Lignite Flotation Research Articles

Influence of oil film on the interaction between bubble and bubble/lignite particle

ABSTRACT The floatability of low-rank coal is poor because of its low metamorphosis, and the oily bubble flotation is an effective means to collect coal particles. In this paper, adhesion angles and forces between watery/oily bubbles and coal surfaces were measured to analyze the influence of oil film on adhesion behavior between bubble and particle. The properties of watery/oily bubbles were analyzed by dynamic foam analyzer (DFA) to reveal the influence of oil film on the bubbles further. The results showed that in the dynamic environment, the maximum adhesion angle of the oily bubble was 36.55°, while the angle of the watery bubble was 31.29°, and the adhesion kinetic constant for oily bubble-particle and watery bubble-particle were 0.0295 and 0.0174, respectively. The measured maximum adhesion forces of the watery bubble and oily bubble were 19.2 μN and 86.8 μN, respectively, indicating that oily bubbles were more prone to attach to the coal surface and were beneficial to flotation. The calculated normalized contact line indicated that the oil film could squeeze a lot of water out from the coal surface, increasing the actual contact area and strengthening the attachment. The results of DFA showed that with the oil film, the oily bubbles could be more stable with a smaller size and lower liquid content than the watery bubbles. The results of the above study show that the oil film covering the watery bubble could improve the adhesion between bubble and particle and reduce the bubble size, which is conducive to promoting the sorting efficiency and thus enhancing the flotation of lignite.

Preliminary Study on the Surface Modification of Lignite and Bioflotation by White-Rot Fungi Hypocrea lixii AH

The efficient utilization of lignite is a crucial area of research for the sustainable management of existing coal resources. One potential technique for cost-effective and environmentally friendly coal processing is the application of microbes or their derivatives to modify the surface of lignite for bioflotation. However, the precise process of surface modification between microbes and coal remains largely unknown. In this study, we focused on the use of a white-rot fungus called Hypocrea lixii AH and its various components, including spores, hyphae, extracellular polymer substances (EPSs), and culture solution, as biosurfactants for lignite modification. By employing techniques such as zeta potential analysis, induction time measurement, contact angle measurement, and Fourier infrared spectroscopy, we investigated the changes in the surface properties of raw and modified lignite. Furthermore, we conducted a preliminary bioflotation test using biosurfactants as collectors in order to explore the potential application of fungal modification in this context. Our results revealed that all biosurfactants were effective in improving the surface properties of lignite, with the EPS demonstrating the most prominent effect, followed by the culture solution, hyphae, and spores. The zeta potential and induction time of the modified lignite decreased, indicating enhanced hydrophilicity, while the contact angle exhibited a slight increase, suggesting a minor increase in hydrophobicity. Analysis of the Fourier infrared spectra indicated that EPS treatment resulted in the highest abundance of functional groups, including carboxyl, hydroxyl, and amidogen groups. Although fungal cells were found to improve the hydrophobicity of coal, they did not exhibit a significant effect on the flotation of lignite. Nonetheless, our findings suggest that fungal cells and their derivatives have the potential to remove or transform minerals present in lignite, particularly those containing sulfur. While they may not serve as effective bio-collectors in microflotation, their capability in mineral alteration makes them valuable candidates for lignite processing with a focus on mineral reduction.

Determining the flotation upgrading effect of shale oil on lignite via molecular dynamics simulation and experiment comparisons

ABSTRACT In this study, we combined experiments with molecular dynamics simulation to investigate the improvement of lignite flotation performance by shale oil and microscopic promotion mechanism. Through FTIR and GC/MS tests, our preliminary findings showed that shale oil contains polar groups and long-chain alkanes. Moreover, XPS tests confirmed that shale oil could render the C–C/C–H and cover the C–O, C=O and O=C–O functional groups. The induction time between lignite particles and shale oil bubbles was 15ms lower than that between kerosene bubbles. Besides, the flotation results indicated that shale oil could improve the yield and reduce the ash content of clean coal significantly. The molecular dynamics simulation results showed that shale oil molecules could preferentially adsorb on lignite pore surface and weak the direct adsorption and seepage of water molecules on lignite surface. This was consistent with the results of an analysis of the whole system’s relative concentration distribution and mean square displacement of water molecules. These data provide further evidence that shale oil can clearly improve the flotation recovery of low-rank coal, which is of great importance for the clean utilisation of low-rank coal.

