obtaied for. It was assumed that these correlatios ca be described by the followig relatios: (% ) = A (% ) (4) real measured ) = B (% ) (5) (% real where: A the slope of the calibratio straight lie for, B the slope of the calibratio straight lie for, (% ) real = V %, %, V N 100 V + V + V - the aalyzer readigs for ad, respectively, V - the flow rates of ad i [dm 3 /h]. measured With the least squares methods ad the calibratio results, the A ad B coefficiets were determied: (% ) = 1,058 (% ) (6) real ) real measured (% = 0,978 (% ) (7) measured Relatios (6) ad (7) were used for the determiatio of the flow rates of the ad formed durig the reductio

5 process betwee two cosecutive readigs of the gas aalyzer. V 5 (% ) = 94,48 (% ) 0,94 (% ) (8) As the aalyzer readigs were adjusted to 73 K, the umbers of the ad moles per oe secod could be calculated from the relatios: The umber of the oxyge moles reduced from the slag durig a period of 5 secods was determied from the relatio: where: V 5 (% ) = 10,5 (% ) 1,08 (% ) i i = O i + V = V = i i+ 1 5 (9) (10) (11) (1) i, i+ 1 - the umber of the moles formed durig the reductio process per oe secod, recorded i two cosecutive measuremets, ( i), i+ 1 - the umber of the moles formed durig the reductio process per oe secod, recorded i two cosecutive measuremets. 4. Experimetal procedure A slag produced by the Głogów direct-to-blister flash smelter was used i this study. The mai costituets of this slag are listed i Table. Table. Compositio of the Głogów direct-to blister flush smelter slag used i this work Compoets Cu Pb Fe Z SiO MgO CaO Al O 3 wt-% The crucible with the slag of 160 g was placed i the reactio tube of the furace. I the upper cap of the reactio tube a graphite peetrator was situated. A itroge stream of 5 dm 3 /h flow rate was itroduced to the reactio tube of the furace through its bottom cap. After about 5 hrs, the furace was switched o ad the temperature cotroller adjusted to 573 K. The furace was kept i these coditios for approximately 1 hours. Next, the temperature of the furace was elevated to 1573 K. The sample was kept at this temperature for oe hour ad the the alumious tube with the graphite peetrator was trasferred ito the slag. The immersio of the graphite peetrator i the slag was take

6 as the begiig of the reductio process. However, the first sigal of the reductio process was detectable after about 60 secods followig that momet. The gas livig the reactio tube was aalyzed for the ad cotet every 5 secods by the gas aalyzer ad the results were recorded by the computer. It was assumed that the reductio would take place o the graphite/slag iterface ad that it was equal to the surface of the graphite peetrator. A example of the obtaied results is show i Figure 4. I the first stage, the temperature of the peetrator was equalizig with the temperature of the slag, ad the reduced slag was foamig, because of the oticeable icrease of the cotet observed i the gas phase. It resulted from the reactio: ( MeO) = [ Me] + (13) slag alloy + The the height of the slag foam decreased ad this fact was idicated by decreases ad a simultaeous icreases of the cotet. I the ext stage, the foam decayed ad the reductio took place o the slag/peetrator iterface. Whe the reactio came to a ed, the ad cotet decreased steadily diluted by the icomig itroge. Fig. 4. Gas aalyzer readigs for the reductio of the slag By a summatio of the values with the relatio (1), the equatio (t) i O O describig the oxyge removed from the slag as a fuctio of the reductio time was determied. Figure 5 shows a example of such fuctios.

7 Fig. 5. Relatio betwee the removed oxyge from the slag for the case whe peetrator o 4 was employed Table 3. Results of the chemical aalyzes of the slags before ad after the reductios process by meas of differet graphite peetrators. Compoets, Slag before Peetrator o 1 Peetrator o wt-% experimets Ru 1 Ru Ru 3 Ru 1 Ru Ru 3 Na O K O CaO MgO SiO Al O Fe Z Pb Cu Table 3 (cotiued). Results of the chemical aalyzes of the slags reduced by meas of differet graphite peetrators. Compoets, wt-% Peetrator o 3 Peetrator o 4 Ru 1 Ru Ru 3 Ru 1 Ru Ru 3 Na O K O CaO MgO SiO Al O Fe Z Pb Cu

