Silica-saturated Iron Silicate Slags Research Articles

Solubility of Chromium in DON Smelting

ABSTRACT Chromia-bearing raw materials in nickel and copper matte smelting are difficult to process due to their tendency of forming solid chromite spinel precipitates, leading to formation of mushy slag and buildups in the smelting vessel. The solubility of chromia in smelting slags, and especially in mattes, are not known accurately and new data for iron-silicate slags in equilibrium with low-iron nickel mattes have been measured at 1350–1450°C. Typical copper-bearing nickel mattes with Ni:Cu≈2 (w/w) in the DON (Direct Outotec Nickel) process with 2 to 10 wt% [Fe]matte have been equilibrated in carefully controlled S2-O2-SO2-Ar gas atmosphere experiments with the corresponding silica saturated iron-silicate slags. The phase assays post quenching were measured by electron probe X-ray microanalysis, including the molten slag and matte as well as the solid phase of chromite spinel. Laser ablation ICP mass spectrometry was used to measure the trace elements in the matte. An additional variable in the slag composition was magnesia concentration, varying from zero to 10 wt% (MgO)slag. The solubility of chromium in the slag at 1400°C was ≈0.7 wt% (Cr) and in the nickel matte 30–100 ppm [Cr], depending on the iron concentration of the sulfide matte. The impact of MgO on the chromium concentration in slag was small and within the experimental error of the measurements.

Equilibrium of Copper Matte and Silica-Saturated Iron Silicate Slags at 1300\xa0\xb0C and P_{{{text{SO}}_{ 2} }} of 0.5 atm

Experimental study on the phase equilibria between copper matte with silica-saturated iron silicate slags was conducted at 1300 °C and P_{{{text{SO}}_{ 2} }} = 0.5 atm. The high-temperature isothermal equilibration in silica crucibles under controlled flowing CO-CO2-SO2-Ar was followed by quenching in an ice–water mixture and direct phase composition analyses by an electron probe X-ray microanalyzer. The equilibrium compositions for matte and slag, as well as the distribution coefficients, were displayed as a function of matte grade. The data set obtained at P_{{{text{SO}}_{ 2} }} = 0.5 atm and the previous study at P_{{{text{SO}}_{ 2} }} = 0.1 atm by the authors enabled an investigation on the impacts of P_{{{text{SO}}_{ 2} }} as well as Al2O3 and CaO additions on phase equilibria in the multiphase copper matte smelting system. Thermodynamic calculations using MTDATA software were performed to compare the experimental results with modeling. The present results enrich the fundamental thermodynamic information for the matte/slag/tridymite/gas equilibria in the primary copper smelting process at high P_{{{text{SO}}_{ 2} }} .

Distribution of Ni, Co, Precious, and Platinum Group Metals in Copper Making Process

The distribution coefficients of Ni, Co, Ag, Au, Pt, and Pd between molten copper and silica-saturated iron silicate slags ( {text{L}}_{text{Me}}^{{{text{Cu}}/{text{s}}}} ) were measured experimentally. The distribution behaviors were studied under typical conditions of copper converting and fire refining, i.e., from 1250 °C to 1350 °C, and from 10−8 to 10−4 atm oxygen partial pressure. The coefficients were determined as the ratios of the trace element weight concentrations measured in situ, directly from the equilibrated metal and slag phases. For the quantitative elemental analysis of the phases, state-of-the-art analytic techniques, including electron probe microanalysis and laser ablation-inductively coupled plasma-mass spectrometry, were employed. The distribution coefficients {text{L}}_{text{Me}}^{{{text{Cu}}/{text{s}}}} determined can be arranged in the following order: Pt > Au > Pd >> Ag > (Cu) > Ni > Co > (Fe).

Mechanism of Selenium Loss in Copper Slag

During smelting of copper sulfide concentrate, selenium is distributed between silica-saturated iron-silicate slag and copper-iron sulfide matte. The recovery coefficients of selenium between slag and matte were determined as a function of the initial concentration of selenium at 1523 K (1250 °C) under an inert atmosphere in a vertical tubular furnace. The initial concentration of selenium was varied by the addition of metallic selenium as well as selenium dioxide to the mixture of slag and matte. Analysis of the results indicated high affinity of selenium for matte. The apparent loss of selenium with the slag was attributed to the presence of selenium-enriched matte particles entrapped in the slag, rather than dissolved SeO2. The mechanisms proposed by previous investigators were discussed and also compared with the results of the present investigation.