Effect of hydrothermal pretreatment on surface physicochemical properties of lignite and its flotation response

Flotation is the common method for fine low rank coal upgrading while it is always inefficient due to the rough surface morphology and rich oxygen-containing functional groups. Hydrothermal pretreatment is widely used in dewatering for low rank coal. The physicochemical properties of coal surface considerably vary following the hydrothermal pretreatment. In this study, hydrothermal pretreatments at different temperatures for different times were applied to enhance lignite flotation. The hydrothermal pretreatment at 200 °C can significantly improve the flotation efficiency, while the temperature raised to 300 °C, the flotation recovery did not increase or even decrease. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Zeta potential, Brunauer–Emmett–Teller, and particle size distribution analysis were conducted to explain the underlying mechanism. The contents of pore and crack on coal surface considerably decreased and more fresh and smooth surfaces exposed following hydrothermal pretreatment, according to SEM analysis. The FTIR spectroscopy and XPS showed that the contents of oxygen-containing functional groups were decreased, while the hydrophobicity of lignite was increased following pretreatment. The decrease of Zeta potential also indicated the decrease of oxygen-containing functional groups and increase of hydrophobicity on coal surface. However, excessive temperature of hydrothermal pretreatment could increase the pore diameter and fine particle fraction, leading to a higher collector consumption and lower bubble–particle collision efficiency. Consequently, the flotation recovery was not improved or even decreased at the hydrothermal pretreatment temperature of 300 °C.

Enhanced lignite flotation using interfacial nanobubbles based on temperature difference method

Froth flotation is the primary method for the separation and upgrading of fine coal particles. However, this method is ineffective for lignite which is more hydrophilic than other types of coal due to the abundant oxygenated functional groups, cracks, and micropores on its surface. This study develops a new method that introduces interfacial nanobubbles (INBs) based on the temperature difference method for enhancing lignite flotation. The mechanism of lignite flotation enhanced by INBs is systematically explained through the induction time and bubble-particle collision-attachment behavior. The experimental results show that the lignite flotation efficiency is evidently improved using the temperature difference method. AFM imaging of the changes on a highly oriented pyrolytic graphite surface due to temperature difference demonstrate the production of INBs. In the presence of INBs, the induction time of lignite can be reduced from 400 ms to 27.21 ms, the number of bubble-particle collisions from 4 to 3, and the attachment time from 208 ms to 128 ms. When a macroscopic air bubble approaches to a lignite surface with INBs, the air bubble first merges with the INBs, not only decreasing the induction time but also increasing the apparent contact angle and length of three-phase contact line.

Effects of NaCl/CaCl2 on the surface hydration and flotation of lignite particles

ABSTRACT This study focused on the mechanisms of NaCl and CaCl2 enhancing the oily-bubble flotation of lignite. The degree of surface hydration of coal particles before and after conditioning with NaCl/CaCl2 was evaluated with the Einstein theory of dispersion viscosity, while the effect of these two electrolytes on lignite floatability was evaluated via attachment time and flotation tests. The results indicated the adsorption amount of Ca2+ on the coal sample was more than that of Na+ in the same electrolyte concentration. Owing to the cationic adsorption, the zeta potential of lignite particles increased with increasing NaCl and CaCl2 concentrations, which thus decreased the electrostatic repulsion between coal particles and oily bubbles. Moreover, the hydration of the coal surface decreased when NaCl/CaCl2 was added to flotation pulp, meaning the surface hydrophilicity of the coal sample was reduced. As a result, the attachment time between coal particles and oily bubbles decreased significantly, and the combustible-matter recovery correspondingly increased up to a maximum of 50.97% and 90.06% with increasing NaCl and CaCl2 solutions concentration, respectively. However, it is necessary to keep the electrolyte solution concentration within a reasonable range for a good selectivity during the oily-bubble flotation.

