This objective of this project was to develop a new dewatering device that could produce a lower moisture content and better fine particle recovery than current technology. To meet this goal, a hyperbaric horizontal belt filter was designed and constructed over the course of 18 months. Once built, the filter was then thoroughly tested to determine operational capabilities. The test data showed that the lowest moisture content that could be achieved with a coarse feed (minus 1 mm screen-bowl centrifuge feed) was 8.8%. This value could be further reduced to 8.2% and capacity increased with the use of dewatering aids. When testing with a fine feed (minus 0.15 mm column product feed), the lowest moisture content was 35% without chemicals and 29% with chemicals. A 50/50 mixture by volume of coarse and fine feeds was artificially created and provided a moisture of 10.8%, which was reduced using reagents to 8.4%. The machine provided a very high recovery rate for all feed materials. Of the coal input, no less than 94% of it reported to the dry product. The pressure used to dewater the coal was the controlling factor for the air consumption of the unit. The data from these tests suggest that a full size production unit is feasible, although the power requirements for gas compression would be high. / Master of Science

Recent hydrodynamic studies suggest that small air bubbles can be used to improve the performance of column flotation. Tests carried out at Virginia Tech during the past several years have shown that various types of inline motionless (or static) mixers can successfully produce microbubbles for column flotation. Unfortunately, few guidelines exist for selecting the proper size and type of motionless mixer for generating microbubbles. In the present work, the mean bubble size produced by various types of in-line motionless mixers has been experimentally determined over a wide range of operating conditions and generator geometries. Test results indicate that generator performance is described by a series of expressions derived from a dimensional analysis. These expressions demonstrate that bubble diameter is primarily determined by the generator geometry and a dimensionless term known as the Weber number. Tests have also been conducted to determine the reduction in the performance of centrifugal pumps under air admitting conditions. A semi-empirical pump model has been utilized which allows the proper size of pump to be selected for microbubble generation. This information should prove useful for the design and operation of microbubble generation circuits on an industrial scale. / Master of Science

The implementation of process control in fine coal processing operations has traditionally been limited by the lack of adequate on-line ash sensors. Several nuclear based analyzers are available, yet none have seen widespread acceptance by the coal industry. This is due largely to their high cost, the influences of seam type and pyrite content on accuracy, and the inconvenience of having radioactive sources in a plant. Thus, reliable process control of fine coal circuits is often unobtainable due to the lack of on-line monitoring devices for ash content in process slurry streams. Recently, a video-based slurry sensor for ash analysis of coal tailings has been developed which provides a low cost, reliable ash-monitoring system suitable for use as a process control sensor. The video-based slurry sensor is mounted in a small sump which is continuously fed with coal tailings. The slurry presentation system uses a pressurized tube to rapidly acquire samples of tailings slurry. The video-based sensor employs a black-and-white television camera to acquire live images of the slurry samples. These images are then processed by the PC-based image analysis system to rapidly determine ash content. An adaptive calibration system is used in conjunction with manual monitoring and sampling to provide a means for continuous improvement of the measurement accuracy. Problems with sample illumination and sample presentation have plagued previous developments of on-line optical sensors. The video-based slurry sensor developed in this work uses a unique sample presentation system to provide high-quality slurry images online. The possibilities of using this technology in other mineral processing applications are abundant. / Master of Science

The development of Infrared Spectrometry as a High Performance Liquid Chromatographic detector is presented. Early work with both a conventional dispersive instrument and a Fourier Transform Infrared (FTIR) Spectrometer is presented coupled via a flow cell to size exclusion chromatography. These were used for the analysis of the non-volatile components produced in the liquefaction of coal. Additional work is presented for the coupling of FTIR to analytical scale normal phase chromatography via a flow cell technique. Analysis of both model mixtures as well as a complex process solvent used in the liquefaction process is discussed. Use of deuterochloroform as an improved IR transparent solvent is demonstrated. Work with microbore (1 mm i.d.) columns coupled with on-line flow cell detection is presented. Modification of the flow cell design for microbore compatability is shown as well as the benefits of microbore columns for fiow cell FTIR. Detection limits as amount injected for both analytical and microbore scale HPLC-FTIR are shown. / Ph. D.

