Coal Tailings Research Articles

Effect of slurry conditioning on flocculant-aided filtration of coal tailings studied by low-field nuclear magnetic resonance and X-ray micro-tomography

The present work aimed to study the effect of slurry conditioning on flocculant-aided filtration of coal tailings by the analysis of filtration kinetics and filter cake structure. Laboratory filtration tests of the coal tailings showed that both the shear rate and agitation time have significant effects on filtration rate and cake moisture. Moderate agitation at the shear rate of 92 s−1 was favorable for fast filtration, but high cake moisture was encountered. The low-field 1H nuclear magnetic resonance (NMR) measurements of the filter cake showed that the slurry conditioning has a significant effect on the residual water in large pores and a negligible effect on the residual water in small pores. The X-ray micro-tomography (XRM) measurements indicated that the filter cake formed at the shear rate of 92 s−1 has more macro-pores and higher porosity than that formed at the shear rate of 53 s−1, hence more residual water was entrapped in filter cake. The slurry conditioning in the presence of flocculant will change the structure of filter cake and affect the filtration performance. There was a paradox between fast filtration rate and low filter cake moisture. The findings enable better understanding of the effect of slurry conditioning on flocculant-aided filtration of coal tailings.

Interaction between STAC and coal/kaolinite in tailing dewatering: An experimental and molecular-simulation study

The presence of clay minerals in coal tailings leads to a significant deterioration during the dewatering process. In this study, a cationic surfactant, stearyl trimethyl ammonium chloride (STAC), was considered to enhance the dewatering efficiency of coal tailings. The effect of STAC on coal tailing dewatering was evaluated by the filtration test. Results indicate that STAC can reduce filter cake moisture by increasing the hydrophobicity of particles, decreasing the surface tension of the filtrate, as well as neutralizing the associated charge. Furthermore, to investigate the interactions between STAC and coal tailings, the morphology of adsorbed STAC, interfacial adsorption structure, and dynamic behavior of water molecules were determined by atomic force microscopy (AFM) and molecular dynamics (MD) simulations on an atomic scale. AFM results revealed that the morphologies of STAC adsorbed on coal and kaolinite surfaces differed, owing to distinct interaction mechanisms. The adsorption of STAC on the kaolinite 001 surface is more uniform than on the 001- face and is predominantly based on monolayer adsorption through electrostatic interactions and hydrogen bonding. The MD simulation results suggest that the adsorption of STAC significantly inhibits the attachment of water molecules on coal and kaolinite surfaces. The nitrogen atoms of STAC were adsorbed to the particle surface, such that its alkyl chains were oriented towards water, thereby weakening the interaction between the particles and water. The above findings indicate that the addition of STAC can improve the hydrophobicity of coal and kaolinite effectively and thus, enhance the dewatering performance of coal tailings.

Ultrafast Plug Flow Agglomeration—Exploiting Hydrophobic Interactions Via a Concentrated Water-In-Oil Emulsion Binder

The selective agglomeration of a fine coal tailings stream using a high internal phase emulsion binder was investigated using a continuous steady-state plug flow through a high shear constriction. The emulsion binder effectively switches off the viscous resistance to particle–binder collision and adhesion, revealing the remarkable underlying speed of hydrophobic interactions. The emulsion binder is permeable, meaning the lubrication force between the particle and binder vanishes. The binder comprised a 95% aqueous solution dispersed within a 5% organic liquid (including the emulsifier). The agglomeration occurred within a high shear zone formed using a flow constriction within a 25 mm diameter pipe. The performance of the process was investigated at different flowrates in the range of 20–128 L/min, equating to extraordinarily high superficial flow velocities of up to 4.2 m/s and pressure drops in the range of 20–220 kPa. This rate greatly exceeds the nominal superficial feed velocity in flotation of order 0.01 m/s. Provided there was sufficient shear within the flow constriction, it was possible to process fine coal tailings with a feed ash of 50.1%, and generate a product ash of 8% at a combustible recovery of ~78%.