Preparation and evaluation of lignite flotation collector derived from waste hot-pot oil

Due to poor hydrophobicity, large amounts of petroleum-based collectors are required for upgrading lignite. In this paper, Waste Hot-pot Oil (WHPO) collectors from the catering industry were prepared via filtration, heating, and catalysis. The catalytic experiment was optimized using the Design-Expert software. The optimum catalytic conditions were found to be a pyrolysis temperature of 85 °C, alcohol-oil ratio of 35:1, catalyst dosage of 2%, and reaction time of 1 h. The Separation Efficiency (SE) of WHPO was 3.04 percentage higher than that of the conventional collector (kerosene), while the ash content of Lignite Surface Treated with WHPO (LWHPO) was 1.14 percentage lower than that of kerosene. Response surface methodology was used to analyse the factors influencing the SE; the effect of the studied factors followed the order catalyst amount > alcohol-to-oil ratio > reaction temperature. GC–MS showed that WHPO contained both long-chain alkyl groups and other ester and hydroxyl groups. XPS tests confirmed that the hydrophobic group (CC, CH) content of LWHPO increased, while its hydrophilic group content (except CO) decreased, demonstrating the improved hydrophobicity of lignite after WHPO treatment. FT-IR analysis indicated that WHPO more effectively decreased the content of hydrophilic groups and increased the content of hydrophobic groups than kerosene. Contact angle (CA) analysis showed WHPO was more conducive to lignite surface hydrophobicity improvement than kerosene. WHPO possessed strong collecting ability and better selectivity, and could be used as an alternative collector for lignite flotation.

Lignite flotation in inorganic salt solutions

ABSTRACT The flotation of low-quality lignite coal in the presence of NaCl, MgCl2 and CaCl2 inorganic salts with/without the use of kerosene and MIBC as flotation chemicals was investigated in this study. In addition, the zeta potential and contact angle measurements were performed. The lignite sample exhibited a negative surface charge over a broad pH range and had no isoelectric point (iep). It was determined that the magnitude of negative charge significantly decreased above 10−2 M concentration of the salts and the flotation of lignite without flotation reagents also started to take place at concentrations higher than the same value. The contact angles measured on the lignite surfaces also increased with increasing salt concentration. The lignite sample was hydrophilic, and therefore very difficult to float. Consequently, the flotation of lignite with collector and frother was not achieved to the desired extent, even using high reagent concentrations. In the absence of flotation chemicals, high concentrations of these salts also provided low flotation performances. However, the flotation of lignite could be achieved with kerosene and MIBC in the presence of inorganic salts. In addition, it was determined that MgCl2 and CaCl2 salts were more effective on the lignite flotation than NaCl salt.

An experimental study on the effects of some process parameters on lignite flotation

ABSTRACT Flotation, as an efficient method for separating fine coal particles (−500 µm), is making slow progress for use with lignite, which basically remains at the laboratory stage. Lignite flotation is more difficult than flotation of other coals, and flotation efficiency here is very low. The difficulty in floating lignite primarily includes two aspects, abundant oxygen containing groups on the coal surface and porous surface of the coal particles. Therefore, it is of paramount importance to clean lignite by flotation. In this article, the effects of some process parameters for lignite flotation were studied. Laboratory experiments were carried out, and the effects of depressant (sodium silicate) dosage (0–1000 g/t), collector (kerosene) dosage (50–3000 g/t), frother (methyl isobutyl carbinol) dosage (15–1000 g/t), pulp pH (2–12), solid ratio (10%–20%), flotation time (1–7 minutes) and particle size (500–63 µm) on flotation performance were investigated. A concentrate with 37.18% yield and 40.11% combustible recovery was obtained at 250 g/t sodium silicate (Na2SiO3), 250 g/t kerosene and 100 g/t methyl isobutyl carbinol (MIBC). Within the studied range, the optimum pulp pH was 2, the solid ratio was 10%, the flotation time was 5 minutes, and the particle size was −500 µm. Under these optimum conditions, the ash content of lignite coal was reduced from 19.08% to 12.70%.

Effects of simultaneous ultrasonic treatment on the separation selectivity and flotation kinetics of high-ash lignite

