The precipitation of hematite from ferric chloride media at atmospheric pressure

The precipitation of hematite from ferric chloride media at temperatures <100 °C and at ambient pressure was studied as part of a program to recover a marketable iron product from metallurgical processing streams or effluents. Hematite (Fe₂O₃) can be formed in preference to ferric oxyhydroxides (e.g., β-FeO·OH) at temperatures as low as 60 °C by controlling the precipitation conditions, especially seeding. The hematite product typically contains >66 pct Fe and <1 pct Cl, and its composition does not change appreciably on repeated recycling. The amount of product formed increases significantly with increasing FeCl₃ concentrations to ∼0.2 M FeCl₃, but nearly constant product yields are obtained thereafter; the precipitates consist only of hematite, provided that an adequate amount of seed is present. The contamination with Zn, Ca, and Na is <0.1 pct, even for high concentrations of dissolved ZnCl₂, CaCl₂, or NaCl. The extent of the precipitation reaction depends principally on the temperature and the free-acid concentration; accordingly, the controlled addition of a base allows the nearly complete elimination of the iron from metallurgical processing streams or effluents, as readily filterable Fe₂O₃.     

The tempering of iron-nitrogen martensite; Dilatometric and calorimetric analysis

The aging behavior of iron-nitrogen martensitic alloys (0.8 to 7.0 at. pct N) between -190 °C and 450 °C was investigated by quantitative analysis of the corresponding changes in volume and enthalpy. Martensitic specimens were prepared by gaseous nitriding of pure iron in a mixture of NH₃ and H₂ and subsequent quenching in brine and liquid nitrogen. Both X-ray diffraction analysis and metallography (light microscopical analysis and microhardness measurement) were used for interpretation of the structural changes. Analysis of the transformation kinetics was achieved by employing a range of heating rates. At least five different stages of structural change could be distinguished, which were quantitatively analyzed in terms of their effects on volume and enthalpy: (1) transformation of retained austenite into martensite (between-160 °C and -40 °C); (2) segregation and “ordering” of nitrogen atoms (below 100 °C); (3) precipitation of incoherent α′ nitride (between 100 °C and 220 °C); (4) conversion of α′ nitride into γ′ nitride (between 220 °C and 290 °C); and (5) decomposition of retained austenite (between 240 °C and 350 °C). Differences with the tempering behavior of analogous iron-carbon martensites were discussed.     

Experimental study of phase equilibria in the Al-Fe-Zn-O system in air

The phase equilibria in the Al-Fe-Zn-O system in the range 1250 °C to 1695 °C in air have been experimentally studied using equilibration and quenching techniques followed by electron probe X-ray microanalysis. The phase diagram of the binary Al₂O₃-ZnO system and isothermal sections of the Al₂O₃-“Fe₂O₃”-ZnO system at 1250 °C, 1400 °C, and 1550 °C have been constructed and reported for the first time. The extents of solid solutions in the corundum (Al,Fe)₂O₃, hematite (Fe,Al)₂O₃, Al₂O₃*Fe₂O₃ phase (Al,Fe)₂O₃, spinel (Al,Fe,Zn)O₄, and zincite (Al,Zn,Fe)O primary phase fields have been measured. Corundum, hematite, and Al₂O₃*Fe₂O₃ phases dissolve less than 1 mol pct zinc oxide. The limiting compositions of Al₂O₃*Fe₂O₃ phase measured in this study at 1400 °C are slightly nonstoichiometric, containing more Al₂O₃ then previously reported. Spinel forms an extensive solid solution in the Al₂O₃-“Fe₂O₃”-ZnO system in air with increasing temperature. Zincite was found to dissolve up to 7 mole pct of aluminum in the presence of iron at 1550 °C in air. A meta-stable Al₂O₃-rich phase of the approximate composition Al₈FeZnO_14+x was observed at all of the conditions investigated. Aluminum dissolved in the zincite in the presence of iron appears to suppress the transformation from a round to platelike morphology.     