A Comparison Between Predictive Tests Results and Natural Weathering in the Figueira Mine, in Southern Brazils

Many studies on acid mine drainage (AMD) use predictive methods, such as humidity cells (HC), to study this problem, as it is often not possible to predict acid generation from field tests. However, some comparisons of HC testing with reality have proven to be unrealistic. In this study, we compared the results of the HC test with historical data from the Figueira mine, in the State of Parana (southern Brazil). To carry out the work,we collected a fresh coal tailings sample from the Figueira Mine, and compared monthly measurements of pH and electrical conductivity (EC), and concentrations of Fe, Al, Mn, and Zn, over a 5 year period (from 2013 to 2017) with the predictive test results performed following protocol B of the ASTM D5744-13 (2018) standard. The elements were analyzed by ICP-OES. The pH and EC of the HC test were lower than the field data. The HC test underestimated the concentrations of Fe and Mn, while Al and Zn were overestimated. We believe that the overestimations were due to the aluminosilicate buffering capacity and cation exchange capacity of the soil.

Settling, consolidation and shear strength behaviour of coal tailings slurry

The volume change and shear strength behaviour of tailings slurry with the changes in gravimetric moisture content is important to effectively utilise the storage volume and analysis of dam failure potential. Consolidation testing of tailings from a slurry-like to soil-like state is a critical task, and conventional consolidation apparatus does not have the capability of doing such testing, as the tailings slurries contain high water content. Settling tests conducted on slurries having a 25% solids concentration showed very low efficiency; final sediment was still slurry-like. An intrinsic point was identified based on pore water pressure dissipation during consolidation tests in a slurry consolidometer that can define two states of the tailings i.e. slurry-like and soil-like. In the slurry-like state, the volume change was greater for Slurry 2 than Slurry 1, while the inverse was observed in the soil-like state. The evolution of peak vane shear strength with the changes in moisture content was almost similar for both samples and obeyed the power function. Regression models have been developed and validated to predict the shear strength of materials at any gravimetric moisture content or void ratio.

Bacterial degradation of coal discard and geologically weathered coal

The biodegradation of coal discard is being intensively studied in South Africa in an effort to develop passive methods for the successful revegetation and rehabilitation of waste dumps, to mitigate pollution, and facilitate mine closure. Bacteria were isolated from slurries of coal tailings and diesel-contaminated soil, screened for coal biodegradation competence, characterized, and the colonization and degradation of coal discard and geologically weathered coal investigated using individual isolates and consortia. Ten novel coal-degrading bacterial strains were isolated and characterized, the gene sequences deposited with GenBank, and the (wild-type) strains deposited at Microbial Culture Collection, India. The results from the present work show that bituminous coal discard and geologically weathered coal is used by these isolates as carbon and energy source. Isolated strains and consortia colonized and degraded both coal substrates.Growth rate of the isolates is faster and stationery phase achieved sooner in minimal medium containing geologically weathered coal. This observation suggests that the oxygen-rich weathered coal is a more friable substrate and thus readily colonised and biodegraded. A reduction in mass of substrate is demonstrated for both individual isolates and consortia. The changes in pH and associated media colouration occurred concomitant with formation of humic acid-like (HS) and fulvic acid-like substances (FS) which is confirmed following analysis of these products by FT-IR spectroscopy. It is concluded that preferential metabolism of alkanes from the coal substrates provided the carbon and energy for bacterial growth and transformation of the substrates to HS and FS.

Use of coal beneficiation tailings as solid sorbents in the treatment of nitrate-contaminated real wastewater

This work evaluates the application efficiency of coal tailings beneficiation as a solid sorbent in the treatment of real wastewater contaminated with nitrate. The solid was characterized by XDR, SEM, FTIR and TGA. Adsorption experiments were performed in batch evaluating the effects of pH, solids concentration and contact time parameters. The kinetics of nitrate adsorption was evaluated using pseudo-first-order and pseudo-second-order models. Equilibrium isotherms for this system were analyzed at three different temperatures (298, 308 and 318 K) by Langmuir, Freundlich and Sips models. The best results from the adsorption experiments were pH 6, contact time of 60 min and 1 g 100 mL−1 of solid. The thermodynamics model that best described the behavior of the process was Sips. By applying these conditions to real wastewater, a nitrate removal of 93% was achieved. This result shows that adsorption using coal beneficiation tailings is technically possible.

In Situ Seismic Investigations for Evaluating Geotechnical Properties and Liquefaction Potential of Fine Coal Tailings

Abstract This paper presents a field seismic investigation that is effective in evaluating the in situ geotechnical properties and liquefaction potential of fine coal tailings subjected to mine bla...

