R.Q. Honaker

Application of the Falcon Concentrator for fine coal cleaning

Abstract An enhanced gravity separator (EGS) commercially known as the Falcon Concentrator has been evaluated for its ability to treat fine coal. From a comparison with other EGS technologies, the magnitude of the applied centrifugal force was found to determine the overall separation performance and throughput capacity. Using the relatively high g-forces supplied by a continuous 25-cm diameter Falcon unit, a low density cut point of 1.6 was achieved for the 210 x 37 μm size fraction of a fine coal sample which is significantly lower than that achieved by other EGS units. As a result, ash rejection values between 60% to 75% have been obtained from the treatment of several fine coal samples while recovering greater than 85% of the combustibles, which corresponds to an organic efficiency of about 90%. In addition, the sulfur rejection values achieved on various particle size fractions comprising a -⊥ mm coal sample were superior to that achieved by a spiral concentrator and a flotation column. Due to an insufficient centrifugal force, the metallurgical performances achieved on the basis of ash rejection for the −37 μm size fraction of all coal samples were insignificant. The ability to achieve efficient, low gravity cut points on fine coal and the operational simplicity of the Falcon Concentrator indicate potential for near term application in coal processing plants.

Nanobubble generation and its applications in froth flotation(part II):fundamental study and theoretical analysis

Abstract Froth flotation is a commonly employed technology to improve the quality of raw coal and minerals. Coal and minerals particle size and surface hydrophobicity are two main parameters that affect three key steps in froth flotation process: particle-bubble collision, adhesion, and detachment. This paper fundamentally investigated the effects of nanobubble on coal and phosphate flotation. It has been found that the presence of nanobubble in flotation pulp could widen the coal and phosphate flotation particle size range, increase the particle surface hydrophobicity, and thus improve the coal and phosphate froth flotation recovery.

Nanobubble generation and its application in froth flotation （part I）： nanobubble generation and its effects on properties of microbubble and millimeter scale bubble solutions

Abstract A special nanobubble generation system has been developed for evaluating the effect of nanobubble on froth flotation. In this study, an eight-factor five-level Central Composite Experimental Design was conducted for investigating eight important parameters governing the median size and the volume of nanobubbles. These process parameters included surfactant concentration, dissolved oxygen (O 2 ) content, dissolved carbon dioxide gas (CO 2 ) content, pressure drop in cavitation tube nozzle,

Application of dense-medium in an enhanced gravity separator for fine coal cleaning

Abstract Dense-medium separators have proven to be the most efficient processes for removing the undesirable gangue material from run-of-mine coal. The application of high-pressure feed injection into dense-medium cyclones to provide an elevated centrifugal force has recently been found to allow efficient separation performances for the treatment of fine coal (i.e., A test prograrn has been conducted to evaluate the potential cleaning of 1000 x 44 μm fine coal using dense-medium in an enhanced gravity separator (EGS), which mechanically generates enhanced gravity field. Test results indicate that the use of dense-medium in an EGS resulted in an 8% weight unit increase in mass yield compared to the use of water-only for the treatment of an easy-to-clean Illinois No. 6 fine coal sample. For a difficult-to-clean coal, the mass yield improvement was significantly greater at nearly 20% by weight. From the treatment offour different coal samples, organic efficiency values greater than 90% were obtained over the entire range of product quality values. These findings are reflective of the highly efficiency, low density separations provided by the dense-medium as indicated by probable error values below 0.05.

Coal maceral separation using column flotation

Abstract Recent studies have found that coal macerals have properties which may allow their use as high-valued products. A conceptual approach for the production of individual maceral concentrates utilizing column flotation is presented in this publication. Before maceral separation,the coal was ground to the particle size corresponding to near complete liberation of the macerals, which was approximately 4 gmm for an Illinois No. 6 seam coal. The production of maceral concentrates using flotation was based on the differences in the flotation rates among the various macerals, which was manipulated by adjustment of the medium pH. An increase in pH from 8 to 11 resulted in an order of magnitude reduction in the flotation rate of the vptinite maceral group while the corresponding reduction for the inertinite group was about 50% . On the other hand, the kinetic rate for the vitrinite group remained unchanged. By using pH control and column flotation, the inertinite content was increased from 7.5 % to 50% . Although the upgrading of the other two maceral groups was not as significant, it was evident that the success of the maceral enrichment for a given coal is dependent on the maceral liberation characteristics and the magnitude of the flotation kinetic rate differences among the macerals.

