Flotation of Low-Grade Graphite Ore Using Collector Derived from Low-Density Polyethylene Waste

Abstract

Polymorphs of carbon ranges from soft, blackish graphite to hard, transparent diamond. From the early fifteenth century itself graphite was widely used as it shows the properties of both metal and non-metal, has an extraordinarily low specific gravity, incredibly soft and cleaving with noticeably light pressure, exceptionally heat resis­tant and inert when in contact with other materials. That is why it is called as a "Mineral of Extremes" [1]. Crystalline forms of natural graphite have small flake size and as metamorphic grade increases it leads to microcrystalline forms. These flake graphites are graded based on the graphitic carbon content and flake size. Hexagonal crystal structure is the thermodynamically stable form of graphite which results in tremendous properties. The properties of graphite vary from place to place as the geography of the mined area play a crucial role in metamorphism. Among various beneficiation techniques, froth flotation is more suitable for treating fines and naturally hydrophobic ores. Flotation is a surface phenomenon based on the surface hydrophobicity of the mineral surfaced to be separated [2-4]. Due to the natural hydrophobicity of graphite, this technique is adopted for benefi­ciation. The hydrophobic mineral particles which are attached to air bubbles floats on top as froth and is separated, while the remaining hydrophilic gangue particles that attach with water molecules stay in liquid [2-6]. Nanobubbles can be produced by ultrasonication, but this doesn't have any effects on the floatation performance of graphite [7]. Ultrasonic-assisted flotation has effects on floatability which enhances the recovery flaky graphite from low-grade graphite ore [8]. The particle size has crucial roles in the overall multi-stage grinding-regrinding-flotation steps [9]. Selec­tive adsorption of particular reagents on the mineral surface depends on the particle size of the mineral present in the pulp [10]. Controlled grinding is very important to achieve ideal cost-effective separation [11]. Surface chemistry can be affected by flotation. The purity of single graphite particles, on the other hand, is rarely compro­mised. Flotation reagents, viz., collectors, frothers, etc., are added to transform the mineral-water mixture suitable for flotation by controlling the relative hydropho­bicity of particles and maintain froth characteristics [12]. These chemicals have crit­ical role and importance in the entire process as they involve complex interactions. Graphite has natural affinity towards air bubbles. The chemical reagents commonly used in graphite flotation increase the selective hydrophobicity and a variety of non­polar hydrocarbon-based oils such as kerosene, diesel, and fuel oil are generally used collectors in combination with frothers such as pine oil, Methyl Isobutyl Carbinol (MIBC) or higher alcohol [13-15]. A jump-in phenomena exist between non-polar collectors and the hydrophobic surface, indicating the existence of an attractive force. Polar collectors form hydrogen bonding with water results in a weaker adhesive force. Jump-in distance, jump-out distance, friction force, and adhesion force are greater and play crucial role in the interaction of collectors with graphite surface [16]. Diesel oil as collector and MIBC as frother was found to yield best results in graphite flota­tion comparing other hydrocarbon oils like dodecane, kerosene, pine oil, iso octonal in terms of total carbon content and total carbon recovery of the rougher concentrate of graphite [13, 17]. In graphite flotation, the selectivity index between collector and graphite increases as the average droplet size of collector emulsions (e.g., Kerosene) lowers [18]. Conventional reagents are not economic when used in industrial scale due to the continuous price escalation of fuel oils. Synthetic plastic, the world's most used polymer, whose disposal poses the utmost threat to environment as it is not readily bio-degradable and uses non-renewable resources as key ingredient in manufacturing of plastics. Around 12. 7 tonnes per year of plastic waste is produced around the world which pollutes the entire ecosystem. The present work evaluates the flotation performance efficacy of the oil ( collector PE) derived using LDPE, i.e., low-density polyethylene waste as collector in combi­nation with MIBC as frother and compares with the conventional reagent combination of diesel and MIBC for flotation of low-grade graphite ore (run-of-mine) from Tamil Nadu.