Timothy C. Eisele

Mineral carbonation for carbon sequestration in cement kiln dust from waste piles

Alkaline earth metals, such as calcium and magnesium oxides, readily react with carbon dioxide (CO(2)) to produce stable carbonate minerals. Carbon sequestration through the formation of carbonate minerals is a potential means to reduce CO(2) emissions. Calcium-rich, industrial solid wastes and residues provide a potential source of highly reactive oxides, without the need for pre-processing. This paper presents the first study examining the feasibility of carbon sequestration in cement kiln dust (CKD), a byproduct generated during the manufacturing of cement. A series of column experiments were conducted on segments of intact core taken from landfilled CKD. Based on stoichiometry and measured consumption of CO(2) during the experiments, degrees of carbonation greater than 70% of the materials potential theoretical extent were achieved under ambient temperature and pressure conditions. The overall extent of carbonation/sequestration was greater in columns with lower water contents. The major sequestration product appears to be calcite; however, more detailed material characterization is need on pre- and post-carbonated samples to better elucidate carbonation pathways and products.

A review of binders in iron ore pelletization

The majority of iron ores must be ground to a fine particle size to allow the iron oxides they contain to be concentrated, and the concentrate must then be agglomerated back into large enough particles that they can be processed in blast furnaces. The most common agglomeration technique is pelletization, which requires the use of binders to hold the iron oxide grains together so that the agglomerates can be sintered into high-strength pellets. Although bentonite clay is the most commonly used binder, there are many other possibilities that could be competitive in a number of situations. This article reviews the numerous types of binders (both organic and inorganic) that have been considered for iron ore pelletization, including discussion of the binding mechanisms, advantages and limitations of each type, and presentation of actual pelletization results, so that the performance of the various types of binders can be compared and evaluated.

Review of Reductive Leaching of Iron by Anaerobic Bacteria

Leaching of iron, either as an impurity to be removed or as a metal to be recovered, requires a different approach than that of the oxidative leaching that dominates biohydrometallurgy of other metals. In particular, the significant increase in solubility that results from reducing Fe3+ to Fe2+ suggests that a reductive leaching process is most suitable. A wide range of anaerobic iron-reducing bacteria have been demonstrated to exist in the last few decades, which reduce Fe3+ to Fe2+ as part of their respiration. More of these organisms are continually being discovered, and many of these have promise for reductive bioleaching of iron. This review examines the many types of bacteria that have been demonstrated to reduce and solubilize iron, and the environments where such organisms can be found. The cultivation requirements of these organisms are also discussed, along with descriptions of the work that has been done to apply them to specific applications. These applications include decolorization of kaolin and silica, iron removal from bauxite, recovery of iron from low-grade or difficult-to-process ores, and promoting breakdown of iron-rich rocks to liberate other metals. Reductive iron leaching in these applications has been shown to be most effective for dissolving the more hydrated and amorphous iron oxides, with low dissolution rates for highly crystalline oxides such as hematite. It has also been shown that, the given sufficient adaptation and leaching time, these microorganisms can produce iron-bearing solutions containing as much as 1800 mg of Fe2+ per liter.

Pyrite recovery mechanisms in coal flotation

Abstract In most operating coal-cleaning plants, a significant amount of pyrite is recovered in the froth during flotation of high-sulfur coal. This pyrite recovery is commonly believed to be a result of pyrite particles floating due to hydrophobicity. However, even though a wide range of pyrite depressants have been reported over the years, there is no use of these depressants for industrial coal flotation, which suggests that the mechanism of pyrite flotation is not properly understood. In order to reduce the pyrite recovery during flotation, it is first necessary to identify the primary recovery mechanism, so that the appropriate method for correcting the problem can be selected. In this paper, it is shown that flotation of liberated pyrite due to its intrinsic hydrophobicity is not an important mechanism for recovery of pyrite from freshly ground coal, and that the bulk of the floated pyrite reaches the froth either as a result of simple entrainment or by mechanical locking with floatable coal particles. The experiments were carried out using both a conventional flotation cell, and a horizontally baffled flotation column.

Rheological effects in grinding circuits

Abstract The grinding efficiency of circuits using tumbling media mills in closed circuit with hydrocyclone classifiers may be improved by control of the mill slurry rheology. The rheology affects both the rate of fine material production by the grinding mill, and the separation performance of the hydrocyclone. In addition, the manner in which rheology changes are produced will affect hydrocyclone performance. This parameter is neglected in process control situations due to the difficulty of making rheological measurements of dense slurries on-line. In recent years, a number of new viscometers has been developed which may be useful for this purpose.

