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Acid mine drainage (AMD) due to the oxidation of sulphide bearing waste rock (WR) is a common environmental problem associated with coal extraction. Therefore, WRs from the Lakhra coal field in Pakistan, were studied to i) perform a mineralogical and chemical characterisation, ii) determine the AMD generating potential and iii) estimate the leachability of elements. The chemical and mineralogical composition was studied using ICP, XRF, XRD and SEM. Acid base accounting and weathering cell test determined the acid producing potential of WRs. Besides organic material, the WRs were composed of quartz, pyrite, kaolinite, hematite and gypsum with varying amounts of calcite, lime, malladerite, spangolite, franklinite and birnessite. The major elements Si, Al, Ca and Fe were in the range (wt.%) of 8–12, 6–9, 0.3–3 and 1–10, respectively, with high S concentrations (19.4–113.3 g/kg). Trace elements were in the range (mg/kg) As (0.3–8), Cd (0.2–0.4), Co (15–75), Cr (67–111), Cu (25–101), Hg (0.1–0.2), Ni (50–107), Pb (8–20) and Zn (75–135). The AMD potential of WRs ranged from − 70 to − 492 kg CaCO3/tonne. During the test period of 192 days, the pH of leachates from very acidic WRs was maintained from 1 to 2.5, whereas, the less acidic WRs produced leachates of mildly acidic (2.7) to neutral (7.3) pH. The leachates from very acidic WRs ranged in the element concentrations of Fe, SO42 − and Al from mg/L to g/L and As, B, Co, Cu, Mn, Ni and Zn from μg/L to mg/L. However, the leachates from less acidic WRs contained all major elements in mg/L and trace elements in μg/L concentrations except for B and Mn that ranged from μg/L to mg/L. The results show that the studied WRs have mild to strong acid producing potential and have the capacity to deteriorate natural water quality significantly. Therefore, necessary preventive or/and acid neutralising measures are strongly suggested.

Solid waste generation is one of the main problems in the steelmaking process. One of the most problematic waste products is the electric arc furnace dust, which is a by-product rich in iron and zinc and is present as zincite (zinc oxide) or franklinite (zinc ferrite). This work focuses on the reduction kinetics of synthetic zinc ferrite by gases containing hydrogen and carbon monoxide. This process was examined via forced stepwise isothermal analysis. The test was conducted at temperatures ranging from 500 to 950 °C. Reduction of zinc was accomplished using a mixture of hydrogen and carbon monoxide in order to simulate reformed natural gas. The results indicated that reduction of zinc ferrite occurred in two stages (550–750 °C and 800–900 °C). The first stage was characterized by iron oxide reduction, where a mix control between nucleation and diffusion was determined. The apparent activation energy obtained was 71.5 kJ mol−1. The second stage was characterized by zinc oxide reduction, where the controlling mechanism was identified as a mixed control between diffusion and phase boundary reaction. The apparent activation energy was 135.5 kJ mol−1. The formation of a dense layer of metallic iron around the unreacted core may have caused the apparent activation energy to increase.

This work covers initially a general thermodynamics assessment regarding the zinc ferrite (ZnFe2O4) behavior toward direct and reducing chlorination. Then, the use of alternative chlorination agents were also theoretically appreciated, before a set of experiments has been carried out with industrial residue (electric arc furnace dust). Besides identifying zinc ferrite (95.4 pct), the XRD analysis indicated the presence of ZnO (4.6 pct). Therefore, the main objective of the present work is related to a theoretical (thermodynamics) and experimental (kinetics) evaluation of the mentioned residue chemical behavior as submitted to chlorination methods. Several characterization methods were used, such as X-ray diffraction, scanning electron microscopy, X-ray fluorescence, mass spectroscopy (ICP-MS), and energy-dispersive X-ray spectroscopy (EDS). It was observed that zinc was present, mostly, in the form of zinc ferrite (franklinite). The thermodynamics study revealed that Zn has a more susceptible behavior regarding the oxides conversion into chlorides. However, this tendency is not necessarily associated with a selective reaction, as showed for the chlorination in the presence of carbon, as both iron and zinc chlorides formation is feasible. The experimental results have indicated that some reaction systems can be further studied in order to identify operational conditions that enable selective formations. So, it was observed that for the calcium chloride reaction conducted at 1273 K (1000 °C) for 30 minutes, the iron content in the residue slightly increases (with 15 pct removal), whereas the zinc content decreases from 20 to 12 pct (53 pct removal), suggesting complementary studies where this possible selectivity could be even more determinant. Such results have also indicated that the direct action of chlorine at 1073 K (800 °C) allowed complete removal of zinc, followed by conversion in the order of 40 pct in iron. Therefore, a complementary investigation over these alternatives is identified as a promising option in the field of electric arc furnace dust treatment, particularly when the Zn content is very low.

Electric arc furnace dust (EAFD) is a toxic waste which is mainly rich in iron oxide, zinc, and lead. Hydrometallurgical extraction of zinc from Jordanian EAFD in alkaline medium was investigated; NaOH, NaHCO3, and Na2CO3 were used as leaching agents. The pH values for the prepared solutions were 8.3, 8.2, and 12.55 for NaHCO3, Na2CO3, and NaOH, respectively. The effect of NaOH concentration (1, 3, 5, 7, and 9 M), contact time (5 min to 3 h), temperature (20, 40, and 60), and solid-to-liquid ratio (SLR; 20, 40, 80, and 120 mg/ml) on the leachability of zinc from EAFD were tested. The initial EAFD and the resulting leach residues were characterized using X-ray diffraction (XRD) and X-ray fluorescence (XRF). EAFD contained 25.9% Zn, 18.0% Fe, and 3.2% Pb. A maximum zinc recovery of 92.9% was achieved using 6 M NaOH at 60 °C with solid loading of 20 g/L and 3 h leaching time. NaHCO3 and Na2CO3 were not efficient leaching agents for Zn extraction since the recoveries were only 2.6 and 4.5%, respectively. Zn and Pb were depleted in the residues with an E-factor of 0.5–0.6 and 0.1–0.25, respectively. Iron was enriched in the residues; the E-factor was around 2. The EAFD contained mainly zincite, franklinite, and magnetite. After 3 h leaching, only traces of zincite exist in the residues, while sylvite and halite were completely dissolved.

In this paper, we describe the discovery and characterization of shelled structures that occur inside galleries of Pyrenees mines. The structures are formed by the mineralization of iron and zinc oxides, dominantly franklinite (ZnFe2O4) and poorly ordered goethite (α-FeO(OH)). Subsurface oxidation and hydration of polymetallic sulfide orebodies produce solutions rich in dissolved metal cations including Fe2+/3+ and Zn2+. The microbially precipitated shell-like structure grows by lateral or vertical stacking of thin laminae of iron oxide particles which are accreted mostly by fungal filaments. The resulting structures are composed of randomly oriented aggregates of needle-like, uniform-sized crystals, suggesting some biological control in the structure formation. Such structures are formed by the integration of two separated shells, following a complex process driven likely by different strategies of fungal microorganisms that produced the complex macrostructure.

