Coal Tailings Research Articles

98/00058 Effect of magnetite size on the coal purification process in a fluidized bed

Characterization of fine coal tailings using a variety of techniques reveal that it is composed of 30% clay minerals (kaolinite and illite), 23% muscovite, 26% quartz and 20% coal with little amount of carbonate minerals. Various flocculant combinations and their order of additions are utilized to understand the ability of dual flocculant systems on dewatering of these fine coal tailings. Settling rate and turbidity are used as criteria for screening and measuring the performance of anionic, cationic and nonionic flocculants. Dual flocculation of tailings has been tested with the aim of identifying if the synergy reported for mono-disperse systems is also valid for multicomponent systems. While the nonionic–cationic combination leads to the highest settling rates, the lowest turbidity values were obtained when using the anionic–nonionic combinations. The mechanism of interaction of dual polymers with particle surfaces and their synergy are discussed with the help of settling and turbidity data. The turbidity values obtained in mono-flocculation tests using nonionic and cationic flocculants and those made with dual flocculation combinations reveal that this kind of flocculant combinations play an unfavorable role in the flocculation of coal preparation plant tailings though there are contrary systems reported in the literature.

Improving clay‐based tailings disposal: Case study on coal tailings

AbstractThe role of swelling clays in hindering the compressional dewatering characteristics of coal‐mine tailings is examined. The effects of electrolyte concentration and ion exchange in improving the shear and compressional rheology are compared. Suspensions studies include actual mine tailings (thickener feed and thickener underflow) as well as synthetic clay dispersions made from clay collected from the coal seam. It was shown that the most important parameter in controlling the properties of the tailings suspension is “controlled” dispersion in the presence of a Ca2+ electrolyte concentration in excess of that required to (1) prevent initial swelling and (2) provide full cation exchange of the clay. Under these electrolyte conditions, complete delamination of the clay did not occur, and both the dewatering and handling characteristics of the resultant suspensions improved dramatically.

97/01644 Recovery of anthracite from coal preparation-plant tailings

97/01644 Recovery of anthracite from coal preparation-plant tailings

Cement stabilisation as an aid to the disposal of coal preparation plant tailings

ABSTRACT This paper presents the results of a programme of laboratory-based research into factors which may influence the geotechnical properties of dewatered coal preparation plant tailings which were mixed with small quantities of Ordinary Portland cement. Oedometer and consolidated undrained triaxial tests demonstrated that the characteristics of the tailings were significantly altered by the addition of cement. The consolidation of the cemented tailings caused the gradual degradation of the cemented structure, resulting in a reduction in strength of the material. After total degradation of the cemented structure, consolidation to higher stresses resulted in the cemented tailings gaining strength in a similar manner to that of uncemented tailings. This behaviour indicates that cement addition cannot be relied upon to induce tip stability through a permanent increase in shear strength. In current practice, cement is only added to dewatered tailings in sufficient quantities to improve their handling and placement characteristics and is not exploited for tip stability.

96/04673 Method for dewatering coal tailings using DADMAC/vinyl trialkoxysilane copolymers as a coagulant

96/04673 Method for dewatering coal tailings using DADMAC/vinyl trialkoxysilane copolymers as a coagulant

Coal-Oil Agglomeration and Combustion Studies for a Bituminous Coal Pond Tailing

Abstract The poor quality of coal tailings used as one of the feeds in a coal-power generation station can lead to combustion problems. A coal-oil agglomeration technique has been tested as a possible option to treat the feed in order to improve the quality. The recovered coal from this agglomeration / flotation treatment had a significantly reduced ash content and increased calorific value. Char reactivity was determined using thermogravimetry and results show no difference in reactivity between the raw and treated coal tailings feed. Evolved gas analysis performed during the thermo-gravimetric runs also showed no significant difference in the evolved gases except for an increase in volatile hydrocarbon release. The final product would lead to improved flame stability and reduced mechanical and ash-handling problems.

Improvement of coal tailings disposal via understanding of clay chemistry : R. G. De Kretser & D. V. Boger, in: Adding value to our resources - our future. Proc. conference, Newcastle, NSW, 1995, (AusIMM), 1995, pp 149–153

Improvement of coal tailings disposal via understanding of clay chemistry : R. G. De Kretser & D. V. Boger, in: Adding value to our resources - our future. Proc. conference, Newcastle, NSW, 1995, (AusIMM), 1995, pp 149–153

Freeze-Thaw Dewatering and Structural Enhancement of Fine Coal Tails

An 18.2-ha coal tailings impoundment that reached full capacity in 1989 has since been undergoing reclamation activities. The impoundment is sectioned into coarse, intermediate, and fine tails regions. The fine tails region, which consists of saturated silt and clay-size soil and coal particles of high void ratio and negligible shear strength, offers unique problems in terms of reclamation to a dry-surface landscape condition. Freeze-thaw consolidation and dewatering is an effective process for transforming these fine coal tails to a condition of a weak soil with measurable shear strength. Consolidation of the fine tails is found to occur both within and below the frost front. Within the frozen zone, localized moisture migration results in the development of a three-dimensional consolidated soil ped and ice-lense structure. Upon thaw, the consolidated peds settle by gravity, with the water escaping to the surface through the fissured soil ped structure. Thermal-induced suction gradients developed at the advancing frost front result in moisture migration and dewatering of saturated fine tails below the frost front. These two freeze-thaw consolidation and dewatering processes are described, along with models for predicting potential volumes of freeze-thaw treated material for given climatic conditions. Field results showing the significance of these processes on the dewatering and strength enhancement of fine coal tails are also presented. This dewatering and strength development provides the opportunity to implement dry rather than wet landscape reclamation procedures during reclamation of these waste-storage facilities.

