The behavior of selenium and tellurium in metal-matte systems

The distribution of selenium and tellurium between molten metal and matte was determined at temperatures of 1100° to 1250°C. The experimental technique permitted separate sampling of each phase while at temperature. Partition coefficients (ratio of weight percent selenium or tellurium in the matte to weight percent selenium or tellurium in the metal) varied from 10.5 to 16.9 for selenium and 5.5 to 8.1 for tellurium. The coefficients decreased with increasing temperature but were essentially independent of impurity concentration, iron content and oxygen and SO₂ partial pressures over the ranges studied. Application of these results to actual operations is discussed. The similarities in the chemical behavior of S, Se, and Te during smelting are also considered.     

Thermodynamics of Copper Matte Converting: Part II. Distribution of Au,Ag, Pb,Zn, Ni,Se, Te,Bi, Sb and As Between Copper,Matte and Slag in the Noranda Process

The solubility of minor elements in fayalitic slags was assessed thermodynamically assuming exclusively oxidic dissolution for Pb, Zn and Ni, metallic dissolution for Au and Ag, molecular and monatomic dissolution for Se and Te, and monatomic dissolution for Bi, Sb and As. Based on these assumptions as well as the thermochemical data in the literature, an analytical method was developed to calculate the distribution equilibria of minor elements between copper, matte and slag phases. As an example of the application, the method was demonstrated for the analysis of behavior of minor elements in the Noranda Process producing metallic copper or high grade matte. The distribution of minor elements was expressed in terms of concentration ratios of an element for copper/matte, copper/slag and matte/slag phases. Using the concentration ratios and also formulae compensating for mechanical suspension, apparent distribution coefficients of the minor elements in the actual process were calculated as a function of the process parameters: temperature, partial pressure of SO₂, magnetite activity and matte grade. An excellent agreement was observed between the calculated and observed data, thus providing logical basis for interpreting operating data of the Noranda Process. The behavior of minor elements under various operating conditions can also be predicted by the present model.     

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.     

Effects of O,Se, and Te on the rate of nitrogen dissolution in molten iron

The effects of oxygen, selenium, and tellurium on the rate of nitrogen dissolution into molten iron have been investigated at 1973 K using an isotope-exchange reaction and the results are summarized as follows. The rate constant of nitrogen dissolution measured at lower oxygen concentration ([mass pct O] < 0.015) is larger than previously reported ones under an atmospheric pressure and agrees well with the value from desorption rate under reduced pressures. Selenium and tellurium retard the nitrogen dissolution into liquid iron more significantly than oxygen, and the degree of the retarding effect is in the order of tellurium, selenium, and oxygen. The adsorption coefficients are calculated to be K_O = 144, K_Se = 1120, and K_Te = 1640 with respect to [1 mass pct solute] from present results. A model that surface active elements and nitrogen are adsorbed on the same site at the interface and the dissociation reaction of nitrogen molecule on the site represented by the equation is the rate-determining step reasonably expresses the retarding effect of the surface active elements on the reaction rate on the assumption that all sites at the metal surface have a uniform adsorption energy for each solute.     

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     

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.     

Thermodynamics of copper matte converting: Part IV. A priori predictions of the behavior of Au,Ag, Pb,Zn, Ni,Se, Te,Bi, Sb,and As in the noranda process reactor

The general formulae are derived which allow calculation of the weight of each molten phase (copper, matte, slag) in the Noranda Process reactor as a function of matte grade and suspension indices. These expressions and the volatilization constants are then inserted in the steady-state volatilization equation (derived in the Part III) to calculate the overall distribution of minor elements and their concentrations in all the reactor productsi.e., copper, matte, slag, and offgas) in the Noranda Process. The overall distribution of ten minor elements can be predicted for any set of controllable process parameters such as feed composition, temperature, degree of oxygen enrichment, slag composition (or magnetite activity), and matte grade. The computer predictions are in good agreement with the commercially observed values with the exception of selenium. Formerly Associate Professor, Department of Metallurgical Engineering, University of Utah, Salt Lake City, UT.     

