Activities of As,Sb, Bi,and Pb in copper mattes—impurity elimination

The theoretical possibilities for the elimination of As, Sb, Bi, and Pb from copper matte were evaluated on the basis of the activity behavior of these impurity elements in the matte, considering removal by purge gas blowing, chlorination, vacuum evaporation, and slagging. The calculations were made assuming equilibrium conditions between the prevailing phases and using different combinations of sulfur, oxygen, and chlorine potentials. Present evaluations show that (1) As can be evaporated from the matte, using moderate amounts of purge gas at a high sulfur pressure of about 10⁻² atm (1013.3 Pa) and a temperature of 1200°C (1473. 15 K); (2) Sb, Bi, and Pb can also be eliminated under similar conditions using a chloridizing purge gas; (3) the purge gas, consumption can be decreased by lowering the total pressure of the system; (4) on a thermodynamic basis, the vacuum evaporation rates of these impurity elements should be much higher from the matte than from copper, the actual differences not, however, having been so apparent in previously published experimental studies, due possibly to kinetic reasons; and (5) the distribution coefficients of As and Sb between slag and matte increase along with the sulfur pressure, although not sufficiently to utilize this phenomenon on an industrial scale. A. ROINE, formerly with Institution of Process Metallurgy, Helsinki University of Technology, SF-02150, ESPOO, Finland     

Kinetics of As,Sb, Bi and Pb volatilization from industrial copper matte during Ar+O<Subscript>2</Subscript> bubbling

A kinetic study on minor elements removal during copper matte oxidation was designed under the presumptions of low FeO activity and of no fayalite slag formation. Copper matte with a mass fraction of Cu of 59 pct was mixed by Ar gas blowing during preheating. The matte was oxidized at 1523 and 1673 K by bubbling Ar+O₂ gas through a submerged nozzle. The effects of melt temperature and input oxygen content on the oxidation rate of matte and the volatilization rate of minor elements in copper matte are discussed. The competition reaction composed of the oxygen dissolution into matte and SO₂ gas evolution rate results in the preferential oxidation of FeS in copper matte. The desulfurization rate of matte and the volatilization of minor elements in copper matte were primarily controlled by the mass-transfer rate through the gas film boundary layer around rising gas bubbles. The As, Pb, and Bi were significantly removed during Ar gas blowing with the volatilization rates of Bi and Pb markedly increasing with the melt temperature. However, the dependences of the volatilization rates on the input oxygen partial pressure were affected in a complicated way by the effects of the melt temperature and the reduced amount of exhaust gas.     

Activities of As,Sb, Bi,and Pb in copper mattes— Effect of O,Ni, and Co

The effects of oxygen, nickel, and cobalt on the activity coefficients of As, Sb, Bi, and Pb in copper mattes were measured at 1200 °C (1473.15 K) using the transportation method. The transportation experiments concerning the effect of oxygen were carried out as a function of the SO₂ content (1 to 100 vol pct) in the carrier gas and using high- and low-grade matte samples, ≈80 and ≈40 wt pct Cu, respectively. The prevailing sulfur and oxygen partial pressures were evaluated on the basis of matte and carrier gas compositions. The effect of the SO₂ pressure on the activity coefficients was found to be very small compared with the effect of the sulfur pressure, whereas the effect of the SO₂ partial pressure on the vaporization behavior, especially of As, was very significant, due to the additional vaporization of As as AsO gas molecules, which caused an increase in the As removal rate. At a higher oxygen partial pressure than 10^−8.5 atm (3.2·10⁻⁴ Pa) a noticeable decrease in the Sb activity coefficients was observed due to the oxidation. This did not, however, decrease the Sb removal rate, since the relative proportion of the oxide gas molecules in the gas phase increased simultaneously. The interactions between dissolved Ni or Co and the impurity elements were investigated by doping (1 wt pct) the high grade (Cu ≈75 wt pct) matte samples with Ni or Co. At stoichiometric and sulfur-deficient matte compositions, Ni and especially Co decreased the activity coefficients of As and Sb, but did not have any effect on the activity coefficients of Bi and Pb, compared with the corresponding sulfur content in the Ni- and Co-free mattes. For mattes of higher sulfur content Ni and Co did not show any marked effect on the activity coefficients of As, Sb, Bi, and Pb. A. ROINE, formerly with Institution of Process Metallurgy, Helsinki University of Technology, SF-02150, ESPOO, Finland     

Thermodynamics and phase relations of the Fe-O-S-Si2(sat) system at 1200 °C and the effect of copper

