Flocculation-flotation of ultrafine hematite from quartz using anionic polyacrylamide as a selective flocculant

• Anionic polyacrylamide (APAM) raises hematite flotation recovery from 26% to 88%. • Sodium hexametaphosphate (SHMP) reduces quartz entrainment by reducing froth. • APAM and SHMP boost recovery and selectivity, improving grades by another 11%. • APAM and collector doses must be optimised due to competition for adsorption sites. Conventional flotation cells are widely used for concentrating iron ores, yet one major challenge remains – the low recovery rate of ultrafine particles, particularly when processing low-grade deposits. This study explores the application of anionic polyacrylamide (APAM) in hematite and quartz mixtures (D 50 : 1 μm, feed grade: 27.2 % hematite) to selectively aggregate hematite for enhanced flotation recovery. The role of sodium hexametaphosphate (SHMP) was examined as a dispersant to prevent heterocoagulation and to enhance selective aggregation towards hematite, evaluating its effect on the combined flocculation-flotation performance. Detailed insights are provided into the interactions between each reagent combination with sodium oleate (NaOL) as collector, along with an analysis of the limitations of this approach. Flotation with NaOL alone resulted in a hematite recovery of 44.5%. The addition of APAM increased hematite recovery to 82.7%. There was limited improvement in grade due to increased quartz entrainment and entrapment within the aggregates. When combined with SHMP, hematite grade improved by 11.4% as SHMP reduced heterocoagulation between hematite and quartz, and reduced entrainment by regulating the froth. Over 99% hematite recovery was achievable with optimised reagent doses. Since SHMP also functions as a depressant, the dose must be optimised to avoid excessive froth destabilisation. Overdosing APAM resulted in overly hydrophilic flocs which negatively impacts recovery. Balancing the dosage of all three reagents is crucial for optimum results. The highest grade achievable was 45.2% due to quartz entrapment and entrainment which is difficult to minimise in conventional lab scale mechanical flotation cells when handling ultrafine minerals.