Distribution of Precious Metals (Ag, Au, Pd, Pt, and Rh) Between Copper Matte and Iron Silicate Slag

The distributions of precious metals (Ag, Au, Pd, Pt, and Rh) between copper matte and silica-saturated iron silicate slag were determined at 1523 K to 1623 K (1250 °C to 1350 °C), in controlled CO-CO2-SO2-Ar gas mixtures. The experiments were done in silica crucibles and a fixed partial pressure of sulfur dioxide for matte grades of 55, 65, and 75 wt pct Cu. High-temperature equilibration/quenching/electron probe X-ray microanalysis technique was used to obtain compositions of the equilibrated matte and slag. The technique was applied for the first time to the distributions of precious metals in simulated flash smelting conditions. The resolution of electron probe microanalysis became critical as the detection limits were insufficient to measure reliably the precious metals concentrations (except silver) in the slag. The distribution coefficient of silver, L m/s[Ag] = [wt pctAg in matte]/(wt pctAg in slag), was found to be between 200 and 300, which agrees well with the latest studies in the literature. For other precious metals, the minimum values of distribution coefficients were determined according to the detection limits in the slag. The values obtained were for gold and platinum >250, for palladium >1000, and for rhodium >900. The distribution coefficients of palladium, although locating above distribution coefficient of the detection limit, formed a clear dependency with a good repeatability as a function of the matte grade. It increased along with matte grade and was approximately 1000 at 50 pct Cu and 2000 to 3000 at 70 pct Cu. The precious metals replace metal in the matte structure and they are present as sulfides in the copper matte.

Equilibrium Distribution of Precious Metals Between Slag and Copper Matte at 1250–1350 °C

Metal value recoveries in extraction are the key issue for sustainability of metals. The distributions of precious metals (Ag, Au, Pd, Pt, and Rh) between copper matte (a Cu–Fe–S–O melt) and silica-saturated iron silicate slag were determined at 1250–1350 °C, under controlled oxygen and sulfur pressures and at fixed partial pressure of sulfur dioxide, in silica saturation for target matte grades of 55, 65, and 75 wt% Cu. High-temperature equilibration/quenching was performed followed by electron probe X-ray microanalysis and laser ablation–inductively coupled plasma–mass sectrometry for measuring the major elements of the matte and slag, and trace elements of the slag, respectively. The distribution coefficient of silver at 65 % matte was found to be 150, which agrees well with the most recent studies in the literature. The other values obtained were gold 1500, palladium 3000, platinum 5000, and rhodium 7000–8000. The distribution coefficients increased along with matte grade, and for palladium it was approximately 1000 at 50 % Cu and 4000–5000 at 70 % Cu. The distribution coefficients decreased along with temperature but its impact was small. The distribution mechanism of the trace elements between iron silicate slag and copper matte appear to be dominated by properties of the matte phase.

硫化製錬における非鉄金属とNaのマット－スラグ間の分配

Distribution behaviors of non-ferrous metals of copper, lead, nickel, cobalt and sodium between matte and slag were studied using slags with a composition similar to industrial copper matte smelting of low grade secondary materials. The distribution ratios of copper, lead and nickel increased with the increasing copper concentration in matte, i.e., matte grade. In contrast, those of cobalt and sodium decreased with the increasing matte grade. Two interesting effects of sodium were found out in the present study. One is to reduce copper, lead and nickel concentration in slag; and the other is suppression of lead evaporation from matte. Both effects results in the increasing distribution ratios of copper, nickel and lead; however, sodium has no influence on the distribution ratio of cobalt. The effect of silicate degree, SD, of slags on the concentration of non-ferrous metals in slag was also found out. Distribution ratios of copper, nickel, lead and cobalt in present study, in which the SDs of slags were comparatively low (0.7 ～1.3), were 2 ～4 times higher than those in the previous study using silica-saturated iron silicate slag (SD ≃ 1.5). Variation in copper and nickel concentration in slag with matte grade was also dependent on the SD. These decreased with the increasing matte grade for the slag with low silicate degree. In conclusion, we proposed that the efficient recovery of rare metals, such as nickel and cobalt, in the copper matte smelting of low grade secondary materials is expected when the influences of sodium in secondary materials and a slag with low silicate degree are effectively utilized.