A laboratory investigation was carried out in which iron was reacted in silica crucibles with an atmosphere of controlled oxygen and sulfur partial pressures. The equilibrium compositions of the melts were determined over the range 10⁻¹² to 10⁻⁹ atm oxygen and 10^−2.75 to 10⁻¹ atm sulfur and it was found that the Fe-O-S-SiO₂ system can exist as either a slag or oxysulfide. The oxysulfide contained appreciable quantities of dissolved oxygen and silica, although the levels decreased as the sulfur content was increased. Sulfur also had the effect of reducing the solubility of silica in the slag. When copper was added to the system, the solubility of oxygen and silica in the oxysulfide phase decreased dramatically. The results are examined in terms of the thermodynamics of the relevant reactions, and the predominance area diagram for the copper-free system was established by combining the present results with those of earlier investigations. Formerly with the G.K. Williams Cooperative Research Centre for Extractive Metallurgy     

Interfacial phenomena in the liquid copper-calcium ferrite slag system

The surface and interfacial tensions of the copper-calcium ferrite slag system were determined at 1573 K as a function of oxygen and sulfur pressures and CaO content in the slag. The effect of a 2.9 mass pct SiO₂ addition to the calcium ferrite slag was also investigated. The measurements were carried out using the sessile drop technique with a high-temperature X-ray setup. The surface tension of copper was found to be a strong function of oxygen and sulfur partial pressures. The surface tension of the calcium ferrite slag decreased slightly with CaO addition. On the other hand, CaO had a negligible effect on the interfacial tension of the system. Surface tension of the slag and the interfacial tension were influenced by the oxygen partial pressure in the system. Sulfur partial pressure also altered the interfacial tension between the copper and the ferrite slag. Based on the experimental data, filming and flotation coefficients were calculated to predict the entrainment behavior of copper, by bubble attachment in the ferrite slag.     

Bubble bursting phenomenon in Gas/Metal/Slag systems

Iron droplets can be ejected into the surrounding atmosphere or entrained into the slag phase when gas bubbles pass through the metal surface or the metal/slag interface. The phenomena occurring during passage of single bubbles through the free surface and the interface were investigated by using the in-situ X-ray transmission technique. The mass of droplets ejected into the atmosphere attained a maximum value at a certain bubble size, which depended on the surface tension of the iron melt. Bubble bursting on the free surface of iron melt ejected numerous fine iron droplets called “film droplets” and a few much larger jet droplets. Two different groups of iron droplets were also observed as entrained in the slag due to bubble passage through the iron/slag interface, although the physical phenomena are to some extent different from bubble bursting to the gas phase. This article is based on a presentation given in the Mills Symposium entitled “Metals, Slags, Glasses: High Temperature Properties & Phenomena,” which took place at The Institute of Materials in London, England, on August 22–23, 2002.     

Comparison of Ferrous Calcium Silicate Slag and Calcium Ferrite Slag Interactions with Magnesia-Chrome Refractories

The cost of maintaining and eventually replacing refractories as a result of slag attack is a significant cost component in the copper industry. Converting matte to blister copper takes place in reactors lined with direct-bonded magnesia-chrome refractories, and several continuous converting operations use calcium ferrite slag. Unfortunately, the low viscosity of calcium ferrite slag makes it aggressive toward the refractories. Ferrous calcium silicate (FCS) slag has been proposed as a replacement; however, the effect of this slag on magnesia-chrome refractories has not been studied. In this work, the interactions between FCS slag and magnesia-chrome refractory at 1573 K (1300 °C) with an oxygen partial pressure of 10⁻⁶ atm were studied and compared with that experienced with calcium ferrite slag under the same conditions. Both slags penetrated the pores in the refractory and caused compositional change in the chromite spinel intergranular bonding phase through cation interdiffusion, which resulted in cracking and debonding of periclase grains. It was observed that the refractory was penetrated much more deeply by calcium ferrite slag than FCS slag because of the higher surface tension and lower viscosity of calcium ferrite slag. As a result, the refractory was attacked less by FCS slag than it was by calcium ferrite slag. It is concluded that the use of FCS slag in continuous copper converting is likely to extend refractory life.     

Equilibrations of copper matte and fayalite slag under controlled partial pressures of SO2

Equilibrium distributions of Cu, S and O between silica saturated fayalite slags and copper mattes (25 to 79 pct Cu) have been examined experimentally under controlled partial pressures of SO₂. The temperature range of the experiments was 1423 to 1573 K and pSO₂ was varied between 0.1 and 1 atm. Concentrations of copper in the experimental slags were found to be low (<1 pct Cu) under these conditions, as long as the grade of the coexistent matte was below 60 pct copper. Copper in slag concentration rose dramatically, however, when matte grade was increased above this level. The work also showed that whereas FeS has a high solubility for oxygen and is itself soluble in slag under oxidizing conditions, Cu₂S and slag are almost completely immiscible. Cu-Fe-S mattes behave in an intermediate manner. Formerly graduate student with the Department of Mining and Metallurgical Engineering, McGill University.     