Nanoparticles (NPs) often play significant roles in dictating the transport, distribution, bioavailability and toxicity of contaminants in the environment. Incidental NPs (i.e. NPs of anthropogenic origin but not purposely engineered) are often overlooked in contaminant transport and fate studies; yet in many systems they dominate contaminant transport processes. Using surficial contaminated regosols from Trail, British Columbia, Canada, a metal smelting and refining area along the banks of the Columbia River, we show that sequestration of Pb-, Zn-, Sb-, and As-bearing incidental NPs is strongly influenced by their aggregation, crystal growth, and/or particle attachment to mineral surface coatings (MSC) and in mineralized organic matter (MOM). Transmission electron microscopy shows the occurrence of NPs of anglesite (PbSO4), Fe-As-phosphate, kintoreite (Pb[(Fe,Al)3(P(As)O4)(PO3(OH))(OH)6]), and franklinite (ZnFe2O4) in matrices of amorphous silica which retain different stages of their agglomeration and aggregation. Other identified nano-size phases in the MSC and MOM indicate a complex and previously unrecognized mineralogy of Pb-, Zn-, Sb-, and As-phase in surficial soils. Mineralogical complexity and the various sequestration processes observed in this study indicate a new dimension of nano-scale processes on mineral surfaces and organic matter that have been previously overlooked when studying the fate of contaminants with bulk-analytical tools such as micro-X-ray diffraction or synchrotron-based spectroscopic methods.

This paper aims to study the dielectric properties and carbothermic reduction of zinc oxide (zincite, ZnO) and zinc ferrite (franklinite, ZnFe 2 O 4 ) by microwave heating. To achieve this aim, the dielectric properties were measured with an open-ended coaxial method to understand the behaviour of the samples under microwave irradiation. The effects of microwave power, duration time and sample mass on the heating rate, and the effects of the stoichiometric amount of graphite on the reduction of ZnO and decomposition of ZnFe 2 O 4 were investigated. The results show that ZnFe 2 O 4 has significantly higher dielectric properties compared to ZnO. Generally, for both samples, the dielectric values at room temperature were quite low, indicating that both ZnO and ZnFe 2 O 4 are poor microwave absorbers. It was found that the temperatures have a more significant effect on the imaginary permittivities than on the real permittivities. The heating rate showed that the sample temperature increased with increase in microwave power and sample mass. Using 700 W of microwave power and two times the stoichiometric amount of graphite, almost complete reduction of ZnO was achieved in 12 min, while ZnFe 2 O 4 completely decomposed to zincite and wustite in 3 min.

The reduction of small, dense zinc oxide (ZnO) and zinc ferrite (ZnFe204) samples with and without impurity oxide additions in CO/CO2, CO/N2 and H2/N2 gas mixtures has been investigated at temperatures between 600 and 1100oC . Microstructural examination of fractured and polished samples using optical and scanning electron microscope (SEM-EDX) techniques has enabled the conditions for the formation of a range of product microstructures to be defined. The microstructural characterization of the reacted and partially reduced samples were complemented with measurements of the rates of the reactions.The mechanisms and kinetics of reduction of zinc oxide were found to be dependent upon the CO and H2 partial pressure, the oxygen potential of the gas mixtures, temperature, degree of reduction, and the type and amount of impurity oxides(i.e. FeO, PbO, MgO, CaO, SiO2. MnO, AI2O3) in the samples. The reduction of ZnO solid solutions resulted in the formation of a planar ZnO reaction interface and a porous product layer composed of impurity oxides whereas the reduction of pure ZnO resulted in selective attack of particular crystal planes and an irregular growth interface. From the analysis of the relative rates of the various chemical reactions and transport processes, the rate of reduction of ZnO with or without impurity addition were found to be controlled jointly by chemical reaction at the ZnO reaction interface and pore diffusion of reducing gas through the porous ZnO layer or reaction product layer.The reduction rates of zinc ferrites were also found to be dependent upon temperature, particle size, reaction gas composition, and the type and amount of impurity oxide (i.e. MgO, MnO, AI2O3, CaO) additions. The presence of CaO and MgO In ZnFe204 increased the region for porous Iron growth whereas AI2O3 and MnO reduces the range of gas conditions over which the porous iron microstructure may be formed. Five broad microstructural types formed during the reduction of pure and impure zinc ferrites in the system studied have been identified. These structures were porous iron (type A), porous wustite covered with dense iron (type B), dense wustite covered with dense iron (type C), wustite phase (type D), and porous magnetite grains (type E).The reaction mechanisms of ZnO, ZnFe2O4 and dissolved impurities were explained in terms of the relative rates of the various chemical reactions and mass transport processes both in and out of the solid. The changes in growth mechanisms and reduction kinetics which occur with changing reduction conditions are discussed.The results obtained for the reduction of ZnO and ZnFe204 both with and without dissolved impurity oxides have been used to explain the reactions involving zincite and franklinite phases within the sinter microstructure in the simulated blast furnace conditions. Initial and partially reduced samples were examined using optical, electron-probe microanalysis, SEM-EDX, and XRD to characterise the structural and compositional changes occurring during reduction reaction. The principal phases identified in the sinter microstructure were franklinite, zincite, copper oxides, lead oxide, Ca-Pb silicates, and calcium silicates.The reaction mechanisms and reduction sequences for the various oxide phases within the sinter structure during reduction of types 6 & 7 sinters under the system studied are discussed. The reduction of sinters resulted in structural modification of zincite, franklinite, slag phases, and the formation of new oxide and metallic phases. The rate and behaviour of these complex phase transformations and phase coarsening were found to be dependent upon reduction time, temperature and the reacting gas composition. The eutectic in the ISF sinters was positively identified to consist of two separate compounds, Ca-Pb silicate rod-like structure in a zinc ferrite (franklinite) honeycombed-type matrix.

EAF-dust containing metal oxides can be regarded as an important source for zinc and iron. In this study, the reduction behavior of zinc ferrite with CO gas as a reducing agent under different temperatures was investigated to develop a new process for the recovery of zinc and iron from EAF-dust. The results of the phase studies with synthetic franklinite show that zinc substituted wustite, and spinel with low zinc content formed at lower temperatures from 450 to 850 °C due to incomplete zinc-iron-separation. Zinc ferrite was completely reduced to metallic zinc and iron at 950 °C. After evaporation and condensation, metallic zinc was collected in the form of zinc powder while iron, the reduction residue, was obtained in the form of direct reduced iron (DRI). The mass balance indicates a high zinc recovery ratio of over 99%. The new treatment process by thermal reduction with CO gas as a reducing agent achieved higher recovery and metallization grade of both zinc and iron from EAF-dust at lower temperatures than other commercial processes. The metallic products can be used directly as semi-products or as raw materials for refinery.

Microwave treatment of electric arc furnace dust (EAFD) with poly(vinyl chloride) (PVC) was studied in this work. A comprehensive characterization of the dust as well as assessing the suitability of using the thermal de-chlorination of the common plastic (PVC) under inert atmosphere was carried out to assess the possibility of Zn and other heavy metals extraction (Pb and Cd) from EAFD. The dielectric and thermal properties of EAFD, PVC and their mixtures were measured. Once combined and heated the metal oxides present in the dust reacted with HCl released from PVC during thermal de-chlorination, forming metal chlorides which were subsequently recovered by leaching with water. It was found that zinc chloride could be almost completely recovered in the leaching stage, with the overall recovery of Zn reaching 97% when the EAFD:PVC ratio was 1:2. The investigation highlighted that franklinite, the most refractory mineral to leaching, was completely destroyed. The leaching residue was found to compose mainly of magnetite and hematite.

Evident discrepancy (by six times) between low-temperature heat capacities of two different samples of magnesioferrite (MgFe2O4) with a different thermal history is analogous to that (by four times) for franklinite (ZnFe2O4) found 50 years ago. The reason is supposed to be in the different magnetic ordering caused by different cation ordering after quenching–annealing. Magnetic nature of the discrepancy in low-temperature thermodynamic functions of minerals with variable cation ordering is out of quantitative consideration so far. This effect can also be found in all oxide phases of magnetic cations with the inversion parameter.

