Coal Flotation Research Articles

Coal slime flotation foam image classification method based on semi-supervised clustering

Coal slime flotation foam image classification method based on semi-supervised clustering

Gutter oil, an alternative collector to traditional diesel collector for cleaner flotation of fine coal

ABSTRACT In order to realize cleaner production of coal flotation and reduce the dependence of traditional nonrenewable diesel collector, renewable collector was prepared from gutter oil and used for the flotation process. For contrast, flotation performance of gutter oil and traditional diesel collector was analyzed. The functional group composition of the two collectors was compared by infrared spectrum analysis (FTIR). In addition, the adsorption properties of collectors on the particle surface were analyzed by X-ray photoelectron spectroscopy (XPS). Then, flotation experiments were conducted to verify the applicability of renewable collector. FTIR results show that the main functional groups of diesel oil are C-C and C-H, while the gutter oil contains C = O and C-O besides hydrophobic groups, which results in higher ash content of clean coal. XPS results show that the hydrophobicity group content of coal increased significantly after the adsorption of collector. The flotation result show that the ash content of clean coal can be reduced to less than 10% and accompanied by more than 80% combustible matter recovery for both the gutter oil and diesel oil. This study demonstrates that the coal flotation process can become cleaner by using gutter oil as green collector.

Effect of Ammonium Salt on the Adsorption Behavior and Surface Characteristics of Sub-Bituminous Coal and Silica.

Ammonium salt is a common collector in coal reverse flotation. This study compared the difference of adsorption behavior on ammonium salt Lilaflot D817M between sub-bituminous coal and silica as well as the surface characteristic change after being processed by ammonium salt. The results indicate that the adsorption capacity of sub-bituminous coal is always higher than that of silica under different experimental conditions, such as different initial concentrations of ammonium salt, different adsorption times, different concentrations of the depressant dextrin, and different pH values. Ammonium salt could increase the isoelectric point of both silica and sub-bituminous coal greatly. However, the hydrophobicity of silica enhances much more significantly than that of sub-bituminous coal after being treated by Lilaflot D817M. This indicates that the surface wettability change degrees of sub-bituminous coal and silica after being treated by ammonium salt are not proportional to the adsorption capacity because of their different surface structures. The reverse flotation test result shows that 2 kg/t Lilaflot D817M dosage could help obtain relatively good flotation indexes.

Predictions of Coal Flotation on the Basis of a Factorial Experiment

The influence of the pulp density and the consumption of collection agent, frothing agent, and air on the flotation of coal fines at OAO MMK-Ugol is studied by means of a factorial experiment. First-order regression equations are derived. The response functions selected are the extraction of flammable mass in the concentrate; and the selectivity of the process, includes miscellaneous flotation characteristics. These equations permit the prediction of flotation outcomes.

Density functional theory study of the structure and properties of C-doped pyrite

The structure and properties of C-doped pyrite are investigated by first-principles density functional theory. The results show that interstitial doping system is more stable than substitutional doping system. With the increase of carbon concentration, the hardness of interstitial C-doped pyrite decreases and the oxidizability increases, leading to the difficulty of coal-pyrite depression in coal flotation. After C doped in an interstitial lattice site the impurity states reduce the band gap and lead to the red-shift of absorption edge. C-doping improves the optical transition characteristics of pyrite electrons in visible light region.

Combined column and cell flotation process for improving clean coal quality: Laboratory-scale and industry-scale studies

ABSTRACT Inherent limitation of the mechanical flotation cell is the entrainment of hydrophilic particles (gangue) in the water reporting to the froth. In this study, a combine column and cell flotation process was proposed to reduce the entrainment of gangue particles and, ultimately, ash content of coal flotation concentrate in Datun coal preparation plant, Peixian County, Jiangsu, China. The froth collected from the third and fourth cells of the 4-cell flotation machines in this plant was further re-cleaned to obtain qualified clean coal. Laboratory-scale results show that both the mechanical flotation machine and flotation column as re-cleaning flotation devices could produce the clean coal with qualified ash content. However, the yield obtained by the flotation column (84.49%) is significantly higher than that obtained by the mechanical flotation cell (68.21%). Industry-scale tests indicate the combined column and cell flotation process could produce qualified clean coal and run stably.