Utilization of compacted coal tailings as a structural fill : B. Indraratna, I. Gasson & R. N. Chowdhury, Canadian Geotechnical Journal, 31(5), 1994, pp 614–623

Utilization of compacted coal tailings as a structural fill : B. Indraratna, I. Gasson & R. N. Chowdhury, Canadian Geotechnical Journal, 31(5), 1994, pp 614–623

Recovery of anthracite from coal preparation-plant tailings

A laboratory study was conducted to investigate the potential for recovering anthracite from coal preparation-plant tailings. The study included washability analyses, cyclone simulations and froth-flotation testing Samples were collected from either the tailings streams or the slurry ponds of five anthracite-cleaning plants. From each sample, a washability analysis was conducted on the 28×100- and 100×200-mesh fractions. Using the above data, along with published partition data, simulations were performed with various cyclone-staging arrangements for both water-only and dense-medium cyclones treating the 28×200-mesh fractions. Separate froth-flotation tests were conducted on the 28×100- and 100×200-mesh fractions from three of the plant samples. The washability, simulation and flotation results are presented as grade-yield curves.

Geotechnical characterization of blended coal tailings for construction and rehabilitation work : B. Indraratna, Quarterly Journal of Engineering Geology, 27(4), 1994, pp 353–361

Geotechnical characterization of blended coal tailings for construction and rehabilitation work : B. Indraratna, Quarterly Journal of Engineering Geology, 27(4), 1994, pp 353–361

The recovery of benthic communities along the County Durham coast after cessation of colliery spoil dumping

Large amounts of coal tailings and minestone have been dumped off the County Durham coast since at least the beginning of the twentieth century. Three sites which have been subjected to colliery waste dumping were studied to assess the effect of the waste on the marine benthos, and the degree of recovery of the benthic communities after the cessation of dumping. A control site was chosen to the north of the impacted sites and presumed to be unaffected by dumping operations. At each site three replicate grabs were taken for macrofaunal analysis and one for sediment analysis (sand-silt ratio and percentage coal by loss on ignition). The colliery waste appears to have had an effect on the benthic fauna present, indicated by the multidimensional scaling (MDS) configurations, which showed a clear separation between the control and the three sites subjected to dumping. The highest diversity was at Easington (6 months after the cessation of dumping) followed by Blackhall and the control, with the lowest at Horden. This suggests that the level of disturbance is such as to result in an increase in diversity of the affected sites. There were clear signs of recovery from the effects of mine waste dumping at Horden 7 1 2 years after the cessation of dumping, although at Blackhall the community is still perturbed 12 1 2 years after the cessation of dumping. This is probably caused by the prevailing southbound current transporting coal waste down to this site, where it appears to accumulate.

Geotechnical characterization of blended coal tailings for construction and rehabilitation work

Abstract Coarse and fine refuse is produced by various coal processing equipment. For instance, fine tailings (100-500µm) are produced by froth flotation cells, whereas coarse fractions (up to 50 mm) constitute cyclone rejects. The relatively wet fine tailings have limited use in construction activities and they are generally pumped as slurries into tailings ponds. The coarse rejects have a greater engineering applicability and are utilized in the construction of tailings dams, mine access roads as well as for landfill and ballast. This study investigates the fundamental engineering properties of blended tailings, where- by appropriate fractions of flotation tailings are mixed with cyclone rejects to produce an acceptable construction or rehabilitation fill. In particular, a practical procedure to optimize the blended ratios is proposed on the basis of fundamental geotechnical testing. The applications of relevant tests are described, including Proctor compaction, California Bearing Ratios, triaxial and consolidation tests. The results confirm that blending of fines with coarse rejects enables enhanced dry densities associated with reduced permeabilities, higher shear and compressive strengths, lower consolidation settlements and increased bearing capacities. The addition of a small quantity of cement (2-5%) further improves the engineering properties of the blended matrix. The practical findings of this study should encourage coal processing plants to modify their existing disposal methods to adopt more efficient co-disposal schemes. Optimization of procedures for discarding fine and coarse rejects together would generate substantial savings, with regard to dewatering of wet tailings and rehandling of distinctly different waste gradations.