An efficient and scalable one-pot synthetic method to prepare nanostructure composite of ZnFe2O4–FeFe2O4–ZnO (ZFZ) has been investigated. This method is based on thermal decomposition of iron(III) acetate and zinc acetate in monoethanolamine (MEA) as a capping agent. Moreover, thermogravimetric analysis (TG-DTG) was performed to determine the temperature at which the decomposition and oxidation of the chelating agents took place. ZFZ was immobilized on glass using doctor blade method and calcinated at different temperatures. The properties of the ZFZ nanocomposite have been examined by different techniques, such as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and diffuse reflectance (DRS). FESEM shows that nanocomposite is monocrystallines and a narrow dispersion in size of 48 nm. XRD confirms that the prepared nanocomposite is composed of franklinite, ZnFe2O4 (54%), magnetite, FeFe2O4 (8%) and wurtzite, ZnO (48%). Photocatalytic activity of ZFZ immobilized on glass was carried out by choosing an azo textile dye, Reactive Red 195 (F3B) as a model pollutant under UV irradiation with homemade photocatalytic apparatus and the results indicated that ZFZ exhibited good photocatalytic activity.

The mobility, bioaccessibility and transfer pathways of metals and metalloids in estuarine sediments have been the focus of much detailed research. However, to date, few studies have examined the mineralogical siting of metals and metalloids in such sediments. This is despite the fact the mineralogy of sediments is an important factor that controls which and how much of a particular metal is released to pore waters and overlying water columns. This study reports on the mineralogical siting of metals in contaminated estuarine sediments, Hobart, Australia, and aims to evaluate the mobility of metals in the contaminated substrates. Mineralogical, mineral chemical and bulk chemical analyses demonstrate that the sediments contain very high levels of several metals and metalloids. The contaminated sediments have concentrations of zinc (Zn), lead (Pb), copper (Cu) and cadmium (Cd) ranging from 0.55 to 4.23 wt%, 0.16 to 0.70 wt%, 415 to 951 mg/kg and 23 to 300 mg/kg, respectively. Franklinite and lesser sphalerit...

The objectives of this study were to prepare leadless crystalline glazes from iron oxide by using low temperature firing (1,100°C) and to study the effect of concentration of iron oxide on the phase composition of the glaze raw materials on phase transformation in leadless iron oxide crystalline glaze. The crystalline phases were investigated by using the DTA, X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The composition of the glaze raw materials compose of nepheline syenite, colemanite, pottery stone, bentonite, ZnO, Li2CO3, SiOSubscript text2 and 10, 15 and 20%(w/w) iron oxide (Fe2O3). The glaze raw materials were ground for homogeneous mixtures by ball milling for 24h. The average particle size of the mixture was 3.86 µm. The glaze bodies were carried to firing at 1,100°C at the heating rate of 2°C/min and soaking for 0.5h. Then, the glaze bodies were cooled at the cooling rate of 1°C/min and maintained at 1,080°C for 3h and then maintained at 980°C for 1h, respectively. From the experiment results, it was found that the crystallization temperatures (Tc) of franklinite (ZnFe2O4) and anorthite (CaAl2Si2O8) depend on the concentration of iron oxide content.

Experimental studies on phase equilibria and liquidus temperature in the PbO-ZnO-CaO-SiO 2 -“Fe 2 O 3 ” system, with the mass ratios of CaO/SiO 2 =1-1.6 and Fe/SiO 2 = 1.3-1.7, and 40% PbO and 8% ZnO, were carried out between 1273 and 1573 K. Slags were equilibrated at 1273 to 1573 K and cooled rapidly by quenching. The XRD and SEM-EDS results showed that the slag compositions are in the franklinite primary phase field. Calcium and lead silicates are formed between 1373 and 1473 K. The Ca/Pb silicate and magnetoplumbite phases are partially formed by an incongruent reaction. The experimental and thermodynamical results showed that the liquidus increased by increasing CaO/SiO 2 mass ratio and decreasing Fe/SiO 2 mass ratio.

The Sterling Hill and Franklin zinc-iron-manganese deposits, Sussex County, New Jersey, are sedimentary-exhalative in origin but were highly deformed and metamorphosed to granulite grade during the Mesoproterozoic Ottawan orogeny. They are unique because the major zinc minerals, zincite, franklinite, and willemite, are oxides and silicates rather than sulfides. However, at Sterling Hill minor granular sphalerite occurs in the central black willemite zone associated with loelling and graphite and sparsely elsewhere in the deposit. Based on textural observations and stable isotope geochemistry, sphalerite was present during metamorphism and was most likely part of the protolith mineral assemblage. It likely formed from a fluid containing seawater sulfate that circulated through volcanic rocks and reacted with igneous sulfides; some contribution from biological reduction of sulfate seems likely. This interpretation agrees with the generally accepted model that the protolith formed on the floor of an ...

A hybrid (pyro + hydrometallurgical) route is evaluated for the selective removal of zinc from the fine fraction of basic oxygen furnace sludges. The route consists of the following steps: i) thermal decomposition of the franklinite (ZnO. Fe2O3) present in the sludge, in the presence of NaOH, ii) staged leaching of the sludge in NaOH solution in order to selectively remove zinc, and iii) washing of the sludge for the removal of reminiscent alkalis from the treatment. The first two steps are evaluated accordingly to three distinct operating conditions: soft, intermediate and severe. It is verified that the thermal decomposition of franklinite is a crucial step to assure the effective removal of zinc. A maximum of 90% of zinc was removed in the best tested condition with practically no loss of iron content, thus demonstrating that the route is very selective. The washing step is also efficient, with total removal of sodium and potassium. Finally, enrichment around 10 times on the Fe/Zn ratio is obtained, from originally 11.6 to 128.8.

The present research investigated the removal of zinc from BOF (basic oxygen furnace) sludges in an attempt to reuse the iron content of the sludge in the production of sinter. The study consisted of two main steps: (i) the characterization of fine and coarse fractions of BOF sludges and (ii) the hybrid treatment of sludge to selectively remove zinc from iron. The characterization study showed that the Fe/Zn ratio is 132.6 in the coarse fraction and 11.6 in the fine fraction; the amount of zinc proved to be 8.5 times higher in the later fraction, while the total content of iron ranged between 50 and 60% in both fractions. Zinc could also be identified in the sludge as zincite (ZnO) and franklinite (ZnO.Fe2O3), whose last phase is quite stable and insoluble in NaOH solutions. Other characteristics, including the granulometry, morphology, and toxicity of both fractions of the sludge, were also determined. To improve the zinc removal efficiency, franklinite must be decomposed by a thermal treatment. For this reason, a hybrid route was investigated using the fine fraction of the sludge. The effect of various materials and reagents was evaluated concerning the decomposition of franklinite, in which NaOH was found to be the most effective. Operating variables, such as temperature, time, and NaOH/sludge ratio were studied. The treatment was found to be quite efficient in the selective removal of zinc from the sludge (zinc removal higher than 90% was obtained with practically no iron extraction), thus improving the Fe/Zn ratio in the fine fraction to approximately 200.

