Large Amounts Of Iron Oxides Research Articles

Hematite enhances the immobilization of copper, cadmium and phosphorus in soil amended with hydroxyapatite under flooded conditions

Hydroxyapatite (HA) is often applied as chemical amendment in soils contaminated with trace metals such as copper (Cu) and cadmium (Cd). Large amounts of iron oxides in red soil may interacts with phosphate released from HA and influence trace metal immobilization of HA. Here we simulated a red paddy soil with 1–5% wt iron oxides by adding hematite and evaluated the Cu and Cd availability in soil amended with HA under flooded conditions. Changes in phosphorus and iron oxide fractions were also evaluated after a 42-day flooding incubation experiment. Results showed that the addition of HA-only and hematite-only decreased soil redox potential and increased pore water pH compared to the control. HA combined with hematite could effectively decrease phosphate, Cu and Cd in soil pore water compared to HA-only. Additionally, HA combined with hematite could also increase soil pH and decrease soil CaCl2-extractable Cu and Cd. In particular, HA combined with 5% hematite was most effective in reducing soil exchangeable fractions of Cu and Cd by 53.7% and 65.6% compared to the control, respectively. The addition of HA-only increased water-soluble phosphorus, NaHCO3-extractable inorganic phosphorus, NaOH-extractable inorganic phosphorus, and HCl-extractable phosphorus. Conversely, HA combined with hematite treatments decreased NaHCO3-extractable inorganic phosphorus by 11.3–43.0% compared to HA-only. Vivianite and metal–phosphate precipitates were not observed using the Visual MINTEQ model, X-ray diffraction, and chemical analysis. The addition of hematite with or without HA increased free and crystal iron oxide fractions, while it substantially enhanced amorphous iron oxides in the soil. Thus, this study indicates that soil with high hematite content could enhance Cu and Cd immobilization while decreasing phosphorus availability in the red paddy soil amended with HA under the flooded conditions.

Synthesis and Characterization of Iron-Rich Glass Ceramic Materials: A Model for Steel Industry Waste Reuse

Wastes deriving from steel industry, containing large amounts of iron oxides and heavy metals, when collected in landfills are subjected to atmospheric agents, with consequent release of toxic substances in the soil and groundwater. The reuse of these wastes as raw materials for the production of advanced materials is a viable way both to overcome the environmental impact and to reduce the disposal costs, proposing new technologically advanced materials. This work aims to simulate these interesting glass-ceramics by using glass cullet coming from recycled municipal waste and high amount of iron(III) oxide (from 25 wt% to 50 wt%), the prevalent component of steel waste. The oxide was mixed with glass cullet and vitrified. The samples composition and the microstructure were investigated by scanning electron microscopy (SEM), and X-ray diffraction (XRD) was used to evaluate the nature of the crystalline phases. The chemical stability of the materials, in terms of ionic release into saline solution, was assessed. The electrical behavior of the samples was also investigated by varying the iron ions content and controlling the crystallization process. It is possible to obtain chemically stable materials with a nearly semiconducting behavior.

Modeling oxyanion adsorption on ferralic soil, part 1: parameter validation with phosphate ion.

Surface complexation models have proved to be valuable tools for predicting processes that occur at the solid-solution interface. Use of such models has become more widespread and nowadays more complex systems are studied, in an attempt to explain processes such as the competition between different species for mineral surfaces and the effect of the presence of organic matter. The aim of the present study was to analyze the mobility of phosphate in ferralic soils. The charge distribution model parameters for phosphate-goethite adsorption were used to predict phosphate mobility on samples from 2 horizons of a ferralic soil containing large amounts of iron oxides. The soil reactivity was attributed to the iron oxides, and some specific parameters were determined by means of phosphate adsorption-desorption experiments and included in the model. Adsorption of phosphate in the upper horizon, which contained more organic carbon and phosphate than the deeper one, was modeled by using the information obtained for the soil and the charge distribution model parameters derived for phosphate-goethite interaction with no need of further optimization. In contrast, some extra fitting parameters were required to improve the modeling of the phosphate adsorption in the deeper horizon.

