Avimanyu Das

CHARACTERIZATION AND PROCESSING OF LOW-GRADE IRON ORE SLIME FROM THE JILLING AREA OF INDIA

Detailed characterization followed by beneficiation of low-grade iron ore slime from Jilling Langalota deposit, India, was studied. The work involved separating the gangue minerals viz. quartz and kaolinite to form iron-bearing minerals, mostly hematite and goethite, as identified using XRD analysis to produce a suitable concentrate for downstream processing. The feed slime sample assayed 37.86% total Fe, 19.08% silica, and 14.4% alumina. Detailed characterization data indicated that a substantial amount of the sample was below 20 µm in size. The finer fraction contained larger amount of gangue while the coarser fraction was richer in iron. Considering the characterization data, two flowsheets were conceptualized for the beneficiation of the slime sample with two- and four-stage processing, respectively. In the two-stage operation, the grade of the slime could be improved to 60.26% Fe, 4.45% silica, and 3.98% alumina with an overall yield of about 20%. The results from the four-stage operation showed that it is possible to upgrade the iron value to 66.97% with a yield of 14.4% while reducing the silica and alumina content down to 1.7% and 1.52%, respectively. A simple flowsheet has been suggested to improve the yield substantially for the production of sinter/pellet grade concentrate from this slime.

Improving the separation efficiency of the knelson concentrator using air injection

ABSTRACT Recent test data have shown that the Knelson concentrator can provide a more efficient separation than froth flotation when cleaning coal in the 150 × 25 µm particle size range. To further improve the performance of this enhanced gravity separator, air bubbles were injected into the feed stream in an attempt to decrease the apparent density of the coal particles due to the formation of bubble-coal particle agglomerates. The test data showed that air injection had a significant impact on operating characteristics and separation performance. Coal recovery was increased by 10 to 20 absolute percentage points, while a 2 percentage point drop in the minimum product ash content was also achieved.

Ultrafine Coal Cleaning Using a Centrifugal Fluidized-Bed Separator

Ultrafine coal (nominal 150 × 44 µm) cleaning using a pilot-scale, centrifugal fluidized bed separator was investigated. The effects of the operating parameter values were evaluated and optimized to maximize mass recovery at a given product grade. Significant ash reductions were achieved from the cleaning of two coal sources having different cleaning characteristics. The concentrator provided a range of separation densities between 1.46 RD to 2.18 RD with probable error (EP) values of around 0.25. Rougher-scavenger circuit simulations indicate that the process efficiencies can be improved significantly while achieving low density separations. EP values ranging from 0.17 to 0.20 were realized, while the organic efficiency increased by 20 absolute percentage points.

In depth analysis of alumina removal from iron ore fines using teetered bed gravity separator

Abstract The performance of floatex density separator (FDS) for alumina removal from iron ore fines of size <1˙0 mm has been studied. Screw classifier feed containing 4˙28% alumina has been used as the raw feed material. Desliming in hydrocyclone helps to reduce the alumina content down to 3˙39% by removing high alumina bearing ultrafine particles. Experimental campaign was undertaken considering a factorial design of experiments with three factors, namely teeter water rate, bed pressure and feed pulp density, to quantify the influence of various parameters. It was found that in single stage processing in FDS, 72% of the feed alumina could be removed. A concentrate containing 1˙66% alumina could be achieved at a yield of ∼57% in FDS. Higher teeter water was found to improve alumina removal albeit with a small decrease in iron recovery. It was observed that higher bed pressure and lower pulp density are favourable for alumina rejection. The present study established that underflow moisture is a good indicator of FDS performance. The misplacement of ultrafines in FDS underflow product increases linearly with underflow moisture content. It has been suggested that a feed with a narrow size distribution would be better suited for processing in the FDS. Splitting the feed into a coarse and a fine size fraction and treating them separately would be beneficial in obtaining still better alumina removal.

Swirl flow characteristics and froth phase features in air-sparged hydrocyclone flotation as revealed by X-ray CT analysis

The time-averaged multiphase flow characteristics of air-sparged hydrocyclone flotation have been studied using X-ray computed tomography. Criteria of froth stability and the relationship between froth phase features and flotation response have been established. Quantification of the spatial extent of the different flow regimes has been done in order to characterize the flow behavior during steady-state operation of a nominal 2-inch diameter air-sparged hydrocyclone (ASH-2C). The influence of different operating and design variables on multiphase flow characteristics has also been established.

Simulation and quantification of creep damage

This paper highlights assessment of creep damage of an 11-year service-exposed reformer tube made up of HP40 grade of steel of a petrochemical industry from replicated creep data. The existence of scatter in the void characterization, creep deformation and rupture data leads to substantial amount of uncertainty in the assessment of creep damage. A discontinuous Markov process, which takes into account the associated scatter observed in damage evolution, has been used for creep damage assessment. The damage parameter A* is compared with the damage prediction by Markov process, where A* is derived as the cumulative contribution from microstructurally determined cavities at grain boundaries (A1) as well as number of creep cavities or voids at the grain boundary triple points (A2). This damage parameter (creep cavitation /voids) is in close agreement with the damage prediction curves at low stress whereas at high stresses it could correlate well till the midregion of the predicted curves, above which cavity measurement was practically not feasible. Also the value of damage tolerance parameter λ (ratio of rupture strain to Monkman–Grant constant) infers that growth of cavities has been attributed to a purely diffusion controlled mechanism, grain boundary sliding mechanism or a combination of two.

