Turpentine oil: a novel and natural bridging liquid for agglomeration of coal fines of high ash coals

Oil agglomeration is an effective way to demineralize high ash coals as compared to froth flotation and density gradient separation. In this process, the choice of bridging liquid is critical with respect to economics and efficiency. Herein, we report turpentine oil as a potential bridging liquid which is demonstrably efficient in coal demineralization at lower concentration (10 vol.%) compared to literature (20-25 vol.%) without inclusion of surfactants, which enhances economic viability. We chose two high ash coals of Indian origin, with 26% and 34% ash. A varied range of particle sizes were examined along with pH, type of electrolytes, agitation conditions and oil dosages. Both coals (200 mesh) demonstrated approximately 50% reduction in ash content at pH 7, which is an improvement over previously known reports on Indian coals. Chemical structural resemblance between primary components of turpentine oil and predominant pi-delocalized aromatic structure of high rank coals could be the reason behind improved adsorption of oil. Our work thus demonstrated the utilization of a natural oil which can be dried easily, readily available and cheap in a significantly demanding commercial process like coal beneficiation. This is expected to deliver a substantial performance and cost improvement over incumbent known bridging liquids.