Dispersion behavior and attachment of high internal phase water-in-oil emulsion droplets during fine coal flotation

Flotation recovery of fine oxidized coal is frequently inefficient when using conventional oily collectors. A large amount of fine coal is discharged as tailings, leading to resource waste and environmental pollution. To solve the problem of high oil consumption and low efficiency associated with traditional flotation, research efforts have been focused on the use of oil-in-water emulsion to reduce oil consumption. Few studies concerning water-in-oil emulsion, especially the high internal phase water-in-oil (HIP W/O) emulsion, have been conducted. Our microflotation results showed a significant oil dosage reduction when a HIP W/O emulsion was used as a collector for coal flotation. The state of the HIP W/O emulsion dispersion in water and the emulsion droplets attachment at the coal surface are vital issues associated with achieving efficient flotation. In this study, optical microscopy and high speed video microscopy were employed to study the dispersion behavior and microstructure of the HIP W/O emulsion in water. This study found that the HIP emulsion tends to be dispersed as a W1/O/W2 double emulsion during mixing in water because of the migration of the surplus Span 80 in the oil phase to the O-W2 interface. The presence of NaCl in W1 is also essential for a stable W1/O/W2 double emulsion, which is formed when equilibrium of the Laplace and osmotic pressures between the W1 phase and W2 phase is obtained. In addition, the W1/O/W2 emulsion droplets are negatively charged, and the emulsion aggregation appears to be inhibited by electrostatic repulsion. More importantly, the Span 80 emulsifier at the O-W2 interface seems to facilitate hydrogen bond formation between the hydrophilic moieties of Span 80 and the oxygen containing functional groups at the coal surface, which is verified by the results from molecular dynamics simulation (MDS). The hydrogen bond formation plays a leading role in the attachment and/or spreading of the emulsion droplets at the oxidized coal surface. The HIP W/O emulsion could be a potential economical and efficient replacement for the traditional oily collectors as a promising collector for the flotation of fine oxidized coal.

Combustion of Coal Flotation Wastes and Woodworking Wastes in Blends and Suspensions

The utilization of flammable wastes in composite fuels for boiler combustion is discussed. The combustible materials considered are coal flotation wastes, long-flame coal, sawdust, and cardboard. These components undergo combustion in the form of a bed of dry mixture or as aqueous suspensions. The following characteristics are determined: the minimum ignition temperature, the delay time of gaseous or heterogeneous ignition, the maximum temperature in the combustion zone, and the calorific value of the fuels. Sawdust-based compositions may be recommended for kindling and to minimize the ignition time. The heat liberation in the combustion chamber may be significantly increased by using mixtures of sawdust, coal slurry or filter cake, and coal dust. The use of such wastes as industrial fuels is very promising.

Effect of Dextrin on the Adsorption Behavior and Surface Characteristics of Sub-Bituminous Coal and Silica.

Dextrin is a derivative of starch produced by partial thermal degradation under acidic conditions, which is usually used as a depressant in the mineral processing industry. Dextrin can also effectively depress coal particles in the reverse flotation process. To study the effect of dextrin on the flotation behavior of both coal and gangue mineral in coal reverse flotation, this research compared the adsorption behavior difference between sub-bituminous coal and silica as well as the surface property change of both sub-bituminous coal and silica after being treated by dextrin. The result illustrates that the adsorbing capacity of sub-bituminous coal on dextrin is much higher than that of silica under different initial concentrations and different interaction times. The isoelectric points of both sub-bituminous coal and silica increase after being treated by dextrin. But the increasing ζ-potential value of silica is larger than that of sub-bituminous coal. Dextrin could enhance the hydrophilicity of sub-bituminous coal and weaken the hydrophilicity of silica slightly according to the result of surface wetting rate tests. Reverse flotation using dextrin as a depressant indicates that good performance could be obtained with the addition of dextrin. Larger dextrin dosage might deteriorate silica flotation slightly.

An investigation of the effect of clay type on coal flotation along with DLVO theoretical analyses

ABSTRACTCoals generally exist with clay minerals, which are very fine-sized minerals, and adversely affect the flotation of coal. For instance, they make the coal surface hydrophilic by coating coal surfaces and therefore, they inhibit bubble-particle attachment. Clay minerals can also cause over-consumption of reagents due to their high surface area. Additionally, clay minerals can transfer into the concentrate during the flotation process by entrainment because of their low weight and small particle size, and thus, increase pulp viscosity and changing froth stability. In this study, the influence of various clay minerals (kaolinite, illite, and bentonite) on the flotation behavior of coal sample was studied in detail by conventional flotation tests. In addition, the values obtained from flotation tests were correlated with theoretical energy barrier values established with classical DLVO theory based on zeta potential values of coal and clay samples measured at different pH values. According to the results of this study, no significant effect of clay minerals was observed on coal flotation. This was probably because of the high floatability of the coal used for this study. Both the results obtained from the experiments and theoretical analysis, DLVO calculations, showed that the type of clay mineral is the main indicator parameter for coal flotation.