Neodymium naphthenate-loaded organic phase stripping using sodium oxalate

Neodymium naphthenate-loaded organic phase stripping using sodium oxalate solution was studied to explore the feasibility of synchronous rare earth-loaded organic phase stripping, rare earth precipitation, and blank organic phase saponification. Experimental results show that loaded organic phase stripping, rare earth precipitation, and blank organic phase saponification can be realized simultaneously. When using 20% excess of sodium oxalate over the stoichiometry with the volume ratio of organic phase to aqueous phase of 1:1 at 25 °C for 40 min, the single stage stripping rate and saponification value are about 40% and 0.29 mol/L, respectively. After 16 stages of countercurrent continuous stripping, the stripping rate of neodymium can reach 99%, the saponification value is 0.42 mol/L, the Nd³⁺ concentration in saponified organic phase is less than 0.0020 mol/L, and the main phase in precipitation is Nd₂(C₂O₄)₃·10H₂O. Afterwards, this saponified organic phase can be used in the extraction of NdCl₃ solution, and then the loaded organic phases (neodymium naphthenate) with 0.16 mol/L Nd³⁺ can be retrieved. The morphology, particle size distribution, and composition of the Nd₂(C₂O₄)₃·10H₂O products are similar to those of the current direct precipitation products. The neodymium oxide prepared by continuous calcination of neodymium oxalate meets the national standard of China (GB/T 5240?2015). These results prove the feasibility of stripping neodymium naphthenate-loaded organic phase by using sodium oxalate solution. Sodium oxalate can serve as a stripping agent, a saponifier, and a precipitator, thereby simplifying rare earth extraction and separation. This study provides theoretical and technical support for the development of a novel method for rare earth extraction and separation.     

Effect of low concentrations of silica,alumina, lime,and lithia on the magnetic roasting of hematite

The conversion of hematite to magnetite was investigated in a mixture of H₂, H₂O, and N₂. In the temperature range of 500° to 700°C, the magnetic roast reaction gives a sigmoidal kinetic curve with a finite induction time. The induction time decreases with rise in temperature and increases in the presence of alkali and alkaline earth oxides. The magnetic roast reaction was also studied in the presence of low concentrations of silica (quartz structure) and alumina (5.0 and 4.3 wt pct, respectively, which correspond to 8.4 × 10^-4 g atom of Si or Al per gram mixture). The addition of SiO₂ to hematite decreases the induction time. At temperatures below 550°C, alumina increases the induction time; at higher temperatures it has about the same effect as silica. For pellets containing SiO₂, a maximum in the relative decrease in induction time, A, was observed at 578°C; for pellets containing A1₂O₃, there was a steady increase in A with increasing temperature. Because the α β quartz transition occurs at 575°C, the enhanced surface activity at 578°C in the presence of quartz is attributed to the Hedvall effect of solid-state chemistry. The induction period of the magnetic roast reaction was exceptionally prolonged in the presence of lithia. Mixing of hematite with silica, alumina, and lithia (8.4 × 10^-4 g atom, respectively, per gram mixture) was found to eliminate the beneficial effect of quartz by inhibiting its α β transformation.     

Phase equilibria in the system Fe-Zn-O at intermediate conditions between metallic-iron saturation and air

The phase equilibria in the FeO-Fe₂O₃-ZnO system have been experimentally investigated at oxygen partial pressures between metallic iron saturation and air using a specially developed quenching technique, followed by electron probe X-ray microanalysis (EPMA) and then wet chemistry for determination of ferrous and ferric iron concentrations. Gas mixtures of H₂, N₂, and CO₂ or CO and CO₂ controlled the atmosphere in the furnace. The determined metal cation ratios in phases at equilibrium were used for the construction of the 1200 °C isothermal section of the Fe-Zn-O system. The univariant equilibria between the gas phase, spinel, wustite, and zincite was found to be close to pO₂=1 · 10⁻⁸ atm at 1200 °C. The ferric and ferrous iron concentrations in zincite and spinel at equilibrium were also determined at temperatures from 1200 °C to 1400 °C at pO₂ = 1·10⁻⁶ atm and at 1200 °C at pO₂ values ranging from 1 · 10⁻⁴ to 1 · 10⁻⁸ atm. Implications of the phase equilibria in the Fe-Zn-O system for the formation of the platelike zincite, especially important for the Imperial Smelting Process (ISP), are discussed.     