Utilization of compacted coal tailings as a structural fill

Detailed laboratory investigations were conducted on coal tailings produced at Westcliff Colliery, New South Wales, Australia. Geotechnical tests were conducted to determine the particle-size distribution, mineralogy, compaction characteristics, compressive strength (California bearing ratio), shear resistance, and collapse potential. The tests show that compacted tailings have good potential as effective fill for embankments, tailings dams, mine access roads, and pavements. Large-scale utilization of these tailings for rehabilitation of subsidence-affected areas and mine backfill is particularly encouraging. It is demonstrated that this waste material can be efficiently compacted to produce acceptable engineering properties over a wide range of water contents. Although the behaviour of one specific type of tailings cannot be generalized to the diverse composition of other coal tailings, the results of this study assist in the interpretation of geotechnical data associated with nonconventional fill. The use of geotextiles in the stabilization of tailings is presented. The effect of moisture content and the number of geotextile layers on the shear strength parameters is investigated, and the influence of geotextiles on the failure modes of triaxial specimens is also discussed. Key words : California bearing ratio, coal tailings, compaction, geotextiles, structural fill, triaxial testing.

Geochemical distribution of metallic elements in the mineral matter of Brazilian coals

Abstract This work is a study of metals’ geochemical speciation for Co, Cu, Pb, Ni, Cr, Mn and Fe, in the mineral matter of coal samples from Southern Brazilian coals. The main purpose is to evaluate the potential mobility of these metals in aquatic and atmospheric environments, affected by coal activities. Two methods of five‐step sequential extractions were used (Tessier and Meguellati), following different leaching orders. A comparative study was done with the data from the two sequential schemes which has shown that the Tessier scheme presented, in general, better accuracy. Results obtained from both schemes, however, suggested that the leaching order of extractions influenced the reproducibility of metals’ geochemical distributions in the mineral matter of the Leão coal. Cr and Mn presented the least and greatest mobilities, respectively, while Pb, Co, Ni, Fe and Cu have shown intermediate mobilities. Coal tailings with different sulphur contents, on which only the Tessier scheme was applied, presented Ni, Cu, Pb and Fe associated to the oxidizable fraction, Mn to the carbonate and reducible, and Cr and Ni to the aluminosilicate fraction. Tailing samples with less sulphur contents have shown better precision in data quality.

Study of the Behaviour of Cemented Coal Preparation Plant Tailings

The results of laboratory-based research into factors which may influence the shear strength of dewatered coal preparation plant tailings when mixed with small quantities of ordinary Portland cement are presented. The effects of cement source and dosage, tailings moisture content, particle size distribution and ash content, together with liquid properties (pH, flocculant type and dosage) are reported. The failure of cemented tailings to regain their shear strength after disturbance through reworking is noted.

COMBINED FIELD DEWATERING: BRIDGING THE SCIENCE-INDUSTRY GAP

ABSTRACT The author's group is active in research on a wide variety of solid-liquid separation and dewatering methods. Processes examined include coagulation/flocculation, sedimentation, consolidation, drainage, filtration, compression/expression, and desaturation. A number of mechanical and electrical techniques have been used. These have been applied to a few well-defined systems such as clays, and to a wide variety of real suspensions from different industry sectors, from small laboratory to large demonstration scale. The experience of a range of techniques allied widi knowledge of the characteristics and behaviour of suspensions is helping to bridge the gap between scientific understanding and practical application. The present paper, based on both published and unpublished CSIRO work with an emphasis on fine and ultrafine coal and coal tailings, summarises the position. The analysis includes: • conceptual evaluation of the applicability and limitations of established dewatering techniques, • consider...

Thermal activation of coal tailings

This paper reports on a study of the thermal activation of coal tailings in order to increase the intrinsic reactivity of this material. Thermal treatment was carried out in a furnace with an inert atmosphere in the temperature range from 100 to 1000°C. The changes in the material following the treatment were determined by X-ray diffraction, thermogravimetric analysis and differential scanning calorimetry. In order to verify the true reactivity of the activated material, leachings with standard solutions of HCl were made and the yield of the aluminium extraction process was determined.

Properties of slurried coal tailings : Proc Conference on Hydraulic Fill Structures, Fort Collins, 15–18 April 1988P410–429. Publ New York: ASCE, 1988 (Geotechnical Special Publication No 21)

The processes of beaching, sedimentation, consolidation, crusting and rehabilitation which fine grained coal mine tailings initially deposited as a slurry undergo are discussed. The relevant engineering properties at different stages of the life cycle of the tailings are given and measured values for them are compared with values for other coal tailings and similar materials. Ongoing research is aimed at building a framework from which the behavior of coal mine tailings deposited as a slurry may be predicted.

Generalized Calibration of a Nuclear Moisture/Density Depth Gauge

Abstract The application of nuclear moisture/density depth gauges to soil deposits has generally relied on calibration by direct correlation with measured values of moisture content and density. In very soft variable deposits such as coal tailings, direct calibration is not possible. A generalized calibration can be developed from first principles based on the elemental composition of the soil being tested and the application of existing theories. Density and moisture content calibrations are considered separately for two different access tubes, and reasonably reliable calibrations are obtained. In applying these calibrations, an iterative procedure is required since the moisture content has a direct bearing on the elemental composition of the moist soil. The paper gives an insight into the operation and important features of a nuclear gauge.