The purpose of this study was to investigate the effects of conventional flotation and simultaneous ultrasonic flotation in the pulp/froth zones on the separation selectivity and kinetics of high-ash lignite flotation. Particularly, the mechanism of ultrasonic flotation in the froth zone, which improved the flotation performance of lignite, was elucidated. Flotation tests, wet screening, SEM, and froth layer observation tests were employed to reveal the mechanism by which simultaneous ultrasonic flotation improved lignite flotation. The flotation results indicated that the lowest concentrate ash content was obtained using ultrasonic flotation in the pulp zone, while the highest concentrate yield and water recovery were achieved using ultrasonic flotation in the froth zone. The wet screening and SEM results indicated that ultrasonic flotation in the pulp zone afforded the best surface cleaning on the coal surface, which significantly improved the flotation selectivity of lignite. Ultrasonic treatment in the froth zone produced large bubbles and a thin froth layer due to ultrasonic cavitation and oscillation, thereby improving the recovery of fine particles by water entrainment. However, simultaneous ultrasonic treatment in the froth zone did not improve the separation selectivity of lignite flotation. In addition, the second-order model with rectangular distribution of floatability provided the best fit with the experimental data of all the flotation types, based on the analysis of the model fit and stability. Notably, the flotation rate constants of ultrasonic flotation in the froth and pulp zones were 1.8981 min−1 larger and 1.476 min−1 smaller, respectively, than those of conventional flotation.

Effects of ultrasonic pretreatment on particle size and surface topography of lignite and its relationship to flotation response

ABSTRACT The aim of this investigation was to study the effects of different ultrasonic powers and treatment times on particle size and surface topography of low ash fine lignite (<0.125 mm) combined with flotation, wet-screening, surface roughness, scanning electron microscopy (SEM), and induction time tests. Flotation results show the concentrate yield gradually decreased with the increase of ultrasonic power and treatment time except 18 W. The wet-screening results indicate that increasing ultrasonic power and treatment time had more significant crushing effect on lignite particles and produced more fine particles (<0.045 mm), which was harmful for the improvement flotation performance of lignite. SEM results show that crack was gradually expanded into a gap as well as some new cracks and cavities on the surface of lignite are produced with the increase of ultrasonic power. The generation of these gaps, new cracks, and cavities increases the roughness of lignite surface. The higher the ultrasonic power is, the rougher the lignite surface becomes, which promotes its surface to entrap more water during the flotation process resulting in a formation of thick hydration shell. The induction time increased as ultrasonic power and treatment time increased except 18 W. Hence, there will be a negative impact on lignite flotation if the lignite particles are treated by higher ultrasonic power for longer. The findings of this paper may provide some guidance to understand the effects of ultrasound on surface topography of lignite and makebetter use of ultrasound to assist coal flotation.

Optimization of collector and its action mechanism in lignite flotation

The flotation performance of lignite is poor even if a high dosage of the collector is used. In this work, the lignite in the Huolinhe Coalfield of Inner Mongolia was used, and its physicochemical properties were determined by proximate analysis, particle size analysis and Fourier transform infrared spectroscopy. The flotation performances of lignite using six collectors were investigated. Moreover, the flotation responses of lignite with combined collector and two emulsified collectors were compared. It was found that the polar groups in the collector structure were helpful to improve the flotation of lignite through reducing the induction time to 15 ms, only 1/12 of that of the traditional collector (190 ms for diesel). The induction time was in the order of diesel> kerosene> emulsified kerosene> emulsified diesel> C1 (one of the nameless collectors), consistent with the flotation performance. C1 and emulsified collectors significantly improved the flotation performance of lignite by promoting the floating of coarse coal (−500 + 250 μm).

A series of nonionic surfactants for lignite flotation and adsorption performance

ABSTRACT Nonionic surfactants have been applied to improve the lignite floatability in the flotation process. In this paper, Inner Mongolia lignite was pretreated by three type surfactants, including sorbitan monolaurate, sorbitan monostearate, and sorbitan monooleate, respectively. It was investigated that the effect of the length and saturability of hydrocarbon chain on the collectivity and selectivity of surfactant. The flotation results indicated that the optimum efficiencies were found at the dosages of about 35 kg/t for the three surfactants. However, the recovery of combustible material of lignite pretreated by sorbitan monolaurate is comparatively low, which may relate to the weak collectivity of this shorter hydrocarbon chain surfactant. On the other hand, XPS results showed that the C1s can be fitted to C-C, C-H, C-O, and COO- with the contents of 10.99%, 9.19% and 2.11% on the raw lignite surface, respectively. After the pretreatment, the contents of hydrophobic C-C, C-H were increased to 13.53%, 16.07% and 17.18% for the three surfactants. Obviously, the hydrophobic functional groups were much higher after pretreated by sorbitan monooleate, which was corresponded with the better flotation results. Therefore, the longer and unsaturated hydrocarbon chain in sorbitan monooleate molecule is beneficial for the collectivity and selectivity for lignite.

