EXPERIMENTAL STUDY OF GAS/SLAG/MATTE/SPINEL EQUILIBRIA AND MINOR ELEMENTS PARTITIONING IN THE Cu-Fe-O-S-Si SYSTEM
Taufiq Hidayat, Ata F Mehrjardi, Peter C Hayes, Evgueni Jak
PYROSEARCH, School of Chemical Engineering, The University of Queensland, Brisbane, Queensland, 4072, Australia.
Keywords: Matte-slag equilibrium, copper making process, spinel liquidus
Abstract
New data on gas/slag/matte/spinel equilibrium in the Cu-Fe-O-S-Si system at T=1200 C and P(SO2)=0.25 atm covering a wide range of matte grades for copper smelting and converting are presented. High temperature equilibration and rapid quenching technique, followed by Electron Probe X-ray Microanalysis are used. The use of substrate made of solid spinel ensures equilibration strictly within the Cu-Fe-O-S-Si system and avoiding contaminants from crucible.
The research is extended to measure partitioning of minor elements between slag and matte phases using this technique based on microanalysis. The system selected closely resembles the equilibrium condition of the actual copper smelting process. The information provided is essential for the evaluation of effect of fluxing towards the amount of chemically dissolved copper and quantity of solid in the slag. Present study is part of a larger integrated experimental and thermodynamic modelling research program on copper-making high-temperature systems.
1. Introduction
Fundamental information on slag-matte equilibria in the Cu-Fe-O-S-Si system is essential for understanding and improving the existing copper smelting and converting processes. Most of the previous investigations on the slag-matte equilibria at controlled P(SO2) have been carried out at tridymite saturation [1-6]. Analysis on the industrial sample however showed that spinel is common solid found in equilibrium with matte and slag phases [7]. Few studies available dealing with the equilibria between matte and spinel at fixed P(SO2) [8-11]. Not many attempts have been made to investigate the equilibria in the slag/matte/spinel at controlled gas atmosphere. This is due to difficulty in performing experiment since the system contains aggressive slag and matte liquids and there is no crucible that can suspend the sample without introducing contamination.
Equilibration experiment using substrate techniques has been developed in PYROSEARCH to tackle this issue. In this technique, a thin film of liquid phase is equilibrated on a substrate made of the spinel primary phase. This technique gives advantages compared to the conventional bulk refractory crucible experimentation since it improves direct exposure to gas, the quenching process of the sample, as well as avoids contamination of unwanted elements into the sample.
The application of this method enables the measurement of gas/slag/matte/spinel system.
Advances in Molten Slags, Fluxes, and Salts: Proceedings of The 10th International Conference on Molten Slags, Fluxes and Salts (MOLTEN16) Edited by: Ramana G. Reddy, Pinakin Chaubal, P. Chris Pistorius, and Uday Pal TMS (The Minerals, Metals & Materials Society), 2016
2. Development of Experimental and Measurement Techniques
2.1. High temperature equilibration technique
Experimental technique used to study the complex multi-component gas/slag/matte/spinel equilibria in the Cu-Fe-S-O-Si system involves high temperature equilibration in controlled gas atmospheres, rapid quenching and direct measurement of equilibrium phases with electron probe X-ray microanalysis (EPMA), which is similar to the technique previously used to investigate gas/slag/matte/tridymite system [7, 12].
First, an artificial oxide mixture was prepared from the analytically pure powders or pre-sintered solids or pre-melted master matte/slag to obtain after equilibration a predetermined bulk composition. The starting materials thoroughly mixed using an agate mortar and pestle, and then pelletised in a die using a press. The starting composition was selected to obtain two or more phases in the final sample after equilibration. Spinel (Fe3O4) substrate was used for holding slag and matte sample. The spinel was prepared from 99.5 wt pct pure iron foil folded into required shape and then oxidized at 1200 oC at P(O2) corresponding to condition where spinel is stable.