Study of Organic and Inorganic Binders on Strength of Iron Oxide Pellets

Bentonite is a predominant binder used in iron ore pelletization. However, the presence of a high content of silica and alumina in bentonite is considered undesirable for ironmaking operations. The objective of this study was to identify the alternatives of bentonite for iron ore pelletization. To achieve this goal, different types of organic and inorganic binders were utilized to produce iron oxide pellets. The quality of these iron oxide pellets was compared with pellets made using bentonite. All pellets were tested for physical strength at different stages of pelletization to determine their ability to survive during shipping and handling. The results show that organic binders such as lactose monohydrate, hemicellulose, and sodium lignosulfonate can provide sufficient strength to indurated pellets.

WATER CHEMISTRY EFFECTS IN IRON ORE CONCENTRATE AGGLOMERATION FEED

ABSTRACT In two different iron ore processing plants, it was demonstrated that when magnetite concentrate was filtered to prepare it for use as pelletization feed, the moisture that remained in the filter cake had greatly elevated levels of cations compared to the water removed by the filtration process. In particular, calcium concentrations in the filter cake were 565 times higher than in the filtrate water in Plant 1 and 19.4 times higher than the filtrate water in Plant 2. This effect is due to the adsorption of divalent cations on the magnetite surfaces resulting from electrostatic attraction when the pH of the solution is in the range where magnetite has a negative Zeta potential. Measurements of the Zeta potential as a function of pH for magnetite from Plant 2 determined that its point of zero charge (PZC) occurred at pH 3.0 to 3.5, which was much lower than is commonly reported in the literature and demonstrates that the PZC for magnetite is much more variable than is commonly thought. Plant experiments were carried out using carbon dioxide to reduce the pH of filter slurry so that the PZC could be approached. This was intended to allow adsorbed cations to be released from the magnetite surfaces during filtration. The pH adjustment was demonstrated to improve filtration rates by as much as 23%.

Effects of temperature on hydrocyclone efficiency

Abstract Plant investigations and laboratory experiments have been conducted in order to study the effects of temperature on the classification efficiency of a cyclone. It was demonstrated that, under otherwise constant operating conditions, alterations in temperature produced a nearly linear change in d 50(c) size. However, the sharpness of the separation, as defined by the reduced efficiency curve, showed no dependence on temperature.

Removal of Pyrite in Coal Flotation

In most operating coal-cleaning plants, a significant amount of pyrite is recovered in the froth during flotation of high-sulfur coal. Reducing the pyrite recovery first requires that the primary recovery mechanism should be identified, as different measures are required for reducing entrainment, locked-particle flotation, or true hydrophobic flotation. In this paper, evidence is presented which suggests that hydrophobic flotation is not an important mechanism for recovery of liberated pyrile when the collector is a neutral oil, and that the bulk of the floated pyrite occurs either as a resut of simple entrainment or by mechanical locking with floatable coal particles. Column flotation results are also presented which show that significant sulfur reductions can be achieved by reducing level; of entrainment.

The Effect of Calcined Colemanite Addition on the Mechanical Strength of Magnetite Pellets Produced with Organic Binders

Iron ore pellets must have sufficient mechanical strengths against degradation in all stages of pellet production. Low strength is also a problem for product pellets since they abrade during transportation to the reduction furnaces. The use of a binder is necessary to provide sufficient strength to the pellets and for better operation and handling of pellets. Bentonite is the standard binder in the industry; however, it is considered an impurity due to its acid oxide contents. Organic binders have been tested for many years as alternative binder to bentonite. They have been found to give sufficient wet pellet properties. However, they failed to provide sufficient strength to the preheated and fired pellets due to lack of slag bonding. It has been assumed that one possible effective method to improve the preheated and fired pellet strengths is addition of a slag-bonding constituent. In this study, calcined colemanite was added to the pellet feed to overcome the lower strength problem encountered with organic binder use. The strength of pellets produced with organic binders and calcined colemanite alone and in combination was comparatively studied against the strength of pellets made with standard bentonite binder in magnetite concentrate pelletizing. The results showed that addition of calcined colemanite into the pellet mixture improved the preheated and fired pellet strengths of pellets produced with organic binders.