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.     

Trace element distributions between matte and slag in direct nickel matte smelting

ABSTRACT

Behaviour of trace elements in the nickel matte smelting was studied at 1673 K (1400°C) by equilibration-quenching techniques followed by direct phase analyses using electron probe X-ray microanalysis and laser ablation-inductively coupled plasma-mass spectrometry. The matte-slag samples at silica saturation were equilibrated with SO₂-CO-CO₂-Ar mixtures of fixed p_SO2, p_S2 and p_O2 in order to obtain a pre-determined oxidation degree for the sulphide matte, and thus to generate a targeted iron concentration of the nickel-copper–iron sulphide matte (Ni:Cu = 5, w/w), depending on the slag chemistry. The slag composition was varied from 0 to 2 wt-% K₂O and 0–10 wt-% MgO in silica saturation. The studied trace elements were Co, Ge, Pb, Se and Sn, but also the matte-to-slag distributions of the slag forming fluxing components Mg (MgO) and Si (SiO₂) were determined experimentally. Selenium was the only trace element studied which strongly enriched in the low-iron nickel mattes, and the deportment became larger when the sulphide matte depleted with iron. All the other trace elements behaved in the opposite way.     

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.     

当今最先进的镍冶炼技术——奥托昆普直接镍熔炼工艺

对近十几年的奥托昆普直接镍熔炼（DON-Direct Outokumpu Nickel）方法的作业经验（包括对环境的显著影响）进行了回顾。在DON工艺中,闪速熔炼炉中直接产出含铁低的高品位冰镍,不需要进一步吹炼。熔炼炉渣中的有价金属在电炉中以含铁冰镍回收。DON炉中产出的低熔点高品位冰镍（尤其是那些含铜低的）,对炉子设计提出了挑战,特别是对炉膛和热工的设计。参考产出的冰镍,对DON工艺、电炉冰镍及高氧化镁炉渣的热力学模型的选择结果进行了总结,对闪速炉和电炉的设计原则也进行讨论。     

Properties of Na2O–SiO2 slags in Doré smelting

Solubilities of metals in sodium silicate slags have been studied at 1000–1300°C in oxygen pressures of P(O₂) = 10^?4 to 0.5 atm, in Doré alloy smelting of copper anode slimes. The boundary conditions for the slags were silica saturation, magnesia saturation with about 10 wt% and without BaO. The trace elements studied were copper, gold, palladium, rhodium, and tellurium. The analytical methods used in the phase composition analyses of equilibrated samples, quenched in brine, were electron probe X-ray microanalysis and laser ablation-inductively coupled plasma-mass spectrometry. Thermodynamic features of the slags, trace element solubilities with the given constraints, and their oxidation mechanisms were determined. The data allow optimizing the anode slime-smelting for the metals’ maximum recovery in sodium silicate fluxing.     

Metal loss to slag: Part II. oxidic dissolution of nickel in fayalite slag and thermodynamics of continuous converting of nickel-copper matte

FeO-Fe₂O₃-SiO₂ slags were equilibrated in pure nickel crucibles under a CO-CO₂ atmosphere. The Fe/SiO₂ ratios in the slag were fixed at 1.51 and 1.97 at temperatures of 1200 and 1300°C. The CO₂/CO ratios were varied up to values corresponding to magnetite saturation. On the basis of solubility data obtained, a computer model was developed to predict the solubilities of nickel and copper in slag during the continuous converting of nickel-copper matte. These are given as a function of five parameters: temperature, iron content and Cu/Ni ratio in the matte, partial pressure of SO₂ in the gas phase, and magnetite activity in the slag. The model is helpful in comprehending converting reactions and of practical applicability in optimizing the conventional as well as continuous converting processes. Noranda Research Centre, Pointe Claire, Quebec.     

Precious Metal Distributions in Direct Nickel Matte Smelting with Low-Cu Mattes

Base metal (Cu, Fe, and Ni) and trace element (Ag, Au, Co, Pd, and Pt) distributions between low-iron nickel mattes with [Ni]:[Cu] = 4 (w/w) have been studied at 1623 K to 1723 K (1350 °C to 1450 °C). We equilibrated small slag–matte samples with CO–CO₂–SO₂–Ar atmospheres in pre-selected \( P_{{{\text{S}}_{2} }} \)–\( P_{{{\text{O}}_{2} }} \) points, maintaining silica saturation by fused silica crucibles. The slags studied contained about 0 to 8.5 wt pct MgO. The matte–slag distribution coefficients L ^m/s[Me] were obtained from assays by electron probe X-ray microanalysis for the matte and by laser ablation-ICP-mass spectrometry for the slag. The measured L ^m/s[Me] values were clearly dependent on iron concentration of the matte and on MgO concentration of the slag, with values on the order of 10⁴, 10⁵, and 10⁴ for gold, platinum, and palladium, respectively, in the 5 wt pct iron in matte experiments. The obtained data for silver were scattered, due to volatilization, resulting in depletion of most silver and its escape from matte to gas phase during the 3-hour equilibration period. The matte-to-slag distribution coefficient for silver was estimated to be L ^m/s[Ag] = 100 to 400. We also measured the distributions of the base metals Cu and Ni in the same conditions as the trace elements.     