Experimental Investigation of Gas/Slag/Matte/Tridymite Equilibria in the Cu-Fe-O-S-Si System in Controlled Gas Atmospheres: Experimental Results at 1473 K (1200 °C) and <Emphasis Type="Italic">P</Emphasis>(SO<Subscript>2</Subscript>) = 0.25 atm

Experimental studies were undertaken to determine the gas/slag/matte/tridymite equilibria in the Cu-Fe-O-S-Si system at 1473 K (1200 °C), P(SO₂) = 0.25 atm, and a range of P(O₂)’s. The experimental methodology involved high-temperature equilibration using a substrate support technique in controlled gas atmospheres (CO/CO₂/SO₂/Ar), rapid quenching of equilibrium phases, followed by direct measurement of the chemical compositions of the phases with Electron Probe X-ray Microanalysis (EPMA). The experimental data for slag and matte were presented as a function of copper concentration in matte (matte grade). The data provided are essential for the evaluation of the effect of oxygen potential under controlled atmosphere on the matte grade, liquidus composition of slag and chemically dissolved copper in slag. The new data provide important accurate and reliable quantitative foundation for improvement of the thermodynamic databases for copper-containing systems.     

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 CuO^0.5 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.     

Settling of copper drops in molten slags

The settling of suspended metal and sulfide droplets in liquid metallurgical, slags can be affected by electric fields. The migration of droplets due to electrocapillary motion phenomena may be used to enhance the recovery of suspended matte/metal droplets and thereby to increase the recovery of pay metals. An experimental technique was developed for the purpose of measuring the effect of electric fields on the settling rate of metallic drops in liquid slags. Copper drops suspended in CaO−SiO₂−Al₂O₃−Cu₂O slags were found to migrate toward the cathode. Electric fields can increase the settling rate of 5-mm-diameter copper drops 3 times or decrease the settling until levitation by reversal of the electric field. The enhanced settling due to electric fields decreases with increasing Cu₂O contents in the slag.     

Electrocapillary motion of copper and nickel matte droplets on fayalite-based slag surfaces

The electrocapillary motion of Cu₂S and Ni₃S₂ droplets on the surface of fayalite-based slags under 50% Ar-CO atmosphere has been studied for the effects of droplet size, temperature, electric field strength. Cu content m Cu₂S-FeS droplets, Ni content in Ni₃S₂ FeS droplets and slag composition. The copper matte droplets migrate to the anode (positive electrode) while the nickel matte droplets migrate to the cathode (negative electrode). Typical speeds encountered are of the order of 0.05–0.80 cm/s (Cu) and 0.16–0.62 cm^−s (Ni) with droplet diameters between 0.10 and 0.28 cm, applied potentials between 0.17 and 2.0 V/cm (Cu) and 0.75 and 3.3 V cm (Ni) and for temperatures between 1473 and 1573 K. The migration rate appears to be independent of droplet size for droplet diameters between 0.10 and 0.28 cm, but it increases with applied potential field and temperature.The effects of matte and slag contents on the migratory behavior are complex. As the Cu content in the Cu₂S-FeS matte droplet increases above 40% Cu. the migration rates also increase. Below 40% Cu matte grade, the migration rates are not significantly different. As the Ni content in the Ni₃S₂-FeS matte droplet increases, the migration rates decrease. These migration rates are also affected by the slag composition. As the Cu and Ni matte droplets migrate in opposite directions under the influence of the electric field, electrocapillary phenomena may be used to enhance metal recovery in slag cleaning operations using electric furnaces.     

Cobalt distribution during copper matte smelting

Many smelter operators subscribe to the “precautionary principle” and wish to understand the behavior of the metals and impurities during smelting, especially how they distribute between product and waste phases and whether these phases lead to environmental, health, or safety issues. In copper smelting, copper and other elements are partitioned between copper matte, iron silicate slag, and possibly the waste gas. Many copper concentrates contain small amounts of cobalt, a metal of considerable value but also of some environmental interest. In this work, the matte/slag distribution ratio (weight percent) of cobalt between copper matte (55 wt pct) and iron silicate slag was thermodynamically modeled and predicted to be approximately 5. Experiments were performed using synthetic matte and slag at 1250 °C under a low oxygen partial pressure and the distribution ratio was found to be 4.3, while between industrial matte and slag, the ratio was found to be 1.8. Both values are acceptably close to each other and to the predicted value, given the errors inherent in such measurements. The implications of these results for increasingly sustainable copper production are discussed.     