Effect of shear-induced breakage and reflocculation on the floc structure, settling, and dewatering of coal tailings

Effect of shear-induced breakage and reflocculation on the floc structure, settling, and dewatering of coal tailings

Recovery and cleaning of fine hydrophobic particles using the Reflux™ Flotation Cell

The Reflux Flotation Cell (RFC) consists of a vertical vessel located above a series of parallel inclined channels. This novel system, which is the inverse of an existing gravity separation system known as the Reflux Classifier, provides a powerful mechanism for enhancing bubble-liquid segregation. The usual link between the imposed gas flux and water recovery in the froth product is decoupled through this mechanism, resulting in the establishment of a concentrated bubbly zone throughout the upper section of the cell, and no froth zone. A downwards fluidization arrangement promotes strong washing of the flotation product, to remove the hydrophilic slimes from the hydrophobic concentrate. The mechanism also provides for strong control of the bias flux, allowing a significant positive bias flux to be established. A feed suspension of fine coal tailings containing hydrophobic coal and hydrophilic mineral matter was subjected to the novel flotation, providing an ideal basis for studying the interplay between the hydrophobic particle recovery, inferred by the combustible recovery, and the product grade, inferred by the mineral matter content of the product, expressed by the ash %. The feed ash % was about 43 wt%. The product cleaning was compared to firstly, the results from the tree flotation method, and secondly, a newer method known as Coal Grain Analysis (CGA). The RFC results were found to lie to the left of the tree curve, converging to the limit described by the CGA analysis. This work suggests the RFC and CGA provide a form of mutual validation on the limits of cleaning, though more work will be needed to confirm this finding. The RFC was operated with a volumetric feed flux of the order 1 cm/s, a rate comparable to that of conventional flotation systems, with the bias flux ranging from 0.0 cm/s to 1.9 cm/s. For a fixed gas flux of 1.1 cm/s, increases in the liquid bias flux from 0.0 cm/s to 1.0 cm/s resulted in a decrease in product ash from 18.2% to 7.8%, and a reduction in combustible recovery from the order 87% to 75.6%. Operating at the lowest gas flux of 0.6 cm/s, and the strongest bias flux of 1.9 cm/s yielded a low product ash of 6.7% at the reduced combustible recovery of 64%.

Natural oxidation of coal tailings from Middelburg area (South Africa), and impact on acid-generation potential

SYNOPSIS The aim of this study was to determine the acid-generating potential of coal mine tailings located in the Middelburg area, South Africa, using conventional assessment techniques. Four coal-tailing samples were collected from different layers of a coal-tailing pile. The acid-base accounting (ABA), acid-buffering characteristic curve (ABCC), and net acid generation (NAG) methods were used in conjunction with a mineralogical investigation to assess the potential of acid mine drainage (AMD) formation from the tailings. The results showed that the top layer of the pile, which was exposed to the atmosphere, was most likely to form AMD, exhibiting the lowest paste pH (2.5) and ABA of zero kg H2SO4 per ton. The ABA results were compared to ABCC results and mineralogical calculations to confirm the findings. The results from the ABCC test and calculations based on mineralogy indicated that the ABA method overestimates the effective or readily available acid neutralization capacity (ANC) and the true MPA of each sample; only three of the four samples could therefore be classified as acid-forming, but with low acid-generating capacity. Although the findings show that the top layer of the coal tailings in the Middelburg area is most likely to form AMD, it is important for future studies to further investigate the kinetics of acid formation. Keywords: acid mine drainage, acid-base accounting, mineralogy, net acid generation, coal mine tailings.

Effect of coal on mine tailings’ water permeability and water retention

For safe and efficient mining operations to occur the management of waste materials is required, which often takes the form of geotechnical structures constructed from this waste. The safe use of these structures requires a number of resources, one of these being sufficient information about the waste material properties. For example, the drying process of a tailings dam is predicted with the water retention and permeability of the tailings. When considering coal tailings, which are comprised of coal and mineral soil particles (typically), the presence of coal may be problematic. The localised hydrophobicity of coal molecules may have a unique effect on water permeability and retention; this is relevant to geotechnical analysis where hydrophilic behaviour is assumed. To explore the possible effect of localised hydrophobicity, mine tailings were obtained from a coal mine of the Hunter Valley, NSW, Australia, and the coal fraction was separated via density separation. After this, three materials were available: unchanged mine tailings and a coal and mineral fraction of tailings. The goal was to characterise the three materials and allow deeper insight on what effect the addition of coal has on retention and hydraulic properties. Characterization involved measuring particle size distribution, pore size distribution, soil water retention curve, and saturated water permeability. The results show that there are distinct differences in the water retention and permeability properties of each material, and a number of these differences could be explained by the differing particle/pore sizes observed in each material. However, the coal containing materials desaturated at low suctions (< 10 kPa) compared to the mineral fraction, which could not be explained by particle/pore size differences and points towards localised hydrophobicity as a possible cause.

