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Surface disposal of mill tailings and fly ash is a major concern for many countries, as it pollutes the environment including air, water, and soil. Paste backfilling is an emerging mine backfilling technique, wherein the industrial wastes such as mill tailings, fly ash and blast furnace slag are backfilled inside the stopes. This study examines the physico-chemical characteristics of lead–zinc mill tailings, fly ash and their mixtures for their possible utilization in paste backfilling in underground metalliferous mines. Three different mill tailing–fly ash mixtures, viz., 95:5, 92:8 and 90:10 (wt%), have been considered. The chemical, morphological and mineralogical compositions are analyzed by XRF, SEM and XRD. The morphological analysis revealed that the mill tailings are irregular in shape and fly ash particles are almost spherical in nature. The filling of inter-particle spaces of irregular mill tailings with spherical fly ash and finer mill tailings (− 20 µm) particles will enhance the rheology of mill tailing–fly ash mix paste backfill. Chemically, the lead–zinc mill tailings is enriched in SiO2, CaO, Fe2O3, and Al2O3, whereas fly ash is mainly composed of SiO2 and Al2O3 with small amounts of Fe2O3, CaO, K2O, TiO2, MgO, SO3, Na2O, and P2O5. The XRD analysis revealed that the lead–zinc mill tailings mainly contain quartz, pyrite, dolomite, hematite and calcite, while fly ash contains quartz, mullite, kaolinite and hematite. This study proved that lead–zinc mill tailings and fly ash together can be suitably used for paste backfilling in underground metalliferous mines.

The majority of the power plants in India are fed with non-coking coals where the coals are dispatched from their respective mines via wagons loaded by a rapid loading system or pay loader. The usual top size of coal is 200 mm and sampling is carried out manually from wagons. The manual method of wagon-top sampling of large size raw coal is not only difficult but also violates some of the fundamental principles of sampling. As per sampling requirements, samples are to be drawn from the full depth of the wagons, which is impossible to be done manually. Since the ash distribution in the different size fractions is not homogeneous, the results from the samples, which do not reflect the true size distribution of the lot, are likely to be biased. More importantly, sample collection by shovel from the top is a function of human discretion and not governed by the equiprobability rule. In another case, the sample has been collected by a cross-belt type auto mechanical sampler for 200 mm size coal at one o...

The settling rate of coal fine particles by interaction with proper coagulants and flocculants is important in the water treatment/dewatering process. The standard test for measuring sedimentation rates is the jar test; the method is simple and direct. However, this method suffers from a number of disadvantages, despite its widespread application, it runs the risk of introducing large error due to the possible misinterpretation of the interface and the error may vary from person to person. To overcome this problem, different methods have been used for measuring the settling characteristics. In the present article, a German-made DCAT-11 instrument having bottom load weighing facilities synchronized with a computer to record the data and having facilities to measure up to 0.01 mg accuracy was used for testing a coal fines sample collected from an operating coal washery. The results show that the data obtained by the jar test are replicated by the data obtained from the instrument.

India is blessed with enormous coal reserves (one fifth of the world reserves) and is characterized as high ash and difficult to wash. With a 66% share of installed power generation capacity (255 GW, plus about 40GW captive power plants), the coal industry has a major role to play in the nation’s development. The coal consumption in 2013-14 was 643 MT against the indigenous production of 462 MT (mostly from Coal India Limited). The coal washing capacity from all the 52 washing plants is 131Mtpa, indicating that around 30% of the coal is being washed before it is used for power generation. It is envisaged that by the end of 12th five year plan coal washing capacity will be increased to 250 Mtpa. In India wet coal washing is usually practiced by crushing, sizing followed by beneficiation. The coal fines are usually recovered from the thickener, were flocculants are added to increase the settling of the coal fines. Normally, the coals are hydrophobic in nature and affect settling processes to a large extent. In the present paper four Indian coals of different characteristics are taken and their settling behavior in presence of industrial flocculent was investigated and correlated with the hydrophobicity of coal. Key words: coal washing, coal fines, effluents, contact angle, hydrophobicity, settling, flocculent, etc