Showing papers by "Peter C. Hayes published in 2010"

Phase Equilibria of “Cu2O”-“FeO”-CaO-MgO-Al2O3 Slags at PO2 of 10-8.5 atm in Equilibrium with Metallic Copper for a Copper Slag Cleaning Production

Abstract: Limited data are available on phase equilibria of the multicomponent slag system at the oxygen partial pressures used in the copper smelting, converting, and slag-cleaning processes. Recently, experimental procedures have been developed and have been applied successfully to characterize several complex industrial slags. The experimental procedures involve high-temperature equilibration on a substrate and quenching followed by electron probe X-ray microanalysis. This technique has been used to construct the liquidus for the “Cu2O”-“FeO”-SiO2-based slags with 2 wt pct of CaO, 0.5 wt pct of MgO, and 4.0 wt pct of Al2O3 at controlled oxygen partial pressures in equilibrium with metallic copper. The selected ranges of compositions and temperatures are directly relevant to the copper slag-cleaning processes. The new experimental equilibrium results are presented in the form of ternary sections and as a liquidus temperature vs Fe/SiO2 weight ratio diagram. The experimental results are compared with the FactSage thermodynamic model calculations.

Investigation of Liquidus Temperatures and Phase Equilibria of Copper Smelting Slags in the FeO-Fe2O3-SiO2-CaO-MgO-Al2O3 System at PO2 10−8 atm

Abstract: Copper concentrates and fluxes can contain variable levels of SiO2, CaO, and MgO in addition to main components Cu, Fe, and S. Metal recovery, slag tapping, and furnace wall integrity all are dependent on phase equilibria and other properties of the phases and are functions of slag composition and operational temperature. Optimal control of the slag chemistry in the copper smelting, therefore, is essential for high recovery and productivity; this, in turn, requires detailed knowledge of the slag phase equilibria. The present work provides new phase equilibrium experimental data in the FeO-Fe2O3-SiO2-CaO-MgO-Al2O3 system at oxygen partial pressure of 10−8 atm within the range of temperatures and compositions directly relevant to copper smelting. For the range of conditions relevant to the Kennecott Utah Copper (South Magna, UT) smelting furnace, it was confirmed experimentally that increasing concentrations of MgO or CaO resulted in significant decreases of the tridymite liquidus temperature and in changes in the position of the tridymite liquidus in the direction of higher silica concentration; in contrast, the spinel liquidus temperatures increase significantly with the increase of MgO or CaO. Olivine and clinopyroxene precipitates appeared at high MgO concentrations in the liquid slag. The liquidus temperature in the spinel primary phase field was expressed as a linear function of 1/(wt pctFe/wt pctSiO2), wt pctCaO, wt pctMgO, and wt pctAl2O3. The positions of each of the liquidus points (wt pctFe)/(wt pctSiO2) at a fixed temperatures in the tridymite primary phase field were expressed as linear functions of wt pctCaO, wt pctMgO, and wt pctAl2O3.

Stability Criteria for Product Microstructures Formed on Gaseous Reduction of Solid Metal Oxides

Abstract: A range of different solid oxide and metal product morphologies can be formed on gaseous reduction of metal oxides. These product morphologies have been shown in previous studies to be critical in determining the rate limiting reaction mechanisms and the overall rates of reduction. By considering (1) established criteria for the stability of moving interfaces in a thermodynamic potential gradient, (2) the relative rates of chemical reactions on the oxide and metal surfaces, and (3) key process phenomena and physico-chemical properties of the solid phases, the conditions for the formation of various product morphologies are identified. The analysis also demonstrates the theoretical basis for the development of morphology maps that define the product morphologies as a function of thermodynamic driving force for reaction and reaction temperature. The methodology is shown to be general and can be applied to the analysis of any system involving the decomposition of metal compounds in reactive gas atmospheres.

Phase Equilibria Studies in the System ZnO- FeO -Al2O3-CaO-SiO2 Relevant to Imperial Smelting Furnace Slags: Part I

Abstract: The phase equilibria and the liquidus temperatures in the system ZnO-“FeO”-Al2O3-CaO-SiO2 have been determined experimentally in equilibrium with metallic iron. Specifically, the effects of Al2O3 concentrations in Imperial Smelting Furnace slags are identified, and the results are presented in the form of pseudo-ternary sections ZnO-“FeO”-(Al2O3 + CaO + SiO2) in which CaO/SiO2 = 0.93 and (CaO + SiO2)/Al2O3 = 5.0 and 3.5, respectively. It was found that, in the presence of Al2O3, the spinel phase is formed, the spinel primary phase field expands, and the wustite and melilite primary phase fields are reduced in size with an increasing Al2O3 concentration. The implications of the findings to industrial practice are discussed.

Effects of Oxidation on the Microstructure and Reduction of Chromite Pellets

Abstract: Fine chromite ore can be made into pellets in preparation of feed material for use in submerged arc ferrochromium smelting. During the pelletising process the charge is subjected to a range of temperature and gas conditions. The aim of the study was to determine whether changes to pelletising practice that could improve pellet reducibility in the smelting furnace. To this end a series of experiments have been undertaken to determine the effects of preoxidation of chromite pellets in air on the product microstructure, and on the subsequent of rates and extent of reduction in CO gas. The principal findings of this research are The rates of preoxidation of the chromite spinel M3O4 to M2O3 phase increase with increasing temperature. The rates of reduction of the pellets below 1200oC are enhanced by the oxidation to M2O3. Low temperature reduction to form iron metal in addition reduces the effective particle size of the chromite grains with the potential to enhance the subsequent rates of dissolution in the slag. The rates of reduction above 1200oC are not influenced by preoxidation since above this temperature M2O3 is rapidly reduced back to spinel, and no advantage in preoxidation to reduction kinetics is obtained. The results indicate that optimum reduction and dissolution of the chromite in submerged arc smelting may be achieved by enhancing preoxidation of the pellets during pelletising to maximise M2O3 formation.

