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

Abstract

The increasing wide range of applications of graphite for electrode, lubricants, refractory applications especially the recent surging electric automobile industry results in significant need of graphite in future. Graphite demand in the energy storage industry is expected to grow 15 times faster than today's demand by 2030. Due to depleting high-grade ore, utilization of low-grade ore by beneficiation becomes utmost importance for sustainable development and resource management. In this work, low-grade graphite ore from Tamil Nadu, India, with 86.84% ash was beneficiated by flotation technique for recovering graphite with lower ash content. Flotation, a surface phenomenon, based on the surface hydrophobicity of the mineral surface to be separated and since graphite is naturally flotation mineral, this technique is adopted for beneficiation. The most commonly used collector in graphite flotation is diesel. In view of continuous cost escalation of diesel, an alternate collector was developed utilizing the low-density polyethylene (LDPE) waste paving way for plastic waste utilization. The flotation efficacy of this new collector (Collector PE) derived from LDPE waste was compared with that of diesel in graphite flotation. The run-of-mine graphite ore was initially size reduced for liberation of values from its associated impurities, followed by flotation. The mesh-of-grind, dosages of collector (diesel and PE), and frother (Methyl Isobutyl Carbinol, MIBC) were optimized for better process efficiency for increasing the surface hydrophobicity of graphite particles leading to better separation efficacy. The ore characterization by X-ray diffraction revealed that graphite was accompanied predominantly by quartz with minor fractions of pyrites and several other phyllosilicates such as kaolinite and muscovite. Exfoliated morphology of graphite with thick layers were observed from SEM images. Flotation reagents such as diesel, collector PE, and MIBC were characterized by FTIR to analyze their functional groups that enhance the efficiency of the separation process. A graphite float (rougher concentrate) with 15.2% weight recovery and 17.7% ash content was obtained after 10 min of grinding (d80: 240.5 µm) with 0.85 kg/t of collector (diesel) and 0.07 kg/t of frother (MIBC) dosages and on two-stage cleaning, a final concentrate with 12.66% weight recovery and 8.70% ash content was obtained. A graphite final concentrate with 13.04% weight recovery and 8.90% ash was achieved with two-stage cleaning, when treated with 0.57 kg/t of collector PE and 0.07 kg/t of MIBC. These results indicate that the flotation efficiency of the collector PE derived from LDPE wastes is comparable with that of diesel and would be economical when used in large-scale industrial graphite flotation.