Sustainable selective flotation of cassiterite using (1-hydroxy-1-phenylethyl) phosphonic acid: green chemistry approach and performance

Cassiterite flotation remains challenging because many collectors show limited selectivity and their performance depends on operating conditions. Here, we investigate (1-hydroxy-1-phenylethyl) phosphonic acid (HPPA), a phosphonic-acid-type reagent structurally related to styrene phosphonic acid (SPA), as a promising collector for selective cassiterite flotation. At pH 6 (25 °C) and 1.5 × 10−4 mol/L HPPA, cassiterite recovery reaches 94.5%, whereas calcite recovery is limited to 20% and quartz recovery remains below 10%. Mechanistic studies combining microflotation, FTIR, XPS, and AFM suggest that HPPA chemisorbs on cassiterite via phosphonate coordination (Sn-O-P interaction), enhancing surface hydrophobicity without metal-ion activation, which can simplify the reagent scheme and potentially reduce process complexity. These findings highlight HPPA as a potentially lower-impact collector for cassiterite flotation, while further validation in mixed-mineral and real-ore systems is needed to assess practical robustness.