Phase chemistry of lead smelting slags

Abstract: Recent advances in understanding of the phase chemistry and phase equilibria in primary lead smelting slags are presented. The slag chemistry in primary lead smelting slags, as described by the system ZnO-FeO-Fe O-PbO-CaO-SiO, is systematically examined and presented so as to reflect the various process conditions encountered at different stages of the smelting operation, from sintering and direct smelting to zinc fuming. The commentary is illustrated with examples from both experimental and thermodynamic modelling studies. These fundamental studies have been used to assist in process developments and improvements, and have the advantage that they are applicable to a range of process technologies.

Research on indium and germanium distributions between lead bullion and slag at selected process conditions

Abstract: The recovery of indium and germanium during lead metal extraction processes has the potential to add value to existing pyrometallurgical operations. Few experimental data are available that describe the partitioning of these species between major phases at the industrial process conditions. In addition, the bulk chemical analysis techniques used in previous studies have limited accuracy since the solid phases and their proportions in slag are not identified. A novel methodology was developed for the high temperature equilibration and quenching technique where the composition of the quenched liquid slag phase was analysed by Electron Probe X-Ray microanalysis (EPMA) and the metallic lead phase by Inductively Coupled Plasma (ICP). The improved methodology developed in the present study provides the opportunity to resolve differences between the data presented in the literature, and accurate description of the systems. Results of the study show that at the selected experimental conditions, indium is predominantly present in the slag as In , and germanium as Ge . Germanium partitions preferentially to the slag phase between PO of 10 to 10 atm. Indium partitions preferentially to the metal under low PO and to the slag at high PO . Additions of copper, arsenic or antimony at levels below 5 wt% in the lead metal phase do not affect the partitions of indium or germanium. Increasing the temperature from 1150 °C to 1300 °C increases the partition of indium. At the experimental temperatures in the range of 1200 °C to 1150 °C no significant change in the partition ratio of germanium was observed.

Lead Smelter Survey

Abstract: Continuing the series of periodic surveys, a global rundown of primary and secondary lead production and refining is presented. The aim is to provide information on technology and production trends for the benefit of all involved in the industry. Recent changes in the global lead industry include closure of several two-stage production processes (sintering and lead shaft furnaces or Imperial Smelting Furnaces), mainly in the Western world. New producers can treat secondary materials from the more and more dominating lead-acid battery scrap sector; this compensates for the loss of primary production in the Western world. Production in Asia has grown very fast and so the world production has grown to 8.5 Mt/y in 2008. However the impact of the recent global financial crisis may bring some changes. Summaries of production statistics and technologies used will help the lead industry to benchmark its operations.

Slag phase equilibria and viscosities in ferronickel smelting slags

Abstract: The properties of the slag phase are critical to the smooth operation of ferronickel smelting operations. Phase equilibria studies have been carried out on the "FeO"-SiO2-MgO-Al2O3 system in equilibrium with iron in the range of compositions and temperatures directly relevant to the nickel laterite ores. The results of recent studies on liquidus temperatures and primary phase fields in the range 1500 -1650oC have been incorporated in FactSage databases, and the updated databases have been used to develop a fundamentally-based, quasichemical slag viscosity model capable of predicting the effects of changing temperature and slag composition at liquid and sub-liquid conditions over a wide range of compositions. The results of the model predictions of phase equilibria and viscosities are presented in the form of pseudo-binary sections. The study demonstrates the value of model predictions in identifying trends and the sensitivities of the system to changes in bulk composition and temperature. In particular the influence of the extensive solid solutions in the olivine (Mg,Fe)2SiO4 primary phase field on subliquidus equilibria, and the effects of alumina on phase equilibria and slag viscosities.

Microstructures and softening behaviours of lead sinters and their correlation to sintering temperatures in Mount Isa lead smelter

Abstract: Temperature profiles in the lead smelter sinter bed at Xstrata Zinc Mount Isa sinter plant have been measured using a wireless temperature probe. Corresponding sinter samples have been collected for characterisation. The sinter peak bed temperatures were found to be in the range of 1000-1200°C. Microstructures and softening temperatures of these sinters have been characterised. Strong correlations have been observed between peak bed temperature and peak hood temperature, and between mean sinter softening temperature and peak bed temperature. It was found that higher peak bed temperature results in higher sinter softening temperature. For the feed material used in the trials, to obtain sinters with mean softening temperatures above 1050°C, peak bed temperatures above 1130°C are required. There appears to be a direct correlation between granule size distribution in the feed and peak bed temperature attained. High peak bed temperatures are observed in sinters with narrow granule size distribution. © 2010 Maney Publishing.

Phase equilibria studies in zinc-containing systems and applications to lead and zinc blast furnace slags

Abstract: Phase equilibria studies have been experimentally carried out in the ZnO-"FeO"-AlO-CaO-SiO-MgO system in equilibrium with metallic iron using high temperature equilibration, quenching and electron probe X-ray microanalysis techniques Wustite (Fe,Zn)O and spinel (Fe,Zn)O·(Al,Fe)O are the major phases in the composition range investigated The effects of AlO and CaO/SiO ratio on the stabilities of the wustite and spinel phases, and the liquidus temperatures have been systematically investigated in the composition range relevant to lead and zinc blast furnace slags Partitioning of ZnO has been determined between liquid and solid phases Applications of the results to the prediction of liquidus temperature and proportion of the solid phase are discussed for lead and zinc blast furnace slags