Estimating the escalation of mine tailings disaster risks by using a life cycle assessment approach

Mine tailings should be managed properly to avoid the tailings accident that recorded more than 230 tailings accident worldwide. These accidents caused human and environmental losses. This paper estimates the escalation of mine tailings dam failure using a life cycle assessment (LCA) approach. The LCA functional unit (FU) is defined as 1 tonne of fine coal concentrate slurry generated by flotation cells. SimaPro software was chosen to analyze the material flow data of a mine coal tailings disposal system and focused on impact categories associated with disaster issues including human toxicity, terrestrial eco-toxicity, freshwater eco-toxicity, and marine eco-toxicity. The results showed that the impact escalation of coal mine tailings during 20 years of operation for human toxicity, terrestrial eco-toxicity, freshwater eco-toxicity, and marine eco-toxicity were 13,740 DALY, 27.40 species year, 0.04 species year, and 0.001 species year respectively. These results indicated that a good mine tailings management should be applied by mine site to prevent a human and environmental disaster from mine tailings accident.

Coal recovery from coal washing plant tailings with Knelson concentrator

ABSTRACT Due to the increasing technology, the energy requirement is also increasing, this situation causes rapid depletion of our underground resources. In such a case, the efficiency of coal washing plants should be increased. In addition, coal waste should be enriched and brought to the economy. In this study, the enrichment of slime coal waste at the Koyunağılı coal washing plant had been examined. These wastes had 61.7% ash and 1740 kcal/kg LHV (Lower Heating Value) on dry basis. Experimental design methods were used in the study. The aim of the first phase of the study was to obtain coarse-size coal with 0.5 mm sieving. Coal was obtained with an ash content of 31.20% and ash of 3,980 kcal/kg LHV. The second aim was to enrich of −0,5 mm particle size with the Knelson Concentrator and a fine coal containing 2210 kcal/kg LHV with 55.89% ash content was obtained with 67.81% combustion recovery. In addition, 81.61% combustible recovery was obtained when two products were evaluated together. Thus, as a result of two-step enrichment, 45.61% ash and 2947 kcal/kg of calorific value of fine powder coal were obtained.

Biomining of iron-containing nanoparticles from coal tailings.

Sulfur minerals originating from coal mining represent an important environmental problem. Turning these wastes into value-added by-products can be an interesting alternative. Biotransformation of coal tailings into iron-containing nanoparticles using Rhodococcus erythropolis ATCC 4277 free cells was studied. The influence of culture conditions (stirring rate, biomass concentration, and coal tailings ratio) in the particle size was investigated using a 23 full factorial design. Statistical analysis revealed that higher concentrations of biomass produced larger sized particles. Conversely, a more intense stirring rate of the culture medium and a higher coal tailings ratio (% w/w) led to the synthesis of smaller particles. Thus, the culture conditions that produced smaller particles (< 50 nm) were 0.5 abs of normalized biomass concentration, 150 rpm of stirring rate, and 2.5% w/w of coal tailings ratio. Composition analyses showed that the biosynthesized nanoparticles are formed by iron sulfate. Conversion ratio of the coal tailings into iron-containing nanoparticles reached 19%. The proposed biosynthesis process, using R. erythropolis ATCC 4277 free cells, seems to be a new and environmentally friendly alternative for sulfur minerals reuse.

Some Laboratory Scale Tests on An Australian Coal Tailings Sample

As a country with rich mineral resources, Australia, is amongst the top five world's leading exporter of minerals. As such, coal tailings, one of the by-products of mineral exploration, pose ample challenge for its handling, management and disposal in tailings dams. These usually are encountered with high moisture content. In order to avert the risk of fluidization and associated failures of coal tailing dams, dewatering is necessary to be applied for reducing their water content. With this in mind, some laboratory experiments based on a local coal tailings sample has been presented in this manuscript. The coal tailing sample has been characterized by conducting the liquid limit test, plastic limit test and shrinkage limit test. Sieve analysis and hydrometer test have been conducted to establish the gradational property of the material. Modified compaction test and one-dimension consolidation test have been performed and the load-deformation response of the material is described in detail. Also, the vane shear test has been conducted to figure out the relationship between gravimetric moisture content and shear strength. Furthermore, hydraulic and volume change response of the sample subjected to changing moisture content have been studied through soil-water retention curve (SWRC) and soil shrinkage characteristic curve (SSCC).