Effect of Slag Composition on the Distribution Behavior of Pb between FetO-SiO2 (-CaO, Al2O3) Slag and Molten Copper

The distribution behavior of Pb between molten copper and FetO-SiO2 (-CaO, Al2O3) slags was investigated at 1473 K (1200 °C) and \( p_{{{\text{O}}_{2} }} = 10^{ - 10} \,{\text{atm}} \) in view of the reaction mechanism of Pb dissolution into the slag. Furthermore, the lead capacity of the slag was estimated from the experimental results. The distribution ratio of Pb (LPb) decreases with increasing CaO content (~6 mass pct) irrespective of Fe/SiO2 ratio (1.4 to 1.7). However, the addition of alumina into a slag with Fe/SiO2 = 1.5 linearly decreases the LPb, whereas a minimum value is observed at about 4 mass pct Al2O3 at Fe/SiO2 = 1.3. The log LPb continuously decreases with increasing Fe/SiO2 ratio, and the addition of Al2O3 (5 to 15 mass pct) into the silica-saturated iron silicate slag (Fe/SiO2 < 1.0) yields the highest Pb distribution ratio. This is mainly due to a decrease in the FeO activity even at silica saturation. The log LPb linearly decreases by increasing the log (Fe3+/Fe2+) value. The Pb distribution ratio increases and the excess free energy of PbO decreases with increasing Cu2O content in the slag. However, from the viewpoint of copper loss into the slag, the silica-saturated system containing small amounts of alumina is strongly recommended to stabilize PbO in the slag phase at a low Cu2O content. The lead capacity was defined in the current study and shows a linear correlation with the activity of FeO in a logarithmic scale, indicating that the concept of lead capacity is a good measure of absorption ability of Pb in iron silicate slags, and the activity of FeO can be a good basicity index in iron silicate slag.

Nature of Copper Dissolved in Silica-Saturated Iron Silicate Slag Studied by X-ray Photoelectron Spectroscopy.

Quenched copper-containing samples of silica-saturated iron silicate slag were subjected to X-ray photoelectron spectroscopy (XPS) in an attempt to distinguish oxidic and sulfidic copper dissolved in slag as a function of sulfur partial pressure in the gas phase. First, slag and matte samples obtained by smelting industrial copper concentrate under controlled oxygen and sulfur potentials at 1,573 K are studied. Subsequently, synthetic SiO2-saturated iron silicate slags containing a small amount of copper equilibrated with different sulfur potential gases are subjected to XPS study. Oxygen and sulfur potentials were similar to those encountered in the industrial pyrometallurgical extraction of copper. The oxygen partial pressure was maintained constant at 10-3 Pa with different sulfur pressure from 0 to 3.5 - 102 Pa. The XPS Cu 2p3/2 and Cu L3M45M45 Auger spectra for copper contained in slag were reported. The presence of Cu2O dissolved in slag was identified. The increase of sulfur pressure in the gas, hence the increased sulfur dissolution in slag, does not result in a consistent core-peak shift to cuprous sulfide species in the slag. The sulfide capacities have been also determined.

Distribution of gold and silver between nickel-copper matte and silica-saturated iron silicate slag

Distribution coefficients of gold and silver between matte and slag during the pyrometallurgical treatment of nickel-copper sulfide concentrates were evaluated as a function of matte and slag compositions in the temperature range of 1,250°C to 1,300°C. It was observed that the composition of the matte phase, including matte grade and copper content in the matte, significantly affected the distribution behavior of gold and silver in the matte-slag system. Both gold and silver preferentially concentrated in the matte phase as the matte grade increased. With increasing temperature and copper content in the matte, the distribution coefficients of silver increased, while the gold distribution coefficients decreased. It was also found that slag additives such as CaO, MgO, and Al2O3 caused a significant decrease in the solubility of both gold and silver in silica-saturated iron silicate slag. An activity coefficient of gold in matte was derived from the experimental results.