Effect of ultrasound on the true flotation of lignite and its entrainment behavior

ABSTRACTIn this study, the ultrasound was fixed in the pulp zone of flotation cell and its effect on the true flotation of lignite was analyzed. Flotation results indicated that the simultaneous ultrasound treatment increased the concentrate yield and decreased the concentrate ash content. Screening analysis of flotation products revealed that the ultrasound could crush coarse coal to fine coal and scanning electron microscopy (SEM) tests indicated that the ultrasound could reduce the coverage of high-ash coal fines on the coarse particle surface. Thus, the flotation recovery of coarse lignite particle was increased. In addition, the true flotation and entrainment of −0.074 mm fine particles were studied by the sink-float test and the method of Trahar. It was found the ultrasound significantly enhanced the true flotation of fine particles and improved the overall water recovery in lignite flotation.

Ultrasonic flotation cleaning of high-ash lignite and its mechanism

Lignite, as a low rank coal reserve plays an important role in energy supply. However, fine lignite is difficult to upgrade using the conventional flotation because of its high surface hydrophilicity. This investigation was to enhance the flotation recovery of high-ash lignite combined with wet-screening, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and induction time measurer to reveal the mechanism of simultaneous ultrasonic treatment enhancing the lignite flotation. Flotation results indicate the clean coal yield is greatly increased whereas the clean coal ash content is highly reduced by simultaneous ultrasonic flotation compared with the conventional flotation. SEM and XPS results show coal surface is physically cleaned and hence the clay coating is reduced by simultaneous ultrasonic flotation. The removal of high-ash mineral particles from coal surface benefits the coal-bubble attachment. Furthermore, ultrasonic treatment creates many micro-bubbles that enhance the floatability of lignite through micro-bubble-based coating on coal surface. The micro-bubbles play a bridging role in the coal-bubble attachment. The water film on lignite surface may be also unstable and easy to rupture during bubble-coal attachment under the condition of ultrasonic treatment.

Research on cationic surfactant adsorption performance on different density lignite particles by XPS nitrogen analysis

Lignite is well known for its hard-to-float property. Many surfactants, including anionic, cationic and non-ionic have been applied to improve the floatation efficiency. In this work, cationic dodecylamine was applied to pretreat the lignite samples with different densities, which are −1.45 g/cm3, 1.45–1.80 g/cm3 and +1.80 g/cm3. The surface charged properties of the raw samples were determined by a zeta potential analyzer. The adsorption performance was characterized by XPS and UV/VIS spectrophotometer methods. From the surface zeta-potential results, three curves of zeta-potential figures versus pH value are similar to each other qualitatively in the pH range 5–8, which indicates that the organic structure has the similar ionization/ protonation ability with inorganic minerals at neutral pH. The negatively charged surfaces attract the cationic dodecylamine molecules at neutral pH for the three density fractions, which is shown by the XPS narrow sweep of heteroatom nitrogen before and after the pretreatment process. On the lignite surface, nitrogen was mainly existed in two forms of pyrrolic and quaternary. After the pretreatment, the quaternary-N peak was increased on the lignite surface due to the adsorption of dodecylamine molecules, especially on the surface of the highest density fraction. Correspondingly, UV/VIS spectrophotometer results showed that the adsorption amounts of dodecylamine molecules were 11.4, 18.7 and 20.0 mg/g on the surface of the samples from low to high density. On the other hand, the flotation result showed that more high ash particles and some low ash ones were both floated with the increase of dodecylamine dosage. Hence, if dodecylamine is to be used in lignite flotation, reagents should be added to selectively depress the adsorption process of cationic dodecylamine on the low or high ash particles.

Enhancing lignite flotation performance by mechanical thermal expression treatment

ABSTRACTThe developed pore distribution and large amount of oxygen functional groups have a detrimental effect on lignite flotation. The effect of mechanical thermal expression treatment (MTET) on lignite flotation performance was investigated in this study. The pore distribution and functional groups of the lignite before and after MTET were analyzed using static nitrogen adsorption method, mercury intrusion porosimetry, and Fourier transform infrared (FTIR) spectroscopy. The results showed that the clean coal yield after MTET at the 9 MPa and 200°C condition was 21.11% higher than that of untreated coal under the same flotation conditions. Both hydrophilic oxygen functional groups and porosity of the lignite decreased after MTET, increasing the absorption efficiency of oil collector on the lignite surface and the probability of bubble–particle attachment. The results of this study are expected to provide a basic understanding of the effect of MTET on lignite flotation.