X-ray absorption spectroscopy, scanning electron microscopy (SEM) and X-ray diffractometry (XRD) have been used to study the solid-phase speciation of Zn in urban road dust sediments (RDS) in Manchester, UK. X-ray absorption near-edge structure (XANES) analysis using linear combination modelling suggest that the soluble species Zn(NO3)2·6H2O and ZnCl2 represent 70—83%, and Zn-sorbed goethite 17—30%, of the Zn species present. The presence of goethite is not corroborated by extended X-ray absorption fine structure (EXAFS) modelled first shell scattering Zn—O distances of 2.01—2.03 Å, but this may be due to distortion of the Zn octahedra on the goethite surface, or the existence of Zn-sorbed species with other metal hydrous oxides, as inferred by the EXAFS-modelled second shell Fe and Al scatterers. Analysis by EXAFS also suggests that metallic Zn-Cu-Sn-Pb and Zn-silicate phases are present in the RDS, and this is corroborated by SEM and XRD. Other phases suggested by EXAFS include ZnO, franklinite, Zn-sorbed birnessite and zinc formate. Differences between the XANES and other results suggest that model compounds such as Zn-bearing phyllosilicates and metallic Zn phases may have been missing from the XANES fitting. Long-term low-level exposure to the RDS Zn phases identified may lead to an increased risk of cardiovascular or pulmonary diseases.

Residues from the zinc roast–leach–electrowin process contain zinc mainly as finely dispersed particles of franklinite. Thus, floatation, sulfuric acid leaching, and alkali leaching are ineffective methods for zinc extraction. An efficient technique was used for the extraction of zinc from hydrometallurgical zinc residues by sulfate roasting of a residue–sulfur–oxygen–H2O mixture followed by water leaching. The effects of various parameters, such as roasting temperature/time, the sulfur amount, leaching time/temperature, and liquid/solid ratio on zinc leaching were studied. Systematic studies indicate that high zinc leaching rate can be achieved under the following conditions: sulfur addition, 1.2 times theoretical value; duration, 2 h; temperature, 250 °C at roasting stage; and room temperature, liquid/solid ratio 4, and duration time 0.5 h at leaching. X-ray diffraction analysis indicates that the zinc-containing compounds convert into water-soluble zinc sulfate after roasting.

For 33 years, a primary lead smelter operated in Santo Amaro (Brazil). Since the 1970s, large amounts of Pb and Cd have been widely documented in the blood and hair of people living near the smelter. The plant closed down in 1993, and several years later, the Pb levels in the blood of children under 4 years of age living near the smelter were high, where the disposed lead slag was suspected to be the main source of this contamination. The objective of this study is to elucidate the source of the Pb contamination and any other potentially toxic contamination, focusing on the characterization of the slag. The samples used for this characterization study were taken from the slag heaps. The results of the chemical analysis showed that the major constituents of the slag, in decreasing order of wt%, were the following: Fe 2 O 3 (28.10), CaO (23.11), SiO 2 (21.39), ZnO (9.47), MgO (5.44), PbO (4.06), Al 2 O 3 (3.56), C (2.26), MnO (1.44), Na 2 O (0.27), S (0.37), K 2 O (0.26), and TiO 2 (0.25). The Cd content of the slag was 57.3 mg/kg, which is relatively low. The X-ray diffraction and the electron probe microanalyzer X-ray mapping indicated that the major phases in the slag were wustite, olivine, kirschsteinite, and franklinite. Only spheroidal metallic Pb was found in the slag. The leaching study showed that the slag was stable at a pH greater than 2.8, and only in an extremely acidic environment was the solubilization of the Pb enhanced significantly. The solubilization of Zn was very limited in the acidic and alkaline environments. These results can be explained by the limited leachability of the metallic Pb and Zn-bearing compounds. The leaching study used TCLP, SPLP, and SWEP and indicated that the lead slag was stable in weak acidic environments for short contact times.

International audience; Zinc isotopes have been studied along two smelter-impacted soil profiles sampled near one of the largest Pb and Zn processing plants in Europe located in northern France, about 50 km south of Lille. Mean delta(66)Zn values along these two soil profiles range from +0.22 +/- 0.17 parts per thousand (2 sigma) to +0.34 +/- 0.17 parts per thousand (2 sigma) at the lowest horizons and from +0.38 +/- 0.45 parts per thousand (2 sigma) to +0.76 +/- 0.14 parts per thousand (2 sigma) near the surface. The delta(66)Zn values in the lowest horizons of the soils are interpreted as being representative of the local geochemical background (mean value +0.31 +/- 0.38 parts per thousand), whereas heavier delta(66)Zn values near the surface of the two soils are related to anthropogenic Zn. This anthropogenic Zn occurs in the form of franklinite (ZnFe(2)O(4))-bearing slag grains originating from processing wastes at the smelter site and exhibiting delta(66)Zn values of +0.81 +/- 0.20 parts per thousand (2 sigma). The presence of franklinite is indicated by EXAFS analysis of the topsoil samples from both soil profiles as well as by micro-XANES analysis of the surface horizon of a third smelter-impacted soil from a distant site. These results indicate that naturally occurring Zn and smelter-derived Zn exhibit significantly different delta(66)Zn values, which suggests that zinc isotopes can be used to distinguish between geogenic and anthropogenic sources of Zn in smelter-impacted soils. In addition to a possible influence of additional past sources of light Zn (likely Zn-sulfides and Zn-sulfates directly emitted by the smelter), the light delta(66)Zn values in the surface horizons compared to smelter-derived slag materials are interpreted as resulting mainly from fractionation processes associated with biotic and/or abiotic pedological processes (Zn-bearing mineral precipitation, Zn complexation by organic matter, and plant uptake of Zn). This conclusion emphasizes the need for additional Zn isotopic studies before being able to use Zn isotopes to trace sources and pathways of this element in surface environments

High purity Fe 2 O 3 /ZnO nanocomposites were annealed in air at different temperatures between 100 and 1200 °C to get Fe-doped ZnO nanocrystals. The structure and grain size of the Fe 2 O 3 /ZnO nanocomposites were investigated by X-ray diffraction 2 θ scans. Annealing induces an increase of the grain size from 25 to 195 nm and appearance of franklinite phase of ZnFe 2 O 4 . Positron annihilation measurements reveal large number of vacancy defects in the interface region of the Fe 2 O 3 /ZnO nanocomposites, and they are gradually recovered with increasing annealing temperature. After annealing at temperatures higher than 1000 °C, the number of vacancies decreases to the lower detection limit of positrons. Room temperature ferromagnetism can be observed in Fe-doped ZnO nanocrystals using physical properties measurement system. The ferromagnetism remains after annealing up to 1000 °C, suggesting that it is not related with the interfacial defects.

Steelmaking dust, collected from four different steel plants, was examined by X-ray diffrac-tion powder technique using phase analysis. Some lead compounds, namely oxides, a silicate, a sul-phate and a chloride hydroxide, were identified. The quantities of the main phase components as franklinite, magnetite, hematite and zincite were determined, applying the Rietveld method. The importance of application of the microabsorption correction was shown.

Zinc has no particular bearing phases in soils, and it forms very diverse compounds; this complicates zinc’s identification by chemical fractionation. However, Zn-containing particles may be identified using synchrotron X-ray analysis. Franklinite, willemite, hemimorphite, and Zn-containing magnetite are found to be the main technogenic Zn-containing pollutants in the heavy fraction of the contaminated surface soil horizon. Among the secondary zinc compounds, Zn-containing trioctahedral structures and clay minerals (unidentifiable by chemical extraction), as well as zinc fixed by manganese oxides and iron hydroxides, predominate in the soil clay fraction. Being a chalcophile element, zinc precipitates in the form of sulfides and forms complexes with organic substances in organic soils and peats. The degree of affinity to chalcophile metals increases in the following sequence: O-, P-, N-, and S-containing functional groups of organic substances.