Effects of CaO, Al2O3, and MgO additions on the copper solubility, ferric/ferrous ratio, and minor-element behavior of iron-silicate slags

The effects of CaO, Al2O3, and MgO additions, singly or in combination, on the copper solubility, the Fe3+/Fe2+ ratio in slag, and on the minor-element behavior of silica-saturated iron silicate slags were examined at 1250 °C and a p O2 of 10−12 to 10−6 atm. The results indicated that copper solubility in slag was lowered with the addition of CaO, MgO, and Al2O3, in decreasing order. The Fe3+/Fe2+ ratio in the slag decreased with the additions, but this effect was smaller at lower oxygen potentials. The presence of small amounts (about 4 pct) of CaO, Al2O3, and MgO in the slag resulted in increased absorption of Bi and Sb into molten copper, but had a smaller effect at large additions (about 8 to 11 pct). The distribution behavior of Pb was a function of oxygen partial pressure, which indicates the oxidic dissolution of Pb in the slag as PbO, while the behavior of Bi, Sb, and As was found to be independent of oxygen potential, supporting the atomic (neutral) dissolution hypothesis of these elements in the slag. The distribution behavior of Pb and As was not significantly affected by the additions. The activity coefficients of Bi and Sb in the slags were determined to be as follows: (1) for no addition, γ Bi=40 and γ Sb=0.4; (2) for small additions (about 4.4 pct), γ Bi=70 to 85 and γ Sb=0.8; and (3) for large additions (about 8 to 11 pct), γ Bi=60 to 75 and γ Sb=0.5 to 0.7.

Distribution behavior of cobalt, selenium, and tellurium between nickel-copper-iron matte and silica-saturated iron silicate slag

The distribution coefficients (DX) of cobalt, selenium, and tellurium between nickel-copper-iron matte and silica-saturated iron silicate slag were determined as a function of matte and slag compositions, temperature, and the partial pressure of oxygen. The effect of slag additives, such as CaO, MgO, and Al2O3, on the distribution behavior of the minor elements was also investigated. Analysis of the data indicated that DCo, DSe, and DTe were strongly dependent on the matte grade and slag additives. The effect of slag additives on the solubility of Co, Se, and Te in slag was discussed in terms of various experimental conditions. Cobalt distribution coefficients were found to decrease with increasing oxygen partial pressure, indicating the oxidic dissolution of cobalt in the slag. Based on the experimental results and available thermodynamic data, the activity coefficients of CoS in the nickel-copper-iron matte were estimated as a function of mole fraction of FeS in the matte at 1250 °C. Meanwhile, the distribution coefficients of both selenium and tellurium increased when raising the partial pressure of oxygen, implying that there was molecular dissolution of selenium and tellurium in the slag within the oxygen partial-pressure range investigated in this study.

The activity coefficient of cobalt oxide in silica-saturated iron silicate slags

The solubility of cobalt oxide in silica-saturated iron silicate slags (1.16 to 10.00 wt pct) in equilibrium with cobalt-gold-iron alloys (1.10 to 6.52 wt pct cobalt) and oxygen pressures of 10−9 to 10−10 atm (1 atm = 1.013 x 105 Pa) has been investigated at 1573 K. The activity coefficient of cobalt oxide, γCoO, has been calculated relative to pure solid cobalt oxide as standard, namely, γCoO = 0.91 ± 0.09

Evaluation of the behavior of selenium in silicate slag

The solubility of Se in silica saturated iron silicate slag was examined at 1458 and 1523 K using a static distribution technique. The procedure involved equilibrating slag with a molten Cu-Se alloy. The final Se content of both the slag and metal phases was determined using hydride generation in conjunction with atomic absorption. The slag specimens were also analyzed for their ferrous and ferric ion content. The results of this investigation indicate that the solubility of selenium in slag increases as the Fe2+/Fe3+ ratio increases, and that the solubility is constant at lower values of that ratio. These results are consistent with the model proposed by Nagamoriet al.1,2 In that study selenium is postulated to exist in both a neutral state and as an Fe-Se complex. In this work a method is presented whereby one can evaluate the nature of Fe-Se complexes. Analysis of the data obtained in this study, and the data obtained by Nagamori and co-workers, suggests that the Fe-Se complex has an Fe/Se ratio of approximately 1∶2. This study also presents a method, for calculating the fraction of neutral selenium present in slag.

