Response of mineral separator for fine coal beneficiation

Indian coking coal washeries employ coarse and medium coal gravity concentration techniques for processing of 80-90% of coal and balance being processed by f lotation mainly. In case of fine coal also new develop¬ments are oriented towards the use of gravity concentration systems. Washability of coal is an important criteria to evaluate the performance of the separating systems. Washability studies consumes expensive reagents like bromoform, carbon tetra-chloride, benzene, acetone etc. Washability of fine coal is still more complicated due to reagent retention, use of heavy liquid centrifuge etc. An attempt has been made to use Mozley Mineral Separator to produce an ash-yield relationship using a coal sample of 36% ash. The results have been compared and analysed against the washability data to find out efficacy of the Mineral Separator. Tabling and flotation studies were also carried out on the same sample. The study reveals that while there is a deviation at low ash level, Mineral Separator can produce an ash-yield relationship nearly similar to washability data at higher ash level. While sink float provides an ideal separation the mineral separator provides data obtainable in separating system. Studies on tabling and flotation with the sample also indicate that the ash yield relationship is quite close to that of mineral separator

Release Analysis of Coal

Washing of fines is more problematic than the washing of coarse coal. One of the perceived barriers in large scale application of flotation in the cleaning of Indian coking coal is the absence of benchmarking. Release analysis is the counterpart in froth flotation to float and sink analysis in the gravity concentration of coal. Thus it provides a benchmark for the coal flotation actually carr-ied out in plants. The present work has been carried out with a LVC coal following the BS 7530 procedure of release analysis. Reagents used include MIBC as the common frother and n-dodecane and a synthetic collector, as the two colle-cting agents. Current published research indicates that with LVC coal only about 20- 30% yield at 18-19% ash cont-ent could be obtained. However, in the present work yields, up to 62% at about the same ash content could be obtained

Split flotation of LVMC coal to generate multiple products for complete utilization

A low volatile medium coking coal from Jharia coal field, India was used for this investigation. The proximate analysis of the sample shows that it contains about 25% ash, 21.4% volatile matter and 52.4% fixed carbon. The sizewise ash analysis of -0.5 mm coal indicates that -0.5+0.15 mm fraction contains lower ash (21.9%) than -0.15 mm fraction (29.7%). The flotation characteristics of the -0.5 mm coal were determined by release analysis. The study reveals that recovery of combustible at 15% ash is about 27% and 43% at 17% ash level. The low recovery is due to the presence of high ash in finer fraction. In order to improve the recovery, the -0.5 mm feed was classified into -0.5+0.15 mm and -0.15 mm fractions, and subjected to flotation separately. The recoverable combustible obtained from the release analysis of -0.5+0.15 mm at 15% ash level is 46%. The effect of collector dosage, frother dosage and aeration rate on flotation was studied. The responses of these variables in collectorless flotation of the -0.5+0.15 mm fraction containing low ash were also studied. A lower aeration and frother dosage favored the generation of clean coal with low ash. The ash content in the tailing stream from -0.5+0.15 mm flotation circuit is close to that of the original -0.15 mm fraction. The former is ground to -0.15 mm and the two fractions are processed together. As -0.15 mm fraction contains relatively higher ash, collector aided flotation using sodium silicate was performed to recover the clean coal with 17% ash. The products of the overall flotation circuit having different ash levels were recommended for use in different applications. The reject from -0.15 mm flotation circuit contained 56.4% ash which can be used for fluidized bed combustion (FBC). This eventually leads to complete utilization of coal

Frother Dependency in Coal Flotation

Frother dependency in coal flotation was examined using four coals varying in origin, rank, type, proximate analy-sis and feed size distribution and three different types of frothers, natural product (pine oil), synthetic alcohol (MIBC) and a polyglycOl based synthetic frother, N 8586. No frother was found to be unique. MIBC and N 8586 were found to produce the best results for Bhelatand and composite coals, respectively; two coking coals of same origin and maturity with small difference in proximate analysis and feed size distribution. For the two non-coking coals of different origin and maturity with signifi-cant difference in proximate analysis and feed size distribution frother dependency appeared to be manifested in the choice of frother, its dosage and in particle surface characteristics and their interaction with the frothers used. MIBC, at a lower dosage produced the best result for Maltby coal, whereas, no frother could deliver encouraging result for the Amlorhi coal. Therefore, frother dependency in coal flotation appears to have many dimensions. These include origin, maturity and surface characteristics of the coal and also the frother type and dosage, collector — frother interaction and finally frother — particle surface interaction

Coal Preparation - Recent Trends

Indian coal reserves constitute about 1% of the world reserve; the gross reserve is 1,92,884 million tonnes as on 01-01-1990, including Gondwana coalfields of tertiary coals (with high organic sulphur of North Eastern Coal-field) and tertiary lignite in Neyveli area etc., as shown in Table 1. Out of this, the coking coal reserve is only 28,690 million tonnes which is only 15% of the total. Again, out of the total coking coal (Table 2), hardly 18.5% is prime coking coal and about 27.5% is high volat-ile medium coking coal, a part of which is presently beneficiated for utilisation as blend charge for the coke ovens. But the low volatile medium coking coals comprising about 47.7% of the coking coal reserves remain unutilised or used in thermal power plants for want of suitable technology for their beneficiation