Pyrite (FeS₂) is the major source of sulfur in various coals, and its efficient removal has proven to be a more difficult task than expected. Flotation is generally considered to be the most practicable process for the preparation of coal fines. However, even this technique is usually unable to remove more than 50% of pyrite from a 65-mesh coal sample, which is the typical feed to flotation. There are three major reasons for the low separation efficiency of liberated pyrite from coal by flotation. They include self-induced hydrophobicity of pyrite caused by superficial oxidation, nonselective hydraulic entrainment of pyrite particles into froth product, and incomplete liberation of pyrite from coal that results in composite coal-pyrite particles, i.e., middlings. The present study was undertaken to address problems associated with these recovery mechanisms of pyrite and develop techniques to enhance pyrite rejection in coal flotation. To better understand self-induced hydrophobicity of pyrite, chronoamperometry and voltammetry on freshly fractured electrodes were used to explore incipient oxidation and reduction of the mineral. Voltammetry on rotating ring-disc electrodes (RRDE) was carried out to provide information on soluble species and kinetics of oxidation and reduction processes. X-ray photoelectron spectroscopy (XPS) was used for chemical identification of oxidation products. Galvanic coupling with sacrificial anodes was investigated as a practical method to cathodically protect pyrite and prevent its oxidation. Microflotation tests were conducted under controlled potentials at different solution pH's, and the results were correlated with electrochemical studies. The feasibility of improving pyrite rejection by controlling its surface chemistry was tested in flotation experiments conducted with a 2"-diameter microbubble flotation column and a conventional 5-liter Denver flotation cell. Effects of froth stability on the microbubble flotation of coal were studied with an objective of minimizing hydraulic entrainment of pyrite. The operating parameters were systematically varied to study their effects on water recovery which was used as a measure of froth stability. It has been demonstrated that the upgrading of coal in a flotation column can be significantly improved when froth stability is properly controlled. In an attempt to enhance the rejection of pyrite in middlings, various column circuits were experimentally examined and theoretically analyzed. The effect of circuit configuration on the overall circuit performance was evaluated by separation efficiency and separation curves. It has been shown that the overall separation efficiency of column flotation is rather insensitive to circuitry due to the unique characteristics of the unit flotation column, i.e., the addition of the wash water into the froth. / Ph. D.

The objective of this study was to evaluate various multi-stage circuit arrangements that may be used to improve the column flotation of micronized coal. Laboratory flotation tests were performed with two different samples of Pittsburgh No. 8 seam coal. The first coal, Coal A, was ground to two different particle sizes and subjected to both column and conventional flotation. These tests were performed to obtain an initial understanding of the operational behavior of the column process and to compare the results with those of conventional flotation. The second coal, Coal B, was used in the actual testing of three different column circuit arrangements. The experimental test results were compared to simulated results obtained using a rate-based flotation model constructed in the present work. Several hypothetical flotation circuits were also examined using the simulation model and experimental flotation rate data. The circuit test results showed that each of the different circuit configurations possessed specific advantages in terms of throughput capacity, combustible recovery, ash rejection and sulfur rejection. However, the overall performance curves for each circuit were all found to fall on or just below the maximum separation curve predicted using the release analysis technique. Also, the simulated results in almost all cases predicted better results than what was actually obtained. This discrepancy was attributed to the inability of the rate-based model to adequately describe restrictions associated with the carrying capacity of the column froth. / Master of Science

In order to demonstrate the ability of microbubble flotation to superclean coal to ash levels of less than 2%, several Eastern U. S. coals have been tested. The results show that the process is capable of producing superclean coal with improved recovery as compared to the conventional flotation process.To further improve and understand the microbubble flotation process, electrokinetic studies of the hydrocarbon oils used in flotation as collectors have been conducted. Also, the effect of oil emulsifiers on the zeta potential of oil droplets has been studied. In general, oil droplets are negatively charged and negative zeta potential is reduced with the addition of nonionic and cationic surfactants. On the other hand, the negative charge is increased with the addition of an anionic reagent. It has also been shown that the negative zeta potential of oil droplets increases with increasing hydrocarbon chain length.The effects of different collectors on induction time and flotation have been determined by conducting microflotation and induction time experiments using an Elkhorn seam coal sample. The results show that industrial oils combined with the coal have the shortest induction times and, therefore, the highest flotation yields as compared to pure hydrocarbon oils. It has also been shown that oil emulsifiers tend to increase flotation yield and reduce particle/bubble induction time. / Master of Science