Improving bubble-particle attachment during the flotation of low rank coal by surface modification

Based on the problems caused by many oxygen-containing functional groups and poor floatability on the surface of low rank coal, the characteristics of low rank coal were analyzed systematically by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-Ray photoelectron spectroscopy (XPS) techniques. The bubble-particle induction time was used to determine the characterization of the bubble-particle attachment, and the bubble-particle attachment of low rank coal modified by soaking the coal samples in an acid or alkaline solution was analyzed. The floatability of the modified coal surface was verified by flotation tests. The results show that the particle size of 0.125–0.074 mm of the coal sample exhibited better bubble-particle attachment characteristics. The small bubble, the larger approach velocity of bubble and the larger bubble deformation were more helpful to enhance the bubble-particle attachment. For an acid solution, the smaller the pH was and the longer the soaking time was, the better the floatability of the coal sample and the higher the combustible material recovery were. The combustible material recovery of low rank coal was increased to 78.79% by soaking the sample in an acid solution of pH = 0 for 180 min. On the contrary there was a best concentration for the alkaline solution.

Flotation of low rank coal using dodecane after pretreatment by dielectric barrier discharge (DBD) air plasma

Non-polar oils are commonly used as collectors for coal flotation but they are generally lack of collecting efficiency to low rank coals even at a high dosage. In this study, dodecane, a representative of the non-polar oily collectors, was treated by dielectric barrier discharge (DBD) air plasma and the product was employed in the flotation of a low-rank coal slime, attempting to improve its flotation performance. Results show that the dodecane treated by DBD air plasma led to a high concentrate yield and combustible material recovery. The mechanism underpinning the observed effect was investigated using gas chromatograph-mass spectrometer (GC–MS), Fourier transform infrared spectroscopy (FTIR) and contact angle measurements. The effect of UC (untreated collector) and TC (treated collector) on coal and gangue were detected, respectively. It was found that abundant polar substances were produced after the air plasma treatment. The functional groups including OCO and OH enhanced the adsorption of collectors onto the oxygenated surface sites of the coal and gangue, and thus increased the hydrophobicity of coal and gangue. According to the contact measurements, the increase of coal in hydrophobicity is stronger than that in gangue, as evidenced by their measured contact angle of organic matter increasing from 78.23° to 95.82°, and gangue increasing from 75.11° to 83.22° after conditioning with the TC. This implies that oily collectors after air plasma treatment is effective to improve low rank coal flotation performance, which may have great potential for industrial applications.

The flotation intensifying of low-rank coal based on the ultrasonic field

ABSTRACTIn this study, effect of flotation agitating based on ultrasonic field on low-rank coal flotation was investigated. The results showed that flotation agitating based on ultrasonic field reduced slime coating and collector droplets size; the flotation results showed the combustible recovery was significantly increased, whereas concentrate ash was highly reduced. Moreover, the flotation kinetics performance increased significantly with aid of flotation agitating based on ultrasonic field with increasing ultrasonic power. Compared with the flotation agitating in the absence of ultrasonic field, a better flotation selectivity was observed using flotation agitating based on ultrasonic field according to Fuerstenau upgrading curves.

The prospects of burning coal and oil processing waste in slurry, gel, and solid state

This paper presents the experimental investigation results of ignition and combustion characteristics of fuels based on typical coal flotation waste which is formed and accumulated around the world in large volumes (about 200–300 million tons per year). We focus on the comparison of these characteristics for waste-derived fuels in different states: slurry, gel, and solid. We analyze the ignition delay times, minimum (threshold) ignition temperatures, combustion heat, concentrations of anthropogenic emissions, and the relative efficiency of fuels. We have determined that minimum ignition temperatures and shorter ignition delay times are achieved in the solid state (50–80% lower than in the slurry and gel state). The lowest concentrations of the most hazardous emissions are present in the liquid (slurry) state (NOx and SOx are 18–75% lower than from the combustion of coal in the solid state). The conditions were identified for the efficient use of coal and oil processing waste as part of composite fuels. The relative fuel effective utilization factor of waste-derived fuel mixtures in different states ranged from 0.11 to 45.5. It is maximal for fuels in the slurry state. The obtained data has been compared with the results of other studies.

Analysis of a coal preparation plant. Part 1. Changes in water quality, coal seam, and plant performance

Coal preparation plants are under increasing pressure to reduce their consumption of fresh water leading to the use of recycle water. Recycled water generally contains a large quantity of dissolved inorganic electrolytes, which affect coal flotation. This paper reports the conductivity and pH measurements of water in the tailings stream of an industrial scale flotation cell covering a period of approximately two years. The different coal seams processed at the site were also compared and the influence the water quality on the overall yield of coal assessed. This study presents the large variation in inorganic content in recycled water observed for a wash plant and determines its possible effect on coal preparation. The maximum daily temperature was found to be an important factor controlling the amount of inorganic electrolytes in the water and, very significantly, the water management system implemented. The overall plant performance was somewhat affected by the use of water containing high concentrations of inorganic electrolytes. The effect of the quantity of ions in the water on the flotation process is explored in Part 2.