Distribution equilibria of Sn,Se and Te between FeO-Fe2O3-SiO2-AI2O3-CuO0.5 slag and metallic copper

The distribution of tin, selenium and tellurium between alumina-containing fayalitic slags and metallic copper was measured at 1200 and 1300°C under controlled CO-CO₂ atmosphere with oxygen partial pressure (pO₂) in the rangePO ₂ = 10_-6 to 10_-11 atm (1 atm = 1.013 x 10² kPa). The solubility of Sn in slag was observed to increase linearly with increasing P^1/2O₂. It was deduced that Sn is present in the slag in the form of SnO or Sn² and the activity coefficient of SnO in the slag was calculated to be 1.9 at 1200°C and 0.8 at 1300°C. The solubility of Se in the slag decreases with increasing oxygen partial pressure up topO ₂l = 4 x 10₋₈ atm, but above this oxygen partial pressure it becomes practically constant and the ratio (pet Se in slag/pet Se in copper) = 0.018 (at 1200°C) and 0.036 (at 1300°C). The solubility of Te shows a similar variation with oxygen partial pressure and the ratio (pet Te in slag/pet Te in copper) = 0.026 (at 1200°C) and 0.032 (at 1300°C) abovepol ₂ = 10⁶ atm. A concept of molecular dissolution of chalcogen elements in slag was developed on the basis of thermodynamic properties of slag, and the observed solubility of Se and Te was explained in terms of the chemical stability of the molecular cluster FeSe and FeTe iη the slag. M. Nagamori is with Centre de Recherche Industrielle du Québec, Ste-Foy, Quebec and P. J. Mackey is Smelter Technical Superintendent, Noranda Mines Limited, Noranda, Quebec, Canada. Both authors were Formerly with Noranda Research Centre, Pointe Claire, Quebec.     

Vacuum distillation of copper matte to remove lead,arsenic, bismuth,and antimony

Vacuum-refining experiments were carried out on copper matte melts, containing 35 to 73 pct Cu, to measure the removal rates of lead, bismuth, arsenic, and antimony over the temperature range of 1373 to 1523 K under pressures in the range of 50 to 130 Pa. High rates of refining, controlled by mass transport in the liquid phase, were achieved for all impurities in melts containing up to 65 pct Cu and for chamber pressures less than 100 Pa. After 40 to 60 minutes of treatment, lead elimination was between 70 and 96 pct, bismuth elimination was between 88 and 98 pct, arsenic, elimination was between 60 and 93 pct, and antimony elimination was between 40 and 92 pct. The overall mass transfer coefficients for vacuum refining for the impurities considered fell in the range of 5×10⁻⁵ to 2×10⁻⁴ m s⁻¹. The values were insensitive to small changes in melt temperature but decreased with increasing pressure above 250 Pa. Also, the rates of refining were seen to be influenced by the sulfur and oxygen activity in the melt. The evaporation and subsequent elimination of the impurities were mathematically modeled by extending previously published models beyond consideration only of evaporation of monomers to consideration of the evaporation of monomers and dimer compounds. The model showed that due to the contributions to the refining by evaporation of each of the metallic, oxide, or sulfide vapor species, arsenic and antimony exhibited a maximum in refining rates atP _{o 2} andP _{s 2} potentials corresponding to matte grades of about 55 pct copper, whereas lead showed a minimum at about the same matte grade, and bismuth showed a continuously decreasing rate of refining with increasing matte grade. The model was also used to simulate the refining behavior of copper matte melts. An example of a commercial-scale operation is given.     

The activities of sulfide and oxide components and the solubility of oxygen in copper-iron-sulfur-oxygen mattes at 1300 °C