Phase equilibrium and minor-element distribution between Ni3S2-FeS matte and calcium ferrite slag under high partial pressures of SO2

Calcium ferrite slag has been successfully used in the copper smelting process, but no attempt has been made to use it in the nickel smelting process. The phase equilibrium and the distribution of minor elements between the Ni₃S₂-FeS matte and the CaO-FeO_x-based slag (containing about 2 wt pct MgO) in a magnesia crucible were investigated at 1523 K under controlled partial pressures of S₂, O₂, and SO₂ of 10.1, 50.7, and 101.3 kPa, respectively. The results were compared with those for the iron-silicate-based slag, and the following conclusions were obtained: (1) there is no significant difference in the solubility of nickel between both slags in the high-matte-grade range, (2) the dissolution of cobalt in the calcium ferrite slag is clearly smaller than that in the iron silicate slag, (3) detrimental arsenic, antimony, and bismuth are preferentially collected and fixed in the calcium ferrite slag rather than in the iron silicate slag, and (4) it is considered, with regard to technical feasibility, that the use of the calcium ferrite slag in a converting process of the Bessemer matte will have a prominent future for the nickel converting stage.     

Influence of Partial Pressure of Sulfur and Oxygen on Distribution of Fe and Mn between Liquid Fe-Mn Oxysulfide and Molten Slag

The authors proposed an innovative process for recovering Mn from steelmaking slag. The process starts with the sulfurization of steelmaking slag to separate P from Mn by the formation of a liquid sulfide phase (matte). Then, the obtained matte is weakly oxidized to make a Mn-rich oxide phase without P. High-purity Fe-Mn alloys can therefore be produced by the reduction of the Mn-rich oxide phase. However, to the authors?? knowledge, the sulfurization of molten slag containing P and Mn has not been sufficiently investigated. It was recently found that P was not distributed to the matte in equilibrium with the molten slag. To gain knowledge of the process??s development, it is important to investigate the influence of the partial pressures of sulfur and oxygen on the equilibrium distribution of Mn and Fe between the matte and the molten slag. In the current work, a mineralogical microstructure analysis of the matte revealed that the existence of the oxysulfide and metal phases was dependent on the partial pressure of sulfur and oxygen. The Mn content of the matte increased with partial pressure of sulfur while the O content of the matte decreased. In contrast, the ratio of Mn/Fe in the matte was constant when the metal phase of the matte was observed at a log $ P_{{{\text{O}}_{2} }} $ below ?11. These results also corresponded to the relationship between the activity coefficient ratio of MnS/FeS and the mole fraction of MnS/FeS in the matte. The ?? _MnS/?? _FeS value decreased exponentially as the mole fraction of MnS/FeS increased.     

Thermodynamic prediction of melting of copper-electrolyte slime

Balance calculations of multicomponent equilibrium compositions in the gas–liquid–solid system under oxidizing smelting of the copper-free copper-electrolyte slime, during which sulfur, selenium, and tellurium dioxides transfer into the gas phase, while compounds of lead, copper, antimony, iron, and aluminum are concentrated in the composition of the silicate slag, are performed with the help of the Outotec’s Chemical Reaction and Equilibrium Software HSC Chemistry program. It is established that, under optimal conditions of oxidizing smelting of the charge (100 kg) of the electrolyte slime (O₂ ≈ 0.9 kg, SiO₂ ≥ 6%, CaO ~ 3%, t = 1200°C), lead, antimony, and arsenic almost completely transfer into the silicate slag, while copper and silver (above 91%) transfer into the matte. Selenium is distributed between the gas phase (49.8%), matte (24.1%), and metallic phase (26.1%), while tellurium is distributed between sublimates (14.4%), silicate slag (8.4%), and matte (77.2%).     

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.     

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.     