8 The obtaied results are partially similar to those reported i paper [5], however there are very distiguished differeces, which are maifested by the fact that the process of the oxyge removal from the ivestigated slag was a reactio of the first order. For every size of the peetrator, three experimets were coducted, ad the obtaied results are eclosed i Table 3. The reduced Cu-Pb-Fe alloys were chemically aalyzed ad the obtaied results are give i Table 4. Despite the fact that the samples of these alloys were take from their differet places, quite big differeces are observed. This is because the Cu-Pb-Fe system exhibits limited solubility i the liquid ad solid state. Table 4. Results of the chemical aalyzes of the Cu-Pb-Fe alloys obtaied durig the slag reductio by meas of differet graphite peetrators. Elemet, Peetrator o 1 Peetrator o wt-% Ru 1 Ru Ru 3 Ru 1 Ru Ru 3 Cu Fe Pb Table 4 (cotiued). Results of the chemical aalyzes of the Cu-Pb-Fe alloys obtaied durig the slag reductio by meas of differet graphite peetrators. Elemet, wt-% Peetrator o 3 Peetrator o 4 Ru 1 Ru Ru 3 Ru 1 Ru Ru 3 Cu Fe Pb Discussio It was foud that the results caot be described by the equatio for the reactio of the first order. However, this relatio was successfully applied also for the slag from the direct-to-blister process i paper [5]. The compariso of the compositios ( see Table 5) of these slags, reveals that the slag used i this work cotais more silica. This suggests that the ivestigated slag has a higher viscosity which hampers the mass trasfer i this slag. This hypothesis is supported by the fact that the slag layer of about 5 mm i thickess situated below the peetrator is of differet colour tha the slag i the viciity of those peetrators where it was agitated by the, ad gases geerated by reactios () ad (3). This part of the slag cotaied more copper tha the slag above this layer. Table 5. Mai costituets of the slags used i these ivestigatios ad i paper [5]. %Cu %Pb %Fe %Z %SiO %MgO %CaO %Al O 3 This work Paper [5] The viscosity of a slag depeds o its temperature ad degree of depolymerizatio. The degree of depolymerizatio of the slag ca be determied with the parameter D:

9 where: N Me p O q N SiO q NMepO q D = (14) N SiO - umber of metal oxides moles i 100 g of the slag, - umber of silica moles i 100 g of the slag. The umerator of the expressio (14) is equal to the umber of the oxyge moles [O] associated with basic metal oxides, while the deomiator of this expressio is equal to the umber of the oxyge moles [O] which ca be joied to all the silica atoms to form exclusively 4 SiO4 aios. The computed values of the parameter D for the ivestigated slag equals 0.511, while for the slag ivestigated i paper [5], it is almost twice higher ad is equal to This ca explai the differece i behavior of these slags durig the reductio process. The ifluece of the reducer surface o the rate of the slag de-copperig process is demostrated by the relatio betwee the time i which all the oxyge associated with the copper dissolved i the slag (Cu O) is removed ad the surfaces of the peetrators. Fig. 6 shows this relatio. Fig. 6. Relatio betwee the time required for the removal the oxyge associated with the copper dissolved i the slag i form of Cu O. However, it is clear that durig the de-copperig proces, copper, lead ad iro are reduced simultaeously, but with diffret rates formig Cu-Pb-Fe alloy. The employed experimetal techique is uable to determie the reductio rates of the particular metals.

10 Figure 6 suggests that the rate of the slag de-copperig process icreases with icrease of the peetrator s surface, yet to a certai limit. This limit would deped o the geometry of the ivestigated system. A similar depedece is observed betwee the fial copper cotet i the slag ad the peetrators surface, as ca be see i Fig 7. Fig. 7. Relatio betwee the copper fial cotet (mea value from three measuremets) ad the peetrator s surface. Figure 7 suggests that the effectiveess of the slag de-copperig process icreases with the icrease of the peetrator s surface, yet agai oly to some extet. Further icrease of the slag/carbo iterface does ot result i the lowerig of the copper cotet i the slag after the reductio process. Ackowledgmets We would like to thak the Polish Natioal Ceter Research ad Developmet (NCBiR) for the fiacial support grat Nr Refereces [1] Toop G.W., Samis C.S.: Activities of Ios i silicate Melts, Tras. TMS-AIME 4 (196) [] Masso C.R.: A approach to the problem of ioic distributio i liquid silicates, Proc. Roy. Soc. A87 (1965) [3] Gaskell D.R.: The Thermodyamic Properties of the Masso Polymerizatio Models of Liquid Silicates, Met. Tras. 4 (1973) [4] Kucharski, M.: Solubility of copper i Outokumpu slag, Metals Techology, (1979) [5] Rogóż K.: Kietic of reductio of the slag from direct-to-copper process with elevated basicity, PhD thesis, AGH-009.