The furnace temperature was controlled within ±1 K by an alumina-shielded B-type thermocouple placed immediately adjacent to the sample, and was periodically calibrated against a standard thermocouple. The overall temperature accuracy is estimated to be within 5 K or better. The gas atmosphere was maintained by mixture of 20%CO in Argon, CO2 and SO2 gases added in proportions calculated using reliable thermodynamic information (e.g. FactSage thermodynamic software). The required gas flow-rates were maintained with calibrated U-tube capillary flow-meters. The calibrations of 20%CO-Ar and CO gases were checked by an oxygen probe made of a yttria-stabilized zirconia solid electrolyte cell (SIRO2®, DS-type oxygen probe;
supplied by Australian Oxytrol Systems, Victoria, Australia). After equilibration for predetermined time the samples were quenched into cold water or brine solution so that the phases present at high temperature and their compositions are retained at room temperature.
The samples were mounted, polished and then examined using optical microscopy and Scanning Electron Microscopy (SEM) with Energy Dispersive Detector (EDS). The compositions of the phases were measured using a JEOL JXA 8200L (trademark of Japan Electron Optics Ltd., Tokyo) electron probe X-ray microanalyzer (EPMA) with Wavelength Dispersive Detectors (WDD). An acceleration voltage of 15 kV and a probe current of 15 nA were selected. The Duncumb-Philibert ZAF correction procedure supplied with the probe was applied. The appropriate standards were selected to the oxide or sulphide phases. The phase compositions were measured with EPMA with accuracy within 1 wt % or better. EPMA was used to measure the element concentrations; no information on the proportions of the same element having different oxidation states were acquired. For slag and solid phases, all element concentrations were recalculated to selected oxidation state for convenience of presentation and to unambiguously report the compositions of phases.
Experimental study in gas/slag/matte/spinel equilibria in the Cu-Fe-S-O-Si system has been extended to study distribution of Ag as minor elements. In this work, Ag was introduced into the initial mixture in small quantity corresponding to a total of less than 1wt% Ag in the matte phase.
Two techniques were used to measure Ag composition in different phases: (i) EPMA for
elements in matte phase; and (ii) LAICPMS (Laser Ablation Inductively Coupled Plasma Mass Spectrometry) for elements in slag phase with concentration below the detection limit of EPMA.
2.2. Development of spinel substrate
Several different shapes of spinel substrate were tested. The final adopted type of substrate was the envelope shape with open ends shown in Figure 1. The bottom end of the substrate is open ensuring pathway for gas to get into contact with condensed phases and also ensuring direct contact of sample with quenching medium. Although, the envelope type substrate used in the present study is structurally stronger than that used in previous study [13], special attention on planning of the initial mixture was still needed to ensure no excessive reaction takes place between liquid slag and spinel.
Figure 1. Shape of spinel substrate for gas/slag/matte/spinel experiment.
2.3. Confirming the achievement of equilibrium
The achievement of equilibrium in the gas/slag/matte/spinel system was confirmed by a 4-points test which covers [14]:
i) Equilibration time variation ii) Phases homogeneity analysis
iii) Equilibrium achievement from different directions iv) Analysis of possible reactions specific to the system.
This 4-points test approach with particular attention to the kinetics of the reactions taking place during achievement of equilibria was applied to the gas/slag/matte/spinel system in addition to continuous application and development of a number of other common measures to minimise the uncertainties. Alternative approaches or techniques and independent confirmations by different researchers were also introduced to ensure the reliability of the experimental results.
2.4. Analysis of possible reactions taking place during equilibration
Various elementary reactions take place simultaneously throughout the equilibration process.
Analysis of their effects on equilibration process is important to avoid any barrier in the equilibrium process, thus ensuring that the final equilibrium point is approached from the right
before oxidation after
oxidation
direction within the required time. Several possible reactions in the gas/slag/matte/spinel equilibration process are listed below:
(i) Reactions in a single phase, such as within gas, slag, matte and spinel.
For example: CO2(gas) = ½O2(gas) + CO(gas) SO2(gas) = O2(gas) + ½S2(gas)
(ii) Reactions between two phases, such as between gas-slag, gas-matte, gas-spinel, slag- matte, slag-spinel, and matte-spinel.
For example: Fe2O3(slag) + CO(gas) =2FeO(slag) + CO2(gas) CO2(gas) = O(matte) + CO(gas)
FeS(matte) + Cu2O(slag) = FeO(slag) + Cu2S(matte)
(iii) Reactions between three phases, such as between gas-slag-matte, gas-slag-spinel, gas- matte-spinel, and slag-matte-spinel.