In this study, pure ZnO microbullets, ZnO–ZnFe2O4 composite, and ZnO–Fe2O3–ZnFe2O4 composite with micron structured balloons, rods, and particles were prepared by a simple solvent thermal process using methanol or ethanol as solvents. The influence of solvents on the composition and morphology of the products was studied, and their gas-sensing properties were also investigated. The morphology of ZnO microbullets synthesized in ethanol is similar to but more uniform than that of ZnO microbullets synthesized in methanol. The Fe-doped ZnO synthesized in ethanol contains many micron particles homogeneously dispersing on the surface of the microbullets, which is composed of hexagonal wurtzite ZnO and franklinite ZnFe2O4, while Fe-doped ZnO prepared in methanol consists of micron structured balloons, rods, and particles, which is composed of hexagonal wurtzite ZnO, hematite Fe2O3, and franklinite ZnFe2O4. Compared with pure ZnO and ZnO–ZnFe2O4 composite, the ZnO–Fe2O3–ZnFe2O4 composite presented high response, rapid response/recovery characteristics, good selectivity, and excellent stability to acetone at relatively low operating temperature of 190 °C. This sensor could detect acetone in wide range of 1–1000 ppm, which was expected to be a promising gas sensor for detecting acetone.

Mesoproterozoic marble in the New Jersey Highlands hosts small magnetite deposits that occur in discrete groups along linear trends and are concentrated mainly in the western part of the region. Magnetite also forms a layer structurally beneath the Zn-Fe-Mn orebody at the Franklin mine. Marble host rocks are interlayered at Fe and Zn-Fe-Mn deposits with bimodal metavolcanic rocks (amphibolite and rhyolitic gneiss) that were deposited synchronously in a back-arc basin developed on the eastern margin of Laurentia between 1.3 and 1.25 Ga. Magnetite in the deposits ranges from massive to disseminated and is characterized by low Ti, variable Mn, and locally high S. Concentrations of As, V, Sb, and Zn are enriched in magnetite compared to marble host rocks and associated metavolcanic rocks. Carbon and oxygen isotope ratios of the marbles are consistent with water-rock interaction between the marble protolith and a mixture of igneous fluids and seawater. Regional geology, petrology, and isotope data indicate that Fe was introduced into the carbonate protolith as low-temperature Fe oxides and hydroxides via hydrothermal fluids discharged along basinal fracture zones on the sea floor. Related marble-hosted Zn-Fe-Mn deposits at Franklin and Sterling Hill contain the assemblage willemite + zincite + franklinite. Stable isotope compositions of the Zn deposits are consistent with alteration of host rocks by water-rich fluids, preserving protolith carbon isotope ratios. Stable isotope modeling suggests that Zn silicate + oxides or hydroxides represent an appropriate protolith for the high-grade Zn ores. Alteration of metavolcanic rocks at the Fe deposits, combined with the isotope data and other petrologic and geochemical evidence, document the presence of an extensive hydrothermal system of Grenville age centered in the western Highlands. Metals precipitating from this hydrothermal system were responsible for Fe in the marble-hosted magnetite deposits and Zn in the deposits at Franklin and Sterling Hill from the same or a related hydrothermal system. Underplating of the back arc by mafic magma provided the heat to melt the lower crust and drive the hydrothermal system, resulting in carbonate-hosted Fe and Zn ore deposits and associated bimodal volcanism.

Iron-Zinc oxide films were deposited by the well known ultrasonic spray pyrolysis method from an aqueous solution of iron nitrate and zinc acetate ([Zn]/[Fe] = 0.30). A Franklinite structure of these films turned out from XRD measurements. Additional basic characterization with UV-Vis and infrared spectroscopies and AFM was also performed. Electrical measurements under a small alternating current signal (15 mV RMS) were performed under dry air, humid air (53 % R:H.) and humid air plus propane. Frequency scans yielded sensitivities as high as 260% to humidity and  475% to propane at 30 °C. At 250 °C lower sensitivities were obtained, but in all cases the highest values came from the reactive response of the film. From dynamical response measurements, the response time was also assessed. The mechanisms of sensing are discussed as well.

It is shown that the iron content in zinc silicate concentrates with either high (8–11%) or low (3%) iron does not significantly affect the kinetics or overall recovery of zinc extraction in sulphuric acid. Most of the iron was present as hematite and franklinite with little iron contained in willemite. A small reduction in zinc recovery from 98.5% to 97.5% was observed for silicate ores containing 12% iron. The activation energy determined from high-iron concentrate leaching, 78 ± 12 kJ/mol, is statistically similar to that from low-iron concentrate, 67 ± 10 kJ/mol, suggesting the same rate-controlling step. The leaching of high high-iron concentrates enables a higher mass recovery during flotation. A flowsheet is proposed comprising a magnetic separation step to produce a magnetic and a non-magnetic product so that iron dissolution from the magnetic concentrate acts as a source of soluble iron for impurities removal.

A weathered and a recent sample of electric arc furnace dust (EAFD), generated in a southern Brazilian steel industry, were characterized by X-ray fluorescence spectroscopy (XFA), powder X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) probe and Fourier transform infrared spectroscopy (FTIR). A quantitative phase composition model, that accounts for the observed data and for the physico-chemical conditions of formation, was postulated for each material. One sample, in the form of a wet paste, was collected from the lowest part of a landfill and corresponds to a weathered material whereas the other sample was collected from the top portion of the landfill and corresponds to a recently produced material. The dominant cations present in both samples are iron, zinc and lead with minor amounts of manganese, calcium and silicon. The dominant mineralogical phases identified in both materials are Magnetite, Franklinite and Zincite. The recent sample has Laurionite whereas the weathered sample has Hydrocerussite and Hydrozincite.

La Oroya zinc ferrite (19.5% Zn, 26.6% Fe, 0.052% Ga, 0.075% In) was roasted with coal under conditions more oxidizing than normally used in a Waelz kiln, and the roasted residues were leached with 200 g/L H{sub 2}SO{sub 4}. Overall zinc recoveries of up to 97% were achieved, with 35% of the zinc reporting to the fume after roasting at 1,100{sup o}C with a bituminous coal addition of 20%. Under these conditions, 93.2% of the Cd, 13.4% of the Cu, 33% of the Ga, 61% of the In and 18.2% of the Pb were recovered either in the fume or in the leach solution. At 2006 metal prices, the value of the recovered metals is comparable to that obtained from commercial Waelz kiln processing of this residue. Zinc in the franklinite (ZnFe{sub 2}O{sub 4}) mineral is reduced to zinc vapor, and, after oxidation, some of the zinc is found as ZnO or as Zn{sub 2}SiO{sub 4} in the roasted residue. Iron reacts to form either hematite (Fe{sub 2}O{sub 3}) or magnetite (Fe{sub 3}O{sub 4}), with no metallic iron detected in the roasted residue, and less than 2% of the iron is solubilized during leaching. The residue produced after roasting andmore » leaching is, therefore, much more stable than the residue from Waelz kiln processing and should be suitable for disposal in a landfill.« less

During the production of steel from Electric Arc Furnace (EAF), large amount of by-product called EAF flue dust is generated. The major proportion of flue dust is comprised of Zn (41.5 % wt.). Different phases identified by XRD analysis are zincite, franklinite and magnetite with zincite being dominant. In this study, we have performed flue dust treatment using sodium hydroxide as leaching medium. Different concentrations of alkali were used to optimize maximum recovery of Zn. XRF and Wet Chemical method were used to characterize the dust samples both before and after leaching. The optimum alkali concentration for selective leaching of zinc was found to be 4 M with a zinc recovery of 90 %.