A comparative mineralogical and geochemical characterisation of iron ores from two Indian Precambrian deposits and Krivoy rog deposit, Ukraine: implications for the upgrading of lean grade ore

Abstract Iron ores from two important Precambrian belts in India are studied in detail. The first of these is the Jilling-Langalota deposit, hosted by banded iron formations along with generations of shales, tuffs belonging to Iron Ore Group of Eastern India and is hosted in the Singhbhum-North Orissa Craton. The second group of ores is from the Chitradurga basin in Eastern Dharwar Craton, Southern India. These form part of the Archaean greenstone belts and show a typical oxide–carbonate–sulphide association. The Jilling-Langalota deposit contains considerable amounts of blue dust that is absent in the Chitradurga deposit. Comparisons are made between the Indian iron ores and those of the Krivoy Rog province of the Central Ukrainian Shield. The Indian iron ores are relatively richer in Fe and contain higher amounts of alumina and phosphorous compared with those of the Krivoy Rog deposit. The Indian iron ore samples contain porous and friable oxides and hydroxides of iron with kaolinite, gibbsite and quartz. In contrast, the ores from Krivoy Rog are massive with negligible clay and a higher quartz content leading to very low alumina and very high silica contents in the ores and slime. The Indian ores and slimes are manganiferous in nature with high alumina, which is deleterious to processing and is due to the presence of intercalated tuffaceous shales and clay. The Eastern Indian iron ore deposits could have been formed due to enrichment of the primary ore by gradual removal of silica. It is believed that the massive ores result from direct precipitation while powdery blue dust is formed owing to circulating fluids, which leach away the silica from the protore. The host rock is exhalatic banded iron formation and the ubiquitous presence of intercalated tuffaceous shales point towards a genesis that could have involved Fe leaching from sea floor volcanogenic rocks. The nature of these ores along with the parting shale is responsible for production of large amounts of alumina rich slime during mining and handling. The detailed mineralogical characterisation studies aided by X-ray diffraction, scanning electron microscopy—energy dispersive spectroscopy, physical parameters and chemical characteristics have indicated the presence of various mineral phases and established the nature of iron-bearing and gangue assemblages of the bulk ores and slime samples from the three iron ore deposits. These in turn are useful in understanding the amenability of the ores and slimes for beneficiation and waste utilisation.

Processing of electronic waste in a counter current teeter-bed separator

Advanced gravity separation of ground electronic waste (e-waste) in a teeter-bed separator was investigated. It was established that the Floatex Density Seprator (FDS) is a promising device for wet processing of e-waste to recover metal values physically. It was possible to enrich the metal content from 23% in the feed to 37% in the product in a single stage operation using the FDS with over 95% recovery of the metals. A two-stage processing scheme was developed that enriched the metal content further to 48.2%. The influence of the operating variables, namely, teeter water flow rate, bed pressure and feed rate were quantified. Low bed pressures and low teeter water rates produced higher mass yields with poorer product grades. On the contrary, a high bed pressure and high teeter water rate combination led to a lower mass yield but better product quality. A high feed rate introduced en-masse settling leading to higher yield but at a poorer product grade. For an FDS with 230 mm × 230 mm cross section and a height of 530 mm, the process condition with 6.6l pm teeter water rate, 5.27 kPa bed pressure and 82 kg/hr feed rate maximized the yield for a target product grade of 37% metal in a single pass.

Development of a Generalized Strategy for Dry Beneficiation of Fine Coal over a Vibrating Inclined Deck

Beneficiation of coal fines of size −1.0 + 0.1 mm using an air table under controlled fluidization was investigated. Widely different feed coals with ash values ranging from 30–50% were shown to respond well to the process. Interactions among process variables towards influencing the separation performance were studied carefully to have a firm control over the process. Detailed statistical analysis of the experimental data was carried out and in-depth understanding of the process was accomplished through various statistical plots. The preferred operating regimes were identified for three different coals to achieve maximum mass yield for targeted product qualities. Flow sheets were developed for all the three coals investigated in order to obtain multiple usable products using a maximum of four stages of operation of the air table. A generalized strategy for dry cleaning of any coal with given characteristics was developed such that application potential of the air table can be enhanced.

Recovery of Combustibles from Fine Coal through Controlled Air Fluidization over Inclined Deck

The segregation pattern for dry beneficiation of fine coal (–1.0 + 0.1 mm) in an air table was investigated. The feasibility of cleaning a high ash (~49%) coal to the ash level specified for application in a thermal power plant (34%) was established. The density (ash) distribution pattern on the deck surface at steady state established the progress of segregation under various operating conditions. The operating regimes for a desired product at suitable mass yield were identified. A strategy was developed to process the high ash thermal coal and the flow scheme was established through which around 47% mass yield of the clean coal was obtained at 34% ash level. A second product was generated which was suitable for application in a fluidized bed combustion unit. A completely rejectable tailing was also obtained with 69% ash having a mass yield of 33%. Thus, it was established that high ash coal fines can be treated efficiently by controlled air fluidization over an inclined porous deck. The present study also brought out the features of separation and how segregation progresses over the deck as the material moves towards the discharge end. The effects of important process variables on the separation performance as well as on the segregation pattern were also established.