Hematite formation from jarosite type compounds by hydrothermal conversion

Abstract

The hydrothermal conversion of K jarosite, Pb jarosite, Na jarosite, Na–Ag jarosite, AsO₄ containing Na jarosite and in situ formed K jarosite and Na jarosite to hematite was investigated. Potassium jarosite is the most stable jarosite species. Its conversion to hematite in the absence of Fe₂O₃ seed occurred only partially after 5 h reaction at >240°C. In the presence of Fe₂O₃ seed, the conversion to hematite was nearly complete within 2 h at 225°C and was complete at 240°C. The rate of K jarosite precipitation, in situ at 225°C in the presence of 50 g L^?1 Fe₂O₃ seed, is faster than its rate of hydrothermal conversion to hematite. In contrast, complete conversion of either Pb jarosite or Na–Pb jarosite to hematite and insoluble PbSO₄ occurs within 0·75 h at 225°C in the presence of 20 g L^?1 Fe₂O₃ seed. Dissolved Fe(SO₄)_1·5 either inhibits the conversion of Pb jarosite or forms Pb jarosite from any PbSO₄ generated. The hydrothermal conversion of Na–Ag jarosite to hematite was complete within 0·75 h at 225°C in the presence of 20 g L^?1 Fe₂O₃ seed. The Ag dissolved during hydrothermal conversion and reported to the final solution. However, the presence of sulphur or sulphide minerals caused the reprecipitation of the dissolved Ag. The conversion of AsO₄ containing Na jarosite at 225°C in the presence of 20 g L^?1 Fe₂O₃ seed was complete within 2 h, for H₂SO₄ concentrations <0·4M. Increasing AsO₄ contents in the Na jarosite resulted in a linear increase in the AsO₄ content of the hematite, and ～95% of the AsO₄ remained in the conversion product. Increasing temperatures and Fe₂O₃ seed additions significantly promote the hydrothermal conversion of in situ formed Na jarosite at 200–240°C. However, the conversion of previously synthesised Na jarosite seems to proceed to a greater degree than that of in situ formed Na jarosite.

On a examiné la conversion hydrothermale en hématite de la jarosite de K, de la jarosite de Pb, de la jarosite de Na, de la jarosite de Na-Ag, de la jarosite de Na contenant de l’AsO₄, et de la jarosite de K et de la jarosite de Na qui sont formées in situ. La jarosite de potassium est la plus stable des espèces de jarosite. Sa conversion en hématite ne se produisait que partiellement après 5 h de réaction à >240°C en l’absence d’amorce de Fe₂O₃. En présence d’amorce de Fe₂O₃, la conversion en hématite était presque complète à moins de 2 h à 225°C et était complète à 240°C. La vitesse de précipitation de la jarosite de K, in situ à 225°C en présence de 50 g L^?1 d’amorce de Fe₂O₃, est plus rapide que sa vitesse de conversion hydrothermale en hématite. Par contraste, la conversion complète soit de la jarosite de Pb ou de la jarosite de Na-Pb en hématite et en PbSO₄ insoluble se produit à moins de 0·75 h à 225°C en présence de 20 g L^?1 d’amorce de Fe₂O₃. Le Fe(SO₄)_1·5 dissous soit inhibe la conversion de la jarosite de Pb ou forme de la jarosite de Pb à partir de tout PbSO₄ produit. La conversion hydrothermale de la jarosite de Na-Ag en hématite était complète à moins de 0·75 h à 225°C en présence de 20 g L^?1 d’amorce de Fe₂O₃. L’Ag se dissolvait lors de la conversion hydrothermale et se rapportait dans la solution finale. Cependant, la présence de soufre ou de minéraux sulfurés avait pour résultat la re-précipitation de l’Ag dissous. La conversion de la jarosite de Na contenant de l’AsO₄ à 225°C en présence de 20 g L^?1 d’amorce de Fe₂O₃ était complète à moins de 2 h, avec des concentrations d’H₂SO₄ <0·4 M. L’augmentation de la teneur en AsO₄ de la jarosite de Na avait pour résultat une augmentation linéaire de la teneur en AsO₄ de l’hématite et ～95% de l’AsO₄ demeurait dans le produit de conversion. L’augmentation de la température et d’additions d’amorce de Fe₂O₃ favorisait significativement la conversion hydrothermale de la jarosite de Na qui est formée in situ à 220–240°C. Cependant, la conversion de la jarosite de Na synthétisée antérieurement semblait se produire à un plus grand degré que celle de la jarosite de Na qui est formée in situ.     