Investigation of CTAB and DBP esters on low-rank coal flotation selectivity

ABSTRACTTo enhance low-rank coal flotation efficiency, dibutyl phthalate (DBP) and cetyltrimethylammonium bromide (CTAB) were used as collectors, respectively. The adsorption selectivity performance of CTAB and DBP on coal samples with different densities were characterized by the total organic carbon content, contact angle, and Fourier-transform infrared spectra. The results indicate that both DBP and CTAB greatly improved flotation yield compared with diesel, but only DBP can yield a concentrate with a low ash content. DBP had a higher adsorption capacity and bestowed a greater change in contact angle for low-density coal, while CTAB followed the opposite behavior. Furthermore, the ester group of DBP consumed the oxygen-bearing functional group and increased the alkane chain content on the coal surface, leading to a noticeable increase in hydrophobicity of the low-density coal sample.

Improved Coal Flotation with Sinterol Modifier

The flotation of coal with different ash content when using Sinterol modifier is studied. If the modifier consumption is 1.0–3.0 g/t of coal fines, the extraction of the coal’s combustible mass in the concentrate is increased; the selectivity of the process is increased; and the loss of the coal’s organic mass with the flotation wastes is decreased. The improved flotation may be explained as follows. The Sinterol modifier is adsorbed on active sections of the coal surface by means of hydrogen bonds with its polar groups, in a configuration such that the hydrocarbon groups face the water. That results in a more hydrophobic surface of the coal particles and improves their floatability. The modifier is more effective in flotation when supplied before the collection agent.

Ozonized petrochemical products used to intensify coal flotation

The ozonization method was used to improve the efficiency of oil-based flotation agents for coal dressing. Ozonation of petroleum products contributes to transformation of their hydrocarbon composition with the formation of oxygen-containing compounds of different functionality. The resulting reagents acquire the properties of complex reagents such as collector + foaming agent. The use of ozonized petroleum products leads to an increase in the efficiency of flotation of coking coals: a decrease in reagent consumption, an increase in the yield of concentrate and ash content of waste. Analytical processing of petroleum products is more effective for crude light oils, medium-temperature oil fractions and mixtures of low-boiling and high-boiling fractions.

Evaluation of effects of operating parameters on combustible material recovery in coking coal flotation process using artificial neural networks

In this research work, the effects of flotation parameters on coking coal flotation combustible material recovery (CMR) were studied by the artificial neural networks (ANNs) method. The input parameters of the network were the pulp solid weight content, pH, collector dosage, frother dosage, conditioning time, flotation retention time, feed ash content, and rotor rotation speed. In order to select the most efficient model for this work, the outputs of different models were compared with each other. A five-layer ANN was found to be optimum with the architecture of 8, 15, 10, and 5 neurons in the input layer, and the first hidden, second hidden, and third hidden layers, respectively, as well one neurons in the output layer. In this work, the training, testing, validating, and data square correlation coefficients (R2) were achieved to be 0.995, 0.999, 0.999, and 0.998, respectively. The sensitivity analysis showed that the rotor speed and the solid weight content had the highest and lowest effects on CMR, respectively. It was verified that the predicted ANN values coincided very well with the experimental results.

Effect of polyaluminum chloride on coal flotation performance with different reagent addition regimes

The flotation tests of an artificial mixture of coal (250–125 μm) and kaolinite (−100 μm) were conducted with two different reagent addition regimes to improve understanding of the effect of polyaluminum chloride (PAC) on coal flotation with n-dodecane as collector. The flotation results suggested that improved separation efficiency with reduced kaolinite entrainment could be achieved by addition of PAC at a proper concentration. The kaolinite entrainment mitigation was insensitive to the sequence of addition of PAC and the collector whereas addition of the collector prior to PAC appeared to be conducive to increasing the flotation rate and alleviating the requirement for close management of PAC dosage. A real-time particle characterization tool, Focused Beam Reflectance Measurement (FBRM), was used to measure the particle size distribution of kaolinite and coal in aqueous solution. It was found that the kaolinite particles formed aggregates with PAC at 10–20 mg/L, which matched well with the optimum dosage of PAC for mitigation of kaolinite entrainment in coal flotation. The induction time measurement was conducted for the coal particles, and the results suggested that addition of PAC would decrease the probability of bubble-particle attachment.