For example: FeS(matte) + 3CO2(gas) = FeO(slag) + 3CO(gas) + SO2(gas) 3FeO(slag) + CO2(gas) = Fe3O4(spinel) + CO(gas)
3FeS(matte) + 10CO2(gas) = Fe3O4(spinel) + 10CO(gas) + 3SO2(gas)
Different combinations of these elementary reactions will result in different overall process kinetics.
Figure 2. FactSage prediction of equilibria in the Cu-Fe-O-S-Si system between gas-slag-matte- spinel at T=1200˚C and P(SO2) = 0.25 atm: a. Partial pressure of gases vs matte grade; b.
Composition of matte vs matte grade; and c. Composition of slag vs matte grade.
-4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
-10.5 -10.0 -9.5 -9.0 -8.5 -8.0 -7.5
50 55 60 65 70 75 80
Log10[P(S2),atm]
Log10[P(O2),atm]
100*Cu/(Cu+Fe+S) Log₁₀[P(O₂),atm]
Log₁₀[P(S₂),atm] 0
5 10 15 20 25 30
50 55 60 65 70 75 80
100*Fe/(Cu+Fe+S) or 100*S/(Cu+Fe+S)
100*Cu/(Cu+Fe+S) Fe in matte S in matte
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
-8 -6 -4 -2 0 2 4 6 8
50 55 60 65 70 75 80
Fe2+/FeTotal or 100*Cu/(FeO+SiO2+Cu2O+S) Fe/SiO2 or 100*S/(FeO+SiO2+Cu2O+S)
100*Cu/(Cu+Fe+S) Fe/SiO2 in slag S in slag Fe2+/Fe-tot Cu in slag
(A) (B)
(C)
Figure 2 provides the predicted compositions of phases as function of copper in matte/matte grade from gas/slag/matte/spinel equilibration at 1200 °C and at P(SO2)=0.25 atm from calculation using FactSage public database [15]. From this set of figures, it can be observed that approaching equilibrium point from low to highcopper in matte leads to:
a. An increase in effective equilibrium oxygen partial pressure and a decrease in sulphur partial pressure in the system as reaction progresses Figure 2(a);
b. A decrease in concentrations of Fe and S in matte Figure 2(b); and
c. A decrease in Fe/SiO2 and S in slag and a slight increase in Fe2+/Fe total Figure 2(c).
Approaching equilibrium point from high to lowcopper in matte will give composition changes in opposite direction.
Investigation on gas/slag/matte/tridymite equilibrium [16] showed that precipitation of solid can take place on the surface of sample and may block further reactions with gas phase. In the gas/slag/matte/spinel systems, the solid (spinel) will precipitate when approaching equilibrium point from low to highCu in matte (high to lowFe in matte) as shown by this simplified reaction:
3FeS(matte) + 10CO2(gas) = Fe3O4(spinel) + 10CO(gas) + 3SO2(gas)
It may be reasonable to approach the final equilibrium point from high to lowCu in matte to avoid the precipitation of solid on the surface of sample that may block further reactions with gas phase. However, it is worth to note that this approach will result in a significant dissolution of spinel (Fe/SiO2 of the liquidus increases drastically, see Figure 2(c)). Since spinel substrate is fragile and easily reacts/dissolves in slag, it is practically more convenient to approach the equilibrium point from lower Cu in matte/lower matte grade (precipitating spinel) so that the integrity of the substrate can be maintained. Several trials were carried where the final equilibrium points were achieved from lower matte grade. No blockage of sample surface by the spinel precipitation was detected. The spinel most likely precipitated in the liquid or on the existing spinel substrate. To avoid excessive precipitation of spinel, the initial mixture in the final experiments was planned as close as possible to the expected equilibrium point.
2.5. Microanalysis approach to obtain representative equilibrium phases compositions
A complete equilibrium may not be achieved across the whole sample if starting composition is far from final equilibrium point. Inhomogeneities at micro and macro scale may appear in the sample. Analysis of these compositional gradients is important to identify reactions taking place during equilibrium process. Eventually the analysis result can be used in the experiment to confirm the achievement of the final equilibrium point, for example by modifying experimental methodology, adjusting starting composition, or varying the equilibration time.