The present paper deals with the synthesis of porous, sintered glass-ceramics obtained at temperatures below 1150°C, originating from inorganic polymers based on fayalite slag. Firing led to the evaporation of water, dehydroxylation, and oxidation of Fe2+ above 345°C. For heating >700°C, the Si–O stretching band shifted from the 1160 and 750 cm−1 to the 1255 and 830 cm−1 region, due to a structural reorganization of the amorphous phase, whereas Fe–O bands appeared at 550 cm−1. The final microstructure consisted predominantly of an amorphous phase, hematite, and franklinite. The open porosity and compressive strength decreased and increased, respectively, as the firing temperature increased. The final values suggest properties comparable to that of structural lightweight concrete, still, the materials synthesized herein, are lighter, and made primarily from secondary resources.

The possibility of metals recovery from zinc ferrite residues using transformational roasting processes was examined by roasting zinc ferrite residue from Doe Run Peru’s La Oroya plant (Peru), containing 19.5 pct Zn, 26.6 pct Fe, 750 g/t In, and 520 g/t Ga, with Na2CO3 and leaching with 200 g/L H2SO4 solutions. The X-ray diffraction (XRD) and diagnostic leaching tests indicate that approximately 87 pct of the zinc in this residue is present as franklinite (ZnFe2O4), with the remaining zinc present as entrained ZnSO4 or unleached ZnO. Both preliminary and design of experiments (DOE) testing, using a 22 central composite design (CCD), were performed to test the effects of temperature and a Na2CO3 addition on metals extraction and on the formation of minerals during roasting, and the solubility of these minerals during leaching. Both methods of testing showed that zinc and iron extractions increased with increasing temperature and Na2CO3 additions over the range of conditions tested. Roasting at 950 °C and 80 pct Na2CO3 produced a roasted residue from which 99 pct of the Zn, 88 pct In, and 85 pct Ga could be recovered by leaching, but from which up to 81 pct Fe was also dissolved. Mineralogical analysis using XRD and scanning electron microscopy (SEM)/energy dispersive X-ray (EDX) analysis showed that, for these conditions, ZnFe2O4 decomposes in the presence of Na2CO3 to form ZnO and either α-NaFeO2 or β-NaFeO2. Some of the ZnO formed reacts with Na2CO3 and silicates in the residue to form Na2ZnSiO4 and some unreacted Na2CO3/Na2O/Na2SO4 was also identified after roasting using SEM/EDX. All these phases are dissolved in acid leaching, leaving unreacted ZnFe2O4 and precipitated PbSO4 as the only phases identified in the leach residues. These results indicate that NaFeO2 is formed preferentially to Fe2O3 during roasting and that the NaFeO2 formed during roasting is highly soluble in acidic solutions. The results were also compared with studies on the roasting of more ZnFe2O4-deficient electric arc furnace (EAF) dusts with Na2CO3 or NaOH and indicated that, although roasting with Na2CO3 required higher roasting temperatures to achieve high zinc extractions, much lower Na2CO3 additions are required and higher indium recoveries are possible, if the combination of Na2CO3 roasting and H2SO4 leaching is used.

The major geochemical forms of Cr, Ni, Cu, Zn, Pb, and V in a soil from an industrial polluted site in the south of Italy were determined by means of synchrotron X-ray microanalytical techniques such as coupled micro-X-ray fluorescence/micro-X-ray diffraction and micro-X-ray absorption near edge structure spectroscopy in combination with bulk extraction methods (sequential extraction procedures, EDTA extractions, and toxicity leaching characteristic procedure tests). Cr, Ni, Zn, and Cu were found in spinel-type geochemical forms (chromite, trevorite, franklinite, zincochromite, and cuprospinel) and often in association with magnetite and hematite. Vwas mainly present as V(V) associated with iron-oxides or in the form of volborthite [Cu3(OH)2V2O7.2H2O]. Pb was speciated as minium (Pb3O4), lanarkite [Pb2O(SO4)], and, in association with Cr(VI), as crocoite (PbCrO4). In general, despite a high total concentration, metals appear to be speciated for the most part as rather insoluble geochemical forms. However, particular attention should be paid to Zn, Cu, V, and Pb that show non-negligible mobilizable fractions. On the basis of the geochemical forms identified, among others, two major former industrial activities were tentatively ascribed as being responsible for the observed major pollution: polyvinyl chloride and cement-asbestos productions.

The color of red willemite (Zn 2 SiO 4 ) from Franklin, New Jersey, has been attributed in the past to inclusions of franklinite. We have examined these inclusions, which are rod-shaped and 5–20 μm in diameter, and found them to contain multiple phases. Polarized-light microscopy shows the rods to be oriented uniformly parallel to the c axis of willemite, and to have hexagonal or pseudohexagonal cross-sections. Phases identified by standardless EDS analysis and electron back-scatter diffraction include franklinite, friedelite, zincian kutnohorite, serpentine and rhodonite, as well as a sparse, unidentified K-bearing phase. Possible explanations for the origin of the rods include exsolution, primary fluid inclusions, and epitactic growth contemporaneous with willemite crystallization. Although rod-like exsolution is known in some geological settings, and an original exsolved phase might have been altered to the present assemblage, some of the elements in that assemblage ( e.g., H, C, Cl, K, and Ca) are incompatible with the willemite structure at any temperature. An origin as fluid inclusions is supported by the shapes of the rods ( i.e. , negative crystals with a hexagonal cross-sections), the presence of phases containing OH, Cl, Ca, K, and CO 3 , and void space visible around solid phases. The tapered shapes of the rods seems inconsistent with epitaxy. We suggest that willemite-generating metasomatic fluids were preserved as inclusions rich in elements incompatible with willemite, and that subsequent conditions led to their crystallization, possibly by reaction with the host. Reaction ceased with complete consumption of the fluid, resulting in relict fluid inclusions that impart color on the macro scale.

Immiscibility in the trevorite (NiFe{sub 2}O{sub 4}) - franklinite (ZnFe{sub 2}O{sub 4}) spinel binary is investigated by reacting 1:1:2 molar ratio mixtures of NiO, ZnO and Fe{sub 2}O{sub 3} in a molten salt solvent at temperatures in the range 400-1000 C. Single phase stability is demonstrated down to about 730 C (the estimated consolute solution temperature, T{sub cs}). A miscibility gap/solvus exists below Tcs. The solvus becomes increasingly asymmetric at lower temperatures and extrapolates to n - values = 0.15, 0.8 at 300 C. A thermodynamic analysis, which accounts for changes in configurational and magnetic ordering entropies during cation mixing, predicts solvus phase compositions at room temperature in reasonable agreement with those determined by extrapolation of experimental results. The delay between disappearance of magnetic ordering above T{sub C} = 590 C (for NiFe{sub 2}O{sub 4}) and disappearance of a miscibility gap at T{sub cs} is explained by the persistence of long-range ordering correlations in a quasi-paramagnetic region above T{sub C}.

This paper reports phases identified in samples of crud (activated corrosion products) from two commercial boiling-water reactors using transmission and analytical electron microscopy and selected-area electron diffraction. Franklinite (ZnFe2O4) was observed in both samples. Hematite (α-Fe2O3), crystalline silica (SiO2), a fine-grained mixture of iron oxides probably including magnetite (Fe3O4), hematite (α-Fe2O3), and goethite (α-FeOOH), and an unidentified high-Ba, high-S phase were observed in one of the samples. Willemite (Zn2SiO4), amorphous silica, and an unidentified iron–chromium phase were observed in the other. Chloride-bearing phases were found in both samples, and are assumed to represent sample contaminants. Because of the small sample volumes and numbers of particles studied and the possibility of contamination, it is not clear whether the differences between the phases observed in the two crud samples represent actual differences in the assemblages formed in the reactors.