The Chemical and Electrochemical Coal Cleaning (CECC) process, designed to remove mineral matter from coal, has been investigated by treating coal samples in acidified slurries. Various coals, characterized by different maceral structures and mineral matter contents, were subjected to several experimental procedures under mild conditions. Substantial amounts of mineral matter (up to 70%) could be extracted from coals which were resistant to physical cleaning, while 22% of sulfur could be removed from pyritic coals. The operating conditions of the CECC were studied in order to determine their influence on the process efficiency. Analyses conducted on solids and leachates resulting from the tests demonstrated that different mechanisms were achieving demineralization by the CECC. Between 50% and 95% of the feed mineral matter was removed by dissolution, whereas the balance could be ascribed to liberation. The CECC process is suitable for cleaning middlings, as well as for further extracting mineral matter from physically clean coals, especially from pyritic vitrinite and fusinite type coals. / Master of Science

Pretreatment of Pittsburg seam B coals to decrease its ash content and increase its solvent extractable material was investigated by anodically electrolysing acidified coal-water slurries at potentials around 1.0V SCE. The effects of the pretreatment were examined as functions of coal particle size, acid strength of the slurry, time of electrolysis and applied potential. The coal electrolysis was found to be most efficient at low acid strengths and short electrolysis times. The morphology of the coal surface changed with the conditions of the electrolysis and related to the percentage ash removal and the amount of solvent extractable material present in the coal. The anodic oxidation of the coal is suspected to occur via an electrocatalytic(EC) mechanism, whereby ferrous ions in the coal are first oxidised at the anode to the ferric state. The ferric ions migrate into the coal and accept electrons from accessible bonds in the coal micelle thereby reducing themselves back to ferrous ions and return to the anode for re-oxidation to the ferric state. The acceptance of electrons from certain bonds in the coal micelle results in the break-up of the micelle in to simpler compounds. Accordingly, the solubility of the coal in an organic solvent should increase and this was found to be so when ferrous ions were externally added to the electrolyte. The electrolytic process was also found to transfer metallic ions present in the coal into solution in the electrolyte. / Master of Science

A new method for demineralizing coal has been developed which is based on the osmotic pressures that occur when electrical double layers overlap. In this technique, coal is exposed to ferric ions in an acidic medium which causes the coal to lose electrons and become positively charged, thereby establishing ionic double layers in the vicinity of its surface. Inside the pores and crevices in which mineral matter is entrapped, the ionic double layers overlap and reduce the chemical potential of water, creating an osmotic pressure. The build-up of such pressure pushes the mineral matter out of the crevices, resulting in mineral liberation. Since the process, which is termed electro catalytically induced liberation (EIL), relies on surface-chemical reactions, the energy consumption is substantially lower than in conventional liberation processes based on comminution. Tests on several different seams of coal from varying geological locations have indicated that the process may be used to remove over 70% of the mineral matter present in coal. Mass balance studies conducted on a Wyodak coal indicate that approximately 90% of the ash removed is by the EIL mechanism, while the balance may be attributed to acid dissolution and the loss of material during handling. Scanning electron micrographs of the coal samples taken before and after treatment show morphological changes consistent with the proposed EIL mechanism. The technique has been used successfully to clean bituminous coals, low-rank coals and preparation plant refuse, and to further reduce the ash content of coals pre-cleaned by other means. A theoretical model has been developed to calculate the osmotic pressure that occurs inside a typical coal crevice during the EIL treatment. The changes in the aqueous chemical potential are calculated using semi-empirical equations derived from solution theory, while partial molar volume changes are accounted for in the final calculation of the osmotic pressure. The model indicates that pressures on the order of 4-7 atmospheres can develop inside crevices with walls 100-1000Å apart. These values are numerically consistent with those predicted by other models developed using different approaches. / Ph. D.