Effect of Slag Basicity on Phase Equilibria and Selenium and Tellurium Distribution in Magnesia-Saturated Calcium Iron Silicate Slags

New measurements have been made on the phase equilibria of magnesia-saturated CaO-FeO_x-SiO₂ slags at 1573 K (1300 °C) and an oxygen partial pressure of 10⁻⁹ atm. The thermodynamic behavior of selenium (Se) and tellurium (Te) in the slag and the stability of oxide mineral phases within the slag were examined as a function of slag composition. The measured equilibrium distribution of Se and Te between the slag and the copper showed nonlinear dependence on the slag basicity, reaching maxima at CaO/(CaO + SiO₂) ratios of about 0.2 and 1 and a minimum at a ratio of about 0.5. The solubility of the copper oxide in the bulk slag also passed through a minimum value at a ratio of about 0.5. Results from drop-quench experiments confirmed the stability of various oxide solid solution phases at 1573 K (1300 °C) that had virtually no solubility for Se and Te. The deduced capacity of the liquid slag for Se was found to be independent of basicity in relatively basic slags, and decreased sharply as SiO₂ replaced CaO in relatively acidic slags.     

Phase equilibrium and distribution of minor elements between Ni-S melt and Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-CaO-MgO Slag at 1873 K

Distribution of nickel and minor elements such as Au, Ag, Fe, Co, Cu, As, and Sb between the Ni-S alloy and the CaO-Al₂O₃ based slag phases in a magnesia crucible was studied at 1873 K. Partial pressure of SO₂ was controlled at 10.1 kPa, while partial pressures of O₂ and S₂ ranged between the point of NiO precipitation (po₂ of 10.1 Pa) and the point at which Ni₃S₂ is formed (ps₂ of 4.0 kPa). The nickel content in the slag and the sulfur and oxygen contents in the metal at a given po₂ or pso₂ decrease when the temperature is increased from 1773 to 1873 K. The distribution ratios of iron, cobalt, and copper, defined by (wt pct X in slag)/{wt pct X in alloy}, where X is the minor element in the slag, have larger values than that of nickel, while the values of Au, Ag, Sb, and As are lower than that of nickel. The distribution behavior of nickel and minor elements is discussed based on the concept of oxidic and sulfidic dissolution.     

Thermodynamic Modeling of Arsenic in Copper Smelting Processes

Published data on the activity coefficients of arsenic in liquid copper, matte and, slag have been reviewed, assessed, and used in the development of thermodynamic databases for solution models of melts. The databases were validated against the literature data on the equilibrium distribution of arsenic between the matte and the slag. The models and databases were used in investigating the effects of matte grade, slag chemistry, SO₂ partial pressure, arsenic loading, and temperature on the equilibrium distribution of arsenic between the melts and gas phase during copper smelting and converting. The results obtained show that the continuous smelting processes operates close to equilibrium between condensed phases with most arsenic reporting to the gas phase. A comparison of the batch and continuous converting processes showed a considerable difference with respect to the elimination of the arsenic from condensed phases. These results indicate batch processes to be more efficient in the removal of arsenic through the gas stream.     

Thermodynamic modeling of lead distribution among matte, slag, and liquid copper

Recently, a thermodynamic database was developed for the calculation of equilibria involved in the production of copper. The present study is concerned with the further development of the thermodynamic models and the database of model parameters for the matte, slag, and blister copper phases with a view to including Pb in the database and permitting calculations in the seven-component system Pb-Cu-Ca-Fe-Si-O-S. Thermodynamic and phase equilibrium data available in the literature are reviewed, critically assessed, and optimized with the modified quasi-chemical model. When used with the Gibbs energy minimization software and other databases of the FACT thermodynamic computing system, the database developed in the present study can be used for the calculation of matte-slag-copper-gas phase equilibria during copper smelting and converting. The distribution of lead among these phases can be computed. For example, the distribution of lead among matte, silica-saturated slag, and copper has been calculated at metal saturation, or under fixed partial pressure of SO₂, and has been compared with the available experimental data. The Pb distributions among the equilibrium phases have been calculated under various conditions, which are difficult to study experimentally, such as at magnetite saturation or under various oxygen partial pressures and iron to silica ratios in the slag.     