Corrosion and passivation of iron and its nitrided layer in borate buffer

The aim of this work was to gain better understanding of the reasons of enhanced resistance to pitting corrosion of nitrogen-containing iron. Gas nitrided (570 °C, 4 h) and untreated Armco iron were examined in a borate solution of pH 8.4 without and with chlorides or ammonia. Enhanced pitting resistance and enhanced anodic currents were exhibited by nitrided Fe and also by untreated Fe in the solution with added ammonia. XPS showed that anodic films on nitrided Fe contained much larger amounts of iron oxides, in particular of magnetite, than those on untreated Fe. It is suggested that the anodic behaviour of nitrided Fe is determined mainly by the effect of evolving ammonia on corrosion products. Increased anodic dissolution can be explained by the formation of soluble complexes with ammonia, whereas increased amounts of magnetite can be due to the ammonia-promoted conversion of FeOOH + Fe(II) to Fe 3O 4. It is proposed that the enhanced pitting resistance of nitrided Fe results mainly from the formation of large amounts of iron oxides and from binding of chloride anions into a Fe–NH 3–Cl complex.

Ocean productivity before about 1.9 Gyr ago limited by phosphorus adsorption onto iron oxides.

After the evolution of oxygen-producing cyanobacteria at some time before 2.7 billion years ago, oxygen production on Earth is thought to have depended on the availability of nutrients in the oceans, such as phosphorus (in the form of orthophosphate). In the modern oceans, a significant removal pathway for phosphorus occurs by way of its adsorption onto iron oxide deposits. Such deposits were thought to be more abundant in the past when, under low sulphate conditions, the formation of large amounts of iron oxides resulted in the deposition of banded iron formations. Under these circumstances, phosphorus removal by iron oxide adsorption could have been enhanced. Here we analyse the phosphorus and iron content of banded iron formations to show that ocean orthophosphate concentrations from 3.2 to 1.9 billion years ago (during the Archaean and early Proterozoic eras) were probably only approximately 10-25% of present-day concentrations. We suggest therefore that low phosphorus availability should have significantly reduced rates of photosynthesis and carbon burial, thereby reducing the long-term oxygen production on the early Earth--as previously speculated--and contributing to the low concentrations of atmospheric oxygen during the late Archaean and early Proterozoic.

Optimal Iron Oxides for Obtaining Hexaferrites

Presently, the ferrites industry consumes large amounts of iron oxides chromed by spray roasting of steel pickling liquors. The aim of this paper is to propose the synthesis of optimal iron oxides by oxyprecipitation of steel pickling liquors in order to obtain Bahexaferrite with high magnetic properties using the ceramic process. As a raw material, it was used sulphuric liquors with iron concentration of 43 g/l. The studied variables for tie oxyprecipitation step were temperature, pH, stirring speed flow of oxidizer to obtain goethite and magnetite. The samples were characterized by XRD and SEM. These oxides were wet milled with barium carbonate and the mixture was calcined in order to obtain Ba-hexaferrite. A VSM was used for determine the magnetic properties and the morphology was studied by XRD and SEM. With these results five iron oxides were selected and the conditions of the ceramic process (calcination temperature and time) for obtaining hexaferrite were optimized versus H c .

Characterization of the low-temperature ash component of the herrin 6 coal seam (southwestern illinois) by thermal methods of analysis

A low-temperature ash (LTA) specimen of the Herrin No. 6 Seam (Southwestern Illinois) was analyzed using the computerized thermal analysis techniques of differential thermal analysis (DTA), thermogravimetry (TG), and derivative thermogravimetry (DTG). The major features of the thermal curves were dominated by a large pyrite (FeS 2) and hydrated iron sulfate component, illite and illite-smectite mixed-layer clays, and a small calcite component. The presence of hydrated iron(II) sulfates was observed to catalyze the decomposition of pyrite in inert atmospheres. The presence of large amounts of iron oxides, generated from studies in dynamic air (oxidizing) atmospheres, was observed to interact or change the nature of the calcite decomposition relative to that normally obtained by DTA and DTG techniques. The use of multiple atmosphere techniques allowed the recognition of pyrite in DTA as both an endothermic event in flowing nitrogen and carbon dioxide and as a multi-step exothermic event in dynamic air atmosphere. Due to the fact that ferrous sulfate heptahydrate exhibits a different mechanism for the loss of the final water of hydration in inert atmospheres than in oxidizing atmospheres, recognition of ferrous sulfate monohydrate was possible by both DTA and DTG thermal curves. The amount of calcite present in the LTA specimen was quantified in dynamic carbon dioxide atmosphere by thermogravimetry. This value was compared to that found by X-ray diffractometry. Sulfur analysis and X-ray diffraction data were also obtained for this LTA specimen.