Equilibria between silica-saturated iron silicate slags and molten Cu-As, Cu-Sb, and Cu-Bi Alloys

The solubilities of copper, arsenic, antimony, and bismuth in silica-saturated iron silicate slag, equilibrated with molten copper which included the corresponding element, were measured at temperatures 1473 and 1523 K under oxygen pressures ranging from 10−1 to 10−7 atm. The results confirm that copper is dissolved as CuO0.5 in silica-saturated fayalite slag. Dissolution of As, Sb, and Bi was found to be dependent upon the oxygen potential, suggesting oxidic rather than atomic dissolution. The data obtained also support models in which these elements exist in the slag mainly as two different types of oxides, but occasionally these oxides coexist with neutral atoms. Based on these models, equations were obtained that related the solubilities of these elements in the slags to the oxygen potential in them. The knowledge obtained in this investigation will be helpful in eliminating deleterious minor elements in copper smelting.

A thermodynamic study of silica-saturated iron silicate slags in equilibrium with liquid copper

A thermodynamic study of silica-saturated iron silicate slags in equilibrium with liquid copper

A thermodynamic study of silica-saturated iron silicate slags in equilibrium with liquid copper

The thermodynamic properties of silica-saturated iron silicate slags in equilibrium with liquid copper have been studied from oxygen partial pressure measurements in the temperature range from 1490 to 1580 K by means of a solid electrolyte galvanic cell. The following cells were used: Pt, Ni-NiO/O=/slag-Cu(l), Cr2O3, Pt; Pt, Fe-FeO/O=/slag-Cu(Fe sat.), Fe. A strong correlation was found between oxygen pressure and the copper content of the slag; the copper content increased from less than 1 pct near iron saturation to about 4 pct at an oxygen partial pressure of 7.2 x 10−3 Pa. A similar correlation was found between the ferric iron/total iron ratio and the oxygen pressure. The oxygen content in liquid copper decreased with increasing iron content in liquid copper and increased slightly near iron saturation. This behavior could be explained qualitatively by using the standard free energy of formation of FeO and the activities of components.

Oxygen pressure measurements of silica saturated Fe-O-SiO2 melts by the emf method using zirconia solid electrolyte

The thermodynamic properties of silica-saturated iron silicate slags have been studied from oxygen partial pressure measurements using a solid electrolyte galvanic cell. The oxygen activity in molten silver bath equilibrated with iron silicate slags was determined by the following cell type, Pt, Ni-NiO/O=/slag-Ag(O), LaCrO3, Pt at temperatures between 1473 and 1573 K for the slags ranging in compositions from iron saturation to magnetite saturation. The oxygen partial pressures obtained in this investigation were in good agreement with those given by the previous study using the CO-CO2 gas equilibrium method. The data showed that the Fe+++/Fe++ ratio is proportional toPo2¼

溶銅-マット-スラグ共存時の微量元素の分配

Distribution of nickel, cobalt, lead, antimony and arsenic among three liquid phases of copper, white metal and silicasaturated iron silicate slag was investigated. The melting experiments were carried out at 1300°C under varying oxygen partial pressure which was realized by controlled SO2 pressure. In the lower oxygen pressure region, copper content in the matte was designated under flow of nitrogen gas. On the basis of the analytical results for the minor elements in the solidified samples, the distribution ratios for an element X, defined by equations 1 to 3, were derived, and are plotted against oxygen potential as illustrated in Figs. 1 to 3. As are thermodynamically expected by equations 8, 11and 12, considerable dependences on oxygen pressure are observed in the distribution ratios between copper and slag, and also matte and slag, but any appreciable dependence can not be recognized in the distribution ratio between copper and matte. Under reducing conditions, minor elements tend to be concentrated in the metal and matte phases, while are oxidized into the slag phase under higher oxygen potential. In the conventional smelting condition characterized by the coexistence of considerable SO2 pressure, Co is highly concentrated in slag, Pb and Ni are distributed among all three melts in rather similar concentration, while As and Sb arehighly concentrated in copper metal.

銅-アンチモン合金とシリカ飽和鉄珪酸塩スラグの平衡について

銅-アンチモン合金とシリカ飽和鉄珪酸塩スラグの平衡について