Shobhana Dey

Effective Processing of Low-Volatile Medium Coking Coal Fines of Indian Origin Using Different Process Variables of Flotation

The low-volatile medium coking coal fines from the eastern part of the Indian coalfield was used for this study. The proximate analysis of the composite sample designates that the fines contain about 25% ash, 21.4% volatile matter, and 52.4% fixed carbon. The ash in the size fraction of −0.5 + 0.15 mm is lower (21.9%) than the −0.15 mm fraction (29.7%). The flotation characteristic of the composite coal reveals that recoverable combustible at 15% ash is 27% and 43% at the 17% ash level. The low yield of the concentrate is due to the presence of fines comprising high ash. To enhance the yield, the −0.5 + 0.15 mm and −0.15 mm fractions were subjected to flotation separately. The effects of reagent dosage and aeration rate were studied with a composite and the −0.5 + 0.15 mm fraction to produce low-ash clean coal. Release analysis carried out with −0.5 + 0.15 mm coal improves the recovery of combustibles to 42% at 15% ash%. The spilt flotation of −0.5 + 0.15 mm feed at the lower frother dosage and lower aeration favors generating the clean coal with low ash. The −0.15 mm fraction was floated with collector using sodium silicate as a depressant. The products having different ash levels could be used in specific purposes.

Utilization of Iron Ore Slimes: A Future Prospective

In India, iron ores processing industries play a vital role in the Indian economy. During the washing and processing of iron ores, slimes less than 0.15 mm are generated and discarded into the tailing pond. These slimes need processing as they cannot be used directly in blast furnaces. In the present investigation, a typical iron ore slime sample containing 59.22% Fe, 4.76% SiO2, and 4.57% Al2O3 was taken. The desliming operation was carried out by using 2” Mozley hydrocyclone. The process variables used to attain the optimum condition of desliming include the spigot opening, the feed pressure, and the diameter of the vortex finder maintaining the pulp density at 10% solid. The deslimed sample was treated by different techniques including an enhanced gravity separator to achieve iron concentrate with 65% Fe so that it can be used for steel making through pelletization. The yield of the magnetic concentrate is about 46.8% with 65% Fe. To improve the yield, the overflow from 2” hydrocyclone and the rejects from magnetic separation were deslimed and processed to recover the iron values. The final concentrate is 74% yield with 64.8% Fe, 1.76% SiO2, and 1.8% Al2O3.

Performance of Different Classes of Organic Compounds as Frother in De-ashing of Indian Coking Coal by Froth Flotation

Flotation studies were carried out on a high ash coking coal sample using different classes of organic compounds as frothers. The organic compounds used as frothers in the present study were the following: (a) Frothers from natural sources (cyclic alcohol/phenols), (b) Synthetic frothers: Aliphatic alcohols, Polyglycols, Alkoxy alkane and Cyclic ethers. The time-recovery flotation data were analysed using a modified first order kinetic model. The performances of different frothers were evaluated using the parameters such as yield, ash, recovery of combustible, rate constant and selectivity. It was observed that synthetic frother, in particular poly ethylene glycol (molecular weight 400) showed overall better performance against others. The mechanism of performance of typical frothers was studied. The improved performance of poly-ethylene glycol was attributed to the higher surface activity and the enhanced frothing characteristics.

Enhancing the Utilization Potential of a Low Grade Chromite Ore through Extensive Physical Separation

Low grade chromite ore with less than 30% Cr2O3 was investigated with a view to enhance its utilization potential. The ore contained olivine, serpentine, and chrysotile as the gangue minerals. The chromite mineral contained alumina, magnesia, and FeO in its lattice. Critical mineralogical assessment indicated that enrichment to a level of 39-43% Cr2O3 may be possible. Beneficiation of the ore was undertaken using gravity based methods. Inadequate liberation prevented any significant enrichment at 0.9 mm top size. At 0.3 mm top size, the spiral concentration generated a concentrate with 40.5% Cr2O3 from the coarser fraction. The finer fraction was treated in a shaking table to generate another concentrate with 41.6% Cr2O3. The final combined concentrate assayed 41.2% Cr2O3 with a Cr/Fe ratio of 2.27. The middling from both treatments were rich in chromite content and were recommended to be included in the concentrates. Chromite recovery from the coarse reject was also beneficial. It was recommended that 8-10% solids content of the reject stream with 0.02 kg/t of Magnafloc flocculant may be used to achieve best settling characteristics of the reject fines.

Quantification of Sulphydryl Collector-Mixture Used in Sulphide Ore Flotation

Sulphydryl collectors are used for the flotation of sulphide ores. Sometimes a combination of various types of sulphydryl collectors having different functional groups are used to improve the flotation performance. Usually UV spectrophotometry technique is used to quantify the unabsorbed amount (residual concentration) of single sulphydryl collectors left after the adsorption or flotation studies. When a mixture of these collectors is present, UV spectrophotometry gives erroneous results as there is an interference of the spectra over the other. An alternative approach, ion-pairing chromatography (high performance liquid chromatography) gives encouraging results. This practice utilises the separation of chromatograms and determines the concentration of sulphydryl collectors spectrophotometrically. It can effectively quantify the mixtures of sulphydryl collectors of different functional groups and thus estimates the amount of chemicals needed for effective flotation, and also minimises the adverse effect of the same on the environment.

Scavenging of High-Value Product from High-Ash Medium Coking Coal: A Compulsion for Less Endowed Regions

Beneficiation of a high-ash (35%) medium coking coal to obtain a low-ash (12%) clean coal product is investigated. Characterization studies indicated that this coal can be processed after reducing the size to 1.18 mm in order to achieve reasonable yield of the clean coal at such a low target-ash level. The desired ash reduction is possible only after treating different size fractions of the −1.18 mm crushed coal separately. A gravity-based processing scheme comprising of a spiral-floatex circuit along with multigravity separator for the −1.18 + 0.5 mm fraction is developed to generate clean coal at 12% ash with 10.3% overall yield. Mechanical cell flotation circuit for the −0.5 + 0.15 mm size fraction resulted in additional 5.2% yield at 12% target ash level for the clean coal. A flotation circuit for the ultrafine fraction (−0.15 mm) is also developed using Jameson cell flotation that added further 4.4% yield in the overall mass recovery of the combustibles at the desired ash level. Thus, a total of 20% yield of the clean coal with 12% ash is achieved by treating various size classes separately. Application of the clean coal is recommended for metallurgical purpose. Out of the remaining 80% material, 35% is recovered at a 27% ash level that is recommended for use in sponge iron sector. The balance 45% with an ash level of 50% is marked for use in fluidized bed combustion for power generation. A complex flowsheet such as the one described in the present article is likely to be the future requirement for processing high-ash medium coking coals to a high-value low-ash product to enhance its utilization potential for metallurgical purpose.