Upgrading Coal Using a Pneumatic Density-Based Separator

The potential of dry cleaning coal of varying ranks using a pneumatic table concentrator has been evaluated as part of an ongoing investigation. The evaluation has been performed at several sites throughout the United States where coal is extracted from surface open cast, highwall and underground operations as well as from coarse reject. The treated coals varied in feed ash content (i.e., 7–70%). Regardless of the mineral matter type, pure rock removal into the reject stream was achieved in all applications with little coal loss. Field data obtained when treating 50 × 6 mm run-of-mine bituminous coal indicate that 70–90% of the >2.0 Relative Density (RD) rock can be rejected. As a result, a clean product having acceptable market quality was generated from several coal sources including lignite, sub-bituminous, and bituminous coals. This article provides an overview of data from recent field testing of the dry air table technology and discusses the potential implementation strategy for the various sites evaluated.

Enhanced column flotation performance for fine coal cleaning

Abstract Past studies have found that the froth flotation process is efficient in recovering heavy middling particles, which negatively affects the recovery-grade curve achieved for fine coal recovery. Experimental and theoretical results indicate that the recovery of middling particles can be reduced from 25% to 10% using flotation columns in a multi-stage cleaning approach, thereby improving the overall separation performance. Tests conducted on a −48 mesh coal sample found a 7% improvement in mass yield using a rougher-cleaner column circuit while producing a flotation concentrate containing 8% ash. Similarfindings were obtained from the treatment of a −65 mesh coal sample using a different flotation column technology. To fundamentalty evaluate the use of multi-stage cleaning, a continuous column model has been developed which incorporates selective and non-selective froth drop-back, and feed component flotation kinetics. For kinetic rate limiting conditions, separation performance was found to substantially improve with the use of multi-stage cleaning, which agrees with the experimental findings. Under carrying capacity conditions, the improvement is a function of the degree of selectivity in the detachment process. Economic justification of the use of multi-stage column treatment must be based on enhancements in product grade and/or mass yield.

A Review of the Occurrence and Promising Recovery Methods of Rare Earth Elements from Coal and Coal By-Products

Previous research indicates that coal and coal by-products are a potential source of critical elements including rare earth elements (REE) with estimated amounts in the range of 50 million metric tons. Despite the proven presence of elevated REE concentrations, commercial extraction and recovery have not been realized. This article provides a review of the abundance, mode of occurrence, and recovery methods of rare earth elements in coal and coal by-products. The feasibility of using established REE extraction and recovery technologies is discussed along with issues associated with their use with coal resources.

Apex water injection for improved hydrocyclone classification efficiency

Abstract Classifying cyclones are a widely used device for achieving ultrafine particle size separations in industrial applications. However, inherent deficiencies include particle density effects in multi-component suspensions and ultrafine particle short-circuiting to the underflow stream due to hydraulic entrainment. A detailed in-plant test program has been conducted to evaluate the benefits of tangential water injection into the apex portion of a classification cyclone for the removal or minimization of the ultrafine by-pass. Based on models developed using the test results, ultrafine bypass can be reduced by 50% or more while maintaining the same corrected d 50 value through complex manipulation of operating and geometric parameters. In a subsequent test, the by-pass was reduced from 15% to about 7% while maintaining a d 50(c) value of 26 microns. However, the magnitude of the benefit in by-pass reduction is subject to the geometric parameters of the conventional classifying cyclone.

High capacity fine coal cleaning using an enhanced gravity concentrator

Abstract Recent research has shown that enhanced gravity separators provide the opportunity to effectively clean 1 mm x 37 micron coal. A detailed experimental program was performed on a continuous Falcon Concentrator, which was found to achieve separations at mass throughput capacity values in excess of 75 tonnes/hour. The apparent particle separation density for 1 mm x 75 micron coal was about 1.60 with relatively high efficiency ( Ep = 0.12). Typical ash and sulfur rejection values of 85% and 70%, respectively, were achieved while recovering 85% of the combustible material. Metallurgical and efficiency data from the evaluation are presented in this publication.