Simultaneous Extraction of Clean Coal and Rare Earth Elements From Coal Tailings Using Alkali-Acid Leaching Process

With the supply restriction from traditional rare earth deposits, alternative sources of rare earth elements (REEs) such as coal are being studied. The United States National Energy Technology Laboratory has identified US coal deposits as a potential source of rare earth elements. Several techniques such as physical separation, flotation, ion-exchange, agglomeration, and leaching are being evaluated for the successful exploitation of these elements from coal and its by-products. A previous study published in the Geoscience BC 2018 mineral report on the characterization of REE in the British Columbian coal samples have shown that a major portion of the rare earth in the run of mine coal reports to the middling and tailing streams. Hence, this study is focused on the extraction of the rare earth from coal tailings. Several studies have shown the use of an alkali-acid leaching process to successfully demineralize various high ash coals to produce a clean coal concentrate since the ash-bearing components such as clay and quartz were removed from the coal during this process. In this study, the alkali-acid leach process was adopted to chemically clean coal tailings as well as to extract rare earth elements. Different process parameters such as sodium hydroxide (NaOH) concentration, temperature, and time were studied. Results showed that it is possible to extract more than 85% of REE with this process and simultaneously produce clean coal from coal tailing.

Analysis of settling performance of coal fines tailing polymer using central composite rotatable design optimization

ABSTRACT In the present investigation, the settling performance of coal fine tailings was optimized with central composite rotatable design and response surface methodology. Pulp density, pH, and flocculant dosage were considered as theoperating parameters in the study. The maximum settling rate was observed as 230 mm/min while minimum turbidity was observed as 26.7 NTU. Coefficient of correlation (R 2) between the experimental and the predicted values of the settling rate and the turbidity wereobserved to be 0.99 and 0.99, respectively. The optimum conditions of pH 7.6, flocculant dosage 16.43 gpt, and pulp density 5.4% solid, w/w, were obtained from the desirability function at the desirability of 89%.

Genotoxicity of the vegetables juice grown in garden built on the tailings coal deposits

The aim of the present study was to evaluate the genotoxic effect of lettuce (Lactuca sativa L.), beet (Beta vulgaris L.), broccoli (Brassica oleracea var. italica), and kale (Brassica oleracea var. acephala) grown in vegetable garden built on the deposits of coal tailings. For this, we used 72 healthy male Swiss albino mice that received juice from the vegetables in an acute or chronic treatment. Using comet assay, we determined that acute administration of the juices of all vegetables from the coal-mining area was genotoxic, and increased the DNA damage in the blood, liver, and cerebral cortex of mice. Therefore, the present data suggest that intake of vegetables cultivated over coal waste results in an increase in DNA damage in some organs; this situation may pose a risk to health.

Biosynthesis of iron oxide nanoparticles from mineral coal tailings in a stirred tank reactor

Chemical oxidation of mineral coal tailings is one of the most important environmental issues during the lifetime of a mine. The presence of sulfur compounds favors the occurrence of metal acid leaching, which contaminates water with bioaccumulative metals, rendering it unsuitable for domestic and agricultural use. The biomining of residual iron present in these tailings and its transformation into high added-value by-products is economically and environmentally attractive. The extraction of residual iron from rhomboclase and its transformation into nanoparticles by Rhodococcus erythropolis ATCC 4277 free-cells in a stirred tank reactor was studied. R. erythropolis ATCC 4277 biomining capacity was improved by diminishing stirring rate and oxygen flow rate of stirred tank reactor. According to the results of the 22 full factorial design, smaller sizes of iron-based nanoparticles (<50 nm) were achieved when a stirring rate of 100 rpm and an oxygen flow rate of 0.1 L.min−1 were used. Composition analyses (XRD, FTIR, TEM, EDS and Mössbauer spectroscopy) showed that the synthesized nanoparticles are formed by iron oxide (β-Fe2O3 and α-Fe2O3). The proposed biomining process represents an environmental-friendly and sustainable process for the transformation of mineral coal tailings into products with greater added value.