The activities of iron and copper and the solubilities of oxygen in copper-iron-sulfur-oxygen mattes have been determined by equilibrating mattes with CO−CO₂−SO₂ gas mixtures of fixed partial pressures of oxygen and sulfur and equilibrating a small mass of platinum with the melt. Iron and copper transferred from the matte to form a platinum-iron-copper alloy in which the activities of iron and copper are the same as in the matte. The activities of iron and copper in the matte were then determined from knowledge of the activities of iron and copper in the system platinum-iron-copper. Sulfides ofW _Fe=0.1, 0.3, and 0.5 were studied, whereW _Fe=wt pct Fe/(wt pct Fe+wt pct Cu), and sulfur pressures of 0.005, 0.0158, and 0.025 atm and oxygen pressures of 3.16×10⁻¹⁰, 7.94×10⁻¹⁰, 2.00×10⁻⁹, and 3.16×10⁻⁹ were used. The activity of copper, which varied in the range 0.06 to 0.165, decreases with increasingp _{O 2} at constantW _Fe andp _{S 2} and decreases with increasingp _{S 2} at constantW _Fe and constantp _{O 2}. The activity of iron, which varied in the range 0.002 to 0.06, increases with increasingp _{O 2} at constantW _Fe andp _{S 2} and decreases with increasingp _{S 2} at constantW _Fe andp _{O 2}. The activities of the components Cu₂S, FeS, Cu₂O, FeO, and Fe₃O₄ were calculated from the activities of iron and copper, the partial pressures of oxygen and sulfur, and the approapriate equilibrium constants. The variations of the activities of these components with matte grade, oxygen pressure, and sulfur pressure are presented and discussed. Within the range of experimental conditions studied, the solubility of oxygen in the melts is given by wt pct O=2.59pO₂/0.225pS₂/−0.18 (1+9.0W _Fe)^1.86     

某含铜转炉渣回收铜浮选试验研究

某铜转炉渣中铜品位为2.78 %,铜元素主要以冰铜微珠的形式赋存于炉渣中,冰铜分布较为分散,嵌布粒度大小悬殊,不易单体解离.为了高效回收二次资源,针对该铜转炉渣的性质特点,进行了浮选试验研究.结果表明:在磨矿细度≤0.074 mm占80 %,酯-200作为捕收剂,粗选时间为9 min的条件下,采用“一粗-一精-一扫”浮选工艺,实验室闭路实验可获得铜品位和回收率分别为31.64 %和94.16 %的铜精矿.      

On the kinetics of oxidation of liquid copper and copper-sulfur alloys by carbon dioxide

The rates of transfer of oxygen between CO₂-CO gas mixtures and liquid copper and copper-sulfur alloys have been studied by a steady-state electrochemical technique. For sulfur-free stagnant copper, and under the conditions of the experiments, the rates are shown to be controlled by the diffusion of oxygen in the metal. The resulting diffusivities are in close accord with the bulk of the previous determinations. At high sulfur concentrations, the rate is found to be controlled by an interfacial reaction which is first order with respect to the pressure of CO₂ and inversely proportional to the sulfur concentration. The rate constant, in mole (at. pct)cm⁻² s⁻¹ atm⁻¹, is approximately 8 × 10⁻⁹ at 1146°C. Formerly a Graduate Student.     

The solubility of Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> in calcium ferrite slags at 1573 K

Continuous converting of copper matte based on calcium ferrite slag has many attractions for the copper smelting industry. However, a serious drawback is that this slag leads to shorter furnace campaigns because it is aggressive toward the magnesia-chromia refractories that form the furnace lining. As part of an investigation into the causes of this aggressiveness with a view to devising strategies to mitigate it, the solubility of Cr₂O₃ in calcium ferrite slag has been determined. The standard drop-quench experimental technique was employed at a temperature of 1573 K and a relatively high oxygen partial pressure of 3.7×10⁻⁴ atm, conditions similar to those used in continuous converting. It was found that approximately 2 wt pct of Cr₂O₃ can dissolve in calcium ferrite slag under these conditions. The Cr₂O₃ solubility was found to be unaffected by the Cu₂O content of the slag, but may decrease as CaO content decreases. The implications of these findings on the mechanism of attack of magnesia-chromia refractories by calcium ferrite slag are discussed.     

Surface and interfacial tension of the Ni-Fe-S,Ni-Cu-S,and fayalite slag systems

The surface tensions of the Ni-Fe-S system together with the Ni-Cu-S and fayalite-type slag systems were measured using the sessile drop technique. Drop images were obtained by X-ray radiography. For the Ni₃S₂-FeS pseudo-binary system, the surface tension of the matte increased with matte grade and showed a positive deviation from ideality with matte grade. This suggests that Ni₃S₂ dominates in the nickel matte system. The results also indicated that a fluctuation in the matte nickel content can alter the surface tension quite significantly. A ternary surface ten-sion plot of the Ni-Fe-S system showed that the addition of either Ni or S to the matte alters the surface tension. On the other hand, at a constant Ni:S ratio, the addition of iron has neg-ligible influence on the surface tension of the matte. The measured surface tension of the Ni-Cu-S system also showed a nonlinear relationship with the Cu₂S content in the matte. The surface tension decreased with Cu₂S content. The interfacial tension of the Ni-Fe-S and slag system was found to increase with increasing matte grade. The presence of MgO and A1₂O₃ in the slag did not affect the interfacial tension value.