Exploration of Natural Graphite Resources of Northeast India: Fixed Carbon Enrichment and Conversion to Advanced Carbonaceous Nanomaterial and Prospects for Sustainable Waste Valorization

Abstract The accessibility of critical minerals is crucial for supporting renewable energy systems, decreasing reliance on imports, and promoting locally available resources for scientific progress and economic resilience. Graphite, a versatile material with a wide range of applications, has been sourced from the natural deposits located in Arunachal Pradesh (36%), a Himalayan state in Northeastern India. The mineralogical and physico-chemical evaluation of these raw graphite deposits indicated a notably low fixed carbon content (20.4 ± 0.02%) with silica (80.10%) being the predominant impurity alongside metal (Fe/Al/Mg/Ca) oxides. This work presents two distinct facets: Firstly, it illustrates a simple and one-pot method for improving the grade of raw graphite concentrates through an acid-leaching technique, followed by its conversion to graphite oxide, graphene oxide, and reduced graphene oxide. The chemically upgraded graphite resulted in good-quality industrial-grade graphite with a high carbon content (96.06 ± 0.62%) having a significantly reduced silica content (0.86 ± 0.29%). Secondly, it explores the waste utilization of the primary byproduct, aqueous hexafluorosilicic acid (H2SiF6) waste produced during the chemical treatment of raw graphite, as an effective silicon precursor for the synthesis of mesoporous silica. The research also demonstrated the effect of surfactant hydrocarbon chain length on the pore size development of mesoporous silica. In summary, this study emphasizes on enhancing the valuation of natural graphite resources by a simple chemical process, while also addressing potential waste management issues to obtain mesoporous silica materials.