As part of the analysis of the inhomogeneity in the sample, a classification of different phases and locations has been proposed during the investigation of gas/slag/matte/tridymite equilibrium [16]. Similar classification was used in the present study on the gas/slag/matte/spinel equilibrium. Figure 3 shows modified micrograph from the gas/slag/matte/spinel to demonstrate schematically different type of phases and locations within sample. Definitions of symbols used in Figure 3 are given in Table 1 and Table 2.
Some local areas (pockets) in the sample may achieve the final equilibrium point locally. For example, location in Figure 3 at which there is contact point between gas-matte-slag (matte = b’
or b, slag = B) may reach equilibrium readily. At these locations, matte and slag may have sufficient exposure to the gas atmosphere and may have shorter path for diffusion and exchange of elements between phases compared to other locations. As a result, the compositions at this location may be taken as a final result. This approach requires a careful analysis of the sample since each sample/system may be exposed to the experiment condition / may behave differently.
Figure 3. Schematic of different phases and locations within sample from the gas/slag/matte/spinel equilibrium.
Table 1. Definition of various types of matte related to proposed classification in Figure 3 [16].
Matte Terminology Abbreviation
Entrapped matte, droplet a
matte-Gas exposure close to slag, Chunky shape b matte-Gas exposure close to slag-small particles b'
matte-Gas exposure far from slag c
matte far from gas far from slag d
matte far from gas close to slag, channel-shaped e matte far from gas close to slag, chunky-shaped f
Table 2. Definition of various types of slag phase related to proposed classification in Figure 3 [16].
Slag Terminology Abbreviation
slag-matte far from gas A
slag-matte close to gas B
slag far from matte close to gas C
slag far from matte far from gas D
gas
spinel matte
slag
matte-a d
f b
b’
matte B
B A
C D
e
3. Experimental Results
The equilibrium result in the gas/slag/matte/spinel system is represented in selected graphs which is minimum in number but sufficient to completely describe the equilibrium phases, i.e. gas, slag, and matte. A set of graphs has been developed and include the following:
i) For matte phase:
Log10[P(O2),atm] versus matte grade (matte grade = %Cu/[Cu+Fe+S])
Sulphur in matte versus matte grade ii) For slag phase:
FeO/(FeO+SiO2+Cu2O+S) in slag versus matte grade
Sulphur in slag versus matte grade
Cu2O in slag versus matte grade
All expressed as a function of matte grade. Oxygen concentration in matte and Fe2+/Fe3+ in slag were not measured in this study.
Each of the graph contains experimentally measured values, values predicted with FactSage using the existing public database, and current “believed-to-be-true” equilibrium values. The
“believed-to-be-true” equilibrium line is generated based on the preceding experimental results, it is continuously corrected using validated equilibrium points from on-going experimental work so that the equilibrium values are obtained systematically through iterative experiments.
3.1. Typical appearance of phases
Figure 4. Micrograph of sample from gas/slag/matte/spinel experiment at T=1200˚C, P(SO2) = 0.25 atm, Log10[P(O2),atm]= -8.5, and equilibration time=24h.
Typical “well-quenched” sample image taken using scanning electron microscope with backscattered electron detector (SEM-BSE) is shown in Figure 4. Copper veins, most of the time associated with cracks, were observed within the matte phase. Based on numerous test, it was
spinel slag
matte gas
poor quench area
High-Cu vein
decided to perform EPMA measurement using large probe diameter and across the Cu veins to obtain representative composition of the matte phase. Well crystallized spinel solids (light grey phase) were observed. It can also be seen in Figure 4 that slag phase (dark grey phase) close to the surface are relatively homogeneous, the slag phase near the spinel on the other hand was found to have few bright spots possibly due to poor quenching. Careful selection of measurement area is required to obtain true/representative compositions of phases.
3.2. Experiments with extended time
Experiments of gas/slag/matte/spinel system at extended time up to 48 hours have been carried out to ensure that 24 hours equilibration time is sufficient for the achievement of equilibrium.