Aqueous oxidation of chalcopyrite in hydrochloric acid

The aqueous oxidation of chalcopyrite flotation concentrate is faster in HC1 than in H₂SO₄. Under certain conditions, FeCl₂ formed during reaction undergoes oxidation and hydrolysis (or vice versa) yielding α-Fe₂O₃ or β-FeOOH depending on the initial acidity, O₂ pressure, and temperature. A small fraction of sulfur oxidizes to soluble SO ₄ ^2- and a part precipitates as Fe(OH)SO₄. The precipitation of FeOOH is more enhanced in HC1 than in H₂SO₄ solution. Optimum leaching conditions are 110°C, 2010 kPaO₂, 2 N HC1, molar ratio CuFeS₂/HCl 0.8 to 0.9, and time of reaction 45 min. Under these conditions practically all the iron precipitates and the reaction can be described by the equations: CuFeS₂ + 2 HCl + 5/4 O₂ → CuCl₂ + FeOOH + 1/2H₂O + 2S and CuFeS₂ + HC1 + O₂ → CuCl + FeOOH + 2S. Copper ferrite, CuFe2O₄, precipitates if the final pH of the leach solution is ≥2.2, while CuCl precipitates if the initial acidity is increased to 3 N HC1.     

Diffusion-limited sulfidation of wustite

The sulfidation of wustite in H₂S−H₂O−H₂−Ar atmospheres has been studied at temperatures of 700, 800, and 900°C with thermogravimetric techniques. Polycrystalline wustite wafers were equilibrated in a flowing H₂O−H₂−Ar gas stream and then sulfidizedin situ. During an initial transient stage a protective layer of FeS formed on the sample, and an intermediate layer of Fe₃O₄ formed between the FeO and FeS layers. Subsequently, the reaction followed a parabolic rate law. The parabolic rate constant varied from 0.22×10⁻² mg² cm⁻⁴ min⁻¹ at 700°C to 6.5×10⁻² mg² cm⁻⁴ min⁻¹ at 900°C. The reaction rate was limited by the diffusion of iron through the intermediate Fe₃O₄ layer which grew concurrently with the FeS layer and at the expense of the FeO core. After the FeO core was completely converted to Fe₃O₄, the process entered a passive stage during which no further mass changes could be detected. SCOTT McCORMICK, formerly Graduate Student, Purdue University is currently Assistant Professor, Department of Metallurgical and Materials Engineering, Illinois Institute of Technology, Chicago, Illinois 60616.     

Phase transformations during heating of llmenite concentrates

llmenite concentrates were heated in argon and oxygen in the temperature range 700 °C to 1000 °C to study the behavior of the pseudorutile phase and other changes which occur. Pseudorutile does not persist in argon or oxygen in the temperature range studied. In argon at 700 °C, pseudorutile decomposes into hematite and rutile, while at 1000 °C, it combines with ilmenite to form ferrous-ferritic pseudobrookite solid solution. A new phase “Fe₂O₃-2TiO₂” was identified as an intermediate product during the heating of ilmenite or pseudorutile in oxygen. This compound decomposes into hematite and rutile below 800 °C and to pseudobrookite and rutile above 800 °C. The sequence of reactions during the heating of ilmenite and pseudorutile in oxygen is proposed. Formerly with the Department of Metallurgy, Imperial College of Science, Technology and Medicine, London. Formerly with the Department of Metallurgy, Imperial College of Science, Technology and Medicine, London.     

Transforming Hematite into Magnetite Using Mechanochemical Approach as a Pretreatment of Oolitic Hematite

Potential transformation of oolitic hematite into magnetite by mixing iron powder using the mechanochemical method has been achieved and discussed in this paper. The phase transition of pure hematite in the preliminary test was identified by X-ray diffractometer (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) techniques. The experimental results have shown that the crystallographic planes of magnetite, (220), (311), (400), and (511) were observed clearly in the Fe/α-Fe₂O₃ mixture after milling for 15 h, indicating that α-Fe₂O₃ had been effectively transformed into Fe₃O₄. The diffraction peaks of magnetite were also observed at d = 0.29605 nm (2θ = 30.163°), 0.25226 nm (2θ = 35.559°), 0.24156 nm (2θ = 37.190°), and 0.20898 nm (2θ = 43.458°) after 13 h milling-time. It suggests that the oolitic hematite is transformed into magnetite successfully by mechanochemical processing. The processing might be applied potentially for the magnetic separation of oolitic hematite.     

