Eco-friendly alcohol-based frothers used in plastic and mineral flotation separation: Performance, recent advances, and future directions

The role of frothers in flotation separation is pivotal because they generate stable bubbles and facilitate the transport of particles to the froth phase. Owing to increasing environmental concerns about hazardous plastic handling and stricter regulations in the mining industry, there is a growing need for less toxic, more environmentally friendly reagents. Frothers, which are typically synthetic, non-green, and unsustainable chemicals, have historically received less attention than other flotation reagents, including collectors and depressants. This is contrary to their significant role as the most critical reagent in plastic flotation separation. They also have a governing influence on ore separation, significantly affecting froth zone height and durability, consequently impacting selectivity and recovery. Alcohol-based frothers are a well-known group of frothers utilized in froth flotation. They are generally divided into aliphatic, aromatic, and cyclic alcohol categories. Several investigations have reported promising results from using natural and non-hazardous alcohol-based frothers, demonstrating enhanced flotation performance and reduced health risks. This comprehensive review focuses on natural alcohol-based frothers (eucalyptus oil, pine oil, and terpineol alcohol), providing an in-depth analysis of their structure, application, effectiveness in flotation separation, and comparison with conventional hazardous frothers. Despite promising results in flotation using alcohol-based frothers, substantial gaps remain, notably interactions and adsorption mechanisms with the particle surface and other flotation reagents, performance across various flotation systems, industrial scalability, etc. This robust review highlights the existing gaps, identifies challenges, and proposes future research directions to advance the adoption of natural alcohol-based frothers.