One condition was selected for this test at T=1200ºC, P(SO2)=0.25 atm, Log10[P(O2),atm]=-8.2 with matte in the initial mixture estimated to have 70 wt % Cu. The experiment results are represented in set of graphs compiled in Figure 6. The matte compositions measured in samples after 24h and 48h equilibrations were between 73.8 and 75.1 wt% Cu. There was no clear trend or significant increase in matte grade with extending time (Figure 6(a)); the observed variation was within the experimental uncertainty. The measured slag compositions from normal equilibration time and extended time are plotted in Figure 6(c) until Figure 6(e). The figures indicate that there were no systematic changes in Cu, “FeO” and S concentrations in the slag with extending equilibration time. It can be concluded that 24 hours provides sufficient equilibration time for the gas/slag/matte/spinel system to reach equilibrium.
3.3. Independent confirmation by different researcher
Independent confirmation has also been carried out by different researcher (Dr Mehrjardi) to confirm the present experimental result. Spinel substrate with spiral shape (Figure 5) was adopted to improve equilibration process and enhance the quenching result. The experimental results for equilibrations at 1200ºC, P(SO2)=0.25 atm, and Log10[P(O2),atm]=-8.5 using two different substrates (envelope with open ends and spiral substrates) are plotted in Figure 6. There was no significant difference in matte and slag compositions between the two trials.
Figure 5. Spinel substrate with spiral shape made by oxidizing iron wire.
1.5 cm
3.4. Ag distribution between slag and matte
The experimental results for the gas/slag/matte/spinel system containing Ag as minor elements from 24 hours equilibration at 1200oC, P(SO2)=0.25 atm and Log10[P(O2),atm]=-8.1 are plotted in Figure 6 and Figure 7. The major elements compositions in matte and slag phases were found to be in agreement with those from experiments without Ag minor elements (Figure 6). The Ag concentration in matte of different particles was uniform around 0.15 wt%, while the Ag concentration in slag of different locations had high variation between 2 and 8 ppm. Distribution coefficient of Ag (𝐿𝐴𝑔𝑠/𝑚) expressed as logarithmic value of ratio between Ag concentration in slag and Ag concentration in matte was approximately -2.51. The distribution coefficient of Ag from equilibration in gas/slag/matte/spinel system is compared to those from equilibration in gas/slag/matte/tridymite system in Figure 7.
4. Discussion
The results from equilibration experiments in the gas/slag/matte/spinel systems without and with Ag as minor element are compiled in Figure 6 together with previous results in gas/matte/spinel system and FactSage prediction calculated using public database [15].
Figure 6(a) gives relationship between matte grade and oxygen partial pressure. Only results by Kaiser & Elliot [9] are included in the figure since their investigation in the gas/matte/spinel system was carried out at the same range of P(SO2) as the present study. Kaiser & Elliot [9]
carried out experiment using mixture with known Cu/Fe ratio. The matte was equilibrated in alumina crucible at 1195 °C for 24 hours under CO/CO2/SO2 gas stream. The oxygen partial pressure in the gas stream was adjusted to the point where spinel started to precipitate from matte, this was confirmed using optical microscope. Using scanning electron microscopy equipped with energy dispersive X-ray analysis (SEM-EDAX), it was found that the spinel contained less than 0.5 wt% Al. The present results in the gas/slag/matte/spinel system show a clear relationship between matte grade and oxygen partial pressure. The experimental results show that with increasing P(O2) from 10-8.5 to 10-8.2 atm increased the matte grade from around 63 wt% to 75 wt%. Data reported by Kaiser & Elliot [9] seems to be an extension of the present data at lower matte grade. FactSage prediction using public database reproduce the current and previous results [9].
Figure 6(b) shows that the sulphur in matte from present measurements increases with decreasing matte grade. Similar trend is shown by FactSage prediction, the prediction however cannot reproduce the trend at lower matte grade suggested by Kaiser & Elliot [9]. The discrepancy is most likely due to the matte solution in the public database was modelled as sulphide solution without oxygen component. In reality, matte at high-Fe content is an oxy- sulphide solution.
“FeO” concentration in spinel liquidus as function of matte grade is plotted in Figure 6(c). The present results suggest lower “FeO” concentration than that given by FactSage prediction. The
“FeO” concentration in the liquidus indicates that the spinel solid becomes more stable with increasing matte grade.