In the present study, zinc-substituted magnetites of the Fe3−XZnXnX 4 type were prepared by co-precipitation in the range 0≤s X≥ 1 and, further, annealed in free atmosphere, at 800° for 3 h. The samples were characterized by X-ray diffraction and Mossbauer spectroscopy. The results showed that the annealed samples were oxidized and converted into Fe2a03 and ZnFe204, in relative amounts that varied with X.

High-energy ball-milling of powder mixtures of zincite (ZnO) and iron (α-Fe) at different weight ratios was performed in air using a planetary ball mill with a stainless steel milling assembly. Structural and microstructural changes during the ball-milling (up to 30 h) were monitored using X-ray powder diffraction, field emission scanning electron microscopy (FE-SEM) and UV-Vis diffuse reflectance spectroscopy. The mechanism of iron oxidation was determined from the results of Mossbauer spectroscopy. It was found that an early phase of ball-milling caused the oxidation of iron from Fe(0) to Fe(2+) followed by the formation of a solid solution structurally similar to wustite. The wustite-type phase rapidly disappeared upon prolonged milling, which was accompanied by further oxidation of iron from Fe(2+) to Fe(3+) and the formation of spinel-type ferrite structurally similar to franklinite (ZnFe2O4) in the products with a high zinc content, or magnetite (Fe3O4) in the products with a high iron content. Further milling or annealing had a low impact on the franklinite-type phase, but caused the transition of the magnetite-type phase to the phase structurally similar to hematite (α-Fe2O3). The results of energy dispersive X-ray spectrometry (EDS) showed a dramatic increase in the degree of contamination with the increase in the proportion of the starting iron (∼9 times higher contamination during the milling of pure iron compared with pure zincite). It was shown that the source of contamination (balls or vial) strongly depends on the type of milled sample. Ball-milling of relatively big and heavy grains (starting iron) caused preferential contamination from the vial whereas ball-milling of smaller and lighter grains (products obtained after prolonged milling) caused preferential contamination from the balls. After prolonged milling the contamination due to wear of the balls was dominant in all the products. An explanation for the observed impact of grain size on the source and the degree of contamination was proposed.

At Angleur (eastern Belgium), a 53,000 m3 dump site, related to former Zn extraction, contains high concentrations of heavy metals and arsenic associated with minerals such as arsenopyrite (FeAsS), franklinite (ZnFe2O4) and willemite (Zn2SiO4). Eight representative samples were investigated by means of a modified availability test, which pointed towards a considerable availability of Cd, Pb and Zn. In addition a detailed analysis of leaching behaviour as a function of pH was performed by means of a pH(stat) leaching test. The results of this test were supported by modelling predictions with MINTEQA2. pH(stat) titration results also allowed determination of the acid neutralising capacity, making it possible to predict heavy metal release upon acidification, assuming a worst-case scenario. On a short- to medium-long term (+/-100 years) a release of 900 mg/kg Zn has to be expected upon assumed natural acidification. However, a leaching test performed at the natural pH (i.e. pH 8 for the sample studied) indicates that heavy metal release is very limited and far below the European limit values for slag material on dumps category 1. Therefore, despite the elevated total heavy metal and As concentrations on the site, leaching is relatively low under present environmental conditions. Moreover, the slag material has a rather elevated pH (6.5-8) and no acid mine drainage is produced. Glass phases seem very important in controlling heavy metal mobility since potential reactive minerals that are locked up in a silicate matrix are protected against leaching.

Chalcopyrite concentrate (83% CuFeS2, 3% FeS2 and 14% ZnS) which is a typical feed to the matte smelting process for copper extraction via pyro metallurgical route has been roasted with microwaves. Comparison of mineralogical phases obtained was made with the case of conventional roasting. Resulting calcines were characterised with Mossbauer spectroscopy and XRD. It was observed that complete oxidation (dead roasting) of the chalcopyrite was achieved after 10 min with microwaves while 20 min were required in the conventional route. The mineralogical phases found in the deadroasted calcines produced from microwave roasting of this chalcopyrite concentrate were the hematite (Fe203), franklinite (ZnFe2O4), copper-rich ferrite (Cu1−x Zn x Fe2O4, x≤0.5), and copper ferrite (CuFe2O4). The findings of this work indicated that it was technologically feasible to oxidize the chalcopyrite with microwaves using a 2.45 GHz multimode applicator.

Nous documentons la presence de grenat riche en calderite et un spinelle riche en franklinite et en jacobsite dans les roches metasedimentaires d'origine hydrothermale, maintenant recristallisees au facies amphibolite, qui reposent sur le gisement proterozoique a Zn-Pb de Gamsberg, en Afrique du Sud. On ne trouve ces mineraux que dans une unite (la Formation Gams) enrichie en Mn-Fe developpee de facon irreguliere dans la partie superieure du niveau mineralise; ce niveau aurait un lien genetique avec la mineralisation sous-jacente. Les roches sont bien laminees sur une echelle centimetrique ou decimetrique, et faites d'alternances de grenat, pyroxenoide, clinopyroxene manganesifere, et oxydes de fer (spinelle ferrite a Zn-Mn, magnetite, hematite). Le grenat contient jusqu'a 36% du pole calderite en solution solide avec andradite et spessartine, tandis que le spinelle atteint un maximum de 39% du pole franklinite dans une solution solide avec magnetite et jacobsite. Leurs sont associes les mineraux accessoires calcite manganesifere, tremolite manganesifere et zincifere, epidote riche en Sr, hyalophane, pyrophanite, melanotekite et mimetite. La presence et la distribution du grenat calderitique, du spinelle riche en Zn et Mn, et de l'hematite limitent la fugacite de l'oxygene au cours du metamorphisme a des conditions proches du tampon HM dans la partie superieure de la Formation Gams, et temoignerait de gradients importants en f(O 2 ) et f(S 2 ). Les assemblages preserves resultent de reactions complexes de reduction et de decarbonatation des protolithes, contenant carbonate riche en Mn et Ca, oxydes et hydroxydes de Fe-Mn, silice et des argiles, sources d'aluminium. Aux conditions atteintes de P, T et f(O 2 ), les parageneses diverses refletent des variations delicates en composition globale des sediments precurseurs. Selon l'enrichissement en Mn et Fe et l'absence relative de Zn et de S, ces roches metahydrothermales representeraient une aureole de dispersion de fluides de basse temperature et relativement oxydes qui circulaient suite a la mineralisation en metaux de base. Prises dans leur ensemble, les compositions mineralogique et chimique inhabituelles de ces roches fournissent une indication du spectre de lithologies qui peuvent etre associees aux gisements de sulfures de metaux de base metamorphises.