Effective flotation of weathered coal using frother blend

Froth flotation of weathered coal is a challenging task in a conventional flotation cell using commonly used collector and frother. Generally weathered coal shows the erratic flotation behaviour due to the surface oxidation as it makes the coal surface hydrophilic. When the surface gets oxidized, surface modifier is employed to float the clean coal. Frothers play significant role in stabilizing the mineralized bubble. It reduces the bubble size by reducing the interfacial tension at the air water interface. During this investigation, the flotation was carried out with two types of frothers namely; methyl isobutyl carbinol (MIBC), a weak frother and a strong polyglycol type. The Factorial design matrix was used for carrying out the experiments with the different ratio of frother blend, collector and promoter dosage. The high concentration of MIBC is found to be not effective for recovering the significant amount of carbon value as it causes less reduction of the interfacial tension at the air-water interface. The presence of a correct dosage of strong frother with weak one dramatically improves the flotation behaviour as it stabilizes the air-water interface and also reduces the consumption of the frothers

Advanced Coal Cleaning Technology for Challenges in Near future

Beneficiation potential of a high ash (36%) medium coking coal to a low ash (12%) level is investigated. Characterization studies indicated that the coal must be processed after reducing the size to 1.18 mm in order to accomplish substantial yield of the clean coal. A gravity based flowsheet for the -1.18+0.5 mm fraction is developed to generate clean coal at 12% ash with 9.2% overall yield. Mechanical cell flotation circuit for the -0.5+0.15 mm size fraction resulted in additional 3.5% yield at the desired ash level. A flotation circuit for the fine fraction (-0.15 mm) is developed using Jameson Cell only that added further 3.0% yield in the overall mass recovery at 12% ash. Thus, a total of 15.7% yield of the clean coal with 12% ash is achieved by treating various size classes separately. Recycling of some of the intermediate product streams is recommended for continuous operation to enhance the overall yield of the clean coal significantly

Recovery of Iron Values from Waste Manganiferous Iron Ore Fines for Pellet Making

A large volume of overburden and mine wastes is generated during the extraction and beneficiation of the low grade ores. The waste low grade manganiferous iron ore fine from southern part of India was studied for recovery of iron values. The chemical assay of the sample is 52.36% Fe, 4.75% Mn, 8.5% SiO2 and 2.82% Al2O3. The characterization study of the sample indicates the presence of microplaty hematite, goethite, pyrolusite, cryptomelane with minor amount of quartz and kaolinite. The beneficiation study of the sample does not respond to the conventional route of desliming the ground feed followed by gravity separation and magnetic separation. Therefore, an alternative technique of reduction roasting using a producer gas was attempted at different conditions. The characterization of roasted product reveals the phase transformation to magnetite and microplaty magnetite. The low intensity magnetic separation conducted with the roasted products generated at optimal condition shows that 70% concentrate having 64.5% Fe and 1.87% Mn could be produced. The high manganese in the concentrate works as an additive for making pellet with enhancement in pellet strength and drop in reducibility. Utilization of mines waste has significant impact on mineral resources and environmental hazard

Comparative Performance Analysis of Collectors in Flotation

Choice of collector in coal flotation worldwide has been limited to kerosene and diesel oil. For various reasons, mostly related to reagent properties, the latter has been traditionally used in coal flotation in India. In a recent development, commercial synthetic collectors are being launched in the market. Objective of the present work is to compare between the performance of two collectors, diesel oil and one such commercial synthetic collector for the size fractions; -0.5+0.1mm &-0.1mm. These are the typical feed sizes in split feed coal flotation. The compa-rison was done on the basis of a flotation performance evaluation parameter called “Separation Efficiency Rate (SER)” and also the reagent cost

Nanometer Thick Microplaty Hematite in Indian Iron Ores: Its Implication on Washing

Occurrence of nanometer to submicron thick microplaty hematite in the iron ore of eastern India is reported for the first time. High grade soft laminated ore and biscuity ore contain randomly oriented microplaty hematite along porous lamellae and pseudo-foliation planes. These microplaty hematites have a thickness of 70 nm to 500 nm or more. The thicker ones also show cleavage planes within, indicating the possibility of generating nanometer thick flakes. These microplaty hematites bridge the lamellae/laminae and interlamellar zones providing strength to the ore. On gentle tapping or by scrubbing with water, the ore breaks to fragments and fines of free microplaty hematite. On washing, the microplaty hematite grains get liberated and washed out to fine fraction of -150 m. It results in the fines of higher grade and low alumina in comparison to the associated lumps. It carries importance in the washing circuits using such ore types as feed