High-temperature phase relations and thermodynamics in the iron-titanium-oxygen system

Phase equilibria and thermodynamics in the FeO-TiO₂-Ti₂O₃ ternary system were studied at 1500 °C and 1600 °C. In particular, the liquid slag-phase region and its saturation boundary with respect to metallic iron, titania, and lower titanium oxides was investigated. The liquid slag-phase region extends substantially toward an anosovite (Ti₃O₅) composition, and considerable concentrations of divalent iron coexist with trivalent titanium in the liquid-slag phase. This seems to be a consequence of the complete solid solution between ferrous pseudobrookite (FeTi₂O₅) and anosovite (Ti₃O₅), which exists at subsolidus temperatures. The liquid-slag field is significantly enlarged toward the anosovite composition upon increasing the temperature from 1500 °C to 1600 °C. Activities of the components “FeO” and TiO₂ in the liquid-slag region were determined by Gibbs-Duhem integration of the measured oxygen partial pressures at 1500 °C. The FeO shows moderate negative deviation, while titania shows a slight negative deviation in FeO-rich slags and a positive deviation in high-titania slags. The experimentally measured activity values were modeled using regular and biregular solution models, and good agreement was obtained with the biregular solution model.     

Reaction sequences in the formation of silico-ferrites of calcium and aluminum in iron ore sinter

Complex silico-ferrites of calcium and aluminium (low-Fe form, denoted as SFCA; and high-Fe, low-Si form, denoted as SFCA-I) constitute up to 50 vol pct of the mineral composition of fluxed iron ore sinter. The reaction sequences involved in the formation of these two phases have been determined using an in-situ X-ray diffraction (XRD) technique. Experiments were carried out under partial vacuum over the temperature range of T=22 °C to 1215 °C (alumina-free compositions) and T=22 °C to 1260 °C (compositions containing 1 and 5 wt pct Al₂O₃) using synthetic mixtures of hematite (Fe₂O₃), calcite (CaCO₃), quartz (SiO₂), and gibbsite (Al(OH)₃). The formation of SFCA and SFCA-I is dominated by solid-state reactions, mainly in the system CaO-Fe₂O₃. Initially, hematite reacts with lime (CaO) at low temperatures (T ∼ 750 °C to 780 °C) to form the calcium ferrite phase 2CaO·Fe₂O₃ (C₂F). The C₂F phase then reacts with hematite to produce CaO·Fe₂O₃ (CF). The breakdown temperature of C₂F to produce the higher-Fe₂O₃ CF ferrite increases proportionately with the amount of alumina in the bulk sample. Quartz does not react with CaO and hematite, remaining essentially inert until SFCA and SFCA-I began to form at around T=1050 °C. In contrast to previous studies of SFCA formation, the current results show that both SFCA types form initially via a low-temperature solid-state reaction mechanism. The presence of alumina increases the stability range of both SFCA phase types, lowering the temperature at which they begin to form. Crystallization proceeds more rapidly after the calcium ferrites have melted at temperatures close to T=1200 °C and is also faster in the higher-alumina-containing systems.     

Kinetics of reduction of hematite with hydrogen gas at modest temperatures

The kinetics of hydrogen reduction of thin, dense strips of hematite were investigated in the range 245 °C to 482 °C. Pure hydrogen gas at 1 atm was used as the reducing agent. Because of the relative thinness (only 136 /μm thick) of the specimens used, the pore-diffusion of gases offered no significant resistance to the reduction process. The interfacial-reaction-rate constantk _s ^* , which has been corrected for film-mass-transfer effects, is found to be given by logk _s ^* = −1.032 (±0.138) -[7860 (±200)]/2.303r where k _s ^* is in g · atom O · cm⁻² · s⁻¹ · atm⁻¹. The activation energy for the reduction process is found to be 65,325 (±1650) J · mol⁻¹; the rate-controlling step appears to be the Fe₃O₄ → Fe conversion step.     

Iron(II) oxidation by SO2/O2 for use in uranium leaching

Iron(III) can be used as an oxidant in the leaching of uranium ore in an acid medium. The oxidation of iron(II) to iron(III) using an SO₂/O₂ gas mixture was investigated in order to provide an iron(III) stream for uranium extraction. The effects of pH, temperature and SO₂/O₂ volumetric ratios were considered. Oxidation of iron(II) by SO₂/O₂ was controlled by diffusion of SO₂ or O₂ at pH 2 and 40 °C. However as the pH decreased below pH 1, the reaction was controlled by a slow chemical step and the reaction rate decreased. Increasing the temperature increased the oxidation rate at pH 0.8, and at 70 °C the rate again became dependent on SO₂ or O₂ diffusion. The oxygen efficiency for a fixed reactor set-up was dependent on the SO₂/O₂ ratio and total flow rate of the gas. In leach tests, the uranium extraction achieved with iron(III) solution prepared by SO₂/O₂ oxidation was the same as that for a standard uranium leach with conventional oxidant.     