Entrainment behavior of copper and copper matte in copper smelting operations

In copper smelting, the loss of copper to the slag due to entrainment is largely influenced by the flotation of copper metal and/or matte in the slag phase. To evaluate this behavior, the surface tension of copper as a function of temperature and oxygen pressure and the interfacial tension of the copper-iron matte-slag system as a function of matte grade were measured. From the surface and interfacial tension values, the spreading and flotation coefficients of the copper, matte, and slag system were calculated. Ternary interfacial energy diagrams were also con-structed using these data. It is shown that matte droplets containing higher than 32 mass pct Cu will not form a film on rising gas bubbles when they collide in the slag phase. However, matte droplets will attach to gas bubbles upon collision and thus can be floated over the entire range of matte composition. Spreading of copper on bubbles is not possible at oxygen pressures between 10⁻¹² and 10⁻⁸ atm. Flotation of copper by gas bubble in slag is possible at oxygen pressure higher than 10⁻⁹ atm. However, it is feasible for rising matte droplets (attached to rising bubble) to trap and float copper irrespective of the matte grade.     

Distribution equilibria and slag chemistry of DON smelting

Equilibrium fluxing chemistry and metal value distributions of nickel matte smelting in the one-step direct nickel matte technology have been determined experimentally at 1350–1450°C in MgO-bearing iron silicate slags at silica saturation. The aim was to approach the detailed smelting chemistry at typical concentrations 2.5–10?wt-% iron in MgO-bearing iron silicate slags at silica saturation by quenching and X-ray microanalysis. The results obtained under controlled P(O₂) and P(S₂) as well as constant P(SO₂)?=?0.1?atm show that copper and nickel solubilities in the slag as well as matte-to-slag distributions favour matte when the slag is modified by magnesia. At the same time, along with increasing magnesia content of the slag, its iron activity is affected by the dissolution of MgO in the slag, and iron concentration of the formed nickel matte is lowered considerably, and its sulphur concentration increased at constant oxygen and sulphur pressures of the gas phase.     

A thermodynamic database for copper smelting and converting

The thermodynamic properties of the slag, matte, and liquid copper phases in the Cu-Ca-Fe-Si-O-S system have been critically assessed and optimized over the ranges of compositions of importance to copper smelting/converting based on thermodynamic and phase equilibria information available in the literature and using the modified quasichemical model. A thermodynamic database has been developed, which can be used for the calculation of matte-slag-copper-gas phase equilibria of interest for the production of copper. The model reproduces within experimental error limits all available experimental data on phase diagrams, matte-alloy miscibility gap and tie-lines, enthalpies of mixing, and activities of Cu and S in the matte and liquid alloy. The calculated solubilities of Cu in both S-free slag and slag equilibrated with matte are also in good agreement with experiment under all studied conditions, such as at SiO₂ saturation, in equilibrium with Fe, Cu, or Cu-Au alloys, at fixed oxygen or SO₂ partial pressures and at different contents of CaO in the slag. Sulfide contents (sulfide capacities) of the slags are predicted within experimental error limits from the modified Reddy-Blander model, with no adjustable parameters. As an example of the application of the database, the stability field of matte/slag equilibrium is calculated, and the matte and slag compositions are plotted vs iron to silica ratio in the slag at various SO₂ pressures over this field. The matte-slag two-phase field is limited by the calculated lines corresponding to precipitation of copper, silica, and magnetite.     

A thermodynamic model of nickel smelting and direct high-grade nickel matte smelting processes: Part II. distribution behaviors of Ni, Cu, Co, Fe, As, Sb, and Bi

A thermodynamic model has been developed to predict the distribution behavior of Ni, Cu, Co, Fe, S, As, Sb, and Bi in nickel smelting and direct high-grade nickel matte smelting processes. The model has been validated by numerous experimental data and industrial data with a wide range of operating conditions. The effect of operating conditions on the distributions of Ni, Cu, Co, As, Sb, and Bi among the gas, matte, and slag phases has been investigated. It was found that the distribution behavior of Ni, Co, Cu, As, Sb, and Bi in the nickel smelting furnace depends on process parameters such as the smelting temperature, matte grade, oxygen enrichment, Fe/SiO₂ ratio in the slag, Cu/Ni ratio in charge, and oil/air ratio. The parameters also have an influence on the behavior of Fe₃O₄ in the slag.