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.     

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.     

Activities of CoS and FeS in copper mattes and the behavior of cobalt in copper smelting

The distributions of cobalt and iron between metallic copper and high copper mattes were measured at 1400 and 1500 K. A value of 0.40 ±0.02 was found as the Raoultian activity coefficient of CoS at infinite dilution in the Cu₂S-FeS-CoS mattes. The present activities of FeS in the Cu-saturated Cu₂S-FeS mattes were found to deviate more positively than those reported by Krivsky and Schuhmann at 1623 K, and the positive deviation from the Temkin’s ideality was greater at 1400 K than at 1500 K. Using the activity coefficient of CoS, the partitions of cobalt between copper mattes and fayalitic slags were calculated for various conditions of copper smelting. It was found that cobalt exhibits, in the matte-slag equilibria, chemical properties intermediate between nickel and iron, but much closer to iron than to nickel. The overall recovery of cobalt in blister copper depends on matte grade, and is as low as 3 pct at best. When a high cobalt recovery is desired, therefore, a copper concentrate rich in cobalt must not be processed by conventional pyrometallurgical technology in view of the inevitably high loss to slag. M. NAGAMORI, formerly Associate Professor, Department of Metallurgical Engineering, University of Utah, Salt Lake City, Utah.     

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%).     

Copper losses and thermodynamic considerations in copper smelting

A relationship between copper in slag and copper in matte during copper sulfide smelting has been derived using industrial data from 42 plants employing blast furnaces, reverberatory furnaces, flash furnaces, and Mitsubishi smelting furnaces together with the available thermodynamic equilibrium data for Cu-Fe-S-O, FeO-SiO₂, and Cu-Fe-S systems and laboratory slag-matte equilibrium information. A copper smelting diagram showing oxygen potential; sulfur potential; and copper, magnetite, and sulfur contents in slag during the smelting of different grades of copper mattes is developed for mattes containing less than 70 pct copper. The data presented can be used to determine the entrained copper losses in slag. Further, by combining the calculated value of the entrained matte with the corresponding plant data for the sulfur content of the slag, it is possible to derive the dissolved sulfur content of the slag. These calculated values were in excellent agreement with the experimentally determined sulfide capacity of fayalite slags. It is shown that there is no need to assume the presence of dissolved copper sulfide species in industrial slags. The existing equilibrium data that relate the copper content of slags to oxygen potential adequately describe the copper losses in industrial slags.     

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.     

The slag-metal equilibrium in tin smelting

An equilibrium study was undertaken to investigate the effect of the CaO/SiO₂ and Fe/SiO₂ ratios and the SnO and Al₂O₃ contents of slags on the distribution of Fe and Sn between slag and metal in tin smelting. The experiments were performed at 1200 °C by equilibrating Sn-Fe alloys with silicate slags under reducing conditions in closed crucibles. The slag and metal analyses were used to calculate the γ_SnO/γ_FeO ratio in the slags and a multiple-linear regression on these values indicated that, in the range of slag compositions investigated, γ_SnO/γ_FeO is a function only of the CaO/SiO₂ ratio. At 1200 °C, γ_SnO/γ_FeO varies from about 1.1 for CaO-free slags to 3.6 for slags in which the CaO/SiO₂ ratio is 1.0. In practical applications, the slag-metal equilibrium in tin smelting is usually discussed in terms of the variation of the distribution coefficient,k, with the Fe content of the metal, wherek is defined ask = [pct Sn]/[pct Fe] · (pct Fe)/(pct Sn). An equation fork was derived in terms of the atom fraction of iron in the metal, the γ_SnO/γ_FeO in the slag, and the temperature. This equation was used to construct graphs ofk as a function of the iron content over the slag compositions and at temperatures which cover the range of tin smelting practice.     

