The present study illustrates the effect of physical (thermal) and chemical surface treatment on the separation of the coal-quartz synthetic mixture in a tribo-electrostatic separator. The work also reports the effect of applied voltage and splitter position on the tribo-electrostatic separation of surface treated and untreated samples. Different reagents used in chemical conditioning of the synthetic mixture are kerosene, acetic acid, acetone, ethanol, phenol, toluene, and aniline. The study establishes that both chemical and heat treatment improves the tribo-electrostatic separation efficiency of coal and quartz particles. The applied voltage and splitter position affect the product grade and yield of treated and untreated samples. The ash removal and combustible separation efficiency of the synthetic mixture improved after chemical conditioning of the synthetic mixture with ethanol, acetone, acetic acid, and aniline. However, aniline treatment has produced the best separation result. It is possible to achieve 9 and 14% ash clean coal with 40% yield each from 53% ash synthetic mixture at 15 kV applied voltage after aniline and heat treatment, respectively. The ash removal and combustible separation efficiency of the tribo-electrostatic separator for the aniline and heat-treated synthetic mixture are 96, 60% and 90, 70%; respectively.

The present study deals with the surface functionalization of coal and quartz using aniline with an intention to achieve a higher differential charge facilitating their separation in an electric field. The Fourier Transform Infrared (FT-IR) spectroscopic studies confirm the adsorption of aniline on the coal and quartz surface after chemical conditioning. The surface work function of both coal and quartz are found to decrease after being treated with aniline. However, the work function of coal decreases to a greater extent (3.464%) in comparison to quartz which decreases by 1.016%. Thereby, the net work function difference between the coal and quartz particles increases by 129% (from 0.089 eV to 0.204 eV) after chemical treatment. The work function of the copper tribo-charging medium falls between the work function values of both the original and the aniline treated coal and quartz samples. Therefore, the charge density of the treated coal particles increases on contact with copper while there is a minor reduction in charge of the treated quartz. The charge acquisition data corroborates well with the surface work function data. Density Functional Theory (DFT) based simulation has been carried out to validate the trend of the decrease in work function after the treatment with aniline. The DFT calculations are found to be in good agreement with the experimentally measured change in the surface work function data of both coal and quartz sample after chemical treatment.

Investigations were carried out to understand the design aspects of tribo-electrostatic separator to separate ash from high ash Indian coking coal. Initial studies were aimed to evaluate the different physical, chemical and electrical properties of quartz, kaolinite, and carbon particles. The significant design variables such as plate angle and plate gap were evaluated to effect the optimum separation. The absolute charge acquired by quartz, kaolinite, and carbon were observed to be different. The results indicate that the magnitude of charge increases with the increase in the time of tribo-charging using copper tribo-charging medium. A mathematical model was formulated based on design and operating parameters of the experimental set up to simulate the particle trajectories. The particle trajectories were simulated using measured physical and electrical properties of mineral and carbon particles at experimental design and operating conditions. The simulated trajectories were validated with experimental data. The results of plate position and feed particle temperature indicated that there were optimum conditions to achieve the desired performance. The simulation and experimental results were in good agreement. The optimum separation was achieved at plate inclination of 5°. It was possible to reduce ash content by 10% at 61% yield. Better quality clean coal at 33% ash was achieved from 53% ash feed coal with lower yield.

The work reports the systematic investigation on the flocculation, sedimentation and consolidation characteristics of kaolinite using guar gum as a green flocculant. In-situ flocculation behavior of kaolinite at various pH, guar gum dosages, and ionic strength were studied using a light scattering technique. The effect of these parameters on the settling rate, solid consolidation, and supernatant liquid clarity was recorded. The morphology of kaolinite and flocculated kaolinite aggregates were analyzed using FESEM. The morphology studies suggest that it is poorly crystalline with multiple steps on edge, broken edge; laminar with high aspect ratio and have rough basal surface. The complex irregularity on the basal surface and the presence of multiple steps in the edges, broken edges (hydroxyl groups) have facilitated the guar gum adsorption. The isoelectric point of kaolinite is pH 3.96. The pH, ionic strength and flocculant dosage have a significant effect on the kaolinite settling rate. The guar gum has exhibited excellent turbidity removal efficiency at pH 5. The turbidity removal is inefficient at pH 10. However, guar gum has shown high turbidity removal with 80% transmission at pH 10 in the presence of a KNO₃ electrolyte.

At the moment, it is vital for mineral industries to abide environmental regulation to dispose of the wastes generated in the beneficiation process. The redesign of dewatering process is required to meet the present demand. This paper reports the results of systematic investigations on the flocculation, sedimentation and consolidation characteristics of the chromite ore process tailings using different polyacrylamide flocculants. Laboratory batch sedimentation tests were performed to assess the performance of flocculants. Different categories of flocculants such as anionic, cationic, non-ionic with varying ionicity and molecular mass were used to improve the settling rate. The influence of flocculants on the settling rate, solid consolidation, and supernatant liquid clarity was recorded. Ionicity and molecular weight of the flocculants have a significant effect on the tailings settling properties. Anionic flocculants with low ionic strength and molecular weight show higher settling efficiency, whereas, cationic flocculants bearing high ionic strength and molecular weight also display the similar settling behaviour. The opaqueness of consolidated solids is greater with cationic than the anionic polyacrylamide. The anionic Alstafloc 40, 60 and cationic Alstafloc 155XX have exhibited excellent turbidity removal efficiency with 19.5 cm/min settling rate at 15 g polymer/tonne solid dosage. The non-ionic polyacrylamide was not found efficient for the tailings flocculation.

The present paper outlines the characterization, electrokinetic behaviour and flotation response of rejected coking coal fines with 32.5% ash generated in a coal washery in Eastern India. The response methodology and central composite rotatable design (RSM-CCRD) were used for the

process modelling and optimization of the flotation process using diesel, MIBC and sodium hexametaphosphate as a collector, frother and depressant to maximize ash reduction, yield and combustible recovery. At optimum condition, a 9.7% clean ash coal was achieved with a 63% yield at collector, frother and depressant dosages of 0.78, 0.31 and 0.80 kg/ton, respectively. The model prediction and experimental data corroborated sufficiently. Subsequently, within one year, the fines oxidized and did not float with the collector. FTIR confirmed surface oxidation on oxidized coal. The oxidized coal responded favourably to acid oil, a vegetable oil refinery waste. With acid oil as a collector, the oxidized coal can upgrade to 12% clean ash coal with a 60% yield; the combustible recovered is 80%. The work indicates successful upgradation of fresh and oxidized coal using the froth flotation process.