Sustainable coal flotation: Biodiesel from vegetable oil refinery waste as an alternative collector to diesel and acid oil

Abstract

The present study investigates biodiesel synthesis from acid oil, a waste product from a vegetable oil refinery, and evaluates its effectiveness as a flotation collector in coal flotation. The work also compares its flotation response with diesel and acid oil. The coal contains 40.67% ash, 41.08% fixed carbon, and 18.25% volatile matter. Vitrinite and inertinite are primary macerals, and quartz, kaolinite, and siderite are principal mineral phases in the coal. The coal’s isoelectric point (IEP) is at pH 3.5. The functional groups in the coal and collectors were identified using infrared spectrum analysis (ATR-FTIR). The synthesized biodiesel contains both polar (-COOH, -C=O, -C-O-C) and nonpolar (-C-H, -C-C) groups, as well as oxygenated functional groups (hydroxyl, carboxyl, carbonyl). These functional groups promoted hydrogen bonding with oxygen-containing macerals, enhancing flotation. Flotation tests demonstrate that achieving 14% ash-clean coal with 41% yield is possible by consuming 0.74 kg/t bio-diesel and 0.2 kg/t MIBC from 40% ash-feed coal. A further increase to 1.27 kg/t biodiesel dosage achieves 17% ash-clean coal with a 56% yield. These findings suggest biodiesel, derived from renewable resources, is a promising alternative to diesel oil, offering better selectivity in coal flotation.