Distribution of nickel between copper-nickel and alumina saturated iron silicate slags

The solubility of nickel in slag was determined by equilibrating copper-nickel alloys with alumina-saturated iron silicate slags in an alumina crucible at 1573 K. The experiments were carried out under controlled oxygen partial pressures in the range of 10^-10 to 10^-8 atm by use of suitable CO-CO₂ gas mixtures, and at Fe/SiO₂ ratio 1.34. The results showed that nickel dissolves in slag both as Ni²⁺ (nickel oxide) and Ni‡ (nickel metal), and the relation obtained was: (Wt pct Ni in slag) = (ie33-01) The activity coefficient of nickel oxide (γ^dgNio) and distribution coefficient of nickel (A_Ni) is calculated to be 0.375 and 233.3, respectively. γ^dgNio and A_Ni are found to be independent of oxygen partial pressures. The presence of alumina increases the solubility of nickel in slags.     

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.     

Smelting Oxidation Desulfurization of Copper Slags

 According to the mechanism of sulfur removal easily through oxidation, the process of smelting oxidation desulfurization of copper slags is studied, which supplies a new thinking for obtaining the molten iron of lower sulfur content by smelting reduction of copper slags. Special attention is given to the effects of the holding temperature, the holding time and CaF2, CaO addition amounts on the desulfurization rate of copper slags. The results indicate that the rate of copper slags smelting oxidation desulfurization depends on the matte mass transfer rate through the slag phase. After the oxidation treatment, sulfur of copper slags can be removed as SO2 efficiently. Amount of Ca2+ of copper slags affects the desulfurization rate greatly, and the slag desulfurization rate is reduced by adding a certain amount of CaF2 and CaO. Compared with CaF2, CaO is negative to slags sulfur removal with equal Ca2+ addition. Under the air flow of 0. 3 L/min, the sulfur content of copper slags can be reduced to 0. 00467% in the condition of the holding time of 3 min and the holding temperature of 1500 ℃. The sulfur content of molten iron is reduced to 0. 0008% in the smelting reduction of treated slags, and the problem of high sulfur content of molten iron obtained by smelting reduction with copper slag has been successively solved.     

Thermodynamic simulation model of the isasmelt process for copper matte

A computer model has been constructed to simulate thermodynamically the behavior of the minor elements Zn, Pb, As, Sb, and Bi as well as the major elements Cu, Fe, Si, O, and S in the Isasmelt process, producing copper matte. The model is based on the new concept that there are two independent reaction sites in a slag bath: one for fast oxidation and the other for slow reduction. The oxidizing reaction at the first site produces matte, magnetite-rich slag and gas from chalcopyritic concentrate and siliceous flux. The slag is then partially reduced with lump coal at a site removed from the first site. The oxidizing and reducing reactions are assumed to proceed under a separate set of equilibrium conditions. The process heat balance and thermodynamic distribution of the minor elements are united and expressed as functions of varying weights and compositions of concentrate, flux (silica, limestone), coal, oil, and oxygen-enriched air. The process chemistry was analyzed in terms of Fe₃O₄, FeO, and FeS activities, as well as SO₂ partial pressure. The thermodynamic model explains well the minor element distributions observed in the 15 tons per hour pilot furnace, and it is used to project the optimal smelting conditions for the full-scale 100 tons per hour Isasmelt furnace.     

The Viscous Behavior of FeO<Subscript>t</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> Copper Smelting Slags

Understanding the viscous behavior of copper smelting slags is essential in increasing the process efficiency and obtaining the discrete separation between the matte and the slag. The viscosity of the FeO_t-SiO₂-Al₂O₃ copper smelting slags was measured in the current study using the rotating spindle method. The viscosity at a fixed Al₂O₃ concentration decreased with increasing Fe/SiO₂ ratio because of the depolymerization of the molten slag by the network-modifying free oxygen ions (O²⁻) supplied by FeO. The Fourier transform infrared (FTIR) analyses of the slag samples with increasing Fe/SiO₂ ratio revealed that the amount of large silicate sheets decreased, whereas the amount of simpler silicate structures increased. Al₂O₃ additions to the ternary FeO_t-SiO₂-Al₂O₃ slag system at a fixed Fe/SiO₂ ratio showed a characteristic V-shaped pattern, where initial additions decreased the viscosity, reached a minimum, and increased subsequently with higher Al₂O₃ content. The effect of Al₂O₃ was considered to be related to the amphoteric behavior of Al₂O₃, where Al₂O₃ initially behaves as a basic oxide and changes to an acidic oxide with variation in slag composition. Furthermore, Al₂O₃ additions also resulted in the high temperature phase change between fayalite/hercynite and the modification of the liquidus temperature with Al₂O₃ additions affecting the viscosity of the copper smelting slag.