Estimation of hydrophilicity of coals by using the quantum chemistry calculation

The hydrophilicity is an important parameter in characterizing the floatability of coals in floatation. To quantify the hydrophilicity, the quantum chemistry calculation was used to calculate the hydrogen bonding energies in the wetting process by DFT B3LYP 6-31G. It is known that the floatability of lignite is much lower than that of the high-volatile bituminous coal from the natural floatability test. Besides, the hydrophilic sites were mainly oxygen functional groups. From XPS results, it is indicated that there were four kinds of oxygen functional groups, including OH, CO, CO and COOH in lignite, while there were three kinds of oxygen functional groups, containing OH, CO and CO in the high-volatile bituminous coal. On the other hand, the simulation results showed that the hydrogen bonding energy of these hydrophilic sites are in the following order−COOH>−OH>C−O>C=O. The released hydrogen-bonding energies were calculated to be 2.36kcal/mol for lignite and 1.31kcal/mol for high-volatile bituminous coal, respectively. In addition, the calorimetric experiments also showed that the wetting heats were 105.37J/g (lignite) and 47.00J/g (high-volatile bituminous coal). The hydrogen bond energy distribution of each hydrophilic sites showed that all the four kind hydrophilic sites impacted the lignite hydrophilicity remarkably whereas only OH and CO affected the hydrophilicity of high-volatile bituminous coal. It was revealed that the difficulty in lignite flotation was dominated by the complex contribution to hydrophilicity of the oxygen functional groups.

The molecular structure of Inner Mongolia lignite utilizing XRD, solid state 13C NMR, HRTEM and XPS techniques

The chemical-structural properties of Inner Mongolia lignite were investigated by utilizing X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectrum (XPS) and solid-state 13C nuclear magnetic resonance spectrum (NMR). The aromaticity of the lignite coal determined by XRD was 0.7 and compared well with the 13C NMR result of 0.64. The structural parameters from XRD result indicated that lignite coal was poorly organized. HRTEM aromatic fringe image analysis revealed that Inner Mongolia lignite coal contained 31.0% (<5.9Å), 37.5% (5.9–9.9Å) and 31.5% (10–24.9Å) fringes. The oxygen functional groups, detected from XPS fitting analysis were consisted of 38.06% OH, 16.96% CO, 26.93% CO and 18.05% COOR. Similarly, ketone (200–240ppm), carboxyl (175–200ppm), methoxyl (45–60ppm) and O-substituted alkyl (60–100ppm) were found with the relative contents of 0.078, 0.066 and 0.13 NMR results. The molecular model of the lignite was constructed on the basis of HRTEM (aromatic fraction) and XPS (oxygen functional groups). This molecule formula is C166H130O49. Oxygen in the molecule mainly exists in the form of phenolic/alcoholic hydroxyl oxygen, ether oxygen, carbonyl oxygen and ester oxygen. In addition, there is a good agreement in the peak ranges and compositions through comparing the simulated infrared spectrum of the lignite coal molecular model and the measured infrared spectrum. This molecular model will be used to investigate the lignite flotation mechanism and beneficial for improving its flotation efficiency.

Evaluation of combined lignite cleaning processes, flotation and microbial treatment, and its modelling by Box Behnken methodology

In this study, first, the physicochemical cleaning of Cayirhan region’s low-quality lignites was investigated by flotation to reduce ash content. In the flotation experiments, the effects of collector dosage, frother dosage, dispersant dosage, pulp density and air flow rate on ash content and combustible recovery in the concentrate fraction were optimized. Flotation tests were designed with Box Behnken design (BBD) which is a response surface method (RSM). The effective parameters and their interactions in lignite flotation are described with a mathematical model. After physicochemical cleaning, further desulfurization studies were carried out through biological treatment. Alternaria sp. Cf1 strain which was isolated from the same region lignites was used in microbial treatment for desulfurization studies. Sulfur emission values (EV) of studied sample, flotation and microbial treatment’s concentrates were calculated and compared. After flotation and microbial treatments, sulfur emission values reduced from 12.76 to 1.01 to 0.34 for head sample, flotation and microbial treatment’s concentrates, respectively that accounts for 97.37% total reduction in terms of dry ash free basis.