Sulphur solubility in slag as a function of matte grade is reported in Figure 6(d). Both the present measurement and FactSage prediction show that the sulphur in slag decreases with increasing matte grade. The sulphur solubility in slag can be represented by the simplified reaction below:
S(slag) + O2(gas) = SO2(gas)
The oxygen partial pressure increases with increasing matte grade. Consequently at fixed SO2
and assuming the activity coefficient of sulphur in slag remains constant, the sulphur in slag is expected to decrease with increasing oxygen partial pressure (or increasing matte grade).
Copper concentration in slag as function of matte grade is shown in Figure 6(e). The current experimental results give significantly higher copper in slag than that from FactSage prediction.
Present result shows that at matte grade between 63 76 the copper concentration in slag is between 0.8 1.1 wt%.
Distributions coefficient of the Ag (𝐿𝐴𝑔𝑠/𝑚) is presented in Figure 7. 𝐿𝐴𝑔𝑠/𝑚 from other researchers [17, 18] from gas/slag/matte/tridymite equilibration are also compiled in the figure. In general, most of the Ag is contained within the matte phase. Previous investigations show that 𝐿𝐴𝑔𝑠/𝑚 decreases with increasing matte grade up to +72 wt% above which the 𝐿𝐴𝑔𝑠/𝑚 increases with increasing matte grade. It appears that the 𝐿𝐴𝑔𝑠/𝑚 from the gas/slag/matte/spinel experiment is lower than those from gas/slag/matte/tridymite experiments. Experimental confirmation is required to verify this observation.
The fundamental information in the gas/slag/matte/spinel system is significantly important for understanding and improving the copper smelting and converting processes. The information provided can be used to analyse the effect of SiO2 fluxing towards the quantity of solid (magnetite/spinel) and the amount of chemically dissolved copper in the slag. The present work demonstrates the possibility for the investigation of the intricate gas/slag/matte system. Further investigation will be directed toward the investigation of the distribution coefficients of various minor elements in the system, as well as the investigation of the effects of temperature, P(SO2) and P(O2) on the matte and slag compositions. Effect of slagging components, such Al, Ca, Mg, Cr, and Ti, on the equilibrium in the system is also a possible extension of the research program since these components are commonly found in the actual industrial sample. The present work also shows the necessity for re-optimization of the existing FactSage database. The present work is part of a larger integrated experimental and thermodynamic modelling research program on copper-making high-temperature systems.
Figure 6. Set of graphs describing equilibria in the Cu-Fe-O-S-Si system between gas/slag/matte/spinel from 24 hours experiments at T=1200ºC and P(SO2)=0.25 atm using envelope shape substrate with open ends (48 hours experiment and experiment with spiral
substrate are indicated with label).
a. Oxygen partial pressure P(O2) vs matte grade
%Cu/[Cu+Fe+S]
b. Concentration of sulfur in matte vs matte grade
%Cu/[Cu+Fe+S]
c. Concentration of iron oxide in slag vs matte grade
%Cu/[Cu+Fe+S]
0.20 0.20
0.33 0.33
0.33
P(SO₂)=0.41
48h
Spiral -8.8
-8.7 -8.6 -8.5 -8.4 -8.3 -8.2 -8.1 -8.0 -7.9
34 38 42 46 50 54 58 62 66 70 74 78 82 Log10[P(O2), atm]
100*Cu/(Cu+Fe+S)
FactSage - Slag/Matte/Spinel, 1200 °C, P(SO₂)=0.25 atm Kaiser & Elliott (1988) - Matte/Spinel, 1195 °C, P(SO₂)=0.2-0.4 atm Present study - Slag/Matte/Spinel, 1200 °C, P(SO₂)=0.25 atm Present study - Slag/Matte/Spinel+Ag, 1200 °C, P(SO₂)=0.25 atm TRUE
0.20 0.20
0.33
0.33 0.33
P(SO₂)=0.41
48h Spiral
20 21 22 23 24 25 26 27 28
34 38 42 46 50 54 58 62 66 70 74 78 82
100*S/(Cu+S+Fe)
100*Cu/(Cu+Fe+S)
FactSage - Slag/Matte/Spinel, 1200 °C, P(SO₂)=0.25 atm Kaiser & Elliott (1988) - Matte/Spinel, 1195 °C, P(SO₂)=0.2-0.4 atm Present study - Slag/Matte/Spinel, 1200 °C, P(SO₂)=0.25 atm Present study - Slag/Matte/Spinel+Ag, 1200 °C, P(SO₂)=0.25 atm TRUE
48h Spiral
64 66 68 70 72 74 76 78
40 45 50 55 60 65 70 75 80
100*FeO/(FeO+SiO2+Cu2O+S)
100*Cu/(Cu+Fe+S)
FactSage - Slag/Matte/Spinel, 1200 °C, P(SO₂)=0.25 atm Present study - Slag/Matte/Spinel, 1200 °C, P(SO₂)=0.25 atm Present study - Slag/Matte/Spinel+Ag, 1200 °C, P(SO₂)=0.25 atm TRUE
d. Concentration of sulfur in slag vs matte grade
%Cu/[Cu+Fe+S]
e. Concentration of copper in slag vs matte grade
%Cu/[Cu+Fe+S]
Figure 7. Distribution of Ag as minor element between slag and matte as function of matte grade in the Cu-Fe-O-S-Si system at spinel saturation from equilibration at T=1200°C and
P(SO2)=0.25 atm.