Magnetizing roasting of leucoxene concentrate

The phase transformations occurring during magnetizing roasting of leucoxene concentrate in the temperature range 600–1300°C are studied. It is demonstrated, that in the temperature range 600–800°C, only iron oxides are reduced to a metallic state; at temperatures above 800°C, combined reduction of iron and titanium oxides takes place. At 1050°C, reduced specimens are represented by the Ti₅O₉ and Ti₆O₁₃ Magnéli phases. The formation of iron metatitanate (FeTiO₃), under reduction conditions and the existence of ferrous iron ions in the Magnéli phases slightly degrade the magnetic properties of the products of magnetizing roasting. In high temperature region (1200–1300°C), a similar effect is exerted by the formation of iron dititanate or anosovite in the system. The possibilities of eliminating the undesired factors decreasing the magnetic properties of the products of magnetizing roasting are determined.     

Kinetics of silver leaching from manganese-silver associated ores in sulfuric acid solution in the presence of hydrogen peroxide

Kinetics of silver leaching from a manganese-silver associated ore in sulfuric acid solution in the presence of H₂O₂ has been investigated in this article. It is found that sulfuric acid and hydrogen peroxide have significant effects on the leaching rate of silver. The reaction orders of H₂SO₄ and H₂O₂ were determined as 0.80 and 0.68, respectively. It is found that the effects of temperature on the leaching rate are not marked, the apparent activation energy is attained to be 8.05 kJ/mol within the temperature range of 30 °C to 60 °C in the presence of H₂O₂. Silver leaching is found to be diffusion-controlled and follows the kinetic model: 1−2x/3−(1−x)^2/3=Kt. It is also found that particle size presents a clear effect on silver leaching rate, and the rate constant (k) is proportional to d ₋₂ ⁰ .     

Kinetic study of the chlorination of gallium oxide

The kinetics of the chlorination of gallium oxide in chlorine atmosphere was studied between 650 °C and 800 °C. The calculations of the Gibbs standard free energy variation with temperature for the reaction Ga₂O_3(S)+3Cl_{2 (g)}→2GaCl_3(g)+1.5O_{2 (g)} show that direct chlorination is favorable above 850 °C. Thermogravimetric experiments were performed under isothermal and nonisothermal conditions. The effect of temperature, gas flow rate, and Cl₂ partial pressure were studied. The solids were characterized by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The nonisothermal results showed that chlorination of Ga₂O₃ starts at approximately 650 °C, with a mass loss of 50 pct at 850 °C. The isothermal results between 650 °C and 800 °C indicated that the reaction rate increased with temperature. The correlation of the experimental data with different solid-gas reaction models showed that the results are adequately represented by the model proposed by Shieh and Lee: X=1−{1−b ₂₂[b ₂₁ t+e ^−b ₂₁ ^t−1]}^1/(1−γ). From this model, it was found that the rate of reaction for the chlorination of Ga₂O₃ is of the order 0.68 with respect to Cl₂ and the activation energy is 113.23 kJ/mol. On the other hand, the order of the activation rate of the interface surface is 0.111 with respect to Cl₂ and its activation energy is 23.81 kJ/mol.     

Removal of Metallic Iron on Oxide Slags

It is possible, in some cases, for ground coal particles to react with gasifier gas during combustion, allowing the ash material in the coal to form phases besides the expected slag phase. One of these phases is metallic iron, because some gasifiers are designed to operate under a reducing atmosphere (p_O2{p_{\rm {O}_{2}}} of approximately 10⁻⁴ atm). Metallic iron can become entrained in the gas stream and deposit on, and foul, downstream equipment. To improve the understanding of the reaction between different metallic iron particles and gas, which eventually oxidizes them, and the slag that the resulting oxide dissolves in, the kinetics of iron reaction on slag were predicted using gas-phase mass-transfer limitations for the reaction and were compared with diffusion in the slag; the reaction itself was observed under confocal scanning laser microscopy. The expected rates for iron droplet removal are provided based on the size and effective partial pressure of oxygen, and it is found that decarburization occurs before iron reaction, leading to an extra 30- to 100-second delay for carbon-saturated particles vs pure iron particles. A pure metallic iron particle of 0.5 mg should be removed in about 220 seconds at 1400 °C and in 160 seconds at 1600 °C.