Selective flocculation of hematite in quartz–hematite–ferric ion–polyacrylic acid system. Part 2. Effect of grinding and a hydrofluoric treatment on selectivity of flocculation

•Polyacrylic acid selectively flocculates hematite from mixtures with SiO2.•Fe2O3 flocculation selectivity is reduced for porcelain mill ground quartz.•Flocculation is negligible for quartz co-ground with Fe2O3 in quartz mill.•HF treatment of co-ground quartz–Fe2O3 mixtures restores flocs quality.•HF facilities selective flocculation of iron minerals from ore using PAA

A variety of materials and particle preparation methods were investigated to delineate their effect on the selective flocculation of quartz and hematite suspensions with polyacrylic acid (PAA) as flocculant. Synthetic hematite particles were effectively separated by selective flocculation with PAA in the 3 to 8 pH range from a mixture of quartz that had been ground in a quartz mill. However, grinding the quartz in a porcelain mill or co-grinding it with the hematite fines in a quartz mill resulted in non-selective flocculation due to cross-contamination of the quartz particles by coating of impurities from the porcelain or from hematite. Treatment of the ground product with hydrofluoric acid restored the purity of the quartz particles, thereby restoring selectivity in the flocculation step. Effective selective flocculation of Tilden hematitic taconite ore was achieved by hydrofluoric acid treatment of the minus 37 μm fraction of the crushed ore.