48h Spiral
0.0 1.0 2.0 3.0 4.0 5.0 6.0
40 45 50 55 60 65 70 75 80
100*S/(FeO+SiO2+Cu2O+S)
100*Cu/(Cu+Fe+S)
FactSage - Slag/Matte/Spinel, 1200 °C, P(SO₂)=0.25 atm Present study - Slag/Matte/Spinel, 1200 °C, P(SO₂)=0.25 atm Present study - Slag/Matte/Spinel+Ag, 1200 °C, P(SO₂)=0.25 atm TRUE
48h Spiral
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
40 45 50 55 60 65 70 75 80
100*Cu/(FeO+SiO2+Cu2O+S)
100*Cu/(Cu+Fe+S)
FactSage - Slag/Matte/Spinel, 1200 °C, P(SO₂)=0.25 atm Present study - Slag/Matte/Spinel, 1200 °C, P(SO₂)=0.25 atm Present study - Slag/Matte/Spinel+Ag, 1200 °C, P(SO₂)=0.25 atm TRUE
-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0
0 20 40 60 80
Log10[wt%Ag in slag/wt%Ag in matte]
100*Cu/(Cu+Fe+S) [2000Rog], 1300 °C, P(SO₂) = 0.1 atm, + MgO [2000Rog], 1300 °C, P(SO₂) = 0.5atm, + MgO [2000Rog], 1300 °C, P(SO₂) = 1.0 atm, + MgO [2015Ava], P(SO₂) = 0.1 atm, 1250 °C [2015Ava], P(SO₂) = 0.1 atm, 1300 °C
Present study - Slag/Matte/Spinel+Ag, 1200 °C, P(SO₂)=0.25 atm
5. Summary
Experimental technique has been developed to study the gas/slag/matte/spinel equilibrium in the Cu-Fe-O-S-Si system at controlled gas atmosphere. Several measures have been taken into account to ensure/confirm the achievement of equilibrium. New data on the gas/slag/matte/spinel system and the distribution of Ag in the phases within the system at T=1200 C and P(SO2)=0.25 atm have been obtained. It was found that matte grade 63 and 75 wt% correspond to P(O2) from 10-8.5 to 10-8.2 atm, respectively. It was observed that an increase in matte grade lead to a decrease in sulphur in matte, a decrease in “FeO” in slag, and a decrease of sulphur in slag. The chemically dissolved copper in the range of matte grade under investigation was found to be around 0.8 and 1.1 wt%. The distribution coefficient of Ag between slag and matte at spinel saturation from 24 hours equilibration at T=1200 C, P(SO2)=0.25 atm, and P(O2)=10-8.1 atm was found to be approximately -2.51. This indicates that majority of Ag was accumulated in the matte phase.
6. Acknowledgment
The authors would like to thank Australian Research Council Linkage program, Altonorte Glencore, Atlantic Copper, Aurubis, BHP Billiton Olympic Dam Operation, Kazzinc Glencore, PASAR Glencore, Outotec Oy (Espoo), Anglo American Platinum, and Umicore for the financial and technical support. The authors also thank Dr Jeff Chen for performing measurement on the sample using Laser Ablation Inductively Coupled Plasma Mass Spectrum (LAICPMS).
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