The most commonly used route in the hydrometallurgical extraction of zinc and copper from a sulphide ore is the concentrate-roast-leach-electro winning process. In the present investigation a zinc-copper ore from the Maranda mine, located in the Murchison Greenstone Belt, South Africa, containing sphalerite (ZnS) and chalcopyrite (CuFeS2), was studied. The 57Fe-Mossbauer spectrum of the concentrate yielded pyrite, chalcopyrite and clinochlore, consistent with XRD data. Optimal roasting conditions were found to be 900°C for 3 h and the calcine produced contained according to X-ray diffractometry equal amounts of franklinite (ZnFe2O4) and zinc oxide (ZnO) and half the amount of willemite (Zn2SiO4). The Mossbauer spectrum showed predominantly franklinite (59%), hematite (6%) and other Zn- or Cu-depleted ferrites (35%). The latter could not be detected by XRD analyses as peak overlapping with other species occurred. Leaching was done with HCl, H2SO4 and HNO3, to determine which process would result in maximum recovery of Zn and Cu. More than 80% of both were recovered by using either one of the three techniques. From the residue of the leaching, the Fe-compounds were precipitated and

Recycling scrap iron and steel in electric arc furnaces (EAFs) generates very fine metal-containing dusts which can present major environmental problems. This paper describes experimental work on a relatively novel, simple, and inexpensive process for decreasing the chloride content and upgrading the zinc level of dust from an Australian plant, to produce saleable products and environmentally safe waste products for disposal. The dust contained about 2.1% Cl as various chlorides, 23.1% Zn as zincite and franklinite, 27.1% Fe as magnetite, franklinite, and hematite, plus small quantities of lead, cadmium, chromium, and other materials. The dust was very fine ( P 80 about 2 μm). Individual particles were commonly aggregates of fine spheres and other shapes. Simple water washing at ambient temperatures and natural pH (12) for 60 min extracted 99% of the chlorides, giving a residue assaying 200 ppm Cl. This residue was strongly coagulated by lime present in the dust and settled rapidly. The wash solution contained low levels of iron, zinc, lead, cadmium, and chromium, most of which could be removed by sulphide precipitation. Wet magnetic separation with a Davis tube was investigated. At the lowest field strength employed (0.6 A), 95% of the zinc was recovered in a non-magnetic product assaying 28% Zn and 24% Fe. At the highest field strength (1.6 A), 91% of the zinc was recovered in a non-magnetic product assaying 29% Zn and 25% Fe. Wet cycloning at a nominal separation size of 2–5 μm gave a cyclone overflow product assaying 31% Zn and 26% Fe, and containing 85% of the zinc. All these results fit a typical zinc grade–recovery relationship. The proposed process of water washing followed by magnetic separation or cycloning would produce a relatively high-zinc, low-iron, low-chloride product suitable for treatment in a lead–zinc smelter or electrolytic zinc plant, a high-iron, low-zinc product suitable for land fill, and a treated waste water for discharge to a sewer.

Nanostructured ZnFe2O4 and zinc oxide−iron oxide composites were obtained by sol−gel processing of a hetero-bimetallic alkoxide. For this purpose the novel molecular precursors Fe2Zn(OR)8 (R = tBu, iPr), fully characterized by spectroscopic and single-crystal diffraction techniques, have been synthesized and their applications in the sol−gel procedure were investigated. The obtained xerogels were annealed at very low temperatures (down to 200 °C) yielding crystalline phases with very small crystallite grain sizes. The phase compositions of the material strongly depend on the polarity of the solvents used in the hydrolysis reaction. When the hydrolysis was performed in the polar propan-2-ol, the spinel ZnFe2O4 (franklinite) formed at annealing temperature of 200 °C with a mean crystallite grain size Dvol of 2.24 nm. However, when using the less polar toluene as solvent in the sol−gel process, iron oxide and zinc oxide are formed together with the franklinite phase. This mixture of phases transforms to the ...

The phase equilibria in the Fe-Mg-Zn-O system in the temperature range 1100-1550degreesC in air have been experimentally studied using equilibration and quenching followed by electron probe X-ray microanalysis. The compositions of condensed phases in equilibrium in the binary MgO-ZnO system and the ternary Fe-Mg-O system have been reported at sub-solidus in air. Pseudo-ternary sections of the quaternary Fe-Mg-Zn-O system at 1100, 1250 and 1400degreesC in air were constructed using the experimental data. The solid solution of iron oxide, MgO and ZnO in the periclase (Mg, Zn, Fe)O, spinel (Mg2+, Fe2+, Zn2+)(x)Fe(2+y)3+O4 and zincite (Zn, Mg, Fe)O phases were found to be extensive under the conditions investigated. A continuous spinel solid solution is formed between the magnesioferrite (Mg2+, Fe2+)(x)Fe(2+y)3+O4 and franklinite (Zn2+, Fe2+)(x)Fe(2+y)3+O4 end-members at 1100 and 1250degreesC, extending to magnetite (Fe2+)(x)Fe(2+y)3+O4 at 1400degreesC in air. The compositions along the spinel boundaries were found to be non-stoichiometric, the magnitude of the non-stoichiometry being a function of composition and temperature in air. It was found that hematite dissolves neither MgO nor ZnO in air.

The paper explores several alternative ways for improving the performance of zinc ferrites, which are common high-throughput sorbents used in hot gas desulphurisation processes (IGCC). The catalysts have been prepared by supporting the pure oxides (zinc and iron oxides) in porous supports (sepiolite, ZrO 2 and zeolite) that provides the necessary strength. The active phase (zinc ferrite) is “in situ” synthesized as combined mixed oxides with a spinel structure, produced after calcination at high temperature. It has been found that the preparation method has a strong influence on the spatial distribution of the chemical species inside the pellet. In some cases, it is even possible to produce a profile where metallic oxides concentrate near the outer edge of the particle. According to XRD, it is found a preferential formation of enstatite phase rather than franklinite, due to substitution of interstitial ions in the framework of supports for Fe 2+ and Zn 2+ . These conclusions set up strong requirements for the synthesis of specific sorbents in FGD reactions. This can be achieved by means of a combination of different preparation methodologies, which allow selecting the metallic ions and the supports in order to build the active spinels required for the FGD reaction.

In this work, an ultrasound-assisted leaching process was studied for the recovery of zinc from electric arc furnace (EAF) dust, in which zinc was mainly present in the form of franklinite (60%). Hydrometallurgy is emerging as a preferred process for the recovery of a variety of metals, and the use of ultrasound could offer advantages over the conventional leaching process, especially for the dissolution of franklinite. Franklinite is a refractory phase that is difficult to leach and represents the main obstacle in conventional hydrometallurgy processing. Atmospheric leaching with different sulfuric acid concentrations (0.2–2.0 M) at two temperatures (323 and 353 K) was performed. The tests were conducted using both conventional and ultrasound-assisted leaching. After the leaching tests, the solid residues were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques, whereas the leach liquor was analyzed by inductively coupled plasma spectroscopy (ICP). The use of ultrasound facilitated the dissolution of franklinite at low acid concentrations and resulted in a greater zinc recovery under all of the investigated operating conditions.

The para-goethite (PG) iron removal process is one of the several precipitation processes that is utilised today to remove iron from zinc-rich processing solutions. In this paper, the para-goethite process is reviewed and compared with results obtained from a study of similar Zincor Process. The distribution of iron in the Zincor iron residue was found to be as follows: approximately 50% as a combination of schwertmannite and ferrihydrite, 20% as jarosites, 25% as franklinite and trace amounts of pyrite as well as 5% of an unknown phase. This study confirmed that goethite is not present in Zincor's iron residue and that iron is mainly removed in the form of poorly crystalline, intermediate iron phases such as schwertmannite and ferrihydrite. The presence of these intermediate phases in zinc plant iron residues is proposed to be mainly a function of the specific pH profile employed during iron removal and the coprecipitation of silica. Based on these findings, it can be concluded that the Zincor Process in its current form is distinctly different to that historically considered to be the similar patented para-goethite iron removal process, as practiced at the Porto Vesme and the Pasminco Hobart hydrometallurgical zinc plants.